What diameter are your pins?

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What diameter are your pins?

Post by topherdawson on Tue Dec 20, 2016 10:09 pm

Ours are 28mm but to get them to fit when wet we reduce them to 27mm dry. We have broken oak ones and now make them out of very exotic heavy woods to be strong enough.

I'm thinking that maybe 30mm would be a better standard for making pins out of commonly available woods like oak.

What size are other peoples' pins?

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Re: What diameter are your pins?

Post by Rory Cowan on Wed Mar 29, 2017 7:26 pm

Ours on Arran are 25mm parallel sided - we have not broken any yet, however we are short of very strong people. Noted the larger size at Ullapool and agree that this makes good sense. We are now looking at increasing the size to 28mm diameter tapering over 65mm to 25mm. We will bore a 28+mm hole and finish it with a 25mm hole and line the hole with epoxy using a clingfilm covered pin as former.

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Re: What diameter are your pins?

Post by topherdawson on Wed Mar 29, 2017 7:53 pm

Hi Rory,
Ours (Ullapool) are 28mm and taper over 70mm to 22mm, 2.5 degrees on each side. My hunch is that since acetal or oak have a lower stiffness (E) than steel, a steeper taper than a Morse taper is optimal.

Our experience with oak tapered pins is that if they go in dry and then get wet, they need to be banged to get them out. We normally take them out every time the boat is taken out of the water so they don't get a chance to swell. I'd think this would get worse if the taper is shallower.

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Re: What diameter are your pins?

Post by Rory Cowan on Thu Mar 30, 2017 9:14 am

Hi Topher,
We have already suffered the worst of both worlds!  We drilled 25mm holes - parallel sided and inserted a push fit 25mm pin and have left them there for over a year - so when I came to remove the pin for the Ullapool oarlock system I failed to bang the pin out upwards and had to cut the top off and drive it through.  Not exactly a technique for using when replacing a pin during a race!!  So I think your solution is ideal.  What I need to avoid is the pin coming loose during operation or being too tight to replace easily.  Noting that the parallel pin will in fact move a little under gentle persuasion, as soon as any movement occurs the tapered pin will come loose.  I only went for the morse taper option because that seems to be a good compromise between security and ease of removal.  I am about to glue the hole of such a pin now and will see how it goes.  If necessary I can lengthen the wider 28mm hole to 70mm and cut another pin with a slightly steeper taper.

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Re: What diameter are your pins?

Post by Rory Cowan on Thu Mar 30, 2017 9:20 am

Later,
Rather than going off in different directions, and for this there is a proven system, it is probably a better idea to go for a standard taper. If 28/22 over 70 is proven and works for you then perhaps this would be a good standard to go for. It gives a strong pin that can be swapped between boats if necessary and if acetal pins are to be made centrally and offered to other clubs then a standard size seems a good solution.

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