# Down Tube, Head Tube miter on a mill



## febikes (Jan 28, 2011)

I am getting a milling machine in the next couple of weeks and planning my fixtures.

My hope is that we can get a good discussion going on the fine points in creating a good miter. I want to make the best possible miter and would like to understand the various techniques in terms of pros and cons.

To start the ball rolling, I did a quick drawing of an idea to hold the down tube in a machine vice with a set of custom soft jaws. I plan to make the jaws such that the tube is supported as well as possible by cutting an angle as shown. It should be pretty easy to make a set of soft jaws to hold the tube.










What I am trying to decide now is the pros and cons of various techniques for getting the machine to cut the tube miter angle. For example, I can use a rotary table, the head of the milling machine, or use angle blocks to tilt the soft jaws in the vise.

Of the techniques I have been considering the one that seems the most direct is to adjust the angle of the mill because I don't own a rotary table. The mill has a scale for the angle adjustment and as compared with tilting the tube in the vise it seems the fixturing is more direct if I adjust the head of the milling machine to cut at an angle.

I am also planning for this to be my first operation because in doing so I will not need to worry about maintaining phase with the bottom bracket miter. I am actually thinking about doing the bottom bracket after the Head Tube is welded so that I can use the head tube as a reference for phase alignment (i.e. hockey stick style).

It's been a few years since I did any machining. I want to float this topic for input; I always learn so much here and look forward to your responses.


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## Walt (Jan 23, 2004)

Random thoughts:
-If you want setup speed/replicability you should avoid spending all your time tilting the head around. Best to get it set and leave it. 
-Anvil+rotary table is what I use and it's great. Expensive, though. If you are trying to make money, it's a no brainer, probably.
-If I were operating on a budget/hobby basis, I'd just get Paragon tube blocks (which will solve your phase problem nicely at the same time) and use an angle finder (Iphone app is plenty good enough) to get the cut at the correct angle. 
-If you just love making tools you could make your own tube blocks, but the Paragons will do just fine for anything bicycle-related you want to build and for the price there's really no other good reason to make them. Depends on what you love more - the tools/process or the bikes themselves, I suppose.
-I recommend against joining anything before you're done mitering. There's really no advantage I can think of and you're just increasing the consequences of any mistake you make on the next miter. 
-Get a couple of the long hole saw arbors from Paragon. Cutting acute angles will be much, much easier. 

Hopefully some of that is useful.

-Walt


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## afwalker (Apr 26, 2012)

Mark,
Moving the machine head would mean having to square it back every time. Doable, but annoying after a while. My bridgeport wasn't that expensive, but all the tooling sure added up I'm cutting main tube miters now on a Nichols small horizontal mill on a jig i made out of 8020. It's rotary table based and the big help is using a self-centering vise.







Grizzly H7576 Precision Self-Centering Vise - Amazon.com
Once it's all squared using those 3 dead centers, the table can rotate and all the centers stay together. Little demo here:
IMG_1411 | Flickr - Photo Sharing!
I made support stops for supporting one cut end, looks through my flickr if interested.
It was a fun project for me. I enjoy making tooling as much as building. If I was only doing it for a bike or two, then I wouldn't do a jig. I'm trying for 10-15 bikes per year.
cheers
andy walker


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## j-ro (Feb 21, 2009)

wws.(what walt said)

paragons are perfect for phasing although I find that for the cut you are talking about two of them right next to each other make clamping it in the vise a simpler task.

If you have the angle you need, just cut a little wedge of wood on a chopsaw to the correct angle and set it on the deck of the mill vise underneath the blocks.

tighten, cut and enjoy.

There's lots of super accurate ways to make this harder but you really don't need to.

jake


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## febikes (Jan 28, 2011)

Thanks guys!

I like the self centering vise and a rotary table *might* be involved in some future but I am interested in better understanding the downside of tilting the head on the machine.

It seems I often here people say that tilting the head is something they try to avoid. Is this purely because of the time associated with changing the angle on the head?

My idea is that by tilting the head on the mill I can keep the table and the work very close to the spindle and avoid the long hole saw arbors to obtain a setup that seems like it will make a more rigid cut. Sure it takes longer to set this up but is there a downside other then setup time? Is it more rigid than a stack of stuff holding the work and a long arbor holding the saw?

Is the rotary table just something for quick setup time?

For now I am just building for myself and friends but I want to have the best possible miters and as such if setup time takes a little longer I will do it if it makes a better cut. On the other hand, if a rotary table is going to make the actual cut better I want to understand why.

The rotary tables are also not cheap so I am hoping to kick that can down the road. I also have a very small shop and don't have the space for both a knee and a horizontal mill.

Btw, I am thinking about getting the pro tram system to assist in squaring the machine and setting the head at angle. Also, afwalker were did you get that slick set of finger jaws for your vise?


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## TrailMaker (Sep 16, 2007)

Hey;

Re tramming the head each time is the reason no one likes to move it. It's a pain. The device you featured makes it easier for sure, but it still takes time and that doodad costs you money. I don't have one... yet. I would make my tube blocks like you showed, one each for the BB and HT side, and clamp them on the DT in phase on the mill bed. Phasing locked in. Over to the angle vice, set to angle, saw, "done."

I bought the Palmgren angle vice off ebay for $35. It only LOOKED old and crusty. It's got a couple of drill strikes in the bed that I welded up, but no real wear. Bead blast, spray bomb, like new. CS/SS mitering is where it shines. Only slightly more useful... on occasion... than files, but does NOT replace them. Only gets you close, fast.


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## Walt (Jan 23, 2004)

Randomness 2!

-The main tube miters are the easy part. Seatstays and to a lesser extent chainstays are going to be more challenging. 

-As TM said, tramming the head is not all that fun. You don't want to constantly be doing it. You *can* but it's just a time suck. 

-All of the setups mentioned will be more than rigid enough. A long arbor will not hurt you on mitering in any meaningful way. 

-To be honest, feed/speed/saw selection are far more important than all this setup stuff IMO, at least when it comes to main tubes. 

-The goal of a milling machine for mitering is mostly speed, not absolute miter perfection. Hole saws are inherently not a perfect way to cut steel tubes. 

-Walt


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## graviT (Aug 9, 2009)

TrailMaker said:


> I bought the Palmgren angle vice off ebay for $35. It only LOOKED old and crusty. It's got a couple of drill strikes in the bed that I welded up, but no real wear. Bead blast, spray bomb, like new. CS/SS mitering is where it shines. Only slightly more useful... on occasion... than files, but does NOT replace them. Only gets you close, fast.


I have that same vise (albeit less shiny). It's handy but far from rigid. I'm sure that with 4130 that setup is fine but I imagine you'd run into trouble with higher end steels. Your miters will need less touch up plus you won't dull your hole saws so fast with a more rigid setup.


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## afwalker (Apr 26, 2012)

MAGNETIC 'V' BLOCK UNIVERSAL VISE JAWS
They're nice. I've used them for chain and seat stays also. The tramming just is a time suck. Once it's square I'd rather move the vise. The double indicator is nice, but just a quill mounted one and swing it to both sides will work fine. Like this for Bridgeport:
Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies
or the import for $15
Enco - Guaranteed Lowest Prices on Machinery, Tools and Shop Supplies
cheers
andy


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## febikes (Jan 28, 2011)

Thanks guys, this is going to be fun!

You have convinced me to avoid going down the adjusting the head angle road.

I am stretching my hobby budget a bit to get the mill so I am planning to build all the fixtures that I need. A rotary table will be nice down the road but I want a nice one and will need to wait a bit before I get it.

For my version 1.0 fixture I am now thinking of a setup that uses the Paragon blocks to hold the down tube so I can do all operations in quick setups using a standard machine vise. I might make a custom fixed jaw for the vise with dowel pin locations so the various fixtures can pop in and out of the vise and always index to the proper location. For angles I am now thinking of simple angle blocks to set the angle then bolt it into place.

How about some advice for hole saw RPMs or surface speeds for bicycle tubing? Do you guys calculate surface speed and load per chip (joking). My guess is super slow but what are you guys using?


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## afwalker (Apr 26, 2012)

I like the indexing idea, sounds good. 
Those V-blocks will let you miter say 20-30 deg or more if you have a tube block in the middle for phase checking. I use a digital level like this: Craftsman Digital Torpedo Level - Tool Catalog - Woodworking - Measuring & Leveling













Or mount a drill press vise to an angle plate like on the left of the pics.
cheers
andy


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## BenCooper (Feb 25, 2013)

> How about some advice for hole saw RPMs or surface speeds for bicycle tubing? Do you guys calculate surface speed and load per chip (joking). My guess is super slow but what are you guys using?


High speed, low feed - about 1200rpm for me. Though opinions on this differ...


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## RCP FAB (Jun 15, 2011)

80-150 rpm .0015" / rev


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## Walt (Jan 23, 2004)

Ditto. 1200 rpm seems insane to me - I run as slow as I can (80) and it works great for all the tubes I want to cut/doesn't seem to kill hole saws too fast.

-Walt


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## TrailMaker (Sep 16, 2007)

LOOOOOOOOW Speed!!!!!!!!!!!!!!!!!

ANY saws DETEST speed, be they hack or hole. Drills less so, but they definitely don't work like end mills and such. They vibrate by DEFAULT because of their construction. A good basic rule of thumb is the larger the diameter of the cutter in question for drilling operations, the lower the rpm. Small drills will stand a bit higher RPM because they do not generate so much heat. Larger drills will create exponential amounts of heat. This not only burns the edge off, but they will not cut if run fast. With bigger drills the feed needs to be moderately aggressive to alleviate chatter. If the drill chatters, it needs more feed pressure. With hole saws, not much at all. I use the lowest speed on my mill which I measured at 290. I also use the fine down feed for bike tubing. The drill press feed is far too clumsy. The fine feed is very controllable and allows the saw to take a small bite and not auger in (like climb milling).

Mark, by all means do move your mill head every time you want to do something on an angle, and tram it every time you are done. Everyone needs to learn how to do that properly. You will then also learn quickly and well why there are so many products available to help you avoid doing so!!! Time suck is a great description. I even mount my vice on one end of the tabel so I can simply leave it there for most of my work done on the bed. Tramming anything is like road riding. It rots your brain after a while. Well, tramming is better than that. At least it's not deadly...

Your setup there is reasonable, but the single shear mount block will not be very rigid. I agree that an angle vice is not very rigid in the greater scheme of things, but it is perfectly solid for this procedure. Lash in the table feeds will be activated long before any flex in that vice is noted.


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## febikes (Jan 28, 2011)

TrailMaker said:


> Your setup there is reasonable, but the single shear mount block will not be very rigid. I agree that an angle vice is not very rigid in the greater scheme of things, but it is perfectly solid for this procedure. Lash in the table feeds will be activated long before any flex in that vice is noted.


The photos of "real" fixtures have been a great help.

Thanks for the earlier photo of your setup. It looks like you made your own plate for chainstays and seat stays. I am planning something similar. Did you create blocks to hold non-round chainstays?

I plan to make the fixture pretty rigid so when it goes in the vise it should be rock solid. I may end up making my own tube blocks because looking at the paragon ones it is hard to adapt them to support the tube all the way to the end where the cutter is. What I really want is a block with an angle on it like my first cad design to support the tube close to the point where the cut is made. Hopefully it will not be too hard to make the blocks on the mill with a boring head.

I like slow speed and will be running as slow as possible for good tool life. I might add a coolant system to my mill. I don't yet have the mill but it has been ordered and will be here in a week or so.

For me the general evolving plan is to build dedicated fixtures with locating pins so they can go in and out of the vise to index to the exact location each time. I will make a special back jaw for the vise with locations for the pins. I did something like this years ago when I was working on CNC and there is no reason it will not work in the mill.

What I am evolving as an idea is that after getting tubes from the mail I will open the box bolt the tubes into dedicated top tube, down tube, seat tube, chainstay, and seat stay fixtures. The fixtures will use pins do drop into the vise so all miters can be cut without moving the table or the head. I will need to tool change between cuts but with the dedicated fixtures I think even that can be batched so mitering a frame will done with repeatable results in batch operations.

I am planning to do all my bb related miters in 100% the same way and lock in one standard chainstay length for all my 29ers. I like to build with sliders so my fixtures are not going to be adjustable for areas where I can avoid allowing the adjustments.

The miters that are size specific are the upper downtube, top tube, and upper part of seat stays. These will require the fixtures to be set at an angle but I plan to build angle plates into the fixture rather then use a rotary table. I am working on a design for the fixtures that will set the angle using an angle block then simply bolt down the angle plate. With locating pins in the back side of an angle plate it should be possible to setup each angle before the machine is turned on and then simply do a batch of size specific miters.










Building all the fixtures is part of the fun of getting the mill.


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## Walt (Jan 23, 2004)

You're going to do production runs? Wow. If that's your goal, just buy Anvil stuff. The money invested will be well worth it.

You can easily just cut away part of the Paragon blocks if you want more support around the mitered area of the tube, BTW. 

-Walt


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## febikes (Jan 28, 2011)

Walt said:


> You're going to do production runs? Wow. If that's your goal, just buy Anvil stuff. The money invested will be well worth it.


Ya but I sunk the money into the mill....

But really I also like thinking about the fixtures; who knows tomorrow I might wake up and just buy his stuff.

The anvil stuff looks super nice but it is really all adjustable. It's a different mindset and more focused on professional custom builders. I think he makes awesome stuff.

I am more thinking about an approach that goes in and out of the mill without any adjustments. Not really oriented around the idea of flexibility. What I want in fixtures accurate and repeatable results. Making the fixtures non-adjustable will make them much easier to build especially on a manual machine. I am going to avoid any adjustment in my first attempt at fixtures and use it mostly to learn the ropes on the mill.

The anvil stuff is cool but I also like looking at the fixtures others have built for ideas. I am sure plenty of guys here have some simple setups that work well. Hopefully we can see some more example photos.


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## kazlx (Jun 13, 2005)

Tubing blocks are extremely easy to make on the mill with a boring head. If you have any sort of mechanical ability, you should be able to do it the first time you using the mill. In all honesty, it's an extremely simple machine, it's the setups that are tricky. 

For what Paragon charges for the tubing blocks, it is well worth it to save the time. You don't really need more support or an angled block. If you need something specific, make them, otherwise, you could easily modify the Paragon ones.

Another thing worth mentioning about setting the angle on the head, is not only do you have the time eaten up in tramming, but you also have the time eaten up on getting the head nodded or tilted to the angle that you need accurately, which usually involved a sine plate or the similar. I have a Mitituyo digital level that works pretty well for quick and dirty setups. 

FWIW, I haven't built a frame yet, but have plenty of trial and error on machining other random stuff. I love looking at the setups of all the rest of these guys.

Edit: Also, using 4 sided blocks will by default keep your miters in phase.


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## Walt (Jan 23, 2004)

The Anvil stuff will do accurate and repeatable results very nicely, and the setup time is so quick that you can easily do what you're describing. 

I should take a picture of my setup maybe. It's a little embarrassing because it's all so beat after a decade of my abuse...

I have (from left to right) a rotary table, tilt vise, and normal mill vise. They are all squared up and never move. 
On the rotary table: I can miter main tubes with the Anvil main tube fixture. I can do chainstays as well with a ~30 second swap of fixtures. 
On the tilt vise: I have a dedicated seatstay fixture.
On the mill vise: Anything else gets done here (small parts, non bike stuff, etc).

I have a bunch of random pieces of tape with hash marks on them that, when lined up with each other, let me zero in various fixtures without any extra effort with measuring tools (so cutting tubes on center doesn't require a bunch of wasted time with an edge finder or whatever). 

The end result is that I can do all the operations I want with minimal effort very quickly (I'd LOVE a power knee, though...). If I wanted to build 10 identical bikes, it'd be easy - do all the DT BB miters, do all the DT HT miters, rest of the main tube stuff, etc. Then move on to the chainstays (same station on the mill), then finish with seatstays (tram over a foot to the tilt vise). 

Edit: Attached a picture of my beat-to-snot setup.

-Walt


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## kazlx (Jun 13, 2005)

I'd love to see pics of your setups Walt.


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## TrailMaker (Sep 16, 2007)

febikes said:


> The photos of "real" fixtures have been a great help.
> 
> Thanks for the earlier photo of your setup. It looks like you made your own plate for chainstays and seat stays. I am planning something similar. Did you create blocks to hold non-round chainstays?


Nah...

I bought that CS fixture from Peter Bungum (BungedUp - Whipsmart Fab). Hard to believe it his "old one" that he never used any more. It is elemental in some ways. Quaint even, but very advanced in others. Stainless rulers screwed to the deck are quaint. The machined locating ways on the axle tower and in the bed measure EXACTLY them same for inside/outside width. EXACTLY. Perfect machining. No radial play, and yet silky smooth slip. I have found it to be very versatile and I have thus far found no room for major improvement.

Don't over think the tube block thing. Boring head is another time suck. I have built up a set of tube sized center cutting end mills over time, from .500-to-1.500". Just get a block of aluminum and run the appropriate size end mill through it. Set up a slitting saw to cut the gaps. Done. Snug as can be. I never thought about doing it any other way. They are just tube clamps after all... To test them, I tried fitting a tube through the milled hole before slitting. Perfect. JUST able to slip the tube through the hole, and I mean JUST. No slop AT ALL. Slit the thing in two and it clamps perfectly. Peter sent a bunch of different size clamps with the fixture. I have clamped oval tubes in the round clamps and they seem perfectly stable to me.


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