Thing-O-Matic: X Axis Motor/Belt Adjustment

The socket-head cap screws securing the ball bearings that ride on the left-side Y stage rod prevent the X axis motor from sliding rightward along its mounting slots. The rightmost position, as enforced by the SHCS heads, makes the belt far too tight.

This picture (cropped from one in the MBI Thing-O-Matic assembly instructions) shows the situation under the Y stage with the as-built components:

X axis motor mount - MBI image
X axis motor mount - MBI image

This suggests that the ball bearing assembly was an afterthought, perhaps solving the same overconstrained rod problem as I fixed in the X axis stage. The as-built motor position pulls the X axis belt just slightly less taut than a banjo string, which isn’t a Good Thing.

The solution is to replace the four SHCS with pan-head screws to get a bit more clearance. Fortunately, my Parts Heap had some salvaged 3 mm screws of sufficient length, so I avoided a trip to the Big Box retailer. Rather than put everything together and discover the heads were still too tall, I ground them down so just the barest hint of the slot remained:

Modified pan-head screw
Modified pan-head screw

That provided enough clearance to make the X axis belt entirely slack, which means I probably didn’t have to grind the heads in the first place. In any event, the proper position looks more like this:

Adjusted X axis motor position
Adjusted X axis motor position

If you look very closely, you can see the marks from the original position near the middle of the slots. Here’s a blown-up and contrast-stretched view:

X axis motor mounting slot - detail
X axis motor mounting slot - detail

Those few millimeters make all the difference in the world: the belt is now decently tight, the motor responds well, and all is right with the world.

3 thoughts on “Thing-O-Matic: X Axis Motor/Belt Adjustment

  1. Hello Ed, this isn’t a comment but a plea for advice. I need to solder a pair of leads from a transformer. My 40 watt hobbyist soldering iron cannot heat the ends of the leads to the point where solder melts, I suspect the solid copper wire is sending all the heat to the windings. Is there a trick (technique) that will allow an underpowered soldering iron to accomplish the task, or do I need to move up to a more powerful iron to solder the tips of the leads? I was tempted to tear up our microwave to build your resistance soldering device but the wife talked me out of it. Any help or advice appreciated, thx THL

    1. More power, Scotty!

      Piddly little soldering irons like the ones we use for electronics simply don’t provide enough power to heat the joint. Think of trying to heat a gallon of water with a match: the flame is hot, but without enough energy to make any difference.

      I use a soldering gun for intermediate jobs and deploy the resistance soldering gadget for really tough situations that don’t involve circuitry.

      The soldering gun came from Radio Shack, back in the day, and that one seems comparable.

      My father had a gargantuan electric-powered iron favored by tin-roof contractors, but …

      Good luck… and pick up a dead microwave the next time you see one: it might come in handy!

  2. For such things as #1 asks about I use my little butane-powered portable iron from RadioShack. There’s no power rating on the thing but it gets *monstrously* hot, *monstrously* fast, and drags everything else with it. Not the best thing ever for delicate electronics (although I’ve used it successfully at low throttle), but pretty great for this sort of thing.

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