# grinding a single point threading tool for the lathe



## 12bolts (Sep 21, 2014)

When grinding a lathe tool for turning but especially for threading it is important to get your angles correct and edges sharp.
Get yourself a small magnifying glass or jewellers' loupe. You will be amazed at what defects you can see at 8-10 X. I also have a 20X  lens from an old microscope and what that shows up is just ridiculous!
A grinding wheel will not give you a satisfactory finish. You will need to finish off the faces with a small carborundum stone at least and preferably an Arkansas or India stone or similar as well.
In the following pics a 3/8 HSS bit was first ground to the 60* included angle, then honed with a carborundum stone and polished with an Arkansas stone. The final touch was to put a small radius on the front edge to minimize chipping and strengthen the tool tip.



First the 60 degrees included angle is obtained. Then a close up of the ground surface. Looks pretty good? Ready to use?




Nope! A quick hone shows the high spots and various facets left by freehand grinding




Getting there now. Just concentrate on the 2 front faces. Its not necessary to hone the entire face flat, just bring it back so that the working edges get cleaned up.



Keep an eye on the angle. Although it looked ok after grinding, but once the edges were sharpened up more I was able to see I was too acute and needed to hone a bit more off the front left face to bring the angle back to 60*




The final touch is to hone a small radius or flat on the front of the tool and polish the top edge.
As a rule I dont put any rake on the top of the tool for screwcutting. Generally speaking you dont go hogging off large amounts of material when single pointing threads. Certainly some materials would require some positive rake, or possibly even a chip breaker but most times a flat top suffices.

Cheers Phil


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## GK1918 (Sep 22, 2014)

Amazing photos Phil.  Remembering in school putting a harmless small dead bug under the microscope  that was scary  ..
I have had pretty good results with a flat plate on a palm sander- the fresh ground bit clamped in a vise and using
valve grinding compound (rather than a stone).  I feel I just have more control. Same thing for the roughing cut with a
4 inch grinder bit vised up,  then the real grinder.  The trick with the palm sander is a good one that don't vibrate. 
sam  good work !


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## SirMixAlot (Sep 22, 2014)

Very impressive, I've never spent the time to profect a HSS bit but may try to next time I need to use one. Thanks for the read and photos


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## xalky (Sep 22, 2014)

Excellent write up and great photos. Thanks for taking the time to show everyone.

Marcel


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