Wednesday, October 6, 2010

CNC Machine Build - Part III "It's Alive!"

Finally... after a lot of work and learning, the CNC machine is up and running.

I got the main machine finished and connected to a computer about a month ago, but I've been having trouble getting the z-axes working properly.  I tried tuning/adjusting it as described in the plans and I even remade the leadnut bracket, replaced the leadnut (twice), replaced the leadscrew (twice) and went through 3 couplers (these are only made out of cheap hose so that was no biggie). But, each time I put it back together, the axes would stall part way through a job (ruining the workpiece and usually destroying the coupler).  Eventually, I had to walk away for a week to cool down - at least that gave me time to make the Millennium Falcon dolls house for Carys' birthday.

Last weekend I went back to it.  I replaced the lead-nut and lead-screw assembly (again), this time making sure to buy some new threaded rod that was straight. It turns out that the previous ones were slightly warped and this was causing most of the drag. I guess that's the problem with building a CNC machine with bog standard threaded rod as a lead-screw, they're not meant to be used in applications where the rod has to be straight... I also updated the coupler tubing - I'd been using clear vinyl tube from Lowe's (the kind used for irrigation) which is weak and slippery. I bought some fuel pipe from Kragen and this works a lot better.

I did a couple of test runs on some kitchen cutting board and quickly realized that I'd have to work out how to hold/clamp things down whilst cutting.  I have a few clamps, but none of them fitted well between the slats so I made up a few hold downs using some left over wood and some bolts (you can see them in the picture below).

If I were to start this again, I think I'd opt for the more expensive ACME lead-screws/nuts and associated couplers. I spent a lot of time over the last few weeks tuning the axes and I think a lot of this would have been avoided if I'd gone with the better rods and lead-nuts.  All in all though, I'm very chuffed that this is actually working!  Last year Lin did a detailed pumpkin carving of our CSO, this lead to some geeky conversations at work about how you could automate the process but we ended up deciding that it was too complicated (mainly due to the issues of mapping an image onto the surface of a pumpkin in order to carve it).  I'm wondering if I can actually achieve that this year using the CNC machine - just like this guy did.  I bet all the CNC carving time gets eaten up with hearts and unicorns though... you know how it is ;)

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