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72" Brown & Sharpe Straight Edge Tests

M.B. Naegle

Diamond
Joined
Feb 7, 2011
Location
Conroe, TX USA
In this thread I'll be posting the results of tests I'll be conducting on my Brown & Sharpe 72" Camel-back Straight Edge.

This discussion started here: https://www.practicalmachinist.com/vb/machine-reconditioning-scraping-and-inspection/large-straight-edge-questions-354079/

First off, I want to state that the goal of these tests is to:

1. Accurately determine how flat the straight edge is before and after it is re-scraped, using an appropriately sized surface plate.

and 2. Compare these findings to other methods of determining flatness that don't involve a large enough surface plate.

I'm not doing this as a way to cut corners, but rather to see how these other methods actually stack-up and why. I want to better understand how these large straight edges sit and flex so that I can handle and use them well enough to take full advantage of their size.

72 BS 08.jpg
 
Test #1

Last Thursday night, I started with a few tests out at swatkins place using his 48"x72" Grade B plate. This first test involved having the straight edge sit flat on the surface plate and using feeler gages to check the gap between the SE and the surface plate.I only tested it in one position as a portion of the plate is out of tolerance. The attached file shows the details, but in general, it showed to be touching on all 4 corners but to have a .0025" bow in the middle.
 

Attachments

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I have a 5 foot SE of some origin. Not a Camel back, straight sided.

I've always wondered if the right way to evaluate it is to suspend the device from it's ends, or from the airy points.

Sitting flat on the 3'X5? DoAll .0001 granite never seemed to represent anything useful. Too many points of contact are possible. I would love to hear your take on that.
 
Test #2

The 2nd test I did was to have the SE resting on a pair of 1-2-3 blocks 1/3 from the ends, and sweep a test indicator along the edges. This method showed a higher resolution from the feeler gage test but showed a similar bow.

I'm having trouble with the file size on this one. Once I figure out a smaller format I'll upload the test sheet.

In both these tests, the middle of the SE could flex at least a .01" front to back and spring back. Both Steve and I agree that the Brown & Sharpe curved back design is a bit "flimsy" compared to the King truss back design. IMO it should be reliable, but the rules about where to support, lift, hinge, etc. are going to be necessary to get good results when printing machine ways.

It seems to me that the heavier straight edges (per foot) don't have this issue, but are a pain to handle. B&S seems to be some of the lightest SE's out there, but are consequently less resistant to flex.
 
Test #3

The next test was to print the SE, which didn't do much but confirmed the bow.

The PPI average ranged from 5 to 10 at the 4 corners, 6" in from the ends, then nothing.

One other thing I found was that when taking the temperature reading from the SE, which I was using a hand held laser temp. sensor, the temp fluctuated +/- 2 degrees in various areas. Probably not going to have a huge bearing on things, but we decided to leave the SE in Steve's AC'd shop until the next tests and see if the temp. normalized.

The next test will be using a Master Precision Level (Starrett 199) and see if it will show the bow in the SE and to what accuracy. I took a stab at it that night but I'll need to get the SE more stable on it's back first. The slightest movement is throwing the level way off (of course) and it isn't level on it's blocks. So I'll need to add some kind of adjustable points under it to run that test.

To be continued....
 

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One other thing I found was that when taking the temperature reading from the SE, which I was using a hand held laser temp. sensor, the temp fluctuated +/- 2 degrees in various areas. Probably not going to have a huge bearing on things, but we decided to leave the SE in Steve's AC'd shop until the next tests and see if the temp. normalized.

If it's an IR sensor without emissivity adjustment, you'll have a tough time getting an accurate reading. The reflectivity of metal items makes a contact thermometer a more reliable choice to get good numbers.
 
what length is the level you will use ?
I hope to be sitting an 18" level on a 30 " parallel on the 6ft SE's in the next fortnight. I am thinking that the level will have to be 'located' on the parallel somehow to ensure that it doesn't move and rule out one contact area variation. My thoughts are to take readings with the 30" 'foot' then 18" and see if they repeat in the manner expected. Then swap to a 12" foot. The Hilgar Watts levels I have sit on 3" long feet at each end (4 off effectively via the V groove cut into the level base).
Its going to be interesting to see how your numbers match up - if I can I will try and repeat the tests I do on my B&S 6ft CBSE. Like you, I think it certainly looks more prone to flex / movement compared to the heavy weight construction of the other SE in my collection.

All the best
Mat
 
I will be posting a photo on the OK class thread showing how we tested a granite table. Remember one thing. I scrape straight-edges to .00005" per 12" So if you are 72" long you can be out .0003". That is Jig Bore spec. If you are going to scraping a lathe bed the spec you scrape to is .0002" per 12". Then the spec on straight edge would be more or approx. .0006" about 1/2 of what you need. Plus if your in a unheated shop it is relative to what you have. All you can do is get it to repeat and as best you can get it. Not sure we discussed it, but test it at the bottom (or top when not flipped over) basil or airy points depending on MFG. Move the blocks and see if the SE improves or get worse. I have a 10' Brown and Sharpe camel back I plan on testing in the next week.
 

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what length is the level you will use ?
I hope to be sitting an 18" level on a 30 " parallel on the 6ft SE's in the next fortnight. I am thinking that the level will have to be 'located' on the parallel somehow to ensure that it doesn't move and rule out one contact area variation. My thoughts are to take readings with the 30" 'foot' then 18" and see if they repeat in the manner expected. Then swap to a 12" foot. The Hilgar Watts levels I have sit on 3" long feet at each end (4 off effectively via the V groove cut into the level base).
Its going to be interesting to see how your numbers match up - if I can I will try and repeat the tests I do on my B&S 6ft CBSE. Like you, I think it certainly looks more prone to flex / movement compared to the heavy weight construction of the other SE in my collection.

All the best
Mat

Both Steve and I have a 12" Starrett #98 that are good to .005" per foot, that will be good to "rough level" the SE, then Steve has a 15" Starrett #199 that is good to .0005" per foot that we can fine level the SE and take our readings.

I'm window shopping for my own master precision level. the Starrett #199's are plentiful as are some Import ones that claim accuracy up to .0001" per 10". We'll see what falls into the tool box....
 
I will be posting a photo on the OK class thread showing how we tested a granite table. Remember one thing. I scrape straight-edges to .00005" per 12" So if you are 72" long you can be out .0003". That is Jig Bore spec. If you are going to scraping a lathe bed the spec you scrape to is .0002" per 12". Then the spec on straight edge would be more or approx. .0006" about 1/2 of what you need. Plus if your in a unheated shop it is relative to what you have. All you can do is get it to repeat and as best you can get it. Not sure we discussed it, but test it at the bottom (or top when not flipped over) basil or airy points depending on MFG. Move the blocks and see if the SE improves or get worse. I have a 10' Brown and Sharpe camel back I plan on testing in the next week.

That's what I'm planning on, and it falls right inline with what the Busch Rep. I talked too claims for their straight edge tolerances. I'd LIKE to scrape mine to the highest accuracy possible, if only because I'll likely fall short. I can always touch it up again in the future, just so long as I can actually see and understand how and why I would need to.
 
Both Steve and I have a 12" Starrett #98 that are good to .005" per foot, that will be good to "rough level" the SE, then Steve has a 15" Starrett #199 that is good to .0005" per foot that we can fine level the SE and take our readings.

I'm window shopping for my own master precision level. the Starrett #199's are plentiful as are some Import ones that claim accuracy up to .0001" per 10". We'll see what falls into the tool box....

Do not get anything that claims more than 0.0002"/foot. The stickiness of the spirit in the vial makes it almost impossible to be more accurate than that. Also, the 0.0002" vials take about 4 times as long to settle than the 0.0005", don't know why, but that is my experience. I have a Starrett 199 and have 0.0002" vials on my Kingway clone. The Starrett is a much more "stable" level.

dee
;-D
 
Both Steve and I have a 12" Starrett #98 that are good to .005" per foot, that will be good to "rough level" the SE, then Steve has a 15" Starrett #199 that is good to .0005" per foot that we can fine level the SE and take our readings.

I'm window shopping for my own master precision level. the Starrett #199's are plentiful as are some Import ones that claim accuracy up to .0001" per 10". We'll see what falls into the tool box....

My 42" level were to "fall into" your toolbox, it'd go right out the bottom, too!. Heavy bugger!

Hardly ANYBODY made a bad Master Precision level, actually. Some are just nicer than others. Sort of the "masterpiece" for a whole company or a whole country. Even the Chinese made ones "can work".

Metric and Imperial measure numbers can confuse. Pay attention to which you are looking at, lest you think you are seeing a level half as good / twice as good as some other. Only a very few are dual-marked.

Better you get a decent one sooner than later. Vet it yourself. Expect to scrape it if bought used.

A great many things are far more than just twice as fast if you have pairs. One level constantly having to be moved, each setup tedious, is a RPITA.

You won't get "stuck". You can always get a better one and/or sell or trade a lesser one.
 
My surveyor friend is back in town so we'll be doing the his tests this week. I went out to Steve's last night to pick up the 72" SE.

It's had plenty of time to normalize in that environment so I re-ran the indicator test while I was there. The surface and ambient temperatures were the same and the temperature at different points around the SE was all within a degree. As a side test, I held my hand on the SE for 1 minute and found that that spot went up in temperature 3 degree's in that time and immediately started to go back down with my hand removed.
 
I have had a few PHD's take the classes and I have asked them their opinion on hand heat changing parts. All agree that wearing a glove will help cut down the chances, but they stress that we are working in a machine shop environment and not in a laboratory. A few years back Abomb79 showed how he took his 3/4 x 3 1/2" x 12" practice plate in his hand and walked 10' from his vise to the surface plate to blue it up.

One of the members here had a fit saying his hand heat would distort the part. I bought a infrared temp gun and started to measure hand heat changing the plates. I never saw any change. One of the PHD's who attended a Keith Rucker class said that was insane because as soon as you lay the plate down on the granite plate the temp changes. So worrying about hand heat on a 72" Brown & Sharpe Straight-edge is much to do about nothing in a machine shop atmosphere.


Now if you are talking about a level then I have seen things change. That is why many precision levels have a plastic cover or buttons you pick it up from. But again as you set it down on a different tempted surface it changes. I say wait 10 seconds for it to settle. Your young and want to discover something and I applaud you for experimenting but in my opinion you have way to much time on your hands...lol...get a girlfriend and have some real fun...LOL Rich
 
I have had a few PHD's take the classes and I have asked them their opinion on hand heat changing parts. All agree that wearing a glove will help cut down the chances, but they stress that we are working in a machine shop environment and not in a laboratory. A few years back Abomb79 showed how he took his 3/4 x 3 1/2" x 12" practice plate in his hand and walked 10' from his vise to the surface plate to blue it up.

One of the members here had a fit saying his hand heat would distort the part. I bought a infrared temp gun and started to measure hand heat changing the plates. I never saw any change. One of the PHD's who attended a Keith Rucker class said that was insane because as soon as you lay the plate down on the granite plate the temp changes. So worrying about hand heat on a 72" Brown & Sharpe Straight-edge is much to do about nothing in a machine shop atmosphere.


Now if you are talking about a level then I have seen things change. That is why many precision levels have a plastic cover or buttons you pick it up from. But again as you set it down on a different tempted surface it changes. I say wait 10 seconds for it to settle. Your young and want to discover something and I applaud you for experimenting but in my opinion you have way to much time on your hands...lol...get a girlfriend and have some real fun...LOL Rich

I know I know, just being thorough;).

The B&S is a more flexible casting than others, but from what I saw, the most it will change from hand-heat and/or environment differences is a few tenths over the whole length. If you let is sit half under a heat lamp or something, then you might get a little more, but that's only if you are TRYING to distort it. I'm typing up the results of the test, but I think there was more error from the indicator needle bouncing in and out of the scrape marks than anything else.

My plan is to make sure the SE is the same even temp as it's surrounding during the final scraping passes. The rest of the time doesn't matter, but then I'll know that in "perfect conditions" I can rule the temperature factor out. That would only be for jobs that warrant a high level of precision, not the usual 20PPI jobs.
 
Also think about the work envelope of the cutter or grinding wheel. It is say 1/2" and your measuring 72". Have to have a PHD to do the math. Never see and error from a 72" surface. More chance of distortion from dull cutter or dull wheel, heat from both, etc...

Your a good machinist and think about the good parts your making on a worn out machine. If you scrape a machine and make it 100 times better then the worn ready for scrap yard machine...lol.. a few tenths in 72" is pretty minor. I am anxious to see your friends results too. Rich
 
If it's an IR sensor without emissivity adjustment, you'll have a tough time getting an accurate reading. The reflectivity of metal items makes a contact thermometer a more reliable choice to get good numbers.
We had similar issue with battery plant maintenance using midtronics gear in that temperature readings not consistent due to inconsistent targeting and surface textures

Did our homework...

Result was stupid simple.

Made battery number labels that we placed on same position on all units so consistent target place and texture.

For the tool just place a strip of paper based tape in places where temp is to be measured and if equipped with a spot laser add an "X" to each one.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 








 
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