Lapping Plate Question

One of my coworkers just had our lapping plate sent over to our main shop to have it reground because somebody used yellow compound which is a 3 when its only for orange which is a 6. I always thought that as long as you didnt use anything more than the 6 you were ok. Am I wrong or is it ok use the finer stuff? Now this plate always has the paste removed so its mainly about the embedded material. The plate is just a chunck of heat treated that was precisionly ground square and parrallel to some degree.

I asked my coworker who threw the fit about it why it was a big deal and his reply was only "Orange (6) is what you use for moving materials and shining them up. Putting anything else on there just Fs that up"

Precision apping done right is a task requiring skill and thoughtful consideration. Great care mut be taken of the laps to ensure their surfaces and contours are up to spec and that they are inspected and reconditioned regularly. Without this care lapping quickly becomes an expensive and uncontrolled process.

I've done a lot of hand lapping to critical tolerances and finishes. My reading of the available literature and consulting with those alleged to know has resulted in more conflicting misconceptions than pre-pubescent discussions of sex. Lapping as presently practiced in the usual shop is not a scientific procedure but an uncontrolled process guided by blind luck and aprocryphy.

I don't know what kind of lapping compound you refer to but yellow in diamond lapping compound is 3 micron. Orange is 6 micron. Does that agree? There are also several colors of Timesaver but I can't recall the grades and grit frangibility.

I understand the topic deals with flat lapping plates. If a lapping plate is used for a specific application where critical parts are lapped to flatness and finish the individual most responsible for preserving the plate has every right to erupt if it suffers negligent use. Naturally it's better if he does so in a constructive way.

Diamond is quite contaminating. Once a coarse grit is embedded in a plate normally used for finer grit it takes a long time to wear it down. Mean time ,critical work lapped on it may suffer from substandard finishes. Only reconditioning - that is, a surface grind (or a re-scrape) sufficient to remove the coarse grit - and recharging with the proper grade will restore it to service. Lapping plates do not stay flat foreever. They wear. There is nothing magic about a fancy figure eight lapping motion. Any lapping motion that keeps the surface to be lapped on the plate without tipping and which covers all the plate more or less uniformly will keep the wear consistant and the plate flatter between re-conditioning cycles.

Further, daily checks of the plate need to be made if the flatness of the work performed is to be economical and meet specifications. For that a straight edge and a set of feelers are necessary. Clean the plate thoroughly and dry it. Place the straight edge across the plate and sandwich it between a couple of 1-2-3 blcoks to keep it vertical. Slip three equal sized feelers under the straight edge one at each end and one to be slid along the length to find the highs and lows. Pull the feelers gently. If all have equal tension through out the length of the straight edge the plate is probably within a tenth or three along the path of the straight edge. Test the plate an inch inside all four edges and down each midline to form a grid. Also test the plate in a corner to corner X. If the plate tests flat you're in good shape. Areas 0.001" higher than the balance of the plate form the working areas of the next day.

Sooner or later the plate will show localised wear and have to be re-conditioned but daily checks can extend this interval to months whereas carelessness may render it useless in a few days.

"The plate is just a chunck of heat treated that was precisionly ground square and parrallel to some degree."

I assume this plate is grooved. What are the parts you are lapping on this plate? Are they steel, aluminum or what? Lapping is a simple process with only a few rules, the rest is baloney.

First off I have to ask Forrest: when are you going to be offering classes on the east coast for scraping? I really like your knowledge base and would love to learn from it.

Well back to the thread we are talking about a flat piece of steel with no grooves and lapping mainly D2 56 to 58 RC. Parts are no more than 35mm in diameter and lapping plate is only used to push a face detail down no more than 10 microns. Plate is used mainly to polish surfaces. We don't have any strict finish tolerances as we are in a tooling support position and not a production one. I completely understand lapping plate maintenance is a must and the process is a lot more technical then what people realize as the die setters I work with have already proven by ruining our plate twice in the last year.

I guess what I'm mainly asking in short is if you use 6 micron compound on a lapping plate thats brand new and you wipe away the leftover paste and then somebody else comes along and grabs 3 micron compound and uses it to just take away the dullness on something is that plate ruined and now in need of being resurfaced? Now that lapping plate is only intended to be used with 6 micron compound and nothing courser (just to specify that).


See I understand that using a courser compound will embed in metal and cause problems, but what I'm talking about is the complete opposite. Will a finer compound cause you problems?

See I've only been doing tool and die for 2 years now and have 2 coworkers who have supposedly 15+ yrs in the trade and they tell me things that don't make sense so I have to come here and post and see what the true word is. Sometimes they're right but most of the time they're on their way to the ball park and haven't realized yet they just drove 500 miles in the wrong direction.

"because somebody used yellow compound" His initials wouldn't be AB would they? Kidding, doesn't matter, I'm waiting for the right answer too, good question.

Obviously the 6 micron compound will start breaking down toward 3, that ruin it too? Or does Forrests careful dissertation cover all that pertains?

Seems to me that the only change in outcome, should one charge with a compound described as "various grits, none exceeding 6 microns", would be that the lapping process would take longer to achieve the same finish. 'Spose a 5 occasionly sneaks in with the 6's?

Bob

AlexBanich said:

The plate is just a chunck of heat treated that was precisionly ground square and parrallel to some degree.
"

Click to expand...

that line surprised me a bit, isn't the idea that the compound (of whatever flavour) gets seated into the lap? the laps i have are cast iron so that they can be charged by pressing the grit into the lap. granted the abrasives are harder than the heat treated steel, but i would think that would be a very hard material to charge properly. Also, if the idea is just let the grit roll around between the two, it'll work, but you will embed the grit in the work if the work is softer than the lap won't you?

edit; Bob makes a good point; how would using a finer compound ruin it as the 6 will eventually break down to a 3 won't it? it might take a special man to notice he was working with 5 instead of 6 were it not for the colour coding; I agree the disaster is if someone loads it up with coarser material not finer.

How do you charge the plate. I've been rolling it in with a large dowel pin. Been working for me but I'm interested in alternatives. I only do this a couple times a year .
Any suggestions for a good book on the process.

If steel is hard to charge, how about ceramic?

Some 37 years ago a tool & die maker friend gave me a 3-1/2"x7" ceramic lap. I'm not quite sure what I might try to use it for, but I would like to find some info. . .

There's absolutely no problem using a grit finer than the one normally used.

I'm curious like the others why you are using heat treated steel? You usually want the lap significantly softer than the material being lapped.

honestly I couldn't tell you why its made that way. Probably because it was there I would assume. See now the thing about the plate is that its basically used all the time with 6 micron so if 3 gets thrown in there one time say out of a 100............? Thats why I don't see that one in a 100 use of finer compound is a cause for a resurface. I only ask because of the strong reaction about it. Either way it doesn't really matter to me cause I don't polish I'm an over glorified button pusher

Chunks of steel that are ground will mirror the ground surface flatness when used as "lapping plates".

Therefore lapping plates must be reclaimed by other lapping plates that are conditioned to within your tolerance for flatness.

Lapping plates are normally cast iron or composite plates that are porous so the free abrasive can properly charge into the plate.

THe courser your abrasive the faster your plate will wear.
So using finer grit material is not your problem.

We use Lapmaster lapping machines and rough lap with 15 micron diamond slurry, then finish on the same machine with 1 or 3. No problem.

Alot of this depends on the material you are lapping and what face flatness and surface finish reqiurements you are trying to achieve.

We lap tungsten and silicon carbide seal faces to 1-2 HLB and 1-2RMS finish

True lapping is as much art as it is science.

Trying to Understand..

I can see charging the iron plate with #6 grit.
I can see the plate cross slit with grooves to allow excess media to drain.

I can not see how #3 grit following #6 grit can yield a fine finish without #6 scratches, because #6 will be taller.

I would think all the #6 should be removed before finishing with #3.

Does charging the plate mean embedding the grit? Or does it mean slurring it around on the plate and not embedding it.

If it embeds, how is it removed for the next finer grit?

I'm confused.

I don't feel this process is not a very popular one, however, it is a needed one and understanding it is important.

I'm interested!

Regards,

Stanley Dornfeld

ok so I don't know if I've explained this fully enough so everybody understands the process. You put 6 micron paste on the plate and do your figure 8s and then use a piece of paper/card stock between the work piece and plate and repeat your figure 8s to remove extra paste. Then when you're done you grab 3 micron and do the same process with a different part. Now I can understand how in a shop where you're doing larger work and have to have your work right there you have really fine details to abide by but we have a tolerance of literally shiny. Honestly you could get away with a 60 grit wheel grinding finish. This process for us is not to every day or even every week move material around. Its mainly used to just make a surface look shiny. Oh and no contours or anything just a flat area surface thats no bigger than 99% of the time an inch.

Dredging up this necro thread- I just got some 6" cast iron discs and ground them flat. Charged them with fine diamond compound by rolling it in with a carbide pin. It's amazing that these laps work as well as they do, producing almost no edge rounding like most polishing films and papers do. A 100+ year old technique that's worth it's weight in gold when you need it.

Forrest Addy said:

Precision apping done right is a task requiring skill and thoughtful consideration. Great care mut be taken of the laps to ensure their surfaces and contours are up to spec and that they are inspected and reconditioned regularly. Without this care lapping quickly becomes an expensive and uncontrolled process.

I've done a lot of hand lapping to critical tolerances and finishes. My reading of the available literature and consulting with those alleged to know has resulted in more conflicting misconceptions than pre-pubescent discussions of sex. Lapping as presently practiced in the usual shop is not a scientific procedure but an uncontrolled process guided by blind luck and aprocryphy.

I don't know what kind of lapping compound you refer to but yellow in diamond lapping compound is 3 micron. Orange is 6 micron. Does that agree? There are also several colors of Timesaver but I can't recall the grades and grit frangibility.

I understand the topic deals with flat lapping plates. If a lapping plate is used for a specific application where critical parts are lapped to flatness and finish the individual most responsible for preserving the plate has every right to erupt if it suffers negligent use. Naturally it's better if he does so in a constructive way.

Click to expand...

I lose my mind when i see people using the lapmaster for things they should not...like lapping their India and Arkansas stones flat again. I told the last guy to do it if i see him near my machine again ill shove those stones up his ass...It not technically my machine but since im the only one who knows anything about lapping here and the only one to condition and repair the plate i take offense to someone screwing around withit.

one tiny little itty bitty piece of stone can ruin a $3k part in an instant...and the sad part is it dont even cross their mind.
Ive completely rebuild my lapmaster all the way down to the gear box to ensure everything runs as it should(actually had to have a gearbox custom made cuz its that old)

my 24" can lap a 8" dia alum. plate to .00008 flat all the way across even tho lapmaster said that should not be able to happen..it all comes down to how you take care of it. keep it clean and covered and away from idiots usually does the trick..helps to have it out of the way in a corner so it doesnt turn into a coffee table as well

LOL ALL THAT TYPING I DIDNT EVEN REALIZE THIS THREAD IS A DECADE OLD

Flat lapping is very much in vogue right now. With many of the major youtube guys doing videos on the matter. (Lipton, Renzetti, Steffan) I would consider this necro revival appropriate for current discussions.

I agree with no ill harm of putting a finer grit on a lap. The only issue would be in the resultant part. Also if your lap is harder than your work the best you'll get is a tumbling type of stock removal, the worse case you end up "charging" your part instead.

Cheers.

If regrinding the plate makes the tool holder happy or less mad I would call that cheap satisfaction.

We've got a Lapmaster 12" at work and I'm the only one that's up on its care and feeding. Everybody else wants nothing to do with it. Very easy to let it get out of flat, but capable of greatness when properly monitored and adjusted. Let the plate go a bit convex and you could take hours to days getting it back. A bit concave is easy.