GRINDING WHEEL QUESTION

[ieezitin]

Hello

I have just built a Tool grinder and i now need to learn about grinding wheels.

I have a spindle that goes 4800 rpm, my primary grinding will be HSS tool stock and i need to be able to grind on two faces of the wheel perpendicular to each other, i am interested in the cup designs the spindle dia is 1/2''.

I currently have a Ruby red stone on there and it Burns quickly. This machine will be grinding lathe and shaper tools only so i don't need a mirror finish but a finish that will hone good.

All suggestions and grinding tips are welcome.

thanks for your help.

Anthony.

[Lew_Merrick_PE]

Anthony -- We will need to know more about the wheel you intend to use to answer your questions.  What is the working diameter of the wheel?  What type of abrasive is it made from and what grit?

The thing is that getting things set-up correctly is a balancing act.  Too slow a speed and you spend forever on a task.  Too high a speed and (as you have discovered) you burn your cutters.  A coarser grit cuts faster, but gives a poor(er) finish.  Etc.

[ieezitin]

Lew

on it at the moment it has a 4" dia Ruby Red stone about 100 grt( thats a guess) but i could go larger lets say 6''.  As to the material and grit that was my original question.

The speed is set... saying that i could change drive pulley diameters and put a new belt on it so i could change my speed if needed too.

The burning i referred to was on the wheel, it left black marks on it, the wheel was dressed with a diamond dresser so it was flat and square. So you have my situation i just need to know what will suit me even if i have to modify it.

as to the work i want it to do its just putting clearances, back rakes and angles on hss tool steel for bits.

Thanks

Anthony. 

[Lew_Merrick_PE]

Anthony,

There are a lot of variables involved in grinding.  My grinder is set up for (approximately) 7500 surface foot/minute speed using 60 grit and 120 grit aluminum oxide grinding wheels.  So long as I "cool" (water dip) toolbits with fair regularity, I get no burning.  If I am making small or complex toolbit shapes, I slow things down to about 3000 surface foot/minute speed.

I made my own off-hand grinder.  The primary mounting shaft with bearings and supports weighs in at somewhere close to 150 lbs.  The table supporting my work weighs in at somewhere close to 60 lbs.  The motor driving it is a 3750 RPM 2 HP motor salvaged from a lumber mill's dust collection system (many years ago).  With the base (and tip-back casters) the whole thing weighs in at somewhere close to 450 lbs.

Pacific Grinding Wheel (prior to their demise) was located (almost) in my back yard.  When they were being demolished, I purchased more than 500 8 inch grinding wheels.  As that was 1975, I got them for $0.20 each for aluminum oxide and $0.25 each for silicon carbide -- this is why I am "unfamiliar" with modern tradenames on this side of the street.

[Fergus OMore]

I agree with Lew about the number of variables. I used to make the resin way back in the 1950's! and went on to play with silly things like grinding rubber- and measuring it!

My best advice is to go to a place where grinding wheels are supplied to the trade- none of these awful Chinese efforts which were probably from the Great Wall

What are needed is at least two wheels- say to replace these Chinese affairs that come on the cheap 6" double ended grinders. They push out perhaps around 3000rpm or the English variety does. For ordinary grinding of hss and carbon tools, white Aloxite of a softish grade is common.
Probably 60 grit for roughing out and 80 grit for 'a better finish. My Clarkson book  quotes several grades but one is 38A60K5VBE which is a 60 grit wheel and which does not burn the work. Here opinions differ but I usually hone after the grinding. Others might settle for perhaps 100grit

However, you might consider adding a diamond or CBN wheel to your arsenal. The first means that you can touch up carbide tooling.

There are plenty  of books. I have the Clarkson one but also have the Quorn one.
Trying to conclude, experiment with the suggested two wheels.

By all means, go to Gadgetbuilder.com on the net. There is sound reading and advice.

Norman