Lapping (and honing) - some techniques for discussion

[Maryak]

On the ships I worked we always had several grades of Clover Brand lapping paste. The usual jobs ranged from lapping globe valves made of steel or brass to flat lapping air compressor valves on a flat plate.
Dan

Yep, good old Clover but you forgot Brasso and Bon Ami/Vim and toothpaste

Best Regards
Bob

[ScroungerLee]

Also Soft Scrub cleaner which is a very fine abrasive.  I wonder if it breaks down?

Lee

[Laurentic]

Yes, I know it's four years down the line from the last post, but I just wanted to thank Ramon for describing in detail his lapping/honing device. 

I have just made one, to suit a cylinder of 0.7875" bore, and it worked a treat, I could not believe how well it performed, went from a finish that compared with a ploughed field to a nicely hatched and very smooth cylinder bore - delighted, using just 'coarse' and 'fine' grinding paste (as used by motor mechanics everywhere) and finished with cutting oil and then finally 'Brasso'.  Cannot (at the moment) see any reason to try anything else.........

Chris
 

[carrdo]

Regarding making a split aluminum lap with a tapered bore and held on a tapered mandrel as briefly described and pictured in building the Westbury Atom Minor Mk III by Jan Huning (modelenginenews.org). I am building a very similar Westbury engine to the Atom, the 2 stroke Kestrel which has a one piece "Meehanite" cast iron cylinder with a finished inside bore of 18 mm (why Westbury would specify a metric size bore when everything else on the engine is Imperial...)

Since I could not get in touch with the author, I am going to ask it here. Could someone please expand on this. What is the ideal included angle of the tapered mandrel and the matching lap piece with the tapered bore? No one seems to have discussed this aspect when making a lapping tool and it is very important. My research, such as it is, seems to suggest a very shallow included angle of only 1-2 degrees because this will give very fine dimensional expansion of the lap as the lap is tightened on the tapered mandrel. However, I have also been told it comes with problems if one wants to remove the lap from the mandrel as, one most likely needs to make a special removal fixture to separate the two parts as they will likely be "locked" together (not a problem in my case as I have the necessary pressing equipment).

Also on the lap itself, I would have three 1/32" wide slits spaced 120 degrees apart equally, one of the slits passing through into the slightly tapered bore and the other two not quite leaving a bridge of metal only 1/32" thick. This makes the lap piece both flexible and rigid. This appears to be what is on the Atom Minor lap from what I can see from the photo in the article but no dimensions are given.

I have seen other tapered lap designs (albeit on much larger laps) where there are up to 8 internal and external slits (every 45 degrees apart) running from each end of the lap piece each terminating in a drilled hole much like that found on an expanding arbor or on some collets. But for small bores, such as found on the Kestrel or Atom Minor, I think the three slot lap is easier to produce in a home shop environment.

Comments please.

[Admiral_dk]

Have you read the whole thread ..??
As far as I can tell - Ramon did describe this in Reply #63 ....
Unless I misunderstood your question ....

There are many ways to skin this proverbial Feline. Ramon has tried a number of them and has been good to tell us about the one that has served him best - and this one is very educational
He has build a good number of Amazing Engines (and more), and I have had the privelige to visit and hold / touch a good number of them 
Though at this point in time he had sold most of the ones he had been flying earlier in life (together with the Models they where mounted in).

All that said - we all have differen't preferences etc. - so your mileage might differ 

Best wishes

Per

[Boo]

Just to ask where in the UK can you get a set of different grades of silicon carbide powders in grits up to 1000 in "model engineering" quantities ? Apologies if the answer was mentioned earlier but I did skim through looking for it without success.  (I see the Timesavers compound is readily available in the UK but the price is rather high for me.)

Thanks,

Boo

[Jasonb]

Axminster do it down to 600g, e-bay is your friend after that - often sold for stone polishing/tumbling

https://www.axminstertools.com/hand-tools/sharpening-tools/lapping