Lapping

Lapping seems to be a term that encompasses several different processes of similar nature.
I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this: From dedicated lapping compounds obtained in Auto part stores (which here nobody has heard of) to mixing up a scouring powder with oil to make a lapping paste. It brings up several questions:
1) When does lapping stop and grinding starts (Permatex make a "valve grinding compound" which some people use for lapping)? 2) What is the maximum/minimum grit suitable for lapping? 3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?
FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings. Not having anything "lapping-like" to hand I mixed up Fast Orange with oil and used that. It contains pumice and GOK what the grit of that is. The shaft is smoother. I think.
BTW it is now virtually impossible to get the old scouring powders for cleaning - everybody is so proud that their product is "scratch free".
While browsing in the Auto part stores I found several cleaning pastes which contain abrasives. Would they be suitable? Too harsh?
--
Michael Koblic,
Campbell River, BC
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Michael Koblic wrote:

How about the old stainless steel cleaner, 'Barkeeps Friend'? It says it is abrasive, but not how much. I've seen it used in kitchens for years to keep old stainless steel sinks & tables clean and looking good.
http://barkeepersfriend.com/products.htm
http://barkeepersfriend.com/BKF_MSDS_01_09.pdf
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On Sun, 17 May 2009 21:21:33 -0700, Michael Koblic wrote:

Where's "here" for you?
In the US you can get lapping compound (and diamond grinding/lapping compound) from McMaster and from Small Parts, Inc.
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wrote:

IIRC, Michael's in BC.
I haven't done any myself since engine rebuilding on the farm days (decades), but usually it means charging abrasive to a softer metal form to lap a harder metal. The abrasive embeds in the softer metal, then the lap (softer is moved across the harder material to improve finish and fit.
This implies that you wouldn't want to lap a babbitt bearing because you'd never get the abrasive out, and it'd continue to wear the shaft it was supposed to protect. Very deformable laps also wouldn't be effective because they wear the low spots almost as fast as the high spots.
Brass makes a good lap for cast iron or steel. I intend to use lead bullets charged with abrasive to fire lap a rifle barrel. There's lots of other combinations.
The abrasive must be removed completely from the lapped part after lapping. I have read of abrasives that break down quickly so they are not a problem, don't know how effective that is.
As far as obtaining lapping compounds, I'd google Clover compounds British Columbia. Hmmm. Just tried that, there's a supplier in Ontario, and the stuff is pretty easy to ship. They also have some info on grit sizes and uses. http://www.newmantools.com/clover.htm
Pete Keillor
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Michael Koblic wrote: ...

Uh oh ... that wasn't a good idea. The pumice will embed itself in the bronze and continue to lap the shaft, even when you think that you have cleaned it out. Or, maybe pumice is soft enough that it will break down - I dunno.
Bob
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On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"

Greetings Michael, It's too bad you used pumice to lap your shaft. This is because the pumice will embed itself into the softer bronze and continue to lap the shaft. For lapping plain bearings (AKA bushings) the stuff to use is called "TIMESAVER". You can find it online. It is an abrasive that breaks down completely and will not keep cutting. It is available in a sampler kit that contains several different grits of two different types of compound. One for soft metals like bronze and babbit and the other for steels and the like. Unlike regular lapping compounds when this stuff is used the softer material is lapped, just the opposite when using, for example, Clover Compound. ERS
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wrote:

Ah. Live and learn. Though the stuff washes off my hands fine. Maybe the shaft will live...I honestly do not know how much effect it had in the first place. Anyway, calling it a "shaft" requires a fit of enthusiasm in the first place.
Now I am still confused: Why go to all this kerfuffle to smooth out a bit of metal, particularly if it is flat. I see the grits available are anywhere between 50 and 1200 so one can take pretty big chunks of material. Why can't you achieve the same result (on a flat and accessible surface at least) with steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if you are using the coarser grits). How is the lapping compound behave differently from these other gizmos?
But thanks for the references - I have been able to bookmark the web site that sells both Clover and Timesaver just in case I decide I cannot live without it.
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Michael Koblic,
Campbell River, BC
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Lapping implies a rigid guide holding the abrasive. You could use a flat steel block behind sandpaper but the paper has some give and the relatively thick abrasive layer wears down unevenly. I wrap sandpaper around a form such as a dowel to clean up rounded inside corners and such if the geometry isn't critical.
I suppose you could burn sandpaper to separate the abrasive. Caustic soda dissolves alumina to some extent, without damaging metals except aluminum.
jsw
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Jim Wilkins wrote:

OK, now I get it. This was the critical element I was missing. So to lap, say, a lathe way, you would spread the paste on a flat piece of brass or aluminium and rub it on the ways?
I won't even ask how they lap the automotive valves...
--
Michael Koblic,
Campbell River, BC
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On Mon, 18 May 2009 20:06:35 -0700, the infamous "Michael Koblic"

I learned this way: apply lapping paste to valve seat, insert valve, stick rubber suction-cupped, hand-crank egg-beater/drill thang to valve face, and turn handle. like this: http://tinyurl.com/pdscsu or <
http://www.goodson.com/store/product_images/b1_imgshop_528.jpg
I have no idea what grit we used in 1971/72.
Here's another semi-manual way: http://fly.hiwaay.net/~langford/corvair/valvejob.html
And a VERY manual way: http://tinyurl.com/r6ab8a or <
http://www.holtsauto.com/images/products/repair-and-maintenance/maintenance/holts-valve-griniding-kit-hi.jpg
-- No matter how cynical you are, it is impossible to keep up. --Lily Tomlin
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wrote:

And no matter what they call it, it's a GRINDING operation, not lapping. The abrasive doesn't embed in the valves or the seats, it just rolls around between(at least you HOPE it does).
Stan
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On Mon, 18 May 2009 21:02:36 -0700, Larry Jaques

Coarse then fine if you bought the double ended can from Canadian Tire for $2.29 that has the yellow label painted over with black paint. I suspect I bought this one in 1958.

That's similar to the tool I had - a section of broom stick with one of the suction cups from an electric defroster screwed into a hole in the end. Gerry :-)} London, Canada
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Lapping is about getting two parts to fit each other, as in lapping valves into their seats, or pins into holes. Scotchbrite is about getting parts clean and shiny.
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If, by some miracle, it is "flat", then using scotchbrite or sandpaper will render it not flat - on the microscopic precision scale one cares about with lapping - areas where the stuff is pressed harder will wear down more, etc.. If it's not flat to start with, scotchbrite or sandpaper won't do any thing to improve it, as they conform to the surface (removing material form both low and high spots) and also have the above behavior of possibly putting new gouges (on a fine scale) into the surface.
A lap only grinds at the high points of contact between the rigid (soft) lap and the rigid (harder) item being lapped, where the (even harder) abrasive trapped in the soft lap scrapes the high points of the item being lapped. Thus, it makes the surface flatter, or rounder, or more whatever shape the lap is.
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On May 18, 8:05pm, Ecnerwal

Actually, what I should have said is that "lapping" with Scotchbrite will make your previously flat surface conform to the shape of your fingers,
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On Mon, 18 May 2009 20:34:34 -0700, "Michael Koblic"

Essentially a "lap" is a piece of material in which abrasive can be imbedded. Think of it as similar to a grinding wheel. A "diamond hone", diamond particles imbedded in a steel plate, is a lap, for example.
Normally a soft material is not lapped as the abrasive grains will imbed in the softer material and you will essentially make a lap. Babbet bearings, for example are scraped to fit. Not lapped.
A "lapping plate" is traditionally a flat cast iron plate and is "charged" by spreading abrasive on the plate and imbedding it by using a hardened roller like a rolling pin to force the abrasive grains into the cast iron. The plate is then washed free of loose abrasive before use.
Regarding the shaft in bushings you mention the traditional method was to polish or grind the shaft to size and then ream the bushings after installation.
Generally a lap is used to provide a certain surface finish rather then to provide a certain surface dimension, although that is not a iron bound description.
The O.P. question about "lapping" a lathe bed seems almost a contradiction as nearly all lathe beds are finished by grinding and sometimes scrapping to provide oil retention.
Cheers,
Bruce in Bangkok (bruceinbangkokatgmaildotcom)
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High-speed internal grinding attachments for lathes were once made with extremely close hardened steel-on-steel bearings without oil that reportedly would coast for a long time although they seemed to stick a little at rest. They were fitted by lapping with fine diamond dust, which didn't embed in the steel. I think I saw that in one of Fred Colvin's books.
I fit pressed-in bronze bearings with a reamer and make slight changes to the drag with an adjustable reamer. Mine are mostly the cheap imports and they begin to chatter if asked to remove more than a hair.
I've read that a half-round or D reamers works well and you can make one to any size on your lathe.
jsw
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wrote:

It is most strongly recommended that you do not lap the ways of lathes and mills.
If the flatness obtained from the surface grinder on a hardened way is insufficient and if you have the use of an autocollimator and if you are working in microns or less, then you might consider lapping. Otherwise, use scraping or surface grinding.
Mark Rand RTFM
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1) The instructions that come with the Taig lathe specifically recommend lapping the ways before use. This is where I got the scouring powder/oil paste mixture from. I did not do it. The ways seemed smooth and the carriage moved like silk. I was concerned (justifiably it seems) that I was more likely to screw things up than improve them.
2) Many owners of mini-mills have reported improvement in properties of theirs X and Y axes' movements after lapping the ways. I was considering it for various reasons but wanted to make sure that I understand the process first. I seem to remember that there was a thread on this very group discussing it some time ago.
I am beginning to wonder if these sources freely confused "lapping" with "polishing". I certainly was.
--
Michael Koblic,
Campbell River, BC
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