Subject: Need help grinding threads

From: [email-masked] (Rebecca or Jim Schwitters)
Date: Mon, 02 Dec 1996 04:08:56 GMT

I am planning to make new cross slide and top slide screws for a lathe
I'm reconditioning.  I would like them ground rather than cut.  Has
anyone had experience doing such a thing? 
I don't know enough about grinding threads to know all the right
questions to ask, but the following come to mind.   What kind of
grinding wheel is suitable?  What are the tricks to dressing it?  How
much can be safely ground in a single pass?  Can it be ground without
coolant?   I have a decent quallity Dumore toolpost grinder.
Since this is not a production operation, I would guess that my best
bet is to remove the bulk of the material with normal thread cutting
leaving just enough to clean up by grinding.  My toolpost grinder does
not have the ability to be "tilted" to correspond to the thread angle
but I could probably rig something up or alternately compensate by
adjusting the wheel profile.
The leadscrews in question are 3/8" x 10 Acme about 8" long.  Any
thoughts or comments will be appreciated.

TIA
Jim Schwitters

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From: [email-masked]
Date: 7 Dec 1996 22:25:48 GMT

Jim, 

Unless you are planning tom make new nuts and etc,. or are planning to
make re-circulating ball screws.  I think you are going to alot of
unnecessary work.  The reason for grinding screws is usually for fine
threads that are used in micrometers and similar tools.  I've made many
lead screws from 3" long & up.  The accuracy of the screw is dependent on
the accuracy of the lead screw on the lathe not on the finish you put on
them.  The Brass or Bronze nuts are fast to wear into the lead and pitch
of the screw and will "Break in" fast.  As for the accuracy of the pitch, 
well....
as long as you don't amke any glaring errors in the major and minor dia's
you will end up with an accurate screw by cutting it an a craftsmanlike
manner.