by Ed-vancedEngines » Mon Jan 15, 2007 12:14 pm
Tis is probably above your budget to just ocassionally use but in my books there is nothing to beat the Brown & Sharp Slant Line with carbide faces and friction thimble with .0001 capabilities. That is what all of my Outside mices are. I also check then very frequently with a *Standard* to keep accuracy.
Next in my books are the Starret of whatever a person't choice would be.
Next would be the Mitutoyo. Mitutoyo began as an acceptable lower cost measuring tool years ago but by now is highly accepted by most machinists as being a very good tool. Not bad at all for the price.
I have been in shops that are using tools from Central, which I have never used. Fowler is also one that I see used but have limited experience with them. Maybe their mics may be ok. Don't know.
I did buy a Fowler Digital Bore Guage that was supposed to have .00005 accuracy which in my opinion is a joke, and after trying to use got put back in the box to never again be used. It is far tooo inconsistent. Maybe their actual Dial Bore might be better.
The Mitutoyo Dial Bore Guages are actually some pretty good pieces in my opinion.
One suggestion is to visit your local pawn shop and check what they have. At least you can see it and hold it in your hand. I do this myself too.
Using a Telescope Guage and fransfering the measurements to an Outside Mic is not supposed to be very accurate at all. This does really depend much more on the user's experience with precision measuring tools, and their feel of measuring. It can get real trickey and can yield some really bad measurements. BUt it can also be very close. It does depend on you and your abilities and experience.
The Machinists hand book which I have not read in years, will tell you that measuring ID with an ID mic is recognised as capability of .001 accuracy, and measuring with transfer measurement devices will decrease accuracy by .001 for each measurement transfer. So by thier words this would mean that for most users you could reasonably expect to be in a tolerance range of .002 when using Telescope Guages and transfering those measurements through OD mics.
I have held precision tools most of my life and can get very accurate to within .0002 by using telescope Guages and transfering to my mics. Do not expect this though. I have done this for off an on 45 years. I am good. Even though I feel that I am very good at using precision measuring instruments and guages, I check and double check and even triple check myself all the time. I never ever measure anything with any mic or other instrument and blindly accept my first readings as fact.
You can buy precision mics by size as you need them or you can buy a big set which will give you options by using one large frame with several different sized anvils to make it usable in many different sizes. When buyng any precision mics over 1 inch try to get a measuring standard with them and a spanner wrech to adjust them with. That way you can keep them accurate. When buying a 1 inch mich first wipe both anvil and thimble faces clean with your finger and measure by feel to a zero measurement so that the thimble and anvil are contacting the other and see how accurate they are reading. They should be reading zero and the marks should be lining up perfectly. IF the marks are a long ways apart that mic is already probably ruined by mis-use. If the marks are within .001 to even .002 of each other it is probably ok and just needs recallibration.
I would not buy used mics over the internet.
Dial or digial calipers also do come in handy very often. Mitutoyo, Brown & Sharp, Starret, Smiec, are all good brands. With a Digital Caliper watch for an uneven movement or inconsistent reading when buying them used. The O indication should always be at the top at 12:00 o'clock unless they have been damaged. By at the top, I ean hold it in your right hand with the ID part up and the OD part down. The Central, Fowler, Craftsman, and possibly others may be acceptable. Those sold by Harbor Freight aren't.
Dial indicators made with brands of Sunnen, Starret, Brown & Sharp, Mitutoyo, are all very good instruments. Acceptable and actually very good are Peacock, and Phase II. Don't know about other brands. Dial indicators should always have a smooth movement.
Plastiguage can still be used for checking of bearing clearances. IT is not as accurate and checking parts before assembly with mics dial bore guages or inside mics but it can be used and can be used acceptably by understanding the shortcomings and reading the thickest mashed plastiguage strip and not those that didn't mash. I have found on the average that plastiguage is within .0002 of actual measuinring with mics.
All of the previous written are the opinions and experience of only this one person. Hope it helps you some.
Ed
Let all things that hath breath Praise the Lord. Praise Ye' the Lord. Ps-150 vs 6
Back then I just took the word of the shop that things were done right! I have since "grown up" and realized it is best to check things twice, and save myself 3X the headache.
