New Toy - Rahn Repeat - O - Meter

[Dabbler]

There's an easy way to 'approximate' an evaluation of a BB surface plate. You use a scratch or height gauge base with a tenths indicator, using a gauge block to average out the bumpy surface. My first BB surface plate was well withing 1/10, and the second is untested. My Mitutoyo is not yet tested (horrors)...

 

[Tom O]

I belive NYC did a build on these in one of their videos.

 

[TOBARApprentice]

I did some more preliminary measuring of the surface plates. The Repeat-O-Meter (fortunately) came with the instructions. I will post them as they talk about calibration and ironically speak to using a surface gage, gage blocks and a test indicator instead of needing the instrument. My 24 x 36 Starrett granite was generally -.00008 to + .0001. There is one spot that was + .0003 (weird). The other Starrett granite 12 x 18 was -.00012 to + .00024. SO...... have to go to Miami tomorrow for 737 Max training, but when I get home Saturday I am going to get going on scraping flat the 13 x 15 Taft Pierce Cast plate to make the lap I need to redo the 2 granite plates...... I’ll start a new thread Monday and get going with some pics and progress. Rabbit hole...... here I come.


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[Proxule]

Lucky guy, Wish I had that sort of expendable income. But I guess this hobby is as expensive as you want to make it.
Fly safe and keep those pratt and witney motors happy

 

[trlvn]

My 24 x 36 Starrett granite was generally -.00008 to + .0001. There is one spot that was + .0003 (weird).

I'm far (FAR) from knowledgable but aren't you into the realm where minor thermal differences could affect your readings? Maybe from your hand resting on a spot? Or maybe radiant heat from an incandescent bulb?

Also, I recall watching a video about 3-point support for granite surface plates [1]. As it happens, he was setting up a 24X36X6 granite.

What spec are you aiming for? AA?

[1]

Craig

 

[TOBARApprentice]

Shooting for A on my large granite and if possible I am going to shoot for AA on the small granite. We’ll see. I looked up what this thing new costs.... for the Repeat-O-Meter, the storage case and the Supremess indicator is $4000 CAD. I paid nowhere near..... it was genuinely garage sale priced.....

 

[Dabbler]

I paid nowhere near

Even more jealous!

 

[PeterT]

Is your ultimate goal restoring or re-tuning machines, or you are just keen on metrology in general? Not judging, just wondering LOL.

 

[TOBARApprentice]

I genuinely want to learn this part of the trade. I think I would like to eventually be able to make a few bucks re re-certifying and resurfacing plates, but from a hobby standpoint. If I can get good enough, and get some experience then maybe 5 - 10 years down the line I might be able to make a go of it. I got out the autocollimator the other day and made some preliminary measurements..... lots to learn!


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