FWIW Ebay/Amazon Indian ground MT test bars

I received a precision bench center today, so to try it out I put some ebay/Amazon MT series test bars I'd bought between centers and put my tenth indicator on the bars. There was no discernible needle movement anywhere I tested. And a tenth mike showed no variation in diameter of the cylindrical section of the bars.

Given the pittance these cost I am agog. They certainly meet any accuracy requirements for machine testing I have.

From what I've seen that could be more luck than anything else. That type of test check equipment seems a bit hit n miss as far as expecting the exact same results buying the same thing next time even from the same vendor. The lack of any known & recognizable corporate name for the manufacturer works against us I guess as who knows where the vendor will be getting the next batch from. Still nice when it does work out though. Maybe 30 + years ago I bought a sub $20 pair of 123 blocks and they were square, to size and under the .0002" the "certificate" guaranteed they were.

That's been my general viewpoint with regard to Chinese and Indian stuff up until very recently. I've got examples of Indian grinding from 20+ years ago that are not anything to brag about.

And I returned all but about 3 of an order from ENCO of Chinese ground arbors that were laughable. I kept the few which tested OK and returned the rest, most untested. Even at the price they were just scrap metal and not worth the time to test them.

This is why I thought it worth mentioning the test bars. I've never seen 0 TIR on a tenth indicator before.

I plan to make a small study testing the ones I have. Setting up to do a proper job will take some time. I'll need to verify all the key surfaces on the test centers and also make a sliding indicator base that fits the central slot. In addition to upgrading my indicator.

I've got 5 of test bars: 0/1, 1, 2, 3, & 4 MT. I'll probably wind up with an MT 5 soon. All bought at lowest price on ebay or amazon.

I'm currently trying to decide which Mitutoyo tenth indicator to buy. I'm currently using an ENCO Chinese made indicator. I've had it a long time; it's been dropped by "helpful" mounts a few times (I now have a Noga :-); and never was properly tested that I can recall. I tested all the stuff I had when I bought my B grade 81 piece gauge block set. But I think this came later and was not tested.

I bought a B&S lever LVDT such as Robin Rennitz uses in a number of his videos. I'm looking for an electronics head for it, but can make a temporary unit using my electronics lab gear. I'd planned to design and build one until Robin said he bought his for $61 on ebay.

These appear to be good enough for general use as is, but it's easy to test them. Put the between centers on a lathe, record indicator readings at 1" spacing, reverse the bar and repeat.

As Dan Gelbart points out in one of his videos, you now have 2 equations in 2 unknowns. So separating the error of the bar from the error of the bed is trivial. This is why algebra is part of the HS curriculum.

I have a couple of the cheap Ebay/India test bars, one MT2 and one MT3. Both are accurate to a few microns. The only problem I have noticed is that on one of them the center mark is quite far off center at one end. So if I spin it between centers then one end wobbles and the other end runs true. But if I test it without using the center marks (spin it in V blocks for example) then all is good.

I bought one of the Indian made test bars with a 3 MT couple years ago. It tested dead nuts end-to-end for concentricity. Where I found a problem with the Morse taper. It was good untill you got to about 3/4" from the end on the small end. It was higher than the rest of the taper. You can see daylight under a straight edge from it. Plus, it would not seat properly in the taper of the spindle, which is pristine. It is like they didn't have their grinding wheel dressed correctly. So, be careful when seating one of these test bars in a MT taper bore, it could give you all sorts of false readings!