Advice about Dremel cutting wheels

[DaveC426913]

TL;DR Summary

Is there a better option than ceramic cut off wheels for going through brass hobby tubing?

As mentioned in another post, I'm cutting brass hobby tubing. I'm cutting a lot of brass hobby tubing. Like several hundred cuts. I'm using a Dremel, but I'm open-minded.

Using the little ceramic cutting wheels is cheap, and easily replaced when they break, but they are slow and they waste a lot of brass.
I'm cutting rings of brass barely a millimeter or two long, and the cutting wheels eats up a mm or so of material, so if I cut 100 cross sections each 2mm long, I have to cut away 1 mm of material. Not that I care about the cost, it's more about the speed.

Does anyone have suggestions about a better way to cut brass hobby tubing?

 

[Baluncore]

Does anyone have suggestions about a better way to cut brass hobby tubing?

Mount a close fitting internal mandrel in the chuck of a lathe. Slide a short stock brass tube onto the mandrel. Mount a tube cutter wheel on the toolpost. Cut brass tube against the mandrel, slide tube along by hand, repeat until mandrel is full, then unload and continue.

 

[DaveC426913]

Mount a close fitting internal mandrel in the chuck of a lathe. Slide a short stock brass tube onto the mandrel. Mount a tube cutter wheel on the toolpost. Cut brass tube against the mandrel, slide tube along by hand, repeat until mandrel is full, then unload and continue.

Took me six reads to understand first what you were describing and second why it was a better method.

But the key is the tube cutter wheel. Interesting.

So, one of the things that works to my advantage is that I have 19 sizes of tube - all the which nest with just a few micrometer's gap - from 5/8" down to 1/16", and I can cut them while nested. I get 19 rings for one cut. And it also ensures that I don't distort the tubes when cutting.

I wonder if I can adapt my idea to use a tube cutting wheel, as you suggest. The nested tubes will take the place of your mandrel...

 

[Baluncore]

I wonder if I can adapt my idea to use a tube cutting wheel, as you suggest. The nested tubes will take the place of your mandrel...

I use it with one tube, but I don't expect it will work with more than two. In effect the tube is free to be pinched between the mandrel and the tube cutter wheel. There needs to be a hard inner support to cut against, and the intermediate tubes need to be driven to rotate against the cutter.

The tube cutter wheel profile will be critical if nested tubes are to be cut to the same length. Maybe consider an asymmetric cutter wheel, flat on one side, so the outer cut-off ends can move away from the cutter as the depth of cut increases?

To cut nested tube in a lathe chuck, I would consider a powered thin cutting disk or saw mounted on a tool post, like a tool post grinder.

 

[berkeman]

Summary:: Is there a better option than ceramic cut off wheels for going through brass hobby tubing?

Does anyone have suggestions about a better way to cut brass hobby tubing?

Sorry if I'm missing the obvious, but why not use a standard plumbing tube cutter?

[Legal disclaimer: I have not read Dave's other thread, so I may be negligent in my duties here. Also, I do not stay up late at night like some other users here <cough>, so I may have missed some other conversations about this. Nolo contendere...]

https://www.dhresource.com/0x0/f2/a...-tube-cutter-cutting-tool-18cm-adjustable.jpg

 

[DaveC426913]

Sorry if I'm missing the obvious, but why not use a standard plumbing tube cutter?

Yeah, now I remember why.

I'm cutting tubing lengths on the order of 2 mm. Like the pic. Tube cutters can't do that.

 

[Baluncore]

Also, I do not stay up late at night like some other users here <cough>, ...

It is 11 AM here, and the Sun has been up since 7 AM. I think you sleep in for too long.

The reason for using the cutting wheel from a tube cutter against an internal mandrel is that the thin tube needs some support to stop it flexing. There is no need for the lathe if the mandrel is a close fit, and the pipe cutter can be kept square with the tube, so it does not cut a helical line.

I cut it in a lathe because I can repeat the cut against a fixed gauge and cut it square, even when the tube is flexible brass of softer plastic.

 

[DaveC426913]

The reason for using the cutting wheel from a tube cutter against an internal mandrel is that the thin tube needs some support to stop it flexing. There is no need for the lathe if the mandrel is a close fit, and the pipe cutter can be kept square with the tube, so it does not cut a helical line.

I cut it in a lathe because I can repeat the cut against a fixed gauge and cut it square, even when the tube is flexible brass of softer plastic.

Right. So it will work whereas a standard tube cutter won't because a standard tube cutter needs a brace in either side the wheel. A lathe does not.

Now all I need is a lathe...

 

[berkeman]

Now all I need is a lathe...

Is your birthday coming up?

 

[DaveC426913]

Is your birthday coming up?

As a matter of fact... it's coming up in exactly 364 days. No guff.

 

[berkeman]

As a matter of fact... it's coming up in exactly 364 days. No guff.

Happy Belated Birthday! Just sayin'...

 

[DaveC426913]

Thanks!

I plan to trade myself in for three nineteen-year-olds: one to sleep, one to work and one to play.

 

[Lnewqban]

If you don't have a lathe, you may be able to achieve the next best by replacing the lathe with a press drill or even the locked-in-position Dremel, doing the cut with a sharp steel knife against a rotating mandrel, previously turned out of aluminum or even hard wood.

For the smaller diameters, you could try this technique, perhaps improving it somehow to increase the precision of the cut:

 

[jrmichler]

Would this work? Slitting saw: https://www.mcmaster.com/slitting-saws. Scroll down to the smooth finish saws.

Possibly mount the saw on an arbor, chuck the arbor in a drill press, then make a fixture to hold the tubing vertically and move the tubing past the saw similar to a table saw tipped 90 degrees.

 

[DaveC426913]

If you don't have a lathe, you may be able to achieve the next best by replacing the lathe with a press drill

Is that anything like a drill press? I have one of those.

or even the locked-in-position Dremel, doing the cut

Yeah. When I was experimenting, I built a jig to hold the Dremel in-place and a tray to slide the tubing into it.

with a sharp steel knife

By this, do you mean a knife made of steel like an Exacto blade, or do you mean something else?

against a rotating mandrel, previously turned out of aluminum or even hard wood.

If I play my cards right, the thinner tubes will act as support for the thicker ones. For all intents and purposes I am cutting slices of a 5/8" solid brass bar.

For the smaller diameters, you could try this technique, perhaps improving it somehow to increase the precision of the cut:

I'm going to stick to tubes of at least 3/16" diameter. Anything thinner will just fold on me when my device is manipulated.

 

[DaveC426913]

Would this work? Slitting saw: https://www.mcmaster.com/slitting-saws. Scroll down to the smooth finish saws.

Possibly mount the saw on an arbor, chuck the arbor in a drill press, then make a fixture to hold the tubing vertically and move the tubing past the saw similar to a table saw tipped 90 degrees.

Cool. Checking that out. Thanks.

I'm not sure how I'd attach this to a drill press or Dremel. Those ... er... "arbor holes"? are huge - like, a 1/2" to 1".

(OK, it looks like there is some sort of arbor chuck that facilitates this.)

 

[Lnewqban]

Is that anything like a drill press? I have one of those.

By this, do you mean a knife made of steel like an Exacto blade, or do you mean something else?

Sorry, I meant a press drill.
I like @Baluncore idea best, mine is just a less precise way to do it because you don't have a micro lathe.

An Exacto blade could work, or any other sharp knife, provide that you wear eye and hand protection while experimenting with that idea.

 

[Tom.G]

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https://www.physicsforums.com/attachments/1615766799541-png.279788/
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@DaveC426913 Would you be so kind as to post a photo of the finished item those rings belong to?

Thanks,
Tom

 

[Ranger Mike]

how about these copper ring shims?

https://www.mcmaster.com/washers/ring-shims-6/

 

[DaveC426913]

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https://www.physicsforums.com/attachments/1615766799541-png.279788/
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@DaveC426913 Would you be so kind as to post a photo of the finished item those rings belong to?

Thanks,
Tom

It's only been in the works for about 20 years, but sure.

Sorry - to clarify: that pic is pulled from the internet. It is not mine. And those hands aren't mine either.

Although I can post a photo of a single piece of a prototype.

 

[DaveC426913]

how about these copper ring shims?

https://www.mcmaster.com/washers/ring-shims-6/

Sorry, the rings are part of a larger structure that is also composed of brass tubing and must be of exact size, down to a dozen micrometers.

The cylinders are about 1" long each, and the rings are stoppers.

Here's six nested cylinders (long, grey), each with 3 stopper rings (short grey) soldered or glued to them (blue.)

This unit will telescope from about 1.25" to about 6".
I need 24 of them. Each of which requires 18 rings.

 

[jackwhirl]

Maybe I'm missing some subtle issue, but with the right mandrels, which everyone else is mentioning anyway, wouldn't you be able to use a standard tube cutter? Just slide a scrap piece down the mandrel to rest against the piece you want to cut, and it will be supported on both sides. You would need a mandrel for each size of tube you want to cut, but it should work.

 

[DaveC426913]

Maybe I'm missing some subtle issue, but with the right mandrels, which everyone else is mentioning anyway, wouldn't you be able to use a standard tube cutter? Just slide a scrap piece down the mandrel to rest against the piece you want to cut, and it will be supported on both sides. You would need a mandrel for each size of tube you want to cut, but it should work.

That's very true.

 

[Dullard]

That looks like it's going to be a lot of fun to assemble.

 

[DaveC426913]

That looks like it's going to be a lot of fun to assemble.

Early prototype, soldered.

The key metric is that it must allow the object's sides to expand by at least a factor of 2 root(2) - i.e. ~1:2.828.

Not too hard, except that this cylinder only a part of the object's sides. The joint/corner elements take up room but do not likewise telescope - which means the cylinders must do a fair bit better than 1:2.828. Which is why I need to add nesting cylinders to the design until I achieve a sufficient telescoping ratio.

 

[DaveC426913]

OK, next troubleshoot.

To cut through nineteen nested brass tubes, I need to find a way to secure them together. Otherwise, the action of the Dremel causes them to move and rotate and fall out and get lost - especially the smallest rings.

In my first trials I simply applied tape to the far end so that the inner tubes couldn't rotate as I cut. But that didn't stop the rings from bouncing about and getting improperly cut at the business end.

I think I need something with which I can lock all the tubes in place until I'm done cutting and can separate them.

I was originally hoping I could dip the whole thing in wax - filling the gaps between tubes - and letting it harden, but of course the Dremel will immediately melt the wax.

I need a substance that is
- thin enough to get into the gaps (which are .0016 inches),
- will harden
- doesn't melt with heat of cutting
- can be completely removed (dissolved?) when done.It's also possible it's overkill to immerse the entire thing in a hardening goo and hope to recover it.

Maybe if I placed a block on the operating end, to secure the ring and its inner parts, while I cut...

 

[jackwhirl]

I presume you're trying to save time by cutting all the layers together, but I'm not sure it's worthwhile...

Superglue? Or just solder/braze them together.

 

[jackwhirl]

Do you know anyone with a laser cutter? You could do all the rings from a sheet of brass in a few minutes.

 

[Baluncore]

I think I need something with which I can lock all the tubes in place until I'm done cutting and can separate them.

Drill a hole half (or all the way) through the block and insert a temporary close fitting pin.

Start with all long tubes nested. Solder one end, cut rings from the other end.

 

[DaveC426913]

Drill a hole half (or all the way) through the block and insert a temporary close fitting pin.

Start with all long tubes nested. Solder one end, cut rings from the other end.

I have no idea why I didn't think of this.

 

[DaveC426913]

Ugh. So frustrating. I habitually get a few dozen hours into this project and conclude all over again that it's just not practical to build it all manually. I need

- 32 tubes, each of which has 2 ends, each end has 8 subtubes, each subtube has 3 stopper rings
- 16 vertices, each of which has 4 posts, each post is a universal joint, each of which has 2 ends and a core

That is a LOT of cutting and soldering. Like, a lot.

It's also not cheap. One 12 inch length of fully-nested tubes come to about $60. And I'll need several.And I end up going back to 3D modeling and printing it. At least I only have to design it once and just make copies.

It's not cheap either. One unit of tube and u-joint costs about $40 with shipping. That's going to add up to about $640 if I can't find a way of cutting costs.

The downsides to 3D printing are manifold:
- material is not nearly as strong as brass. Cannot withstand torque.
- tolerance/fitting is a lot of trial-and-error
- because it's not strong, it need to be thicker, and I end up with assembled parts so fat that they stop being practical (such as a tube that has a larger diameter than length!)

 

[jrmichler]

Now all I need is a lathe...

Now you have a excuse to get a lathe.

 

[Baluncore]

I have no idea why I didn't think of this.

Congratulations, you suffer from the human condition.

Perhaps because the tube came in a box, so it was hard to think outside the box.

The other problem with round tube is that your mind cannot let go of the elegant continuous roundness, so you follow on round in circles, never reaching a solution. Stop the world, I want to get off.

It often takes two perspectives to find a solution. When dealing with a stock material, 'us ideal purists' look for a zero-waste solution. We all know that less can be more. We can see others wasting material, but not ourselves.

Imagine making many flat washers by drilling through the centre of a stack of coins held in a lathe chuck. It becomes impossible if one coin is very slightly larger or smaller than the others, unless you can glue them together first.

Using an annular cutter, or hole saw, to drill through multiple free layers teaches you to drill and pin the material before starting on the hole proper.