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Dec 7, 2022 - 3:15:29 PM
204 posts since 11/14/2018

Is there a reason block rims are usuall pretty thick?

I would like to do something around 1/2" but I'm guessing it may be a bad idea since I've never seen one that thin.

Dec 7, 2022 - 3:40:20 PM
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2633 posts since 6/19/2008

Just a wild guess here - it may have something to do with strength. But I think it would work OK. Why not try it and let us know?

Dec 7, 2022 - 3:40:50 PM
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13883 posts since 6/2/2008

quote:
Originally posted by 98v70dad

Is there a reason block rims are usuall pretty thick?

I would like to do something around 1/2" but I'm guessing it may be a bad idea since I've never seen one that thin.


Are they?

I have a block rim made with an integral wooden archtop tone ring top and cut for two-piece flange. Its thickness in the skirt area and at the base of the "tone ring" area are the same thickness as a three-ply rim cut for flange and tone ring.

A block rim made for flange and tone ring has to match up to those parts, same as a 3-ply.

Maybe you're thinking of block rims for open back banjos that don't have to be any particular inside diameter.

Dec 7, 2022 - 3:49:48 PM
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3103 posts since 12/31/2005

Google "Tony Pass thin skirt block rims"

Dec 7, 2022 - 4:36:34 PM
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3221 posts since 2/18/2009

I regularly make block rims between 1/2" and 3/4" thick. I don't like to go below 1/2" on a block rim without veneering it.

Dec 7, 2022 - 4:44:35 PM
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Alex Z

USA

5108 posts since 12/7/2006

The Tony Pass 500TS rim is 0.5" at the bottom.  So the geometry of the blocking and turning should be OK at that thickness.    

When the blocks are glued together, they would have to be of a thickness and arranged in a polygon such that a 0.5" thick cylinder can be sketched out without overlaying any air space.

For example, the Tony Pass rim appears to be made of 8 blocks.

Dec 7, 2022 - 5:26:47 PM
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15095 posts since 6/29/2005

A 1/2" block rim would be strong enough as long as the joints were good.

Dec 7, 2022 - 10:56:51 PM
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martyjoe

Ireland

241 posts since 3/24/2020

I made one of my early banjos with a 1/4” block rim. Nice banjo the owner loves it!

Dec 8, 2022 - 12:32:10 AM
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Players Union Member

Helix

USA

16373 posts since 8/30/2006

In my opinion it depends on what kind of rim is under the head.

I was asked if I could build a 1/2" rim. I've done it many times with no warranty issues.

I think Tony Pass was using 18 blocks, 6 per tier.

I use 8 blocks, I build lighthouses.

I consider "layup" type rims to be "brick" rims with as many as 30 bricks. Some builders with CNC capability found how easy it is to cut smaller pieces and lay them up.
In my experience Layup rims have inherent limitations that include difficulty of different bricks "talking" with each other.


Dec 8, 2022 - 2:13:39 AM
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Paulf

Australia

3409 posts since 2/1/2012
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I disagree that your design is as strong as a Tony Pass or a layup rim. Not saying that they are weak but I can't see them being as solid in a thin construction as others. There is a video of one of your rims with support blocks at either end and that suggest that the use of 8 blocks in this rim needed to be reinforced for strength. I haven't seen another block rim needing to use support or reinforcement blocks.

Paul


 

Dec 8, 2022 - 5:38:04 AM
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15095 posts since 6/29/2005

I think you have to be aware of the forces working on the rim.

In the case of a block rim, what holds it together is the horizontal joints between the tiers—the tension hooks are pulling the head down and actually squeezing the top two tiers together in compression making that joint stronger. The number of segments in each tier is practically meaningless because un-splined end-grain joints are so weak that more sections actually makes it weaker.

The biggest problem is with anything that puts it into shear, or sideways stress, causing out-of-round, like co-rods, which can even distort a laminated rim. That force can break the horizontal joints or the wood itself if it's thin or has a bad grain orientation.

The weakest construction is a vertical stave type rim, very poor in shear, subject to joint failure from humidity fluctuations, and weak in circumferential stiffness, but very very few people do that with banjos.

You can go down to 1/4" with a lamination and still have a lot of integrity, but I would stick with 1/2 or greater with block rims

Dec 8, 2022 - 6:11:57 AM
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Helix

USA

16373 posts since 8/30/2006

Good job Paul        I've done it many times with no warranty issues.

When I send something out of my shop, it has to be good.

The #001 in that series doesn't have the Jatoba blocks at head and tail. It's been out in my shop in hot and cold weather, dry and wet for more than a decade, since 2009. That's part of my research and marketing.
All the others use Jatoba plate that re-establishes the 9-1/2" inside diameter because the rim is thinner, that's the subject of this thread.

Notice the threads on the rim rods, they look normal to me, nothing out of place. 
 

I haven't seen another block rim needing to use support or reinforcement blocks.

You have your favorites and friends, you have established your antagonism about me personally on several occasions.

I care what the banjos sound like, at what weight.  I play them in public for the last 15 years.

I don't subscribe to ideas about how thick a bluegrass rim should be, nor how thin an open back can be.

I'm glad you got to see and hear the video and see the mag mount rez.

I'm always glad to confer with you off forum, but you don't ever try that open avenue. Feel free to contact me personally.

I also use Bamboo for necks and shop jigs, bridges, inlays and HO racecar bodies. 

I notice you use a picture of a video, not the video itself.  I have never seen anyone do that.  Tell us where yo saw that.

Edited by - Helix on 12/08/2022 06:17:01

Dec 8, 2022 - 11:39:19 AM
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204 posts since 11/14/2018

Thanks folks. I appreciate the comments.

Right now what I have drawn up is 5/8" thick but I would prefer 1/2" or 7/16" to reduce the weight if I can make it work. I am using 12 segments of maple to form 3 rings which will be stacked and laminated together. I've already made jigs and fixtures for 12 segments so I'm committed to that part of the plan.

My concept is loosely based on a proffet style banjo so there is a ring of wood that reinforces the hoop at the top and bottom. There is an internal block on either side where the dowel rod passes thru to spread out the shear load.

I'm calling the project the high tech redneck since its made a bit like a mountain banjo but it will incorporate a carbon fiber dowel rod (old trekking pole) and a inner carbon fiber hoop used to tension the head. Its headless and the tuner will be on the pot. It also has a bunch of homemade aircraft aluminum parts.  Redneck for the mountain banjo roots. High tech for the high tech aerospace materials incorporated into the design.  Its pretty different - its been a fun challenge.

I don't have a lathe so I'm hogging the hoop out with a circle cutting jig and a router. That's the plan although its subject to change.

I've been working on this a couple of years. My dad had a stroke and caring for him stopped my efforts for a couple of years. I'm now just about done sourcing parts, wood, etc. and drawing it all up. I think I now have a workable concept.

Edited by - 98v70dad on 12/08/2022 11:43:23

Dec 8, 2022 - 12:17:31 PM
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martyjoe

Ireland

241 posts since 3/24/2020

Sounds like you’re in for a learning experience & a fun experience in between the frustrating moments. Here’s a couple of headless tenors of mine.




Dec 8, 2022 - 2:06:45 PM
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15095 posts since 6/29/2005

quote:
Originally posted by 98v70dad

Thanks folks. I appreciate the comments.

Right now what I have drawn up is 5/8" thick but I would prefer 1/2" or 7/16" to reduce the weight if I can make it work. I am using 12 segments of maple to form 3 rings which will be stacked and laminated together. I've already made jigs and fixtures for 12 segments so I'm committed to that part of the plan.

My concept is loosely based on a proffet style banjo so there is a ring of wood that reinforces the hoop at the top and bottom. There is an internal block on either side where the dowel rod passes thru to spread out the shear load.

I'm calling the project the high tech redneck since its made a bit like a mountain banjo but it will incorporate a carbon fiber dowel rod (old trekking pole) and a inner carbon fiber hoop used to tension the head. Its headless and the tuner will be on the pot. It also has a bunch of homemade aircraft aluminum parts.  Redneck for the mountain banjo roots. High tech for the high tech aerospace materials incorporated into the design.  Its pretty different - its been a fun challenge.

I don't have a lathe so I'm hogging the hoop out with a circle cutting jig and a router. That's the plan although its subject to change.

I've been working on this a couple of years. My dad had a stroke and caring for him stopped my efforts for a couple of years. I'm now just about done sourcing parts, wood, etc. and drawing it all up. I think I now have a workable concept.


The idea of a carbon fiber trekking pole used as a dowel stick is incredibly interesting—why didn't I think of that as a rudy rod? (I ask myself)

The reinforcement hoop top and bottom will really strengthen it so that you can go thinner—you could easily go 1/2", maybe less with the reinforcement hoops—I've seen that with stave drum shells and they use bent ash hoops.  I can't picture exactly what it will look like, but you have obviously thought it through, know what you are doing, and are respectful of the structural stuff. The blocks are a really good idea.

I would love to see the inner carbon fiber hoop used to tension the head—does it push up creating an archtop effect?

I hope you post pictures of this as you go along—it's intriguing.

Dec 8, 2022 - 2:08:54 PM

204 posts since 11/14/2018

Nice! Mine will be similar. I forgot to mention I'm doing internal tensioning so there won't be any hooks on mine. I'm considering using the cut off ends of spent gun shells for fret markers if I can find the right size. Not that important but the brass gun shell fret markers would be an interesting touch.

Where did you get the clear head? I've been looking for a 10" high crown clear head and haven't had a lot of luck.

Dec 8, 2022 - 2:24:54 PM
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15095 posts since 6/29/2005

quote:
Originally posted by martyjoe

Sounds like you’re in for a learning experience & a fun experience in between the frustrating moments. Here’s a couple of headless tenors of mine.


I love what you are doing— I am still coming to grips with the offset stringing of the fan frets—amazing stuff.

How did you do that graphic on the head?

Dec 8, 2022 - 2:44:05 PM

204 posts since 11/14/2018

quote:
Originally posted by Ken LeVan
quote:

The idea of a carbon fiber trekking pole used as a dowel stick is incredibly interesting—why didn't I think of that as a rudy rod? (I ask myself)

The reinforcement hoop top and bottom will really strengthen it so that you can go thinner—you could easily go 1/2", maybe less with the reinforcement hoops—I've seen that with stave drum shells and they use bent ash hoops.  I can't picture exactly what it will look like, but you have obviously thought it through, know what you are doing, and are respectful of the structural stuff. The blocks are a really good idea.

I would love to see the inner carbon fiber hoop used to tension the head—does it push up creating an archtop effect?

I hope you post pictures of this as you go along—it's intriguing.


I had an old trekking pole that I bought at an REI garage sale for cheap because it wouldn't stay extended.  I tried to fix it and there are no parts available.  So, I'm using it on the banjo.  It's 5/8" diameter and plenty stiff.  I don't think it even needs a threaded through rod.  The 9" diameter inner carbon fiber hoop is cut from a scrapped Wild Ideas bear canister (backpackers use them to protect their food from bears).  I wrote to them and asked to buy something that didn't meet spec and two days later I got a box in the mail from the president of the company.   He loved the idea.  He's probably given up on me but I'm going to surprise him (I hope).

Initially I had planned something like a panjo using just the carbon fiber hoop and its aluminum end but there were two problems.  1) the hoop is only 9" diameter which is too small for my taste. 2) the aluminum end is heavily reinforced and just thuds when you ping it.  It took me quite a while to come up with a concept that honors the gifted carbon fiber bear canister and leaves it visible yet is still playable and relatively "normal".  I am keeping the carbon fiber hoop visible by using a clear head if I can find one as well as having a pretty big sound hole on the bottom..

Regarding structure I am retired structural engineer who used to design, among other things, flat bottom cylindrical water storage tanks.  Those aren't a whole lot different from a banjo pot.  As you mentioned, you have to provide a load path.  If you do that you're in good shape.  My concern with a thin hoop is that the glue joint between the stacked rings is that much smaller.  Also, the end joints in the segment have basically no strength at all and thinner means even less than very little.  I've been thinking of using epoxy on the segment end joints - not sure abbout that.

I am putting this all in a engineering CAD program and could potentially post a pdf of what I'm planning.  I'm drawing it for myself so it won't be a drawing that follows the formal rules. Rudy set the standard for excellent drawings and I fall far short of that.   I based the neck and fretboard on one of Rudy's drawings.  

Dec 8, 2022 - 6:00:24 PM
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RV6

USA

1479 posts since 2/3/2012

I have a Sagmoen with a Dobson ring and 24 3/4" scale that is a block rim that measures .35" (11/32") thick. It's made out of Makore.  It has an Ashborn ring for the attachment of the "J" hooks and I imagine this additional mass gives the pot some extra strength.

It's my "never sell" banjo.smiley


Dec 8, 2022 - 7:43:50 PM

204 posts since 11/14/2018

Here is a crude sketch of a partial cross section. As an engineer I am slightly ashamed of the sketch quality but as a retiree I'm not and don't care. Its to scale and good enough to get an idea of what I'm planning.

The carbon fiber ring doesn't do much other than provide a load path for the head tension from the head down to the bottom plate. The carbon fiber ring I have was too small for what I wanted so I've added a 1/2" wide wood (plywood) spacer to give a 10" diameter support for the head. The spacer will want to roll so it will be supported by some (8 to 12) little vertical stiffeners which aren't shown. They will just be epoxied in place to the carbon fiber ring below the spacer ring. Epoxy has a shear strength of around 3000 psi so epoxy for those stiffeners is plenty good enough to hold them.

The bottom plate is glued up from maple stock with the grain oriented along the long axis toward the neck for strength.  Unfortunately the dowel rod is hard to see.  I made it yellow for contrast and it show up great in autocad ... not so much as a white background pdf.


Edited by - 98v70dad on 12/08/2022 20:02:19

Dec 8, 2022 - 8:10:45 PM

204 posts since 11/14/2018

I changed the dowel rod color back to black and uploaded a revised sketch. Forgot to take the comment about yellow out of the last thing I posted.

Dec 8, 2022 - 11:20:21 PM
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martyjoe

Ireland

241 posts since 3/24/2020

quote:
Originally posted by Ken LeVan
quote:
Originally posted by martyjoe

Sounds like you’re in for a learning experience & a fun experience in between the frustrating moments. Here’s a couple of headless tenors of mine.


I love what you are doing— I am still coming to grips with the offset stringing of the fan frets—amazing stuff.

How did you do that graphic on the head?


Remo do a selection of their clear Emporer of drum heads that have graphics infused into one of the layers look up Emprota. 

Dec 8, 2022 - 11:29:58 PM
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martyjoe

Ireland

241 posts since 3/24/2020

quote:
Originally posted by 98v70dad

Nice! Mine will be similar. I forgot to mention I'm doing internal tensioning so there won't be any hooks on mine. I'm considering using the cut off ends of spent gun shells for fret markers if I can find the right size. Not that important but the brass gun shell fret markers would be an interesting touch.

Where did you get the clear head? I've been looking for a 10" high crown clear head and haven't had a lot of luck.


The 10" clear head on that one is a Remo Encore clear drum head it has the crimped fleshhoop & made in Tiawan. The fleshhoops on drum heads are a bit thicker, so you need to allow for that. The great thing about using drum heads is that they offer more choices of thickness & texture. 

Dec 9, 2022 - 2:20:51 AM
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AGACNP

USA

394 posts since 10/12/2011

quote:
Originally posted by 98v70dad

Nice! Mine will be similar. I forgot to mention I'm doing internal tensioning so there won't be any hooks on mine. I'm considering using the cut off ends of spent gun shells for fret markers if I can find the right size. Not that important but the brass gun shell fret markers would be an interesting touch.


Friend of mine had Marty Lanham (Nashville Guitar Co) build a mandolin and did fret position markers that way...turned out really nice!


 

Dec 9, 2022 - 3:01 PM

204 posts since 11/14/2018

Ken LeVan I posted a sketch last night so you can get an idea of what I'm planning. I'm still trying to work out how to make the ring at the top. A ring made of 12 segments will probably be too weak due to the end grain glue joints. Biscuits might address the weakness concern but they would have to be small so they wouldn't show. I don't have the tool for tiny biscuits. Two dowels per joint would work I think. I also considered (and ruled out) a ring of plywood but I don't want the laminations to show at the edges.

Dec 9, 2022 - 3:22:51 PM

204 posts since 11/14/2018

quote:
Originally posted by Jonnycake White

Just a wild guess here - it may have something to do with strength. But I think it would work OK. Why not try it and let us know?


Check for a PM from me about a month ago.  Would still like those plans if they are still available.

Edited by - 98v70dad on 12/09/2022 15:23:15

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