# New Toy - Rahn Repeat - O - Meter



## TOBARApprentice (Feb 22, 2021)

Last week I inquired for a friend about a granite surface plate here in Ontario. I asked the typical questions including what grade it was and wether it had been calibrated recently. The owner got back to me, that if I wanted, for a whistle, a song and some bread crumbs he’d throw in this “tool” he had for measuring surface plates. I asked for his number and couldn’t dial fast enough. I told him that I had been inquiring about the plate for a buddy but what was the “tool”. I already have an autocollomator and I had my fingers crossed that he wasn’t going to say “autocollimator”; he didn’t. He said (I was dying in the suspense). The second he starter with the Rah..... sound I knew what it was and I wanted to finish the sentence for him, but I bit my tongue. If any of you fish, (I try but am horrible) it is like when you get a really big fish on line that is in no way supposed to be able to handle the fight you now have on your hands. You’re excited, scared, and a bunch of other emotions all at the same time.... I digress

....n Repeat -O - Meter. I told him I’d take it and asked for his coordinates to sent the E-Transfer and within 15 min I had some pics, he had payment (1 whistle, 1 song, and a healthy handful of bread crumbs). By lunch it was on it’s way and I had a Canada Post tracking number. 

It arrived today, nicely packaged and both safe and sound. I poured a cup of tea and went down to the shop and opened the package like an 8 year old on Christmas morning. Here it is...... in all it’s glory; and in what I would describe as “brand new” condition. 

I count myself fortunate to have this awesome little piece of kit. Thanks for reading to this point..... my wife thinks it is a stupid chunk of metal, and when I tried to explain she just laughed, called me a nerd and walked away. Just wanted to share with some of my “Pals”. 

Cheers all, no you can’t borrow it. LOL. 

























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## Hruul (Feb 22, 2021)

Never heard of it before, but nice score.


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## YYCHM (Feb 22, 2021)

Your wife calls you a nerd to eh  Nice score!

Now you have to explain what one does with it


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## Brent H (Feb 22, 2021)

Wow - it is like new - like off the shelf!!

I think Oxtool does a pretty good video on surface plates and the use of this particular tool 

@TOBARApprentice :very nice acquisition!


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## Janger (Feb 22, 2021)

What's the scale on that dial? 0.00002"? one fifth of a tenth? So how accurate is your plate?


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## Dabbler (Feb 22, 2021)

wow I've wanted one for 30 years!  you lucky dog!  AND an autocolumnator!  wow!!


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## Dabbler (Feb 22, 2021)

@Janger, it was available with a Mahr indicator that read in 2 millionths and 20 millionths of an inch.  Mine reads in millionths of a meter but *sigh* not repeatograph to go with (yet!)...


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## TOBARApprentice (Feb 22, 2021)

On the Rahn, it came with a .00002 Mahr Surpramess indicator. I have these other 2 indicators as I was planning to scratch build a Repeat-O-Meter. I’m guessing I’ll keep the Millimess but I plan to sell the Supremess. 


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## TOBARApprentice (Feb 22, 2021)

I tested my Brown and Sharpe 20 x 30 cast iron plate. It was indicated + .0002 to - .0003. Moved on to the Taft Pierce 13 x 15 cast iron plate. It indicated + .0002 to - .0002. Both will be scraped and with some luck I will get them under .0001 total flatness. I have a Starrett 24 x 36 and a Starrett 12 x 18 that I’ll check tomorrow. It’ll be interesting to see how far down the rabbit hole I end up, but I’m guessing that I will find I am in good company on the way. Cheers all.

Derek. 


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## Dabbler (Feb 22, 2021)

Nice kit!!

I have a granite 18X24 mitutoyo AA plate I bought used, but I will one day build a repeatometer and check it.  There are no metrology labs in the West that can check a surface plate.  sigh**.


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## YYCHM (Feb 22, 2021)

So..... I looked this thing up and came up with this "Detects local error, not overall flatness".  What's the point?  

I thought the purpose of a surface plate was to provide a flat reference?


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## David_R8 (Feb 22, 2021)

The least you could do was put some dust on the case so we're less envious! 
What a score!


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## Dabbler (Feb 22, 2021)

Craig, you use a autocolumnator to measure local slopes, but that device cannot measure directly what the mechanical deviations are.  the repeatometer does this.  It doesn't certify the plate by itself:  local deviations can be cancelling or be cumulative,  the autocolumnator will show this.  it can only be used alone when the deviations are very small.

TOgether they can be used to certify a surface plate.


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## RobinHood (Feb 22, 2021)

I’ll be interested in the Supramess.


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## DPittman (Feb 23, 2021)

Cool like new and super precise..what a good combo.   I wouldn't know what to do with it myself but I can appreciate the  joy of owning one. Congrats


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## Crankit (Feb 23, 2021)

Lol...Got to love stumbling across great tools! Keith Rucker just did a video on getting his Repeat-o-meter and had been watching out for one for almost a couple of years.  Enjoy the life of high precision!!


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## Proxule (Feb 23, 2021)

Wow.... beautiful.
So.... Can I barrow it? LOL


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## Crankit (Feb 23, 2021)

Anyone wanting a new one? Starrett has taken over the patent on the Rahn and selling for $1734USD!!


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## PeterT (Feb 23, 2021)

Nice score. 
Just for kicks one day if the opportunity presents, I'd like to see a real life reading of Busy Bee (or similar) cheapo granite. They claim good numbers within the specified grade reference, but I mean who really knows. Not advocating relative value, more just morbid curiosity. Of course a Monday BB granite might be different than a Friday granite too LOL


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## Proxule (Feb 23, 2021)

PeterT said:


> Nice score.
> Just for kicks one day if the opportunity presents, I'd like to see a real life reading of Busy Bee (or similar) cheapo granite. They claim good numbers within the specified grade reference, but I mean who really knows. Not advocating relative value, more just morbid curiosity. Of course a Monday BB granite might be different than a Friday granite too LOL



Shars granite squares were out of spec by a lot, Some members of another forums posted.


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## Dabbler (Feb 23, 2021)

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)...


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## Tom O (Feb 23, 2021)

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


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## TOBARApprentice (Feb 24, 2021)

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 (Feb 24, 2021)

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


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## trlvn (Feb 25, 2021)

TOBARApprentice said:


> 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


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## TOBARApprentice (Feb 25, 2021)

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.....


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## Dabbler (Feb 25, 2021)

TOBARApprentice said:


> I paid nowhere near



Even more jealous!


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## PeterT (Feb 25, 2021)

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


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## TOBARApprentice (Feb 25, 2021)

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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