Side-and-face-cutter sharpening jig

[Pete O]

I started this some months ago, it was put to one side due to other commitments but I stole some time today when I was supposed to be doing something else and instead brought this little project to the 'proof of concept' stage.
The general idea is to be able to sharpen horizontal milling cutters on the surface grinder. I set the jig up today to grind a 4" diameter x 1" wide 14-tooth cutter.
   
The aluminium plate is moved up or down to place the tooth at the appropriate angle, it is pivoted out to index to the next tooth and then locked back in position with the knobs. I forgot to take detail photos of the indexing business.
Primary and secondary angles are visible if you can see through the glare:
   

The corners of the teeth on one side were badly damaged; having sharpened the face teeth, I thicknessed the cutter flat on the mag chuck to get down below the damage- this took ages.
   

Having ground the cutter away to below where the tooth corners were damaged, it was time to grind the angles into the sides of the teeth.

The sides of the teeth are ground on a different jig, simply a 7 degree wedge with a 1" spigot on which to rotate the cutter. The indexing business is yet to be added but I experimented with this cutter, indexing by eye to a scribed mark (I did say this was for proof of concept).

The 7-degree angle built into the jig gives the side clearance angle. As discussed on this forum a few months ago, the sides of the teeth also have a slight taper to prevent rubbing on the sides of the milled groove; the taper is only about a thou over the length of the tooth. I used a simple means to achieve this small taper.
   
The two thicknesses of copy paper under one end give the appropriate amount of tilt to get the taper angle. The paper is moved to the other end when the cutter is flipped over for the other sides, which are ground on the left side of the jig.

I was happy with the test results, miced the teeth and there is .002" taper from tip to root so the paper did it's job, the lands on the side that had the damaged corners ended up being very wide as due to the thicknessing, also obviously regrinding a cutter that has significant corner damage means the cutter is a lot narrower than it started out- this 1" cutter is now about 0.918" wide. It will be interesting to see how it cuts. I have the vertical attachment on the mill at present, will need to make sure there are no jobs for that before I remove it so I can do a test cut in horizontal mode as it is a pig to put on and off.
I also ground a few nicks in the hub as I sorted things out, as can be seen in the photos. First time for both myself and the jig so there was a bit to learn.
   
   

[Mayhem]

Nice work Pete.

[TomG]

It's always fun to bring old cutters back from the dead.

What is supporting the arbor in the first pic?

Tom

[f350ca]

Nicely done Pete, second what Tom asked and whats holding the cutter down when grinding the sides? From what I've tried a solid piece of steel won't transfer much magnetism from the chuck.

[Pete O]

The arbor in the first photo is cradled in this gadget
   
This pic was taken before the indexing apparatus was added. Still need to add a clamping arrangement to hold the arbor down into the vee.

Grinding the sides, the hold-down clamp for the 'proof of concept' run was the big fleshy lump attached to my right wrist. Holding the cutter down onto the jig is not so much an issue as preventing it rotating with the wheel, which wants to pull the tooth uphill and into the wheel. The indexing stop will have to be set up in a different way to my original plan in order to counter that unforeseen problem. I think that the hold-down will stay manual as I haven't been able to come up with a clamp with a low enough profile to clear the wheel.

[randyc]

Horizontal mill cutters can be obtained at reasonable prices from eBay, I found. I've purchased a lot of them but about 1/3 are not usable without sharpening. Your idea is very attractive since I don't mind spending time but reluctant to spend $$$, LOL. Thanks for the idea, sir !

[Pete O]

The place I've had make bandsaw blades for me has one of these cutters in their 'things we sharpen' display case, I asked about cost of sharpening last time I was in there. The bloke said they charge by the time taken, said they usually work out around $60     That was the motivation to come up with a sharpening jig. I have several dozen purchased as a job lot from a clearing sale and they almost all need sharpening.
Next time I get a chance to mess with this thing I'll take some more detailed photos.

[SteveG]

Very nice work Pete.
At those sort of prices, having the ability to sharpen your own cutters would quickly recover the cost of buying the grinder.
Sounds like a line I might need to rehearse.... ;)

Steve

[Pete O]

I spent some more time on this today- I'm putting off a hated job that I should be doing elsewhere- and took some more photos along the way.
A little more detail on the face cutter grinding jig:
This is the adjustment setup for positioning the tooth to be ground
   
Yes I know my knurls are crap.

A plate straddles these two posts and is adjusted for height so the the tooth being ground is rotated forward of the vertical to give the primary or secondary clearance angle.
The plate is slotted on one side so that it can be swung aside for indexing between teeth, then the top knobs are tightened down to hold it in place.
   
there's a locking nut under each adjustment nut, a copper washer allows the locknut to be tightened without the tendency to turn the adjusting nut.
   
The plates are specific to a diameter of cutter, these two take 4" and 6" cutters, I made 3 more blanks that will be slotted to the appropriate depth for other cutters.
   
I can't see any reason why form cutters couldn't be sharpened on this jig with an appropriately shaped indexing plate and the right wheel
   
I also envisage being able to sharpen plane milling cutters cantilevered off the end of the jig, the finger for following the flutes would need to be mounted from the wheel guard rather than on the jig.
   
I was surprised to find that this 18" arbor cleared everything on my test run, I'm contemplating cutting it up for use on this jig as I could never quite get the bend out of the middle. All my cutters have 1" bore and imperial sized ground shaft is hard to come by here.
   

Still to be done on this one (other than to cut the excess height off the two 3/8 UNC all-thread posts) is the addition of clamps to hold the arbor into the vee, has to be low enough profile to clear the wheel when the smallest diameter cutter is being ground. I think I will then dismantle the jig and case harden the components, the vee will then have to be re-ground after reassembly. I spent a lot of time on the surface grinder making the two main components. Side-wheeling the width of big the slot in the base was the only thing that got it hot, no coolant system on my grinder. The relief slots were done with a parting tool mounted in the shaper, proved ideal for the task.
   
Darn thing is scratched up already- all the more reason to harden it I guess.


I made the indexing arrangement on the side-cutter grinding jig today. A series of holes, with a simple T-piece that is placed in the best hole for the particular cutter and the stop length is adjusted to hold the tooth in line with the table. In both of these photos, the tooth set for grinding is the one above the indexing finger.
   
   
The finger always has to hold the cutter in the same direction regardless of which side is being ground, as the tooth being ground is always in the top half of the circle and of course the wheel direction doesn't change. Holding the cutter down manually is not a problem, the left hand works the crank while the right hand holds the cutter down and against the stop and rotates it between cuts.
   

I'm very happy with how these jigs work, I need to make some test cuts with sharpened cutters before calling it good. Then I need to figure out a way to hold the big wedge piece on the grinder so that the top working surface is horizontal and I can get it properly flat before (and after) hardening it.

On a side note, today was actually the first time I have used reamers to properly match a hole size to a shaft size; I had never owned any straight reamers until I picked up a selection of metric and imperial ones at the clearing sale where I bought the surface grinder. The bouncy cushion of air when I put that precisely 10mm O.D. drill rod into that precisely 10mm I.D. hole, and the 'pop' as I pulled it out again, were very satisfying. As was the perfect sliding fit of the 6mm indexing finger in the cross-drilled post.
One small 'live and learn' experience though, the first hole I did, I selected a 9.8mm twist drill to finish the hole prior to reaming only to find the 10mm drill rod was already a sloppy fit after drilling. Switched to a 9.5mm drill for the rest of the holes and the reamer took them nicely to 10mm. I guess there must be a rule of thumb for what undersize drill to use prior to reaming?

[f350ca]

Very impressive Pete.
Could you grind the face of the form cutters with a thin wheel.
It appears your braver than me, i still haven't tried grinding the face of my magnetic chuck.