Mat'l for a lap?

Snag, Depending on the lapping compound, the lap should always be softer than the material being finished to size. Some lapping compounds break down, but don't expect it. I would use brass, it machines much better than 4140, so you should get a better final bore. Dave

Laps should be soft enough to hold the grit, and softer than the metal you're lapping. What they don't often tell you is that the lap also should be gummy, which goes hand-in-hand with holding the grit firmly. In general, you want the lap to be somewhat softer than the material being lapped but not greatly softer. In other words, don't use a lead lap on hardened steel.

Gummy laps are lead, aluminum, annealed copper, annealed brass, and dead-soft annealed steel. Not 4140. But you could make a fancy expanding lap "core" out of whatever decent steel you have on hand, and cover it with a tube or sheet of softer lap material. In fact, some commercial laps have been made this way in the past. You have to key the lap material somehow to keep it from slipping on the core.

You may also want to consider using plastic-backed (usually polyester) lapping film. It's very efficient and it cuts very consistently. If you do that, make a hard lap and clamp the edge of the film in place in a split on the lap.

-- Ed Huntress

Why not change from the old needle bearings to new tapered roller bearings? This is a conversion that most builders do to old harley cases.

cheers T.Alan

Terry Coombs wrote:

Ooohhh , I like that idea ! I was considering using some wet/dry sanding paper , 600 grit or finer as a cutting medium , but a machinist friend thought that it would "thread" the race . FWIW I did use sandpaper wrapped on a socket to final size a cluster gear race and it worked all right . I'm not even certain yet they need to be lapped , just trying to be ready if they do ... Thanks Ed ! Snag

I'm not sure that's possible on a 45 ci flathead ... Snag