Cheap and effective lapping compound

[Mick BaileyParticipant @mickbailey28509]

I was in need of some different grades of lapping compound and thought I’d try burning some wet and dry paper and mixing it with grease. 1 sheet makes a useful  quantity and the resulting product is superb. I just tore it into strips and burned it in a stainless pot. The first sheet was done in the workshop, which was a mistake. I hadn’t accounted for the resin in the paper and the stink. The main thing to watch for is that the paper burns completely – I used a small propane torch which worked well.

Perhaps this is common practice, but it’s new to me and maybe there are others who weren’t aware of this.

[DC31kParticipant @dc31k]

Are you aware that silicone carbide grit is available to buy in small quantities?

https://www.ebay.co.uk/itm/182746658717

[BazParticipant @baz89810]

There is also valve lapping paste available in fine and coarse grades from car accessories shops.

[SillyOldDufferModerator @sillyoldduffer]

New paper only I presume?  Grit extracted from used paper will be contaminated with metal, making it necessary to chemically clean re-cycled grit.  Burning is another potential source of contamination.

Just a guess contamination might be an issue;  I see lapping as a high-polish process, where the last thing I’d want to risk  is scratches due to dirty grit.

Be interesting to compare laps done with new grit and those with Mick’s stuff.  Needs a microscope.

Dave

[Andrew TinsleyParticipant @andrewtinsley63637]

I have done the same thing when I ran short of lapping material . Despite SOD’s pessimism. I found it to be very effective.

Andrew.

[Mick BaileyParticipant @mickbailey28509]

I’m fully aware you can buy silicon carbide grit in small quantities. Not within 10 minutes of needing some, though. New paper of course – there would be little point in using anything else.

Valve lapping paste (even fine) is often too coarse and I already have that for engine rebuilds.

All I can say that burning wet and dry it worked perfectly for me. Sure, it’s contaminated with ash, but I tried it up to 1200 grit and it gives the result I’d expect. I have a couple of microscopes but don’t have commercial grit to compare.

[Mick Bailey]

On Mick Bailey Said:

Not within 10 minutes of needing some, though

I have never had an emergency need to lap anything with only ten minutes notice. Maybe you could describe how that immediate need arose so others could plan against it.

[derek hall 1Participant @derekhall1]

Look for Timesaver lapping compound. Different grades and two types, one for ferrous and another for non ferrous.

I always use Timesaver rather than the very abrasive lapping paste that needs lots of cleaning after use.

Timesaver did a great job on the critical areas of my Quorn grinder!

[FulmenParticipant @fulmen]

I think it’s a brilliant hack, thank you so much for sharing.

 

And DC31k, what’s your problem? You know you don’t have to do it if you don’t want to? We KNOW everything is available from ebay, but that takes DAYS. And we might not need 100g of each grade, just a little bit to lap two small parts together one time.

[Charles LamontParticipant @charleslamont71117]

Quite. Some folk round here seem to start from the presumption that everyone else is an idot.

[FulmenParticipant @fulmen]

Well they are, I’m just too polite to say it  🙂

[DC31k]

On DC31k Said:

On Mick Bailey Said:

Not within 10 minutes of needing some, though

I have never had an emergency need to lap anything with only ten minutes notice. Maybe you could describe how that immediate need arose so others could plan against it.

I thought this forum was more mature than this and wasn’t expecting such a facetious reply to an innocent tip intended in good faith.

The bearings in the pump motor on my oil boiler had seized and spun on the armature shaft. I ordered new bearings and took the burner assembly off but the oil hose was dripping slightly as the main shutoff valve wasn’t sealing completely. I pressed the new bearings into the end castings and found the drive side shaft to be ever so slightly loose on the shaft – just an easy slide fit, so used Loctite 638 to be sure it didn’t move. When I came to push on the rear casting it went on so far then stuck really tight about 10mm short of seating. The Loctite had grabbed the front bearing and I didn’t want to disturb it so used a split external copper lap to get the opposite shaft parallel to get a precise fit for the bearing.

The urgency was down to me thinking originally that this would be a quick and simple bearing replacement that I could perform while the bundle of rags was soaking up oil. My options were limited in order to quickly restore heating and hot water. The motor unit is no longer available new and used motors are suspect. The leaking shutoff valve is another matter and a much more involved job.

The DIY lapping paste left such a good and accurate finish that I made up some different grades and put them in jars for future use.

 

[Andrew Tinsley]

On Andrew Tinsley Said:

I have done the same thing when I ran short of lapping material . Despite SOD’s pessimism. I found it to be very effective.

Andrew.

I’m sure recycled grit will still work!  But is it suitable for quality work?

Andrew says he found the mix to be ‘very effective’, but his reassurance doesn’t help because the context isn’t explained, no figures and no microphotographs.   I’m almost prepared to bet the farm that Andrew judged the effectiveness of his laps by eyeballing them when an x150 microscope is needed.

The problem may be sloppy terminology.  What do we mean by lapping?  Is it:

1. A final polishing process, not accurately applied, perhaps intended to take the worst imperfections out of the cylinder bore of a model steam engine.  No specification needed, and it’s “good enough” when the builder is happy.  Minor defects don’t matter.  OR
2. An accurately applied polishing process, done to a specification, and measured by a well-equipped inspector.    In optical systems, minor defects matter because tiny imperfections in a lens spoil the image.  Likewise, the cylinder of an manufactured IC engine is precision lapped (actually super-finished), because a quality finish improves the efficiency and reliability of the engine.

My guess is Andrew means lapping in the first sense, where top quality results aren’t needed.  I suggest Andrew means that recycled grit is ‘fit for purpose’ and ‘value for money’ in his workshop, rather than recycled grit being universally ‘very effective’.

My warning is aimed at anyone using lapping to get a quality surface finish.   Using recycled grit introduces the risk of scratching due to contamination.  Therefore, if quality matters, the risk of spoiling the surface is avoided by using clean grit.  Simple enough isn’t it?  However, if best results aren’t needed, no harm in recycling grit!

I recommend lappers have a quick think about the job in hand, and then decide what to do.   Here’s another pair of risks:

1. SillyOldDuffer may have no idea what he’s talking about, but his recommendation to use clean grit is fail-safe.
2. Andrew has positive experience of recycling grit, but provides no details.  His experience may not match your requirement, and, how he recovered the grit is unknown.  This route is fail-danger.

Of these two assessments, mine is less risky!  Anyone disagree, and why?

Dave

 

[Andrew TinsleyParticipant @andrewtinsley63637]

SOD, I obtained the grit in exactly the same way as the OP described. I have had a fair amount of experience  lapping piston / liners  for replacements in model diesel engines.  As you probably know this is quite critical for both performance and longevity. I used a microscope to check the results for my emergency lapping and the results were every bit as good as commercial lapping compounds. I use a full spec Delapena lapping machine, or should I say honing machine, rather than the split  type laps favoured by model engineers

What is your practical experience of lapping, it sounds as if you have a fair bit of experience from your posts?

Andrew.

[CirclipParticipant @circlip]

And don’t forget the ultimate fine lapping compound – – – – TOOTHPASTE.

Regards  Ian.

[BazyleParticipant @bazyle]

If people want to get anal about it have a look at what the amateur telescope makers do. Mix the finest compound you can find with lots of water, place in jar. After a period the particles stratify as the heavy particles sink at different rates. Syphon off the mixture from different levels to get different grits. Polish your subject aiming for both accuracy and scratches to be better than a wavelength of light.

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