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Apr 20, 2021 - 7:18:01 AM
5941 posts since 8/19/2012

Ok I know you can work this out with a paper and pencil or the calculator app on your smart phone but this link is more than that. I started out trying to work out the distance between holes for bracket shoes for an 11" open back rim and after fighting it with a protractor and straight edge, etc I found this site. About the only thing is does not have is fret spacing but there are plenty of apps for that.  Check this out for almost any construction application.  You can also print templates.

By the way if you need the angles and lengths for a gambrel roof this site can calculate it.

https://www.blocklayer.com/circle-dividereng.aspx

Apr 20, 2021 - 7:28:37 AM

beegee

USA

22330 posts since 7/6/2005

Does it allow for the width of the neck notch and tailpiece notch?

Apr 20, 2021 - 7:40:06 AM
like this

mbanza

USA

2329 posts since 9/16/2007
Online Now

This is also easily done mechanically using evenly spaced parallel lines. Wrap a strip of paper around, mark for neck notch and tailpiece, and divide the remaining two segments in the desired way. Here is an abbreviated example, add more lines for more segments.


Apr 20, 2021 - 8:12:10 AM

468 posts since 2/6/2011

I think it depends on the spacing at the nut end and the tailpiece end. If those spaces are going to be equal to the bracket spacing, then the calculation is easy. I always just use a tension hoop and mark the rim at each notch.

Apr 20, 2021 - 8:21:12 AM

2562 posts since 6/19/2008

Interesting, and very applicable to me at this stage of construction of my next banjo. It is to be a James Ashborn tribute banjo. One of his ideas that I want to incorporate was the use of metal tabs that go around the tension hoop, to which the hooks are secured (as seen at the 20 second mark of this video).  Presumably, these tabs could slide around the tension hoop before tightening the hooks, so there is no way to use the hoop as a guide for the hole spacing.  The same could be said of a banjo with a grooved, rather than notched, hoop.

Apr 20, 2021 - 9:15:39 PM

3724 posts since 5/29/2011

quote:
Originally posted by banjukebox

I think it depends on the spacing at the nut end and the tailpiece end. If those spaces are going to be equal to the bracket spacing, then the calculation is easy. I always just use a tension hoop and mark the rim at each notch.


I do the same thing even if I plan to use a grooved hoop on the finished banjo. The notches in the tension hoop give an accurate spacing for spacing bracket shoes.

I set the rim on a Lazy Susan, put 1/2" blocks around the rim, then set the notched hoop on them. That sets the notches at the right height to mark for the holes.

Edited by - Culloden on 04/20/2021 21:17:14

Apr 20, 2021 - 11:22:07 PM
likes this

11300 posts since 10/27/2006

Are you using a notched or grooved stretcher?

If grooved, calculate away. You won't be wrong, no matter what as long as you allow for the neck and tailpiece width. Yep, that.

If notched, buy the stretcher first and take your placements from that.

Apr 21, 2021 - 1:23:49 PM

Fathand

Canada

11739 posts since 2/7/2008

One way I have done it is to multiply the diameter of rim x pi, then divide that by the desired number of hooks +2. The +2 allows you to skip a hook for the neck and tailpiece locations.

So for a 11" rim with 24 hooks , 11x 3.1415 /26 = 1.329"

Now lay out a strip of sheet metal( I like aluminum) with several holes drilled at that distance, 4-8, preferably the same distance from the side as the hole distance from the top of the rim for a template

Drill one hole in the rim then bolt a shoe through one end of your template to mark or drill your holes through the rest of your template. You can move your template as you go but skip a hole when you get to the neck or tailpiece position.

This works with a grooved rim. You may want to make another template if you are making a notched hoop using the outer diameter of the hoop or transfer marks from the rim using a transfer punch from the inside.

Apr 22, 2021 - 5:43:47 AM

13535 posts since 6/29/2005

I like Verne's method—drawings and transferring increments from the drawing, or making a template / pattern always works better (for me) than calculating and transferring measurements with a ruler or caliper, especially around a round surface.

I make the rim, the neck, fingerboard with fret spacings, and all the metal parts—shoes,  bracket bands, hooks, nuts, tension hoop, flanges for my banjos and never measure anything with a ruler, always transferring measurements from patterns and templates.

I always start with the bracket band first—I used to have tension hoop circumference templates with the notches on the template, but have abandoned that and mark the tension hoop notches directly from the spacing of the shoes, where the bracket band becomes the template—you could do the same thing with a rim that had the shoes installed.

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