Rockwell tester - China made - worth of buying ?

These look like Wilson clones. Hardness testers are pretty basic units: a dead weight, a lever, a comparator and a diamond indenter encased in a very heavy and rigid body. So regardless of the way you choose keep in mind that calibration is not rocket science, but calibration labs may charge you the same amount you paid for an old unit...

Here is what I did to calibrate mine:

Most Hardness testers come with a testing block with the hardness engraved on the side, mine is 64.5 +/- 1RC and also the dead weights on the back are adjustable, meaning at least one of them is hollow filled with steel balls, the same used for blasting.

So with your testing block and some of these filler steel balls you can adjust your unit very well, having a digital scale to measure initial weight and the increments helps.

When I purchased mine (used) I did a "knife community calibration" which translates to:

Bought a bar of round K460 (O1 steel)
Sliced it in 10mm "cookies" , 10 units
Turned both sides flat on a lathe
Hardened according to K460 datasheet
Without tempering I surface grinded both sides
They came dead on 64-65RC
Took 4 and tempered according to datasheet to 60-61RC
Took 3 and tempered according to datasheet to 55-56RC

Kept one sample of each and gave to other knifemakers with access to Hardness testers the remaining pieces with my measurements written with a sharpie (and a big DO NOT USE THIS SIDE on the opposite side)

They measured using their hardness testers, kept one sample and informed me the results, they were within +/- 1RC which is the acceptable range, at least for me. Now we know at least our testers measure the same :)

Keep in mind when you measure hardness that the initial 3 readings must be discarded, then you get accurate readings.

Good Luck!


Pablo
 
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I'm not a 100% sure, but I believe that's the same Chinese clone I have. It works perfectly and I've also used a similar method of verification as PEU suggested. Really all you need is good test blocks in a range of hardnesses. They're probably provided with the machine like mine was. It was in the 800$ shipped range and worth every dollar.
 
I'm in the market for one and can't justify the cost of a new domestically produced tester. I've seen them for sale by large companies that machine parts and plan on buying one that way. I've been at a couple sales or auctions for companies moving or going out of business and they go for about $1000 for the nicer models. The upside is they are usually high end brands and they have to get them certified every year or more for accuracy. I've bought several machinist tools that were certified a few months before I bought them telling me they are good to a level I will never need, at least for another year :)
 
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