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

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.

On 31 October 2024 at 23:01 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 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.

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

On 31 October 2024 at 20:42 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

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

Regards  Ian.