Last Updated on the 8th April 07
 

 

 
 
 
 
 

 

 
Building the Mk2 CNC machine
 
I was pretty pleased with the old Mk1 cnc router, but I felt that the MDF frame let it down a bit. Although it is capable of milling Aluminium, it worked best with some kind of lubrication / coolant on the cutter, usually a strategically timed squirt of WD40. This did not agree well with the MDF, causing it to move and swell. Even the moisture content in the air seemed to effect the stability of the MDF, which I guess you would have to expect. A lick of paint to seal it wouldn't have hurt, but I could feel the idea of a metal framed machine beckoning.....
 
With this in mind, I started looking at suitable materials and bearings with which to build a new cnc machine. I wanted to keep the costs as low as possible, so I knew the search would take some time. In the meantime I was keeping a keen eye on ebay for suitable parts, when I happened across something very interesting..... I picked it up for just £10
 
This is some kind of table used for scanning arial reconissence negatives, built for the the Ministry of defence, but no longer in use. It has X, Y & Z linear slides, is very sturdily built, and it's on wheels too. All 3 axii are chain driven by manually turning a small hand wheel. I hope to remove the hand wheels and extend the shafts to accept timing pulleys, for coupling to a stepper motor pulley.
 
Overall it looked like it should make a pretty good conversion to cnc, and not too much work involved either. It even has a ballscrew to adjust the table height within the frame. I won't be needing that, so I can remove the ballscrew and nut for use on another project. As the machine stood there were quite a few bits and pieces to remove. so I got down to business and started to strip it down.

 
Here you can see the frame stripped of all the unnecessary components and after a quick poke about I came up with a plan to attach a Y axis motor mounting plate to the manual chain drive mechanism.
 
The mounting plate needed to be more accurate than I could cut by hand, so I made a quick model of the existing Y axis parts in CAD, designed a mounting plate to fit that, and a 23 size stepper. I could now generate gcode from the model and use the Mk1 CNC to cut out the part.
 
Well that's one axis almost finished. There are just a couple of odds and ends to tidy up. I did make a quick video of the Y axis moving back and forth. If you would like to see it, you can download it here.
 
 
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