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Sheave Sizing

**Please read all of the sizing specifications below in order to provide the correct dimensions for each different size sheave.**
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Materials I use Black Acetal (also known as Delrin®) to make my sheaves. It is the most durable, cost effective material for the application that I have found. I press in bearing bronze bushings to take the pin load and wear. Bearing bronze is oil impregnated cast bronze. It is self lubricating and does not corrode like straight bronze or brass. I use minimum 1/8” wall bushings for strength and longevity. Bushings are standard sizes to facilitate future replacement. Sheaves are grooved for specific line size. (5/16”, 3/8”, etc.)
Sheaves can be deceptively simple looking to measure. Please read all of the following very carefully. When measuring for your new sheaves, take your time. Be sure to measure and examine each sheave box, be it a block, a masthead, boomend or whatever. Do not assume any measurement without checking it.
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Sheave Boxes Many sheave boxes on blocks, mastheads or boomends are not cut true or square, resulting in the sheave binding at some point. This is very common, even on otherwise very nice looking mastheads. Also common is for the pin seats (the hole through which the pin passes) to be drilled out of square, producing a pin angle other than 90 degrees. Remember, there are two planes in which a pin can be out of square. One plane is easily visible when looking through the box, the other plane is perpendicular to the first, and not so easily seen. Do not assume your sheave box to be square or the pin angle as it should be. Careful inspection and accurate measuring is necessary to ensure a good spin to your sheaves.  
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Sheave Diameter Sheave diameters are best expressed in inches and fractions of inches. Line clearance in the box is a function of sheave diameter and groove depth.
Groove depth is usually about 1/3 to 1/2 the rope diameter. Measure and record your groove depth and related clearances to prevent binding. On new sheaves, 1/3 the rope diameter is enough for bearing and control. A full rope diameter between outer sheave edges and upper or inner face of sheave box is a good rule of thumb to provide adequate clearance.

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Wire to Rope conversion Often I make new sheaves when wire halyards are switched out for low stretch rope. The width of those old wire sheaves, and thus the sheave box, is often less than is necessary for clearance for the desired new halyard diameter. The rule of thumb (above) goes into action here because the old wire needed little or no clearance beyond the outer sheave edges. One more consideration, we don’t want the new halyard to ride on the surface of the mast as it enters or exits the sheave, so we want the new sheave diameter large enough to prevent this, but small enough to preclude binding at the top of the box. Sometimes all of these are not obtainable, and some recutting of the box is necessary, or some compromise of these factors must be made.  
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Sheave Width

Sheave widths measured in thousandths are sometimes necessary on refits, though usually I get measurements in fractions. Sheave width can be critical in many situations. Optimum working total side clearance in a clean, square box is generally around .062” (1/16”) Sheave width and pin angle are directly related. The more out of square the pin angle, the narrower the sheave must be to prevent binding. If there is doubt about squareness, cut a round piece of wood the desired thickness with the pin hole drilled square through it (hole saws work great) and try it out.
When making new blocks, or designing any sheave box, I use these dimensions:

For 3/8” rope, use a 1/2” sheave, with a 9/16” slot
For ½” rope, use a 5/8” sheave, with an 11/16” slot

Remember to leave plenty of room for varnish inside the slot on wooden blocks.


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Pin diameters are best measured in thousandths. This accuracy is needed to ensure a good spin. Some pins appear to be a standard fractional size, but are actually slightly oversize or metric size. It can be worth the effort to obtain a set of calipers or a micrometer to check exact pin size if in doubt. Much better than getting your new sheaves and discovering they will not spin on your pins. I cannot guarantee a proper fit without your pin measurements in thousandths of an inch, or fitting your pins to bushings at my shop.
Often pins are gnarled up at the ends, so a little judicious filing is necessary to get the bushings to slide onto the pin easily.
Pin diameters are generally not changed because changing the hole diameter in the sheave box is usually not easy, necessary or desirable.
Pins are available in stainless steel or silicon bronze. Titanium also makes a good pin material, especially aloft where weight is critical, though it is spendy stuff. I usually drill the pins to take 1/8” cotter pins, supplied in bronze.

Pin Measurements:

  1. Pin diameter
  2. Overall length of pin
  3. Grip Length (measured between cotter pin holes, not center to center)
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Sheet Rollers Sheet rollers are measured just like sheaves, with careful attention to the groove depth and diameter. I often rebuild complete sheet rollers cars.  
Trademark Disclaimer:
Delrin?is a registered trademark of E. I. du Pont de Nemours and Company or its affiliates.

**After reading and understanding all of the above, you are ready to provide the dimensions for each different sized sheave.** You are now ready to proceed to the request for quote (RFQ) form.

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Call or email before sending any packages or correspondence to Zephyrwerks

Ed Louchard
tel: 360 385-2720    email: edlouchard@gmail.com

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