Shop Stuff: November 2010 Archives

SCORE! or not...

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My own attempt at getting noted on the Fail Blog or There-I-Fixed-It.... Apparently a brass bushing is not recommended for threaded rod. Looks like I'll have to spring for bearings.

Z-Axis version 2.0 nearly complete!

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After a minor setback, I took another crack (I hope not!) at the Z-axis mount. This time, with some decent success.

Z-Axis version 2 - with rotary tool installed.

After final assembly, I tried it out and it can lower and RAISE the rotary tool - as shown in this short clip:

The stepper is running off 12V to give it enough torque. To be honest, I am not sure what the step / feed rate is right now as it is not calibrated. It is quite slow, however, I am ok with that. The first generation home built shopbot like CNC machine will have many glitches.

Z-axis version 2 with rotary tool

One other improvement I have made is to use 3/8 inch plastic plumbing pipe (risers, used for the last 12-24" of plumbing before a fixture like a sink or toilet) as spacers. I also changed the weight bearing plate to be wider and used 3 bolts instead of 2.

CNC - planning - X axis

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Well, this is bigger than a bread basket, and so I figured I should probably make some real plans. After a few pencil drawings, I thought, why not try Google Sketchup. Here is the results of the table and X-axis.

Looking down from the top.

Lookup up from the bottom.

The table will glide on the frame. The threaded rod does not travel the entire length, hopefully that will be ok.

The table will be 24x24 inches.

Z-Axis version 2

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So I started with a simple frame to hold the rotary tool and built a basic rig to raise and lower the frame on a bolt. The bolt was turned by a Lego NXT Mindstorm motor. I have since managed to get all 3 stepper motors turning and began figuring out how to mount the stepper in place of the NXT motor. Here is the next version of the z-axis assembly. The small dot matrix printer stepper motor is geared down to a longer 3/16" bolt. Over all the idea seems to work well.

Z-Axis Version 2 - top
From the top

Z-Axis Version 2 - front
From the front

I need to redo the support plate that holds the weight. In this side shot, you can see that the gears are not 100% straight. I plan on using a wider support plate and 3 bolts (not 2) in a triangle pattern to better align the gears.

Z-Axis Version 2 - side
From the side

The next step is to prevent the frame from swinging around on the bolt that raises / lowers the tool. I plan on using hardened steel rods and bushings from printers to guide the frame up and down in a straight path. Unfortunately, this is where the project took a step back, as I did not do a good job of drilling the plexiglass and broke a couple of key pieces that will have to be rebuilt.

Broken :-(

Step 2 (and maybe 3) of 3 drivers are done.

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I finished the 2nd driver board tonight and tested it. Works great!

Next stepper driver

And the final major axis driver is complete. Very similar to the previous driver. Added some heat shrink tubing the resistors to reduce shorts. Oddly, this side of the prototype board had 1 fewer row of pins and so some last minute re-jigging had to occur.

I also revived an older driver board I built for a flight sim I was working on years ago.

Old stepper drivers

An old stepper driver I built years ago for a flight simulator. This board drove the compasses. The chip in the middle is an STA401A driver from a printer, the chip on the right is a bipolar driver from a floppy drive. This one will drive the Z-Axis (does not require as much torque, can go slower and driver a smaller stepper).

Step 1 (of 3?) done - CNC moves forward

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I have been busy trying to build a PIC based stepper driver for my CNC machine. That is still in the works, however, I have in the mean time found a simpler solution. EMC can direct drive the coils - well, almost. One still needs to build the power circuit. Which I have completed 1 of 3 (X,Y and Z). This one, and the next, use heavy duty transistors (D1392) from a 9-pin dot matrix printer. It has been tested with big (30oz torque) 5V 1A steppers.

Power driver