Working to Tenths with Economy Tooling

I go back to the last 2 sentences in my previous post. "In this incident the OP is "assuming" the micrometer is properly calibrated and the gauge block is in error. It could very well be just the opposite." Without a controlled atmosphere how can the OP be certain which component is causing the difference from the measurement stated on the block. Simply handling the block long enough to raise the temperature a few degrees can cause the dimensions to change. Given a micron is .000039" and tool steel expands at a rate of 12.8 microns per degree, it would take less than a 5* change (from the standard of 68*) in temperature for a block to expand .0001". Any lint or even a finger print on either on the micrometer or the gauge block could account for the difference in measurement.

I agree with John York's assessment of the use of gauge blocks in a hobby shop. Mine were originally purchased to setup a sine bar. I must admit however I have been known to use them to check the accuracy of a micrometer. I have a number of micrometers in the shop. The newest were purchased in the 1980's. The oldest date back to WWII. Even the oldest ones are good to within a tenth. That's close enough for anything I do.
 
I bought the gage block set at the same time as a 6” sine bar. I only have 30/60/90 and 45/45/90 angle blocks, and I don’t plan to buy an angle block set, thus the sine bar. I am new to machining so I am probably getting a lot of things wrong.

The truth is that I will probably try to achieve a few tenths tolerance and be happy with a .001” tolerance. When I took machining classes, a thou was the goal (except for cutting threads).

Using the economy micrometer to measure the economy gage blocks led me to question whether or not I have handicapped myself by buying cheaper import tools. Generally speaking, the Shars equipment seems to hover very close to the “is it good enough?” standard. Yesterday I organized all of the Shars tools into two large tool chests, and it looked like I had purchased inferior quality equipment.

Personally, I would advise new machinists such as myself to adopt a policy of only purchasing higher quality equipment. If this were happening with a Mitutoyo micrometer and a Starrett gage block set, it would probably be a different conversation.
 
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projectnut said:
I go back to the last 2 sentences in my previous post. "In this incident the OP is "assuming" the micrometer is properly calibrated and the gauge block is in error. It could very well be just the opposite." Without a controlled atmosphere how can the OP be certain which component is causing the difference from the measurement stated on the block. Simply handling the block long enough to raise the temperature a few degrees can cause the dimensions to change. Given a micron is .000039" and tool steel expands at a rate of 12.8 microns per degree, it would take less than a 5* change (from the standard of 68*) in temperature for a block to expand .0001". Any lint or even a finger print on either on the micrometer or the gauge block could account for the difference in measurement.

I agree with John York's assessment of the use of gauge blocks in a hobby shop. Mine were originally purchased to setup a sine bar. I must admit however I have been known to use them to check the accuracy of a micrometer. I have a number of micrometers in the shop. The newest were purchased in the 1980's. The oldest date back to WWII. Even the oldest ones are good to within a tenth. That's close enough for anything I do.
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My mikes date (for the most part) to the 1960s, when I bought them new, all Starrett, and are still accurate enough for anything that I do, I have checked them with "mike checks", and there is no visable deviation, some have 60 years of use on a daily basis and are still accurate.
 
Point taken regarding clean hands and materials, temperature and humidity.

When I set out to buy welding equipment, I was advised to buy Miller. I did, and things worked out very nicely. I don’t know why I cheaped out when it came to machinist tools.

Like I said, I will use the Shars equipment while I am learning and saving up for Starrett, Mitutoyo, etc. and then keep the good stuff in the inspection room.
 
I always suggest that newer people buy good used tools. If you watch Craigslist, Facebook Marketplace or whatever you can usually find a retired machinist or tool maker selling their collection. You might end up spending a grand + or so, but end up with machinist boxes as well as some nice tools. eBay's prices are too high IMO.

To help set your mind at ease, or to really make you disappointed, you can always send one of the tools you question to a calibration service and see if it passes. Good or bad you will find out the truth.

Ted
 
benmychree said:
A gage block set of 50 millionths accuracy (1/2 of a tenth of a thousandth) is quite at the low end of the totem pole so far as accuracy is concerned ...
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True. To really test a tenths reading mic, you need gauge blocks that adhere to the 4:1 Rule so I would need blocks certified to 0.000025" to certify the mic. However, I am not certifying it; I'm just checking to see if it reads close enough for my shop and a 50 mil block will do that. I do adhere to the 5-point recommendation to be sure the mic is reliably reading at the level of my blocks so I'm okay with it at this level of accuracy.

The problem for hobby guys is the "chicken or the egg" situation. Is the block off or is the mic off or is it both, or is it your technique, ratcheting/friction force, speed, etc. The best way to know is to send your blocks to a lab and have it certified, with the true reading noted for each block. Personally, I cannot afford to do that so I take the cheap way out. I put my mic in a stand, wipe and then hold each block with a microfiber towel and run through the 5-point process and if it passes, then good. I run several mics through the same process with the same blocks and if all of them read the same then I assume the blocks are pretty accurate. No, not perfect but it works well enough to give me confidence to use the tools, which is really all I want.

Working to the level of the mic, now that is another thing ...
 
Back in the day , our tools had to be inspected and calibrated every 6 months per the DoD contracts . Calibration was performed by inspectors on site who didn't have the nimblest of hands and feel . When we received our tools back , we all put them back into spec where they started out . I never liked lending tools out or having less qualified personnel messing with any of my tools .
 
Technical Ted said:
I always suggest that newer people buy good used tools...
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Having learned the hard way, now I know! If you buy quality, you get quality.

I wonder if anybody is able to consistently work to the nearest tenth using an import mill and "econo-tools".
 
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