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Jun 13, 2018 - 6:27:40 PM
182 posts since 5/11/2018

Here's one for the builders: I am planning a banjo which will use closed ball-end tension hook nuts, which are quite long. I would like to keep the nuts screwed well up onto the hooks so that the ball ends don't protrude past the edge of the rim. But at the same time, I want to make sure I don't run out of threads when I bring the head up to full tension (there's no way I'm adding more 28 tpi threads).

So my question is: Say you've got a pot assembled with everything in place and snug, but with no tension on the hooks. About how many turns of the nuts would you estimate it typically takes to bring the head up to full tension? Another way to look at it is, how far down does the tension hoop move when the head is brought from snug with no slack, but not tight, up to full tension?

Once I have an idea of this value, it will tell me how high on the rim I can place the shoes and still have enough reserve travel to tighten the head.

Thanks in advance.

Jun 14, 2018 - 3:23:11 AM

2303 posts since 2/18/2009
Online Now

The way I do it is to look at how far down the tension hoop would likely be if the head were tight, and then add in another bit of space for a safety factor, maybe 1/8" to 1/4". On shallower rims I sometimes have to cut some of the threaded portion off the hooks in order to keep them from bottoming out in the closed end nuts, but that's not hard to do. I would put a shoe on a hook and put a nut on, and either test it out on paper or better on the banjo rim if you have that done, just to see where you need to drill the holes to get the nuts where you want them, and if you will have enough space. If not you can add a rim cap and drill the holes lower down.
Zach

Jun 14, 2018 - 4:08:22 AM
Players Union Member

Helix

USA

11368 posts since 8/30/2006

In Scrugg's book they make a nice little block rim so shallow the hooks protrude way past the bottom of the rim.

Just adjust the rim height. Write it down, try to standardize. Zach knows.

Jun 14, 2018 - 4:36:06 AM

4258 posts since 11/20/2004

I understand the question, but with variations in head types, crown heights, and different opinions on full tension, I would think it hard to give an accurate answer. Some heads continue to stretch for months, some stop after 2 weeks, and others longer.

Jun 14, 2018 - 6:08:06 AM
Players Union Member

rudy

USA

12870 posts since 3/27/2004

quote:
Originally posted by frisco slim

Here's one for the builders: I am planning a banjo which will use closed ball-end tension hook nuts, which are quite long. I would like to keep the nuts screwed well up onto the hooks so that the ball ends don't protrude past the edge of the rim. But at the same time, I want to make sure I don't run out of threads when I bring the head up to full tension (there's no way I'm adding more 28 tpi threads).

So my question is: Say you've got a pot assembled with everything in place and snug, but with no tension on the hooks. About how many turns of the nuts would you estimate it typically takes to bring the head up to full tension? Another way to look at it is, how far down does the tension hoop move when the head is brought from snug with no slack, but not tight, up to full tension?

Once I have an idea of this value, it will tell me how high on the rim I can place the shoes and still have enough reserve travel to tighten the head.

Thanks in advance.


Draw a side view of your assembled profile, using the dimensions of all of the parts you are using.  On a new design I place the tone ring, head, and tension band over the rim and pull them down over the rim and mark where the bottom of the head bead will end up on the rim's side.

You can then assemble one of your hooks, a shoe, and a nut to see the "interplay" between those components and the portion of the rim between the mark you made and the rim bottom.  I usually shoot for setting the nuts 1/8" back from the rim's bottom edge, as I really dislike pokey banjos.  For that same reason I make my shoes so the hook shank is as close to the rim as possible while still allowing a wrench to slip easily over the nuts.  Having your hardware pulled in will substantially increase the comfort factor of an open back.  Seeing banjos made that have the hooks splayed outward makes me cringe.

The other important point as you do your hardware layout is to make sure you allow sufficient room between the top of the shoe and the bottom of the head bead so there's room to pull the head down.

You'll find on the average mylar head it generally takes about 4 turns of a nut (if you're using standard 26 tpi hardware) to go from "hand-snugged" to full tension.

Jun 14, 2018 - 8:45:44 AM

182 posts since 5/11/2018

"...You'll find on the average mylar head it generally takes about 4 turns of a nut (if you're using standard 26 tpi hardware) to go from "hand-snugged" to full tension..."

THAT is exactly the number I was looking for, and I AM planning to use a mylar head, which I should have mentioned in my opening post. A 26 TPI thread gives .038" travel per turn of the nut. Four turns gives .154". Maybe double that to provide a generous safety factor. So I'll place the shoes so that there's .300" of thread inside the shoe when things are finger tight, and size the height of my rim cap so the nuts don't protrude past the rim.

As a side note, I plan to use ball-type shoes, just because I like the old-fashioned way they look. But I'm surprised that the commercially available ball shoes -- I only know of two sources -- hold the hooks out so far from the rim. .375" to .400" from surface of rim to center of hook hole is typical, which causes the hooks to incline inward at about a 3° to 4° angle. I actually plan to turn down the outer diameter of the rim by about .100" once it gets south of the tone ring skirt and head bead so that the hooks can sit more vertically, maybe at a 1° angle max.

Thanks to all who took the time to answer, much appreciated.

Edited by - frisco slim on 06/14/2018 08:46:03

Jun 14, 2018 - 10:15:14 AM

Fathand

Canada

11153 posts since 2/7/2008

You can do all of the below on paper first and then check your measurements by only drilling and installing one shoe/hook/nut. If you got it wrong on paper then you will only have to fill one hole before moving your shoes to a better place.

  1. Attach your shoes to your rim so that the bottom of the shoe is far enough away from the bottom of the rim so that your nut bottoms are the desired distance from the rim bottom. i.e. if your nuts are 3/4" long and you want them 1/8" from the bottom of your rim then your shoe bottoms should be 7/8" from the rim bottom.
  2. Now put your head and tension hoop on the rim without tightening yet. Hang your hooks on and through the shoes and measure the protruding threads against the depth of your nuts to make sure they do not bottom out. They should be about 1/4" to 3/8" inch shorter than the depth of nut. As long as you have about 3 threads protruding, that will be enough to get hold of the hook and start tightening.
  3. If the hooks are now too long, your options are to add a taller tone ring, install a lower crowned head, buy shorter hooks or cut the hooks shorter. If you decide to cut your hooks, first obtain an open bottomed nut and thread it up past the cut line. After you cut (with a hacksaw?) remove the burrs from the threads with a file or grinder then remove the nut which will chase the threads as your remove it.
Jun 14, 2018 - 11:42:23 AM
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11048 posts since 6/29/2005

90% of the tension nuts I make are closed-end.  The dimensions of mine is not germane because they are probably not the same as standard ones, I don't know.

What I do know, and this is how you would design for what you are asking about, is that on an 8-26 thread pitch, 10 full turns will move the nut up the hook 1/2", so wherever you locate the bottom of the shoe, or the bottom of the flange, the threaded part of the j hook shouldn't extend down farther than 1/2", and essentially, where you position the bottom of the shoes or flange is what drives where the bottoms of the balls are going to be.

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