Risk involved in buying used Jo Blocks

I am considering buying a set of Jo Blocks. They are used, and at a bargain price for a grade 00 set of 81 blocks. The grading system changed in 2003, so these are newer than that. How risky is this? What should I check for? Any words of advice/ caveats are appreciated.

They may have been used as marker blocks on somebody's surface or blanchard grinder......

Would there be some telltale sign of this?

If you plan on having them calibrated then there is very little risk. The new calibration will tell you the exact sizes of them now, no matter what they were when made.
That said, unless they are visibly scratched or damaged it is pretty unlikely that they changed size enough to matter for most work.
if you were actually doing work where millionths might matter, I suspect you would pony up for a new set of blocks.
Worst case is that you have a "shop grade" set of blocks which can be very handy for fixturing things that that would be considered rude treatment of a new set.

-mike

Wring or not wring is the decider. Basically if they all wring together in a satisfactory manner then odds are that they will still be sufficiently close to calibration for general work. Obviously not high end inspection purposes but still good enough to track variations in micrometers or similar measuring instruments.

If they wring poorly its an open question but its probably affordable to have the faces restored and the blocks re-calibrated. Arguably starting with a poorly wringing set and having them re-polished and calibrated could be preferable to an out of calibration set that still wrings well.

If they don't wring then you have high grade spacer blocks. I have a non-wring set that does just fine to set the bed stop on the lathe and similar duties.

Always assuming they are a decent, proper material and properly heat treated, brand of course. Low end imports can be expected to move after 5 years or so but its all very unpredictable so at under 10 years even a low end set ought still to be close to calibration. Actually given that a low end set can be got for around calibration costs and decently precise probes can be got at, by historical standards, very affordable prices its arguable that setting up to track varation and buying new sets at fairly regualr intervals is a viable way to go about things. Good luck at getting that idea past an ISO9000 inspector tho'. Given an appropriate degree of low cunning and sweet talking of the laws of physics tracking variation is a lot easier than calibration but you can't use the results to give a new size. Pure go - no go.

Clive

Yup, as mentioned : wringability is a decent indication of their condition.

If the price is right and you feel like taking a risk you`ll have a set to use on the machine in the worst case scenario.

Of course having them compared to traceable standards by an acredited calibrationlab is the only way to be sure of their condition

Few things I would check, calibration records, is that company still in business?
Are the markings still readable?
Grab a few randomly and check to see if there in the right slots.