Sorry to make you all wait, life got in the way last weekend. The good news is that my family is going in on a property together, and me and my brothers will get our shop! The sale closes at the beginning of April, so the Maslow will soon get a more suitable home!
I was able to do the tests for the top mount yesterday. I spent about the same amount of time calibrating the machine. I got these results from the auto calibration process:
I’m scratching my head a little as to why the chain sag value changed. Maybe it’s because the rotation radius is smaller, so the chain is a little longer than it would be for the 45?
I had a couple of issues with the linkages, but I was still able to complete the tests. The results aren’t as good as the 45. There is quite a bit more distortion that happens with the top mount. The X-Y tolerances aren’t atrocious, but I had much more trouble with square tolerance and positional tolerance. The top mount I used also scored a 2 : 0.75 on the benchmark test, so it’s a little worse than what I got with the 45 degree.
The chain slipped just before the machine cut square 4, so that particular square is certainly an outlier. I was able to reset the chains and get consistent results for the rest of the test.
and for comparison here is the 45 degree’s results (so you can see them side-by-side):
I would be very curious to see the difference in the square and positional tolerances with the new version of the top mount. I think that the tighter tolerances on the holes will mean that the linkages will rack less when they’re at their most tension. @pillageTHENburn and I investigated just how much play there was in the linkage assembly a little while back. I measured between centers for the top bolts and where the chains attach to the linkages.
Well, really, I measured to the outside of the bolts for the top and to the outside of the pins, then subtracted the diameter of the pins/bolts to get the actual between centers distances. I used my 12" calipers to get as accurate a result as possible. You can see my math in the table below:
The difference in the two distances gets very extreme at the extreme ends of the bed. In some places, it’s almost an inch difference between the top distance and the bottom distance.
I also encountered an issue with the linkages when the chains get close to vertical. Once it gets past a certain piont, the linkage bars slip on each other and throw off the cut.
This may simply have been because my top beam is shorter than most, so chain is more vertical than it would be with a “stock” top beam. It started happening on the outer two rows of squares, I would have to work within 600mm (~24") of the centerline of the bed to avoid this issue. However, I was able to cut out to this area with no trouble with the 45 degree linkage kit, so I believe the system works more reliably across the entire bed.
So my conclusions on the comparison between systems is that I think the 45 degree is a better system all around. If the tighter hole clearances mean that there is less error in the linkages than it should have similar performance to the 45. However, design considerations will need to be made to make sure the linkages don’t slip.
As a last little bonus, here are the summaries of the torture tests I’ve done so far:
And here is the current version of my test spreadsheet in case anyone wants to stare at a wall of numbers:
BedAccuracyTest.xlsx (42.3 KB)