Educate me on "brass barrel laps" please

[Brian Rupnow]

I am thinking of buying a "brass barrel lap" from Travers Tool to use for lapping the 1" bore on the cast iron cylinder of the engine I am building. I have never used one, and I don't know anyone who has. I have always made my own "one time use" laps by turning a piece of round aluminum to .002" to .003" less than the diameter of the cylinder bore, and using successive grades of carborundum paste to lap the bore. I would like to hear from anybody who has used these adjustable brass barrel laps. Does lapping wear them out?---are they a valuable item to purchase in terms of usage?---I am ready to move up a notch from my home made laps, but I would like to hear a bit about these brass barrel laps from knowledgeable users.----Brian
http://traverscanada.com/skulist.asp?RequestData=CA_Search&navPath=All+Products%2F%2F%2F%2FUserSearch1%3Dlap&q=block+id+112470+and+class+level3+id+29980&minPrice=$3.23

[Will_D]

The theorey of lapping relies on asimple fact:

The abrasive embeds into the soft metal and so removes abrades the harder metal.

This is why you should never put felt disks on chair legs to protect your wooden or marble floors. The grit embeds in the felt and just gauges the wood. The absolute best would be carbide!

Is brass better than Aluminium or lead (was also used for lapping)? - no idea.

If you want to drill a large hole ( say 1.5" ) in glass:

Chuck up some brass tubing, square it off. Build a well of putty or blue tack on the glass, add some carborundum and water and slowly drill away.

Support the glass on some sheets of newspaper on a bit of mdf on the drill table and as we say "Bob is your Father's brother"

HTH

Will