Oversized !23 blocks, why?

[Cannonmn]

1. Ran across a set of “123 blocks”’very neatly finished, signed, but was surprised to learn they all measure 1.003 X 2.010 X 3.016 inches I haven’t measured many 123 blocks but have always thought those made with any care at all would measure very close to 1, 2, and 3 inches respectively. Is this set unusual, or are 123 blocks always only nominally those measurements?

 

[AD Design]

My limited experience shows me that one can/could/should expect more expensive tooling to be on size AND square/parallel within stated tolerances. The last set of blocks I purchased, rather than made, were oversize. I brought mics with me to verify that they were oversize as I prefer to grind them in myself when possible and save a few bucks. I prefer through hardened to case hardened if I'm going to grind in. With less expensive blocks/tooling I don't feel I can trust the stated tolerances to be met. Leaving .015 is just a tad much but it's not unreasonable. If you want dead nuts size and Sq./parallel within a few .0001's you'll have to pay for it. Higher priced items are often that way for a reason. JMO

 

[mhajicek]

You can buy blocks that are slightly oversized, with the intention that you will grind them in to nominal to your preferred standards. I'd expect a couple tenths to a few thou over on all faces, but 16 thou is too much. Someone's tech school project?

 

[MCMLXIX]

I purchased a pair of Moore blocks back when you could still bid and get a good deal on ebay.
When they arrived I was surprised to find that one of the blocks was as expected on the 2 large faces but still black oxided and .005" over sized on the 4 smaller sides.
Just need to be careful when I use that one.
The Moore 123 blocks when combined with their smaller brothers seem to be the most useful to me, with the Hermann Schmidt blocks a close second.

 

[fciron]

I have a shop made pair that is <1,<2,>3 but they’re consistent shop made across the pair and good and square. They work for lots of things.

 

[eKretz]

As a shop-made set I would say that they were probably just never finished. All set for you to finish grind.

Some manufacturers leave their blocks several tenths oversize on purpose so that they can be finished by lapping if so desired.

 

[fciron]

Oh, they’re already undersized in 2 dimensions. They just big, handy parallels now.

 

[Limy Sami]

I'm wondering if they weren't finished to size - like ''pre ground'' or another job came alone - etc etc ...so they never got finished.

Just a thought.

 

[michiganbuck]

Hitting size and square to .0002 and better takes pretty high skills and a decent machine. Possible someone decided to waiit for better skills or a better machine before finishing.

 

[Lost in LA]

In the late 60's and 70's my father made commercial 1-2-3 blocks. He was in production for 4 or 5 years and made a lot of them. Cross holes every direction in groups of 3 and made out of a form of cast iron called mehanite--Hope the spelling is correct.

They were Blanchard ground to about .005 inch oversize in all 3 dimensions.

I believe what Cannon is seeing is a homemade set, partly finished in each direction. The maker either ran out of time or skill or proper machine to finish them. Or perhaps they have not been hardened--yet.

The act of finishing them required pairs to be ground together and then forevermore to be kept as a matched set. They were to be 2 to 3 tenths oversize and parallel to 1 tenth.

The idea of oversize was to allow nominal lapping by a skilled machinist or left alone (as most did) and let years of use wear them in.

Lost
Fisher Machine