“Zero’ing” a surface grinder wheel or blade wrt workpiece

[chale4incolo]

Ok surface grinder gurus, another real basic question here, please. So I’m doing some work where I need to “zero” the front edge (the edge that’s ‘toward me‘) of a diamond wheel (and also a thin delicate diamond dicing blade) with respect to the back edge of the workpiece (in this case the back edge of a fused silica optic that I don’t much want to touch with the wheel if I can avoid it). I.e., I want to know that the front edge of the wheel is closely coincident with the back edge of the workpiece in the Y axis, so that I can then translate the workpiece in Y by a known precise amount, etc. How do guys do this to within no more than a few thousandths of an inch? So far I’m doing it “visually”, i.e. I’m looking down the X axis with the edge of the wheel down close to touching the workpiece, and tweaking the table in Y until the wheel front edge looks very close to the back edge of the piece. It seems I can do this consistently to within about 0.005”, not bad (my myopia helps!), but what if I needed to do it to within a thou? What’s the equivalent of like an “edge finder” on a mill, for a surface grinder?? I’m guess I’m really not sure. Thx—Charley

 

[eKretz]

Ok surface grinder gurus, another real basic question here, please. So I’m doing some work where I need to “zero” the front edge (the edge that’s ‘toward me‘) of a diamond wheel (and also a thin delicate diamond dicing blade) with respect to the back edge of the workpiece (in this case the back edge of a fused silica optic that I don’t much want to touch with the wheel if I can avoid it). I.e., I want to know that the front edge of the wheel is closely coincident with the back edge of the workpiece in the Y axis, so that I can then translate the workpiece in Y by a known precise amount, etc. How do guys do this to within no more than a few thousandths of an inch? So far I’m doing it “visually”, i.e. I’m looking down the X axis with the edge of the wheel down close to touching the workpiece, and tweaking the table in Y until the wheel front edge looks very close to the back edge of the piece. It seems I can do this consistently to within about 0.005”, not bad (my myopia helps!), but what if I needed to do it to within a thou? What’s the equivalent of like an “edge finder” on a mill, for a surface grinder?? I’m guess I’m really not sure. Thx—Charley

If I have to do it without nipping the work at all I use a paper feeler gage. Then comp the paper thickness.

 

[michiganbuck]

I don't like using XYZ on a non-CNC surface grinder. Down, Cross and Long travel are better descriptions for a manual or power feed surface grinder. IMHO..

It is tough sneaking up to the front edge of a part with a thin Diamond cut-off-wheel
A slip of paper or a tab of masking tape is a common method but time-consuming and chancy to .oo1.

I like to precision set my part in an exact location by having something set off the properly ground back rail that I can touch my part against and clamp it on that spot.. Sometimes a tab of masking tape on the face of that bump-stop if I expect heat expansion to be a problem. A 123 block, a parallel, or a utility JoBlock to bump the part. Sometimes one may remove the bump-stop and then cut-off or grind a feature to the part.

So you may have to painstakingly sneak up to the first part fo feel the part or your spot location, but then you know where your cross number is in relation to your spot location for all following parts.. , even those parts that have a different length to hIt.

The same procedure can be making an L with two 123 blocks so the bump stopping the part is off the back end of the part..very easy to get .oo1 wheel to part location off the front, or off the back end with this method.
Cutting off carbide you get a tab/nub at the bottom edge that has to be snubbed off..To avoid this one can clamp the cut-off part and the remaining part so as the wheel passes through there is no tab left on either side of the cut.
I used to cut carbide pieces at square and at angles this way to .001 and better this way.

Cutting off carbide you don't travel back and forth with long travel, you just slowly down feed through the part...and have a piece of material on the chuck to fall on so it doesn't mar the chuck.

Keep in mind that you cant travel both ways..the spot location and changes has to be in one direction or the free travel/slop on thefeed screw willmaffect the distance traveled.

 

[chale4incolo]

Thanks for the thoughts and comments on this; the 'cigarette paper' sort of approach is certainly sensible, I hadn't thought about that nice simple approach. Yesterday I got a very neat little digital microscope/camera (one of those Chinese guys you see everywhere; black case, knurled knob to adjust focus, about 5" long) that displays on one's phone, or an iPad, etc. Wireless, even, truly amazing for $30! It can focus as far away as about 60 mm, which is workable for my setup. I'm thinking this could be a very neat 'non-contact' way to zero the blade with respect to the edge of the workpiece; I've still got to sort of 'calibrate' the thing, but I think it'll provide one with very good ability to dial the 'y=zero' in real close (surely to a thou or two, looks to me like) without fiddling with paper, without contorting oneself to 'sight' down the x axis like I was doing before, etc. I'll attach a quick photo I took yesterday; the blade (vertical feature in photo) is exactly 0.020" thick, and you can see how the 'front edge' of the blade is closely coincident with the 'back edge' of the workpiece (the bright white square thing in photo).

 

[CarbideBob]

Turn wheel off.
Bring wheel down below surface off part off the back.
Slowly bring the part into the wheel while rotating the wheel by hand.
You will hear the high spot on the wheel scrape. Back off the in/out and come back in more slowly turning the wheel back and forth with this high spot.
This should get you within 5 tenths or better.
Bob

 

[Hobby Shop]

Not sure if Diamond wheels would load up or not but we always used different thickness of layout blue. Put the regular blue on then a red over that after it dried. We had some thick light blue stuff that would go on about .0015” thick.

You could peel off the colors one at a time with the DRO.

 

[eKretz]

Turn wheel off.
Bring wheel down below surface off part off the back.
Slowly bring the part into the wheel while rotating the wheel by hand.
You will hear the high spot on the wheel scrape. Back off the in/out and come back in more slowly turning the wheel back and forth with this high spot.
This should get you within 5 tenths or better.
Bob

That's how I do it with the paper - wheel not running. Just find the high spot and turn back and forth by hand.

 

[michiganbuck]

Not sure if Diamond wheels would load up or not but we always used different thickness of layout blue. Put the regular blue on then a red over that after it dried. We had some thick light blue stuff that would go on about .0015” thick.

You could peel off the colors one at a time with the DRO.

I did much the same on surface grinders and Blanchards.
I would grease pencil the part and then lay on a strip of masking tape. The mashing tape would give me a .002 (or what) warning and then getting the grease pencil to smear would get .0002 or so. Mostly for topping not what the OP is doing coming in with the wheel side.

Feeling the part with the wheel like Carbide Bob mentioned is the best.