How to determine anvil or shim angle for single pointing an acme thread with a lead angle of 5.59 degrees

WobblyHand

WobblyHand

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I made an attempt to single point an acme screw (nominally 3/4-5) and it didn't quite come out right. The tool was ground from a 3/8" HSS blank. It's 5 TPI, but the cut thread seems wider than it should be. The pitch is correct. I do know that I didn't make an attempt to compensate for the lead angle.

What I don't understand is the relationship of the lead angle to the shim angle. (I think this is the amount that the tool is rotated to become more aligned with the lead angle.) My Aloris AXA-8 HSS threading tool has a means to make this adjustment, but I don't have acme blades. Not sure I'd want to buy an acme blade right now, as this is most likely a one or two of build. (5 TPI acme blade = $67 from Aloris, which isn't bad, if I was doing this a lot. But this is good for one pitch only.)

Can someone enlighten me on the subject? Or point me to a source that might show pictures and math? Don't want a "calculator" since I'd like to know what it means geometrically first. I haven't yet found a good explanation. Is it just set to the lead angle?
 
Can't help with your question , but . When cutting Acmes , I always ran a regular threading tool to depth and came back with a slightly narrow Acme tool . Did this on manuals and CNCs . I have a tool for the surface grinders that grind both 60s and Acmes . The Acmes are ground small . You can then pick up either flank and machine to the correct size .
 
mmcmdl said:
Can't help with your question , but . When cutting Acmes , I always ran a regular threading tool to depth and came back with a slightly narrow Acme tool . Did this on manuals and CNCs . I have a tool for the surface grinders that grind both 60s and Acmes . The Acmes are ground small . You can then pick up either flank and machine to the correct size .
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What do you mean the acme's are ground small? Same 29 degree angle, but smaller tip, or something else? How do you pick up the other flank on a manual lathe? I'm simply setting to #1 every time.

Next time I will try modified flank and set compound to 14.5 degrees. Last time I went straight in and my poor little 10x22 really wasn't liking it that much once the thread was 3/4 deep.
 
WobblyHand said:
What do you mean the acme's are ground small? Same 29 degree angle, but smaller tip
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Yep ! Cut to depth , move cross slide and compound accordingly as you would pick up any other thread .
 
WobblyHand said:
Next time I will try modified flank and set compound to 14.5 degrees. Last time I went straight in and my poor little 10x22 really wasn't liking it that much once the thread was 3/4 deep.
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I guess NOT . :grin: Full profile of the thread . If it didn't stall , bet you had some serious chatter .
 
mmcmdl said:
I guess NOT . :grin: Full profile of the thread . If it didn't stall , bet you had some serious chatter .
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Had chatter. First acme thread. Got to learn somehow. Learn by doing, screwing up, and trying again. (and maybe one more time...)

I had a stall of my ELS lead screw on one occasion. Easy to reset the controller and keep on going. Stalled the spindle too when I ran into the shoulder, oh well. Should have made the thread relief a hair wider, things happen fast at 5 TPI.
 
You have a surface grinder , don't you ?
 
WobblyHand said:
Had chatter. First acme thread. Got to learn somehow. Learn by doing, screwing up, and trying again. (and maybe one more time...)

I had a stall of my ELS lead screw on one occasion. Easy to reset the controller and keep on going. Stalled the spindle too when I ran into the shoulder, oh well. Should have made the thread relief a hair wider, things happen fast at 5 TPI.
Click to expand...
are you cutting steel to a 3/4" depth on the 10x22 lathe?
 
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