End mill relief

I've just completed the end-mill accessory for the Worden, and am keen to try it out. I need to establish the correct angle of relief behind the end-face teeth on an end mill. I can find plenty of learned treatises which refer to it as 'dish angle' or 'end relief', but nothing which tells me how many degrees it should be. The usual helpful books (Sparey, Bradley, Tubal Cain) don't seem to specify it, and it doesn't appear in the Workshop Practice series books I have either. The end-mills are the sort of tool-steel items used by model engineers 30 years ago, and will be mainly used on mild steel and brass, in a Myford VMB mill.

Lateral thinking: you might get some help from looking at the YouTube videos about the Acute system; there is one about sharpening two flute endmills.

Edited By ega on 10/04/2020 14:10:24

I don't know the official answer, but why not just use the same angles as on the cutter.

A.

Some others call it 'axial relief', with primary and secondary values.

Unless you're hogging out volumes of metal, I dunno if a secondary relief is really necessary.

I couldn't see a ready value for either of 'em on the net, but general knowledge would suggest trying somewhere around 15 degrees for (say) mild steel, then suck it and see.

I've got an 8mm slot drill that I sharpened offhand, and I don't even know what the relief angle is, other than it looks about right and works well.

I did on my Worden, 3 deg for the cutting edge and 5 deg for the clearance.

Bob,

In your opening post, you mentioned "dish angle". Can I take it that what you meant was the very cutting edge being angled from the centre to the outer, sharp corner? This is somewhere around 3/4° or so. Quite important to have that as well as the primary and secondary angles. It applies to 2 and 4 tooth end mills.

John

I usually dish about 2 degrees and 5 degrees primary clearance, so very similar.

I use a Stevenson endmill grinding fixture on a magnetic table, no need to worry about the angles because they are all built in to the fixture.

Brian

Thanks folks. Re: the 'dish' angle, do I take it that this slopes up from the outside edge of the cutter to the middle - i.s. the 'dish' is in the end mill itself, not in the resulting cut ?

All my end-mills are old and second hand, and have been reground by amateurs to all sorts of different angles...

Edited By Bob Unitt 1 on 10/04/2020 15:25:01

Bob, the dish is in the cutter so that the outside edges cut, a couple of degrees should do the job it’s not critical.

Is that just the end mills, or does it apply to the slot drills too ?

No, it slopes down from the outside to the middle if you're holding the cutter with the cutting end uppermost. This is to make sure that the bottom of the cut is flat.

Holding a straight edge against the face of even a 1/4" slot drill showed distinct slivers of daylight touching the straight edge at the periphery. The slot drill has had very little use, mostly on delrin, and I'd guess the dish angle could be as much as 5 degrees.

Bob ; Have a look at “ Brook Cutting Tools “ Milling cutter user guide , it will give you all the guidance you are looking for .

regards

David

There is also a very illuminating article by “ George Pruitt “ about end mill sharpening , includes some photos which are most helpful.

David

Found both, thanks.