HELP - Lapping a Surface Plate

Hi Guys,

I think I'm in trouble. I am trying to lap a granite surface plate
and I think I've managed to get some diamond lapping compound worked
into the granite surface plate.

I don't know how to get the diamond lapping dust out of the surface plate.

Are there any ideas out there on what I can do?

Regards,

Paul

toolnuts said:

Hi Guys,

I think I'm in trouble. I am trying to lap a granite surface plate
and I think I've managed to get some diamond lapping compound worked
into the granite surface plate.

I don't know how to get the diamond lapping dust out of the surface plate.

Are there any ideas out there on what I can do?

Regards,

Paul

Click to expand...

Don't worry about it. It's full of quartz anyway. Otherwise, vacuum cleaner.

AlexO said:

Don't worry about it. It's full of quartz anyway. Otherwise, vacuum cleaner.

Click to expand...

The problem is that the surface plate laps everything you put on it - things like Jo blocks - not good.

toolnuts said:

Hi Guys,

I think I'm in trouble. I am trying to lap a granite surface plate
and I think I've managed to get some diamond lapping compound worked
into the granite surface plate.

I don't know how to get the diamond lapping dust out of the surface plate.

Are there any ideas out there on what I can do?

Regards,

Paul

Click to expand...

What have you done to try to clean it?

This thread does bring again the question of how are granite plates finished to such close tolerances. Perhaps garnet compound makes more sense since it is said that garnet breaks down to finer and finer sizes until it is no longer capable of cutting, but I don't know.

I was also told that diamond compound breaks down likewise though, perhaps an abrasives salesman can answer this?

you may be in trouble. In general, I'm not sure where people get their ideas on lapping; its not throwing a bunch of abrasive between moving parts......its properly charging a lap and then using it as a cutting tool. The surface of the granite has little pockets and crevices and pores.....not sure how you'd get the abrasive out out of them. like after blueing a plate for scraping, you can rub a solvent until the cows come home but it will still have a bluish tinge from whats hiding in the crevices

What type of "granite" plate are you using. am guessing something with prominent crystals and veining that has trapped diamond grit more than embedded it. Granite is so hard that it seems unlikely to actually have it embed.

If you cannot get an authoritative answer from a plate maker or resurfacer, I have a couple of possible untried and unproven ideas. I am assuming you already tried air blast and vacuum.

So, I am thinking application of duct tape (solves all problems, right?) might be a first trial. It might help grab and dislodge particles trappped in the granite veining.
If that does not work, then some rubbery stripable material like the two-part rubber (Smooth-On is one brand) materials. Apply a thick coat, let it set up, strip off. Hopefuly the grit comes off with it.

Denis

Granite is not ductile like iron or steel. Pardon the expression, but it is hard as granite. I seriously doubt that any of the diamond abrasive is embedded in it. A good cleaning with soap and water or alcohol should remove all the diamond abrasive from the granite plate. Heck, just hosing it down with the garden hose would remove all of it. More likely you have just left a rough surface on the granite and that is what is lapping your Jo blocks and other tools.

What grades of diamond did you lap it with? You should have started with a somewhat coarse grade, perhaps around 220 grit, depending on how much you needed to remove, AND THEN proceeded with progressively finer grades of diamond until it has an almost polished, mirror surface. If you stopped with a coarse grade of diamond, like 50 or 80 or 100 grit, then you created a piece of granite sand paper. Or a granite file.

Each successive grade of diamond should be used with a NEW lap. The diamond will embed itself in the laps as they are usually made with ductile material.

The diamond is not going to imbed in the granite surface like it does in copper, brass, and other metals. A good soap and water cleaning as suggested will probably remove most of the grit. I suggest following that cleaning with a pressure washer. The high pressure jet should help blast out the grit in the pores of the stone.

Hi Guys,

I think some diamond powder got loose and got stuck in the pores of the
granite.

I am using 20 to 40 (micron?) sized diamond. When I first started, I used 325 grit,
but I ran out of it. I roll the diamond powder onto the granite lap with a steel roller,
and then brush off any excess, and then wipe it again before lapping.

I have used alcohol and water, and then went to vacuum. The vacuum did the best job
but still not perfect. I will try the duct tape next.

Thanks for all the good suggestions, it's much appreciated.

For those of you thinking about lapping your surface plate - it's harder
than it looks. I have been almost there several times, only to go off
into the weeds. I am trying for .00005" flatness and .00005" repeatability.

Thanks again,

Paul

Jim Williams said:

The diamond is not going to imbed in the granite surface like it does in copper, brass, and other metals. A good soap and water cleaning as suggested will probably remove most of the grit. I suggest following that cleaning with a pressure washer. The high pressure jet should help blast out the grit in the pores of the stone.

Click to expand...

As opposed to a pressure washer maybe a small carpet shampoo machine or use both - put the appropriate detergent in it - it might vacuum the abrasive particles as they are washed out of the granite surface.

Here is an idea completely out of the blue: high viscosity oil, preferably plant based. Camellia oil is very light and if applied to a surface plate might bring out stubbnorn abrasive particles to be wiped up with a cloth then washed with soap and water. Would the oil "lubricate" stuck particles of abrasive and allow them to be removed? [EDIT: oil should not be used on a surface plate]. I used it today to free up stuck blades on a Starret collapsible thread gauge, after I soaked it in straight Simple Green and rinsed.

Give it a good going over with Steel Wool. I use it a lot,the soft (relatively)steel fibres are very searching and will pluck any abrasive grains out. Alternatively,you cd use mild Scotchbrite with a granite surface!?

toolnuts said:

The problem is that the surface plate laps everything you put on it - things like Jo blocks - not good.

Click to expand...

True. But it does that anyway. Couple of dia particles/sqinch won't make a diff.

toolnuts said:

Hi Guys,

I think some diamond powder got loose and got stuck in the pores of the
granite.

I am using 20 to 40 (micron?) sized diamond. When I first started, I used 325 grit,
but I ran out of it. I roll the diamond powder onto the granite lap with a steel roller,
and then brush off any excess, and then wipe it again before lapping.

I have used alcohol and water, and then went to vacuum. The vacuum did the best job
but still not perfect. I will try the duct tape next.

Thanks for all the good suggestions, it's much appreciated.

For those of you thinking about lapping your surface plate - it's harder
than it looks. I have been almost there several times, only to go off
into the weeds. I am trying for .00005" flatness and .00005" repeatability.

Thanks again,

Paul

Click to expand...

This is not how it's done if you want to ever finish. Sprinkle diamond powder on the plate and rub it with the lap. I wouldn't use anything over 120 grit. It'll take forever.

I've never lapped a surface plate, but for everything I do at work, 30 micron diamond is the coarsest we use, and usually too coarse for most things. I'd think you need to polish with something finer. A clue- watchmakers will take a sapphire bar and make a pass in one direction over it with coarse diamond compound, making cross-wise scratches. That creates a pivot polishing tool, much like a very fine file. Probably not the finish you want on your surface plate.

I work with a lot of granite so have some experience. DO NOT use oil or duct tape!!!!!!! The oil will stain and the duct tape goo can be a real pain in the ass, but it does come off with laquer thinner, which is a pretty general purpose stone cleaner. I would suggest soapy water with a good scrubbing with abrasives and rinse, perhaps with a pressure washer, I do like that idea.

20-40 micron is around a 650 mesh, which if used correctly results in a pretty coarse finish. Try going down to at least a 10-20 micron to get a finish closer to what comes new.

DavidScott said:

20-40 micron is around a 650 mesh, which if used correctly results in a pretty coarse finish. Try going down to at least a 10-20 micron to get a finish closer to what comes new.

Click to expand...

Which mesh is that ?

DavidScott said:

I work with a lot of granite so have some experience. DO NOT use oil or duct tape!!!!!!! The oil will stain and the duct tape goo can be a real pain in the ass, but it does come off with laquer thinner, which is a pretty general purpose stone cleaner.
<SNIP>

Click to expand...

Hmmmm, the duct tape problem might be brand dependent. I have some pretty good Made In USA duct tape that I tried on my surface plate and could neither see nor feel any residual. I have come in contact with crappy generic duct tape that probably would leave residual adhesive on a plate like it does everything else. I dont buy that crap.

Oils and staining. Well, maybe, but, Dykem Hi-Spot Blue is a prussian blue suspended in oil.... On the other hand, I suppose a lot of plates never see spotting ink.

In some ways the OP's problem and solution is analogous to the precision ground stone concept recently discussed here.

http://www.practicalmachinist.com/v...s-posted-new-video-precision-deburing-337778/

If the coarse trapped diamond particles cannot be removed by the methods suggested above, then as was suggested, trimming off the offending peaks of the particles much like what Robin did with finer grit diamond will solve the hone-like behavior of the stone.

Denis

How do you know the diamond is a problem ?

What about plastic wire brushes on suitable rotary impeller with soap/water wash ?
Just an idea. (18V lion battery drivers).

I mean, you were using a lap with perhaps 100x or more local pressure to adjust some small area of the plate, by sub micron amounts at a time.
Slowly getting towards the 1 micron goal via successive approximation and mechanical wear.

Thus,
it seems to me,
that any large-area bristle/brush/wipe etc would have a much smaller effect, by about 100x less, probably less since there is no rigid pressure into the stone as such.
I do think that if the plastic wire brushes do work, they could mar/wear the surface by a minute amount near the grit.

It would have to be minute, otherwise they would be the lapping tools of choice, no ?

I am referring to something like a pristine industrial perfect-demo ultra grind of perfect mirror steel surface...
(saw one at emo in germany, behind glass, maybe 10 metric tons machine),
that would likely show a surface finish difference after the plastic brush+diamond cleanup.
But of likely much less than 1 micron error.
(But perhaps not. Things are tricky with diamond and all good=strong abrasives.)

A high-pressure water jet 200 bar+ is quite abrasive/strong and will eat metal surfaces.
No idea why - technically - but it sure will.
(Cavitation - bubbles ? vacuum ?).

I think it would also eat granite, at maybe ? some fairly rapid rate.
Canyons in rock aka granite were carved by rivers going slow.
A high pressure waterjet is vastly more aggressive.

Any info/experience from someone re: granite to surface-plate resolutions == 1 micron level, please share.

I was just pointing out ideas that come to mind.
A pressure washer + diamond dust ==> industrial waterjet cutter of very low efficiency and power.
But it *will* cut and abrade to some extent, so..
judicial testing is in order.

I think garden-hose or low-pressure washer setting would be fine.

Other ideas - maybe useless.
Would other materials embed into the diamond.
Ferrobend, lead, tin ?
Epoxies ?
A backer strip could be used in strips, to maybe-perhaps lift off the diamond particles.

This thread is asking for a solution to a problem that does not exist.

Lapping counts on refreshing the abrasive, just as grinding does. Free Abrasive lapping as applied to ceramics doesn't even want the medium to fall out of suspension.

Refresh your understanding of how abrasion removes material. Once the peaks have been worn off the diamond, there is a flat facet remaining that is parallel to the surface. It is only a hard spot at that point.

If you want to "hurry" the dulling process along, rub over the entire plate surface with some random chunk off flat ground steel O1 would be fine. Everyone knows that steel "pulls" diamonds right out of the matrix.

Life is not always as complicated as we make it out to be.

If you want to see something abrasive, rub your jo blocks on a piece of common copy paper. Inspection with magnification will surprise you.