Precision Cutting Jig Options for Brass Tubing: Buy or Build?

[DaveC426913]

I need to make a lot of precision cuts in brass tubing for a project I'm working on. I'm using a Dremel with a cutoff wheel and a vise. The Dremel is strapped to my workstation via a set of wooden tracks so it can slide to and fro, enabling me to cut the tubing in the vise.

It's not accurate enough. I need sub-millimeter precision.

I am considering re-making a jig using metal tracks so it's more rigid, but the effort may be prohibitive, since I'd need ways of securing and releasing it, and that adds complexity.

My question is: does something similar exist (or something I can adapt)? I'm happy to start with a base and modify it as-needed. I'd Google it, but I'm not even sure what I might call it, except "jig".

 

[phinds]

Dave, if you don't get a good answer here, try the WoodWorkingTalk forum. There are a lot of people there who do metalwork as well and although I quit that forum it utter disgust at their gross over commercialization, there are a lot of helpful folks there. Even the woodworkers might have a good idea for a home-brew jig.

 

[DaveC426913]

Thanks. I had thought of asking you, but I assumed you only worked in wood.

 

[phinds]

Thanks. I had thought of asking you, but I assumed you only worked in wood.

Which IS the case. I wouldn't know how to reliably get the tolerances you're looking for, but again, the folks at WoodWorkingTalk and WoodBarter would likely have good ideas.

 

[Baluncore]

Fine engraving or machining is often done using a pantograph arrangement. The pattern can easily be ten times larger than the object being machined. I have one pantograph here that is used to engrave the surface of small circular cylinders from much larger patterns. The pattern and the work are mounted at different ends of the same shaft. The cutter is controlled by the follower through the adjustable ratio pantograph. google 'pantograph' for many possibilities.

 

[berkeman]

Is there a reason you are using a Dremmel tool cutoff wheel instead of a traditional plumber's copper pipe cutter?

 

[phinds]

Is there a reason you are using a Dremmel tool cutoff wheel instead of a traditional plumber's copper pipe cutter?

Perhaps you missed where he said he is looking for sub-millimeter precision. Hard to think you could get that w/ a pipe cutter.

 

[berkeman]

I guess that's true, but you could cut it slightly long and grind it down to spec maybe...

 

[phinds]

I guess that's true, but you could cut it slightly long and grind it down to spec maybe...

Yeah, but then you need a jig to get the grinding to come out even and the right length. Better to do it all w/ one jig, one cut.

 

[Baluncore]

If you only need to cut the end square and to the right length then using a lathe will give an accurate square cut. For length I would make a simple collet with an adjustable screw as the rear stop. I would make if from steel with only one slot so the three jaw lathe chuck tightens the collet onto the tube to be cut. Eccentricity of the collet is not important for square cuts. The lathe could then be used to finish the second end, flush with the end of the collet.

 

[DaveC426913]

So ... I'm gettin' a metal lathe now?

What's that? A solid G-note? Second-hand? oo)

 

[DaveC426913]

Something like these would do. But I doubt they're affordable.

 

[Baluncore]

What range of diameters and lengths do you require?

 

[DaveC426913]

What range of diameters and lengths do you require?

I am cutting 12" stock hollow brass tubing (from a hobby shop) between 1mm and 10mm in diameter.

I want to cut lengths between 1mm and 40mm. It is these 1mm lengths (one might call the final product a ring) where I have trouble with my homemade jig. Even a small amount of play gives me lousy raggedy-edged pieces that I have to spend precious time grinding to a flat end.

I misrepresented the sub-millimeter accuracy. It's not that it needs to be accurate - it just needs to be steady. (i.e. my 1mm rings could be 1.2mm, no big deal, but they need to have a clean, flush, flat cut, not ragged).

 

[DaveC426913]

Thus.

 

[Danger]

Thus.
View attachment 74710

I can't believe that you're still too cheap to buy your wife real jewellery after all of these years.

You didn't mention which kind of cut-off wheel you use. I don't know if they make a metal one large enough to handle a 10mm tube without having it rotated. I assume that you mean the K7 style that uses a fibreglass disk. If you require a deadly flat end for the tube, bear in mind that those disks diminish in thickness as well as diameter while in use. I would recommend a 3-jaw chuck arrangement for holding the tube, such as you might scavenge from a scrapped 1/2" electric drill. You could also buy such a thing as a separate part from a mechanical repair shop. It shouldn't run more than about $20.
Hmmm... come to think of it, you could just clamp the whole drill down on a slab of plywood with pipe straps... then you could rotate the piece if necessary without losing zero... hmmm...

 

[DaveC426913]

I can't believe that you're still too cheap to buy your wife real jewellery after all of these years.

Ar ar ar.

You didn't mention which kind of cut-off wheel you use.

I've been using the standard ceramic cutoff wheels.

I don't know if they make a metal one large enough to handle a 10mm tube without having it rotated.

With a new wheel, I can juuust get a 10mm cut without needing to rotate. But it's not something I can count on sicne I'm not about to put a new wheel in every time.

I assume that you mean the K7 style that uses a fibreglass disk.

No. What's that?

If you require a deadly flat end for the tube,

No, just flush and not ragged. (I got to de-burr it, but it is very wasteful of time and material if I have to d it a second time.)

bear in mind that those disks diminish in thickness as well as diameter while in use.

Diameter is a no-brainer but It had not occurred to me that it would diminish in thickness. I wonder if that is part of my problem! By the time I'm almost finished a single cut through, it often seems like I've already gone off true. I've been attributing that to the bending of the brass as the cut proceeds.

I would recommend a 3-jaw chuck arrangement for holding the tube, such as you might scavenge from a scrapped 1/2" electric drill. You could also buy such a thing as a separate part from a mechanical repair shop. It shouldn't run more than about $20.

A simple flat vise works fine. I've got one like this:
http://www.fine-tools.com/york307791b.jpg

Hmmm... come to think of it, you could just clamp the whole drill down on a slab of plywood with pipe straps... then you could rotate the piece if necessary without losing zero... hmmm...

Yes. Got the drill clamped to my worktable. The issue is being able to slide the work through the Dremel (or the Dremel through the work). This is what I need the tracks for. Tightly-controlled movement with virtually no play.

 

[phinds]

Have you looked at Incra jigs?

 

[DaveC426913]

Have you looked at Incra jigs?

Not yet. Thanks.

 

[Baluncore]

Machining principles suggest that you should avoid sliding the cutting disk across the tube. Instead, rotate the tube. If the tube rests in a 'V' it can held in place and rotated by hand. The position of the tube can be controlled by the flat end of a square bar that also rests in the 'V'. The cutter then has two positions, firstly; clear above the tube and secondly; cutting the first mm into the tube. The tube is then rotated in the 'V' while being held against the square stop until the part between the cutting disk and the stop is separated. The process can then be repeated if needed with the same setting. By having a 10 mm AF square bar as the stop, rings of all sizes will be cut square. Careful control of pressure against the stop at the end of the cut will keep the end of the stock tube square, ready for the next ring.

 

[phinds]

Baluncore, I'm missing how your method feeds the next section to be cut, over and over, providing the consistency in length that Dave needs.

 

[DaveC426913]

Machining principles suggest that you should avoid sliding the cutting disk across the tube. Instead, rotate the tube. If the tube rests in a 'V' it can held in place and rotated by hand. The position of the tube can be controlled by the flat end of a square bar that also rests in the 'V'.

Hm. Good advice. I will reconsider my setup with that in mind.

One problem here, is that my stock material is between 1 and 12" long. To put a stop on the end of both a fresh piece and an almost-finished piece would require a stop-movement of at least 12". This is one of the reasons why I chose to clamp the stock - then it can be any length.

The process can then be repeated if needed with the same setting.

No, my stock would now be shorter. I'd move the stop in a millimeter, or whatever. That's not a problem.

It is however one of the reasons why I want to ensure that unlocking-moving-locking the stop is convenient (ideally without having to shut off the Dremel, and ideally without losing a finger).Cool. So, I can see the setup taking shape, and it is pretty simple. A 12" groove with a stop, The Dremel clamped to the table.

The only component left is giving the Dremel some up/down freedom to engage/disengage the material. And the material has different diameters, so it would need to be lockable at a fixed distance from centreline (centre of rotation for tube). (i.e. to cut 10mm tube, it would be fixed with wheel ~5mm from centreline, to cut 4 mm tube it would need to be virtually 0mm from centreline)

 

[Baluncore]

The tube is then rotated in the 'V' while being held against the square stop until the part between the cutting disk and the stop is separated.

Maybe not clearly explained. I think you have reversed my suggestion.

The distance between the stop and the cutting disk sets the thickness of the unit being cut. You hold the unused stock, where necessary with some form of extension such as a wooden dowel or the next stock soldered to the short end.
The positions along the V bed are; Adjustable stop, unit being cut, cutting disk, remaining available stock held by hand beyond the V bed.

 

[Danger]

Okay, there has to be some sort of communications gap happening here. I thought that you had the Dremel under control and just were looking for a way to stabilize the tubing. That's why I recommended using a drill chuck, which can be still attached to the drill and strapped down. Now you say that you already have a drill bolted down. If so, what else do you want to hold? And why would you use a V-notch to hold the drill? This is all very puzzling.
K7 was (is?) a cutoff wheel mounted on a chainsaw that was used back in the 70's by firefighters along with things like the Jet Axe and the Jaws of Life to access structures or vehicles. I just used that as a type-descriptor for what Dremel calls the 426. It's a wicked cutoff wheel made of fibreglass. I've used those in my Dremel to slice off hardened steel padlock shackles and carve up reinforced steel doors in order to install after-market locking units. The only other Dremel cutters that I was aware of were the 409 and 420, which are essentially rotary emery boards, and the steel toothed wheel that I first mentioned. I've never even heard of a ceramic wheel, so I can't be of any assistance there.

 

[DaveC426913]

I've never even heard of a ceramic wheel, so I can't be of any assistance there.

 

[DaveC426913]

Okay, there has to be some sort of communications gap happening here. I thought that you had the Dremel under control and just were looking for a way to stabilize the tubing.

I'm not picky. Whatever works. Baluncore has suggested rotating the tubing, rather than moving the Dremel, as a better way of cutting.

That's why I recommended using a drill chuck, which can be still attached to the drill and strapped down.

Not sure how that's better than a vice. I guess it can rotate. Which means I could do what Baluncore is suggesting - rotate the tubing as opposed to slicing laterally through the tubing.
Unfortunately, it's not very practical for when my tubing is 12" long.

Now you say that you already have a drill bolted down. If so, what else do you want to hold? And why would you use a V-notch to hold the drill? This is all very puzzling.

No one suggested the V-notch for the Dremel (or drill).

 

[Danger]

Those look like 409's to me, which are emery rather than ceramic. The 420's are also emery, but 15/16" in diameter. I've used 409's, and avoid them whenever possible except for polishing stuff with the faces of them. They flex in use, like spinning pizza dough, and shatter into pie-type shards if they encounter anything that they don't like or are fed in even the tiniest bit too quickly (which binds them; at 30,000 rpm, that's an easy slip to make). I'd maybe use one to cut light plastic, but certainly nothing made of metal.

edit: You sneaked in your last post while I was composing this one. Cheater!
Damn, but I miss those old smilies.

Okay, I think that I've got it now. You meant Dremel when you said drill, in reference to it already
being bolted down. That didn't occur to me, since you aren't using the Dremel as a drill. My idea with the chuck was to insert a stop inside the chuck as your "jig", and just support the outer end of whatever length by hand or on blocks. You can just finger-tighten the chuck to easily spit out the cut piece and push in the new stock.

 

[DaveC426913]

Maybe not clearly explained. I think you have reversed my suggestion.

The distance between the stop and the cutting disk sets the thickness of the unit being cut. You hold the unused stock, where necessary with some form of extension such as a wooden dowel or the next stock soldered to the short end.
The positions along the V bed are; Adjustable stop, unit being cut, cutting disk, remaining available stock held by hand beyond the V bed.

I see.

There's a problem there though. The Dremel's cutting wheel is a smaller diameter than the Dremel's body. Which means it cannot lie next to the remaining stock. (see top diagram in attachment)

I guess I can flip the Dremel, but it means the stop will have to lie next to the Dremel chuck and that will limit the longest piece I can cut.

BTW, I don;t know how the Dremel would rest in the V-groove and still be in the right cutting position. Gotta be separate units, secured to a base, methinks.

And I still need a way to engage/disengage the wheel from the tubing. So the Dremel has to slide sideways a little bit. And accurately, so I don't have the same old problem as when holding it by hand.

 

[DaveC426913]

They flex in use, like spinning pizza dough,

That might explain some of my problems.

Yet, I know they flex when you use the face, not sure how much they flex when cutting.

and shatter into pie-type shards if they encounter anything that they don't like or are fed in even the tiniest bit too quickly (which binds them; at 30,000 rpm, that's an easy slip to make).

Yeah. Happens alla time. No biggie. Frankly, since I've been using my make-shift jig, I very rarely have any exploding wheels anymore.

As long as I protect my eyes I'm OK. Frankly, I'm more concerned about all the brass dust I'm breathing...

I've never tried a different type of cutter. Not sure what the advantages are (though not flexing would be a big plus).
How long will they last? (i.e. how many will I go through compared to what I'm using?)
How wide a cut do they make? (less an issue now that I'm not cutting grooves anymore)

 

[Danger]

They (409's) most definitely flex excessively while cutting. That's why they're so easy to bind if over-fed. And you have to run at close to max rpm's to get anything done; they won't cut wax at low speed.
I can't give you an endurance estimate for 426's, since I've never used them on anything soft. They were reserved for stuff that bolt cutters or hacksaws couldn't do because they're a bit pricey. The trick to a Dremel, as I'm sure you know, is to keep the speed up and the pressure down. With a light touch at 30,000 rpm, it would take maybe 1/2—3/4 of a wheel to cut through the 5/16" shackle on a standard-duty padlock. Taking pauses to let things cool down extends that life. Also, effectiveness diminishes with wear, since the rim (cutting edge) speed at the same rpm is related to the diameter, and the loss of diameter accelerates. Off the top of my head, I'd guess that you could do at least 400—500 cuts through your 10mm brass tubing. According to my trusty dial mike, the thickness varies from .045" to .052"... so let's just call it 1mm.
You did effectively shoot down my idea, though, with your observation that the tool would be in the way of the stock. I somehow overlooked that, much to my embarrassment.

 

[phinds]

The positions along the V bed are; Adjustable stop, unit being cut, cutting disk, remaining available stock held by hand beyond the V bed.

Ah ... I see why I was confused. Good design. I'm not used to thinking in terms of the cutter not just slicing all the way through in a chopping motion.

 

[DaveC426913]

They (409's) most definitely flex excessively while cutting. That's why they're so easy to bind if over-fed. And you have to run at close to max rpm's to get anything done; they won't cut wax at low speed.

Oops. I've been running only at medium-high, to cut down on noise.

Also, effectiveness diminishes with wear, since the rim (cutting edge) speed at the same rpm is related to the diameter, and the loss of diameter accelerates.

Yes. I've been finding this. I step up the speed as the diameter drops. Or better yet, get a fresh disc.

You did effectively shoot down my idea, though, with your observation that the tool would be in the way of the stock. I somehow overlooked that, much to my embarrassment.

This is actually a systemic issue. All setups have it in common. One of the factors in determining my max length of ~40mm is that that is the maximum length I can cut anyway.

But putting a stop inside that 40mm distance reduces it correspondingly (see attachment in post #28, bottom diagram).

 

[Danger]

This is actually a systemic issue. All setups have it in common.

Okay, let's set that aside for now and get to the staging mechanism. Would your required tolerances allow the use of a model flat-car on a piece of HO gauge toy train track? (I'm not being facetious; I've made some assuredly adult-only devices using parts from toys.)

 

[phinds]

Not yet. Thanks.

http://www.incrementaltools.com/Metric_Original_INCRA_Jig_p/ij32metric.htm

 

[DaveC426913]

Okay, let's set that aside for now and get to the staging mechanism. Would your required tolerances allow the use of a model flat-car on a piece of HO gauge toy train track? (I'm not being facetious; I've made some assuredly adult-only devices using parts from toys.)

That's an idea. Though I see two problems:
1] They tend to rock. I'd need ... four?
2] They tend not to stay on the tracks. I'd be constantly having to put it back together.

But the gist of it - trucks on tracks might be modifiable. Hm.