EMG-12 Endmill Re-sharpening module

Musing on how this works and noting the comments made about the "striations" on the ground faces, I had a close look at one of the photos.

I've superimposed some arrows that indicate ground lines visible on 3 of the 4 teeth (and probably on the 4th but there isn't much reflected light). They are in virtually the same position on each primary clearance and also line up on the secondary clearance. I would guess that these are due to a slight prominence of a diamond on the wheel surface? It indicates I think that the action of turning the cam advances the cutter directly onto the wheel surface, so small irregularities in the wheel get transferred "negatively" onto the tool. This of course doesn't matter at all since its only the end of the teeth that cut, but it helps to explain the action of the machine.

By contrast, on a grinder of the Quorn / Clarkson type, the face is ground by stroking it across the wheel until it sparks out. Any prominence on the wheel effectively acts like a little "flycutter" and you can get almost a mirror surface. It's maybe because people got hung up on designing TCGs that would hold the tool to permit this kind of action that it took so long for this new design to appear.

Edited By John Haine on 01/06/2015 21:55:36

Useful analysis, John

MichaelG.

The idea of plunging the end of an end mill into a rotating wheel is not new, I first saw it in issue 14 of MEW. I then published a more detailed version (drawings, etc.) in issue 170. This now being the subject of the link I mentioned earlier.

If you did not see my earlier comments this would have been because my contributions again went AWOL (absent without leave) for some reason, do go back a read my comments if you have missed them. Note, I will now be away from the PC for the next five weeks.

Harold

I think Harold and many are missing the point.

Not everyone who comes into either this hobby or starts a small business or uses machines to follow another hobby like vintage bikes and cars are born with 6 fingers on each hand and have all the time in the world.

Because someone is able to think up an idea and even get it into print doesn't mean to say that everyone can follow it, has the skills to replicate what has been shown or even the time.

I have seen pictures uploaded of the generic 4 position toolpost and someone wants a drawing ????

Chances are it won't fit their lathe, tool is too high, central bolt is the wrong size and by the time they have modified this they have designed their own, but tell them to design their own and they will tell you they can't.

There are a myriad of tool and cutter grinders out there, there are hundreds more of jigs and fixtures to do all this work. The authors of who think theirs is the best thing since sliced Hovis but they can't all be right can they ?

What they do have in common is needing time and skill to build them and the same time and skill to operate them.

There are far more users lacking either of these skills than users who do. If they have one skill they are probably lacking in the other or lets be honest, can't be bothered.

The ratio of Quorns sold to Quorns built and finished must be 10:1

Where the EMG- 12 scores is it does what it says on the tin, It's quick, its easy and it can be used by people with no tool making or grinding skills and time. And that believe me is a higher percentage of people than those that who build jigs and fixtures.

Nothing wrong with jigs and fixtures, just that this thread is about the EMG - 12.

I have heard back for 5 people who have bought one of these. All are very pleased with it. None of them visit this forum as they don't build models and are not interested in posting comments, more interested in doing what they do.

On the subject of the EMG-12, here is an email response sent to me by Bill in Australia. It does not specifically cover the questions raised, but still, I am posting it here. I am finding it difficult to persuade others to post. They have their own reasons, but I have obtained permission for this message to be posted. (Thank you Bill)

Before reading the comments, please note that this is only being posted to address certain attributes of the EMG-12 from a user of the product. ARC has the greatest of respect for other T&C grinders - home built or commercial. We have no axe to grind with anyone or any other T&C Grinders, all of which have their own attributes and/or additional features. For the record, I get on well with Ivan Law (the respected gentleman responsible for the Quorn) and Derek (DAG) Brown, both of whom I meet at the Harrogate Show recently, where Derek was showing/demonstrating his Quorn T&C Grinder. Glad to see that both are in good health

"Hi Ketan,

Having said my bit in the early stage of the discussion, I would like you to know how much I appreciate the opportunity to have been able to buy an EMG-12 from you and have you ship it out to me in Australia.

I bought it with the anticipation of it meeting 3 criteria which are important to me.

1. I wanted it to recover and produce sharp end mills repeatedly.

2. I wanted it to do that quickly?

3. I wanted it to be easy to use so even I could get the desired results.

I am happy to report that it has achieved 100% in each criterion.

All my end mills, 1/2" and less, both metric and imperial, are razor sharp. I have tested each one and they cut as well as when they were new. I will now not use or need to use larger cutters other than to enlarge 13mm holes in the lathe to accommodate a boring bar.

I must admit the add in MEW did not attract my attention until I read the review. It was the concept of being able to quickly sharpen a cutter after use in readiness for its next job that really appealed to me. I have been using a Quorn T&C grinder for years. I think I can say that I became frustrated every time I used it. I always had blunt cutters and it would take me a whole session in the workshop just to sharpen the ones I needed at the time. I will now sharpen my few large end mills on the Quorn as they wont t get a lot of use and my smaller end mills will always be razor sharp. At 77 I don't want to waste any of the time I have left getting frustrated.

Thank you again. I hope those last 3 EMG-12s have been sold and that you are getting more in because I am sure model engineers will eventually see the real benefits of the machine and then they will "justify" the purchase of one.

Bill Adamson"

Ketan at ARC

An observation on Andrews 'counter-iintuitive' result:

1500 rpm at 4 flutes is 6000 cuts per minute. At 450mm per minute that's a feedrate 0.0.075mm or about 2 thou per cut. Halving the feedrate might noticeably improve the finish and reduce the surface roughness with the new cutter.

But why is the 'blunt' cutter better? - It seems it's either acting like a lathe tool where you stone off the end or burnishing the work (I suspect a combination of the two, with the 'bright' areas being more burnished. As this is a raher rough and ready approach the visual appearance is poor and less consistent (variation in roughness readings 1.15um with the blunt tool, 0.99um with the sharp one).

Lesson learned? Possibly that, if your main use for end mills is using the ends to clean up flat surfaces, having a few endmills with the corners neatly ground off may give the best results, but if you use sharp ones, drop the feedrate on the finishing cuts.

Your thoughts, gentlemen?

Neil

Howard,

there's a guy called Geoff Josey who'll sharpen your end mills for a small fee. He regularly puts an ad on the Home Workshop site.
The fee is actually a donation to Farleigh Hospice, which is a damn fine thing I reckon.
This is a link to it

**LINK**

Steve

I've been called many things, but a gentleman wasn't one of them; nevertheless you're still going to get my thoughts.

I'm not entirely sure I believe my surface roughness measurements. It's a bit of a black art, or so it seems. The finish with the nearly new cutter certainly looks better. Spot on, I did the calculations in my head based on 2 thou per tooth. That's pretty conservative, I'm happy to run faster. As JohnS has pointed out endmills and slot drills are slightly hollow ground, but only by about 1°. So for a 2 thou advance that's a height difference of about 35 microinches or about 0.86µm. That's rather less than I am measuring? I am measuring Ra, which is an average. The conversion to a peak to peak measurement (Rz) is rather fuzzy, but generally somewhere between 10 and 20 times?

A facet of finish that is often neglected is uniformity. As well as aiming for a 'good' finish I try and achieve a uniform finish, even if it is a bit rougher. It's no good if the finish starts off looking like a babies bottom and then reverts to looking like a badgers rear end.

When I really need a good, smooth, finish (sub-micron) I use cutters with a radius ground on them.

Andrew

Botheration, I've missed my 1957th post, the year of my birth. This post will be my 1960th post, the year my brother appeared.

Andrew

Tubal Cain in "Milling Operations in the Lathe" (WPS 5) comments on corner rounding spoiling the cut and how this may be stoned to improve surface finish. He goes on to say "Naturally, if the cutter is required only for surfacing, you can put a deliberate bevel here, with great advantage to both cutter life and finishing"

By the way, don't be fooled by the title of this book, it is an excellent general treatise on the action, use and maintenance of milling cutters - much better IMHO than Arnold Throp's "Vertical Milling in the Home Workshop" (WPS 2) .

Cheers,

Rod

Well yesterday I had to buy a new milling cutter, a sharp one

What !!! buy a new cutter when I had all these resharpened ones kicking about ????

Yup because it was a special one in a size I didn't have or close to it and also outside the reach of the EMG _ 12

£74.12 each including VAT It's a 3 flute 25mm Tiain coated rougher, the one with the serrations on the sides for chip clearance and guess what this one has deep grooves in all three cutting faces, two in each for breaking the chips up.

However at 10,500 rpm and a feed of 1 metre per minute and 12 mm depth of cut in some alloy plate the bottom finish is like a mirror. Side finish does show striations as you would expect from the chip serrations on the side.

Perhaps Ketan should advertise the new lot as having advanced chip clearance. I know the EMG - 12 won't do these on size but I'd could buy a machine for the price of 11 cutters.

This same cutter in 12mm which I thought about getting but cycle time would have been too much is £38.83 and that is with all my discounts so that's only 20 cutters.

With regard to end mills for surfacing. I have a 3/4 inch cutter (bought second hand) which I ground the corners at 45 degrees (Quorn TCG) to give about 2 mm depth of cut without cutting on the side of the cutter. This is the cutter I use most. The 135 degree corner angle gives me a robust cutting edge similar to a roughing lathe tool which does not overheat easily and means you don't have to regrind the flutes. It produces a good finish and removes material quickly (Myford VMC mill). I would recommend this to anyone who has the facilities to regrind as described.

I'm sure this is not a new idea at all. In fact I copied it off the telly. (Old Fred Dibnah Video)

One has to bear in mind that the function of a milling cutter is to remove metal! Re-sharpening a cutter on the end lips is the easiest way of refurbishing, in many cases the flute edges get damaged and re-sharpening the flutes is a different thing again. Small size cutters need to be thrown away or converted for other use but large cutters are worthwhile recovering due to initial cost as JS has just stated. The machine covers the middle sizes used by model engineers but not the larger engineering sizes. If you have justification or need one then buy it. I cannot justify it at my lower scale of engineering so a Worden is all I need to sharpen the lips which will take up to 18 mm in my case. Making adaptors to suit all my size cutters in both metric and imperial. The only down side is the secondary clearance which on the Worden means adapting the motor mount to be raised to accomodate angle/height problem.

Clive

Well it touched down yesterday, will report my findings in a day or two

One small step for Jason ?

Thanks to all who provided details of where to get End Mills sharpened.

Will follow up in the near future.

Howard

> As JohnS has pointed out endmills and slot drills are slightly hollow ground, but only by about 1°. So for a 2 thou advance that's a height difference of about 35 microinches or about 0.86µm.

Google suggests a bit more than that is typical, up to 2 degrees, about 1.7um? Still about half your figure.

Neil

Remember that we're calculating a peak-to-peak value, whereas I am measuring an average value. So, depending upon the crest factor, the calculated values are much smaller than those measured.

Andrew

So as its been about a month since MEW232 came out has anyone got any comments on the results from this little machine that were in my review?

Have any members been tempted to raid the piggy bank?

Could have done with one myself the other evening when I hit a hard spot while milling off some weld that took the corners off a sharp 1/2" cutter

In a word, no and no.

However, since I had the opportunity to try out the unit a while back I thought I ought to finally extract my digit and write something up. First impressions were good. The machine is nicely made, the instructions are well presented, and I had no trouble getting it up and running. The motor controller is slightly odd in that when switched on the motor oscillates, as if deciding which way to go, before the motor spins up to speed over a couple of seconds.

I didn't try the machine with HSS cutters, as the few that I have that need sharpening were too big. However I did have a range of uncoated carbide cutters in various states of disarray, from simply blunt to having corners knocked off due to operator incompetence. For the tests I had 2mm and 4mm 2-flute slot drills and several 6mm and 10mm 3-flute slot drills. Where the slot drills were badly damaged I first removed the damaged length using a bench grinder with a 'green grit' wheel.

I found the instructions easy to follow. For some of the larger cutters several passes were needed before all the cutting edges were properly ground. This may be because I hadn't taken enough care when roughing out. I was impressed by the rate at which the grinding disc removed the carbide. I found the 6mm and 10mm cutters easy to sharpen and the fresh cutting edges look really good. For the 2mm and 4mm cutters I had some trouble lining the edges up correctly, so that the finished edges, although properly ground didn't seem quite right? Since I only had one each of the 2mm and 4mm cutters to play with this may well be operator error. I haven't had the chance to try the re-ground cutters in anger, but have no doubt they will be fine.

So in summary the unit does exactly what it says on the tin and is simple and quick to use. It is very good for regrinding blunt, or damaged, ends of cutters. Of course the big question is would I buy one? Probably not, although that is no reflection on the unit, for the following reasons:

1. I tend to make heavy use of the side flutes when milling so the side flutes often end up damaged, more so than the ends. The unit is unable to regrind side flutes.

2. Most of the HSS cutters I use are bigger than the 12mm limit of the unit.

3. I already have a well equipped Clarkson T&C grinder for regrinding and modifying cutters.

Andrew