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Estimating
Cost
CUSTOM
SHEAVE COST DRIVERS
Three
cost elements determine 80% or more of custom sheave
costs:
1.
Size (OD and Width)
2. Quantity
3. Material
Figure
1 shows the impact of size and quantity. This chart
shows the changes in size to size and at different volume
levels. The greatest quantity savings come from spreading
the engineering, programming, tooling and set-up costs across
more units. Volume savings from material, including bearings,
is small to non-existent. Our material costs are based on
our total volume with selected vendors.
Size
and quantity are actually related to a small degree. The price
spread between one and a hundred of a 6 inch OD sheave is
a factor of 3. However, for an 18 inch OD sheave the factor
jumps to 5. Larger sheaves require larger turning
centers, more setup time and more expensive fixtures.
Custom
sheaves over 18” OD step up considerably in price.
A look at our stock sheave prices illustrates this
quite well. A 20 inch sheave costs $30 or 22% more
than a 16 inch, but the next 4 inch increase – 20 to
24 inch – costs $100 or 60% more. The increases in custom
sheave prices would be at least as dramatic.
Figure
2 shows the relative cost differences of common sheave
materials. This comparison is based on a volume cost, not
a per pound cost. While this shows only the material costs,
a buyer must be aware that aluminum will incur higher machining
costs as well.
Although
the relative cost of Gar-Dur is shown to be slightly higher
than generic UHMW, that most often is not the case due to
material yield. Gar-Dur comes in boards of a variety of widths
and thicknesses, and is always nominally oversize. Therefore,
a 6 inch OD x 1” thick Gar-Dur sheave can be
made from 1 x 6 board stock.
However,
HDPE and generic UHMW are only available in 2 x 2, 2 x 4 or
4 x 8 sheets and thickness runs ±10%. We can cut only
(9) 6 x 6 pieces from a 2 x 2 sheet because of cutting losses.
Further, we would have to buy 1-1/4 inch thick material to
be assured of thick enough sheet to finish up a 1 inch wide
sheave. Therefore the higher grade Gar-Dur UHMW is
often a more economical choice in spite of an apparent higher
unit cost.
Custom Process & Mechanical Sheaves
| Guide to Material Selection
Quotation Request
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