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 A tip to increase dimensional accuracy when using a manual lathe

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rjw
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PostSubject: A tip to increase dimensional accuracy when using a manual lathe   Wed Mar 31, 2010 3:28 pm

I've been meaning to post this for a while, but have been kind of busy getting reamed (just kidding ...kind of)

In that it seems that more of us are purchasing manual lathes and some may find it a bit of a challenge to get high accuracy for bearing housings or journals, etc. here is a little tip

Most (amercian) lathes have crosslide dials that are graduated in .001" increments.

Let's say that you turn the bearing surface of a shaft down to within 1 or 2 thousandths(or less) of the desired size. Now what do you do?

1) you could tweak the crosslide handle a very small amount and hope for the best

2) you could mount a precise dial indicator against the toolpost. but this can present it's own set of problems

3) You could use emery cloth or whatever to sand to the desired size

or you can try this...if your lathe has a compound rest (also with .001" resolution dial)

1) Set the compound rest to between 5 and 6 degrees...the exact angle can be calculated by drawing up the geometry, if anyone cares to. Which way you rotate the compound rest depends on whether you are turning (OD) or boring (ID)

2) at this angle, a .001" movement of the COMPOUND slide, will result in a .0001" movement radially or towards the work

3) The result is that .0002" will be removed from the diameter of the workpiece.

Hope this helps anyone looking to increase dimensional accuracy

btw: this is not my brilliant idea, I read it in a South Bend lathe book from the 30's or 40's .Also, if this has already been posted here, then please disregard.

edit..changed the angles after drawing it up...actual angle is 5.7 degrees

must be OFS

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