Starrett Micrometer for Sale
- Thread starter KustomKartKid
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Yeah good question Ogy. Noramally I would say it was kept in a climate controlled toolroom, but it seems a mic that large was more likey being used out in the shop to check a job as it was being turned in a lage lathe or centerless grinder....like a huge crankshaft or something. And as you point out, the larger the mic the larger the error factor due to expansion/contraction.
How do you even come up with a metal alloy for the frame that is so stress free and stable that it just doesn't "spring" or change on its own over time...
For instance, hot rolled steel as ugly as it is, is more stable than the prettier cold rolled steel that machinsts prefer for jobs. The cold rolling process sets up some sort of stress within the metal...and if you were to machine just one side of it, it's like removing a skin which causes the piece to distort. Hot rolled is more stable simply due to the fact that it is not subjected to the added finishing process.
I would imagine the mic frames are cast aluminum...perhaps that is more homogeneous and stable than machined billet...:shrug:
If you look close in the box there are long gauge pins/rods for checking or setting it to a "standard". Here again..the standards would normally have to be kept in a controlled climate in order to be accurate.
Somewhere in my archives I have an interesting book that shows where all the "master" guage standards were kept in a special controlled vault at Starrett or Brown & Sharp I forget. I will try and dig it out and scan it.
How do you even come up with a metal alloy for the frame that is so stress free and stable that it just doesn't "spring" or change on its own over time...
For instance, hot rolled steel as ugly as it is, is more stable than the prettier cold rolled steel that machinsts prefer for jobs. The cold rolling process sets up some sort of stress within the metal...and if you were to machine just one side of it, it's like removing a skin which causes the piece to distort. Hot rolled is more stable simply due to the fact that it is not subjected to the added finishing process.
I would imagine the mic frames are cast aluminum...perhaps that is more homogeneous and stable than machined billet...:shrug:
If you look close in the box there are long gauge pins/rods for checking or setting it to a "standard". Here again..the standards would normally have to be kept in a controlled climate in order to be accurate.
Somewhere in my archives I have an interesting book that shows where all the "master" guage standards were kept in a special controlled vault at Starrett or Brown & Sharp I forget. I will try and dig it out and scan it.
I looked at it quick because it was freezing in there, but I remember it was in the 2ft range...there were some different anvils you could swap in to change the range.
It did have a dial indicator on it which would make it easier to re-zero against the rod standard vs using the regular thimble. I think Ogy's question is how reliable or stable does it remain, even over the course of the work day, when you're dealing with a frame that large.
It did have a dial indicator on it which would make it easier to re-zero against the rod standard vs using the regular thimble. I think Ogy's question is how reliable or stable does it remain, even over the course of the work day, when you're dealing with a frame that large.
I think Ogy's question is how reliable or stable does it remain, even over the course of the work day, when you're dealing with a frame that large.[/QUOTE]
Like you said if they didnt use it in an area that had stable temp they would have to re-zero quite often. We have plunge type dial indicators (digital)here at work and they do hourly checks on the molding floor. They will re zero (off of a gauge block) after each series of checks. Example: re-zero check 5 SPC points per cavity then hour later re-zero and check again. But they use ours as a QC control not a run to spec. (like on a lathe or grinder where you're taking off material down to a certain size).
Imagine the labor it took to use that one correctly.
Like you said if they didnt use it in an area that had stable temp they would have to re-zero quite often. We have plunge type dial indicators (digital)here at work and they do hourly checks on the molding floor. They will re zero (off of a gauge block) after each series of checks. Example: re-zero check 5 SPC points per cavity then hour later re-zero and check again. But they use ours as a QC control not a run to spec. (like on a lathe or grinder where you're taking off material down to a certain size).
Imagine the labor it took to use that one correctly.
OK i talked with our "Gauge,instrument inspection and calibration Tech" and he said that frame is probably alluminum, Aluminum would acclimate rather quickly but other metals are slower. So once you wait and both the product and the Micrometer have acclimated they would stay very stable under gradual temp. changes.for example at a +/_.0001 accuracy,40 deg.over 8 hr you wouldnt see. Now with rapid temperature changes the aluminum would react violently and you would have to wait longer for your product to acclimate then re-zero. For slow gradual changes the variance is absorbed in the accuracy.
Aerospace stuff.... in general
Quality measuring instruments must be stabilized at 68 deg. for about 24 hours before calibration to the standard supplied with instrument.
The standard that comes with the instrument is generally traceable to the National Institute of Standards and Technology.
To accurately measure the part in the shop the shop must be the same temp. +/- very little. Generally the tolerance given on the drawing will take care of the difference from the final word of the temp. controlled room at final inspection .
By far the biggest biggest biggest hugest most catastrophic mistakes made are by the operator when handling micrometers, the bigger the micrometer the bigger the mistakes.
Getting the "feel" of micrometers takes a ton of practice.
Quality measuring instruments must be stabilized at 68 deg. for about 24 hours before calibration to the standard supplied with instrument.
The standard that comes with the instrument is generally traceable to the National Institute of Standards and Technology.
To accurately measure the part in the shop the shop must be the same temp. +/- very little. Generally the tolerance given on the drawing will take care of the difference from the final word of the temp. controlled room at final inspection .
By far the biggest biggest biggest hugest most catastrophic mistakes made are by the operator when handling micrometers, the bigger the micrometer the bigger the mistakes.
Getting the "feel" of micrometers takes a ton of practice.
All micrometers of any quality (especially old Starretts like this one) have frames that are made from forged steel. If you picked that mic up you'd be able to tell right off that it isn't aluminum. The frame is heavy duty so it doesn't flex when measuring and also to minimize radical swings in thermal expansion.
Aluminum has a greater coefficient of thermal expansion than steel does and also greater thermal conductivity. With a micrometer that large the accuracy would be crap if it was made out of aluminum. It would grow just from the person holding it in their hand. I've never seen an aluminum micrometer.
Starrett is an American icon synonymous with the ultimate in quality like Snap-On. Although both companies now sell some equipment made in China (especially electronic stuff like digital calipers and mics and other tools) they both still sell ultra-quality made in USA products too.
Both companies have the best slogans in their respective industries.
Starrett's slogan is: "The World's Finest Toolmakers".
and of course Snap-On's is: "Nothing Else Even Comes Close".
Starrett mics are second to none just like Snap-On hand tools.
As far compensating for thermal expansion on the shop floor, that is done very carefully. Since each metal has it's own known thermal expansion factor, you can calculate the thermal expansion of both the gage and the part being measured and compensate for the reading on the mic. Theoretically when you bring them both into the climate-controlled metrology lab then they will measure as expected.
I am involved in the design of plastic mold tooling. The cores are all designed to have a precise centerline at operating temperature in order to properly mate with the cavities. So the thermal expansion of each material must be taken into consideration. The larger the mold is (like this big micrometer) the greater the thermal expansion and a lot more challenging it gets. A lot of our molds will not close at room temperature because one half of the mold is designed to be hotter than the other half. You must bring the hot half up to operating temperature before it will mate with the cold half. The centerline distance is intentionally designed smaller on the hot half so it can "grow" to size after heating up and will then mate perfectly with the cold half. Some of the tolerances are as tight as 50 millionths of an inch (or one half of a ten thousandth of an inch).
That big Starrett micrometer was a very expensive metrology instrument when it was new. Because of it's size, it isn't one that most toolmakers would own. That's something the company would buy most-likely for a specific part of the manufacturing process. It is still worth a lot of money if it isn't damaged. You can send it back to L.S. Starrett in Athol, Massachusetts and they will refurbish it and re-certify it for a fee and then it is as good as new.
How much were they asking for it?
Aluminum has a greater coefficient of thermal expansion than steel does and also greater thermal conductivity. With a micrometer that large the accuracy would be crap if it was made out of aluminum. It would grow just from the person holding it in their hand. I've never seen an aluminum micrometer.
Starrett is an American icon synonymous with the ultimate in quality like Snap-On. Although both companies now sell some equipment made in China (especially electronic stuff like digital calipers and mics and other tools) they both still sell ultra-quality made in USA products too.
Both companies have the best slogans in their respective industries.
Starrett's slogan is: "The World's Finest Toolmakers".
and of course Snap-On's is: "Nothing Else Even Comes Close".
Starrett mics are second to none just like Snap-On hand tools.
As far compensating for thermal expansion on the shop floor, that is done very carefully. Since each metal has it's own known thermal expansion factor, you can calculate the thermal expansion of both the gage and the part being measured and compensate for the reading on the mic. Theoretically when you bring them both into the climate-controlled metrology lab then they will measure as expected.
I am involved in the design of plastic mold tooling. The cores are all designed to have a precise centerline at operating temperature in order to properly mate with the cavities. So the thermal expansion of each material must be taken into consideration. The larger the mold is (like this big micrometer) the greater the thermal expansion and a lot more challenging it gets. A lot of our molds will not close at room temperature because one half of the mold is designed to be hotter than the other half. You must bring the hot half up to operating temperature before it will mate with the cold half. The centerline distance is intentionally designed smaller on the hot half so it can "grow" to size after heating up and will then mate perfectly with the cold half. Some of the tolerances are as tight as 50 millionths of an inch (or one half of a ten thousandth of an inch).
That big Starrett micrometer was a very expensive metrology instrument when it was new. Because of it's size, it isn't one that most toolmakers would own. That's something the company would buy most-likely for a specific part of the manufacturing process. It is still worth a lot of money if it isn't damaged. You can send it back to L.S. Starrett in Athol, Massachusetts and they will refurbish it and re-certify it for a fee and then it is as good as new.
How much were they asking for it?
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Here's a page out of the Starrett catalog for you chum :
In the hands of a skilled operator, the precision micrometer is the most accuratehand-
held tool available.
When close measurementsare
necessary,
the micrometeris
the ideal tool for the job because measurementand
reading are on the same axis and the anvil end is supportedby
a strong frame.
• Balanced frame and thimble for better “feel” on measured surfaces
• Tapered frame allows the anvil to be positioned in confined areas
• Ring-type lock nut for quick and sure locking
• Available with either friction thimble or combination ratchet/speederfor
uniform pressure
• Micrometers above 6" use webbed frames to lighten the weight and
increasestrength
• Large micrometers, above 24" (600mm), are constructed of tubularsteel,
honeycomb aluminum or round tubing for lightness and rigidity•
Available in sizes up to 120". Special configurations can be ordered
through our Special Order Department
You did notice that the mic says "Special" on it....right?
We discussed the gauge earlier....it's still considered a micrometer:
Again...from the Starret Catalog
• Micrometers can also be purchased with dial indicators installed in
place of the micrometerheads
to handle unique applications
MeasureShop.biz: External micrometers with dial gauge and adjustable anvil
External Micrometer - Series ABY ISOMASTER with Adjustable Dial Gauge Element - EuroPac Precision
Here's the link to the Starrett catalog in case you don't believe me:
http://www.starrett.com/docs/data-sheets/precision-product-guide---bulletin-356.pdf
That's the problem with making broad brush definitive statements like you made. Do a little research first before trying to make others look foolish...sometimes it backfires.
.
In the hands of a skilled operator, the precision micrometer is the most accuratehand-
held tool available.
When close measurementsare
necessary,
the micrometeris
the ideal tool for the job because measurementand
reading are on the same axis and the anvil end is supportedby
a strong frame.
• Balanced frame and thimble for better “feel” on measured surfaces
• Tapered frame allows the anvil to be positioned in confined areas
• Ring-type lock nut for quick and sure locking
• Available with either friction thimble or combination ratchet/speederfor
uniform pressure
• Micrometers above 6" use webbed frames to lighten the weight and
increasestrength
• Large micrometers, above 24" (600mm), are constructed of tubularsteel,
honeycomb aluminum or round tubing for lightness and rigidity•
Available in sizes up to 120". Special configurations can be ordered
through our Special Order Department
You did notice that the mic says "Special" on it....right?
We discussed the gauge earlier....it's still considered a micrometer:
Again...from the Starret Catalog
• Micrometers can also be purchased with dial indicators installed in
place of the micrometerheads
to handle unique applications
MeasureShop.biz: External micrometers with dial gauge and adjustable anvil
External Micrometer - Series ABY ISOMASTER with Adjustable Dial Gauge Element - EuroPac Precision
Here's the link to the Starrett catalog in case you don't believe me:
http://www.starrett.com/docs/data-sheets/precision-product-guide---bulletin-356.pdf
That's the problem with making broad brush definitive statements like you made. Do a little research first before trying to make others look foolish...sometimes it backfires.
.
Interesting on these large mics they attach plastic or rubber grips to insulate it from the heat of your hands and mininmize expansion...
They go to collage to learn how to properly use these things to get correct readings. I prefer digital.
And by the way Mauser made dam good Quality stuff back in the day. I got a set of manual calipers with 6" jaws. that look pretty cool.
This Shars aluminum frame 12" micrometer claims accuracy to .0001" and included that standard. Works well, reasonable cost, seems to be accurate despite varying shop temperatures:
The surface plate was well used and chipped before I got it for 25 bucks.
The Mitutoyo bore gauge set up for 12" operation also holds accuracy:
The surface plate was well used and chipped before I got it for 25 bucks.
The Mitutoyo bore gauge set up for 12" operation also holds accuracy:
