# Let's talk Surface\Inspection Plate!



## G-reg (Jan 12, 2004)

I built frame #1 with careful mitres, lugs, and a bush league chainstay jig. One of the very many lessons learned in butchering #1 was that a better jig and some form of inspection table would be needed from here on out. 

The infinite and infallible wisdom of the internets has me convinced that building on a surface plate is the next best move for a hack like myself. 

Questions rolling around in my head:

Is scrap/used kitchen quality granite flat enough? In my head it has to be well within the margin of error for a noob framebuilder...I'm not grinding mirrors for the Hubble here. Other cheap options?

Tubing blocks are readily available. But what about BB posts, especially one you could honk on to fine tune alignment? 


Anyone actually use a surface plate instead of a jig or is it just something to tell the flood of new hobby builders?


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## febikes (Jan 28, 2011)

IMHO, truth be told you don't even need the table to be flat.

All you really need is something heavy and solid that does not move and a way to mount the frame by the BB shell in a controlled way. Provided you measure from the exact same spot and flip the bike over to measure the other side you don't "need" an true alignment table and at the same time you can get results that are better then +/- 2mm.

I made my own table and it is dead simple. 
Alignment Table « Farnsworth Engineering

I really like this one as well, it is just as accurate as mine.
Bicycle Frame Building Jig and Alignment Table

When you measure then flip the frame over and measure again from the other side to the exact same point your measurement will be as accurate as the technique you are using to hold the bike at the BB shell. The technique works best if you have good heat sinks in place to minimize distortion in the shell and/or face the shell after welding.

A true alignment table is something I would love to have. Mostly the only benefit of a true table is that it would make things go faster because I would not have to flip. I doubt it would allow me to build with better alignment because in truth I align based on the miters and welding rather then cold setting. The tolerance that I aim to hold is +/- 2mm and frankly in terms of a true granite table that is like a football field.

I look forward to the thoughts of others.


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## alexmeade (Jan 4, 2012)

For BB posts and other stuff that you might want to use to build on a surface plate, I humbly submit my own offerings. I'm a newbie here so I can't post a URL, but my website is

alexmeade.com

Also, if you add the usual htpp, colon, double-slash in front of the following link, you can see a setup I recently made for another builder. It's designed to be used over a drawing on a flat surface. Simple, easily portable, and you can made an entire frame including fork:

flickr.com/photos/[email protected]/6629187815/


Please click on the "Tools" tab.

Thanks

Alex


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## jay_ntwr (Feb 15, 2008)

G-reg said:


> I built frame #1 with careful mitres, lugs, and a bush league chainstay jig. One of the very many lessons learned in butchering #1 was that a better jig and some form of inspection table would be needed from here on out.
> 
> The infinite and infallible wisdom of the internets has me convinced that building on a surface plate is the next best move for a hack like myself.
> 
> ...


Greg, I've been battling with this for so long now.... I've been building on the top of my table saw and it's been super helpful. I can get a front triangle pretty straight on it most of the time.

One of the things that helped me was having the tube blocks from Paragon Machine Works. I'd intended (after talking with Don at NAHBS2011) to buy two (and maybe 4 in a couple of the sizes) sets of 1.5/1.375/1.25/1.125/1.0 all drilled into the same size block and he said he'd do it but would have to charge me for the bigger blocks--no biggie. But think of being able to clamp all the tubes no matter the size and then laying the blocks on the sides (as to keep the centers the same in all blocks) and clamping them to your table on a full sized print. Well, I imagined it would be a pretty good way to do it (and not too expensive) but never managed to get it done.

Instead, I got a jig. What I think happens is if you make a couple of frames, you can get by with whatever you can put together. But if you plan on making 10 over 10 years, a jig isn't all that expensive when you factor it in (for something used). Now I got a killer deal but it was a case of having a fund set up for a welder and the jig came along as was too good of a deal to pass up. Now that's still not a reasonable solution for everyone and I get that, but I like how I was doing it before and think that would be a good way to build without a jig.

I still want to mount a post on my table saw to use as an inspection table though. Actually, my first thought was to have a table top cut and have a post hole put in it out of the same granite you're talking about. It's cheap, probably flat enough for bikes, and readily available. For now, I do have access to a purpose built table though so I'll keep using it.


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## smdubovsky (Apr 27, 2007)

Countertop granite is often not even remotely flat so be careful. Smooth and pretty: yes. Flat: no. But you could always go pick though remnants w/ a long quality straight edge/level in hand and try to find one that is!

I have a real 2'x3' surface plate for my metalworking hobby that I used. Can get them new for ~$200 delivered when on sale. But it weighs 400# so not an option for some.

Edit:
Alex,
Looks nice. Might I suggest making them double ended next time w/ 2 different tubing diameters for each pair. I'd machine them so the unused endcap stays screwed on so it doesn't get lost (like all things do that have to be removed and stored aside if required for use.)


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## doug fattic (Mar 11, 2010)

G-reg, I think one of the smartest investments any starting framebuilder should get is a good alignment table. It would be near the top of my to-buy list. It provides a basis for accuracy throughout all stages of the build. It can compensate for any inaccuracies in a home-made or less expensive fixture. Of course if someone is only going to build one or maybe two frames a year than alternative methods can be used (the best one I know of is using a saw table like Jay is doing). 

Using a flat table for alignment before and after each braze also reflects my philosophy of building. I only spot braze a front triangle in a fixture (whose accuracy can possibly be trued on the alignment table) and then align the frame on the table and braze it free of the jig. This freedom allows for easier and faster brazing by always being able to position the joint in its most optimum position. Besides the fixtures I sell that I have laser cut out of stainless steel, I also have an Anvil Master and a Bike Machinery Hydra. Whatever fixture I use I still only spot braze the frames in them and then use the alignment table to straighten them out (and then spot and align them again) before fulling brazing each lug. 

I don't recommend the method of flipping the frame over because each face of the bb shell will give a different reading if measured on a true surface. That way is just not accurate enough for me.

I prefer cast iron because of its stability and the ability to use magnetic attachments to hold positions. I also have a cast aluminum one for those that don't have a fixed location for a shop and may need to move it around or carry it to the basement or up flights of stairs. It weighs less than 200 lbs instead of 700. I have alignment posts made to my specifications for resale (Alex Meade who also posted on this thread makes some for sale too). I also have a used 40" X 30" cast iron table for sale that I modified by boring a 1 inch hole and fitting one of new alignment posts for $800. The is the smallest size one can still place an entire frame (including the rear triangle) over the surface. It is possible to use a 36" X 24" table with the post in SE corner. In that case the rear end hangs off of the east end. 

Doug Fattic
Niles, Michigan


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## febikes (Jan 28, 2011)

doug fattic said:


> I don't recommend the method of flipping the frame over because each face of the bb shell will give a different reading if measured on a true surface. That way is just not accurate enough for me.


Thanks Doug, my friend Sara Joe has one of your frames and you do great work.

Do you or other have any thoughts on how much accuracy is lost with the flipping technique?

It seems to me that even if you don't flip you still depend just as much on the face of the BB shell because all the post style tables are holding from the BB shell anyway. If you can't trust both sides how can you trust just one side? Would you agree that the typical one side approach simply reflects the entire alignment from the same potentially incorrect reference point?

Also, In terms of alignment described what tolerances do you try to hold?

The key metrics I check are as follows relative to BB centerline:

Rear axle 
Seat tube (at top of seat tube)
Bottom of extended headtube (using a 200mm headtube)
Top of extended headtube (using a 200mm headtube)

On my current build I have a +/- of within 2mm for all measurements (using flip technique). The bike seems to ride fine and the alignment was post welding with no cold setting. This is consistent with what Steve Garin from BREW described as his approach.

At a certain point it seems that alignment better then a given metric is going to require cold setting and/or repeated welding. My concern is that the harm of seeking a +/- 1mm might be greater then the benefit. Can you or others provide recommendations for tolerances and the trade off between "as built" vs. cold setting?

Thanks!


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## Walt (Jan 23, 2004)

*Long piece of flat plate+bolt*

...is enough for anyone but a pro. The old F*A*G*1 from park tool (let's see if that gets censored!) is a good example of this - it is just a long piece of square tubing that bolts to the face of your BB shell, with a small feeler gauge that can be moved around as needed. You can measure to see if things are in plane with the face of the BB shell, if there's twist in the head tube or seat tube, whether the dropouts are offset to one side or the other, etc, etc. Add a true/dished rear wheel and a piece of string and you're set.

Honestly, the setup I just described is plenty accurate enough for a pro, too. *Alignment is only important to the extent that the bike rides correctly* - which means plus or minus a few full mm in most cases. You can get out a set of calipers or a height gauge and a fancy table that is flat to .0001", and spend hours and hours on alignment, but the end result isn't going to be any better than a frame where the head tube is 2mm off to the left.

Should you shoot for perfect? Of course. But you shouldn't obsess over thousandths. We're not building spy satellites.

-Walt


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## Walt (Jan 23, 2004)

*Math!*

Ok:

-Assume you can face the shell to +/- .001". I'd be pretty shocked if it was better than that no matter what tool you use, and I've used a number of different ones.

-Assume, say, a decent sized 29er, where the head tube is about 750mm from the center of the BB shell.

-Assume a 38mm diameter BB shell.

-Assume the plate and mounting post are *perfect* - no errors introduced from the tool at all.

If we multiply the .001" x the ratio of the head tube distance and the BB shell radius (.001*(750/19)) we get .039", or about exactly 1mm. So assuming facing accuracy of .001", the best you can say about this frame is that it's within +/- 1mm of straight.

-Walt



febikes said:


> It seems to me that even if you don't flip you still depend just as much on the face of the BB shell because all the post style tables are holding from the BB shell anyway. If you can't trust both sides how can you trust just one side? Would you agree that the typical one side approach simply reflects the entire alignment from the same potentially incorrect reference point?


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## Smudgemo (Nov 30, 2005)

Regarding flipping of a frame for alignment, there was a heated debate a few years ago here: Frameforum - THE Handmade Bike Website!
The long-time pros weren't on board with it.


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## jgerhardt (Aug 31, 2009)

I have been using my trusty old F*A*G*-2 (if Walt can say it so canz I?) and Stein Dropout Alignment tools for awhile now and have been having pretty good success. Eventually I plan on getting a table, however the expense is high and definitely not that necessary if you are beginning I would think.

Considering how out of alignment a "real" bike can be (Trek, Specialized, Giant, etc. etc.) before it can be warrantied having a frame only 2mm out of alignment is near perfect. The old Lightspeeds (a pretty high end frame by anyones standard)could be 2mm out of alignment from the center, so they could conceivably be 4mm totally off before it would be replaced.

That said a custom frame is supposed to be "perfect", but the further you go towards that end you would probably find diminishing returns...


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## febikes (Jan 28, 2011)

Smudgemo said:


> Regarding flipping of a frame for alignment, there was a heated debate a few years ago here: Frameforum - THE Handmade Bike Website!
> The long-time pros weren't on board with it.


Wow, five pages over there and it all starts with PVD. I have not read it all but the discussion seems focused on the idea of getting perfect alignment and is very road bike oriented.

I grew up racing road bikes and never really felt a bike needed to be in perfect alignment to win races. My bike was once bent in a crash, I got back up and even won the race although the bike was no longer fun to ride. Once the bike rides correctly there is no such thing as "better" alignment because the wheels, tires, and hub mounting will always produce a +/- of more then .5mm, right now I am certain my front wheel is more then 2mm out of true and it is a little out of dish as well. The rear wheel is a little lumpy but then again I ride on the dirt. I think if my frame was built to tighter alignment it would not make a difference. A lot will come out in the wash.

For mountain bikes, I think perfect alignment is less important then strength and durability. Steve Garin at BREW bikes had the philosophy that it was better to keep the material properties by building with proper alignment and simply accepting that being 2mm out of "perfect" is not really a bad thing. If you cold set to remove the 2mm and make the bike straight his feeling is that you also moved the metal past it's yield point and in doing so you are trading material properties for the joy of having a level of alignment that is just about meaningless.

If you ride on a dirt trail do you really need the bike to be aligned on a perfect granite block especially if doing the alignment makes the frame weaker?


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## doug fattic (Mar 11, 2010)

Your analysis is correct about choosing some specific place as a reference point even though it isn't perfect. Whatever specific one you choose is going to have some error. it is just necessary to pick one reference as the standard for alignment that everything else is based off of. The problem with flipping is that it magnifies the error of each side and they most likely won't agree. In other words the amount the seat tube will be down on one side will not be the same amount it will be up on the other side. That can drive one crazy. I choose to put the derailleur side down since in theory the chain side is the operational side that one would want the straightest. 

Typical industry standards for road frames that are production made would be within 3 mm. Custom frame standards are within 1mm and for the best builders a half mm or less. This is a matter of pride more than function. It can be the example of the standard for quality the builder used for all details throughout the entire frame. My impression is that pro road builders put a greater emphasis on details including alignment than MTB builders since quality is assigned by non-ride quality details like how well the joints are filed to look good. My theory is that while any one detail by itself may not be significant, a number of them together can add up to make a noticeable difference. The British builders I visited in the 70's built frames in a day with just simple tools. I've repainted hundreds of them (including realigning them) and few were anything I'd want with my name on the down tube. 

While it is possible to use just a straight edge with an adjustable screw as the front triangle alignment gauge (I almost mentioned it in my original post) it doesn't work nearly as quickly or efficiently as a flat table. It is perfect for the amateur with limited resources and lots of time. Classic British builders used a length of angle iron clamped in a vise with a bb holder on one end and an adjustable screw on the other. What most pro builders use as a checking tool on the table is a surface gauge. You check by listening to the amount of scratching sound the point makes as it passes over each check point. A digital height gauge is too sensitive for the amount of curve each tube is likely to have. An average of curve in bicycle tubes is around 1/16th of an inch and it isn't uncommon for it to be an eighth of an inch. That is why tubes are rolled on the table (one of its many valuable uses) and marked so that the miter puts this curve in the plane of the frame instead of to the side. An alignment table is by far my most versatile tool in my shop. Like I said it can compensate for all other kind of cheaper or less accurate tooling. It was the first tool I got when I started 35 years ago and it would be the first tool I'd get again. Of course I wasn't planning to make only one or two frames a year either.


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## 3wfab (Aug 1, 2010)

Walt said:


> .. You can get out a set of calipers or a height gauge and a fancy table that is flat to .0001", and spend hours and hours on alignment, but the end result isn't going to be any better than a frame where the head tube is 2mm off to the left.
> 
> Should you shoot for perfect? Of course. But you shouldn't obsess over thousandths. We're not building spy satellites.
> 
> -Walt


Agreed as I have been knocking my brains out chasing numbers BUT....since I got my plate, my desire to be better is now measurable.And because of this, my process and end result has improved greatly. Its not so much for the frame as it is for me, wanting to produce a truly straight frame.

I recommend a plate over using other options.


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## alexmeade (Jan 4, 2012)

Interesting idea to make them double-ended. I'd have to think on that one to make sure I could still get the precision. I try to build fixturing to very tight tolerances; typically my standoff blocks will vary no more than 0.002" in centerline standoff height across an entire set of blocks, and it's often tighter than that. I'll keep thinking about this. Thanks again, Alex (alexmeade.com)


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## Meriwether (Jul 26, 2007)

Being a newbie (9 frames), I love having a good alignment table (C-channel Bringheli). It helps me figure out what and where i'm doing things wrong. I never would've figured some of the things out if I hadn't had this table. I'm sure there are cheaper ways to get it done like those mentioned above, but I'll pay for a good tool if it helps me get it done easier and faster since this is not my day job.

There have been frames where my miters were near perfect, and my welds were pretty evenly good and the frame was off over 4mm. Totally confused me as to why. I was able to figure out how much a 2nd pass did to pull the frame into alignment instead of trying to coldset it. It also pointed out to me that a certain miter was a bit worse than another or that my tig beads were not as even in heat as I initially thought. 

I almost think that a good flat surface is more important than many other tools for a newbie, and that more experienced builders may not *need* alignment tables since they know these things already. Beginner builders may need more help to gain that knowledge of what pulls what which way and so forth.


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## febikes (Jan 28, 2011)

Meriwether said:


> There have been frames where my miters were near perfect, and my welds were pretty evenly good and the frame was off over 4mm. Totally confused me as to why. I was able to figure out how much a 2nd pass did to pull the frame into alignment instead of trying to coldset it. It also pointed out to me that a certain miter was a bit worse than another or that my tig beads were not as even in heat as I initially thought.


Do you check the frame after each weld segment or do you wait until a frame is done? My thinking is that it is best to check after every tack and every weld segment. It takes time and I spent a lot of time taking the frame in and out of my jig.

With the Bringheli table do you flip the bike and measure from each side or do you only measure from one side? My thinking is that if you don't flip your frame the result is less accurate then what I get with a simple home spun table and the act of flipping.

The reason for my theory is the idea if you don't flip you depend 100% on a single face of the BB shell. If you flip the frame on each measurement the alignment of the table actually does not matter. Since the faces of the BB shell are very slightly random flipping tends to cancel some of the random variation out of the equation.

Don't get me wrong an true alignment table is on my short list but mostly because it simply makes things faster and provides flexibility for projects that are not directly bicycle related. Personally I think a steel table is better then granite because it likes magnets and you will not need to worry so much about dropping tools on it.

What I really want for my shop is one of these:
Strong Hand Build Pro Welding Table 47" X 38" Anondized Aluminum










The table is rated as having flatness of .004" / foot. I am a little worried that the plates are a little thin but you could do some real creative stuff with something like that. If I had such a table plus a nice pure flat and big 2" thick metal surface plate I could have lots of fun.


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## Meriwether (Jul 26, 2007)

The Bringheli "small" table (C-channel steel) is about 6" wide so you just loosen the BB post and spin the frame to check different parts - start at the ST/BB to get the center, then move to HT and chainstays/rear axle. It comes with a nice rear axle with the center marked to check rear triangle center. Spinning is much easier than flipping but of course I wish I had a big table like the "big" Bringheli table 

I think what Mr. Fattic says about flipping is the reason most alignment table systems go off one reference point - one side of the BB. Seems to me like you're unnecessarily introducing in more error if you flip. I'm sure your method is no less accurate than mine, mine is just quicker and makes more sense to my simple mind.

I have read a few posts from DWF who says those who measure after each weld are just 'chasing their tail' and that makes sense to me. So, I tack the front triangle and chainstays in the frame fixture and then ream/face the BB before putting it on the alignment table to see where I'm at. Then I can add a tack or two if something's off. Then i weld the front triangle and chainstays out of the fixture, repeat the BB facing, etc. and add a second pass on a weld if needed (it usually is at this point for me). I'm sure I'll change my process 20 times more but this makes sense to me for now...


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## febikes (Jan 28, 2011)

*Sorry if I am making the same point again....*



Meriwether said:


> I think what Mr. Fattic says about flipping is the reason most alignment table systems go off one reference point - one side of the BB. Seems to me like you're unnecessarily introducing in more error if you flip. I'm sure your method is no less accurate than mine, mine is just quicker and makes more sense to my simple mind.


I want a really table but mostly for speed, if my goal was to improve accuracy I would just flip things and not care at all about the table beyond the context of the post holder.

If the reference point is wrong on both faces of the BB then flipping becomes more accurate. It sure seems that using only one reference point simply makes the entire process less accurate because you have a pure dependency on one inaccurate face.

I might be wrong in my analysis but it sure seems like people using one reference are going to end up with less overall accuracy. I guess some of this comes down to an esoteric concept of what the "real" center of the frame is. I don't buy that the drive side face is somehow better then the other face and think if you really want some esoteric concept of alignment you should flip.


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## febikes (Jan 28, 2011)

Meriwether said:


> I have read a few posts from DWF who says those who measure after each weld are just 'chasing their tail' and that makes sense to me. So, I tack the front triangle and chainstays in the frame fixture and then ream/face the BB before putting it on the alignment table to see where I'm at. Then I can add a tack or two if something's off. Then i weld the front triangle and chainstays out of the fixture, repeat the BB facing, etc. and add a second pass on a weld if needed (it usually is at this point for me). I'm sure I'll change my process 20 times more but this makes sense to me for now...


A big advantage of doing each joint independent is that you address the internal stresses in the frame. Think about the forces distortion creates inside the triangle. If you tack everything then weld everything you might have the top tube trying to press the head tube to the right and the down tube trying to press the headtube to the left. The bike might be "straight" but internally it is fighting it's self. When you get a hold of a frame like this you can cut through a tube with a hacksaw and it will jump like a spring because of all the internal tension.

Weld each joint and checking the alignment after each weld reduces the internal stresses on the tubes and *might* result in a stronger frame.


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## bee (Apr 7, 2008)

alexmeade said:


> For BB posts and other stuff that you might want to use to build on a surface plate, I humbly submit my own offerings. I'm a newbie here so I can't post a URL, but my website is
> 
> alexmeade.com
> 
> ...


Great looking tube blocks. It would be much more versatile to use v-blocks turned sideways though. That way you can use non-round (i.e., oval) tubes and all your centerlines are the exact same.


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## Meriwether (Jul 26, 2007)

*sorry if this is going more off-topic...*



febikes said:


> A big advantage of doing each joint independent is that you address the internal stresses in the frame. Think about the forces distortion creates inside the triangle. If you tack everything then weld everything you might have the top tube trying to press the head tube to the right and the down tube trying to press the headtube to the left. The bike might be "straight" but internally it is fighting it's self. When you get a hold of a frame like this you can cut through a tube with a hacksaw and it will jump like a spring because of all the internal tension.
> 
> Weld each joint and checking the alignment after each weld reduces the internal stresses on the tubes and *might* result in a stronger frame.


I think I see what you're saying but I don't understand how checking the alignment after each weld would result in reducing internal stresses any more than what I do. (As an aside, it's amazing the diversity if people's building processes and most of the bikes people make last a long long time). Unless you somehow change your weld's heat input to make it 'equal out' or something along the way? If your miters are tight and you tack it together right, and you can weld well enough to not overheat one side of the tube vs. the other...isn't that good?

But maybe I don't understand what you're saying about your process. I don't see how checking each weld would make a difference in the outcome other than learning for yourself what each weld does to the frame's alignment but that's more of an educational endeavor than a frame strength thing IMO. I read somewhere that Carl Strong said he purposely welds his frames using a sequence that UN-aligns the frame before finishing and making it aligned...or something to that effect.

Here's your thread that I remember DWF's process and also Walt's. It's a great thread.


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## Andy FitzGibbon (Jul 7, 2007)

febikes said:


> I want a really table but mostly for speed, if my goal was to improve accuracy I would just flip things and not care at all about the table beyond the context of the post holder.
> 
> If the reference point is wrong on both faces of the BB then flipping becomes more accurate. It sure seems that using only one reference point simply makes the entire process less accurate because you have a pure dependency on one inaccurate face.
> 
> I might be wrong in my analysis but it sure seems like people using one reference are going to end up with less overall accuracy. I guess some of this comes down to an esoteric concept of what the "real" center of the frame is. I don't buy that the drive side face is somehow better then the other face and think if you really want some esoteric concept of alignment you should flip.


The definition of alignment is_ the process of adjusting parts so that they are in proper relative position._ This is what Doug is getting at when he says that "it is necessary to pick one reference as the standard for alignment that everything else is based off of." He chooses the drive side BB face as his reference point- not because it is "somehow better" than the opposite face, but because it is the face that everything else should be aligned to for mechanical reasons.

The "pure dependency on one inaccurate face" that you speak of is exactly where you start in a true alignment job. In the case of a bicycle frame, you would first make that inaccurate face as accurate as possible (using a facing tool). You then have "pure dependency on one _accurate_ face", which is what you want- you can then use the known flat surface of the plate to bring the rest of the frame in line with that single reference point.

Flipping the frame does not "average out" any inconsistencies. Instead, it introduces more inconsistency- this is the magnification of error that Doug refers to. Unless your shell faces are 100% parallel and your tubes are positioned over the exact center of the shell, you don't know where the error is originating, which makes it harder to correct the error in a logical and accurate fashion.

The idea of a surface plate is not to align the frame to the table, but to use the known flat surface of the plate to align the frame to itself. What you are doing is aligning the frame to the table. As long as you are happy with the results you are getting, I can't think of a reason to stop doing it that way. But, there is a good chance that it's not as fundementally accurate as the method Doug describes, and it's _definitely_ not more accurate.


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## Meriwether (Jul 26, 2007)

febikes said:


> I want a really table but mostly for speed, if my goal was to improve accuracy I would just flip things and not care at all about the table beyond the context of the post holder.
> 
> If the reference point is wrong on both faces of the BB then flipping becomes more accurate. It sure seems that using only one reference point simply makes the entire process less accurate because you have a pure dependency on one inaccurate face.
> 
> I might be wrong in my analysis but it sure seems like people using one reference are going to end up with less overall accuracy. I guess some of this comes down to an esoteric concept of what the "real" center of the frame is. I don't buy that the drive side face is somehow better then the other face and think if you really want some esoteric concept of alignment you should flip.


I guess I don't understand what you mean by one face being inaccurate? If you face the BB shell with a good tool - it's flat - and your BB post hopefully is nice and flat too, and your table is really flat too. So, one side (either is fine I presume) of your BB shell is your reference point from which you measure to the center of the seat tube with a height gauge or whatever. That is frame-center for the head tube, downtube, rear axle. What am I missing?


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## febikes (Jan 28, 2011)

Thanks everyone the thread has been very helpful but we are getting to the esoteric stuff...

The internal stresses from welds fighting each other is "real" but it is likely meaningless as well. I mean if you tubes are fighting each and are under tension at rest then it's not good but it's a bike and not a rocket ship and I don't think it makes a huge difference. Frankly I still have a long way to go in my welding skill. The reason I do each weld independently mostly is because it helps me more easily see the effect of each welding action.

In terms of the faces as accurate or inaccurate I stand by my position that the two faces are never perfectly accurate. The park tool is not going to give you the 0.0001" level, I bet it is more like +/- 0.003" at best but that is a total guess. Since the two faces are each inaccurate an average reading from each side will cancel some of it out unless you happen to get unlucky and have both faces going the same direction but odds are they will have some cancel factor unless as has been pointed out you decide you don't care that much about "true" center. If you care about one face more then the others then by all means use that approach.

I totally agree that an surface plate is a good thing but I don't think it has to be the first thing a new builder buys unless you are into that sort of thing. If nothing else the granite makes for great photos...

For the record, when I get around to buying a true table I will not bother flipping because like I said I am happy with +/- 2mm.


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## DWF (Jan 12, 2004)

Meriwether said:


> There have been frames where my miters were near perfect, and my welds were pretty evenly good and the frame was off over 4mm. Totally confused me as to why. I was able to figure out how much a 2nd pass did to pull the frame into alignment instead of trying to coldset it. It also pointed out to me that a certain miter was a bit worse than another or that my tig beads were not as even in heat as I initially thought.


You probably learned more on this frame than all the rest too. Even heat input is HUGE to alignment. Learning how to move a frame around using heat instead of cold setting is huge too. Make sure that if you do wash a section of weld to pull the frame you're not actually using filler unless you starved it the first time around. Keep in mind that a central tenet of good building is to put no more heat into the frame than needed for good joinery, but a hot wash or a little witch wanding is better than cold setting, IMO.


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## doug fattic (Mar 11, 2010)

Sometimes it is good to review the fundamentals of what and why we do things so the discussion can give new builders a clearer understanding of how to improve and those with experience can double check that their methods are the best. I should make it clear that I am primarily a lug road builder and so my methods are slanted to doing things that way. I can tig a frame okay but primarily I do that when I'm using heavy walled tubing for transportation type of bicycles. 

The primary importance of a seat tube coming 90 degrees out of the bb shell is so that through all the connections, the pedals aren't crooked which could introduce stress into the knees. This is why the New England Cycling Academy (NECA more commonly known by its Fit Kit product) produced an alignment beam for stores that also adjusted cleats. It wasn't possible to get the cleats right If the frame was out of alignment. So our ultimate goal is for the seat tube to be square with the bb threads that position the axle. Of course it isn't simple to use the threads as the datum so a faced bb face becomes an easy to use alternative standard. I've known some to use a head tube. Various methods can work well – although we may not prefer all equally.

Deciding on how accurate to get alignment is a little like asking how many decimal places we should go when we divide by π. Their is a point of diminishing returns. Part of my business over many years was repainting frames including braze-ons and alignment. It was common for old steel road frames to be out a quarter inch or more (Japanese frames tended to be spot on). I would often ask the customer after they had ridden their new reconditioned bicycles if they could tell any difference. Often they would say yes when I aligned them only a little but sometimes no when I did a lot. People vary in their tolerance to inaccuracies.

I might mention I use my alignment tables as a tool and not just as an inspection plate. In other words I will put spot brazes or do other work when the frame is on the table. Others consider this practice sacrilegious. The reason I recommend getting one as soon as one can afford it as a foundation shop tool is that is has so many good varied uses besides checking frame straightness. It makes it easy to position and/or check that seat stay caps aren't twisted and directly across from each other, that brake bridges are square, that binder bolts aren't crooked. I use it to insure that shift lever bosses are exactly on the side. I could go on and on. It takes the frustration out of trying to figure what to use to get things right. Or at least it tells you what is wrong. It is a wonderful standard of accuracy when expensive fixtures are out of the question. I wouldn't call one necessary (I could build a lugged frame without it) but I would make it my first priority to get one if I didn't have one because I find they make many tasks easier to be faster and more accurate.


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## Andy FitzGibbon (Jul 7, 2007)

febikes said:


> In terms of the faces as accurate or inaccurate I stand by my position that the two faces are never perfectly accurate. The park tool is not going to give you the 0.0001" level, I bet it is more like +/- 0.003" at best but that is a total guess. Since the two faces are each inaccurate an average reading from each side will cancel some of it out unless you happen to get unlucky and have both faces going the same direction but odds are they will have some cancel factor unless as has been pointed out you decide you don't care that much about "true" center. If you care about one face more then the others then by all means use that approach.


What you wrote above is a good illustration of how flipping introduces uncertainty into the equation. When working from a single reference, you can determine exactly where an inconsistency exists and what needs to be done to correct it. With flipping, you introduce unknown variables that make identifying the source of the inconsistency much more difficult. As you say, flipping relies on luck, and the odds that your BB faces will be "close enough" that things will come out right. Flipping does not average or "cancel out" error- it just obscures it, by making it more difficult to measure and quantify. That is why it is fundamentally not as accurate as working from a single point.

Like I said before, there is nothing wrong with the way you do it. Some would question if the heightened level of accuracy of the single point method is really necessary. As was said above, building a perfectly aligned frame seems to usually be more a matter of builder's pride than making the bicycle functionally better.


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## customfab (Jun 8, 2008)

Walt said:


> Ok:
> 
> (.001*(750/19)) we get .039", or about exactly 1mm.
> -Walt


 is it about 1 millimeter or is it exactly 1 mm? Make up your mind


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## Walt (Jan 23, 2004)

*Got me...*

Yes, that was a spectacularly silly phrase! Good catch!

-Walt



customfab said:


> is it about 1 millimeter or is it exactly 1 mm? Make up your mind


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## BungedUP (Aug 18, 2003)

Regarding BB facing:

Standard BB facing tools don't always do a good job of returning the BB faces parallel to each other. However, it isn't a mystery as to how to determine how close to parallel they are: measure them! If you measure the shell from face to face with a micrometer or even calipers at multiple points, and the number varies, that variance indicates how much "bananaing" (yes, like Shakespeare, Carrol, and S. Palin, I made that word up) has occurred in the shell. If the shell has no discernible variance from place to place, your facing tool did a really good job. I have measured this many times, and recorded it. You can do this before facing, and after, to get a sense of what you are doing to the shell as you braze/weld to them. Parallelism after facing is usually not good with standard facing tools. You can however adapt tools to do a better job. As to how, that's different topic altogether. 

I think that chasing frame alignment down to the nearest .010" or so per frame member is not productive, and is outside of what can even be discerned without a CMM system. It also isn't discernable for the rider.


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## febikes (Jan 28, 2011)

Thanks BungedUP for the clarification on BB facing. I would submit that another technique to determine if they are parallel is to simply flip the frame over and measure at the end of a long member. You can use some math to determine the repeatability of the measurements on each side and then when you flip you can do the same thing and average the results to arrive at a calculation that will be fairly accurate.

You can average the results from the above to determine how good things are in the context of the true mid plane of the bottom bracket.

In truth people are not made very accurate. For example, one study reported that 32 percent of 600 military recruits had a 1/5 inch to a 3/5 inch difference between the lengths of their legs. This is a normal variation.
Limb Length Discrepancy - Your Orthopaedic Connection - AAOS

In my shop, my measurements seem to be +/- 0.25mm. With very simple tools I can take the frame in and out of my homespun table and get repeatability of 0.25mm for multiple measurements on a member that is about 500mm away from the BB shell. Using the tools I own I could in theory make a frame that is +/- 0.5mm but since I never cold set a main member I choose to be happy with +/- 2mm because the dirt trails I ride tend to be less accurate then even a bad table.

Just for fun, for those of you with "nice" tables, how repeatable is your result can you get when taking a frame in and out? How repeatable are result for flipping?


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## BungedUP (Aug 18, 2003)

febikes said:


> What I really want for my shop is one of these:
> Strong Hand Build Pro Welding Table 47" X 38" Anondized Aluminum
> 
> The table is rated as having flatness of .004" / foot. I am a little worried that the plates are a little thin but you could do some real creative stuff with something like that. If I had such a table plus a nice pure flat and big 2" thick metal surface plate I could have lots of fun.


Go for the Bluco.


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## BungedUP (Aug 18, 2003)

febikes said:


> Just for fun, for those of you with "nice" tables, how repeatable is your result can you get when taking a frame in and out? How repeatable are result for flipping?


If really careful with facing, etc., sometimes as good as .001" (sometimes) when re-tightening the handle on a given side in a given position.

Repeatability when flipping? If you mean as compared with the opposite side, I'd say it never comes out even close to the same. I'd guess rarely better than .030" at the HT. After all, a faced BB is rarely close to .001" of parallelism. Flipping can give you information, but it isn't straightforward, as unless you map where the parallelism is off, it's hard to know where to expect the frame to be misaligned (is it misaligned due to a true offset relative to the datum plane, or is it off because the secondary datum plane (opposite side of the BB) is misaligned in that direction, and by how much).


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