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Rake/clearance on threading tool for acme threads?

anchorman

Titanium
Joined
Dec 19, 2005
Location
Opelika, AL
I need to bore and cut threads in a piece of Aluminum Bronze for an existing piece of acme threaded rod. The rod is nominal 7/8-6 tpi, but measures about .030” smaller in diameter than the nominal standard size should be. *Should I make a close fit for the nut to the existing threaded rod, or make it closer to nominal size for 7/8-6 acme threads?*

I’m making this insert to press/pin into an aluminum casting to replace worn out threading that was originally cut directly into the casting. The assembly is used as a small press.

I’ve got the angle ground close enough, and it fits the threads on the rod. Sides are hollow ground at a slight angle to allow some clearance.

I’ve never made a threading tool for acme threads before, and am wondering if I need any rake on this tool, or best left flat on top? Slight negative rake better than none? I know brass can be grabby with positive rake tooling, and assume the Al-bronze will be too.

*edited for clarity*
 

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Be aware that when you grind a hook or negative on this it changes the angle of the thread section.
How and how much depends on side rakes. On a ten degree top cut vs a flat this is about 0.4 degrees ground different.
Also on any threader there needs to be more side rake on the "left" side due to the thread wrapping around the tool.
 
I’ve never made a threading tool for acme threads before, and am wondering if I need any rake on this tool, or best left flat on top? Slight negative rake better than none?
I had to do this for the first time 2 months ago. I can't remember the specific dimensions off hand but the Machinery's handbook has this info in the tool design section. It took me awhile to find it because I was initially looking under the ACME thread section. IIRC, clearance angle is either 5 or 8 degrees. I cannot remember if there was a rake angle or not.
 
The threads cut beautifully. I had to use a protractor to get the angle close enough, and checked using the threads from the screw. We've got a tormek super-grind machine for sharpening knives/chisels, etc, and with the optional carbide wheel, it does nice work on HSS tooling. Mostly freehand, but assisted by a small tool rest. No idea if they're the correct to spec size for 7/8-6 acme, but they fit nicely on the screw from the little press I'm repairing. I was a little nervous to be threading so close to the chuck with my stubby boring bar that I made from a woodworker's fly cutter, but cutting threads all the way past the end of a bushing is easier than a blind hole. I just listened to when it stopped chattering to know it was time to disengage the half nuts, and cut until the screw went in without too much fuss. If they wan't "accurate" threads in the future that fit a standard diameter acme screw, they can run an acme tap through there, since everything but the minor diameter are a little undersized.



Thanks for the help!
 

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Hey. You have the exact same Enco toolpost that I have!
for what it is, it's pretty nice. trying to get a multifix type sometime, but can't seem to get in touch with the people at create tool over in china. A friend bought years ago, and it worked beautifully, and was a fraction of the price of one made in germany or switzerland.
 
Emanuel Goldstein (EmGo) was making noise about importing some from china since Create is mostly shut down. I'm not sure it went anywhere but you could ask.

 
Tough to find the toolholders, I had to roll my own for a bunch of them. My toolpost has three fixed tools, and one QC slot.
 

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Tough to find the toolholders, I had to roll my own for a bunch of them. My toolpost has three fixed tools, and one QC slot.
Hi Jim,

Mine is identical, so far as I can tell. Sadly only have 4 holders total (plus those built in), one standard tool holder, one for boring bars, one for parting tools, and another one for larger boring bars or other cylindrical shank tools with about a 1” or so diameter. Works well enough on a 13” lathe, but having used the multifix a few times, I never got around to finding or making more holders for the enco. I did make a special wrench for my enco, by welding a socket for the tool holder clamp to one end of an Allen wrench that fits the hold down screw for mine. I probably would have been smart to just replace the screw that holds it to the T-nut with one that matched the tool holder clamp screw, but sometimes the smarter solution isn’t the one we see to the problem in front of us. 😅
 
for what it is, it's pretty nice. trying to get a multifix type sometime, but can't seem to get in touch with the people at create tool over in china. A friend bought years ago, and it worked beautifully, and was a fraction of the price of one made in germany or switzerland.
plenty of them on aliexpress.
 
what do you mean by that? do you need the main stud to be within 2µ like j.f. minders? repeatability? no idea. i have a write up a few years back on here where i found the creatools to repeat to low single digit µs on an original toolpost. nobody believed it and its not needed. i havent bought any there, so far. out of memory, do they say the system is not compatible with others? so what?
 








 
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