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Saturday, June 07, 2014

CNC mill conversion - part 17

Computer stand

Running the CNC mill from the laptop had always been a little inconvenient, and I wanted a more permanent solution, so I purchased a used "all in one" touchscreen computer from eBay. 

Taking the stand apart

Next, I made a trip to LOWES for some metal, and a few tools to start working on a new stand.  

Metal tubing and new grinder being introduced

I wanted the computer to be able to turn as well as tilt. 

I started disassembling the mount and removing the plastic cladding, exposing the tilting mechanism. I would later reuse this part after a few small modifications.

As far as being able to turn, I decided to make a mount that would swivel, so I split the main square support tube into two sections, and inserted a round tube inside them. Because the fit was very loose, I made washers out of 4130 steel, and welded them to the top half of the round and square tubes to serve as bearing surfaces, and hinge points. 

Welding the washer to the top of the round tube

Welding the washer to the top of the square tube as well

Welding another washer to the bottom of the square tube

Close up of the bottom of the square tube

Back side of the washer

I also started welding an L channel to a 16 gauge steel sheet to hold the keyboard and mouse. 

Welding this much started warping the steel sheet a little

I ended up leaving some gaps between the welds, in order to minimize warpage.

Unfortunately I ran out of Argon, so I had to stop for the day. The next morning I went out early to fetch more gas, and resumed the fabrication of the keyboard platform.

Mocking up the keyboard platform structure

Deciding on a comfortable angle (-55˚)

Using the square tube to work out the spacing of the frame

Basic frame thrown together 

Additional frame members added to stiffen the structure

I used some of the leftover small square tubing to beef up the structure below the keyboard.

Frame structure supporting the keyboard

Frame top side

The finished keyboard platform is able to rotate.

Keyboard and mouse tray

Tray rotating

Side view

Finally, I concentrated on the mount for the actual computer. 

I butt-welded two small plates together, then welded them a few inches above the keyboard.

Two plates welded together being fitted to the riser

Computer holder plate attachment to the riser

Computer plate attached 

Lastly, I welded the hinge mechanism to the plate, and mounted the computer for the first time.

Computer connected to the stand

CNC computer ready to go to work

I added two spacers to the mount in order to miss the lip on the top of my wooden table.

Small spacer welded to the mount

I was pretty satisfied up to this point, except for a little side to side wobble. I traced it down to the fact that, with only one washer in the bottom square tube, the round tube was free to tilt inside of it.

The solution would be to insert another washer further down in order to capture the round tube, and prevent unwanted motion. This would require cutting the tube in half, welding the washer, welding the tube back, then smooth it all out... oh well!

I measured how far into the square tube the round one went, then sliced the square tube a few inches above it.

Cutting it down

After making a new washer, I installed it in between the split tube, welded it, and cut the excess off.

Square washer

Same washer after initial welding

Cutting off the washer's excess

Trimmed washer

Next, I lined up the other part of the tube, and welded them both together again.

Welding the other half of the tube to the washer

Root pass

Everything looked good at this point, except that the round tube would not fit into the washer anymore.

Further investigation revealed that some excess weld was constricting the passage for the tube. Regrettably this was now a couple of feet into the outer tube, and there was no way for me to get to it and fix it, except perhaps to cut the square tube in half again below the washer, reestablish the proper passage, re-weld both halves back, and grind it all to perfection.

Damn it!

Tube sliced anew just below the washer

Note how the round tube doesn't fit anymore

"All clear" after some work with a Dremel rotary tool

The tube finally fits though the bottom washer

Welding it all back again. Can you spot the original welds over the washer? (hint: they are 2" to the left of this weld)

Grinding down the high spots

All blended in

This fix worked beautifully, the wobble was gone, the welds blended perfectly, and I couldn't even tell anymore where the two cuts were made. So, I moved on to the final task of mounting my contraption to the actual table.

CNC computer final position

Wiring details

Mach3 ready to run the mill

I am very pleased with the outcome, there are only a few wires showing, and they are out of the way. The stand rotates with a pleasant drag, and Mach3's DROs are in line with the mill's ones, making it easier to keep tool drift in check.

I haven't even used it yet, but I like it already.

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