Bench Grinder basic rest improvment

I have one of those chinese 6" bench grinder - had it for maybe 30 years now. I purchased some new Aluminium Oxide wheels for it, and that started a whole saga!

These wheels, 150mm diameter and one is 25mm the other 20mm thick, are supplied by a major tooling retailer, TorkCraft.

When I fitted the wheels they were hugely out of balance, not only concentricity, but side to side as well. So the pain started. First I tried to get them running true side to side. This proved impossible. The dished 2.5mm thick metal 'washers' or hubs that grip the wheels are themselves not true. In addition the grinder shaft is 12.6mm, but the shoulder against which said hubs press, is only 1.4mm larger than the shaft within the wheel, ie, that part of the shaft is 14mm OD. That leaves very little shoulder for the hub to butt up against. On top of it, the wheel has 32mm holes and they supply crappy plastic bushes to fit - the bush OD is around 31.5mm and ID is 12.9mm

All in all a mess! So, first I made new hubs with integral wheel bushings, that fitted the grinder shaft very snugly, and fitted the 32mm hole in the wheel with just a little finger pressure. This would keep the wheel square on the bushes and flat against the hub face.

Fitted it all to the grinder, and almost no change! The grinder vibrated the whole table it stood on - It felt really unsafe!

I then used a fixed edge tool up against each wheel face and side, while turning the wheel by hand to see the runout. The Hubs show around 0.1mm side runout, at the hub perophery. ( hubs are 65mm diameter).

The left wheel shows 1.2mm runout at the periphery, the right 1.4mm....BUT the runout is not that of a flat disc - choosing a high point and rotating 1/4 turn brings the reading down to 0.7mm, then 1/8 turn more it goes up to 1.1mm, then a little more it goes to 0.3mm etc... The wheels sides are wavy! Then I measured the wheel thickness, and the 25mm wheel varies by 0.9mm, the 20mm wheel by 0.7mm. If I could get good quality, reputable wheels I would just ditch these and buy again! But here in Namibia, difficult..

So I decided to try dress these wheels true...

Of course we all know the crappy pressed sheet metal rests these grinder come with - well, I lived with those for the grinders 30 year life..I took one wheel off - impossible to try true the wheel with both vibrating the grinder apart!

The vibration was still so bad, that when I tried to hold the diamond dresser still against the 'rest' trying to just touch the wheel and keep it steady, it was impossible. The rest was vibrating to its own tune, and the wheel was being dressed to some strange standing wave shape!

So....Next, make new rests, and a stand, and get it all steady....

Which I did, new swivel stand, new rests made from 5mm flat plate, angle, some 30mm and 25mm shafting, bolted the whole thing to the wall, and finally manage to dress the wheels to flat and true!

You purchase a 'cheap' off-hand bench grinder to do simple tasks with - sharpen a chisel, drill bit, center punch, and when you fit new wheels, all the worlds shoddy quality conspires to screw you!

Some photos..

The lousy pressed 1.2mm factory rests...

New parts for the left and rights rests

Base is a 140mmx50mmx10mm channel iron.Picture show adjustable left rest in place. Rest base plate has a 6mm slot in it - Will make some guide for simply face grinding of lathe tools maybe..

And there it is , bolted to the wall!

The rests can tilt to any angle, and be raised or lowered.

3 days of work, just because I bought new wheels..

Joe

Edited By Joseph Noci 1 on 05/10/2017 20:51:47

Really good job must do similar to my cheap rests.

David

A good job.

The plans for the acute sharpening system by Eccentric Engineering look as though they would be ideal to make a super platform for any bench grinder. It is on my list when I round to it....

That has inspired me to make new rests for my bench grinder one day ......

Nice job. Well done!

Well done Joseph,

you had more trouble with your grinding wheels than I had with mine. I too had to modify/improve the rests on my bench grinder.

Thor

I'm afraid what you've done is convinced me that it'll be easier to spend 20 or 30 quid on a new cheap bench grinder when my current 20-odd year old cheapie starts to get unusable. Not long now, I think.

Mick, That is kind of the way I felt when this started - except in most cases a 'new' grinder comes with wheels that are not suited to HSS and the likes, so changing wheels will just feed the can of worms again - and the new grinder will come with the same crappy rests..

I'll bet that many 6" bench grinders on these forums just sit straight on the bench, not bolted down? How many of you still chase after the grinder while it walks around the bench top, vibrating its wheels and shaking its hips, or rests..

The idea behind my fix was not to create a George Thomas tool and cutter grinding rest - just to have sturdy, static, adjustable rests..

I should have fixed this long ago!

By the way, in the pictures I posted you can see the Halogen Lamp I added..Well that was a flop! The arm is fixed to the Grinder base, since I can rotate the base around the grinder vertical axis, for easier access to the wheels when needed. Attached to the base, so that it follows the grinder rotation. But..the Halogen globe is so sensitive to the slightest cyclic vibration, and at some frequencies, the filament mechanically resonates and dances a jig in the globe! Presto, an irritating strobe on the job! Touching the grinder reveals no detectable vibration, but its enough to upset the filament.

The lamp is now fixed to the wall..

Joe

Edited By Joseph Noci 1 on 06/10/2017 09:34:56

That's been on my "to do" list for about 30 years!

Russell

I'll bet that many 6" bench grinders on these forums just sit straight on the bench, not bolted down?

I bolt on a peice of wood, with batten attached, so it can be secured in the jaws of the vise or workmate. Has worked for me this last 40 years or so.

There is a useful HSE guide "Safety in the use of abrasive wheels" which says "Bench grinders should be securely anchored to a stout bench".

Congratulations to you for making those pigs ears behave!

I bought a cheap bench grinder a few years ago. First thing I did was bolt it down otherwise I would be chasing it around the workshop! That done it would then shake whatever was on the bench onto the floor! The principle cause of vibration was the wheels, out of true both radially and axially. I had two old lathe top slides of fixed together and clamped to the bench, with a diamond I was then able to true the wheels. Not perfect but usable. I used this awful quality grinder with an equally awful drill grinding attachment as my main means of drill sharpening for many years with much better results than the awfulness of the equipment might suggest.

One suggestion I would make regarding the nice looking work rests, make something that will stop the rests digging/tipping into the wheels should the fastenings loosen, (assuming it has not been done). I have witnessed two bad workshop accidents in my employment, one was as described on a large offhand grinder.

John