[GME]

When stacking block that do not wring, there is not an insignificant error that can be induced. My mentioning 1-2-3 blocks was that they do not wring, as well as not being "accurate" enough to be used as gauge blocks like this. In general.. I completely understand using to the maximum what is available to you. My concern is that you may be assuming that by adding the lengths together you will have an overall accurate dimension. This is difficult with gauge blocks that wring. So my comment is that you have 2 things against you with this set up.

Thank you for sharing your concerns. I agree that 123 blocks lined up are probably not 100% accurate, especially given that I am not using the $100+/pair high precision blocks. And no, I did not make unrealistic assumptions about accuracy. I knew going in that I was not going to get perfection, but believed that using the blocks was likely more accurate than using a steel rule and some sort of pointy object mounted in the spindle, or other alternatives. Wringing was not in the cards, even if the blocks I used could be wrung. There were to many of them. In any event, the method I used was certainly more accurate than using a tape measure, which I seen others use. FWIW, I have an I-Gaging 36" steel straight edge with rule, but elected to use the 123 blocks. I thought I would get more accuracy with the blocks. With a rule, assuming it is very precise, you have to get both zero and the end length dead on. I have no confidence that I could do it well, even with a magnifying glass. I am not capable of making visual judgments in thousands of an inch.

I could have also used a dial indicator and measured over an inch distance. It thought about and rejected it. One problem with the method is the accuracy of the indicator. They are commonly rated at +/- .001", which can introduce a good deal of error over longer distances. Certificates on some of the expensive ones show an error in the .001" range at 2 dial revolutions. At 36", you could be off as much as .036". A huge error. It gets even more complicated, because the indicator's spring pressure can and will move the holding arm by around .0002" at 1/2 inch of movement - even for good brands of arms, like Noga. Of course, as spring tension increases. as would be the case with a 1" measurement, so will the holding arm movement. Assuming .0002" of movement, you would be off .0072" at 36", exclusive of any error in the dial indicator itself.

As I believe is evident, I gave all this a lot of thought. At the end of the day, I had to pick what I hoped was the the best of imperfect choices.

Having identified potential inaccuracies, which I truly appreciate, do you have any suggestions about how I might do it more accurately? As much thought as I gave to the process, I could have overlooked something obvious, or not so obvious. If you have a CNC, how did you do it?

Thank you,

Gary