Grinding the flutes of an end-mill

[Roger HeadParticipant @rogerhead16992]

I was brought up to 'always grind away from the cutting edge'. Good (and logical) advice that I have always adhered to when grinding my HSS lathe tools, all off-hand on a bench grinder. I hollow grind the front, side, and top, so that honing only needs to remove a tiny amount of metal, and repeated touching-up with the hone is simple. I know that this results in a slightly weakened cutting edge, but that isn't a problem for me as I only use the HSS for final finishing cuts. But I digress…

I have recently been looking at various designs for sharpening end mills, and specifically at the arrangements for doing the flutes. I have never seen, let alone used a T&C grinder, so my comments are restricted to looking at books and manuals, but unless my eye-brain coordination is going wonky (always possible), it appears that the flutes are always ground the other way i.e. with the trailing edge of the grind being into the flute, at the cutting edge. It would seem that the benefits of the wheel rotation holding the cutter onto the finger while following the helix take precedence over any other consideration.

Have I got it wrong? Is there never any problem with burrs, feather edges etc when grinding the flutes this way? What do the end results look like (under a strong magnifier) from the home-built devices? There is a huge amount of ingenuity and ability displayed in a number of ME and other forums threads describing home-built systems, but not a lot written about the quality of the product.

I imagine that end-mill production environments use NC controlled motion of the cutter these days, but has anyone tried it in the HWS?

All comments gratefully received.

Roger

Edited By Roger Head on 30/06/2016 05:00:37

[Roger HeadParticipant @rogerhead16992]

[Roger HeadParticipant @rogerhead16992]

Ahhhh, 'but has anyone tried it in the HWS?'

Asked and answered. I knew it rang a bell when I was re-reading my post. The answer is 'yes, John Pace, in MEW 143-147.' And presumably others, also.

Nevertheless, my other questions remain…

Roger

[John PParticipant @johnp77052]

 

Hi Roger,

Most of the hobby type of cutter grinders all copy the guide finger type of system
for sharpening the flute edge.
Whilst this has been used for as far back as anyone can remember to be
able to successfully sharpen cutters one has to be well practiced,this is
where the problem arises .If you are not doing this on a regular basis you
just become rusty ,this is much the same as welding,i find that now i don't
do much welding and just get out of practice.

The cnc cutter grinder gets around this simply because it never forgets
how to do this and the set up for any size of cutter follows the same procedure.
Since the rotational axis takes 7200 motor steps for 1 revolution it becomes very
easy to set the clearance angle with ease very accurately as one step of the motor
is 1/20 th of a deg even with the + – 5 % stepper motor accuracy /error this is
very likely to be somewhat better than any eyeball or other methods.
As far as the rotational direction i sharpen with the rotation away from the cutting
edge but have also ground in the opposite direction it seems to make no difference.
What really makes the difference is how the machine controls the cutter during the
grinding ,since using this machine the success rate is 100% ,if i had a machine
that uses the guide finger method i would chuck it in the bin.
See album  Quorn  and cnc cutter grinder.

John

Edited By John Pace on 30/06/2016 20:39:12

[Martin NewboldParticipant @martinnewbold]

If you have a machine shop near you they usually have someone who will sharpen and coat ends for you . This is much easier and much sharper as they make a suberb job of them

[AjohnwParticipant @ajohnw51620]

I've mentioned that fortunately due to quantity I never used it the grinder I saw used a knife edged thin disc circa 6 maybe 8in dia grinding towards the cutting edge. The clearance was set by the height of the tool to the centre height of the wheel so they were effectively hollow ground. The flute just rested on a finger and was held on it via finger pressure.

They came out very sharp. I cut my finger on one. I assume the near knife edge on the wheel had been dressed on. Only tiny amounts are removed for sharpening and it was the motor and wheel that moved up and down to set the clearance. The tool was swung into contact with the wheel and then pulled back to take the cut. It used an L shaped arm so that the cut depth adjustment was very fine.

Annoyingly i can't remember how it sharpened things like morse reamers but parallel parts need very little thought at all. Odd really because the instructor said look at this carefully as you might want one day and some cutter grinders are very complicated. This one can do them all with pretty simple adaptations. It was demo'd doing a morse reamer as well. I'd guess he thought that a number of use might find ourselves doing "things" away from work.

John

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[Roger HeadParticipant @rogerhead16992]

Thanks for the replies. Perhaps the adage about grinding away from the cutting edge may be more applicable to heavy (off hand) grinding, but not to very light operations such as flute grinding?? Anyway, I'm glad to know that I am not screwing up my interpretations of what I have seen and read.

John Pace: I have dug out my copies of the MEW issues and will have a good read of them this weekend. I'll need to find some info on Compucut to understand your scripts precisely, but as there is no feedback I guess you are relying on hard-coded values for the helix angle drive (i.e. the ratio of the table movement to the cutter rotation). If so, does that imply that there are standard helix angles, and that those standard values are closely adhered to?

Still lots to learn.

Roger

[John ReeseParticipant @johnreese12848]

When grinding flutes using a finger grinding away from the cutting edge holds the flute against the finger. Grinding onto the cutting edge tends to lift the flute off the finger so it requires a lot of care by the operator th keep the flute on the finger. It is supposed to give a keener edge than grinding off the cutting edge. In the past I used an ancient Cincinnatti tool grinder that ground off the edge. It was relatively easy to use. I now have a Delta tool grinder that turns a** backwards so I am going to have to learn grinding onto the edge.

[John PParticipant @johnp77052]

Hi Roger,
I think i should perhaps point out the the cnc grinder is very much considered
to be an extension to the Quorn grinder.The cnc grinder is only used to grind
the helical flute parts of cutter ,it could if adapted be used to grind the ends
but this would need additional parts to written into the control file and possibly
some alteration of the grinding head.
There was some criticism about the lack of this ability when
published.

I expect these days that all new cutters are ground on automated machines
so having a control file to make hundreds or thousands off is a sensible option ,
but as these are new the blank but unground cutters require the same amount of
work to finish .
Things are very different in the home workshop where it is likely that there may only
be a one off cutter to do the control file only needs to be the minimum required to
do that part required ie just the flute edge ,since it is not possible to know what
amount of work to get a cutter back to a serviceable position it would cause
additional conplications to write control file to grind the ends at the same time
when the ends are just a simple job to do manually on the T/C grinder.

Having said that the file is saved and the cutter engraved to identify it
to the file so that it can be used to re-grind the cutter again at some later date.

It is probably easier not to think about helix angle and concentrate as you have
on the ratio of cutter rotation to table movement ,in this way the values are measured
on the machine and written into an already prepared template file in a similar way
to the demonstration in this video.

http://www.youtube.com/watch?v=qxU0K-TmEvI

Obviously this machine has a much better operating system to be able to do this ,
something that would be unlikely to be seen in the home workshop and i expect
beyond home workshop budgets.

I have sent you a pm so if you require any additional info i can send it.

John

[Roger HeadParticipant @rogerhead16992]

John Pace: Thanks for the PM. Yes, I noticed that it appears you didn't pursued other sharpening options on the CNC side. It certainly looks capable of extension.

John Reese: It would be interesting to hear how you get on with the manual control against the wheel direction, and what differences, if any, that you see in the results.

Ajohnw: 'Annoyingly i can't remember how it …' Welcome to my world .

In Harold Hall's description of his flute-grinding attachment I was interested to see his comment about the dramatic difference in ease of use that he found between sharpening the flutes from the tip to the shank, versus working from the shank to the tip (which he found much easier). I don't see any logical explanation for that, and maybe it was just some asymmetric mechanical characteristic in the motion of the tool carrier. But perhaps it is also indicative of the sensitive nature of this operation.

Roger

[John PParticipant @johnp77052]

SteveI, look in your pm inbox , message re drawings.
John

[AjohnwParticipant @ajohnw51620]

Posted by Roger Head on 03/07/2016 03:04:19:

Ajohnw: 'Annoyingly i can't remember how it …' Welcome to my world .

Roger

I haven't been able to remember for about 20 years Roger – good job that my need for resharpening cutters is pretty limited. I just buy new ones. Pity I didn't buy a lathe sooner but I could always use a machine at work in the evenings if needed.

It was an interesting machine. I suspect that there must have been 2 slides. One for parallel and one for tapers. It's the only arrangement that makes sense. The one for tapers must have carried the L shaped arm that was used to swing the cutter into contact with the wheel. The other was a shaft that was also twisted to keep the flutes in contact with the finger. Done that way the part being ground will be as parallel as the shaft is, it's angle to the wheel doesn't matter. This would be at the top of the L and could also handle reamers.

I can't see how it can have worked any other way. There was a large protractor to set angles.

It was also intended for resizing reamers so needed to be easily changed to any diameter cutter.The top sliding shaft had a long hole in it – same reasoning as GEO T's dividing head. A piece of bar was turned up to fit that closely with a portion on the end which was the same diameter as the cutter to be ground. The cutter was held with a small V block. That way it was easy to make accurate parts for any diameter.

There were other bits and pieces in the cupboard but I have no idea what they looked like or did. None of what I remember other than the motor mounting and to some extent the L arm was particularly heavily built so not intended for massive cutters. I'm pretty sure that the motor mounting was on a dovetail slide but with round shafts for height adjustment and a simple inch scale for setting the clearance angle – measure the wheel diameter and get the Zeiss tables out.

John

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[Roger HeadParticipant @rogerhead16992]

Sounds like you've really been dredging through the grey cells, John! Given my lack of experience, I'm not surprised that I am having trouble** envisaging the machine, but your description certainly contains enough detail that anybody who had worked on one would recognize it, so perhaps someone will chime in. Can you put any sort of age to it?

Maybe we need a thread titled ' Do you remember this … ' in which people could ask about almost-forgotten tools, machines, processes, techniques, etc. It would probably be popular with us (we?) old-timers.

Roger

** I get how using a V-block makes it easy to hold varying sized cutters, but that means that the offset of the cutter axis from the V-block base changes, and as it's the cutter axis that needs to be the centre of rotation during grinding, well …? Was the position of the V-block relative to the workhead axis adjustable? Or have I got hold of the wrong end of the stick entirely?

[AjohnwParticipant @ajohnw51620]

It was in what Lucas called an engineering school Roger. It had been there for some time so the machine could date back to the 20's or have been bought more recently. It was a pretty big place. Lots of shops and equipment.

I'm not totally convinced about the top shaft for parallel work but that being push pull was what immediately came out of the grey matter – then just that how could it do tapered parts – it was demo'd sharpening a morse reamer. I saw some one sharpening a bin of end mills and am pretty sure that the top shaft was pulled. It couldn't have been when the morse reamer was sharpened so the tool must have been angled to another slide which carried the L bracket. That could be used for parallel work too if it was clocked up.

Anyway that shaft has a hole in it say 1/2 dia. If a 5/8 dia cutter needed sharpening turn up a bar 1/2" dia stepping up to 5/8 dia at the end. If a 1/2 dia cutter a straight piece of 1/2 dia bar could be used and so on. That way the V block always holds the cutter on centre to the shaft. It was a pretty small V block but there were other bits and pieces in the cupboard.

As with Thomas's dividing head a plain hole is favourite because the clearance of the part that is slid into it set's the angular accuracy. In the grinders case it also makes it very easy to hold various diameter cutters.

In use the left hand was used to push down the bottom of the L to engage the wheel with the tool being sharpened and the right hand used to rotate the cutter to keep the flute in contact with the wheel. As I didn't get on with the grind instructor I was lucky to escape the dustbin of end mills. When I went onto the section he told me that he was determined to stop me – pointing out that all accurate work finishes up on a grinder. Up yours thought me but this is probably why I went into design.

John

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Edited By Ajohnw on 05/07/2016 09:50:34

[Bernard WrightParticipant @bernardwright25932]

This is how I do the flutes on HSS end mills…

**LINK**

End result…

**LINK**

Machine is a Clarkson Mk1+, I may have misunderstood your post, but grinding towards the edge with HSS is OK, but I would imagine that may fracture the edges of Carbide end mills…

Bernard

Edited By Bernard Wright on 05/07/2016 23:28:40

[Roger HeadParticipant @rogerhead16992]

Ah, ok John, I think I get it now – the cutter-sized end of the piece of bar that you turned was used to position the V-block, which was then clamped in place (and the piece of bar removed? ) ??

Bernard: Ok, now that's a serious cutter. I don't think it would fit in my ER32 chuck . Looks like a nice result, though. Is that a bit of green string and a weight to turn it on the finger?

Interesting thought about the grinding direction and carbide. I don't think I've seen anything relating to it one way or the other.

Roger

[AjohnwParticipant @ajohnw51620]

Nearly. The V block was clamped to the end of the piece of bar and the cutter then clamped in the V block as well. Very similar to the usual V block clamps in both cases. I'd estimate that the V block was circa 2" or so long and it would probably comfortably hold end mills up to around 3/4" maybe more. The same arrangement with the holder swung round some how enabled the ends to sharpened as well.

It was easy to put a tool in because the L shaped part swung out to clear the wheel. Once the cut had been set on one size of cutter others of the same size could be done at the same settings.

John

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[Bernard WrightParticipant @bernardwright25932]

I can't say that I've seen anything about carbide grinding Roger, just my own thoughts and observations whilst grinding a carbide scraper, yes the string is for keeping the flute against the finger.

I needed to sharpen that cutter to face across a large thick walled tube, that wouldn't go in the lathe…

**LINK**

It was for a hoist arrangement atop my miller where the overarm used to go, I only use the universal head now, so the dovetails provided a solution to help my ageing muscles…

**LINK**

Bernard

Edited By Bernard Wright on 06/07/2016 22:56:22

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