-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
gage blocks
- Thread starter frankie
- Start date
Couple of things. One is air pressure, since the finish is so good, there is practically no air between them, so they are pressed together. The other is a little difficult to explain, but essentially, there is a weak molecular bond that develops between surfaces that have such a high percentage of true contact. That's why they don't "stick" if they are the least bit dirty. I recently read an article that explained it a bit. I'll try to find it.
From Wikipedia:
"1) Air Pressure applies pressure between the blocks because the air is squeezed out of the joint.
2) Surface tension from oil and water vapor that is present between the blocks.
3) Molecular attraction occurs when two very flat surfaces are brought into contact. This force causes gauge blocks to adhere even without surface lubricants, and in a vacuum.
It is believed that the last two sources are the most significant"
John
"1) Air Pressure applies pressure between the blocks because the air is squeezed out of the joint.
2) Surface tension from oil and water vapor that is present between the blocks.
3) Molecular attraction occurs when two very flat surfaces are brought into contact. This force causes gauge blocks to adhere even without surface lubricants, and in a vacuum.
It is believed that the last two sources are the most significant"
John
John, although it might be perfectly true, I'm not so convinced about the oils and water vapor. I remember reading that, seems like on the Webber site, so being the naturally curious guy I am, I took a pair or 1" blocks, ultrasonically cleaned them, acetone washed them, kept them in a climate controlled lab to soak, all the while in a sealed container with dessicant, and in the room, which was maintained at 68°f and 50% RH, wrung the blocks. I'm pretty confident that there was almost no oil or water vapor there, yet they seemed to wring together normally. I was in the process of measuring the attractive forces when I got busy and never got back to the experiment. It would have satisfied my curiosity if nothing else. I'm leaning more on the molecular attraction.
You remind me of me.:thinking: I was always experimenting at work, every chance I had. It helped out a lot after I got my own shop together, after retirement. Wish I hadn't waited so damn long to retire.
Word of advice to all young-ins', retire as soon as possible.:lmao:
I can't wait... :whistle:
If the room was at 50% RH, there certainly was water vapor when you wrung them together. I wonder what would happen if you put them in a bag with dessicant and wrung them together while in the bag being careful to keep the dessicant off the blocks. Then, no water vapor for sure...
We have a vacuum chamber here at work (goes down to < 10[SUP]-5[/SUP] Torr). If air is holding them together, they should separate in a vacuum...
I'll see if I can drum up some desiccant (silica gel will get me to about 2-3% RH) or calcium chloride (should get me to about 7% RH in the bag if memory serves me right). After they're wrung, I can take 'em out of the bag and put them in the vacuum chamber.
My gut tells me it's air pressure or molecular attraction (akin to surface tension in a liquid). I'm a bit skeptical about the latter because surface finish is all important with regard to wringing. Molecular attraction should sort of work even with a rougher finish. From what I've seen, wringing works or it doesn't...
I'll see if I can find some time to "play" before I leave.
John
Molecular attraction it is for sure... Turns out it was a much more simple test than I thought since I forgot we had liquid and gaseous nitrogen in house.
First I needed to find out the minimum overlap of the two gauge blocks that would allow them to stay together while suspended. I used the same wring overlap for the whole test.
1) Washed gauge blocks with Hypersolve, followed by isopropyl alcohol (to get rid of any moisture), followed by MEK. If anything they wrung together BETTER after being cleaned. So, I don't buy oil being responsible.
2) After cleaning a second time and handling only with clean room gloves, I put them in a dry nitrogen purged oven for 10 minutes to drive off any moisture that may somehow be there.
3) Wrung them together in a HEALTHY blast stream of dry nitrogen (0.003% RH at room temperature). They wrung and held together the same as in air.
4) Left them wrung together after step 4 and put them in a small vacuum chamber with one of the gauge blocks completely suspended horizontally (cantilevered). In other words, nothing holding it to the other block but the wring. Gravity would make the canterlevered one simply fall off if loss of adhesion occurred. I pulled a quick vacuum to about 10[SUP]-2[/SUP] torr (about 29.9 in-hg). Going to the full 10[SUP]-5[/SUP] requires me to use the cryopump or turbomolecular pump system and that takes a goodly while to get those last remaining air molecules out. I don't believe that is necessary to prove the point - just to get rid of most of the 14.7 psi of atmospheric pressure. Guess what? The blocks stayed together!
While not the most scientific methods were used, I think most would agree that it's a pragmatic test and proves Tony's experience is correct.
John
First I needed to find out the minimum overlap of the two gauge blocks that would allow them to stay together while suspended. I used the same wring overlap for the whole test.
1) Washed gauge blocks with Hypersolve, followed by isopropyl alcohol (to get rid of any moisture), followed by MEK. If anything they wrung together BETTER after being cleaned. So, I don't buy oil being responsible.
2) After cleaning a second time and handling only with clean room gloves, I put them in a dry nitrogen purged oven for 10 minutes to drive off any moisture that may somehow be there.
3) Wrung them together in a HEALTHY blast stream of dry nitrogen (0.003% RH at room temperature). They wrung and held together the same as in air.
4) Left them wrung together after step 4 and put them in a small vacuum chamber with one of the gauge blocks completely suspended horizontally (cantilevered). In other words, nothing holding it to the other block but the wring. Gravity would make the canterlevered one simply fall off if loss of adhesion occurred. I pulled a quick vacuum to about 10[SUP]-2[/SUP] torr (about 29.9 in-hg). Going to the full 10[SUP]-5[/SUP] requires me to use the cryopump or turbomolecular pump system and that takes a goodly while to get those last remaining air molecules out. I don't believe that is necessary to prove the point - just to get rid of most of the 14.7 psi of atmospheric pressure. Guess what? The blocks stayed together!
While not the most scientific methods were used, I think most would agree that it's a pragmatic test and proves Tony's experience is correct.
John
John,
I'd say that you reached a reasonable conclusion. I did put the blocks in my experiment in a desiccant bag, but admittedly took them out to wring, thus allowing at least a possibility of some water vapor in, although I was conscious of it and tried to do it as quickly as reasonably possible. I hadn't thought of my vacuum chamber. I have a bell jar and vacuum pump capable of 10[SUP]-2 [/SUP]torr or a little better, but I no longer have the gauging equipment to monitor such low levels. But since you went a couple better with the humidity with the N purge, I'll accept your findings.
I'd say that you reached a reasonable conclusion. I did put the blocks in my experiment in a desiccant bag, but admittedly took them out to wring, thus allowing at least a possibility of some water vapor in, although I was conscious of it and tried to do it as quickly as reasonably possible. I hadn't thought of my vacuum chamber. I have a bell jar and vacuum pump capable of 10[SUP]-2 [/SUP]torr or a little better, but I no longer have the gauging equipment to monitor such low levels. But since you went a couple better with the humidity with the N purge, I'll accept your findings.
This discussion has been going on for a long time. In my 1944 copy of Shop Theory - Henry Ford Trade School, they mention the same theories. Unfortunately, the item is spread over a couple of pages. Start with " Flat Surfaces in Steel" at the bottom of the first page.
View attachment Jo-blocks - Ford.pdf
View attachment Jo-blocks - Ford.pdf