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1925 Ballbearing to Flathead Conversions: Must the rim Necessarily be Cut?

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May 19, 2022 - 10:05:15 PM



605 posts since 7/30/2004

I am interested in possibly buying a 1925 Gibson Mastertone. Like all 25 Mastertones, it originally
had a ballbearing tone ring but was converted to a flathead tone ring at some point. Does such a ballbearing to flathead conversion ALWAYS require the original rim to be cut or modified in some way to accept the flathead conversion ring? The seller, a knowledgeable man whom I respect, tells me that to his knowledge, the rim hasn't been altered in any way to accept the flathead ring. Is such a conversion to a flathead from ballbearing ring possible without cutting or modification? Thanks for your help.

May 20, 2022 - 12:10:05 AM
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469 posts since 12/30/2005

Although I've never owned one, I've always found the idea of bb Mastertones appealing. I did play one many, many years ago and really liked it.
Of course, here in the UK they're even rarer than in the USA.
My understanding is that they can be converted to flat heads without making any change to the original rim, but a special conversion flat head ring is necessary. I've seen one or two banjos advertised for sale on the Hangout with the conversion ring in place and all original bb parts available should the new owner wish to switch back. Of course, to know whether the banjo you're considering was converted in this way, you'd need to dismantle it.
There's a lot of discussion on this subject in the Hangout forums. I found it by typing 'bb conversion ring' into the forum search.

May 20, 2022 - 3:07:13 AM
Players Union Member



577 posts since 3/25/2009
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I have a bb. At one point, about 15 or more years ago, I bought a conversion flathead ring from First Quality. I played it that way for a few years until info I read here got me to set up the bb ring, which I much prefer. Short answer, no you don't have to cut the rim.

May 20, 2022 - 4:49:48 AM

4869 posts since 11/20/2004

No, to ALWAYS. The FQMS BB conversion rings were said to fit 1926 models and some 1925 models without cutting. Some ring makers also machine their rings to custom fit rims when needed.

May 20, 2022 - 7:26:26 AM

76240 posts since 5/9/2007

They have turned the bb ring upside down in the past.
An old BNL classified ad said one of these could "kill chickens at 100 yards."

May 20, 2022 - 9:37:15 AM
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Bill Rogers (Moderator)


26051 posts since 6/25/2005

The ‘25s are different and you have to have either a specially cast conversion ring or one turned and fitted by a machinist like Steve Huber. The standard bb conversion rings fit later shells. Personally, I would not buy a converted bb that was absent the original ring, springs, washers and ball bearings or had the rim holes doweled.

May 20, 2022 - 10:11:40 AM

2866 posts since 4/5/2006

Those ball bearings were only made from 1925/ to maybe 1927/28. The 25's were unique. Gibson changed the skirt design in 1926. There are plenty of banjos, better suited for Bluegrass, for less than the price of a 1925 Gibson ball bearing. Leave the ball bearings for those who appreciate them for what they are.

Earl Scruggs played many Gibson banjos, before settling on the Granada. I'm sure he had plenty of opportunities to own a ball bearing. Nuff said. If you're in the market for a Bluegrass banjo, buy a Bluegrass banjo.

Edited by - monstertone on 05/20/2022 10:23:12

May 20, 2022 - 11:27:01 AM

2850 posts since 4/16/2003

Kind of agree with the post right above this one.

But... as was also mentioned above...
If you buy the '25, you will have to ascertain if it's one the 1925 models that CAN accept a "standard" ball-bearing-to-flathead conversion ring, or CANNOT.

If it cannot, then send the banjo to Steve Huber, who can custom-machine a flathead ring to fit.

But again, you could probably do as well with a "late model" Gibson (1987-2009) or a more-recent 3rd-party maker...

May 20, 2022 - 1:01:05 PM

14767 posts since 10/30/2008

A "standard" flat head ring will not quite fit a BB rim (either 25 or 26). The rim is about 1/10" too tall. Additionally the seating area for the "skirt" is different. Fitting a regular flat head means cutting 1/10" off the top of the rim, or adding a filler piece at the bottom of the skirt area to give a smooth surface viewed from the outside. The diameter of the top of a BB ring is also a bit too small to fit a regular flat head tone ring. A regular flat head tone ring wouldn't "center" itself on the rim. Way beyond a "slip fit". More like a "slop fit".

I went the second route on my 26 conversion. Jimmy Cox used a "regular" Cox flat head that had had no holes drilled. He thought the added weight would help make up for the lighter weight rim (with all the drilled holes in it for the springs and bearings). He made a 1/10" filler piece from a complete new rim (!!!) and fit it beautifully like a collar at the bottom of the tone ring/skirt area, and also filled in EXACTLY the gap from the too-small-diameter rim. The whole assembly was "press fit" onto the BB rim by our four hands.

It worked GREAT except my pot was now 1/10" taller than it used to be so I had to waller out the coord. rod holes to get the neck to sit higher than it used to.

I played the banjo this way for almost 20 years and loved it. Sounded like the Gong of Doom. Then after I got other post 1987 Gibson flat heads, I put the BB guts back in the 26.

If you want to try your BB out as a flat head, save yourself a lot of custom woodworking and just buy the correct BB conversion ring. I can remember when there were conversion rings that ONLY fit 1925, and later, conversion rings that only fit 26. Just be sure you know what you need, and drop it in place, and save the BB guts very carefully.

May 20, 2022 - 4:18:17 PM



605 posts since 7/30/2004

I appreciate all the insights. As usual, BHO people are knowledgable and helpful. I am actually interested in the 1925 as a Ballbearing Banjo but the one I'm looking at presently has a flathead conversion ring on it. If I bought it, I would want to change it back to the original tone ring.

I was trying to find out if a flathead conversion always required that the rim be cut or otherwise modified, because I'm looking for one with an uncut/unmodified rim (And I don't think you can tell if the rim has been cut without taking the head off.) I agree that flatheads are great for bluegrass, but I'm interested in that "ballbearing sound."

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