indicators?

[mikey]

Coomba, this is from Long Island Indicator Service's site:

Test indicators can also be calibrated on a surface plate using certified gage blocks. The indicator is securely fastened to a stand and the contact point is brought in contact with a gage block of a given size. The contact point must be parallel with the surface of the block for most manufacturers. Interapid test indicators are an exception and should be at a 12-degree angle, approximately. The gage block can then be removed and replaced a number of times to check for repeatability. Be certain that discrepancies in repeatability are not due to poorly tightened clamps, flimsy stands or other factors. Usually one quarter of a graduation repeatability is allowable, but check with the manufacturer's calibration specs for your particular model.

Errors in repeatability indicate a need for cleaning and, possibly, repair. Do not attempt this without experience.
Accuracy in travel is checked by replacing the gage block with one larger. Very small intervals are required. Ideally you'd want to check the travel at every half revolution, or better. During this procedure be certain that the gage blocks are properly wrung to each other and to the surface. In general, accuracy should not vary more than one graduation per dial revolution on .0005" indicators.

 

[Ray C]

I use the tenths DTI probably more than the half-thou... On the surface grinder, many finished parts are in the tenths. On some areas of the boat propeller shafts I make and recondition, the bearing races are pressed on and a typical shaft is 1.25" -0.0000 +0.0003. Also, some of the shafts have various gears and lobes that are pressed and keyed. They all have similar tolerances. On the lathe, I can take things to the far half-thou then TPG it home. Everything is 316 SS.

I have a home shop but I do work for some marinas -also do work for a local lawnmower/tractor repair place...

EDIT: Oh yeah, then there's the tool cutter/grinder... I've been making some taper reamers for my own projects and I want them drop-dead-on...

Ray

If you could tear the DTI apart and look at the insides the difference between a chinese and a Good american brand the difference would be obvious. the parts in the chinese ones look like brass clock parts. the more expensive American ones are made out of hardened steel parts and jeweled pivots. Also what you plan to do with the DTI may make a difference. I find Interrapid to be better on a mill while Brown and Sharpe is better on the lathe. And when i can i would use a simple Dial Indicator instead of a DTI on a lathe. Easier to read for old eyes.
I also wonder what you are going to be doing that you need a DTI with one ten thousanths divisions for. Remember the smaller the divisions the less total travel the dial has. Unless you have a compelling reason to use such a fine instrument you would be far better served by a less sensitive indicator. The .0005 indicator would be more than accurate enough for 99.9 percent of all hobby machinists.

 

[Coomba]

Hey, Thanks guys for all the input, its has been very helpful.:thinking: