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Old 11-04-2013, 15:49   #1
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Mast Sheave Material

Greetings, Hopefully my attempt to upload a photo will work...I have 6 mast sheaves originally installed in 1974 that I'm attempting to replace. Can anyone identify the material (based on the photo if it uploaded...) used to manufacture these sheaves. I'd like to get some kind of baseline on what's been on the boat all these years...It actually looks like they haven't worn all that bad.

The second part of the question is; What's the best type of material out there now that I should be looking for to replace these with? Many thanks in advance for any insight on this.
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Old 11-04-2013, 16:05   #2
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Re: Mast Sheave Material

^^ the old ones are a Phenolic, probably medium weave cotton cloth. There are several common brand names of this stuff - Garolite is one. G10 is the more modern (epoxy based) equivelant of this product (also sold under the Garolite brand I think).

Its real old technology (original patent mid-1800's), but still pretty good stuff.

More modern materials for sheaves: Delrin Acetal, UHMW Polyethelene, Torlon.
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Old 11-04-2013, 16:55   #3
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Re: Mast Sheave Material

Many thanks estarzinger! That will give me something to go on and be able to compare. I appreciate the reply!! Best-
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Old 11-04-2013, 18:47   #4
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Re: Mast Sheave Material

zephyrwerks.com
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Old 11-04-2013, 18:52   #5
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Re: Mast Sheave Material

The key is what is the diameter? Yo may find anodized aluminum ones also.
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Old 11-04-2013, 18:59   #6
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Re: Mast Sheave Material

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zephyrwerks.com
I appreciate the tip- I'll check it out.
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Old 11-04-2013, 19:01   #7
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Re: Mast Sheave Material

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The key is what is the diameter? Yo may find anodized aluminum ones also.
I'll keep that in mind- I have six to replace and the dimensions are 3-1/2" x 5/8" with a 1/2" pin. Best-
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Old 11-04-2013, 19:03   #8
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Re: Mast Sheave Material

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Originally Posted by akswimdog View Post
Greetings, Hopefully my attempt to upload a photo will work...I have 6 mast sheaves originally installed in 1974 that I'm attempting to replace. Can anyone identify the material (based on the photo if it uploaded...) used to manufacture these sheaves. I'd like to get some kind of baseline on what's been on the boat all these years...It actually looks like they haven't worn all that bad.

The second part of the question is; What's the best type of material out there now that I should be looking for to replace these with? Many thanks in advance for any insight on this.

1. why replace? worn badly?
2. Garolite Garolite Phenolics - GAROLITE - Order Online
3. The alternate equiv. you could use is Ryertex
4. I would consider an engineering plastic. Try Nylatron - Moly filled nylon. This is extrememly tough, machinable and self-lubricating.
5. McMaster-Carr McMaster is an easy source for all kinds of these materials. Also, TPI (Total Plastics)
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Old 11-04-2013, 19:19   #9
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Re: Mast Sheave Material

Nylon degrades badly from UV, not sure if that's an issue in the masthead or not.
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Old 11-04-2013, 19:25   #10
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Re: Mast Sheave Material

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Originally Posted by Cheechako View Post
Nylon degrades badly from UV, not sure if that's an issue in the masthead or not.
White unfiled plain Nylon degrades in UV.

Nylatron is jet black and highly filled with Molydemum Disulphide. It will still be viable after the next ice age.
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Old 11-04-2013, 19:42   #11
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Re: Mast Sheave Material

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1. why replace? worn badly?
2. Garolite Garolite Phenolics - GAROLITE - Order Online
3. The alternate equiv. you could use is Ryertex
4. I would consider an engineering plastic. Try Nylatron - Moly filled nylon. This is extrememly tough, machinable and self-lubricating.
5. McMaster-Carr McMaster is an easy source for all kinds of these materials. Also, TPI (Total Plastics)
Thanks Nick that's good stuff- Actually they're not to the point that I NEED to replace them but we've got the mast down and are re-rigging everything and they haven't been replaced since '74 and since I've not been the guy pulling the sheets I want to be able to know where I stand when we put the mast back up. So far the ones I've been able to get a ballpark figure on won't break the bank, but yanking the mast on and off again just might... Thanks again for the links and info on the materials- Well taken and best-
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Old 11-04-2013, 20:12   #12
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Re: Mast Sheave Material

If using a nylon-based compound, you have to allow for quite a lot of dimensional change with water absorption: in other words, plentiful clearance for the pin.

Acetal on the other hand does not change much in size - it would be my first choice if you go for a solid thermoplastic.
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Old 11-04-2013, 22:07   #13
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Re: Mast Sheave Material

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If using a nylon-based compound, you have to allow for quite a lot of dimensional change with water absorption: in other words, plentiful clearance for the pin.

Acetal on the other hand does not change much in size - it would be my first choice if you go for a solid thermoplastic.
Andrew, thanks a bunch I appreciate the insight!! All the best-
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Old 12-04-2013, 16:39   #14
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Re: Mast Sheave Material

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Originally Posted by akswimdog View Post
Andrew, thanks a bunch I appreciate the insight!! All the best-
Alro Plastics NYLATRON®

Up to 2% growth for fully wetted Nylatron. This is a much over-blown problem. If you were making precision parts AND operating in water AND if the parts were large you would consider this an issue. If your pin is 1/2 inch diameter, 2% means multiply 0.5 inch diameter by 0.002 to get the minimum dry clearance. So, your hole would have to be 0.501 to avoid a compressive interference. I design with this stuff often. We make custome machinery. I ingnore numbers this small in plastic parts. The spring-back and uncertainty in the tooling is greater than this. Use a 1/2 inch drill and if you are picky, go undersize, use a clean, sharp reamer to open the hole. One note; Nylatron is so resistant to abrasives that you must use sharp tools to make cuts. For pulleys, I often use my Shop Smith at home and VERY sharp lathe tools. Take extremely small cuts. If you use a wood gouge be at the ready because it might pull the tool in. If you have access to metal shop tools, the stuff cuts like butter with inserted bit modern cutters.
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Old 12-04-2013, 16:45   #15
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Re: Mast Sheave Material

Not that it is so important, but with an unrestrained shape like a sheave, I think that if the material expands due to water absorption (or anything else) the hole in the middle becomes larger, not smaller. If the outside is constrained, like rudder post bearings inside a metal tube, then expansion is forced inward and the hole becomes smaller (ask me how I know that one!).

Cheers,

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