Working to Tenths with Economy Tooling

[erikmannie]

So after spending about $2500 on Shars tools, I sat down to measure the gage blocks in my economy gage block set with my 0-1” digital electronic micrometer. This went pretty badly.

I am new to machining, so part of this could be attributed to operator error. Put simply, the micrometer and gage blocks are okay to a .001” but not to a tenth. An example of this is that the .0107” block surely measures thicker than the .0108” block.

So many people told me to buy Starrett, Mitutoyo, etc., but I was enticed by the low prices of the import tools. I am afraid that I did not spend the $2500 as wisely as I could have.

Has anybody had success working to a tenth with import metrology equipment? I can definitely work to a thou and maybe even to 3 tenths, but as far as I can see the Shars tools aren’t getting me to a tenth, if the gage blocks and 0-1” digital electronic micrometer are any indication.

I am now at the point were I will only be buying the quality brands moving forward. I plan on relegating all of the Shars equipment to the shop, and saving up for an inspection room later equipped with quality tools.

 

[Technical Ted]

I can't really answer your questions, but want to remind you of a few points...

Measuring that closely requires an atmosphere with controlled conditions (temperature, humidity, etc.). Further, touching gage blocks and/or micrometers with your hands will through your measurements off because of temperature. Micrometers that measure tenths are best if they have friction thimbles that are used, because a machinist' "feel" can be way off when measuring that closely.

Edit: And everything needs to be PERFECTLY clean!

In my experience, measuring to within a 0.0001" repeatedly, with a basic hand held micrometer, is extremely difficult and results will vary.

So, regardless of the brand of tools you use, if not used correctly you will get inaccurate readings.

Good luck,
Ted

 

[C-Bag]

I can't really answer your questions, but want to remind you of a few points...

Measuring that closely requires an atmosphere with controlled conditions (temperature, humidity, etc.). Further, touching gage blocks and/or micrometers with your hands will through your measurements off because of temperature. Micrometers that measure tenths are best if they have friction thimbles that are used, because a machinist' "feel" can be way off when measuring that closely.

Edit: And everything needs to be PERFECTLY clean!

In my experience, measuring to within a 0.0001" repeatedly, with a basic hand held micrometer, is extremely difficult and results will vary.

So, regardless of the brand of tools you use, if not used correctly you will get inaccurate readings.

Good luck,
Ted

+1. Ted nailed it. The allure of perfection through metrology is very strong for some of us. But it takes years of experience to attain it consistently and more than that to know when it's even necessary. It's easy to go into a perfectionist loop especially when new because you don't know all the variables. Working to .0001 is getting into some pretty fussy territory and besides a temperature controlled clean room that you keep your metrology equipment in do you have a set of ground tool room stones? A set of precision ground tool room stones has become my first step down the rabbit hole of chasing tenths.

 

[Bob Korves]

Gage blocks should be accurate to within .00005" or better, depending on the grade. I have heard of gage blocks being mislabeled in Chinese import sets, and I also check mine each time I use them as a reality check to make sure that mistakes were not made in labeling them. We cannot test them to their exact accuracy in our shops, as explained in the posts above. Part of what makes the Chinese stuff so cheap, even with a boat ride across the ocean, is bypassing strict quality control and quality assurance. It leaves us to be the final inspection techs, like it or not...

 

[projectnut]

I would agree to the above statements. The shop I worked in was temperature and humidity controlled. Even then the inspection room was sealed off with it's own heating, air conditioning, and humidity control. Critical parts were allowed to acclimate in the inspection room for 24 hours before final inspection and certification. To insure accuracy the inspection tools were calibrated and certified on an annual basis. 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.

In addition to the tolerance problems introduced by humidity, temperature, and handling, I doubt that most hobbyist grade machines could consistently produce parts within .0001" tolerances. Add to that the fact that very rarely do parts need to be held to those tolerances. In my opinion it's a waste of time and effort to machine a part to tenth tolerances, when plus or minus .001" is well within what's needed for the application.

I've said it before, and I'll say it again. In the commercial world time is money. There are a minimal amount of times when such tight specifications are justified. The rule of thumb at our shop was "For every space you move the tolerance decimal point to the left, you move the cost decimal point to the right."

 

[NCjeeper]

I have had good results with Shars stuff. How accurate are the gauge blocks you are using?

 

[pontiac428]

I doubt that most hobbyist grade machines could consistently produce parts within .0001" tolerances. Add to that the fact that very rarely do parts need to be held to those tolerances. In my opinion it's a waste of time and effort to machine a part to tenth tolerances, when plus or minus .001" is well within what's needed for the application.

I can't touch off a face on my mill or square my vise to .0001 inch, and I can't center stock in my lathe to .0001 either. Most of the time I can't even make a part to .001 all around. Most dimensions on a part can be fine at .005, with only the important fitted features on the part at higher tolerances as necessary. Most of the time, unless I'm using a dial indicator or have some critical fit, I leave the tenths alone...

 

[Janderso]

All my machines are 50+ years old. I'm happy dabbling in the .001" world..
I do have some Shars blocks, they are very accurate.

 

[mikey]

I am guessing here but when most of us check our tools against a known standard it is to confirm that the tool is accurate enough to trust it. This has nothing at all to do with whether or not some new hobby guy can work to tenths or not; its about confidence in the tool. If I check a set of digital calipers with a gauge block set that is accurate to 50 millionths of an inch, that gauge block set should tell me if the calipers can read within 0.001" accurately. If it can, then it can be trusted to function within its known or stated range.

While I agree that the ideal is a temp and humidity controlled environment and the standards and the tool is left to soak for 24 hours, we are not trying to certify a tool in our shops; we just want to know that the tool reads accurately within the stated limits of the tool. A caliper should read within a thou, a mic should read within a tenth and so on. If it does, we trust it and if it doesn't then we don't. I don't think we need lab conditions to get that level of trust.

My gauge block set came from a German metrology lab. It is used but is supposedly accurate to 50 mil. I use it to check my tools in my air-conditioned home but I don't worry too much about the conditions beyond that. I work cleanly and those blocks are accurate enough to give me confidence in my tools, all of which are high end tools except one - a Chinese caliper I recently bought to abuse in the shop - and even that one falls within specs.

If a hobby guy's mic reads 0.1234" then he can plan his cuts to come in on size from there IF the reading is true. He may want a diameter of 0.120" but he can't get that unless he knows where he is starting.

It's as simple as that.

 

[benmychree]

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, truly accurate sets such as an A+ set is something like +3, -5 millionths accuracy tolerence. In my opinion, gage blocks are nearly useless in hobby shops, except possibly for bragging rights among other like minded hobbyists. Their only real use is to set up sine bars or fixtures. They are not very good for setting mikes because of the difficulty of achieving a parallel fit, plus the stacking error inherent in cheap block sets; half a tenth here, half a tenth there; it adds up or subtracts down the more blocks used in a stack.