Cutting threads with a die

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Tallystick
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Cutting threads with a die

Post by Tallystick »

I'm trying to cut 10-24 threads on a 3/16" 544 high-strength bearing grade bronze rod http://www.mcmaster.com/#red-metals/=ey2o2h to make the little pins that serve as the hinges on the Pearson Triton opening ports. I couldn't find anyplace to buy these so I thought, why not buy a bronze rod, thread the ends and trim to size? Well I'm having difficulty cutting the threads. The major diameter for 10-24 is .19 and the 3/16" is .1875 so the rod diameter should be fine. I've chamfered the end of the rod, used slow steady pressure, and cutting oil, but I seem to be mushrooming the rod slightly where the chamfer ends. The die isn't pulling itself onto the rod. Do I need a shallower angle chamfer?

Any suggestions on what I'm doing wrong?
barrybrown
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Re: Cutting threads with a die

Post by barrybrown »

You can buy them at http://www.bristolbronze.com/
they are not cheap but are available.
Hirilondë
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Re: Cutting threads with a die

Post by Hirilondë »

Maybe this is a dumb question, but have you oriented the die in the right direction?
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
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Tallystick
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Re: Cutting threads with a die

Post by Tallystick »

Yeah, the labeled side is facing the rod. I tried both ways just to be sure. Maybe my chamfer angle isn't correct. Maybe 544 bronze is a difficult alloy to work with, although the McMaster description says it's "highly machinable". Maybe the die is a piece of junk. It's from an auto parts store, although I've used the taps from the set without any issues. I guess I'll try a few different chamfer angles to see if that's the issue.

Bristol Bronze uses investment casting to replicate the parts. I'm not sure if they cast the threads, and then chase them, or if they cast unthreaded and machine them. I need to replace enough small bronze parts that I could spend a decent fraction of the boat's purchase price at $30 per part. I did some investment casting in grad school and furnace construction as well, so I may go ahead and implement those capabilities in my garage shop. A portable carbon arc furnace could come in handy. That would allow me to cast copper-nickel alloys like monel.
Carl-A259
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Re: Cutting threads with a die

Post by Carl-A259 »

Well for one thing, it is the hardest bronze available from what I've read. Don't know the Brinnell rating but I would guess harder than mild steel.
boatsnh
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Re: Cutting threads with a die

Post by boatsnh »

It's often that the rod is not ground "deep" enough to get the die to follow. Cut it down a bit so the die drops over it....Use more pressure than you think you "ought" to.....once you get 3-4 threads cutting, it ought to pull itself with no issue.

The rod is hard, but it ought not to be a big deal.

I suspect that you have a fair amount of rod & a bit more chamfer won't hurt you.
Tallystick
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Re: Cutting threads with a die

Post by Tallystick »

Success! Ok, here's what worked for me. I used my drill press to hold the rod and die, with the die in the vice, and the rod in the chuck. My mold release fluid is around 10% vaseline and 90% mineral spirits, so I used that for lubrication. You don't turn the drill on, just rotate the chuck by hand or insert the key into the chuck for additional leverage if needed. Quite a bit of downward pressure was used at the start, and after a few rotations the die grabbed and I could ease off the pressure. Once the die was mostly engaged, I began getting some resistance turning the chuck, so I used the standard 1/4 turn forward, 1/2 turn back, advance back to where I left off, another 1/4 turn forward, 1/2 turn back and so on to remove the metal chips. It cut beautiful threads that way actually. Freshly machined 544 has a really nice color.

That was with a chamfered rod. Northstar is probably right that the pre-chamfer isn't necessary. I'll try a normal rod probably tomorrow and report back.
Tallystick
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Re: Cutting threads with a die

Post by Tallystick »

A large chamfer isn't needed using the drill press method. I used a file to remove the flash after cutting the rods, and that tiny bevel is enough to easily seat the rod in the die.
Tallystick
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Re: Cutting threads with a die

Post by Tallystick »

Oh sorry for the confusion, I wasn't making the swing bolts. These were the threaded hinge pins that join the part of the port that holds the glass to the frame which is fastened to cabin wall. I set up a jig for cutting the slot in the hinge pins on the drill press as well. I do have a decent system worked out now for making these hinge pins, and the ones on the other side of the port which hold the swing bolts. It would probably take me 3-4 hours to manufacture another set of 24 hinge pins out of the 544 high-strength bearing grade bronze. If anyone needs a set or spares, message me and I'll make them at a reasonable cost, or possibly trade for parts I need.

I still need the swing bolts and oversize wing nuts. These will be investment cast. The silicone mold and wax replicas are already done. I had made a really cheap electric furnace, not bothering to add a thermocouple and temperature controller. It heated up faster than I expected and melted the element. Had some scrap copper and broken solar cell dust in a graphite crucible, and ended up with a nice looking little ingot which took on the drill marks from the bottom of the crucible hehe. I have to either get a new element and add temperature control, or I may make a carbon arc furnace instead.
Quetzalsailor
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Re: Cutting threads with a die

Post by Quetzalsailor »

I recently cut 5/16 coarse threads further down a 316 stainless steel eyebolt. At least the die was completely threaded onto the existing threads. What a lot of effort! Lots of oil and lots of backing and forthing to break chips. I was sure I was going to break the die or the holder. And I was worried about work-hardening the stainless, but apparently got away without the problem.

I've never had a problem starting a die but I'm happy to have heard of your experience.
Ric in Richmond
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Re: Cutting threads with a die

Post by Ric in Richmond »

Send them to me and I will do it on my lathe.....
Ric Bergstrom

http://andiamoadventures.blogspot.com/

Archived old blog:

http://andiamo35.blogspot.com/

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