Drivers quartered

There is a saying in the Maker community: if you can’t make it perfect, make it adjustable. The corollary is surely that if you can’t make it adjustable, make it perfect.

These drivers are a one-shot deal. Either I get the quartering perfect, or I’m soaking them in acetone to loosen the epoxy, which will melt the spokes and take me back about four weeks. So, my quartering jig is meant to remove as much variability as possible and get the setting perfect on the first try. Time will tell if I was successful.

The quartering jig relies on those ridiculously long axles protruding from the wheel faces to hold the wheels on centre. The axles themselves are hollow, admitting a 1/16″ inner axle that holds the parts of the split axle together. Tiny holes in the quartering jig admit the crank pins, and hold the wheels rigidly in position while the epoxy cures. Finally, two machined L-shaped back to back gauges – one from Alan Gibson, the other by Gérard Huet – hold the wheels against the jig bosses to ensure they are the correct gauge.

Once the epoxy is spread and everything is pushed together, it’s impossible to see how things are going in there. My current favourite epoxy, JBWeld, takes something like four hours to set. For an awful half-day, I thought surely the wheels had gone together too easily and I must have crushed a crankpin. I hadn’t: the wheelsets are as perfect as I can make them.

13 thoughts on “Drivers quartered

      1. …without a full metrology lab!

        Understood: somethings are easier/cheaper to test than measure.


  1. One down, and how many more to go? 😉

    One thing I’ve learned from you is; jigs, jigs, and more jigs. Jigs are well worth the time spent.

    Craig Townsend

    1. Not to step on Rene’s toes here but jigs often come “for free” when you digitally design the assembly in the first place. What I mean is: very little independent design is required to produce a highly accurate jig that can be manufactured along with the parts – they tend to “fall out” of the assembly design you are doing anyways to design the details parts. Hope that makes sense…


      1. I searched in vain through your Flickr stream, looking for an example, Mark.

        I don’t think I’d appreciated how much work went into the diesel house before scrolling through all the photos at once. Absolutely a tour de force!

    1. Absolutely!

      Here is a very simple laser cut jig that was used to hold the sides of tall, spindly staircase parallel and properly spaced while the treads were glued in place:

      and the final stairs:

      Here is a more involved jig to hold a 16″ row of track pedestals plumb and equi-spaced:

      and the pedestals:

      A laser cut painting jig:

      And here is a jig intended for the assembly of some of the 70+ windows in a depot:

      In the end, because of the clearance needed to assemble the 6 different window elements, I found it easier and more accurate to assemble the windows by eye, which can discern subtle inaccuracies very well.


      1. Another thing to think about as you’re designing is the order in which parts are coming off the fret. For example, don’t make the first part come from the middle. Also, you can make sub-frets to allow for easier finishing of collections of parts. Wish I’d thought of these ideas when laying out 622!

      2. Good points. I will have to remember these as I design.

        Sorry for derailing your blog Rene.


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