Using my gauge block wrong?

[drcrea]

I'm new to metrology and have been watching a bunch of youtube videos on how to measure various things. I came across one such video by Suburban Tool from about 8 years ago where they were measuring a surface plate for flatness. Not to certify or anything, but just to get a general idea of the flatness. In the video he was using a gauge block between the test indicator and the surface plate. So after watching the video, I grabbed one of my brand-new Mitutoyo Grade-AS-1 gauge blocks and my test indicator and I was off to collect some measurements.

After taking a number of measurements, I noticed that I was imparting some light surface scratches in my highly polished, previously perfect, gauge block. Seems sliding the block around on the granite surface left very, very, light scratches. Now one side is no longer a perfectly mirrored surface

My questions:
Should I not have used my gauge block in this manner?
Is it normal, and expected, that a gauge block will get light scratches in the mirrored finish from use and this is perfectly fine?
Is there anything I can do to restore the perfect mirror finish, e.g. like polishing with toothpaste or something similar, that won't change the block? (it's that fine)

 

[benmychree]

It would seem that your surface plate is not particularly clean. it is more like a lapping plate with coarse abrasive particles on it. In my opinion, gage blocks should not be used in situations where a lot of sliding is involved, perhaps a 123 block would be a better choice, in addition to s thourough cleaning of the plate.

 

[Dabbler]

I agree.

Here's a dump of ideas surrounding the use of a surface plate and gauge blocks: They are so often used together that they have to be treated with the same respect...

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Whenever you use a gauge block, everything has to be surgically clean... The only time a gauge block is rubbed over anything else is on another perfectly clean gauge block in order to wring them into a gauge block stack. Another essential skill in using gauge blocks.

Unless your scratches raised a burr, tiny surface scratches won't affect your block in any meaningful way.

You do cover your surface plate? You do clean it thoroughly before and after use? You only allow thoroughly cleaned items to touch the surface plate? You only use your plate in a place that is as dust and particle free as possible? For instance, I won't uncover my shop surface plate within 24 hours of using a grinder in the garage shop. I have another surface plate in my basement for measuring if I need to do stuff right away.

I use pre-wetted ammonia wipes to clean my surface plate, as they are essentially lint free, and even then, after the plate dries, I check again with my hand. I wipe all tooling with the same wipes, but use a low-lint polyester towel to dry off the tool, and then my hand again to wipe away any fibres that might have been shed off the cleaning cloth or wipe.

 

[stupoty]

I have a cast iron surface and I put a couple of scratches in when moving my height gauge last week , I had given it a wipe over but a few bits of grit had escaped the clean.

I like to put a little oil on the plate to help with sliding about but i'm not sure if this is done with granite ones.

Stu

 

[Bone Head]

Oil on a metal plate would be a good protectorant. No oil on granite plates. If you have a reasonably good granite surface plate use a suitable cleaner. If you have compressed air handy blow it off, then denatured alcohol and a clean microfiber cloth is good.
Clean it daily and for the love of all things holy DO NOT beat on it with anything!

 

[jbaccell]

I have read about and actually now use GoJo waterless hand cleaner (without pumice) on my granite surface plate with good results. I was using Windex prior to that.

 

[sdelivery]

Did you debur your surface gauge?
Second on surgical cleanliness.
For what you described you were doing I probably would have "spilled" a little alcohol on the plate to act as a lubricant.

 

[drcrea]

Did you debur your surface gauge?

No. I was using a brand new Mitutoyo gauge so I didn't think that process was needed. I also don't have a stone for deburring at this time.

I read that Mitutoyo recommends their Cerastone for gauge blocks and also running the stone across the surface plate. I looked and these stones are somewhat expensive, ~250.00. Is there less expensive options? Recommendations for a deburring stone that I can use on the gauge blocks?

Are these the same as ceramic water stones? I can get a 15,000 ceramic water stone for half that price.

Second on surgical cleanliness.

I think I'm cleaning it good. First I wipe it clean with ammonia, per Don Bailey recommendation. Then I clean it with Goop, wipe it dry and then another cleaning with ammonia. Finally I wipe with with my bare hand. It feels smooth and silky.

I do notice that even the bottom of my surface gauge, as I slide this around, shows signs of being polished. Could it be that my surface plate isn't lapped fine enough? It's not an expensive plate, Chinese Gray granite I think, very flat though, grade A.

My gauge block isn't damaged, beyond the cosmetic issue. Wrings better on that side that the other. In fact the act of wring leaves very fine scratches too. At least it does for me. This is similar to what the surface plate did, just a lot more.

 

[Dabbler]

In fact the act of wring leaves very fine scratches too.

@drcrea There is all kinds off floating dust in the air, some of which is abrasive. My good set of gauge blocks (ironically offshore) don't have any scratches in them, despite 35 years use. (okay, just one on one block, but my fault). Perhaps you are pressing too hard when wringing the blocks together? It doesn't take much, just firm pressure. Contrary to old world wisdom you are not wringing the air out. You are introducing the surfaces together, and they are attracted together by atomic forces - some debate amongst physicists about how it works, but the air pressure theory has been disproven by using a vacuum and wringing at various pressures.

I bought an extra used set at auction, and one of the members sold me his extra blocks from an auction find (with which I nearly completed the heavily used set) I use the 'shop blocks' for most of my work, and use the pristine offshore set to do metrology.

If you want to redo the sliding thing, you can get individual ceramic gauge blocks for a price. Sometimes an inexpensive one (smiley face).

Are these the same as ceramic water stones?

In a word, no. Those ceramic stones still need to be precision ground, and unless you are spending north of 200$ they aren't. to get them to be a precision surface, you have to surface grind them using a diamond wheel. This removes enough of the wheel to make precision stones (especially ceramic ones) expensive...

There are about 25 guys selling paired precision ground stones out there for around 100-150$ The price on the Mitutoyo Cerastone isn't really out of line. Some of the sellers are youtubers, and have videos with Precision ground stones in the title somehow.

You can make your own precision ground stones using the 3 plate method - but I'd only do that with 4000 grit stones and up, and you would have to buy 3 of them, again you are up over 150$. In this case there is no free lunch.

Your brand new Mit Hieght gauge shouldn't have any burrs on it. You can tell by wiping it with your hand, firmly. Frankly if you have a brand new Mitutoyo height gauge, at that price, I'd use **their** recommended stone. My Mitutoyo Height gauge was bought for a song, so a Cerastone is too rich for me...

 

[Dabbler]

First I wipe it clean with ammonia, per Don Bailey recommendation.

I use a container of prewetted ammonia wipes. I settled on that because of Don Baily, but then I called Standridge Granite and they confirmed it. I don't do anything else, however.