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Thermal Insulators on Micrometers...

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Splat

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#1
If the operator is only handling a micrometer for a few seconds at a time, as a home machinist possibly might.... how important are thermal insulators on a micrometer? Are they a definite must-have on micrometers for you?
 

mikey

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#3
I don't worry about it. My Mit and Etalon mics have them and my Helios and B&S don't - haven't noticed a difference in use. When boring, I use a mic stand that eliminates this variable.
 

RJSakowski

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#7
An interesting question. Steel has a linear expansion coefficient of around .000012"/" - ºC. For a six inch micrometer, if you were able to raise the frame temperature by 5ºC (9ºF), the expansion would be .00036". In practice, I expect that the temperature change caused by holding the micrometer would be no more than a degree or so, if that.

My micrometer set has the insulated grips but I measured my 5" standard and then gripped the micrometer by the uninsulated parts of the frame for about a minute. I could detect no significant change in the reading. (within .0001")
 

grzdomagala

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#8
Tesa micrometer with 25mm range and 0.002mm resolution moved visibly after a few seconds in hand. Don't know why so much - maybe the frame distorted due to nonuniform temperature.
It wasn't nasa - just a prototype of small high speed spindle.
 

Nogoingback

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#9
Tesa micrometer with 25mm range and 0.002mm resolution moved visibly after a few seconds in hand. Don't know why so much - maybe the frame distorted due to nonuniform temperature.
It wasn't nasa - just a prototype of small high speed spindle.
You could see it move .002 mm? You have good eyes! :)
 

ch2co

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#10
Just tried this with my 2" Starrett micrometer and starting from a shop temp of 65F I inserted a 1" reference rod and zeroed it then warmed
the thing (just the frame) up as much as I could in my hands which are considerably below internal body temp, which I measured to be 86.7F.
The difference was less than a ten thousandth". There must be an expansion of the metal frame going on, and no doubt can be measured, but...
I think this is a moot point for any home machinist. Yes there will be a tiny difference, but there are a LOT of other variables to worry about that
have much greater consequences for the finished part.
 

higgite

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#11
Seems to me that for hobby machining, one could drive oneself wacko chasing thermal expansion from just handling stuff. Not only will the mic in one hand expand, but how about the work piece or gauge block being held in the other hand?

I work a lot on the ignorance is bliss principle. ;) ymmv

Tom
 

mikey

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#12
Seems to me that for hobby machining, one could drive oneself wacko chasing thermal expansion from just handling stuff. Not only will the mic in one hand expand, but how about the work piece or gauge block being held in the other hand?

I work a lot on the ignorance is bliss principle. ;) ymmv

Tom
Yeah, we can measure it but cutting it is another thing! Then again, we're hobby guys and have all the time in the world to split microns. In a job shop ... I suspect not so much.
 

ch2co

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#13
How about when we are turning something on the lathe, for example, we stop the lathe and measure the diameter etc. of our part and, at least me,
never even think of the expansion of the part even though it's quite often too hot to touch? Those of you that have coolant flowing over the part
are, of course, not included in this thought experiment. The expansion of the part is far greater than the expansion of the measuring device warmed
by our hand, and yet I have never found a part that measured correctly while in the hot state that changed after it cooled. This of course is actually
false, but for any of our needs, is a moot point.
 

RJSakowski

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#14
The bottom line is that, as hobbyists, we make parts to fit together in assemblies. The only surfaces that are anything close to critical are mating surfaces and very few of them require measurements to tenths of thousandths.
 

grzdomagala

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#15
Skf catalogue calls js5 tolerance for standard bearing sit. On a 15mm shaft it's +- 0.004mm. If you want "machine tool" quality (for example for small high speed spindle) its js4 +-0.0025mm - almost exactly +-tenth.
Maybe holding this tolerance is not necessary (maybe even futile if all you have is a minilathe) but im not a pro - i don't have experience to tell where it's safe to skimp.

Wysłane z mojego GT-N7100 przy użyciu Tapatalka
 

higgite

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#16
Skf catalogue calls js5 tolerance for standard bearing sit. On a 15mm shaft it's +- 0.004mm. If you want "machine tool" quality (for example for small high speed spindle) its js4 +-0.0025mm - almost exactly +-tenth.
Maybe holding this tolerance is not necessary (maybe even futile if all you have is a minilathe) but im not a pro - i don't have experience to tell where it's safe to skimp.

Wysłane z mojego GT-N7100 przy użyciu Tapatalka
Not futile, if you have enough time on your hands. I have been known to sneak up on a critical OD of a round matching part by using a strip of emery cloth to buff off the last few nanomillimicrons while spinning it in a mini or bench lathe. Can get a spectacular finish like that, too.

Tom

P.S. I didn’t measure the final OD though. It was trial and error fit. I don’t have a measuring tool with that fine of resolution.
 

mikey

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#17
Many a good workman has brought a part in on size with a lathe file and sand paper. You're in good company, Tom.
 

4gsr

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#18
My luck usually is. It mic's .001" over, put some emery to the surface, get it looking pretty. Measure again and it's .0005" under! Hello Loctite. And I keep three different flavors of it, too!
 

RJSakowski

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#19
My luck usually is. It mic's .001" over, put some emery to the surface, get it looking pretty. Measure again and it's .0005" under! Hello Loctite. And I keep three different flavors of it, too!
Been there, done that....more times than I care to think about. It is amazing how high those tiny little ridges can be.

I'm a little smarter now. When I have a critical diameter, I will cut slightly oversized and do my polishing to get a sense of how much material will be removed. Then I will make any correction and make my final cut.
 

pstemari

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#20
(pocket posting [emoji15] )
 
Last edited:

kd4gij

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#21
My luck usually is. It mic's .001" over, put some emery to the surface, get it looking pretty. Measure again and it's .0005" under! Hello Loctite. And I keep three different flavors of it, too!

I make inboard boat shafts from marine grade SS. straight motor coupling need to fit so you can drive them on with a block of wood and a hammer. the shafts can be on size to .001 over. the couplings are 1.5 to 2 thou under. We have to polish it with 80 grit emery to size. I have to ice it down before micing. after till it gets there. need about .0005 for a good fit. I have miced a shaft when hot and it was .0005 bigger than when I started then ice it and it is .0005 under.
 

Wreck™Wreck

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#22
Yes, they are vital, also never touch a part bare handed as the natural oils in your skin will change the dimensions, for best results NEVER take the tools out of the packaging that they came in and use them, this will cause distortion every time.
 

4gsr

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#23
Yeah, don't touch the part after making several heavy cuts. :cussing:
 

benmychree

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#24
Fits matter, dimensions for the most part do not. Using a file and abrasive cloth to achieve close fits will usually result in out of round parts (if they were ever truly round to start with). Mechanical perfection is perhaps a state of mind.
 

Doodle

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#27
I make inboard boat shafts from marine grade SS. straight motor coupling need to fit so you can drive them on with a block of wood and a hammer. the shafts can be on size to .001 over. the couplings are 1.5 to 2 thou under. We have to polish it with 80 grit emery to size. I have to ice it down before micing. after till it gets there. need about .0005 for a good fit. I have miced a shaft when hot and it was .0005 bigger than when I started then ice it and it is .0005 under.
This is disconcerting. Are you saying that you allow a press fit for a shaft used in marine propulsion? So if I am of in the gulf and it slips and falls apart before I can get back home before being destroyed in a fast approaching storm it's because of a poorly engineered design? Does anyone wonder why manufacturing in the USA is replaced so easily by foreign companies?

A solution might be to use inductive heating to heat the coupling. The shaft can then be pushed in with either pneumatic or hydraulic force. Let the parts cool and it will be like it was welded in place. Look up induction heating in the internet, it is an interesting system. It can be used for small items soldered, or huge parts being joined. That would make your measurements and machining much easier and the part would be significantly improved.
 

Doodle

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#29
As a generalized statement I deserve a bit of correction. I do speak from experience in part as I have seen many jobs go overseas because of greed and ignorance.
 

higgite

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#30
How did we get from thermal effects on micrometers to inboard motorboat drive shafts to global manufacturing? Did I take a wrong turn in St. Louis? :confused 3:

Tom
 
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