X-Axis: Bigger Stronger Faster

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I had trouble with my XZ Carriage flexing a bit too much for my liking. Before I tried extreme measures of adding a second piece of MakerSlide and another set of wheels, I figured I’d try some Open Rail first. I sponsored the Kickstarter project so I had some samples laying around. I cut two strips of this to the same size as my x-axis MakerSlide extrusion and bolted them on.

That’s a ton of T-nuts and M5 screw. I had to carefully line up all the T-nuts first then hold the Open Rail in place while I put in the screws. If I bumped it and shifted a T-nut away from a screw hold before I put a screw in, I would have to pull everything apart and start over. Luckily this didn’t happen.

I actually had more trouble with trying to use washers as spacers when reassembling my XZ carriage. I helped hold a stack together with a bit of tape. This worked pretty well. Also worth noting is that the orientation of these flat washers matter. These washers are stamped and have one rounded edge and one more sharp edge. The washers also curve just slightly away from the rounded edge. If you stack them so that they are all pointing in the same direction they have a smaller stack height than if you alternate them. I alternated my washers and that got me within about half a mm of where I wanted them.

You can see the alternating washers in the spacer set closest to the camera below. After struggling with that for about 3 minutes you can see my improved assembly method on the far one. You can also see the extra set of V-wheels for the new V-rail.

This modification did add quite a lot of stiffness to the XZ carriage. The z-axis does not flex nearly as much. Now the weak point seems to be a combination of two things:

  1. The carriage plate closest to the z-axis bends in the middle away from the screws. This is bending within the carriage plate itself. Modifications such as these reinforcing blocks shown about halfway down on this forum topic should also help me. (But I will have trouble trying to fit things around my Z Leadscrew.
  2. The z-axis V-wheel bearings are shifting on their races in the same way the x-axis ones did. I’m going to live with this problem for now. Things may improve when the leadscrew is installed.

The architecture for the x-axis on my machine didn’t lend itself to having the same style belt clamps as the x-axis did. I originally wanted to run the belts close to the extrusion as shown in the picture above. I tried putting some eye-bolts on the Y Carriage plate, but this would end up stealing over an inch of my usable x-axis travel on each side. The yellow cable tie shown was an attempt to make a larger radius for the belt to push it closer to the x-axis extrusion.

Next I thought of having some bracket that would push the eye bolt down from the top. This would make it much closer to the carriage plate, but it would be complicated and would not be as friendly to adjust. Also shown here is another attempt at increasing the wrap radius using some home electrical wire (single copper conductor).  I didn’t like this either.

I even tried making something out of Steel Tec parts, but this was a mess.

Next I started playing around with putting the eye bolts on the motor carriage plate instead. I had to route the belt upside down now, around some extra idler pulleys installed on the top corners of the X motor carriage plate. Although the time I put into machining the other idler pulleys so they would fit between the V-wheels would now be a waste (yes, btw, I machined those pulleys) and this setup doesn’t look quite as nice, I think this will be my best option.

I went back to CAD and some sketch paper and figured out what my bracket would have to look like. I needed to make the eye bolt a bit higher than the belt horizon because I needed room for the lock nut over top of the Y motor. If I made the bolt in line with the horizon, then the threads would be just above the motor and I couldn’t tighten it there. I thought about tapping the bracket, but that would mean I would have to remove the belt to turn the bolt and tighten it or else twist the belt. I printed a template and fabbed it up. Apparently I was paying too much attention to the vertical dimensions because my eye bolt mounting hole needed some post-design shifting in the horizontal to get it to line up with the belt. A rat tail file helped me out.

With both brackets completed I used some pieces of Steel Tec to make belt clamps. Those are #8 screws and nuts. This all turned out pretty well.

Ok, I wasn’t going to mention machining these idlers I didn’t end up using, but there are some interesting points. I did some sketching and found out that I could still fit a 9mm idler between my V-wheels when I doubled my rails. These little salvaged idlers are a machined tube with a 5x5x16mm bearing pressed in them. I knew I needed only enough room for 2 shim washers on either side of the bearing and I needed to make sure I machined it symmetrically. So, I put the two washers on the bearing and measured the depth to the outer edge. Then, on my lathe I faced the bearing end until I got to this depth.