# WWTP002: The Front Half



## jay_ntwr (Feb 15, 2008)

Ok, I have a working solid model...

I've got to say, I learned a lot from this exercise and I'm glad I did it. As I mentioned earlier, building off the front axle was a great direction to go and I'm glad that tidbit of information was shared with me at the North Texas Handmade bike show a few weeks back. It dramatically changed my understanding of the front half.

So let's just jump in with what the model does and how it works.

Here is what a 16" version of the same frame I have in 18" would look as a 2D print:










Since the print is associative with the model, this is the 18" version in both the "front view" which is my left side of the frame and the isometric view (note the dummy axle):


















To change the model is simple, I just edit the particular tube, ie, head tube, effective TT, top tube, down tube, seat tube with the parameters I set in the equation editor. The values that start with an "X" are my INPUTS as denoted in the comments section and the values DNM are DO NOT MODIFY values that are associated with those INPUTS. The DNM values are typically involved with reference planes or axes so that I can end up with a sketch plane for the cross section of the tube. Also, values can be entered as mm and the software automatically converts that to inches.










Note that the above is a 100mm head tube. The head tube is also the most complex of the tubes due to locating it via reference planes from the front axle. You'll see a lot of stuff in the DNM values that are used to define where the headtube will be in space.

Once the data is changed, the print updates automagically and this is the result. Note that the seat tube angle, Effective TT, and Head Tube Length are all different:










It took 9 minutes to change all the variables and have a new 2d print (I timed it as I thought you guys may find that interesting).

Notable things that may appear strange with this model:

-The tubes start half way and end half way into the next tube. I did this because due to the references that each part has, if the miters are cut, I lose my reference to the tube ends and those are important to me (from a modeling point of view). I may have to do a sister configuration of the final model that has miters cut but it really isn't necessary for anything that I can think of so I'll probably skip it.

-Effective Top Tube is a solid. Well, I hid that from the pictures above (see below) but there is a tube called the Effective Top Tube that defines the location of the Seat Tube. It turns out, and this is something I learned from making the model, that modeling an ETT is easy and really simplifies modeling the seat tube. Furthermore, I learned that the ETT is a function of Head Tube Angle, Head Tube Length and Seat Tube Angle. What's interesting about this is that it essentially means that the ETT is a junk measurement without those other measurements. All parameters equal and a slacker seat tube and suddenly your ETT is different. So guys, if you like the fit of your bike and any one of those values is different, your ETT is different. Now I'm not sure how different yet--may be negligible, but that will be in the next post as I have to recalculate what mine will be since i am changing my head tube length from the stock version (I will not have headset spacers--hate the look) so with the head tube extending, I suspect the ETT will change. To do so, I'll need more information than just the frame geometry (also learned in this exercise). I will need to know where the bars are in relation to the ETT to find that. So expect a solid of the stem and upper race as soon as I can get done with all these Christmas parties.










-Chainstays are boring--from a modeling perspective and possibly from a building perspective. There is one value and that's length. That's it, it's that easy. The axle aligns with the front at a given distance from the BB. Obviously tire clearance is the other dimension, but for calculating geometry, those appear to be pretty easy. Make them long enough or make them even a little longer. Obviously, handling is affected by this but am I missing something here?

-Seatstays are even more boring. They just connect to the Chainstays/Seattube. Nothing interesting here either...

For now, that's what I have for you. I'd expect to see an update shortly after Xmas but I don't think I'll have a lot more to offer before then. I'll get the new ETT figured since my head tube will change and update the model and then we can talk more about geometry I hope. If you guys all sign off, I'll get a check to Walt and we can get some tubes sent my way.


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## shiggy (Dec 19, 1998)

jay_ntwr said:


> Ok, I have a working solid model...
> 
> I've got to say, I learned a lot from this exercise and I'm glad I did it. As I mentioned earlier, building off the front axle was a great direction to go and I'm glad that tidbit of information was shared with me at the North Texas Handmade bike show a few weeks back. It dramatically changed my understanding of the front half.
> 
> ...


mmmm...The front end is the "easy" part to build. The stays--especially the chain stays--are tough as you need to accommodate tire, chainrings and crank. And they angle outward (at least) to the dropouts. The seat stays are slightly easier. But you can not really see it until you start working with metal. Up to that point 2D drawings work as well or better than 3D.

You are drawing this in reverse from the way I do it. I start with the BB position and place the contact points of the rider relative to that. Then I set the front axle relative to the hand position. The of the fork to be used needs to be factored in to set the bottom of the head tube and the HT angle. Then you should have the basic stem length and an idea on how tall the head tube should be. Connect the rest of the dots to fill in the frame. adjust the ST length for the post length you want to use. TT angle for the stand over. The ETT length is the _*LAST*_ dimension I will know.


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## JerryW (Nov 18, 2008)

~50mm of drop sounds normal, but isn't BB drop normally measured from the BB *center* rather than the top edge?

I don't mean to nit pick. I just want to know for my own info.

Jerry


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## Walt (Jan 23, 2004)

*Few points*

Constructive criticism:

-Shiggy is right that most people build around the BB center. This doesn't mean you have to do it that way, but it will be easier to talk to others about the design. Your call there.

-BB drop should be measured to the center. So you're at about 69mm of drop, assuming a 38mm BB shell. Some people would find that to be on the low side, but we can discuss the drawbacks and advantages in detail at another point in time.

-9 minutes is forever to mess with a few geometry numbers for the front end of the frame. I would encourage you to just use BikeCAD. Alternately, I can send you a set of Excel Macros that will allow you to calculate all of this stuff by typing a few numbers into the boxes. It will not return a drawing, though, just a set of miter angles and numbers. Don't get me wrong, the modeling is neat, and if it's helpful to you, you can certainly keep doing it. I'm not sure that it will really be useful to anyone reading, though. Heck, I don't even do *drawings* of frames - for me, there's just no point, as what I need are the miter lengths and angles.

-The rear end, while perhaps not as interesting for modelling purposes, will be *much* harder to construct. Just warning you now - the front end is, as Shiggy said, the easy part.

-Walt


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## rocwandrer (Oct 19, 2008)

You can fix the tube miters (if you care) by defining a plane as normal to an axis, and define your tube extrusion as concentric with the axis. then two way thin feature extrude the tube from the reference plane using "up to next." That will produce a perfect miter, and automatically update when you change the reference geometry to change the bike's geometry.

I agree that the front end is boring and unnecessary to model, and there might be signficant value in modeling all the interferences in the rear triangle, and what stay bend angle and positions might be best before building. The rear triangle will be more time consuming and more difficult to model accurately. 

I avoid that problem by doing a very simple 2D view of the cut plane of the chainstays, and separately, the seatstays. I do 2D because it is incredibly quick and easy, and I can visualize in my head quite well.... In this 2D view, the tubes are defined by their horizontal width at the widest part of the section. The tire is drawn as a cut plane into the page, the chain is a 6.6mm wide stripe in the extreme lowest gear, and extreme highest gear, etc. F der clearance can even be guestimated from this.

On a computer, it doesn't feel to me like it makes any difference where you start your drawing. Every parameter can be modified independently, or linked together as desired. I usually don't bother, but it is ever pretty easy to link the side view dimensions with the seat and chain stay views.


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## pvd (Jan 4, 2006)

Ok.

I love the SolidWorks stuff. Very cool.

You have been listening to the wrong people regarding bike geometry. You are way off target.

1. It's a whole bike, not a front triange. You need to get everything on there to see the bike.

2. I know you heard that you start the design from the front axle, but that's completely wrong. You start at the ground. You then go to tires. Tires are where the bike starts. You fit the rider onto the tires.

3. REMOVE 'BB DROP' FROM YOUR PRINTS. It is the most uninformed, meaningless, and waste of discussion number you can use. PEDAL/BB HEIGHT IS WHAT IS IMPORTANT! Pedal height is for cornering clearance and BB height is for chainring clearance.

4. You must anguish over getting the lowest pedal/bb height possible. This will produce the best climbing, best decending, best cornering bike you can build. How do you do that? It's truely hard. I've done a lot of work to help others on this point. see: http://pvdwiki.com/index.php?title=Head_Angle_Change_With_Suspension_Travel

4a. Example: My current trail bike has a 69.5 degree head tube (1/3 sag) , a 140mm front end, 175mm cranks and a 311mm bb height. That sounds like a high 12.25" height, but you need to remember something I call 'catostrophic bb height'. The height when the suspension is bottomed. On my bike, that's 10.75" that's what I'm working around, what I'm building up from. The same goes for the head angle. What started as 69.5 degrees ends up being about 74.5 degrees. Kinda at the crazy side of the limits as you dive into that rocky horseshoe switchback divebomb piled on the front brakes. http://pvdwiki.com/index.php?title=PVD_Winter_MTB

5. TOP TUBE LENGTH MEANS NOTHING. Stem lenght is important, top tube length is not. The rider sits on what I call the 'rider triangle'. This is the grips, the saddle, and the bb/pedals. That's it. No top tube mentioned. It's not a valid driving parameter. It is purely driven. Stem length is used to move the front wheel forward or rearward with respect to the rider.

6. The seat tube angle, seat height. AND AND AND AND AND seat post offset move the saddle into postition. You design the saddle to be in the middle of the rails using these parameters, all of them. Offset can be zero, but zero is a number. The key here is to remember that for most road bikes (for normal adult men) are laid back as slack as they can be SO THAT THEY STILL PROVIDE PROPER REAR WHEEL CLEARANCE. Then post offset is used to get final position. It's a wholeistic approch. When you start seeing it, the world rocks. Note that the seat angle on my MTB is 71 degrees with a zero offset post. PERFECT FIT!!! My road bike has a 72.5 degree tube with a 30mm offset post. PERFECT FIT!!!

7. Chainstays and seatstays are going to be your #1 pre-weding problem. I would have spent all my time modling the rear end for just this reason. You need to model your wheel, your cranks, your chainrings, and your rear rotor. You then need to think ahead to every rotor, gearing, or tire combo you may want to run and make sure that your bends allow for adequate clearance. This is the hardes part of framebuilding (actual fabrication) in my mind.

8. 100mm is a bit short for a head tube. I try to use longer head tubes so I can spread the head bearings apart as much as I can. My current head tube is 144mm, but that is an integrated. It probably would look more like a 120mm if it was a standard design. This give you more handlebar/stem combos. I'll say this again. MODEL AROUND GRIP POSTION AND STEM, SEAT AND PEDALS. That is the stuff up top that matters.

9. So, you've put a huge amount of work into your solid model. Based on what I'm saying, you need to toss it and start over. Sorry. This is the biggest lesson of all: Listening to people screws you up. Hear them. Think about what they say, but if you don't know (KNOW) for a fact why something is how it is, then you are probably doing it wrong.

9a. I'm in the same boat, but I leanred this years ago. I'm currently playing with lots of odd crank sizes because I JUST DON'T KNOW WHERE WE GET OUR SIZING FROM. I've read and talked to a lot of sources and I know one thing for sure, nobody knows what they are talking about, not even close. I don't know yet either. YET. But I'm PVD. I'll figure it out.


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## jay_ntwr (Feb 15, 2008)

Guys, thanks for all the feedback. Notably, I can't believe I missed the BB drop. In the solid, the drop is center to center, I just grabbed the wrong thing on the 2D print when I dimensioned it. I'm sort of shocked I didn't catch that.

So then you guys typically start with the BB it sounds like... That's the way I started this as well (have another full model that I scrapped that was around the BB before I started this one). I sort of see merit in doing it from either way AS LONG as I'm copying a frame like I'm doing in this. After thinking more about it, in my copied frame, I'm planning to extend the headtube about 30mm from 100 to 130 and that should shorten my ETT by 30mm x Sine 19 degrees if I'm thinking correctly in my head, so about 10mm.

Of course, *the dimensions I've come up with for now are only good if I copy the frame I am trying to duplicate.*

If you guys want to help me with a "custom" fit, I'm totally in and will completely abandon the idea of copying geometry that I think fits me now.

So how would we start that? Walt, I have your Excel sheet already (I think) but it confused me more than it helped months ago. Seems like it had a lot of stuff to set up the Anvil jig... I'll see if I can find it...

I've got no issues switching to BikeCAD if it will help us all talk more intelligently with one another. I'll probably still plug that stuff into the model in the end I suppose.

BTW, I didn't mean to belittle the rear of the bike and it's complexity. I think that came across wrong. I clearly understand that the front "half" is probably about 25% of the trouble during fabrication and that the rear is going to be much more difficult.

Thanks again for the feedback and I'm looking forward to working on this more with all the input you guys are giving me.


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## shiggy (Dec 19, 1998)

jay_ntwr said:


> Guys, thanks for all the feedback. Notably, I can't believe I missed the BB drop. In the solid, the drop is center to center, I just grabbed the wrong thing on the 2D print when I dimensioned it. I'm sort of shocked I didn't catch that.
> 
> So then you guys typically start with the BB it sounds like... That's the way I started this as well (have another full model that I scrapped that was around the BB before I started this one). I sort of see merit in doing it from either way AS LONG as I'm copying a frame like I'm doing in this. After thinking more about it, in my copied frame, I'm planning to extend the headtube about 30mm from 100 to 130 and that should shorten my ETT by 30mm x Sine 19 degrees if I'm thinking correctly in my head, so about 10mm.
> 
> ...


If you have a bike you like that you want to duplicate with a few modifications, locate your contact points relative to the BB and the front axle and draw the new frame around those. I can outline how I do that later if you are interested.


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## jay_ntwr (Feb 15, 2008)

shiggy said:


> If you have a bike you like that you want to duplicate with a few modifications, locate your contact points relative to the BB and the front axle and draw the new frame around those. I can outline how I do that later if you are interested.


sure, please outline this if you have the time. I'm sure that I'm not the only one that would benefit. I suppose I should just copy my frame but it doesn't mean I'm not interested in learning how to size one. That is very interesting to me and going through that exercise would be well worth I'd think.


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## NorseRider (Feb 9, 2004)

*Sticky candidate*



pvd said:


> 1. It's a whole bike, not a front triange. You need to get everything on there to see the bike.
> 
> 2. I know you heard that you start the design from the front axle, but that's completely wrong. You start at the ground. You then go to tires. Tires are where the bike starts. You fit the rider onto the tires.
> 
> ...


This should be a sticky. Peter cuts through and delivers an excellent framework for frame design. Excellent.

Truls


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## shiggy (Dec 19, 1998)

jay_ntwr said:


> sure, please outline this if you have the time. I'm sure that I'm not the only one that would benefit. I suppose I should just copy my frame but it doesn't mean I'm not interested in learning how to size one. That is very interesting to me and going through that exercise would be well worth I'd think.


This is going to look a little complicated but it is actually pretty simple.

Start with a bike that fits you well. Have the saddle at full (or normal) riding height.
.
Place the front wheel against a wall. If you do this in a corner you can prop the handlebar end on the side wall. Be sure the bike is not leaning to either side.









Make the following measurements as shown above (black letters A-G):
A=Wall to BB
B=Wall to front axle
C=Wall to center of saddle
D=Wall to center of stem bar clamp
E=Floor to BB
F=Floor to top of saddle
G=Floor to center of stem bar clamp

Now make the calculations to be used to set the contact points for the frame drawing (Red letters H-M):
F - E = H Saddle height
C - A = J Saddle set back
A - D = K Reach
G - E = L Stem height
A - B = M Front center

Now to start the frame drawing using the H, J, K, L and M distances








Everything is based off the BB location. Draw a horizontal line at your chosen BB height/drop and a vertical line to show the BB location. Also draw a horizontal line through the wheel axle height.
Draw in the contact points as shown above.
Connect the "dots" for your new frame considering the fork to be used, seatpost offset, standover height, etc.
This method lets you draw any shape frame while maintaining the same basic fit
 
The disclaimers:
I use the front center and reach as a way to set my hands over the front wheel (weighting the front end). I find this important to have a bike handle the way I like. You may not.
The above assumes using the same bars and crank length as the sample bike. Adjust the reach and saddle offset as needed.
Do not take any of this as the only way or best to draw a frame. It is a way that works for me with repeatable results on a variety of frame designs.


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## pvd (Jan 4, 2006)

That is some good stuff Shiggy. I just forwarded that to a friend that is trying to document his bike fits.

Did you draw that up or where did you find it?

I would revise it to measure to the grip rather than the clamp. Crank length should be noted as well. Front center may not be very important for fit notes. Otherwise, it's great.


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## shiggy (Dec 19, 1998)

pvd said:


> That is some good stuff Shiggy. I just forwarded that to a friend that is trying to document his bike fits.
> 
> Did you draw that up or where did you find it?
> 
> I would revise it to measure to the grip rather than the clamp. Crank length should be noted as well. Front center may not be very important for fit notes. Otherwise, it's great.


I drew it. The measure-against-a-wall method was a reader tip on Velonews.com.

I agree about the grip position. If you measure were the thumb/index finger wraps around the bar you can compare any shape bar. The stem clamp is just easier if you are using the same bar. I made a note about crank length, too.


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## themanmonkey (Nov 1, 2005)

DAMN *shiggy* that's some detailed stuff. I only have one thing I feel you might want to look into. For your "J" and "C" measurement you measure to the center of the seat, this is one step better than most people measuring to the center of the seatpost head, or saddle nose.

I measure to where the sit bones contact on the seat, this is the contact point, not the center of the saddle. This allows for changing saddles of various kinds and compensating for various seatpost head and rail designs.

As an example if you use the nose measurement or center of the seat measurement and go from a standard seat to a long seat you'll be too far back. Also with something like a Brooks you sit more forward in relation to the middle of the saddle than you do with non-suspended saddles.


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## shiggy (Dec 19, 1998)

themanmonkey said:


> DAMN *shiggy* that's some detailed stuff. I only have one thing I feel you might want to look into. For your "J" and "C" measurement you measure to the center of the seat, this is one step better than most people measuring to the center of the seatpost head, or saddle nose.
> 
> I measure to where the sit bones contact on the seat, this is the contact point, not the center of the saddle. This allows for changing saddles of various kinds and compensating for various seatpost head and rail designs.
> 
> As an example if you use the nose measurement or center of the seat measurement and go from a standard seat to a long seat you'll be too far back. Also with something like a Brooks you sit more forward in relation to the middle of the saddle than you do with non-suspended saddles.


Saddles are a big issue in sizing. There are so many different shapes it is had to come up with an accurate standard. Even if a rider always uses the same saddle you need to know where the center of the rails are located to set the seat tube angle. I use the "middle" as it "should" be close to the center of the rails. If you can get the STA so the base position has the post clamp in the center of the rails you have room to fine tune the saddle fore or aft.

Personally I have no idea where my sit bones rest on my saddles, partly because I am always moving around on the saddle.


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## themanmonkey (Nov 1, 2005)

Hey I'm giving this a bump and wondering where the weekly update is? I haven't seen a WWTP003 thread yet.


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## MMcG (Jul 7, 2003)

Nice bump - I was wondering about this and also hoping for a Show and Tell Friday Thread today, but so far nadda on either front.


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## rmb (Feb 9, 2004)

Me too, I have popcorn and I'm in the cheap seats. I just need something to look at.


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## pvd (Jan 4, 2006)

I thought that weekly updates were part of the deal?


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## toddre (Mar 1, 2004)

pvd said:


> Ok.
> 
> I love the SolidWorks stuff. Very cool.
> 
> ...


May I please question/argue against a couple of these points? (I'm strictly asking for my own (and maybe other's) benefit and not to come off sounding like a jerk or anything..I hope anyways...)

#3- BB drop: Wouldn't this be the whole basis of the frame design? It's your drop from the axle line that determines your BB height and from there the rest of the appropriate measurements. Maybe I'm confusing frame "drawing" and frame "designing"?

#5- Top tube Length: I don't understand how you can say that this measurement means nothing. TT length is a set distance that can not be "tweaked" and is a major ride characteristic. You can "fine tune" your fit with stem length. For example, I'm 6'5" and I prefer a bike with an eff. TT length of about 25.5" and a 120 stem ("genesis" type geometry for XL bikes). There is going to be a huge difference between that and some one else's XL frame that may be a 24.75 TT and a 140 stem. The characteristic of the bike changes immensly (spelling?) with the wrong top tube, but the rider triangle can be fine tuned with a stem adjustment

Again, questions, not attacks
Thanks
Todd


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## shiggy (Dec 19, 1998)

toddre said:


> May I please question/argue against a couple of these points? (I'm strictly asking for my own (and maybe other's) benefit and not to come off sounding like a jerk or anything..I hope anyways...)
> 
> #3- BB drop: Wouldn't this be the whole basis of the frame design? It's your drop from the axle line that determines your BB height and from there the rest of the appropriate measurements. Maybe I'm confusing frame "drawing" and frame "designing"?
> 
> ...


I Agree with you on BB drop. Drop is what you use when building a frame. BB height is what you have on the finished bike. When designing a frame you do draw the tire diameter but the axle centerline is really where you start.

Top tube length is meaningless when DESIGNING a frame. It is the length it needs to be after you have set the seat tube angle, head tube angle and total reach.

If you always use the same STA and stem length then the ETT length will be the same. But with the saddle set in the same position relative to the BB the ETT length will change with the STA. A steeper STA will shorten the TT and a slacker angle lengthen it, but the total reach will be the same with the saddle in the right place.

With my own bikes I like to place the hands fore/aft relative to the front axle. This means with the same STA the ETT will be shorter with a slacker HTA (and longer stem) and longer with a steeper HTA (and shorter stem). Total reach remains the same.

Also the amount of BB drop can have an affect on the actual/effective TT length.

With stock/production frames there usually is not much difference in frame angles so the ETT length is meaningful in determining fit. When designing for a custom frame for a specific rider the ETT length is what it needs to be after everything else is positioned. See my illustrated post earlier in this thread for details.


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## Thylacine (Feb 29, 2004)

There's nothing in your posts mate that indicate you've spent more than two seconds thinking about FIT.

There's two equations here.

1) Your three contact points in space, and CG.
2) The bike/frame geometry as a resultant.

You fit the person to the bike, not the other way around. Otherwise you're missing the whole point of what separates 'Custom' from 'Off The Shelf'. The first thing you should do is plot YOUR position, THEN draw the frame in.

I also don't see how the rear triangles on a standard frame are 'boring'. This is where 95% of your interface with tolerance critical parts are - think: Cranks, tyres, disc etc..

Kudos for the use of technology, but are you making a frame, or doing an exercise in Parametrics?


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## timroz (Feb 25, 2007)

Man, I'd a ruined half of them tubes by now if I won.


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## pvd (Jan 4, 2006)

Looks like another bail. In a few weeks the engineer has not been able to learn BikeCad, follow up, or complete posting.

Any way of getting the runner up on line for this project?


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## toddre (Mar 1, 2004)

pvd said:


> Looks like another bail. In a few weeks the engineer has not been able to learn BikeCad, follow up, or complete posting.
> 
> Any way of getting the runner up on line for this project?


Yep..should ahve gone with the guy who is basically teaching himself how to weld and is still trying to figure out how to do the drawing/design by hand...


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## byknuts (Aug 9, 2008)

pvd said:


> Looks like another bail. In a few weeks the engineer has not been able to learn BikeCad, follow up, or complete posting.


agree on the follow-up and posting side of things but learning BikeCAD is hardly required for building a frame!
more concerned with whether tubes have been cut, mitered and are roughly ready to go....
Last post being 2 weeks ago... about time for some news jay!

(and PVD, what's with the "engineer" crack?)


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## jay_ntwr (Feb 15, 2008)

Sorry, guys, the holidays were more complicated than I thought they'd be. I got suckered into a bathroom remodel...

BikeCAD took some getting used to as well. New post on the way after using Shiggy's stuff.

The post will be up today for sure.

Jay


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