Designing the Motor Mount

This has been the single hardest design problem so far.  The stepper motor to drive the spur gear that turns the 60 tooth worm gear needs to be perpendicular to the polar axis.  It also needs to be attached in some way to the polar housing so that it can move as the polar axis adjusts latitude.   Also, getting a good fit of spur to worm gear may require some fine adjustment of position.  This somewhat approximates the relationship of the parts.

I will mount the stepper motor to the overall assembly with this mounting bracket.

The mounting bracket uses slots on the bottom, so sliding the bracket relative to the worm gear gives me motion in that direction.  

That flat section where the motor sits at the far end will have an upright in which I will bore a hole to locate the end of the spur gear.

I will cut a 1.065" slot in a piece of acetal that will slide onto the underside of the polar axis housing.   It will be held in place by two 6-32 screws in slots on the acetal allowing adjustment up and down for precise engagement that direction of spur to worm gear.  The last direction has no obvious way to adjust,  so I need to do that pretty accurately. 

There is no way to put threaded inserts into the polar axis housing walls; they are to thin.   Two possible approaches. 

1. Epoxy 6-32 nuts inside the housing where the screws will go.  To do this usefully I will apply epoxy first then turn the screws (with release agent in the threads), then bake to cure the epoxy.  Remove screws. 

2. Put the screws pointing out from the inside of the housing epoxied in place.  Because I need a slot in the acetal for adjustment,  even a little slop in positioning will not be a problem. 

The downside of acetal making fine bearings is that it is devilishly hard to clamp down in the mill vise.  If the sides are not pretty parallel,  as is usually the case with anything cut on a table or cutoff saw, you will not get a terribly flat edge for clamping  

I am being a bit more precise on this because for the reasons listed above,  at least some of this does need to be pretty precise.  I am squaring pieces using a fly cutter which is both precise and makes a nice finish as well.

I am glad that I have a lot of black acetal lying around.   Design or manufacturing limitations sometimes do not become obvious until you have already wasted a piece such as getting ready to cut a .4" hole through a .5" wide piece.  How do you support that on parallels without the endmill hitting the parallels.   As I write this, I realized the parallels can be removed once the workpiece is clamped.  It is no longer relying on the parallels for support.