Cobbled together a Potts drill grinder this weekend
And it works great!
I have a collection of dull and chipped MT bits from 1/2 in to 1-1/4 and no way to sharpen them.
Don't even mention hand sharpening, clearly that is not where my talents lie.
Anyway, I found this site
where the author explains drill grinding geometry and the geometry of the Potts drill grinder.
He also has an Excel program to calculate the performance of various drill grinding jigs etc..
So after digesting his info and checking my assumptions by hand calculating his inputs I managed to get his outputs.
So off to the jig.
I had a 6" grinder, with a 46 grit plate type wheel all set up for drill grinding with a movable base that I put together for the typical Craftsman/General swinging type drill grinder. Of course I never got good results with that thing and his article explains why.
Well I didn't want to invest much time in making a Potts without dimensions so I went the cobble route to see if it works. I also wanted to simplify building it.
The best feature of the Potts is that both the radius of the ground bit and offset (he calls it the shift parameter "P") are adjustable concurrently not independently by means of a 6 degree sliding skew.
Probably the most critical part is lining up the bottom of the Vee trough, the pivot axis and the grinder wheel face before welding or whatever method is used to assemble. This location is the Zero reference, it is where a drill of Zero diameter, which would have a Zero radius and Zero offset would be positioned.
From there the slide is advanced 1.5 times the actual drill diameter of the drill you are going to sharpen.
Clamped on Vice grips for a temporary lip stop.
Here is two photos of the slide.
I can't take closeups with my camera of the sharpened bits but they look great, basically like factory bits and cut fantastic.
Well worth the time making it.
I am now going to make a second "head" for it grinding smaller and shorter bits.
Last edited by cijuanni; 01-16-2012 at 10:38 AM.
Very cool idea I like it Ive just eye balled it but then most of my drills are under 1 1/2"may be a chuck mounted the same way in stead of a v block and a cam on the end of the shaft to shape the relief for smaller drills
Thanks for posting this. If you do make a smaller one please do post it. I have managed to get by with one of the generic drill sharpners but your looks much better and I may try to make one.
that looks really good, I like the fully adjustable tooth rest look very functional and fast to set up.
Boucher, the Potts, the original, is quite small, likely someone still sells plans for it.