garageFab.cc

I haven't posted in a while, but have done a few things:

Taken apart the drilling contraption since I didn't really need it when the angle no longer had to be accurate; enlarged to 1/4" the holes on the angle from drilling contraption. This created a nice pile of Contraptor parts, ready for the next project. Made several sliding elements of different sizes - full, half, "quarter", installed Delrin nuts in some of them. Revisited the whipping rod/nylon couplings problem and decided to switch over to 0.250"ID aluminum tube for couplings. Tried to couple this tube to 10-24 rod, unsuccessfully. Searched for more powerful but still cheap steppers with lower coil current. Plotted the next contraption to be built.

Quarter inch holes in the angle are working out pretty well. When assembling something, distances and right angles may need adjustments with tape measure and a try square, but it's better than trying to put a screw through 2 holes of just the right size that slightly don't match up. Oversize holes make manufacturability at home much easier, which is an important goal of the project.

New couplings

When I switched to nylon spacer couplings between 1/4" rod and 10-24 rod, there was still some wobble in rotation. Eventually I tracked down this problem to 2 things: first, when you thread small nylon spacer onto the 10-24 rod, it's never perfectly parallel. This becomes visible when rolling the small spacer with 10-24 rod on a flat surface. Second, the inner diameter of the large nylon spacer is slightly more than 0.250" - which means that the ACME screw and the motor shaft can move in the radial direction inside the spacer. Also, the thread in nylon could be easily stripped, so I could not really tighten the set screws. I was working around these problems by wrapping some electrical tape around the motor shaft or ACME screw, and drilling deep set screw hole, going into the rod itself. That kinda worked but only when the coupling was first made. Because the set screw holes were not at the exact right angle to the coupling axis, large spacers slanted if they were not drilled together with the rod. I had thought about making a coupling from aluminum (so that deep set screw holes would not be needed), but could not find appropriately sized tube on McMaster.com, and decided to tackle this whole thing later. Recently I found a reasonably priced 1/4"ID 1/2"OD aluminum tube on OnlineMetals.com. I tried it - it provides a good tight fit for ACME screw and stepper motor shaft, little less so for 1/4" all-thread rod. I still need to test whether rod slips with the tightened set screw - hopefully not. However, the problem with coupling it to the 10-24 size rod remains. One of the earlier reasons that I used 10-24 rod as opposed to 1/4" was the lower price of bearings and pulleys on McMaster.com. However, with some searching one can easily find 1/4"ID bearings and pulleys elsewhere for less than 3/16"ID on McMaster. I ordered those to try and I'm thinking to switch entirely to 1/4" leadscrew/shaft size, which would eliminate the coupling problem. However, 1/4" leadscrew requirement makes it difficult to use the all-thread/coupling nut combination, because 1/4" coupling nut (vs 3/16") needs a lot more filing to fit in the corner of the sliding element.

Delrin nut

Making several Delrin split nuts for sliding elements took a while. Trying to make them faster, I rushed somewhat which resulted in alignment problems with some of the nuts - the leadscrew would go off about quarter of an inch or so away from the rail for every foot. This means that some leadscrews will whip and hit against the inner walls of the sliding elements, creating vibration, wear, noise, accuracy problems. While it was possible to make the lead nuts with better alignment, it would take more time and effort. Ideally, the alignment should not be fixed so that the nut position could be adjusted during assembly. To achieve this flexibility - given extremely limited space in the corner of the sliding element tube, the leadnut would probably have to be moved (with the leadscrew axis) to the center of the sliding element. The component, carrying Delrin (or coupling) nut, would be attached with screws to one wall of the sliding element. I made one draft design of the centrally located leadnut. However, this is a big change impacting many other components - leadscrew supports (rod mounts), belt drive, motor mount etc, and it needs to be thought through. Maybe both options should be available.

Steppers/Stepper driver

Looking for inexpensive, low current replacement for Alltronics stepper motors, I found a $20 stepper which seems to fit the bill - 12V, 0.4A - well under 2A limit of the stepper driver board, with 111 oz/in holding torque (Alltronics are rated at 60 oz/in). I need to order and test one out. Also, there is a beefier stepper driver board apparently in works for RepRap, which I think could be used with existing 2.3A Alltronics steppers.

Minirouter

This is the next contraption that I'm going to build from the set. I hope it will be be stiff enough to mill wood and plastic with a dremel. Another task for it - I need to drill a large number of tiny holes in the cutting mat to make the vacuum table surface for the Paper Prototyper. Finally, I'm planning to build RepRap thermoplastic extruder. This, together with Minirouter, will make a Repstrap.