Need Help!- Best way to make draw rings

[Russ Kaiser]

Background - I am a musical instrument maker and I use draw rings to resize brass tubing. For years I have been able to get by with the few sizes that I use all the time, now I need an entire set and they are very expensive.

What is a draw ring? - A draw ring is piece of steel with a polished hole through it. The steel is normally about 0.250 inches thick. Both the front and back edges of the hole have a matching radius (that would be 0.125 for a 0.250 thickness) that makes the profile of the hole semicircular. Draw rings are available in sets where the holes are graduated in 10-15 thousands increments or a bunch of holes are incorporated into a plate. I need hole sizes from about 0.300 to 1.25.

Normally draw rings or draw plates are chrome plated, but if when they are used with brass, the pieces are properly lubricated, I think a non-plated ring would last a great while.

Since a picture is worth a thousand words here is a ghosted perspective of a simple draw ring. The extra length allows the ring to be clamped in a vise.



I have a good, proven, hobby CNC mill based on the Zay 45, but right now the extents of my tooling are ball and end mills in the typical sizes. I also own a 7x14 inch metal lathe with typical tooling. I am a glorified woodworker, so I don't have a lot of experience milling metal. Software will not be an issue.

I am looking for suggestions on material spec. tooling and methodology to make a set of these. To be honest, I don't even know the best way to make a set of graduated holes.

I have a bunch of questions. Do I start each hole with a drill? Do I need to buy a boring head? Can I simply mill through the stock with multiple passes of an end mill? If I use a lead-containing steel stock "Ultra Machinable" can I do this job dry and still get a good finish?


Once I have holes, I am thinking I can use mills like this for the radius Corner Rounding End Mills but that would involve two sided milling with fairly critical alignment. I have thought about a true ball mill, so I can do the radius work from one side, but they are expensive and couldn't pass through the hole to do the smaller sizes. I also guess if I am doing two-sided milling, a regular ball mill could machine half of the radius on each side.

I would really appreciate advice on this project, but not to be rude, I could care less from hearing from motor-spinners who don't even have a working mill and are only guessing. I would like to hear from the guys that make stuff every day.

Many Thanks,

Russ

[RICHARD ZASTROW]

Your drawing would indicate the perfect application for corner rounding end mills.

You refer to "two sided milling". Is that the top surface and the hole inside diameter surface? If so, that should not be a problem. Place the parts on parallels and secure. Either flat on the mill table or in a vise.

Dick Z

[Russ Kaiser]

Hey Richard,

What I meant by two-sided, was that only half the radius could be machined at a time, (that part looks the same from either side) then the stock would have to be flipped. That makes alignment fairly critical since a misalignment would create a ridge in the bore.

I started thinking that maybe the radius of the cutter needs to be slightly larger than the half the thickness for this reason. A perfectly semicircular interior is not necessary; a round, smooth, hole is. The machining on the second side would assure the hole was round if the mill "reached" more than half-way through the stock.

It looks like these corner-rounding mills do a bit of surface cutting as well, so maybe depth of cut could be a tad more than half the stock width.

Any thoughts on starter holes?

Russ

[MrWild]

Draw rings don't need a semi-circular lead in. They need an exact sized hole, that is a couple of thousandths smaller than the desired finished rod diameter. This is due to spring back of the material. The lead in radius could be just 15* of a circle as long as the circle is tangent with the bore.

When making the draw rings, it is important to finish sand/polish in the direction that the rod is drawn. Sanding/polishing across the material flow is counter productive. The smoother your end polish, the nicer the finish on the drawn tubing.

You really want to use a tool steel. A2 heat treated to 56/58 Rc, gives good toughness with low brittleness. The chrome plating you refer to is a hard chrome for wear resistance. Don't confuse hard chrome with show, or automotive chrome.

[neilw20]

Hey Russ,

have a look at corner rounding cutters.
Carbide tipped drill bits, reamers, slitting saw blades and other carbide tip cutting tools from Super Tool.

I just googled 'radius cutters' to find this.

Or just make your own tiny fly cutter single point tools.
Use the CNC to do the circular interpolation.
Any diameter you like.

I use my CNC to do the final polishing with a wooden stick and some abrasive paper stuck in a slot.

Pretty good finish with 2000 grade!!

[Russ Kaiser]

Mr Wild,

I will be using these draw rings to make a tapered brass pipe starting with straight brass tubing. The rings I already own and use are made exactly as I described them above. When working on a tapered profile, the pipe is not drawn completely through a ring. As the pipe is worked from the largest to the smallest ring, the amount of the pipe worked is decreased.

I often work the tubing over a mandrel that is inserted in the pipe for support. The 180 degree radius allows the most deflection, off-center, during the pull or push and increases the speed the work can be accomplished. Snagging the pipe just once on a sharp edge can ruin it. The pipe is really only squeezed on two sides at a time and pulled over the mandrel. On each pass the tube is rotated.

This work requires time, patience, and a lot of annealing. It is essential that a draw ring for this purpose has a full radius on both sides of the ring since the working motion is bi-directional.

When the taper is close enough the brass pipe is annealed to dead soft one last time and burnished over the mandrel.

[easymike29]

Russ
Consider making all your dies round instead of rectangular. They then could be made entirely in your lathe including polishing. You can then make a rectangular holder if you wish.

Gene

[Russ Kaiser]

Gene,

Good point. I have seriously considered this. It makes sense to turn something that is essentially round versus trying to mill it. The one downfall is getting stock that has an outside diameter accurate enough to flip on the lathe and get easily realigned. I have a 4 jaw independent chuck for my lathe, so I guess it is just a matter of tedious set-up if I am using square blanks.

If I could find some 1/4 thick disks that were about 2 inches in diameter that would be perfect, since I could use a three jaw chuck. I have looked on places like McMaster, but the closest thing I can find is a washer. They tend to be stamped and fairly inconsistent. I guess I could also mount square blanks on the mill and mill the edges circular. That would take a while.

From a tooling standpoint, I am pretty sure I can find 1/8 inch radius tooling to turn the edges.

Russ

[RICHARD ZASTROW]

Russ, If you choose the lathe method, you can turn the O.D. locating from the I.D. on a mandrel.

If you choose the milling method, there are cutters available that will cut half-circle (180 deg. rad.) rather than quarter circle (90 deg.) as do the corner rounding cutters.

Dick Z


add: Harvey Tool concave radius end mills