Tuesday, January 16, 2007


Failures and Setbacks

Tonight my goal was to attach the threaded rod to the stage. It only sortof worked. I realized there were some fairly major flaws in my design. However, none of them are showstoppers (i hope), and also the improvements will make the design much easier for others to do.

Securing the skate bearings / drive nut to the respective places requires epoxy and is a royal PITA. I dont feel entirely sure about the epoxy's performance (especially long term) and it is also quite messy and problematic to apply it (game over if it gets on the threads...)


instead of using epoxy to attach the nuts / bearings to the frame, i'll use a mounting bracket that goes over them and is tightened down until everything is snug and immobile. i attempted to do this with some wood, but it broke in the middle because of too much pressure. i'm not sure... but i think if i use a screw driver instead of a power drill that problem wont be too difficult. on the other hand, this would be a GREAT use for thermoplast, and they can even be hand molded very easily.


Mounting the threaded rod on to the skate wheel bearings is tough. The approach I took was to use bolts to attach a smaller screw to the bearing. That works really well and really awesome. However, the problem is that this screw then needs to be attached to the threaded rod. I tried using epoxy, however this has some problems. As said before, its messy. Secondly, its fairly tough to get the bolt to be exactly center. Thirdly, epoxy + threads = bad. Fourthly, it has to dry and is prone to drooping unless the rod is vertical, which leads to the rod falling over and throwing the bolt off (obviously that is bad).


I'm not really sure. I'm going to try multiple epoxy applications. First i'll just concentrate on attaching the bolt and making sure it is perfectly aligned / straight with the rod. Then once its dry I'll glob a bunch on to make it really strong. This will probably work. I would really like to find a better solution. The only thing I can think of is either drilling and tapping the rod so that i can bolt the bearings directly on the rod, or milling the end and threading it. Both of those options are fairly difficult and require yet more specialized tools (which i'd like to avoid.)

You guys have any suggestions?

Even though I ran into those problems I just mentioned, I've learned some valuable lessons and tomorrow I'm confident that I'll be able to overcome them and actually get a machine that works well mechanically. When the x axis was actually hooked up it turned pretty easily by hand, and the drill worked well on it (this is what killed it... =) The Y axis is shaping up nicely, and I'll probably lay the groundwork for the Z axis soon.

Check out my flickr photo set for more pictures of the work done today.

Great photos and documentation, Zach!

I considered using skate bearings at first but abandoned that in favour of ones I could get at Orchard which had lipped collars. What that meant is that I could drill a hole in a mounting board and push the bearing in to the hole till it reached the lip. Bolting both ends of my threaded rods then secured the bearings in the mounting blocks without glue or anything else.

Those darned skate bearings are better quality than the more expensive ones that I used but they're the very devil to mount.
To stop the wood splitting, try making the bracket with the grain tangential to the bearing surface and normal to the screw axes.
...or use plywood.
or make a pilot hole with a small bit and use an intermediary bit before you go full-diameter
good suggestions on the wood bracket. one of the other problems was that it wasnt exactly flush with the wood when i was securing it, so the screws tried to pull it down that last 1/4" and it snapped. i'm gonna try and get my thermoplast from iowa and then hand mold some brackets... much easier!
I was thinking when you were attaching the smaller bolt to the end of the larger threaded rod that if you had a larger diameter bearing or a smaller diameter rod it would have been much easier.
Had another thought about the mounting method. How about 3 set screws to hold the bearing in a plate you set in front of or behind your surface. You could screw on 3 pieces of wood to hold the set screws and flat washers would be a must here. Should allow for precise positioning and hold it solidly. It might be tricky if you don't have a way of positioning everything, but it would certainly allow you to reposition or replace readily.
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