Video: Scraping a precision level.

Youtube video showing scraping a Pratt Whitney level using quarter moon scraping/flaking
technique.

Restoring Tom Lipton's Level Frame - YouTube

In before every one tells you how they would do it different!

I liked it, never seen a electronic indicator used.

Gary Cude sent me a link to that yesterday. That's not scraping, that's flaking using the Moore style as he doesn't blue it up and he isn't getting any depth. It looks good but that's not scraping. He also is using the indicator wrong, it should be using it laterally or the stem should be running parallel to the level and not at right angles.

Hunter H has been working with a Old Moore employee who showed him how to scrape using the Moore method. Hopefully one of these days he will do a You Tube and share his new talent.

In this video the scraper is using the Moore style to scrape the and not flake. Rich

Rebuilding older machines using the hand scraping method - YouTube

Robin, the presenter in the YouTube link, covered a lot of material in depth ad so deserves detailed comment.

First, he never said he was "scraping the level in" although that was the initial plan. He stated his grinding job was probably closer than he could scrape and pointed to 30 micro-inches linearity thwartships and 20 longitudinally on his instruments. I agree but with a reservation I discuss below. My experiments with several combinations of transfer and contrast media (Prussian blue and red lead are still the best over-all in my book) suggest 40 - 50 millionths is about the lower limit of readable scraping indications. If he scraped the surface in to his best accuracy he might have satisfied sacred tradition but there might be a small sacrifice in flatness.

He went on to mention that his work with a scraper was unnecessary but was included for appearances sake. You notice there was hardly a ripple in the indications of the gage amp readings. But, we all have to admit the pattern and flash of the surface he finished was most attractive.

Something is nagging at me about the way the linearity of the level's reference face was proved. The level was dragged past the gage head registering it was parallel to that point on the plate. If the level was stationary and the gage head stand was moved over the surface plate to scan the level's reference face, the level would be proved by the flatness of the surface plate. If the level was reversed and a second set of readings taken with the gage head stand following the same track the error could be calculated and the true error of the level's reference face determined independent of the accuracy of the plate. I think. My head is spinning.

I hope all paid attention to the presenter's demonstrations of the effect of heat on dimensional and geometric accuracy, lead drag, etc..

He also mentioned Airy points Vs Bessel points and the uses of each, a distinction I've been unaware possibly because the distinction occurs in the third decimal place of the constant..

Airy Points and Bessel Points - Engineering Notes

Anyone note his use of precision diamond ground stones for burring scraped surfaces and dressing mag chucks? I tried that once and after a few uses the stone accumulated a $hitload of pins and scratched finishes .I wonder what he did differently?

I would liked for Robin to have discussed the accuracy of his granite flat on which millionths were hanging in the balance.

Another point Robin missed: master precision levels are factory scraped deliberately concave by 0.0002 to 0.0005" chord per foot. The theory goes this eliminates random teeter when the level is placed on a flat surface and if supported symmetrically when spanning gaps ensures a steadier end bearing. The concave is small but necessary I'm told. I've scraped several levels flat but never noticed any uncertainty of readings. I suspect the effect of a concave scraped level reference face is one of those distinctions without a difference beloved by marketers - but I hesitate to assert this notion as fully credible.

I thought the Robrenz video most informative. I learned several subtle points. I guess there's hope for me: 75 in a few weeks and still learning stuff/

Forrest,

Thanks for adding and highlighting. I wondered too if he would address the intentional slight concavity on the sole of a level frame but there may be sincere difference of opinion about that.

I'm not enough of a theoretical mathematician to prove your proposition about error cancellation but my gut sense is you're right. Somewhat like double entry bookkeeping. If you map consistently and write down the numbers it should be possible to separate surface plate variation from the measured part variation. Of course down at those measurement levels it might get harder to separate random noise the way he was trying to eliminate the change introduced by cable flop (tech term).

I'm curious about the diamond ground stone business too. There's plenty of mention of flattening stones but I think this is the first time I've heard reference to diamond grinding. He suggests it as the ultimate, but I'd wonder how different it really is from lapping a stone with loose compound. We grant that the lapping process can produce flatness so why is diamond grinding superior? Diamond will cut the stone more easily but accuracy should still be dependent on the accuracy of the underlying machine. Couldn't hand lapping get to the same place if properly done?

Some interesting things here. Overall a good video and for sure in depth.

I was more interested to get to the scraping part, which we can all agree was flaking.

I skipped over the filling in of the lettering ect, I would not see a reason to mess with this.

As Forrest mentioned, you want your levels to be slight concave, for reason to make sure you are not pivoting on the center and we all know when in use you will slide the levels along a surface, hence the ends will wear a bit. So you want you middle to be slight concave. When you get too much wear and you are say dead flat-then it is time to re scrape the bottom.

Professional Instruments Company of Hopkins, Minnesota makes air-bearing spindles, and if my recollection is correct, they have supplied a fair number of their spindles to Moore. They also sell "Precision-Ground Flatstones" which they diamond-grind out of two-grit sharpening stones and then put up in an elegant wooden box. From memory, the Professional Instruments Flatstones are roughly 6 inch x 2 inch x 3/4 inch, and the current price for a two-stone boxed set is US$ 400.

Here's a link to Professional Instruments' website page containing their instructions for using the Flatstones. Gf-5 Precision-Ground Flatstones | Professional Instruments Company

Professional Instruments also makes available, on their Useful Information webpage, a number of papers that will probably be of interest to those interested in such things: Useful Information | Professional Instruments Company

John

The levels I have are made by VIS in Poland and they are actually have a machined clearance in the center and only bear on the ends. They also have a V shape for working on round objects.

I'm always amazed by just how pedantic people can be. I just can't wrap my head around it.

ewlsey said:

The levels I have are made by VIS in Poland and they are actually have a machined clearance in the center and only bear on the ends. They also have a V shape for working on round objects.

I'm always amazed by just how pedantic people can be. I just can't wrap my head around it.

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I had to look up the meaning of pedantic... I learned something today.
Googled and found this:
Pedantic means "like a pedant," someone who's too concerned with literal accuracy or formality. It's a negative term that implies someone is showing off book learning or trivia, especially in a tiresome way.

You should hang out with more engineers. You'll learn all about pedantic people.

I have also scraped levels for years and always ask a student to bring one to the class so they can scrape them. When I scrape them I scrape them flat and on the final 2 passes I relieve the center 40% low by scraping the high spots low on average .0004" low. As others have said is they wear on ends when people "seat" (pushing forward and back about 1 to 2") them. Then when they are low I double check by having the bubble in the middle and press on each end and watch the bubble. It should not move a lick when it is finished. I have blued up brand new Starrett 199Z levels and they are scraped the way I explained. Rich

what is a microinch? micro is 10^-6. so 0.5 microinch is 0.0000005" or 0.000013 mm. that the accuracy of those spindles? something must be wrong.

Alternitive to Grinding

TGTool said:

I'm curious about the diamond ground stone business too. There's plenty of mention of flattening stones but I think this is the first time I've heard reference to diamond grinding. He suggests it as the ultimate, but I'd wonder how different it really is from lapping a stone with loose compound. We grant that the lapping process can produce flatness so why is diamond grinding superior? Diamond will cut the stone more easily but accuracy should still be dependent on the accuracy of the underlying machine. Couldn't hand lapping get to the same place if properly done?

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Hi All,

I use an alternative method to true my stones. I buy inexpensive Harbor Freight
stones. They are fairly soft, so they can be trued very quickly, and the method I
use is the 3 stone method - which is the same as the 3 plate method that is used
on surface plates or any other item(s) you want flat. This is called, by engineers,
voting out the errors.

Once you have your three stones, you can use them by themselves, or use them to
true up any other stones. At this point I use the the three stone method only using
all four stones. If the fourth, different, stone is very hard it takes awhile to true
it up again, but it works very good. Just don't let your good scraping stones get
badly warn.

I use this method with all my good stones. If you let a stone get to far out of true
better to just purchase a new one and keep it in good shape using this method on a
regular basis.

Paul Hoffman

Diomnd lapping or sharpening plates

I have been using diamond lapping or sharpening plates for over 20 years and can't imagine a shop without them. Not the cheap plastic backed honeycomb crap but 1/4" thick plates with mono crystalline diamonds trapped or sealed onto the plate.
Some of the plates get used every day a still cut. I have about 10 with varying grits, concentrations and sizes.
Flattening a water stone takes very little time and polishing faces or removing swirl marks is fast and easy. I am always amazed at the number of people who have never used them.

I still use lapping plates with loose compounds and also diamond past on CI wheels but every tool has its advantages. Lee Valley Tools sells a few sizes and grits.

Give them a try, Poly crystalline are cheaper and cut fast but do not last as long.

Al

This is all very interesting, and speaking of pedantic: Forrest, in speaking of the relieved base, I believe you mean sagitta, not chord. Stepping down from my soap box, and back to tigging.

E.F. Thumann said:

This is all very interesting, and speaking of pedantic: Forrest, in speaking of the relieved base, I believe you mean sagitta, not chord. Stepping down from my soap box, and back to tigging.

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Yep. Mis-use of the word "chord." You'e right. My bad and I should know better.

Chord is the span of a sector and the sagitta is the length of a perpendicular from the center of the chord to its intersection with the arc. I always called it "chordal height" borrowing from gear terminology because no-one knows what a sagitta is whereas "chordal height" can be intuited.

Don't apologize for politely pointing out an obvious error. Clear information exchange trumps preserving egos every time.

Dude takes a perfectly good level and ruined it for cosmetic purposes.

Same as a concave scraped level

How do you qualify a concave surface?

Where do you get a convex master?

How do you produce a convex master and qualify it?

On purpose

Forrest Addy said:

Chord is the span of a sector and the sagitta is the length of a perpendicular from the center of the chord to its intersection with the arc. I always called it "chordal height" borrowing from gear terminology because no-one knows what a sagitta is whereas "chordal height" can be intuited.

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Holy Geometric Goodness, Batman! I have not seen or heard "sagitta" since the school daze. Yikes. Nice pull, E.F. Thumann! I have always done as you have, Forrest.

Forrest Addy said:

Don't apologize for politely pointing out an obvious error. Clear information exchange trumps preserving egos every time.

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Turth. Cheers!

Heavey Metal said:

Dude takes a perfectly good level and ruined it for cosmetic purposes.

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How do you figure he ruined it? The bubble is only accurate to .0005/12" so the finish off the grinder was way better than needed. Any other work done was just cake decorating.

I do find it funny that these guys will worry themselves so much about trying to make this tool perfect and explaining every step in mind numbing detail, all so Tom Lipton can "level" a Bridgeport in his hobby shop. A $.99 pocket level would do the job just as well...

ewlsey said:

How do you figure he ruined it? The bubble is only accurate to .0005/12" so the finish off the grinder was way better than needed. Any other work done was just cake decorating.

I do find it funny that these guys will worry themselves so much about trying to make this tool perfect and explaining every step in mind numbing detail, all so Tom Lipton can "level" a Bridgeport in his hobby shop. A $.99 pocket level would do the job just as well...

Click to expand...

All of which brings us around to pedantic again, doesn't it. Like sagitta, a lot of the back and forth is really about two posters both being pedantic, even if it's never named.

BTW, I've always visualized "h" in the chord formulas and can't remember what I've called it if it ever came up in a discussion. Chord height probably. Calling it sagitta might have been technically correct but wouldn't have brought any illumination to the conversation.

No criticism, by the way.