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[kenefick]

Just acquired an older HP 27L Vibro Lap, and being a patient sort of fella, I want to get it in operation yesterday.  It came with a 4 page Operating Manual that I think has me on the right track, but I'm not 100% sure I'm ready to start using it.  I have turned it on without a load, and it appears to be running OK. Any advice on setup would be greatly appreciated.
1).  The unit came with an additional plate assembly, which has a smaller grid pattern than the one installed.  Is there any advantage to the smaller grid?  I'm thinking maybe to use the larger grid plate for the coarse grit, and the smaller grid for the finer grit.  Maybe avoid some cross-contamination that way?
2).  Speaking of grit, the manual says 80 grit for grinding, then 400 grit for Final Grinding.  Is there a better combination?  I get really smooth cuts from my saw, and the grits listed seem a little coarse (80), and kind of far apart.
3).  For polishing, the manual says Tin Oxide with a statement "We don't recommend any other polishing compound."  At about $75 a lb. this could get deep(er) into my wallet pretty quickly.  Is there something else that you could suggest?

[kenny]

http://www.kingsleynorth.com/skshop/product.php?id=46508&catID=110

still not cheap but I use it all the time very good polish

[lithicbeads]

Tin oxide has always been considered the polish that works on more stones than any other. Folks now often put carpeting cut to fit in the tray for polishing. Once the carpet is well charged with polish each additional time it is used only requires  a little more polish so it is more economical than it first appears. Too much oxide polish is always a concern . Leveling is crucial as you do not want the grit moving to form a concentration. I imagine that they reccomend 80 grit for various reasons. One reason is that while a slab may seem flat when it has been finished by  these laps they in fact are not. The outside edge of the pan tends to cause more wear and the stones or part of a bigger slab that is worked near the edge will have to grind more before it is prepared properly for the next stage. A friend who has a factory with dozens of the biggest vibrating flat laps has bitched for years about this grinding problem He finally invented a new type machine that he uses for pieces up to about 14 inches in diameter. the lap spins the stones and they work from the outside edge and backin while spinning so you get a fairly random and uniform grind. I do not think he would appreciate me descibing his machine but he does about 700 fist sized slabs at a time and uses a lon handled shovel to get the grit on the lap. Have patience and have fun.

[kenny]

I concure with Frank, and to add I have a home made flat lap like an  ameritool set up, and was going to use it to polish slabs. The slabs as they came off the saw looked like they were about the same as a 400-600 grit sanding would be. I painted the surface with a black marker to make sure I got a good sanding job, to my amazement there were thickness differences of probably .1 - .01mm on the surface that by eye looked perfectly flat and 100 grit took forever to remove them. 

[Bentiron]

Speaking of a rotary lap, years ago when I was doing HVAC design for various projects at a Motorola plant they had a rotary flat lap machine for their silicon wafers that had them held down with arms that rotated them on rotary lap, it was a huge machine but those silicon wafers were so pretty before they went into the mods for etching on the circuits.

[kenefick]

Thank you very much for the responses.  Looks like I need to go grit & polish shopping.  And try to find a little patience.