Robbin, I'm not a metal expert, ( perhaps someone out there is ?) but I'd be careful with the choice of the pivot pin material. You for sure wouldn't want anything less stiff then stainless, and silicon bronze may be less stiff. The stiffest and higher psi bronze is alumabronze I think it's 2/3 s more stiff then silicon bronze, remember that it's not just the weight of the board but you might want about a 3-4 to 1 safety margin to account for the banging and abuse that all things get (shock loads) . All that kind of data is on the net. I think most 304 stainless runs about 110,000 PSI and you should compare other material to that. If there is any air gap between your board/bushing and the centerboard trunk you could easily slide a big washer or 2 up the trunk when installing the board. use something like a steel ruler and lightly tape the washer to it and slide it up. Should be optional but it sounds like you are trying to be very careful over all. Stan --- On Tue, 12/28/10, robbin roddewig <robbin.roddewig@verizon.net> wrote: From: robbin roddewig <robbin.roddewig@verizon.net> Subject: Re: M_Boats: Bonding in bushings To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Date: Tuesday, December 28, 2010, 4:56 AM Thanks Stan, I actually have two bronze flanged sleeve bearings already from my original plan. I routed out the board with a roto-zip and a grinding wheel to allow the flange of each bushing to sit flush. I am not sure this is much room to leave the bearing proud based on the board being held in the slot (all 300+ lbs of it) by the extra width caused by the rust scale when I was taking it out. I do not want to find that the bushing is a bit too wide for the slot during install, awkward! I was picturing the two flanged bearings bonded in (one from each side) since I expect the new pin to put some lateral force on the bearings when it is pounded in during the install of the board. I plan on rounding the end of the pin. Perhaps a flanged sleeve with a flange on only one side would be a better arrangement. I would put the pivot pin in from the flanged side. I could make it long enough to go through the width of the board. I plan on using silicon bronze for the pivot pin so the only worry would be the bronze and the cast iron. If that is not an issue then bronze bushing it will be! Appreciate your help. Robbin On 12/27/2010 9:39 PM, Stan Susman wrote:
Hi Robbin, I haven't seen all your posts ,so I hope I'm not repeating what has already been said. I would forget plastic all together,all that type of plastic will flow (squish) out of shape,maybe Delrin would work but it could crack. Use a bronze bushing, it is very happy next to the SS pin and the cast iron. Look for something with the correct I D and bore the centerboard if necessary or find bronze rod and drill the i d. If trunk clearance allows you can make it a little proud of the centerboard width. I can't think why it should be bonded with epoxy, if it's only close to being the right size it can't go anywhere. Let me know if I can help Stan --- On Mon, 12/27/10, robbin roddewig<robbin.roddewig@verizon.net> wrote:
From: robbin roddewig<robbin.roddewig@verizon.net> Subject: Re: M_Boats: Bonding in bushings To: "For and about Montgomery Sailboats"<montgomery_boats@mailman.xmission.com> Date: Monday, December 27, 2010, 5:29 PM
Sorry folks, never mind. The System 3 epoxy book says that it does not bond Teflon. Guess I just proved that. It does say it will bond "Thermoplastic materials like vinyl plastics or ABS". Does Nylon fit in the category of a material that epoxy will bond to well?
Thanks Robbin
On 12/27/2010 7:43 PM, robbin roddewig wrote:
Hope everyone is having a good holiday! I just took off my C clamps and tried to remove the tubular rod that had been setting the position of the bushings I had epoxied into my centerboard and the bushings also broke out. I had some weeks ago asked about bonding in brass bushings to the steel centerboard and based on the advise I got decided that teflon or in the case of what I got Rulon bushings (reinforced PTFE) would be best for the center pin hole on the M-23 board I am trying to finish. So I let the epoxy set for a week and a half over some days that exceeded the 35 degree min for the fast hardner mix. The epoxy had definitely cured but the bushings did not bond in very well apparently. The bushings are meant to be very slippery so I suspect I am going to need to help give a rough surface for mechanical bonding by scuffing up or roughing up the surface that mates with the centerboard. I know some sailors said they had teflon bushings in the centerboard hole. Are these bonded in? Press fit? Any ideas of suggestions that might improve the outcome of a second try would be much appreciated.
Thanks Robbin M-23& M-10
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