keyway braoch sharpening

how can davis type keyway broaches be sharpened?.

Hi keithmech:
The traditional way of course is to grind them on a mag chuck using a tool and cutter grinder with the head tilted over or the wheel dressed for the front clearance and a finger from a convenient spot to index the teeth.
So now the job becomes a simple plunge grind one tooth at a time, and there are lots of examples of keyway broach grinding setups in all sorts of old machine brochures.
This works so long as the teeth do not have any back relief (narrower as you go down the tooth toward the cutter body) but as soon as they do, any grind at all will put them out of spec because they get narrower and narrower as the teeth get shortened more and more.
Face grinding the front rake so each tooth gets skinnier and skinnier will always make each tooth narrower and narrower if there's side relief, so I've never seen them done that way.

I don't know that much about the machines, I was exposed briefly to them many moons ago, but so far as I remember, Davis keyseat cutters did have side relief to keep them from rubbing in the slot, so unless my memory is playing tricks on me, the principle applies.
I also do not know if an out of spec narrow broach can be simply run in several offset passes to bring the slot to width or whether the broach has to be tossed out when it gets too skinny.
Logically you'd think they could, but I don't know enough about them to be sure.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi Keith, This is how I approach it. On a tool & cutter grinder, I secure machinist vice up at 90 deg. with the base of the vise at 1-1/2 deg off of 90 to the spindle. This is for the cutting clearance of each tooth(1 to 3 deg is recommended ) place parallel skinnier than the broach behind broach to assure straightness. Make sure you have set the vise so when you load the broach ( flat back side against your parallel ) that the grinding wheel would kiss the back of each tooth first ( hence the cutting clearance ) . I use a cupped CBN wheel ( don't need to worry about wheel wear ) Paint all the teeth with a marker. Secure broach in vise with as many or few teeth being one side or another of the vice. If a long one you may only care to have a few out there. the parallel will allow you to open the vice jaws while sliding the broach to a new position with little worries of maintaining straightness while grinding. Often times I only attempt 2 teeth beyond either side of the vice when I grind. With the lightest of kiss touch off on the first tooth after the lead. Notice how the wheel took off the paint/marker Hope that it takes a good square grind on the tooth. If not you may have to adjust the broach in the vice to make sure it is. after you have made the slightest kiss on the first tooth, grind that tooth an additional 5 to 7 thou a thou or so at a time so as to not overheat that tooth. Back off the wheel, advance the table ( roll ) to grind the next tooth, kiss slightly then grind that tooth as the one before. If the broach has seen considerable wear you may have to rinse and repeat the entire broach. Attempt to keep the kiss of each tooth slight as you start each tooth. you don't want to hit one too hard so as to mess up the nice stair step cutting intended by each tooth on the broach. When finished with grinding of all the teeth, please make sure that the tail ( handle ) is still thinner than the last tooth of the broach.If not you will need to surface that flat ( no taper ) thinner than the last tooth. I hope that wasn't too confusing. Godspeed
Tim