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      A Few Simple Rules   05/22/2017

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dash34

Source for 1 1/2" x 3/8" aluminum sheave on 3/8 axle?

14 posts in this topic

Looking for a source for sheaves like this. I've done some searching on-line but no luck. The sheaves (I need three) are the outhaul and reef line turning blocks from the front end of a Yachtspar boom circa 1981. They have a fibre bushing in the centre.

 

The loads are too high for plastic sheaves. Under normal conditions a plastic sheave would work, but when the main starts flogging during reefing, the shock loads will explode a plastic one.

I can get them made at a machine shop for $40 each. Seems to me there should be some off-the-shelf ones out there somewhere at a better price?

 

thanks in advance for any help!

 

dash

 

 

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Dia. OD Work Load Dia. (A) For Shaft Dia. (B)Wd. Each

2 1/4" 1 3/4" 290 1 1/4" 3/8" 1/2" 3434T24 6.67

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I'll second the rig rite suggestion, if you can't find them elsewhere. I've purchased a couple of items from rig rite in the past. They have a lot of stuff but they are not cheap, at least not for the bits I needed.

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Thanks! Rigrite has one that looks like it will work. Mine have a fiber bushing, and the Kenyon doesn't, but I can probably get the bushing added quite cheaply.

 

Hopefully they won't cost an arm and a leg....

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Just make sure you get a very accurate measurement on the sheave box that the sheave is going into - many times what looks like 1/2" is .550 or .562 and that kind of play will cause havoc in terms of quality of use and durability. BTW, a 1.5" sheave sounds VERY small for anything under 30'. Is it possible that a sheave was retrofitted and not correctly sized?

 

I have turned probably around 200 sheaves just this year, and maybe only 25% of them were conventional, normal fractions of an inch. Mostly they are metric or weird sizes, like .520, .530, .570 in thickness. And almost ALL of them were Delrin which is plenty strong unless you are running wire which will chew them up.

 

Just an FYI

 

Bam Miller

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Good points. I will measure the sheaves and box with calipers to be sure. If it is possible to increase the diameter of the sheave I will definitely do that. I doubt that I can increase the width.

 

These sheaves carry loads for outhaul and reef lines. The outhaul has been modified adding purchase and loads are not high, but the reef lines get big shock loads. I'm guess that the reason for using aluminum vs. delrin is the high loads. Can delrin handle high shock loads?

 

Do you think that the fiber bushing is important?

 

These sheaves lasted 30 years, what finally did them in was corrosion. Unless I get the wrong sheave I won't be replacing them again in my lifetime.

 

And, thanks for the help!

 

gallery_196_490_40491.jpg

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If the sheave axle is a stainless shaft the fiber bushing probably doesn't matter. (In your pic it looks like some flavor of linen or canvas phenolic.) You will most likely find a new sheave with an oil lite (I think that's the spelling/nomenclature) bronze bushing, wich will work just fine on a stainless shaft. One of the items I ended up having to source from rig rite was an outhaul sheave. The thing was fairly narrow at 5/16 and the aluminum was pretty corroded and the bronze bushing had gone all pear shaped.

 

I wish I'd found zephyrwerks a few months back. (Nice bit of info, nobody.) Looks like they make nice stuff and the price is about 40% less than I had to cough up for rig rite. If you haven't purchased yet you might give them a call. Couldn't hurt...

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Good points. I will measure the sheaves and box with calipers to be sure. If it is possible to increase the diameter of the sheave I will definitely do that. I doubt that I can increase the width.

 

These sheaves carry loads for outhaul and reef lines. The outhaul has been modified adding purchase and loads are not high, but the reef lines get big shock loads. I'm guess that the reason for using aluminum vs. delrin is the high loads. Can delrin handle high shock loads?

 

Do you think that the fiber bushing is important?

 

These sheaves lasted 30 years, what finally did them in was corrosion. Unless I get the wrong sheave I won't be replacing them again in my lifetime.

 

And, thanks for the help!

 

Dash34,

 

The outhaul is typically 30% of the clew load, and as a guess to what kind of boat you have (34'), I thinking the max outhaul load is in the 750lbs range, but because you are turning the line 180 degrees the sheave is seeing twice that load.

 

Rough calculations for Delrin at 9000psi tensile gives you a sheave strength of roughly 3800lbs = plenty strong. The best part about Delrin is that it is a natural bushing material, so you dont need to bush it for low friction or wear strength.

 

Aluminum, on the other hand, MUST have a bushing. My only suggestion, if you go with oillite, would be to make sure that the wall thickness is at least .125", A typical oillite bronze bushing is sintered where you take a bunch of bronze powder and force it into a mold with a little heat and out pops a bushing - good for cheap manufacturing options, not so good for long term durability - I've seen bronze bushings egged out and squeezing out of the hole they were pressed into. I dont see phenolic used much anymore - it works well, but is a mess to machine, and Delrin works just as well.

 

Bam Miller

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Thanks for all the help everyone, I ended up ordering from Zephyrwerks - great service so far. The price was 25% cheaper than what I was quoted from the local machine shop. I didn't check the rigrite price in the end. Zephyrwerks are almost local - I could sail there in a day....

 

I'll post a picture of the finished product installed in the boom.

 

dash

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Rig-rite shows they have a good selection, but the truth is they make a lot of the stuff on demand. The gal that took my order answered with a "yes" when I asked if they were "in stock." They were in stock I guess, as blank plastic! I called a week before my crossing the Gulf of Alaska and was then told they were just getting to the machine shop. Cancelled the order... I've bought some things from Rig-rite before, and they are undoubtedly an extremely valuable resource, specially for those of us with older boats. Just be sure you get what you ask for in the time frame you need. Going to give Zephyrwerks a call! BTW, $40 from a machine shop seems like a pretty good deal. Around here anyway expect around $70-100 per hour. $40 will get you through the door.

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