Just unexpectedly won a Rek-O-Kut B-12-H (!!)

Is the shaft a standard size? You might be able to buy an oilite from McMaster that's an exact fit or one where all you have to do is ream the plastic a tiny bit to fit it's OD. Keeping the factory ID on the oilite would probably yield the smoothest surface.

The diameter of the steel idler wheel shaft appears to be .22 inches or about 5.61 mm. Assuming that's the correct size, then what' the correct inner diameter of the oilite bronze bushing? Should it be slightly larger than the shaft? If so, by how much?
 
You bring up a very good point, other than an original Micropoise S320 or a new Jelco, what reasonably priced tonearm options are there that would sound good and are drop in replacements for a ROK B-12H/B-12GH?

I asked myself this same question when I got my B-12GH. I didn’t want to spend over $500, and wanted the best possible sound in that price range. My other criteria was that it needed to look period correct and not too modern (ie Jelco or Audiomods), and work well with low compliant carts like the DL103. @beatcomber turned me on to these Gray clone arms built in the Ukraine by Serge Karmadon. It checked all the boxes. I ordered one and couldn’t be happier, it’s beautiful, and the sound is fantastic.

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I asked myself this same question when I got my B-12GH. I didn’t want to spend over $500, and wanted the best possible sound in that price range. My other criteria was that it needed to look period correct and not too modern (ie Jelco or Audiomods), and work well with low compliant carts like the DL103. @beatcomber turned me on to these Gray clone arms built in the Ukraine by Serge Karmadon. It checked all the boxes. I ordered one and couldn’t be happier, it’s beautiful, and the sound is fantastic.

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Here's a link... several models are available:
http://www.karmadon.net/shop/klon-tonarma-gray-108/

One of these is on my short list, for down the road.

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I really like the looks of the Karmadon designed unipivots. I could see one in my collection in the future for sure. :)
 
The diameter of the steel idler wheel shaft appears to be .22 inches or about 5.61 mm. Assuming that's the correct size, then what' the correct inner diameter of the oilite bronze bushing? Should it be slightly larger than the shaft? If so, by how much?

Its probably 7/32 on the axle shaft, which is 0.2187. The bushing needs to be larger, but probably by .001 at most for a shaft that size.
 
Thanks! 7/32 for the ID looks like it might work. It worth trying, but the other dimensions look off.

I took some additional measurements of the bearing embedded in the old ROK wheel. It is nearly .5" in length (or height, if you will). But McMaster seems to only offer 3/8 for the length. Additionally, the OD of original bearing is .349"
 
So if ROK used fractional sizes back in the day when selecting their bearings for their idler wheel, perhaps these are the correct idler wheel bronze bushing/bearing dimensions for the steel shafts that are 0.22" in diameter:

  • ID: 7/32"
  • OD: 11/32"
  • Length: 1/2"
I think it would be worth trying to find a bearing with these dimensions and test it on the steel shaft to confirm.

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I'd be curious how much work would be involved in replacing the idler shaft with a 1/4" replacement so that you could use off the shelf bushings. 1/2" length x 1/4" ID bushings have to be dime a dozen.
 
I'd be curious how much work would be involved in replacing the idler shaft with a 1/4" replacement so that you could use off the shelf bushings. 1/2" length x 1/4" ID bushings have to be dime a dozen.

I'm pretty sure the OEM 0.22" idler shaft just screws on to the arm from the underside.
 
hm, if that just screws in, it would be possible to make one in a more convenient diameter. Might have to embiggen (its a technical term) the hole in the idler to use a common size bushing, or turn down the OD of a bushing with the right size ID.

Do you happen to have a micrometer to confirm the size of that thing? It definitely wouldn't be a metric size in the 50s. Not a guarantee its a fractional inch either, but that was common practice rather than just arbitrary sizes unless there was a specific reason for said arbitrary size.
 
Do you happen to have a micrometer to confirm the size of that thing? It definitely wouldn't be a metric size in the 50s. Not a guarantee its a fractional inch either, but that was common practice rather than just arbitrary sizes unless there was a specific reason for said arbitrary size.

Not sure how accurate this is, but this measurement is showing the shaft diameter as 0.22 inch. This tool may not be 100% accurate so it should be considered approximate.

0.22 expressed in inches is an oddball size. That's why I'm thinking that a fractional 7/32" may be more likely as to what ROK ordered back in the day. 7/32 was probably more of a standard size option for an orderable shaft and bearing/bushing.

IMG_8715.jpg
 
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Not sure how accurate this is, but this measurement is showing the shaft diameter as 0.22 inch. This tool may not be 100% accurate so it should be considered approximate.

0.22 expressed in inches is an oddball size. That's why I'm thinking that a fractional 7/32" may be more likely as to what ROK ordered back in the day. 7/32 was probably more of a standard size option for an orderable shaft and bearing/bushing.

View attachment 1239360
What I did on my CVS-12 was take the idler wheel to the machinist he reamed the bushing then made a new shaft to fit. Simple and perfect. ;)
 
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