Thursday, September 29, 2011

My DIY CNC Build Log: Part 1, Assembly

This is Part 1 of the build log for my MyDIYCNC kit.  I took part in the Kickstarter for around $400 and received a complete CNC kit.  I plan to use it for modular synth milled circuit boards and aluminum frontpanels.  You can read Part 2 here.

Day 1

I picked up my kit last night and started.  I got this far: (image)

So far it's going quite well!  To clarify one thing in the step-by-step instructions, when assembling the frame be sure that the top frame pieces have their side holes positioned pointing towards the outside, and they should be oriented such that the holes are closer to the "back" of the frame rather than the "front" in order to match the finished CNC images.  I got lost in the wording that is on that page now, hopefully that explains it better.. not sure :)

Other than that to get the rods into the rubber grommets I found the easiest thing to do was slightly twist them as forcing them into place.  Not a lot of twist as I didn't want to slice the rubber, but it got them in without creating any new problems.

Click to read more about the DIY CNC construction and problems encountered.

Day 2

I now am almost done the construction.

I have found that before drilling, taping parts is invaluable in the y axis / z carriage construction steps where things get a little bit vague in the manual.

Some steps in the manual are out of place and you really need to be thinking while you put this together.  For example, step 39 says to use your square to ensure the gantry backbrace is vertical.. but at this point the grantry uprights have not been made square so the backbrace would be on an angle!

My y axis sadly had a lot of trouble with the parallel rod alignment.  I also noticed that the gantry uprights do not really match one another well at all.  I'm guessing they were made separately on a CNC?  It's too bad that they are not a match drilled pair, that would ensure perfect alignment.  Also the holes were about 0.5mm too far apart for the parallel rods compared to the y axis carriage.

I ended up drilling one of the parallel rod holes out a bit bigger on both of the gantry uprights to fix the y axis alignment.  It's not as smooth as the X and Z axis but hopefully it's sufficient.

Here's how mine looks right now.  My z axis carriage is a bit sideways :( but it travels smooth so I can make do.

Day 3
Another day, more progress, more tips.

I can't stress how much you need to confirm the parallel y axis rods before trying to do your gantry uprights.  I ended up making significant holes trying to fix the problem that ended up being non-parallel bars and then had to re-fill most of the holes with tape to get the rods once again relatively tight.

Before attaching the spindle mounts to the z axis carriage, test fit the spindle in position.  I found I had to both slightly increase the size of the bottom mount, and significantly file/drill down the size of the top mount in order to get the spindle mounted vertically.  If I had mounted the top mount higher on the carriage it probably would have fit as stock.

I also seem to be missing my zip ties.  Maybe I misplaced them since unpacking the box.  Whatever, I need to go to home depot to get more polyethylene tubing since my Z axis is not connected.  I also seem to be missing the fasteners that go over the tubing to couple the steppers to the leadscrew?  Hopefully home depot has something that will work.

I did all the electronics work yesterday except for the spindle, and 2 of my 3 axis work!  I'm using KCAM with windows 7, the other changes I had to do to get it to work was change my parallel port to ECP mode in the BIOS, and when starting KCAM, right click and select "run as administrator".  My Z axis is turning but as I mentioned before I need to re-do the coupling.  A sharp end of the leadscrew pierced the tubing once it was softened and I ended up not making a good connection.  One thing to note, when modifying the ATX power supply, most of the "red" 5vcables on the supply sent with the kit was actually using a slightly purple cable.  You can check this when you have the top off by seeing which are connected to the power supply's 5v rail (It's labelled).

If mounting the electronics enclosure on top of the power supply don'tovertighten the power supply screws on the electronics case or you will crack it.

I found, sadly, that at 10 IPM my X and Y axis run into multiple spots where there is too much friction and the axis would skip steps.  I think my axis may need some sort of light lubricant as when I originally built the x axis it was so smooth moving that the table would slide just from gravity when I moved the frame.  I have them working smoothly at 2IPM.  Will investigate lubrication and maybe bumping that up to 4-5 IPM hopefully without much effort.

I'm thinking for the future, and wanting to replace my spindle, of removing the spindle mounts from the z axis carriage and drilling 2 or more holes through, and then installing the spindle onto a plate with matching holes and using bolts and wingnuts to attach the spindle to the z axis.  That would make spindle on the fly a reality!  Maybe rubber washers between the spindle mount plate and the z axis carriage to absorb vibration.  Any comments?

Read Part 2 of my build log here.

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