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Cleaning Granite Surface Plates- what common chemicals/products are safe to use?

Joined
Feb 1, 2019
Location
Central Texas, USA
The Short version of my question: I have 6 Grade-A 24”x18”x6” pink granite Starrett surface plates. They need some serious cleaning. Is Windex, rubbing alcohol, and/or ammonia safe for use on these? Is there some other common cleaner to use that I won’t need to order? Thank you.

Longer (or just plain long) explanation:
The high school machine shop I’m in charge of was left “as is” for like a year and a half when the teacher went on medical leave and everybody here says he was crap at taking care of stuff anyways (like, there is literally a tray filled with a COUPLE DOZEN randomly stacked ½” wide parallels in a crappy metal cabinet beneath a huge vent to the outside).
The machining program limped on without him for a couple semesters, then I was hired as an Instructional Aide but put in charge of teaching the four kids actually still in the program and getting the shop functional without any resources an actual teacher has (cue panic).
The machine shop is also the beginner welding shop, it's not really climate controlled, and there are large overhead doors and a system of automatic vents that let rain in when the winds are right. Plus the outdoor grinding booths were installed in such a way that there’s a 40-ish% chance that is there’s wind and the overhead doors are open, that’s blowing RIGHT on the lathes… and the precision metal storage cage.

When I get hired, there're no covers on anything- no rust preventative on anything. It’s taken me a while to get to the surface plates. 5 of the surface plates are in the shop (I haven't checked that they’re all Grade A, but they are all 24x18x6 Starrett pink granite) and have been exposed to acetylene soot build up, humidity, birds, bugs, and people thinking they were basically countertops. 2 of those 5 were in an unlocked area, so I assume (and have seen) students and staff setting down (hot?) welded scrap and angle grinders, bouncing v-blocks on them, and other things to break your heart.
I know I should look into re-surfacing on them, but I’m having trouble getting clearance to order more tool inserts and WD40, so right now I want to make sure I won’t cause more harm when I try to get the literal bird droppings and other oils and particulates off the ones from the cage. Also, no WypAll or the like in the shop. I’ve got the kids using the brown paper towels from the hand-wash station and some rags I got from the custodian. Should I track down some microfiber cloths for a “final clean” and before storing for the summer, or is that overkill?

I’ve seen some specific surface plate cleaners online, but I can’t get them quickly at all. I’m about ready to bust out the sewing machine to make covers for them myself, it’s so hard for me to order equipment. Other people online have mentioned Windex, ammonia, and rubbing alcohol: this sort of stuff I can get/commandeer from other school departments. But some people online also say “Sure! *slaps granite surface plate with grimy hands” spray whatever on the thing, slap down sandpaper and use it as a lapping plate! I use it as an anvil too! It’s fine……” so I just want to check with some people who use surface plates for more than just “flatness checks”.

Do ya’ll think/know whether Windex, rubbing alcohol, and/or ammonia is/are chemically safe for surface plates? What might work for me here? Any advice is greatly appreciated, and thank you.
 
Starrett surface plate cleaner might not be the cheapest but in my experience if you are doing high precision work its best not to be using cheap stuff on your surface plate
 
If they are grimy dirty plain old soap and water will be fine. Allow to dry (over the summer will be long enough) before using steel tools.

I am certain the surface plate cleaner Rock of Ages used to sell was Dow 409 bathroom cleaner.
 
When I sold plates and such I would tell you Starrett plate cleaner is the only thing to use.
I use Windex or other glass cleaners.
If really bad I'll start with some Tide diluted in a spray bottle.
I'll also sometimes (rarely) use lots of acetone to flush out the what I guess you would call pores or divots which you want clean to hold such dirt and dust.
I've also used WD-40 as the first cleaning pass which gives you much more time.
Bob
 
aaggh i would never ever use water as that swells up granite leaving a high spot til it dries and that can take a long time. and soap or anything that leaves a residue obviously that leaves thickness on the surface plate
 
ISO alcohol to cut the grease.
Follow with ammonia cleaner...then iso alcohol to clean the cleaner residue.

Use microfiber for the first pass, it will do a better job picking up the mess.
 
aaggh i would never ever use water as that swells up granite leaving a high spot til it dries and that can take a long time. and soap or anything that leaves a residue obviously that leaves thickness on the surface plate

Do you have real proof of that measured with the very expensive lab stuff to verify?
I have not been able to see or quantify this "swell" and sort of think it an urban myth.
Yes, if your lighting is not uniform over your plate or your HVAC flow is not I get the distortions due to temps.
I've just never seen the rock suck in water and grow. Perhaps it's a "cold" region thing?
Bob
 
Just scrape the crud off with a razor edge and WD40 it. Not like it's going to take cans and cans of WD40 just to clean a few plates.

Make some wooden covers (melmine coated or arborite covered) so that then they can continue to be used as countertops :D

I really can't imagine what a school shop needs a surface plate for, unless they're into scribing layout lines on a piece and cutting and filing to the line. Something I have never, ever done, and I'm 64 and been machining for 40 years. I do have a plate, and use it for inspection purposes, but it would be a rare case where school students would be inspecting anything much.
 
Am I the only one using brake parts cleaner? Cuts grease/dychem and drys really fast leaving no residue. I use it all around the garage shop and it seems perfect for this.
 
I use straight amonia for the plates I care for. It gets very clean, leaves no residue, and is not flammable.

Typet purly on my fone.
 
For many years, I used Rahn waterless surface plate cleaner (now available from Starrett's Tru-Stone division). The Rahn cleaner is a soft paste, very similar to many of the smooth (no pumice or other grit) waterless hand cleaners used by mechanics.

Sometime in the 1980s, I checked the Rahn MSDS and found 1) the product was actually manufactured for Rahn by one of the major makers of mechanics' hand cleaners, and 2) the composition of the Rahn cleaner was very similar to the hand cleaners. Since all of my local auto parts stores sold mechanics hand cleaner for about 1/10 of what the local precision tool dealers were selling the Rahn cleaner for, I decided to try the waterless hand cleaner as a surface plate cleaner.

In side-to-side comparison, I could find no difference between the two cleaners, and both of the surface tables cleaned with waterless hand cleaner have continued to meet their original grading (one A, one AA) on annual calibration.

It's worth noting that neither waterless surface plate cleaner nor waterless hand cleaner are truely waterless, but are emulsions of petroleum solvent and water with a few other ingredients mixed in. Any surface plate cleaned with either needs time to dry.

Finally, an excerpt from the US Federal Specification GGG-P-463c:

"100.1 Cleaning and moisture. Plates shall be cleaned thoroughly and given 6 hours to dry before testing for tolerance. (This time can be included in the temperature soaking tine.) Water base cleaners which have not dried out will make iron parts rust if left in contact on the surface overnight. Plates should undergo their drying time in a room with less than 50 percent relative humidity.

"100.2 Scratches and nicks. Whenever scratches and nicks appear on granite plates, the resulting burrs should be removed with a flat silicon carbide stone. Any bump which shatters the surface raises fractured material at the rim of the crater."
 
I really can't imagine what a school shop needs a surface plate for, unless they're into scribing layout lines on a piece and cutting and filing to the line. Something I have never, ever done, and I'm 64 and been machining for 40 years. I do have a plate, and use it for inspection purposes, but it would be a rare case where school students would be inspecting anything much.

During my apprenticeship the first tools you used were a height gauge and layout blue, followed by a hacksaw and file for several projects before moving to scribing and center punching holes for work on a drill press.

My technical school has several granite plates, a climate controlled inspection room and some parts were checked with a sine-bar and gauge block build ups so students could never say they weren't familiar with those tools because we had used them years before they did!
 
It is not easy to damage granite. Despite all the abuse these plates have seen, if they came to the school not already worn out, f'll be they will check out well if you can find someone with the needed equipment. I'd ask around to see if there is someone around who is interested in metrology and would check them out for you at no cost just to help you out as a teacher.

I use layout fluid remover (contains ketones and other solvents) available in aerosol for initial cleaning up of old Hi-Spot blue. It cuts the oily dyes easily and well. If I am doing some very fine final scraping of a straight edge, I worry about cooling the stone with solvents or water-based cleaners. So, in that case I use mineral oil as it is not volatile and does not momentarily cool the stone locally. But that is being pretty fussy. Mineral oil will cut the dye, but not nearly as well as the remover.

Starrett does not raise a concern regarding water use causing swelling. Here is what they say:
"[FONT=&quot]The amount of time required for the plate to normalize will vary with the size of the plate, and the amount of chilling. An hour should be sufficient for smaller plates. Two hours may be needed for larger plates. If a [/FONT][FONT=&quot]water[/FONT][FONT=&quot]-based cleaner is used, there will also be some evaporative chilling.[/FONT][FONT=&quot]The plate will also retain the water, and this could cause rusting of metal parts in contact with the surface. Some cleaners will also leave a sticky residue after they dry, which will attract airborne dust, and actually increase wear, rather than decreasing it."[/FONT]
If Starrett is not talking about swelling, I very much doubt it is a concern. Here is the link to their discussion of surface plates and surface plate maintenance. Precision Granite FAQs

Denis
 








 
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