Sunnen bore gauge setting fixture. Accuracy of it and problems?

I recently found a used Sunnen bore gauge setting fixture (0 to 2"). It looks in close to new condition. After setting the zero it reads .0003" off at 1" and .0006" off at 2" using gauge blocks. Yes I know due to errors in the screw thread, no micrometer is gonna read dead on at all points. But I was not expecting this much. If I zero it at 1" it is still off .0003" at 2". It measures the blocks as too small.

So .0003" off for every 1" of travel seems a bit much. My 60 year old Lufkin 1" to 2" micrometer measuring the same gauge blocks is only off only .0001" in a inch.

So what I am wondering, is this the expected result or do I have a worn out Sunnen micrometer? Having to put gauge blocks in it to calibrate it for whatever bore size I will be honing does not make it a very useful tool. I was hoping this would save time instead of using ring gauges or blocks.

The setting fixtures I recall used a 1" travel Starrett mic head. You could find a replacement mic head. I would question how well the gage blocks are setting in the fixture. ISTR Sunnen used round setting masters to check the fixture.

Mine is dead on, You can send it to Sunnen and have it checked and serviced. I had my bore gauge done by them and it is right on and the cost is reasonable.

I have a 0-2 and a 2-6. I would expect under .0001 per inch. I can't imagine that huge micrometer head being that far off without some obvious operational issue.

When used in a production environment, there are wear parts.
Sunnen offers calibration services and replacement carbide ball tips.

jack vines

Never used one but it sounds like factory repair and calibration time, ........eons back I had a Starrett DTI done in their Scottish plant and ''couldn't believe'' I'd got the same tool back (I had, ......lets just say a service was long long over due )

I had a very similar experience when Verdicts did my lever type DTIs

Update: After disassembly and cleaning in an ultrasonic cleaner and then lubed with the lightest spindle oil I have it is now off only .0001" at 1" and .0001" at 1.8" then at 2" it is off .0003"

I think it spent it's previous life being used in the 2" range and the spindle threads are worn there. So will send it back to Sunnen and see what they say. I am guessing a new spindle will fix it?

Sunnen recommends using ring a gauge to check accuracy. The set master should have a .800XXX ring gauge with it for that purpose.