Exactly! Bore dials are a comparative measurement device, they have to be used with a standard and even then are very touchy to use especially the two point ones. The three point ones are much better to use but we still used air gauges, marposs, or CMM to actually measure the bores.
I would surmise that you are the exception. I have a pretty good machine shop with lots of metrology, some that most shops don't have.
All dial bore gauges use a dial indicator. Dial bore gauges are comparative instruments. You set them using a standard, zero them and then measure taper, out of round, and diameter. To measure taper and out of round you don't need a standard you just need a starting point from which to set zero and measure the difference/deviation from there but for diameter a standard is necessary.
Why is it everyone on this thread keeps calling 0.0001 tenths?? I learned .0001 is ten thousandths. Tenths are .1. I’m confused?? Or have I been taught wrong
Measuring devices for basic measuring in the tenths range are both inexpensive and plentiful, especially second hand.
Not disagreeing here but the old saying "Trust but verify" comes into play here. I've not assembled a lot of engines but one time was shipped the wrong bearing inserts for the crank size. So checking saved me a lot of work in that situation.
And no one is saying not to check. That would have been easily been caught by plastic-gauge.
You are absolutely correct, but the plastic-gauge would have added a lost hour or two to the assembly process and probably rendered the inserts non-returnable.
.0001 has been referred to as a tenth for my entire 40+ years in the tool making trade.
Suppose so.
It's only a vernier. Nothing particularly special. So, yeah, probably not many.
Rottler has some good machines out there now too.
Hohn, agree with 99% of what you suggest, other than the above. From experience, the dealbreaker is "if you are skilled". If the OP were skilled, he wouldn't have asked the question. Of all the ways to go wrong measuring in a bore, an inside micrometer is the most likely to get it wrong, tied with using a telescoping gauge and measuring that with an outside micrometer. Seasoned vets have difficulty repeating themselves; new guys will get different tenths every time.
Hey... Great to hear you've stepped up from the yardstick!
That's fair, Jack. I hesitated to put that there because the telescoping gauges are indeed tricky to be consistent with even in skilled hands. I just know that a quality bore guage is sort of beyond the reach of most home gamers, and telescoping gages are perhaps better than nothing.
Oh, we've been carrying on ever since this was explained previously in post 49, then posts 50 and 51, then again in 57 and 59. But thanks for driving it home!
I have found two sets of Starrett telescoping gauges fairly cheap on FB Marketplace. One set was the double leg and the other the single. I just bought the second pair but I think both were around $75. I practiced trying to get consistent results by comparing to a known number. I wouldn't trust myself for .0001 measurements but I know I could be within .0005".
LOL, all engines designed in the past forty years have been metric, but when the US machinist is ordering pistons to rebuild them they'll often still be designated old school; .010", .020", et al. In the rest of the world, they'll be .5mm, .75mm, 1mm, et al. Mahle pistons will usually have both, but the inch bore diameter is laser etched on the piston tops, because most shops use the inch Sunnen dial bore gauge.
Aircooled Veedubs... HeeHeeHee. Put a few together, Plastigage and micrometers for bearings, feeler gauges too. Never had a problem with them, they seemed REALLY tolerant of "Budweiser Rebuilds". As long as you put ALL the parts back in, in the right places, they just work.
You must be a heck of machinist to hold .0001mm tolerances, since by your own admission, you don't work in inches...
