# Challenges with Andymark Compact Elevator 2x1 Bearing Block

I was working on an elevator project, and I wanted to use the Andymark 2x1 bearing blocks. However, I find its dimensions unusual, making it harder for me to work with.

Drawing for the bearing block, from Andymark’s website

The depth of the groove in the center of the bearing block is between 0.139" and 0.134", based on Section A-A, and in CAD, it measures 0.138780". This means the lateral distance between tubes of consecutive stages is supposed to be about 0.1875 in - 0.138780 in + (13 mm/2) which is approximately 0.305 in, with 0.005 unilateral tolerance. Looking at Wildstangs’ 2023 CAD release, they also used the Andymark bearing blocks, and used 0.305" spacing.

I am confused as to why the bearing blocks were designed with these kinds of measurements, since I feel like it would have been simpler to design it with “nicer” numbers, and it would allow the stages to be fully defined with tangent mates.

For instance, the depth of the groove could’ve been something like 0.1875" (looking at the CAD, there would still be a decent amount of clearance for the countersink head) instead of 0.139". With 0.5" bearings, there would be 0.25" spacing between stages, and 0.0625" clearance between the bearing block and next stage (sufficient for the same tolerance).

This is just a random idea off the top of my head, but my question is on why the Andymark bearing blocks were designed in such a way. The mixing of metric and imperial units means that the CAD cannot be perfect, but more importantly, such numbers can introduce confusion during machining and assembly, increasing the risk of wasting materials and time.

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Having just used these: they are tolerant to a fair bit of slop, I am not sure as to why more “round” numbers were not used, but at the end of the day the carriage and stages can have well over 1/8 of an inch of mismatch/slop and it all behaves fine. You should be able to get 95% of the performance these things offer with a carpenters square, hand drill, hacksaw, and a little patience.

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I haven’t used these, but looking over the design briefly, 0.305" is the minimum gap you would design for. As @Skyehawk mentioned, you could have a significant gap and they would still work just fine (with 9mm deep bearings, even 1/8" on each side would “work”). You could find the closest “normal” imperial number above the 0.305" x 2 = 0.610" and go with that, if you wanted to make it easier to cut a tube to length with a tape measure. 0.625"? 0.75"?

The mixing of units seems to come from the particular bearings used. We don’t have insight there, but I would highly suspect sourcing to be a driving factor.

For the pocket depth, if these are used with at most 1/8" wall tubes, it makes sense not to pocket much more than that. If I care more about forces in the “primary” direction (vs lateral, as AM defines them in their description here), then I would want to keep the material in the plane that those 13mm x 9mm bearings attach to as thick as possible.

They also appear to be the same depth as the nut pockets, which may be a DFM decision (no idea what their setup looks like).