Help ! how to remove embedded diamond lapping particles on metal surfaces

[compact8]

Today I tried diamond lapping for the first time on the hole plate I have made for my rotary table. The lap is a piece of HDPE plastic and the hole plate is hot-rolled steel. All went well and the lapped surface appears to be quite flat. No dishing or rounding off near the edge.

However, it appears that the lapped surface is now embedded with diamond particles ( 40 micron according to the vendor ). If I rub a piece of steel against the surface, very fine scratch lines will be formed and I could feel that some abrasion is happening. Some of the diamond particles seems to have transferred to the milling table as well. How should I go about to clean it up completely ? Thanks in advance.

 

[homebrewed]

I think in order to embed diamond into a metal surface you need something that is about as hard as that metal surface, so your HDPE lap didn't do it. It's sort of the equivalent of trying to use a marshmallow to push a thumbtack into a piece of wood. You probably didn't completely clean off the diamond particles, rather than embedding them. I note you've got a number of holes in your metal surface. They probably are the source of the particles that now have been transferred to your milling table. I'd try a combination of cleaning steps -- for the hole plate, a shop vac with a soft brush attachment, followed by soapy water with a brush that's got bristles long enough to get into those holes. Adding a bit of IPA to the soapy water reduces the surface tension even more than the soap alone.

For the milling table, the shop vac followed by clean shop towels, maybe finished up by using tack cloth or the sticky side of wide packing tape. If you use flood coolant on your mill, that would probably do the job.

If you have access to a large-enough ultrasonic cleaner they work well for dislodging particles in otherwise hard-to-reach places. I have wondered if one of those ultrasonic humidifiers could be used for that sort of thing but haven't tried it yet.

For doing stuff with abrasives it's best to do it someplace that's well distanced from your machines, and clean the hell out of items so treated before bringing them into your machine shop. My grinder is in a separate garage that's about 200 feet from my shop. That's overkill -- I just left the grinder where it had been, rather than moving it into the basement of the new house.....but you get the idea. I like it where it is and that's where it's going to stay.

If the particles really are embedded, I honestly don't think it would be that big a problem as far as the usability of your hole plate (or mill table) are concerned. The main issue would be transferring loose diamond particles onto surfaces that rub against each other in normal use -- like gibs in dovetails. A thorough cleaning should take care of that.

 

[compact8]

If the particles really are embedded, I honestly don't think it would be that big a problem as far as the usability of your hole plate (or mill table) are concerned. The main issue would be transferring loose diamond particles onto surfaces that rub against each other in normal use -- like gibs in dovetails. A thorough cleaning should take care of that.

Just did a thorough cleaning with soapy water but the problem persists. Rub a piece of metal on the surface, it goes sack, sack , sack..... followed by fine scratch lines appearing on the metal. Yes, diamond particles falling off onto the mill is my biggest fear. This issue is kind of unexpected. Will use sand paper from now onward. Should be much safer.

 

[ps15toolroom]

The condition you are experiencing is known as "being charged". Your part is now charged with the diamond lap medium. This situation happens more or less depending on the hardness of the lap and the work. I don't know what flatness or finish you are going for but my first suggestion is to re-lapp with less medium and or lapp it with carborundum. There is a product known as Timesaver Lapping Compound which allegedly doesn't charge your part. I've never used it.
You could try cleaning it with an ultrasonic cleaner.

 

[savarin]

If I remember correctly (from zillions of years ago) diamond has an affinity for copper.
It might be worth rubbing the surface with some copper strip thick enough not to bend.
A bit of copper pipe flattened in the vise maybe.
I have no idea if this will work but might be worth a try.

 

[compact8]

The condition you are experiencing is known as "being charged". Your part is now charged with the diamond lap medium. This situation happens more or less depending on the hardness of the lap and the work. I don't know what flatness or finish you are going for but my first suggestion is to re-lapp with less medium and or lapp it with carborundum. There is a product known as Timesaver Lapping Compound which allegedly doesn't charge your part. I've never used it.
You could try cleaning it with an ultrasonic cleaner.

I know this phenomenon of charging but my understanding has been that it only happens to soft materials such as plastic or copper only but my workpiece is made of steel. I have done more searching on line and found that this can happen to steel and the only reliable way to remove the diamond particles is using ultrasonic cleaner which I dont have . The model engine guys say that the particles can be scraped off with a sharp razor / cutter blade. I am going to try it out. In the worst case I will have to toss the parts because it is scratching everything that it contacts. The table of my mill is the first victim

 

[compact8]

If I remember correctly (from zillions of years ago) diamond has an affinity for copper.
It might be worth rubbing the surface with some copper strip thick enough not to bend.
A bit of copper pipe flattened in the vise maybe.
I have no idea if this will work but might be worth a try.

Makes sense ! I dont have copper in hand but will try using soft aluminum. Thanks.

 

[homebrewed]

The steel you rubbed over the surface of your hole plate probably embedded the diamond particles in it, not the HDPE lap. I didn't catch that before.

Hitting the plate with sandpaper (to remove the top surface) might work.

 

[compact8]

The steel you rubbed over the surface of your hole plate probably embedded the diamond particles in it, not the HDPE lap.

That is possible. I have read more about lapping and it seems that embedding is a significant problem for diamond particles of size 3 microns or less. The grit I am using is 40 microns so a lot bigger. I have tried to reproduce the problem on another piece of steel plate but failed. After lapping and cleaning, I rubbed a piece of 6061 aluminum on it and there was not a single scratch mark.

I learned further that besides diamond, there are the choices of Silicon Carbide and Aluminium Oxide powders. As these are used for making sand papers and I have never encountered embedding problem with sand papers before, will they be better choices ?

 

[MikeInOr]

Great thread! I definitely learned something!