dressing grinding stones

[Douglas JohnstonParticipant @douglasjohnston98463]

[Douglas JohnstonParticipant @douglasjohnston98463]

I have been sorting out a number of blunt endmills on my Quorn cutter grinder and have been surprised at how often I need to dress the grindstone. I barely get one 4 flute 12mm endmill done before the stone end becomes quite black and does not cut so well. I am not taking that much off each cutting edge either.

The wheel I am using is a 4" Norton brand cup wheel with 60 grit size. The wheel is marked 38A60-KVBE Alundum and I am dressing it with a single point diamond dresser.

Is this normal since I rather thought I could do a few cutters between dressing.

Doug

[Douglas JohnstonParticipant @douglasjohnston98463]

Just thought I would bump this up the list in the hope of a comment.

[GoCreateParticipant @gocreate]

Hi Douglas

I had the same problem using the straight cup grinding wheel that was supplied with the kit, it's not normal and suggests the wheel is not suitable for HSS. My guess is the wheel is more suited to carbon steel tools.

I got a recommended wheel from a local supplier which worked significantly better, unfortunately I don't have the wheel spec and now use diamond wheels on my T & C grinder.

It's worth contacting a supplier for a recommendation, this link may help is selecting a suitable wheel. Look under cutter grinding/HSS.

Regards

Nigel

Edited By tractionengine42 on 27/06/2016 09:19:57

[Rik ShawParticipant @rikshaw]

Douglas – I worked in a cutter grinding dept. back in the eighties. We always ground small end mills and slot drills using the edge of a 4" saucer wheel with the wheel at 90 degrees to the flutes. I cannot remember the grade of wheel but they were white and were of a medium grit size. This grit size helped to prevent burning of the HSS tools.

I can make a comparison if it helps. If you look at the grit of the wheel on the average chain saw sharpener this would be to fine for HSS tooling.

Frequent dressing of the wheels was done by hand using a chunk of 1" square hard grey abrasive stone with a very large grit size. The idea is to maintain a pointed cutting edge to the wheel to reduce the contact area which again reduces the risk of burning. By the sound of it you are using a wheel with to fine a grit and maybe an unsuitable type as well. Hope this helps.

Rik

Edited By Rik Shaw on 27/06/2016 10:07:38

[AjohnwParticipant @ajohnw51620]

I think Nigel has it the wrong way round – the wheel you are using isn't breaking down when tools are being reground. This seems to be pretty typical of the wheels supplied with most if not all off hand grinders these days. It could be much the same with cutter grinders. I've tried several grinders over the past few years. I also have a grinder I bought at least 20 years ago and apart from changing one of the wheels to green grit it's still on the same wheels and they don't need dressing very often. When I bought this grinder I asked about a wheel for HSS and was told the one on it was fine – Graham Engineering. It's proved to be ok and I believe is a general purpose wheel as per type 8A in Nigel's link. It doesn't choke up if used heavily on mild steel either so might even break down more easily than those.

I started messing with other grinders thanks to another forum. People were having problems grinding HSS using a 6" grinder. I wanted another to fit a scratch brush on one end and a mop on the other so bought one – more than one as it turned out. The things tend to bounce about all over the place. My other one, Nutool isn't even bolted down. I found that the wheels Axminster sell are ok but need to be used gently and slowly otherwise they just clog up and burn the tool. Hard to understand why but this is what they do. The ones supplied on the grinders have been worse. I've also found that wheels can need up to 1.5mm dressing off, even getting up to that amount on the side. Too be honest I have mostly given up on them as truing the wheel really needs a jig because they are so far out. One from Woolworth's isn't too bad but still nvg. My Nutool is an 8". I've always thought I should have bought a 10" as per the usual toolroom size in the past. I did try one more recently but it took a long long time to get up to speed and the grinder itself seemed to be out of balance.

John

–

[Clive HartlandParticipant @clivehartland94829]

One thing I learnt was not to grind surfaces full face on the wheel, I was taught by an oldie to dress the face of the wheel and then go across again but not complete the run, thus leaving a small step/raised portion which reduced the heat and cut better.

Using this method on a vertical grinder always made a good surface. Now that diamond wheels are cheaper that is all I use now.

Clive

[Clive FosterParticipant @clivefoster55965]

I wonder if there is a surface speed issue.

My Clarkson T&C grinder runs at 2,800 rpm. Recommended wheels are 5" plate in 38A60-K5VBE and 3 1/4" taper cup in 38A60-K8VBE. The VBE suggests that bond type doesn't much matter but 5 and 8 refer to the structure. Both are within normal range but there has to be a reason for the difference. Its either due to the wheel and different natural strength or surface speed. If it is surface speed higher numbers for slower speed.

Clarkson book says dress the face at a shallow angle so that only the edge cuts. The taper cup wheel I'm using on mine for lathe tools is the one which came with it, pink and unknown designation, is sensitive to front taper and blacks up the edge very quicky if its too shallow. With the right edge it does a very good job. Lets me save the wheels I bought for teh Clarkson to use on milling cutters.

Clive.

[AjohnwParticipant @ajohnw51620]

One of the things I have always found interesting about re sharpening end and slot mills in the model engineering world is the wheels used. I've only ever seen them sharpened during training. A job to avoid as some one would get a dustbin with rather a lot in and might spend most or all of a week sharpening them. They use a thin wheel edge on – just like some shown in the 8A grade off the link Nigel posted. The flutes were sharpened as well. The same machine and wheel was used for sharpening morse taper reamers. Also for resizing reamers if odd sizes were needed.

All lathe tools were either sharpened on an off hand grinder or one of the auto / lathe tool grinders that use a coolant and the side of a wheel. That is the machine super weld tools ended up on. – welded tipped hss for those that haven't come across them.

John

–

[Douglas JohnstonParticipant @douglasjohnston98463]

Thanks for all the input, I will try a slight taper on the face of the cup wheel, as suggested, and see if that helps. I did wonder if wheel speed was an issue but the speed of about 4000 RPM on a 4" wheel seems as if it should be reasonable.

The other option would seem to be a diamond wheel, although there seems to be some debate about whether diamond is suitable for grinding HSS.

Doug

[mechman48Participant @mechman48]

Posted by Douglas Johnston on 27/06/2016 17:57:35:

Thanks for all the input, I will try a slight taper on the face of the cup wheel, as suggested, and see if that helps. I did wonder if wheel speed was an issue but the speed of about 4000 RPM on a 4" wheel seems as if it should be reasonable.

The other option would seem to be a diamond wheel, although there seems to be some debate about whether diamond is suitable for grinding HSS.

Doug

It is important to not over speed the wheel… 'Spindle speed should never exceed the wheel speed'… thus your motor speed should be below rated wheel speed….usually motors run at 1420 – 1475 'ish rpm, so your max' motor rpm would be in the region of 2800 – 3000 rpm, dependent on h.p. of motor.

George.

[Clive FosterParticipant @clivefoster55965]

A bit more noogling around concerning wheel specifications shows that the 5 in Clarksons recommended 38A60-K5VBE for 5" wheels means that its a denser structure than the 38A60-K8VG (sorry typo in the previous post) suggested for 3 1/4" ones , the 8 meaning its more open. Looks as if open structure goes with lower pheriphal speed and dense with higher. Clarkson runs the 38A60-K5VBE at around 3,650 sfm and the 38A60-K8VBE at around 2400 sfm. Your 4" wheel at 4,000 rpm is going around 4,200 sfm so if there is a speed relationship you'd probably want a denser structure. Maybe 4 or 3 in the wheel code.

From the Clarkson book K is the hardest soft wheel and the normal structure range is from 3 to 8, 0 to 3 is dense, 9 to 12 is open.

Unfortunately there don't seem to be any simple guides to this wheel grade business It seems to be agreed that the art is having a wheel structure open enough so that it doesn't clog and a bond of appropriate strength so the wheel sheds grit particles before they are blunted but doesn't wear away too fast. Which is fairly clear. Then everything devolves into a discussion of whether wheels are actually hard or soft or just cutting hard or soft before disappearing into an impenetratable swamp of wheel codes. Why is it too hard to simply produce starter lists saying this wheel at that speed will work adequately with these materials to at least give folk a chance of starting with something that works. Its obvious you can do much better than a a basic starter suggestion if you wan't to wade in Alpha-Numeric soup..

Clive

[Douglas JohnstonParticipant @douglasjohnston98463]

The wheel I am using has a maximum speed marked on it of 5730 RPM so I am well under that at 4000RPM. I use a dc motor drive so could arrange a reduced speed to see if that helps matters. I guess it is just a matter of trying out a few ideas and see what is best. I have no complaints about the quality of finish I am getting on the endmills, it just came as something of a surprise that the wheel needed dressing so often.

Doug

[Neil WyattModerator @neilwyatt]

This doesn't sound like glazing, caused by too great a speed but excessive wear caused by either working the wheel to hard or to slow a speed – and you are running slow by 30%.

Try running it at closer to its proper speed, this should greatly decrease the wear rate.

Neil

[Ian S CParticipant @iansc]

Are you maybe being a bit aggressive on each pass, trying to hurry things up a bit. Ian S C

[AjohnwParticipant @ajohnw51620]

Looking at the spec of the wheel it mentions light cuts. I'd read that as meaning thou's. That spec of wheel seems to be available in all sorts of sizes and personally I would have thought 4,000 rpm would be about right for a 4" wheel. From memory slowing down needs wheels which break down more easily.

Norton mention 38A60-KVBE as being good for narrow contact moderate stock removal, 0.002 – 0.004 in HSS and tool steels. 32A60-KVBE is listed as better and 5SG60-KVS as best. For heavy stock removal >0.004 the grit sizes go down to 46 but the rest of the spec is the same.

The only speed they mention is 8,500 sfpm and up to 12,500 on request but this is for iD and Race wheels. Not sure what race wheels are but some of the wheels in this section are 6" dia. The one with your grade is 4"x1/4×1/2.

This seems to fit in with the white wheels I have tried – ok if used rather lightly. Intended for sharpening which should only need very very little material removing. A bit slow for shaping lathe tools.

John

–

Edited By Ajohnw on 28/06/2016 10:39:16

Edited By Ajohnw on 28/06/2016 10:40:57

[KWILParticipant @kwil]

The professional regrinders seem to use CBN as their wheel' material.

[Neil WyattModerator @neilwyatt]

Posted by KWIL on 28/06/2016 10:39:50:

The professional regrinders seem to use CBN as their wheel' material.

Diamond is ideal for carbide, CBN for HSS. They have very long life.

Truth told I am still on my original diamond cup wheel which gets light use on HSS.

[AjohnwParticipant @ajohnw51620]

Posted by KWIL on 28/06/2016 10:39:50:

The professional regrinders seem to use CBN as their wheel' material.

Norton's Toolroom catalogue only lists cbn and diamond. They do give speeds there but state a pretty broad range and the usual fixes for problems.

John

–

[Roderick JenkinsParticipant @roderickjenkins93242]

Very nice explanation of the issues concerning diamond grinding wheels for use on steels here. However, for home use there doesn't seem to be an issue with using diamond wheels. I suspect we just don't tend to consistently* reach the temperatures that cause a problem. Speaking to John Stevenson at the Doncaster show, he was using the diamond wheels for sharpening all the end mills he was offered and wear didn't seem to be a problem – might have changed his mind after a few days continuous use.

Rod,

* I'm assured that split infinitives are now acceptable

[Douglas JohnstonParticipant @douglasjohnston98463]

My understanding has always been that the speed marked on a grinding wheel is the maximum safe speed and the wheel would normally be used at a reasonable margin less than that.

On each pass I am advancing the endmill by about half a thou and am getting nice cutting action for a while but then it starts to get more laboured. I take it easy and don't rush it so perhaps I am being too cautious and should take more off per pass. More experimentation me thinks.

Doug

[Author]

Posts