Can this old style digital micrometer be calibrated?

[ltlvt]

I bought this off of Market place last week and received it today. My question is can it be calibrated and if so how. It is reading about .0005 off. Since it is a tenths micrometer, I would like it to be on the money. I have checked it several different ways. Using 2 other micrometers and the snap gage against some feeler gages. The Snap gage only measures in .001 increments so not an apples-to-apples gage. Thanks in advance.

 

[woodchucker]

Nice they can be.you can do your own basic calibration using gage blocks and a mitutoyo wrench
Otherwise Mark Ratkowski Mr tool

 

[ltlvt]

Nice they can be.you can do your own basic calibration using gage blocks and a mitutoyo wrench
Otherwise Mark Ratkowski Mr tool

Any idea what the wrench looks like? I have gage blocks and pins. Looking at it from the front there are 4 screws that hold the window cover on but the Thimble needs to be calibrated as well. The digits only go to the nearest thou and I want the tenths to be dead on. I've used Mark to repair a Starrett back plunge that Starrett said was obsolete, yet they still sell them. I think Starrett has lost/retired its knowledge base and is now dependent on the Chinese I just don't want to mess with the shipping if I can do it myself.

 

[durableoreo]

Gage pins won't do. Well, my set isn't accurate enough to set a micrometer. The gage blocks should be a better reference.

I think you just twist the micrometer head to calibrate. (The stationary part that the thimble rotates around.) There should be a dimple or hole for a tiny spanner

 

[ChazzC]

Rotating the barrel only fixes the zero on the thimble. After you have that done you need to fiddle with the readout. Do a YT search on calibrating a digital mechanical micrometer and also search Mr. Pete’s channel. I’ll see what I can find tomorrow.

This video shows calibrating both the thimble reading & the digital counter (Mitutoyo would be similar):

And here is Mr. Pete's video on calibrating the digital counter:

There are literally dozens of different sizes & styles of micrometer spanners; here is my collection:



I use a Starrett spanner to adjust the barrels on my Starrett & Mitutoyo mechanical digital micrometers:



See attached PDF showing the parts of the Starrett 216MXRL micrometer (non-metric is the same, I just have the 0 – 25mm one); here is the spanner they specify:




EDITS:
1) Changed "thimble" to "barrel"
2) Added video links, photos & Starrett 216XRLM info

 

[woodchucker]

Any idea what the wrench looks like? I have gage blocks and pins. Looking at it from the front there are 4 screws that hold the window cover on but the Thimble needs to be calibrated as well. The digits only go to the nearest thou and I want the tenths to be dead on. I've used Mark to repair a Starrett back plunge that Starrett said was obsolete, yet they still sell them. I think Starrett has lost/retired its knowledge base and is now dependent on the Chinese I just don't want to mess with the shipping if I can do it myself.

Here's a mit wrench for the mic.
The other one just move the rod.

 

[ltlvt]

Gage pins won't do. Well, my set isn't accurate enough to set a micrometer. The gage blocks should be a better reference.

I think you just twist the micrometer head to calibrate. (The stationary part that the thimble rotates around.) There should be a dimple or hole for a tiny spanner

I've calibrated micrometers before . I do not see a hole in the thimble of this one.

 

[ltlvt]

Here's a mit wrench for the mic.
The other one just move the rod.

I have a wrench like that but it's not Mit brand. I do not see a hole on the spindle like most micrometers have. I will look again tomorrow.

 

[extropic]

If you answer a few questions, I can walk you through the mechanics of tuning up the micrometer.
Are the tip of the spindle and the anvil flat and parallel to your satisfaction?
Do the digital numbers and the sleeve/thimble scale readings agree, just not on proper zero?
Do the digital numbers show an acceptable zero when the spindle is in contact with the anvil?
The thimble is mated to the spindle on a taper. Remove the ratchet stop screw and ratchet stop. Then put a little side pressure, back and forth, on the thimble at the scale end (not the ratchet stop end). What you're trying to do is to release that tapered fit. The thimble is only held by the taper (no rotational key). The thimble scale can be zeroed to sleeve scale with no problem at reassembly.

I think @BGHansen has been inside his same type analog digital mechanism so I'd like him to chime in.
Bruce, my thinking, assuming the spindle and anvil are OK, is to turn the spindle down until the two mate. My question for you is, if the digits don't read zero at that time, can the digit set be independently re-zeroed relative to the spindle rotational orientation? Or, are the digits driven without any re-zeroing capability? I have some of the same type of micrometers, but I've never been into the analog digital mechanism.

 

[BGHansen]

If you answer a few questions, I can walk you through the mechanics of tuning up the micrometer.
Are the tip of the spindle and the anvil flat and parallel to your satisfaction?
Do the digital numbers and the sleeve/thimble scale readings agree, just not on proper zero?
Do the digital numbers show an acceptable zero when the spindle is in contact with the anvil?
The thimble is mated to the spindle on a taper. Remove the ratchet stop screw and ratchet stop. Then put a little side pressure, back and forth, on the thimble at the scale end (not the ratchet stop end). What you're trying to do is to release that tapered fit. The thimble is only held by the taper (no rotational key). The thimble scale can be zeroed to sleeve scale with no problem at reassembly.

I think @BGHansen has been inside his same type analog digital mechanism so I'd like him to chime in.
Bruce, my thinking, assuming the spindle and anvil are OK, is to turn the spindle down until the two mate. My question for you is, if the digits don't read zero at that time, can the digit set be independently re-zeroed relative to the spindle rotational orientation? Or, are the digits driven without any re-zeroing capability? I have some of the same type of micrometers, but I've never been into the analog digital mechanism.

Thanks for the memory jog! Here's a link to me pulling apart a Fowler 1-2" screw pitch micrometer (3 1/2 years ago).

What Did You Buy Today?

The local scrap yard sells “stainless” (anything a magnet doesn’t stick to and isn’t aluminum) for $1/lb and anything ferrous for $0.40/lb. I got a lot of barstock from them. A little weather worn, and good in the middle. This is about 300 pounds of material to turn into scrap and chips. The 3"...

www.hobby-machinist.com

Here's a blow-up of the assembled guts:



This is what I did to the mic and a description (granted, a poor description) of the works:



On my Fowler, the thimble has a brass gear that engages with a gear in the read-out gearbox. I manually spun the gearbox to get it close to zero (or 1.0000" for the 1-2" mic) and reassembled.

The YouTube video the @ChazzC posted above should work; it's basically what I did with my Fowler. Zero out your micrometer, and adjust the thimble to zero with a spanner (if needed). Pull the gearbox cover, remove the gearbox and manually turn it to zero, then reassemble.