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

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.

Edited By Y C Lui on 30/04/2022 16:59:55

You could scrape the face of the part and that would remove all of the diamond compound. Done well it would probably be flatter than your lapping exercise too.

Scraping would probably be better than this form of lapping, but it does presuppose the possesion of a surface plate.

For cleaning the diamond particles off, push a sharp razor blade* over the surface at an angle of about 30° positive rake. It'll pop the particles off fairly well. That's the way I clean laps when changing grits.

*single edge blades are pretty safe to handle. Doeble edge ones need a bit more care.

If you use diamond abrasive to lap anything soft including steel it will embed itself as you have found. The only way I know of to remove it thoroughly is to clean it in an ultrasonic cleaner as no form of solvent will remove it completely. It will transfer from soft surfaces to others.

As suggested scraping is a better method to obtain the flat surface you seek but you'll need three items to lap to each other.

Above comments on removing diamond grit is based on a fair amount of lapping piston and liners - cast iron in En1A steel.

Tug

Presumably you'ld risk distorsion but diamond burns at 900C so running a propane flame over it might work?

pgk

Thanks for all the replies. Very helpful. This is the first time I tried lapping and the purpose is not so much to get a perfectly flat surface ( unnecessary for my use ) but just to get some experience on lapping. Turns out to be a bad one unfortunately.

Other than the suggested methods, is it possible to remove the diamond particles by using sand paper ? I am afriad scraping is outside my skill envelope.

Edited By Y C Lui on 30/04/2022 21:55:19

I think you might only make things worse by using sandpaper----the scraping doesn't have to be very precise, you are trying to chisel out embedded hard particles

Regards Brian

As I said. Use a razor blade, it'll pop the particles off with little effort.

Heating will burn off some of the diamonds. However if the steel gets hot, as it will do, some of the carbon will be absorbed into the steel causing hard spots. Hot iron just loves carbon.

I cannot see a mechanical method of removing the diamonds working. These are very small particles.

It may be easier to make a new hole plate.

I feel that diamond abrasives are best avoided.

JA

At risk of repeating myself Y C you will not remove diamond abrasive from a soft surface unless by 'machining' it off completely or a thorough clean in an Ultrasonic Cleaner.

To have lapped the plate initially then reworking the surface to remove the particles defeats the very purpose of the lapping in the first place

Diamond abrasive by it's very nature is usually used for the lapping of hardened (heat treated) steel or carbide. Once embedded into softer material including unhardened steel it will transfer to other soft materials it comes into contact with - as you have found.

Possibly this may be of interest - lapping

Tug

Mark Rand, I have tried out your method of using cutter blade as well as other methods including rubbing the surface with aluminium hoping that the embedded diamond particles will be transferred to the softer metal. Now after a mix of different operations, it seems that the surface is not abrasive anymore so I dont have to make another hole plate.

Tug, thanks for the article, will read it. As diamond is so troublesome ( for me ), will it be better to use SiC powder instead? there is a kind of lapping powder branded “Timesaver.” The manufacturer claimed that the particles will breakdown during use and no embedding will occur. Just wondering if its SiC .

Edited By Y C Lui on 02/05/2022 06:16:16

Silicon Carbide abrasive is a much better product compared to diamond for lapping non hardened material. It does not break down as such but is easily removed with solvents so you do need a range of grit sizes

Time Saver is another product which is equally good and does break down as it is used. I have not used the latter due to the fact that it is expensive to buy for the small quantity required. A range of grits of SiC say 280 - 1000 is available in smaller quantities at much less cost. This is not because of a reluctance to spend on the hobby more a scale of economy for the amount desired. I have done a fair amount of lapping now - the amount of abrasive required is small by comparison to the work done

Hope that helps

Best - Tug

I agree that the Timesaver pastes are very good. I was fortunate in buying a 'trial kit' of all the four green and four yellow powders in small tins a few years ago. I am not sure if this kit is still available. You will have to spend about £100 on the set of eight small glass jars.Heritage Steam

I don't think that the use of diamond pastes on an engine or piece of machinery is wise - a few grains left will cause so much damage when it starts to run. Similarly perhaps with silicon carbide if you cannot do that good washing job.

Timesaver degrades quickly during the lapping process, you can feel it breaking down after ten or twenty turns. It works nicely freeing up tight gear teeth or a small acme screw in a nut you have just made. I have also used it on very small taper stopcocks.

Norm

Edited By norm norton on 04/05/2022 09:44:03

For anyone interested here is the same thread on The-Hobby-Machinist

regards

If worried about embedding of diamond, the best method would be to use a different media to lap these parts together. I would suggest using a conventional lapping abrasive like silicon carbide or aluminium oxide which doesn’t embed or impregnate and instead uses a rolling action to remove material. This will also pluck out and remove the diamond that has already embedded previously. This would be the way to go.

£100 for eight small jars of lapping powder is wayyyyyy too expensive. After some further research on line, I found that Timesaver is actually garnet which can be bought at a ridiculously low price. I have also read that SiC also embeds into steel although I have never come across such problem when using SiC sandpaper.

Now I have decided that garnet is the safest and cheapest way to go. Have just ordered a couple of grey cast iron disc for making the laps and some garnet powder ( 280# , W40 grits ) . Will start working on it next week.

Any lapping compound will embed itself - that's how it works! It's the ability to remove it that is the issue.

SIC is easily removed using a solvent cleaning process - I use cellulose thinner in three stages - three jars - the first cleaning stage in first jar etc.

Having only used it on the eighteen diesel engines made so far plus several rebores of commercial engines and of course the liners for the Bentley I think I can safely say it is effective.

By it's very nature a diesel piston and liner is lapped to extremely fine limits of fit - any trace of the compound will soon ruin that fit once run.

If you still need reassurance YC try reading some of the engine builds on MEM - here for example (scroll down the page for lapping the liners)

I was involved many years go in using cast iron lapping plate to lap in optical slits for spectrometers,the plates used abrasive powders (not diamond) ,the laps ,set of 3 were prepared by lapping them in the Whitworth sequence, Every work bench also had 12 inch circular cast iron surface plates,the company owner said they too had been made by lapping in sets of three,of course the lapping particles had to be "killed" so they would not act as laps,to carry this out the surface was rubbed with a good flat india oilstone,so the hard lapping compound particles were flattened so they no longer acted as laps,the compound was not removed,in those days castings were easily obtained and it was a good method of producing a very flat low cost surface plate,for everyday use.

May I know how it is done ? I believe the solvent does not dissolve the SiC particles.

The solvent does not dissolve the particles but it removes them by a cleaning process. Unlike diamond SiC is mixed with an oil and the cleaning removes this and the SiC - as said if it doesn't on a piston and liner then the fit is rapidly lost. None of the engines I have made/renovated have exhibited any sign of this so based on personal experience I can only say that it works. Three separate cleans in small containers/jars of thinner will remove all traces of compound and oil.

Jar one - the initial clean to remove the worst - the component wiped clean after removing

Jar two - a repeat will soon show there is still a residue as this comes off. The clean is repeated.

Jar three - there should be no or extremely little residue from this clean - if there is then a fourth can be done but experience has found this is unlikely

Anyone who has made a diesel (compression ignition) model engine will no doubt agree - the fit required of the piston to liner has to be of extremely tight tolerances which would quickly be lost if any residue of compound were left.

The requirement to remove diamond particles by using an ultra sonic cleaner on the other hand comes from another but very well respected source - George Aldrich - an extremely knowledgeable model engine 'guru' whose wisdom I hold in high regard.

Hope that helps some

Tug