Lapping compound option

I am building a "Coffee Cup Stirling" to Jan Ridders design. Needed to lap the work barrel. Could not find the tin of "fine" lapping compound that I know I have somewhere! In the kitchen I found a tin of "Astonish" a bit dried out. Scraped out half a teaspoonful and mixed with water to a very wet paste. Spread some on a hardwood dowel I had turned to match the bore. Absolutely perfect. Ran lathe in slow and stroked the bore back and forth and ended with an extremely fine finished bore in very little time.

I believe that the water tended to swell the wood slightly giving a nice firm fit that I have not noticed before when using oil based compounds.

JFI Base compound to "Astonish" is "Fine ground white silica flour".

As an aside I have coated the work piston with "Loctite Hysol epoxy putty" mixed with Fine Foliac Graphite flakes, to see if I can make a low friction piston. Now hardened off and I need to machine to fit the bore. No idea if it will work but worth the experiment IMHO


Reply to
Richard Edwards
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Made a similar discovery some years ago*) when I wanted to lapp a brass tube inside. Also with hardwood (I had some oak at hand), but I used an oil-based compound (for valve grinding-in). But you still can put some water onto the dowel to make it swell a bit.

Yes, that works perfect!

*) I think I wrote it here or in RCM.


Reply to
Nick Mueller


Hi Richard. When I retired from the motor cycle business a decade or so ago, there was a water based valve grinding paste. It was much cleaner to use than the mucky oil base stuff. It used to come in an orange tube, I wonder if it is still available? Ned Ludd

Reply to
ned ludd

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