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Military Firearm Restoration Corner

New Lathe Question


montea6b

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Ok, I got some mail order tooling from Grizzly and made a few chips yesterday evening. Just a few light cuts on some scrap bar stock I had laying around. When setting up to make facing cuts I was dismayed to discover that I could not get the cutter all the way to the center of the piece with the compound set up for travel on the "Y" axis. (I hope I have this right...)

 

In other words the compound was set up to advance the cutter into the workpiece at right angles to the cross slide.

 

So I rotated the compound 90* and was able to face all the way from the center, but in setting it up this way I got two micro-feed options in the same direction, and the only way to advance the cutter into the face of the workpiece is by use of the carriage handwheel.

 

I didn't like that setup, but the only other option is to angle the compound. When I do that I lose the ability to use the increments on the wheel to tell how much the cutter is advanced into the piece. It also changes the relative angle of the cutter to the workpiece.

 

Questions; Is angling the compound an accepable way to get around this issue? Is this standard practice, or a limitation of the machine I bought? What is the best angle for both compound and cutter? Is there a good rule of thumb for the angle that will allow easy trig to determine the amount of advance occuring on the "Y" axis for a given amount of travel along the "hypotenuse" of the compound?

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I assume you mean offset the compound 30 degrees from the X axis? That makes perfect sense actually. It forms a 30 60 90 triangle so that advancing the cutter along the compound results in an advance along the Y axis of exactly half the amount. Keeps the mental math simple. Thanks!

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Pictures would be helpful.

It sounds like you have your tool on the wrong side of the tool post.

Angling the compound is done for a variety of reasons, 29* is the common setting for 60* American standard threads.

 

Try setting up an indicator to measure tool advancement before you begin your facing operation, then you will know exactly how far the tool advances per increment on the compound dial.

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I assume you mean offset the compound 30 degrees from the X axis? That makes perfect sense actually. It forms a 30 60 90 triangle so that advancing the cutter along the compound results in an advance along the Y axis of exactly half the amount. Keeps the mental math simple. Thanks!

I knew you would figure it out.

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Repeat after me, the square root of the sum of the squares. When you advance the compound at an angle, you travel the hypotenuse of an right angle. By changing the angle, you change the depth of cut in relation to the handwheel reading. By doing so you are able to take minor cuts with gross movements of the handwheeel. For instance, angled properly, the .001 increments can be used as .0001 increments. I hope this makes sense. LL

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...angled properly, the .001 increments can be used as .0001 increments. I hope this makes sense. LL

 

It makes total sense now, thanks. 30-60-90 keeps the math elegantly simple. I'd have to ruminate some more to see if any other angles present a similar easy solution.

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