I had a desire to make some small chain drives for some of my [models](http://www.techmonkeybusiness.com/art-project-articles.html), but wanted to use some classic chain link style chair rather than proper chain drive chain. I had a look on the other 3D Printing model repository and discovered that nobody else had made a model for this. So, after scratching around with a pencil to work out what parameters I needed, I jumped on OpenSCAD and came up with two parametric models. One has a neck, holes and nut slots for screwing it onto a shaft while the other is just a disk with the chain recesses which can be more easily adapted to other pulley body designs. Both are included here.
The chain size and number of link pairs determines the size of the pulley. So the important variables to fiddle with are;
**Llength**: This is the outside length dimension of a single link
**Lwidth**: This is the outside width dimension of a single link
**Lthickness**: This is the diameter of the link “wire”
**N**: The number of **chain link pairs** around the pulley. Please note this is *pairs* of links not the number of single links.
The pulley neck size is controlled by the following parameters;
**Pwidth**: Width of the pulley main drum which the chain recesses are cut into.
**PstemD**: This is the diameter of the pulley attachment neck. There is nothing to stop you putting dimensions in here that can't accommodate the retaining screw or the shaft. We leave that to you, the user, to figure something sensible.
**PneckL**: This is the desired neck length
**AxleD**: This is the axle diameter
**ScrewD**: This is the retaining screw diameter
There are a bunch of other parameters that you may wish to tweak too;
**Ptol**: Is the printing tolerance. It is used to provide a bit of space around the chain profile so that chain will fit into the recess despite a bit of spread from the extruded plastic.
**PtolThk**: This is a printing allowance for the "radially" orientated link thickness. This allows a bit of extra on either side of the link slot so any sagging of the printed filament can be easily removed or at least won't interfere with the link sliding into the slot.
**Wclr**: On either side the the tangential link is a cutout slot. This parameter just controls the size of this slot.
**CutD**:There are some very stylish decorative holes in the end of the pulley. This parameter controls the diameter of these.
**CutN**: This controls the number of these extremely stylish holes.
Hopefully this is all clear enough.
I feel the model will work well for larger chains where the printing tolerances are less of a factor in the final printed shape.
I trust this will be useful to you.
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