Cutting a wobbly curve consitently on a bandsaw

[squishio]

Hi Guys,

Bit of an odd one, I need to cut the below curve along the length of a 45mm aluminium tube (300mm long)
I'm practicing with some PVC at the moment, but for a start I'm struggling to get the exact shape I want, then the next problem will be to be able to repeat the same cut consistently (need 8 of the same)

https://cdn.bcf.44bytes.net/files/outline_small.jpg
(ignore the top straight line, thats side of the tube, its just the wiggly one I need to cut.

If this was a flat piece, I could just print and stick my drawing to the material, I have tried stretching the image and wrapping it round the tube once which sort of worked but am not convinced.

Can anyone suggest anything?

Cheers!
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[Ste]

I'd pay a metal fabricator to do it.

[bamt]

Make a jig to clamp the tube, with a wooden guide cut to match the profile you want that will but up to and slide against the saw to ensure consistency?

Googling bandsaw jig will give some ideas.

[BTTD]

As per bamt, a jig. I would make a sled and clamp the tube to it so it can't rotate.
A bit of ply with a 4x2 on one edge to clamp to.
The ply should be cut to shape, only offset say 10mm inwards. Set a pin into the bandsaw top, say a 4mm drill bit end 6mm from the blade, maybe use another piece of ply as a false bandsaw table top so you're not drilling holes in a cast top!
Use the pin to guide the template. Repeatable cuts, should be pretty accurate.

Edit: There is still going to be a bit of technique to it, and it may be that the template needs to be different shape to accommodate the distance from the pivot to the blade, and the fact that you have to rotate the piece around the blade.
Thinking about it, if you put some form of marker in the 4mm hole as you cut the form for a dummy template, you would then have the marking for the actual template.


Hopefully somone can think of an easier way.

[Dave....]

If band saw is only option and consistency is required a jig would be best but I guess that has to be right first time.
Cutting tube is hard at best of times and a band saw is a bit near as damn it sort of tool anyway.
You would need a square block longer than part to be cut with hole bored to suit tube and then cut the flat pattern through that but keeping it in one piece. Every part would be the same thereafter following the saw cut.
Failing that use https://www.youtube.com/watch?v=XygNK1kVKD0 which is what I may consider or a water-jet cutter if accurate consistency is required.
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[duhawkz]

could you not print this then wrap round the tube
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[c_dug]

I hate bandsawing tube.

Do you have spare tube length and a small machine vice?

If I had to do it at work I'd mark the tube up with sharpie. Then I'd give it to some other poor schmuck to do the hard bit (because perks of being the boss), but assuming that isn't an option, i'd maybe clamp the end very hard in a machine vice, with the bit you want to cut poking out, and try and cut close to the sharpie line, then file it finished or die grind it or something. It'd probably vibrate like a bastard and make all sorts of horrible noises! But otherwise I just see it spinning if I'm picturing what you're trying to do properly.

maybe I'd try and Mill it instead, pop it in a rotating vice or something and try and follow the line that way. Guessing that isn't an option for you?

As somebody who has reason to professionally bandsaw stuff on a reasonably regular basis, I'd still not fancy doing that repeatedly accurately on one. And sod all the faff of making a jig out of wood.

Did I mention I hate bandsawing tube?

This sort of job is where CNC really excels!
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[kramdra]

What is it for?

If it were wood you could use a bearing router bit to follow a wooden template. I would not like to cut tube with a router, but you could adapt the idea and make a crude drum sander with follower bearing.

[Omega]

Could you just change the design so these awkward parts aren't needed ?

[BTTD]

Easier jig idea.

Cut that shape into two peices of plywood stacked on top of each other. Then separate the two pieces with a 45mm thick peice of wood, 45mm from the edge.
You have a square C to put your bits of tube in.
Clamp the tube horizontally to the block of wood. Use the plywood as a visual guide of where to cut. Cut close, but leave a bit to file so you don't ruin the jig and can reuse it on the next one.

It's the simplest method I can come up with. I did think about a router with a carbide bit, but from what I understand aluminium can really grab the bit and get messy.
Without a mill, cnc, or other industrial machinery it's going to involve finishing with hand tools.

[bugeye_bob]

can you not cut them all out in a rough shape, clamp them all together and then finish off on a stone wheel/file to precise shape.

[fatjames]

Cut it out of flat stock, then shape over a mandrel?

[MCN]

3D print FTW
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[nowhere.elysium]

Either cut it from flat plate and form it, or cut the basic shape (just a simple triangle) and form it on a belt sander.
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[stinkwheel]

Make a wooden template then use a router, not a bandsaw.
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