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End mill relief

Quest for information on grinding an end-mill

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Bob Unitt 110/04/2020 14:06:16
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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.

ega10/04/2020 14:09:58
2541 forum posts
201 photos

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

AdrianR10/04/2020 14:17:09
583 forum posts
36 photos

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

A.

Mick B110/04/2020 14:23:32
2192 forum posts
122 photos

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.8mmslotdrill.jpg

Clive Hartland10/04/2020 14:23:36
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2820 forum posts
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I did on my Worden, 3 deg for the cutting edge and 5 deg for the clearance.

DMB10/04/2020 14:34:56
1312 forum posts
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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

Neil Wyatt10/04/2020 14:45:41
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Posted by Clive Hartland on 10/04/2020 14:23:36:

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

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

Brian H10/04/2020 15:05:02
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2312 forum posts
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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

Bob Unitt 110/04/2020 15:22:54
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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 ?

Bob Unitt 110/04/2020 15:24:38
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Posted by AdrianR on 10/04/2020 14:17:09:

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

A.

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

Baz10/04/2020 15:29:27
724 forum posts
2 photos

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.

Bob Unitt 111/04/2020 12:51:20
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206 forum posts
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Posted by Baz on 10/04/2020 15:29:27:

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 ?

John Haine11/04/2020 13:17:39
4679 forum posts
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Posted by Bob Unitt 1 on 10/04/2020 15:22:54:

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 ?

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.

Mick B111/04/2020 13:22:43
2192 forum posts
122 photos
Posted by Bob Unitt 1 on 11/04/2020 12:51:20:
Posted by Baz on 10/04/2020 15:29:27:

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 ?

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.

D.A.Godley11/04/2020 22:11:31
120 forum posts
39 photos

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

D.A.Godley11/04/2020 22:57:24
120 forum posts
39 photos

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

David

Bob Unitt 112/04/2020 14:00:29
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206 forum posts
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Found both, thanks.

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