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 ;)

Saturday, October 2, 2010

DIY Millennium Falcon

Carys was turning six at the beginning of October and had recently become StarWars obsessed (we let them watch the original 3 movies a few weeks back and they loved them).  Lin and I like to add a few home made presents to the mix on the kids birthdays; So, we decided to make a few StarWars themed things for Carys' birthday.

Lin started out making a set of StarWars figures using wooden craft pegs (more about that on her post here).  We were going to make a Millenium Falcon using a couple of plastic frisbies, but then thought it'd be nicer to create something a bit larger and more durable so that they could use it with the figures for some make-believe fun.

It took us a little while to decide on the components to use.  We found this weird wooden board at the local thrift/charity store.  I think it's used for carving meat and the grooves capture the juices (there's even a "patent applied for" stamp on the back).  I forgot to get a picture of it in its original state; the picture below shows it after a little bit of modification.  It was originally symmetrical - I rounded off one of the handles/ears and cut a groove in the other in preparation for adding the front prongs.

Here's a quick overview of the components:

There's the weird carving board, a plastic lid (another lucky thrift store find as it fits perfectly in the groove of the carving board), some PVC pipe (2" diameter) and a 90 degree elbow joint (both from Home Depot).  There's a dollar tree airfreshener case (the white tear drop thing by the black pipe) and some wood.  There are some other bits and bobs that aren't in this picture (I hadn't figured out what was going to be used at the time): a hinge for the cargo bay ramp, some more wood for the internal walls, screws, nuts/bolts, wood glue, some grey spray paint, a few plastic bottle caps, and the outside case of a CD spindle.

From the 'ingredients' picture you can see that I cut and sanded the carving board first and then made the front 'prongs'.  For the prongs, I looked at a few online plans and scaled the dimensions to fit the cutting board.  I used a scroll saw to cut out the shapes and then screwed and glued them onto the main board.

While the glue was drying I made the internal structure.  It's made from the outside of a CD spindle and some wooden boards (2" hobby board from Home Depot).  I cut the CD spindle to fit the height of the lid and then measured out the boards to fit up to the edge of the curve.  That was a bit of a mistake as the lid didn't fit with the boards that long and I ended up having to sand the ends down a bit.

I thought it'd be fun to have internal doors but didn't think the spindle would survive with large chunks cut out of them, so I just put some painters tape where I wanted the doors and then painted it all leaving some see-through areas after the tape is removed.

I gave the lid it's first coat of paint, bolted on a few bottle caps and wood disks to mimic some of the structures seen on the original, and then gave it all another coat.  The lid needs to be cut in a couple of places to make room for the cockpit attachment/corridor and for the cargo bay ramp.

I used a miter saw to cut one end off the PVC elbow (so that the cockpit would face forward) and to cut an angle into the corridor (makes it easy to screw the pipe into the base). My first attempt failed as the corridor was too short, but I had plenty of pipe left over for another go.  Everything was given a coat of paint.

I cut the airfreshened body down to a size that would fit snugly over the pipe and then used hot glue to attach it.  I like the fact that the cover comes on and off so we can put pilots in there.

 Here's the final set-up (with cargo bay ramp attached with a hinge):
Lin made some ace characters for Carys' birthday and the two presents go really well together.  I love the fact that Darth Vader's helmet comes off to show his pale splotchy face :)

And, just to finish off, a gratuitous set of action shots: