I'm boring two 0.994" holes in D-2 for a die. The corresponding gauge covers 3/4" to 1-1/4" and it's difficult to get a good reading. It's always a problem for me if the bore is close to the lower end of the range on the gauge. I've been using them for 35+ years (the same set) but now I wonder if I should embrace a new method or new tools. Any recommendations?
"azotic" fired this volley in news:lnfpsd$iph$1 @speranza.aioe.org:
Sure! He's got a fairly limited range to measure on THIS job. But get a set that will handle from .25" up to 3", and tell me how much you spent!
SURE they're 'better'. They impinge on three points instead of two, making centering more sure (but not necessarily 'instant'; ever 'centered' work perfectly in a 3-jaw chuck without fiddling it a bit?).
A set covering any reasonable range would cost a bundle. $100? Phhtttt! Two tools, maybe. Five or six? No way. And if they're Chinese, do you have calibration standards?
Not to belittle the tools. They're useful for the person who needs them frequently, but they are NOT inexpensive enough for any amateur or infrequent machinist to seriously consider them. And Tawm machines because he must to create his own end product, not as an 'end product' in itself.
I purchased a lot of high end tools back in the day 98/99 before ebay was over run by dealers and resellers. I still find high end micrometers at local pawn shops for $15-25 each. No china junk in my collection. Maybe i am just lucky. My old eyes and shakey hands kinda forced me to go digital. Much easier to get good readings for me. Yesterday i visited 13 pawn shops, only ended up getting a shovel for $1.99 so its hit or miss.
I bought a couple of inside spring calipers - maybe Starrett. they had round legs and the points were fairly sharp. I found that I was getting better readings with them than I had been with telescope gauges. Probably because with calipers you tend to sort of wiggle them around until you get a good fit while with the telescope gauges you push them in and they fit tight, no matter whether you have them cocked a bit :-)
Depends on how much accuracy you need. A much more expensive way is the Tesa/Brown&Sharpe "Tri-Mic". It measures directly in 0.0002" steps -- but covers a very small range, and costs a *lot*, so if you need to measure more than one narrow range of sizes, you will not be happy. But -- it is self centering, and is quite accurate. It *should* come with a ring standard for zeroing it. Here is an example on eBay, without the ring standard:
If you get them in sets, typically there will be one ring for every two mics -- at the maximum size of one and the minimum size of the other. Before bidding -- take into account the cost of getting the setting ring to go with it -- you'll probably have to go to someone like MSC for that. (I have in accumulating my collection of TESA tri-mics.)
I have some tapered rods that I use for measuring holes. To use them you just insert in the hole until they seat and then measure the diameter where the rod seats. Much easier to use than a telescoping gauge.