Wednesday, February 21, 2007


Progress Update

Thought I would comment on my progress. I like Zach have a comm board. Nice going Zach! I tested the communications shorting tx to rx using hyperterm with properties set to ansi (took me a while to figure out thats what I needed to set it to). I verified that characters stopped being sent when I disconnected the leads. I cheaped out using a simple design I found using 4 resistors, 3 diodes and 2 npn transistors. I found it while looking for pic programmers and decided to try it because of its simplicity.
So that makes pic programmer and comms unit working. I have my stepper motors. Nichrome 80 is on order. Some teflon blocks on order as well. A little index card box houses my chips and sockets and various electronic sundries. Oh, and I got a lighted magnifying glass so I could see what I was doing with small stuff. You young guys will know what I mean in 20-30 years. I have a drill press and cross slide vise coming in a week so I can do some simple milling/routing to make the extruder. If I can drive the vise with steppers I can try doing some milling of copper clad and quit doing this ugly perfboard stuff. But that means I'll have x and y stepper controllers already working. Well there is always the next version, and anything else I ever make. I'm getting excited.

Sounds great Bart! I know what you mean about the magnifying glass. I've got a big one that goes with my soldering iron.
That IS a simple circuit. You built this thing and have it working. What is a 3K3 resistor and what kind of diodes did you use?
3K3 is the standard abreviation for 3.3K, i.e. 3300 Ohms.

You could 1N4148 diodes.

The "simple" version does not meet RS232 standard levels so expect problems with laptops.

The "better" version requires the PC to set RTS high and DTR low or vice versa so may need software mods.
Are you going to be using the cross-slide vice as the x-y axis of your RepStrap?

If so, let us know how that turns out, it could be a useful way of RepStrapping.

What are you using as the spindle for milling? (Drill spindles aren't designed to handle lateral forces, just up-and-down forces.) You may want to mount a laminate trimmer or rotary tool on your vertical axis for milling, rather than using your drill. People like the proxxon brand rotary tools for homebuilt cnc machines.
Seems nop.head got to answer you first Forrest. Don't know about the "better" circuit, since I didn't build that. Sebastien, seems I will have to get the vise to turn more smoothly or get real hefty steppers. It was a thought. I do intend to use it to mill/route the extruder. I bought some small routing bits just to play with. If I have any luck I'll post some pics. I have given thoughts to getting a small rotary tool mounted above xy axes for doing fine routing. I like being able to mix and match, but different versions of hardware may be built to do different things.
I've cheated more than once by using my drill press as a milling machine. The bearings are not ment to handle lateral force, but they will. That in the end is not the limiting factor, flex in the long path through the structure from the drill/milling bit to the workpiece is the one that gets you. That is why milling machines are so stout compared to lanky drill presses. :)

Anyway, with some carefull fiddling, I've managed to mill a few keyways in mild steel shafts when desperate. Cheating by bracking things against the flex really helps!

Also, dismantling and polishing a cross-slide can go a long way to smooth out its action. I believe tips on doing this could be found wherever machinists gather on the net.
...uugh, that's supposed to be "bracing things against the flex"...!
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