On Thu, 31 Jan 2013 11:18:57 -0800 (PST), Stanley Schaefer
wrote:

On Jan 30, 6:24*pm, wrote:
I have been grinding and lapping carbide tools by hand for over 30
years. I have gotten pretty good at it. But with the relatively newer
micrograin carbides it is possible to buy carbide inserts for aluminum
that are extremely sharp and with a polished finish. It is hard for me
to attain the very highly polished surfaces in a reasonable time. So
normally I just buy inserts. But occasionally I need a special tool
shape or radius or whatever and I make my own tool or modify an
insert. I use diamond paste with cast iron lapping wheels and flats.
When using a wheel to lap a positive rake cutter is it better to have
the direction of the wheel going down in relation to the cutter, as if
the cutter was cutting the wheel, or is it better to have the wheel
rotate in the opposite direction? I am lapping with the flat side of
the wheel, not the periphery. Similar to an Accu-Finish
grinder/lapper. The machine I use is a Leonard Grind-R-Lap which is a
slow spinning machine and the precurser to the Accu-Finish machine.
I'm thinking that if the wheel is going past the cutter in a downward
direction that minute particles of diamond that have been freed from
the wheel surface and particles of carbide removed from the cutter
might tend to pile up on the cutter edge and round it slightly. On the
other hand, if the wheel direction is up past the cutter will the
diamond tend to pull particles from the cutting edge leaving it
ragged? With the older, larger carbide particles it was better to have
the wheel going down past the edge. But now I want to achieve the
sharpest possible edge I can with the better carbide available.
Thanks,
Eric

I'm no expert at it and you've probably got more experience, but the
old tool-making books I've got all seem to indicate that a steel
lapping surface with the diamond grit rolled into it under significant
pressure is the way to go and that some kind of added oil for swarf
removal is needed. They specifically warn against having loose grit
because it rolls and will mark up the work surface. One book
mentioned using olive oil(old book), another said gasoline(inside,
don't think so!) for keeping the lap's surface cleaned off. One
picture showed a hydraulic press with a roller for pressing the grit
into the lapping plate. If you're using the commonly available
diamond lapping pastes, this might be your finishing problem. One
book also had a "listening stick" for determining the optimum pressure
to put on the workpiece, apparently there's a particular sound when
it's cutting correctly. The idea being that you'd put one end on the
workpiece and the other next to your ear. Said that crowding the
workpiece wouldn't make it cut any faster and it messed up the surface
finish because the diamond grit came loose and rolled.

Stan
Greetings Stan,
Thanks for the reply, though I'm not sure if I have a problem or not.
I am charging the laps properly. But even a properly charged lap will
lose some abrasive over time. I use lamp oil, which is basically
deodorized kerosene, as a cutting fluid. It works very well but I know
that some grit may be carried around the wheel and may be affecting
the cutting edge. I am trying for the utmost in sharpness on carbide.
Eric