True Grit

[zeeprogrammer]

Thought I'd try to learn a little about 'grit', 'lapping', 'polishing', et.al. Did a little search on 'grit' tonight. Got a few hits on 'inteGRITy' which this forum has plenty of.

No 'finer' forum than this.

But without being 'coarse'...I have some questions.

No need to go for a higher education...'medium' will do.

But where to start? Aye...that's the 'rub'.
Hopefully it won't take long to 'polish' this off.

Okay okay. Stop the moaning.

I'm basically confused about 'grit'.
Low number...coarse. High numbers...fine. Somewhere in between is 'medium'. Okay.
I've seen numbers down to 60 if not lower and numbers as high as, gasp, 20,000!

Are there different numbers for different materials? Is 800 wet-n-dry the same as 800 diamond hone? And just what is toothpaste? (If you tell me 'a material for cleaning one's teeth'..I'm going to come find you.) Is 'coarse' for one kind of material 'fine' in another?

What's the difference between 'lapping' and 'polishing'?

I don't really have my questions organized...I thought I'd see what this kicks off and where it goes.

No doubt this is an extensive subject but I bet I'm not the only one 'scraping' for info.

 

[joe d]

Zee

I thought GRIT was a really small serving of a corn-based mush that Southern types eat with red-eye gravy.

Hope it helps..... ;D

Joe

 

[Holescreek]

Zee,
I am curious as to why you would choose to lap vs. scrape. I have read about the lapping methods and the outcomes usually resulted with grit embedded in the iron. If you are just trying to smooth out mating surfaces and want to try it out, pick up some Clover brand lapping compound to play with.

We used to lap parts using diamond paste and iron lapping plates before final polish where the surface had to be flat and have at least a 4 micro finish. The lapping plate was always iron so the grit would embed in it, not the steel parts. I have no experience with lapping surfaces that are meant to slide against each other but on the face it seems counter-intuitive. -Mike (who couldn't find a pun anywhere)

 

[mklotz]

I seem to remember that grit numbers are another one of those totally bastardized Imperial measurements like sheet metal gauge numbers that indicate how often the sheet has been through the rolling mill.

It was something like...

grit number = the number of holes/in^2 in the last sorting screen the stuff would pass through.

Maybe OK for a in-house designation used in the grit-grinding factory but why the hell was it adopted as a measurement standard? Any sensible person would have used average particle size in microns (or similar) so larger numbers were coarser and smaller numbers were finer.

Ah, well, it makes as much sense as numbered drills, which, of course, make no sense whatsoever.

 

[ksouers]

Zee,
Lots of interesting questions. I, too, would be interested in seeing the answers.

I'm afraid I have next to no knowledge of the subject, so I will offer up what (I think) I do know.

Grit, or sometimes grid, size is the number of holes per square inch of a sorting grid. Therefore, the larger the number the more holes per square inch, thus the smaller they are. The grit gets sorted by sifting it through finer and finer sorting grids. I don't know if that's a historical perspective, or if it's still done that way. It seems that the grit for a particular paper are pretty uniform in size, so I suppose it's possible a more scientific method has been devised to identify and sort grit of a particular size.

So, my understanding is that the grit size is the same regardless of the material, i.e. an 800 grit garnet is the same size as 800 diamond or silicon carbide. And the same whether it is a paste, powder, stone or glued to paper.

Of course, I will gladly stand to be corrected on any of the above. But this is my understanding of how it works.

As for the rest of the questions I await the more knowledgeable among us. I've seen the terms lapping and polishing used interchangeably so always assumed they were the same thing.

 

[GailInNM]

Carl,
It can get confusing in a hurry, and not all manufacturers of abrasives specify things the same way.

Because of the way the abrasive grains are graded there will be a range of sizes in any given compound. Many of the low cost abrasive papers have a rather large range between the largest and smallest grains, while the name brand papers will have a rather narrow range.

The only absolute measurement is one that calls out the maximum and mininum grain size, normally specified in microns.

As an example, I use a diamond lapping compound that is listed as #30, meaning that the average particle size is 30 microns. Digging a little deeper into the specification it shows that this particular manufacturer uses particle sizes of 22 to 36 microns to make this compound and cross references this as 600 mesh. Comparing this to grit as would be specified for abrasive paper this would give a range of from about 320 to 450 grit sizes and would be compared to 320 abrasive paper as it is common to specify abrasive papers with the larger grit in the range.

A more detailed description of the relationships can be found at:
http://leco.com/resources/met_tips/met_tip15.pdf

I hope this is not more information than you really want to know.

Gail in NM,USA

 

[Holescreek]

Hey Zee!
I just re-read your post and I think I confused it with a post I read somewhere else where a fellow was wanting to lap surfaces on a mill column. Sorry about that, I shouldn't have made that assumption.

Metal surfaces are truly planes of peaks and valleys. Surface grinding or sanding just makes the peaks shorter and the valleys narrower. Lapping evens them out over the entire surface. The grit you choose is guesstimated based on the finish you are starting with. A good place to start if you have something to experiment with would be in the 120 -150 size range. I like Clover compound because it's cheap and cleans up easily. Apply the paste to the plate, put your part face down on it and use a figure 8 motion over the paste. If you keep whittling down the grit size to say 600-1200 you would start to see your reflection in the surface.

That's when you switch to toothpaste. -Mike

 

[zeeprogrammer]

Wow.

Joe: Southern grits are awesome. But lousy for polishing metal unless my Grandma made them.

Mike: Switch to toothpaste cause I can see the reflection of my teeth? Still wondering what the relevant 'grit' is of toothpaste.

Marv: I have the same problem. Some things are measured as 0 then 00 then 000 as they get finer and finer.

ksouers: I had no idea that grid size was used. Thanks.

Gail: Thanks. Certainly not too much information.

So what do people think is the grit of toothpaste? Of brasso?
And why wouldn't we use the very fine grit sandpaper used in plastic models?

This was great. Too bad it reminded me of Grandma's grits though.

 

[gilessim]

As far as I was aware, the sandpaper grit numbering , as Marv says is based on the amount of particles passed through a sieve but I'm fairly sure that it's a metric system, i.e: 1 square cm , as for lapping and polishing it's all down to the sharp edges of the particles wearing down as the compound rubs on the surface being polished or lapped, i.e. diamond grit will not wear down, garnet will a little, sand even more and so on, lapping is a process where you need to mate 2 pieces together so a softer compound is required to keep a good finish without too many scratches ,saying that, there are some diamond lapping pastes that have micron sized particles that remove hardly any metal at all!, the finest polishing compound used to be ,and is still used with jewelery is Balsawood ash mixed with a dash of water.

an interesting thread, thats my 10 cents worth ,I hope this helps but I'm sure we'll get some more informed replies!

Giles

 

[mklotz]

I had grits once when on a business trip to Huntsville. I'd rather eat Clover compound. It tastes better and cleans my teeth instead of sticking to them.

0, 00, 000...

Any logical designation system needs to be open-ended at both ends. Moreover, human minds being what they are, bigger numbers should denote bigger "things".

That's why the numbered drill sequence is such an idiocy. Bigger numbers mean smaller drills. Since there's (a rather large) #1 drill, if anyone were to make a larger drill, it would need to be numbered zero. And, of course, the number tells you nothing about the size hole it will make.* Not only is it counterintuitive, it's just ripe for errors when writing.

Whatever you may think of the metric system (no, I don't want to reopen that can of worms), they had the sense to label most everything by its size. A 1 mm drill is smaller than a 2 mm drill and, since you can't make a zero diameter drill, the series is open-ended at both ends as it should be. Same comment re taps. A 1 mm tap is smaller than a 2 mm tap and you don't have to remember some idiot formula that relates an abstract number to tap diameter as is the case with numbered taps (e.g. #6 = 0.060 + 6*0.013 major diameter).

--
* The numbered drill diameters agree most closely with the sizes of the Stubb's Iron Wire gage numbers so the numbers probably dervive from that ludicrous "standard". They don't agree exactly of course. Oh, there's a Stubb's Steel Wire gage standard too. It doesn't relate to the Iron Wire standard.

I did a regression analysis once to derive a formula that would relate drill number to its diameter. To get 0.001" accuracy across the range required a sixth order polynomial. Can't you just picture a machinist plugging numbers into a sixth order polynomial?

 

[zeeprogrammer]

Can't you just picture a machinist plugging numbers into a sixth order polynomial?

No.

[Edit: I can't imagine anyone doing that...except maybe you Marv ;D]

Thanks Giles.

 

[Holescreek]

A quick Google search on polishing with toothpaste netted this:

Polishing with Toothpaste
When polishing aluminum or chrome wheels on your tractor hauler or on the chrome on your tractor (LOL), it is foolish & wasteful to buy expensive wheel polish. I find that ordinary, white toothpaste works just as well. With just the right amount of fine abrasives needed to clean teeth, it seems ideal for wheels and chrome parts.
It's also readily available if you finish washing your trailer queen before setting up at the tractor/car show car and then realize that you forgot to stop by the local auto haus.

ShepFL, from FL, entered 2001-07-21

I was with him up until:

if you finish washing your trailer queen before setting up at the tractor/car show car

I know several metal polishers that swear by the old Pearl Drops toothpaste. Says they don't sell it anymore and what a shame it is because he could do wonders with it. :toilet:

 

[DavesWimshurst]

Zee,
There are supposedly non embedding lapping compounds, Timesaver is one brand, where the grit crumbles into a polishing grade not requiring cleanup. I got a kit of several grades from Mcmaster Carr several years ago when the price was much less.
http://www.mcmaster.com/#lapping-compounds/=2d5bhu
I have also used Clover brand lapping compounds usually using a soft copper lap which worked well.
Magazines and books have contained detailed articles on lapping. Live Steam October 1979 had one by J. Senft and the book "Using the Small Lathe" by L. C. Mason had a chapter on lapping.
Other articles:
http://www.neme-s.org/Model_Engineer_Files/2959-Lapping Bores #1.pdf
http://www.neme-s.org/Model_Engineer_Files/2960-Lapping Shafts #2.pdf
I'm sure there are many others.
Marv,
Well they are "number drills" aren't they. :big:
Dave

 

[deverett]

A tip on using wet 'n' dry paper when rubbing down: put a drop of washing up liquid in the water and the paper seems to work better.

Now a question on wet 'n' dry paper: Why is it so brittle? (When I am rubbing it on the metal
as compared to rubbing the metal with it laid on a flat surface).

Dave
The Emerald Isle

 

[90LX_Notch]

"Trailer queen" is a derogatory term referring to a vehicle that is trailered to an event rather then driven. The show car crowd is loaded with them. The term does not apply to full on race cars that aren't street legal and must be trailered.

 

[Holescreek]

if you finish washing your trailer queen before setting up at the tractor/car show car

Thanks for clearing that one up for me. I thought he was talking about his sister! Rof}

 

[cobra428]

I don't know for sure but I don't think tooth paste has any abrasive qualities. Tooth polish ie Pearl Drops (don't know if they make it anymore) had a warning....do not use daily, will destroy tooth enamel with prolonged use (or something to that effect).
Tony

 

[zeeprogrammer]

I don't know for sure but I don't think tooth paste has any abrasive qualities. Tooth polish ie Pearl Drops (don't know if they make it anymore) had a warning....do not use daily, will destroy tooth enamel with prolonged use (or something to that effect).
Tony

Googled it. There's Pearl Drops toothpaste and Pearl Drops tooth polish. Different things. You can still get either. According to wiki, the paste has some abrasive quality but is softer than enamel. I would think the polish is more abrasive.

 

[rickharris]

I don't know for sure but I don't think tooth paste has any abrasive qualities. Tooth polish ie Pearl Drops (don't know if they make it anymore) had a warning....do not use daily, will destroy tooth enamel with prolonged use (or something to that effect).
Tony

The majority, if not, all tooth past is very abrasive in a nice mild way that's what polishes your teeth - try it on a cloth on a copper pipe and see. the polishes are more abrasive.

 

[Foozer]

Been reading this discourse and am more confused than ever.

Could be simple semantics, sanding, lapping, polishing. Thought that the first two are similar cases. Both designed to smooth the surface i.e. reduce the differential 'tween the hills and valleys of the part surface. The finer the "grit" the less these height differences become.

Polish, I thought referred to a substance that filled in the valleys with its own surface above the peaks. the polish itself is of such a material that has a natural smooth, or obtainable by buffing, surface that exhibits a peak to valley differential far less than what can be obtained through sanding.

Of course my description is just as confusing as . . .

Robert