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I was asked today to help troubleshoot a tube bandset that wore out prematurely by abrading at the left fork tip as it passes through a drilled hole. Tubes are not my area of expertise, but I have hung out on this forum so much that I can pretty much guess what the experts would say. Just in case others who are more experienced may disagree, I reproduce my response here in the blog for you to comment on.

CAUSE:

Tube-in-hole abrasion occurs because of movement of the tube through the hole in the fork tip. It is exacerbated by sharp or abrasive surface of the hole, particularly the rearward rim, a draw action or release that is not directly rearward and condition (aging) of the elastic material.

SOLUTIONS:

Given that you are having this problem with multiple board cuts, it might be a matter of an uneven draw, a difference in the way you hold the board cut vs natural fork, the thickness of the material or the way you made the holes. Without seeing the damage and the fork I cannot tell more precisely. However, it's not necessary to show me as the solutions are straightforward. Below, I propose five categories of alternative solutions. Please take your pick!

(1) POLISHED HOLE: Chinese players who shoot the very similar ball-in-tube fork attachment method have a similar problem, although their forks are made of metal rather than wood. danny, a Chinese member of our forum recommends polishing the insides of the fork holes with a rotary tool. Note that he does not advocate a bigger hole. Perhaps a larger hole would permit more movement and hence more abrasion.

(2) FLEXIBLE COUPLING: Many people who shoot tubes and solids from both natural forks and board cuts prefer one of several derivations of the traditional the Gypsy-Tab method of attachment. The core concept of this idea is to attach the band to the fork by a flexible cord that robs only an inch of total draw length, but is flexible and does not abrade the elastic. Here is a link to the leather Gypsy-Tab (link) and here is the string knot method (link)

(3) METAL COUPLING FIXING: The bent-rod slingshot attachment is well proven and provides for a long tube life. One method is to embed bent rods into the fork tips. The ends of the rods should be rounded and polished and the fit tight. The rods must be securely affixed. Another method proposed by Hogancastings is to have a Sam-Brown screwed onto the back or top of the fork tip. Hogancastings manufactures these and offers them for sale. (link) I expect a regular Sam-Brown post from a leather work supplier would work too. Another popular method is to screw (and glue) ring eyelets securely into the ends of the fork tips. The tube or rod is run through the eyelet folded back and tied off. (link)

(4) OVER-THE-TOP ATTACHMENT: One common attachment is to tie the band, tube or solid at the front of the fork and run the elastic over the top. The idea is to smooth and polish the tips externally, rather than to polish the inside of a hole, which is considerably harder. This works well for flatbands, but I have not tried it for tubes and solids. Others have though and report good results. (link)

(5) PULLEY ATTACHMENT: A product called the Combow showed that pulleys can be used to reduce friction. Jörg is the master of this attachment. The pulley must be lightweight or it may slow the velocity. (link)

Incidentally, you should refer to this blog post, which has indexed many general attachment methods (link).

Disclaimer As always, I disclaim all liability for the information contained in this blog post and comments . These are my own observations and as I am not a trained woodworker, you should get competent advice and training before attempting any of what you read here.



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Nest Buster
Jan 21 2011 02:30 PM

I think you nailed it.
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Danny0663
Oct 20 2011 10:28 PM

yuuppp pretty much all there, is* all there i should say.

How great is it to have such a member with dedication to write this all up.

thanks dan.


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ZDP-189
Nov 02 2011 07:57 AM

Rufus Hussey style attachment by harpersgrace

http://slingshotforu...-todays-effort/

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Alessandro Italia
Jun 12 2013 12:26 AM

what elastic band is it?It's not thera band gold


Hat Event Cap Fur Art

Alessandro Italia
Jun 12 2013 12:27 AM


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davidjohn
Nov 22 2013 08:12 AM

I think the elastic band can be made out of either natural rubber or synthetic rubber. Natural rubber is generally known for elasticity. The elastic property of the band enables the stretch-ability and an object can aimed at great force.
 
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