Mitering & fixturing shaped tubes

Hey all!

I was having a heck of a time mitering a shaped Spirit HSS down tube and was wondering what process other folks used for that. I was clamping it in my Cobra Miter Buddy, but couldn’t seem to put enough pressure on it to keep it from slipping once the hole saw dug in. Invariably, something would catch and the whole tube would get pulled to the side. I tried applying more clamping force but eventually dented the tube a bit.

Eventually I gave up and resorted to hand-filing the joint, but would love to not have to do that.

Someone else with more experience will certainly chime in with better advice, but I can think of two options. One - I’d have some simple FDM 3d printed mitering blocks made that match the profile. Two - I might try clamping the tube as best as possible in your existing block and then filling the voids with some good rigid expanding foam. It might be a pain to clean up but I’ve seen a similar process used when machining delicate features on a part, i.e. propeller blades.

If you find a good solution please post it! It sounds like a real interesting problem.


Those are great ideas! My brother has been trying to convince me to get a FDM printer, maybe this is the push I need.

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I print phase blocks that match chainstays and seatstays to ensure that are aligned in my gig. I am still hand filing the miters but these blocks are solid enough to clamp in a vise and hold a tube. I have to print them at 102% scale for them to fit the tube properly. I suppose that’s due to shrinkage during print cooling.

I think it would be neat to print something where the ID matched the tube profile and the outside was round to get a good clamp in the Miter-Daddy.


Are you using two of the Miter Daddy clamps? I got mine when it was only one but I see he sends it with two now for better grip.

The other thing I’ve done in my Anvil MTMF is wrap with electrical tape or similar to provide more protection for the tube so it won’t dent but also some anti-slip. The jaws dig into the tape instead of the tube.

Lastly if there’s a round section in the middle of the tube, may not be on that Spirit tube, you can add a tube block and square it up to the fixture or a plate with clamps and hold in place so it doesn’t rotate while mitering. But that may be hard to do on a vertical mill setup.


I got mine used and it’s definitely the V1, I’ll ask Joe about getting a second clamp - I could see that helping out quite a bit! I tried using a bit of leather to give some grip and cushion, but electrical tape is a great idea too. I don’t think there’s enough of a round section for a normal tube block unfortunately.

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I tried to delete my picture because of the message on there. It came when I took the screen shot

These type of clamps maybe?

That’s smart! I even have a pair of those that I didn’t think to use. I’ll try that out next time :slight_smile: