A Simple End Mill Sharpener

[vtsteam]

This thread is about a simple end mill and lathe tool sharpener I built a few years ago, which was made from scrap items. Building note: I happened to have a spot welder, so I used that to make the sliding carrier from pieces of sheet metal, but the same could be done by brazing or even milling from solid.

The idea:

We are often told not to grind on the side of a bench grinding wheel, even though that is where the wheel will produce a true flat, as opposed to the periphery which produces a hollow grind.

I've heard arguments for and against grinding on the side of the wheel as a safety issue and, without entering into that discussion here, it seemed to me that an alternative might simply be to use a bench mount disk sander. That was spurred on because I had a broken but usable one on hand, purchased at a flea market. The disk part would present a true flat surface, and the grit could be varied, and replaced when worn as simply as slipping on a new sanding disk.

Here's the sander as purchased. The belt sander table casting was broken, but the disk sander part was fine.



The broken part:

[vtsteam]

The disk part was okay and with a little cleaning, and holding a bit of sandpaper against the disk, things looked a little more presentable:

[vtsteam]

I had an 80 grit adhesive disk, so stuck that on:

[vtsteam]

The tilting table was fastened in place with some spare screws -- the originals were missing.

For sharpening end mills I wanted a way to position the mills with a couple of degrees of freedom, and two additional set angles. The tilting table provided one set angle, and a fabricated sliding table using the existing miter slot would provide a degree of freedom.

Here are the parts of the sliding table -- just some hot rolled strap material:

[vtsteam]

After cleaning off the two pieces of metal, I spot welded them together, and milled the narrow strip to fit the slot in the sander's table. It was a half inch wide and a little oversize to start with, the slot was .460" actual.

[vtsteam]

Here's the table fitted into the miter slot. In this case it's on the disk side of the tilting table, but it can also be located on the far side by turning it around. And in fact, that's necessary for sharpening end mills.

[crueby]

Very interesting, taking notes here!       

[vtsteam]

The table tilt could provide the first of the two angles I needed for end mill sharpening, but I needed a second set angle. That would be provided by guide strips added to the new sliding table.

Guide strips were spot welded in place square to the table, But the angle needed for sharpening end mills was determined to be 1-1/2 degrees.

To get that angle for the guide strip, first step was to blue it up and mark a line 1-1/2 degrees off square. I decided to do this using a little math since that's a pretty small angle to mark accurately with a protractor.

The piece measured 2.10" long, and I wanted to know how far out to make a mark at one end to yield a 1-1/2 degree angle. The tangent function does that. With the pocket calculator TAN of 1.5 degrees x 2.1 = .055. So I needed to make a mark .055" in from one end, and then connect it to the other end. This is what that all looked like:

[vtsteam]

Thanks Chris, glad it's of interest.

For filing to the line I used a safety file:

[vtsteam]

I have a fair amount of 1"x1" scrap aluminum bar bits, left over from CNC turning centers. Most are a couple inches long. I decided to use these as mill holders while sharpening.

To attach a guide strip for the other side of one of these holders, I clamped the strip tight against a bar placed as a spacer against the newly filed guide strip, and then spot welded the second strip in place. This preserved the angle of 1-1/2 degrees for both guides. These strips were just 1/8" x 1/2" hot rolled, BTW. Nothing fancy.

[vtsteam]

Then I took three of the aluminum cutoffs and faced, drilled, and reamed 3/8", 1/2" and 3/4" to fit some end mills. Set screws were added to hold them in place.

[vtsteam]

This is how it is used. I set the tilting table to 6 degrees ( 5 to 9 is usually recommended for steel and cast iron for end, or primary clearance angle). This is with the table angled UP above horizontal, for end mills.

The 1-1/2 degree offset in the sliding table gives the concave clearance. I just set the center of the end mill visually at the edge of the sanding disk, and press the holder gently forward to cut. I generally just need to take a tiny bit off.

On center cutting end mills, one lip is a little longer than the other, so you place those slightly off center to sharpen. It becomes obvious visually how to sharpen these. For 2 flute mills you rotate the holder 180 degrees to sharpen each lip. For 4 flute mills you rotate the holder 90 degrees.

I don't have stops (yet) on my sharpener, but oddly haven't seemed to need them so far. Nevertheless I'll probably add something soon.



For short mills you put the sliding table towards the disk, or flip it around for longer mills. The 1-1/2 degree concave angle does not change, even though the table is oriented the other way. Quite handy, that.



Shown also above is a lathe tool sharpening holder, patterned somewhat after Harold Hall's design, but working with this sander sharpener.

[crueby]

Thats a quite elegant/simple design (usually the best) to sharpen the ends - I'll have to give that a try! Not having a spot welder, I'll use screws to hold the rails on.  As you say, doesn't sharpen the side fluts but I find my cutters go dull first on the bottom and that corner, this could give them a longer life.


Thanks very much for sharing that with us!   

[vtsteam]

You're welcome Chris, I hope it's useful for you. To show how much really the ends are the most important, here's the rather extreme first test I did, with a very sad looking end mill that had fallen behind a bench been subjected to one of my spring shop floods on a concrete floor:



After cleaning up by electrolysis with washing soda and in its holder:



Then sharpened:



And then cutting:



I guess the moral of the story is, got a junk mill? Then use a junk sharpener on it!

I was a lot happier yesterday, having broken my only carbide mill to go back into the shop and sharpen up a bunch of old steel mills and start cutting again.





 

[RReid]

I really like this, Steve. I use a similar disc sander to sharpen my lathe tooling, mostly freehand, but it never occurred to me that it could be used to sharpen end mills. Thanks for the idea and for sharing it!