Tool & Cutter grinder options...

Acrylic is worse than nothing. I made some acrylic guards and they crack if you look at them in a funny way.

Does anyone know a source of polycarbonate in offcut sizes suitable for making guards? A whole sheet costs an arm and a leg.

Neil

Thinks

Does it really need to be 6mm thick? ... or would a "Double Glazed" version [i.e. two thin sheets, with an air-gap, in a frame] be as good? or maybe even better?

Thin Polycarbonate sheet is very readily available.

MichaelG.

Depends what you're guarding against? An 8" grindstone bursting is not funny. However, with an aluminium/diamond cup wheel there isn't much chance of large pieces of shrapnel flying about, so a fairly thin plate of some sort is all that is needed (IMHO).

.oOo.

Rounding off the end of the plate:

The recess the flange fits into

Looks a bit better now with the bolts sunk into counterbores

Hi Neil I have been getting polycarbonate from **LINK** he was at Harrogate ME show and goes to various autojumbles.

Let him know what you want and he might be able help.

Paul

Edited By Windy on 22/05/2013 13:50:00

The shield/cover for the 4" cup wheel I propose to fit I will make from some brass tube I've had lying around for maybe 40 years... I think it was an old shell casing from WW1 (!) but it had the end cut off and was last used as a poker stand by my grandfather. I cut about 4" off using the bandsaw (actually, I said it was made of brass but I think it's a new alloy - called Brass Carbide, this stuff is HARD).

Chips come off as tiny bits leaving a very nice finish when using a tipped tool.

And this is how it will look, the I.D. is about 4.75" so enough clearnance for the wheel. I'll cut a notch the same width/depth as the rear plate then have one thumbscrew holding it in place. Note I screwed the base back on to the motor so I could muck about with the electrics - it's not a permanent solution.

I would echo what has been said about acylic, it isn't suitable for guards, it can shatter. Polycarbonate is widely available, I have bought it from **LINK**

Chris

Hi Chris H, I admire you ingenuity and don't want to rain on your parade but what is going to stop the grinding dust going into the internals of your milling machine and also the slides? I have a Stent T & C and the dust goes everywhere!

Tony

It's a fair point - there will be a vacuum pipe attached to that brass shield and I will protect the rest of the machine as best I can with plastic sheets when in use. I'm not using grit wheels which would shed copious abrasive grit everywhere (using a diamond cup wheel instead) and I would hate to use a dressing stone on a grit wheel near my machines - did that once on my bench grinder, never again! If I need to dress the grinding wheel I take the whole thing outside. Not a perfect solution I know but in a garage-sized workshop if you do ANY grinding in there with ordinary grit wheels then debris will find its way onto your machines. Regular cleaning and maintenance is the rule.

Far more engineering went into making the cover than warrented - or expected, and it's still not quite finished. Still, we do this for enjoyment, right?

By way of good fortune I had some alloy tube that had exactly the correct dimensions (inside and outside) to allow me to make the cover a quick-release mounting. All I needed to do was cut a slice off, press it in place with a smear of 638, then mill out a section so it fits the back plate.

Thus:

It would have been quick and simple had that 'brass' tube not been such an absolute pain to machine. It would grab the cutter at the least provocation.

Anyway, the cover fits with a couple of thumbscrews and can be removed from the front in seconds.

Edited By Chris Heapy on 23/05/2013 09:10:39

Edited By Chris Heapy on 23/05/2013 09:20:40

The diamond cup wheel turned up this morning so I was able to finish this job and try it out. Are these diamond wheels - the aluminium mounting part - supposed to be finish-turned by the user? I first noted the bore was not even circular so I chuck it up in the lathe (by the inside using external jaws) only to find hardly anything was concentric - the rear face, the external surface, as well as the bore. Anyway, I sorted all that out and made a couple of flanges and it now runs as it is supposed to do.

I made a small T-slot table to mount the tool holder on:

And here's my first try at sharpening something with it (a boring tool - and the shield has been swung back for the photo):

It works as expected. Next I'll get on with working my way through a box of blunt endmills. I may be some time

Does anyone have any gen on this?

Mark P.

What do you want to know? It is a cheap Chinese copy of a design that has been around for years. Yuasa make one (better quality) but the best type of this device uses air bearings. I have not seen an example of the Chinese version, maybe if someone on here has one they can pass comment on how it performs.

I was about to start on connecting a vaccum hose up to the cover on this grinding head, then I thought - what if it sucks sparks into the cleaner? Suddenly it didn't sound like such a great idea. Whilst trying the grinder out on a carbide boring tool and also a piece of round HSS I have to admit there weren't many sparks, but there were some. Any comments?

I doubt the sparks will still be sparks once they get drawn past the mouth of the nozzle.

Whilst each glowing particle might be at quite a high temperature it does not contain much total energy so as long as the nozzle is not made of tissue paper or highly flamable plastic you should be OK.

Ian P

How about passing the vacuum extract through a cyclone to eject any sparks into a separate containerinstead of a vacuum cleaner that could contain other combustable workshop dusts?

Neil

Yes that is the worry - my 'shop cleaner ends up with all sorts of potentially inflammable rubbish inside. I don't want to walk away from it and have it slowly smouldering inside!

Neil: yes, perhaps a separate container (like a 3ltr milk carton) would work. The hose from the grinder could reach into the bottom of the carton, the outlet for the hose to the vacuum near the top.

I found another use for this grinding setup - a poor man's surface grinder

To digress: I bought an old Griptru chuck - something of a mistake because when I tested the chuck the inside jaws were completely useless. The outside jaws (and therefore the rest of the chuck) appear to be fine and hold true, but the inside jaws were so worn they weren't even gripping at the tips and you could see daylight at the ends

OK, accepting the jaws were toast (I will have to look out for a replacement set) I set about trying to figure a way of re-grinding them, and my thoughts turned to the diamond cupwheel mounted on the mill. I checked the squareness of the wheel off against the mill table and as far as I could tell it was nicely orthogonal - although it's difficult to be certain because the face of the diamond wheel is not a smooth machined surface. Nevertheless an 8" square placed against the front edge revealed no errors. Good enough for an experiment then.

I clamped the 3 jaws together and used a parallel to hold them in line, and two clamps to hold the lot down onto the mill table. The 8" square was used again to align them all with the rear edge of the table and overhanging a little.

I could only comfortably take 1/2 thou off each pass - the cup wheels are a bit fragile and I didn't want to break it. Grinding continued until the front of the jaws all looked the same, but by then I realised something wasn't right...

I expected more material to be taken off the bottom edge of the jaws than the top (in the photo above) simply because it was clear that is the way they had worn. However, with grinding complete I expected to see a nice even ground surface but what I got was a definite taper. Oops. It was as if the base (the teeth) of the jaws were not square to the front gripping surfaces. Not what I expected at all. I now realise what I should have done was mount the jaws upside-down onto the parallel because that surface definitely would be square with the inner gripping edge. So I'll have to do it all again.

I've lost nothing though because those jaws really were useless as they stood. I don't know if the jaws are hardened right through or a deep case, if the latter I may well run out of hard steel in the grinding process.

Chris

I have noticed the gripping face of the jaws of my chuck are hollow ground and I believe the method is to clamp a ring and using a small dia. stone travel through the clamped jaws.

Any other methods known? I feel that a flat surface on the gripping part of the jaws is not right.

Clive

I've tried those methods before without success - used a 1/2" diamond lap from the tailstock, and used a die grinder held in the toolpost. The problem I found is that you cannot tension the jaws in their normal gripping configuration AND grind them at the same time. The hollow-ground effect I think is just a by-product of the manufacturing process rather than a required feature. To be honest my feeling is that attempting to re-grind jaws is probably a waste of time because if you have wear in the gripping surfaces I suspect there is also wear in the side slots - which you can't compensate for. Still, it's an interesting exercise.

Chris

Edited By Chris Heapy on 06/06/2013 08:23:55

A concave surface is a by-product of the internal grinding purpose. Generally it does not cause any problems but as it can only be the correct curvature at one jaw position I see no reason not to have the gripping face flat, or even convex.

Use a dial indicator, a bright light, a suitable ground test bar, and a hand held diamond file. Inspect the grip of each jaw against the light, mark with felt tip pen, remove jaw and stone the edge to suit. As a concave gripping edge is not ideal for letting the light pass I aim for a narrow flat. Once any gross errors or bellmouthing are corrected use the dial indicator to see which jaw/s need tweaking.

I have contemplated using the standard internal toolpost grinding technique but always shy off after trying to work out how to 'tension' the jaws whilst having the whole edge to grind.

Ian P