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Shamisen Appreciator
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Discussion Starter · #1 ·
I'm idea collecting. I already have a concept as to how I plan to do this but there's always more to learn.

How do YOU hold a curved tube for mitering? Specifically, if mitering a curved seat tube on a vertical mill...ensuring the miter is square to the tube and in the right location (projected offset).

My intention is to keep the top of the ST at the angle specified in my drawing. It's easy to find the offset at any given point on the centerline of the tube by putting the tube on the surface plate and scribing a line with the height gauge on the side of the tube (after scribing a centerline down the length of the curve.) I figure I can get the miter location to within 0.5mm just by using a pointer in the mill to line up the center with my scribed point.

Is there an even easier way to do this that I'm overlooking?
 

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I would clamp the tube with three narrow V-blocks in the vise, One of them goes to the inside of the radius towards center of vice, the other two go on the outside of the radius towards the sides of the vise (I should take a picture). Since the tube is curved you can use your height gauge to make sure the tube is square to to table and the tool. Your centering setup sound pretty damn accurate.
 

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If the curve of the tube is gentle enough (or if there is a straight section) you could utilze one or two sets of the new bolt on tubing blocks from paragon, using two sets of blocks, do the bolt up on the surface plate, the blocks are square and then transfer into the vise on the mill. Or something like that. On the same note, a pair of these block on a tube would make for easy phasing into a mill vise for a downtube if one didn't have a full on mitering set up. Check out blue raccoons post for funky curved mill mitering setup pics for ideas. Sorry to ramble, just thinking fast here...........but knowing the work you do, all it will take is one glimmer or shred of an idea and you will be off and running
 

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Shamisen Appreciator
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Discussion Starter · #4 ·
j-ro said:
If the curve of the tube is gentle enough (or if there is a straight section) you could utilze one or two sets of the new bolt on tubing blocks from paragon, using two sets of blocks, do the bolt up on the surface plate, the blocks are square and then transfer into the vise on the mill. Or something like that. On the same note, a pair of these block on a tube would make for easy phasing into a mill vise for a downtube if one didn't have a full on mitering set up. Check out blue raccoons post for funky curved mill mitering setup pics for ideas. Sorry to ramble, just thinking fast here...........but knowing the work you do, all it will take is one glimmer or shred of an idea and you will be off and running
I'll check out the thread you mentioned, thanks for that. Unfortunately, the people who bend my tube used 1.5" dies to bend this 1.375" tube and now the cross section is a D shape rather than round. Tube blocks won't work. Mitering for the DM derailleur mount is going to be a be-atch too.
 

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So, just thinking along here, my mitering set up is an abrasive system and I use an angle iron tray to hold tubes at the correct angle, curved tubes are a ***** for me as well and I've been meaning to roll a curved tray to help with this. do you have access to a roller to make a tray to match your tube? if not I'm about 40 minutes west of you.....
Roll an angle to match, zap something square to it, clamp tube in tray, clamp tray in vise, miter, smile.............
 

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smudge said:
I'll check out the thread you mentioned, thanks for that. Unfortunately, the people who bend my tube used 1.5" dies to bend this 1.375" tube and now the cross section is a D shape rather than round. Tube blocks won't work. Mitering for the DM derailleur mount is going to be a be-atch too.
Like I said, V blocks. All of my curved tubes are oval on purpose, I made a bunch of V blocks just for holding weird shaped tubes.
 

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Shamisen Appreciator
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Discussion Starter · #7 ·
vulture said:
Like I said, V blocks. All of my curved tubes are oval on purpose, I made a bunch of V blocks just for holding weird shaped tubes.
That's the plan. I was just going to hold the BB end of the tube with two v-blocks with the BB end in the center of the vise so I can use a height gauge to level out the tube. By using just two blocks, the tangent of the curve will be roughly in line with the back jaw of the vise and if I dial the x feed a little bit it'll minimize alignment drift between cutter and tube along the curve.

It'll happen over the weekend. I'll be sure to update if I goof something up.

Thanks for the brain share all!
 

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smudge said:
I'm idea collecting. I already have a concept as to how I plan to do this but there's always more to learn.

How do YOU hold a curved tube for mitering? Specifically, if mitering a curved seat tube on a vertical mill...ensuring the miter is square to the tube and in the right location (projected offset).
Sean: here is how i do it. if the tube is oval use the next size up block or a pair of "v's" like Vulture says. - Steve Garro, Coconino Cycles.
 

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unterhausen said:
Steve, it looks like that block is hanging free. Is that wrong, or is there some other purpose to the block?
it's held on with the C-clamp. you use the block + a level to keep the miters in phase. I can knock out perfect miters in phase with each other, every time. i've done a few curved tubes in my days........ - Garro.
 

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crux said:
Learned this one the hardway years back. Don't really care what material your working with vibration only dulls ones tools making sloppy cuts. This hold true on both the lathe and mill. For cutting larger diameter tubes I would imagine this is even more true.
chuck up a heatreated 31.8mm x .8mm tube loosely on a mill/lathe & crank the hole saw into it and see what wins - stand back & wear eye pro! - Garro.
 

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Shamisen Appreciator
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Discussion Starter · #16 ·
coconinocycles said:
chuck up a heatreated 31.8mm x .8mm tube loosely on a mill/lathe & crank the hole saw into it and see what wins - stand back & wear eye pro! - Garro.
No kidding. You could do the same with ti, an uber-expensive LAN71 M42 hole saw and a mill with spindle backlash. This was a few years ago but this hunk got me square in the glasses.

 

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Shamisen Appreciator
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Discussion Starter · #19 ·
j-ro said:
So, just thinking along here, my mitering set up is an abrasive system and I use an angle iron tray to hold tubes at the correct angle, curved tubes are a ***** for me as well and I've been meaning to roll a curved tray to help with this. do you have access to a roller to make a tray to match your tube? if not I'm about 40 minutes west of you.....
Roll an angle to match, zap something square to it, clamp tube in tray, clamp tray in vise, miter, smile.............
Jake?
 
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