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diamond grinding wheels

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jomac09/02/2010 12:54:32
113 forum posts

Hi, I intend to build a tool and cutter grinder, and am thinking that a diamond cupped wheel is the way to go.

E/bay has a good selection of 100mm diamond wheels. The only trouble is, that there is is also a large selection of  "grits" rangeing from 100 grit up to 600 grit. The problem is which grit to use for sharpening end mills and drills, and maybe HSS lathe tools.

Am I right in thinking that the finer grits are to used for polishing precious rocks and gem stones.

So any ideas would be very welcome, and the right info could save me/us  money.


Ramon Wilson09/02/2010 13:48:06
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1319 forum posts
382 photos
It's a good ten years or so since I was involved with grinding (not Tand C) but the only time diamond wheels were used was for (surface) grinding of carbide. Diamond 'tooling' in the shape of files, laps burrs and honing stones have moved on considerably though I'm not sure that applies to cupped wheels for HSS - I may be wrong here - just don't want to think you will be shelling out for something that will not live up to your expectation.
I would say that you would be possibly be better off investigating  conventional abrasives and purchasing a really good diamond dresser - wheel dressing is something that needs constantly attending to when grinding fine surfaces whether tools or not.
 
Hope this helps - Ramon
Circlip09/02/2010 15:21:12
1510 forum posts
My own was forty odd years ago Ramon on a "Wickman OPG" ( An excellent one recently fetching the magnificent sum of £275 on the "Flee").
 
  Seems that toy builders affluence not only has carbides with everything, we now have diamonds with everything. As we are now instructed to use indexable carbides and chuck 'em when blunt polishing with a diamond wheel seems a bit frugal. They tell us that usingthem on HSS tends to bung them up (Like grinding alumininininium on conventional wheels) but I remember using diamond "Burrs" used on Jig Grinders for hardened tool steel.
 
   Regards  Ian.
dcosta09/02/2010 17:24:33
496 forum posts
207 photos
Hello!
 
I made an tool and cutter grinder following the Harold Hall's book  (see  http://www.model-engineer.co.uk/albums/member_photo.asp?a=7538&p=132975) and made for it a grinding post and I use in it a cup wheel from Arco Euro Trade.
Not being a professional I've not used the T&CG a lot but I am satisfied with it. And in this case with the grinding wheel.
 
 
Regards
Dias Costa
mgj09/02/2010 18:06:36
1017 forum posts
14 photos
I'm interested in this one.
 
I can tell you what I use on the Quorn. 60grit - (WA 60 JV as I recall) but that is not a diamond grit, that's a white aluminium oxide.
 
That produces a mirror finish. BUT it will load up eventually, and as Ramon says, you have to dress the stone up.
 
Also its absolutely NBG for roughing - youdd be there all day hacking into a HSS blank. So, I do that on the offhand grinder - whatever stones that came with. 1 coarse and one so called fine, but fine is not tool sharpening fine!
 
So do these diamond stones load up? If so how do you clean them? 
 
Also are diamond grit sizes equivalent to ordinary oxide sizes
 
Is there any point to a diamond stone? It takes 2 secs to run a diamond across the front of a stone,  and you only take .001 inch at a time, tops. If you have roughed out, you don't have to dress every time you use it. My 4" 60grit Universal cup has lasted 20+ years and its not really on the way out yet.
Versaboss09/02/2010 22:16:27
490 forum posts
69 photos
Posted by meyrick griffith-jones on 09/02/2010 18:06:36:
...... 
 
Also are diamond grit sizes equivalent to ordinary oxide sizes
 
....

 Yes and no. Sometimes the grit size is given in mesh size, eg lapping plates or sticks in grit 600 or 1200. But for wheels usually the FEPA numbers are used: D91, D151 ...

The higher this number, the coarser the grain!

The same system, but with the letter B instead of D, is used for CBN wheels

A small comparison table is here:

http://www.diamondtoolmfg.com/grit.php


Greetings, Hansrudolf


Ramon Wilson09/02/2010 23:55:37
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1319 forum posts
382 photos
As I've said it's quite some time since I was involved with these matters but unless things have changed this was how it was -
 
Our press tools were made up of individual parts made of hardened (various) tool steels or carbide. The diamond wheels were only used on the carbide and never on the steels. I was not involved with the carbides but I recollect the wheel was brought down on a 'block' of some material which trued the wheel and removed any detritus.
 
The tool steels were ground with a myriad of wheels - sorry but I can't remember all the grits and grades but most were white for form ginding ranging from soft to very hard, brown 46J for basic surfacing and/or roughing, pink for the really hard chrome steels. These wheels were all dressed regularly with a diamond held rigidly in a holder on the chuck or in the optidress wheel grinding attachment. All well to the rear of the technology queue now I guess but it may have relevance.
 
All of our diamonds were 'single point' of varying carats but someone at some time gave me a very small piece of diamond impregnated steel section about 12 x 6mm. This is bolted to a piece of steel for a crude handle. I have no idea what it is called or where to get it from but it is absolutely the best thing for hand dressing abrasive wheels - as the steel grinds away fresh diamonds are exposed - I used it only at the weekend to trim the wheels on the off hand. I'll take a pic of it tomorrow so you can see what I mean.
It's getting rather short - if you know where I can get another I'd be grateful
 
Hope this helps -  Ramon
Regards - Ramon
jomac10/02/2010 08:52:35
113 forum posts

Hi again.

I was getting a bit confused, about the grit size, on the concave diamond grinding wheels, but I had another look at the e/bay sites, and found descriptions of the wheels. The coarsest wheel is 100 grit, the finest is 600 grit, also as a cross reference they also sell 10" flat and half round diamond files, (A$11) the medium grade is 120 grit the fine is 300 grit , so as the price for a 100mmX35mm with 10mm on the outer face and 5mm on the edge is only A$13-A$15, plus postage A$11- A$15, that seems very cheap, although there are dearer one's, probably because of the shape of the grinding edges ???.

Anyway for the equivalent of 5 quid (my keyboard don't have the pound sign), I think I will go with 200 grit wheel to start with.

Because I can't  find ordinary concave/cupped wheels here in oz, the cost of the item plus  postage from the UK could make it a bit pricey, Besides I mainly only want to sharpen end mills and drills, The next step is to design a cutting machine, I know, Harold Hall has a simple design, so does one of forum posts its also simple, The Bonnelle which is on a disk with real cutter grinders is a bit to complex.

Any more info from the forum would be great.

John Holloway

Versaboss10/02/2010 13:10:30
490 forum posts
69 photos

Jomac/John, are the wheels you looked at resin-bonded wheels or galvanic coated ones? A resin bonded with mesh 200 (according to the table I gave above around  D76) is quite fine, but I think would be ok for end mills. For galvanic coated ones I would consider it coarse! I have the lapping plates from ARC Euro trade with grit 600 and 1200, these are perfect for lathe tools.

Greetings, Hansrudolf


Frank Dolman10/02/2010 14:10:26
106 forum posts

     Someone recently (yeah, I know! ) pointed out that liquid iron dissolves
  carbon and so, if you grind ferrous metal fast enough to make sparks, you
   will lose your diamond quite quickly.
     Perhaps this is why Ramon used diamond only for tungsten carbide.
     Did Circlip's burrs cut fast enough to spark?
     Has Dias's wheel cut enough to reveal a drastically reduced life?
     Has anyone used a diamond wheel on iron long enough to answer
   this partly remembered caution?
Circlip10/02/2010 14:48:07
1510 forum posts
Can't remember Frank, the smug B*rstewerds in Jig Grinding wouldn't open their air conditioned "Kennels" to the likes of Apprentices, but as a finishing operation on the punches and dies for stamping my post name they were removing tenths of thous.
 
  Used both the Bakelite bodied resin bonded wheels and also the metal diamond impregnated ones, the latter being £60, as, when as a paid slave on the princly sum of £3 7s 6d a week, was told that was the cost to replace one I'd just dropped. Thus the ref. to the Wickman Optical Profile Grinder.
 
   Regards  Ian. 

Edited By Circlip on 10/02/2010 14:49:20

chris stephens10/02/2010 15:05:55
1049 forum posts
1 photos
Hi Ramon,
I got mine from Chronos many years ago.
 Try the forth item down.
chriStephens 
Ian Welford10/02/2010 15:39:46
299 forum posts
I got a Chronos one and can recommend it- code GEO 1 but Arc Euro also list one except theirs seems to be a hollow square section attached to a handle with diamond on one side of the square bar. Not sure what the benefits of the bar will be ?
 
Having tried 100 grit diamond cup wheels on both steel and carbide they work and give a beauutifully smooth finish but , certainly on HSS , they're damn slow and heat it up something wrotten. Could be I'm taking too bit a cut mind!
 
The great thing is- no grinding dust- it's only powdered steel coming off . I tried runnign with a bit of water on the weel to keep things a bit cooler. RDG told me to run em wet and they last longer. Only 1 year inot use but no detectable wear as yet . Then again only just starting to use it as I learn by experimenting.
 
 
Ian
mgj10/02/2010 18:19:05
1017 forum posts
14 photos
I am sure that any of these fine grit wheels are not for roughing. You have to get the blank more or less to shape first and then sort out the badgers bum with the finish wheel.
Unless you buy and mount a proper coarse cup and swap the wheels over.
 
I usually set about .25 of a thou for a cut on the Quorn, but sometimes less. 
Ramon Wilson10/02/2010 22:28:36
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1319 forum posts
382 photos
 
Hi All, Some good replies here. At the risk of repeating myself a bit perhaps I should elaborate a little.
As said diamond wheels were only used as far as I remember for surface grinding the cutting faces of punches and dies. Most of these P&D's had very complex shapes the forms of which were wire eroded. The use of diamond wheels was purely down to the hardness of carbide. Prior to the accelerated use of carbides in these press tools  these parts were made from varying grades of tool steel and whilst the more complex were wire eroded many were formed by grinding with conventional wheels. The forms were shaped on the wheels by a single point diamond using an 'Optidress' wheel forming attachment.( Big panic when you hooked the diamond out of the end of the dressing 'stick' !) The forms took many different shapes of angles and radii all dressed in this way. To give an idea of the limits of dressing involved it was frequently required to dress a 1/4 wide 6" wheel down to a thin blade with a .8mm (yes that is right) radius on the end. (That form had to be 'dropped in' some 16mm which required an awful lot of re-dressing as the wheel glazed up) Sorry for repeating myself - the wheels came in all sorts of grades, bonds and hardness to allow this to be carried out. I mention this to give you some idea of the (relative) ease of which conventional abrasive wheels can be shaped - not to suggest you do it - or even need to do it - at home but if you have a T&C then this is going to be a lot more beneficial to expose new clean grit than not being able to shape a diamond wheel.
 
Merrick is right to say these are finishing ops or to put it another way if you do intend to cut from solid - eg HSS blank for turning - then you need to take your time. Grinding is not something that can be forced. I don't wish to raise the dreaded H&S but be aware that grinding wheels are not shatterproof and do rotate at a peripheral speed that will shower lumps of abrasive everywhere at a phenomenal rate of knots - it makes a big bang and you don't get an advance warning! Sorry if it sounds like a lecture but it has to be said - Keep your wheel guards on. Really!  And whilst we're on the matter its not good to beathe the dust created when grinding carbide particularly if you use a diamond. The dust, once in the lungs, does not come out and it's accumulative. I know the amount that the home user is likely to be exposed too is very small, probably very very small - but it's a health issue that you should really be aware of.
 
Finally can I just remind you this was ten years ago - the progress since then particularly in the use of carbides and wire eroding has made these techniques very much a thing of the past. Things have moved on - I just haven't so don't beat me up if I'm off the mark!!
 
Thanks for the info on the diamond dresser - I couldn't open the pics on the link but the price was much better than anticipated. This is the type I mentioned, I guess the Chronos one will be similar, as you can see it's on it's last legs so it's good to know I can replace it.
Hope this helps a bit more
Regards - Ramon
 

Edited By Ramon Wilson on 10/02/2010 22:32:28

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