metric 123 blocks??

I have just finished making an extended micrometer, see:

http://mikesworkshop.weebly.com/extended-micrometer.html

This is based on a design by mklotz.

It is fine "as is" for relative measurements but in order to make absolute measurement I need some standard precision blocks that are 25, 50 and 75 mm long to provide calibration standards.

I have some imperial 123 blocks that are certified to 0.0005" but what I really require is the metric equivalent of a 123 block i.e a 25 x 50 x 75 mm block. This would make a good calibration standard for the micrometer.

Do precision 25 x 50 x 75 mm block exist? If they do who supplies them?

Any ideas?

Mike

Mike,

You would be better off with slip gauges.

How about Stevensons 10-20-40 or 20 -40-80 mm blocks from ArcEuroTrade? Not what you asked for I know,but needs must sometimes

I bought some individual Mitutoyo gauge blocks in May.

611675-131 50mm £33.67 +vat

611635-131 25mm £25.12 +vat

Just letting you know the cost if you go this route.

Martin

A bit of 'googling' found this (scroll down for the metric ones) **LINK**

And on aliexpress **LINK**

pgk

Would the outer diameter of ball bearing races serve your purpose? Anyone know what typical tolerances they are ground to? Steve

I would just use the Imperial ones you have and a calculator. Job done for no cost.

Hi Mike:

Google 'micrometer standards' and you will find sources of the little bars with plastic insulating handles that are used to, well, set micrometers. Cheaper than gauge blocks.

Neil

I think Chris has made the most sensible suggestion. Just use 1", 2" & 3" instead of 25, 50 & 75 mm and calibrate the micrometer at the 0.4mm, 0.8 and 1.2mm points on the micrometer scale instead of calibrating using the 0.0 point.

I would go with slip gauges every time.

Tony

Looking at that tool I wouldn't bother, I'd just use a digital caliper or buy a large Mic.

Vic, would you care to elaborate why you think the tool is so bad.

Mike

The extending bar is probably too flexible for "precise" measurement? Micrometer frames are usually very stiff.

Since 1959 the inch has been defined as exactly 2.54 cm so your imperial 123 blocks if made to standard since that date should have precise metric equivalents. Even if before the difference will be so small that you wouldn't be able to measure it.

Thanks for all the responses. They have provided some interesting things to follow up on.

Mike

Too many ways for errors to creep in. I can't help thinking if it was such a good idea it would have been done 60 years ago. I've also seen lots of cheap second hand Mics available over the years.

Exactly.