Cutter grinding

I haven't started building my Stent yet, but istm that if your friend turns the endmill end-for-end as well as reversing the wheel then the force will be downwards and the burr will where he wants it (!) Or if he's using a cup wheel then he doesn't need to reverse the wheel as he can get the same effect by using the other side of the wheel instead.
Hth,
Mike

I have the stent and cannot really see how the problem is arising as the cutter should be held firmly in the tool holder. On mine the cutter is held in its collet (its really a bush) by a 6 BA grub screw against its shaft. The collet is clamped in the tool holder by an Allen head cap screw which in turn is prevented from turning in the toolholder stand by the screwed clamp ring at the rear.
If none of this makes sense I can send a digital photo ..... or two.
Alan

The OP referred to grinding the flutes which seemed to me to imply holding the end mill between centres rather than in the holder ? AIUI you'd only use the holder to grind the end of the cutter, not the flutes.
Mike

Gents, I thought I understood the situation but I am beginning to wonder! As I see it the inside of the flute rests on the support finger when grinding the edge of the flute. The cutter in its holder is traversed across the wheel and at the same time rotated to keep the flute in contact with the wheel. I presumed this was accomplished by hand.
Imagine a disc wheel, edge on, in front of you. The endmill is between you and the disc with its cutting end to your left. It has its centreline slightly below the disc centreline to give the required edge angle. The finger is on the far side of the end mill and very near the wheel. With the wheel rotating with near edge going downwards, the endmill is forced on to the finger. Starting at the cutting end, the end mill is moved across the wheel from right to left to grind the edge of the flute. That puts the burr on the cutting edge.
Rotating the wheel the other way puts the burr behind the cutting edge. However it now tends to lift the end mill from the finger. I presumed you 'simply' had to provide enough torque by hand as you traversed the end mill to stop this. Perhaps not so?? I've found references to air bearings being used in the cutter holder, presumably for very low friction. Is there a clue there?
Have to admit I have never seen cutters ground let alone tried it!
For what it is worth my friend is building a fiendish system of a rack and gears to automatically rotate the cutter as it is traversed.
Henry

His fiendish system will be fine for cutters he makes himself where the ratios are known, but for re-grinding commercial cutters he will have to EXACTLY match the helix angle used to make it each and every time he mounts a cutter and in my experiance they tend to vary.
AWEM

I've just bought a cutter grinder . No knowledge and haven't used it yet. but it says to me this:- it has a table that traverses ....left to right, So as regards flutes ...............I thought that the finger thing was mounted off the table and as it traverses the finger rotates the endmill between the centres. Is this right or are other people talking about other types of cutter grinder. Would be nice if someone could make some small movies on how to do this . or even a sequence of pics as pictures and movies speak a thousand words . and the Internet is a medium to get this across. People could explain away till the cows come home otherwise. all the best.........mark

Yep, and the support finger is fixed relative to the grinding wheel so it does not move when the table, cutter and all, is traversed.
The cutter is mounted between centres on the table so it can rotate freely. The motion of the table / cutter automatically forces the cutter to rotate as the table is traversed because the fixed support finger in the moving cutter flute forces it to rotate.
Well, the table movement is done by moving the rack by hand via the lever but the cutter rotation is a consequence of its lateral motion relative to the fixed finger.
Unless it's on the right ;-)
Or slightly above it ;-) (or actually, better still use a cup wheel and set the edge angle by tilting the finger :-)
If the cutter is on the right then this is still true (so I was wrong about the motor direction - see below).
Well, it depends if it's a left or a right handed cutter doesn't it ? Assuming your particular cutter is handed so as to give a burr when the cutting edge is on the left, then moving the the cutting edge to the right cures the problem. Because the wheel will still be moving down whereas the edge being sharpened will now be pointing up
Of course I agree that the motor must be rotating so as to force the cutter down onto the finger so obviously it shouldn't be reversed as I mistakenly said before.
Don't think so - it's not the friction in the bearing that gives the downward force, it's the friction between wheel and cutter.
Almost certainly unnecessary - as stated above the cutter should be mounted between centres so it can turn freely and the traverse past the fixed finger will automatically force it to turn by exactly the required amount.
Hth,
Mike

OOPs, thanks Mike, so I cannot read proper! Must stop this Xmas indulgence. OK sharpening the flutes. Main problem as understood is that keeping the wheel cutting and flute in contact against the finger resisting the turning force of the wheel and this puts a burr on the cutting edge of the flute. What grit and abrasive wheel is being used? Is the wheel clogged up? I have sharpened flutes and not had the burr problem with a fine grit wheel (WA 80) at 3000 rpm..... well if there is a burr I cannot see it with the naked eye and certainly cannot feel it.Also the cut is extremely light ... no more than a thou at the very most. Alan

Thanks to all who responded.
Can't follow Mike's idea of putting cutter to the right. That would need the finger to support the 'back' face of the flute which doesn't seem correct.
In summary it seems my assumption that wheel forced cutter on to finger was correct and that burrs are not a problem if grinding is done correctly. Interesting comment from Andrew about variability of helix angle.
I'll pass on the accumulated wisdom! What a mine of information this group is!
Cheers Henry

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It's not a UNIVERSAL CUTTER GRINDER. It's a copy of a single lip cutter grinder similar to the Deckel and Alexandra.
These cannot sharpen an end mill or slot drill correctly because they are too restricted in movement. As a single lip grinder for engraving tools that are brilliant but that is all they are.
Just because you call it a Universal cutter grinder doesn't make it one.
John S.

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