Masthead sheaves: re-machine the original aluminum or buy new delrin?

[JVallely]

The 3 pairs of original bronze-bushed aluminum masthead sheaves on my '79 Alajuela 33 cruiser were grooved for wire and rope.
I want all 7/16" rope for simplicity's sake, so I need rope grooves. Machining the old ones will still leave me with about 3 1/8" diameters (7.1 times rope dia.), and aluminum obviously has greater strength.
New Delrin sheaves would be lighter, a little bigger at 3.5" diameters (8 times rope dia.) probably cost not much more than the machine work, and entail less chasing around.
Is there a significant reason to go one way or the other--i.e, re-machine and reuse the aluminum sheaves, or buy the new delrin ones?
Or is it a coin-toss?
Thanks for your thoughts.
John V.

[scottyt]

if you want to machine them just mail em to me, with return shipping in the box plus 10 bucks to make an arbor. or send it with the proper size nut, bolt and some washers, it will only take a few mins for me to do.

[mitiempo]

Not sure which is best, but if you are looking for delrin and are unable to find in the right size here's a link that others have used. Reportably fast and affordable. Zephyrwerks - The Sheave Factory Hope this helps.

[CalebD]

Before having custom sheaves made for your application check with McMaster Carr as they have a large assortment of stock sheaves.
McMaster-Carr
I was able to use a delrin sheave from them that I had to sand down 1/32" to 1/16" to fit in my boom to convert our outhaul to all rope.
YMMV.

[knothead]

Originally Posted by JVallely

The 3 pairs of original bronze-bushed aluminum masthead sheaves on my '79 Alajuela 33 cruiser were grooved for wire and rope.
I want all 7/16" rope for simplicity's sake, so I need rope grooves. Machining the old ones will still leave me with about 3 1/8" diameters (7.1 times rope dia.), and aluminum obviously has greater strength.
New Delrin sheaves would be lighter, a little bigger at 3.5" diameters (8 times rope dia.) probably cost not much more than the machine work, and entail less chasing around.
Is there a significant reason to go one way or the other--i.e, re-machine and reuse the aluminum sheaves, or buy the new delrin ones?
Or is it a coin-toss?
Thanks for your thoughts.
John V.

The only reason not to reuse the existing sheaves that I can think of would be if the reduced diameter led the halyard too close to the lip of the spar and a chafe point was created.
As long as the sheave is big enough to turn down, you will probably save some money.

[JVallely]

Thanks for the replies.
Scottyt, it's nice of you to offer. Turns out my brother in law has a customer who runs a machine shop and can do it locally for cheap or nothing,
I've been in touch with Zehpyrwerks re their prices. I'll check out McMaster-Carr, too.
I'm not sensing a passionate consensus one way or the other--I'm leaning toward keeping the aluminum. At least today, anyway...
Thanks again, guys.
John

[roline]

For my 525, the main halyard sheave was just steel sheave on a hollow stainless shaft (Schaefer brand). I replaced it with a Harken ball bearing sheave designed for wire, modified by grinding the groove larger by spinning the sheave and grinding it on a fine grit grinding wheel. I just took my time to prevent damaging the bearings. Delrin is a common material but is attacked by UV requiring replacement in 10-15 yrs.....

[Liquorice]

Why are you machining them anyway?
If the sheaves currently have grooves for wire and rope - just leave them and run your rope halliards.
I did mine about 4 seasons ago, works great!
sam :-)

[JVallely]

It's my understanding that the groove on a wire/rope sheave will cause premature wear to rope. There are fairly sharp steps where the 2 groove radii meet. One of the halyards on my boat looks fairly new, the other looks like cotton candy.
I have considered trying roline's trick of turning the aluminum sheaves on a grinding wheel, but I'm sure my own results would be uneven from one sheave to another.
If I'm going to pay a small fortune for halyards (probably Stay-set x), the machining cost is incremental.
JV

[BigZ]

Another source for Aluminum sheaves is Rigrite. I think I paid somewhere between 40 and 50 bucks each. They have a fairly large selection at various diameters. Dwyer Mast and Rigging Only are also sources, but have smaller listings. Also be very careful if you machine them down. My halyards are external and if I went to a smaller diameter there would have been some chafing on the mast at each side on the main halyard.
I was able to use my old sheaves when switching to all rope, but they are a single V groove, not the combination style you have.