CNC Router Build

This page is primarily to document the build of my latest project, a cnc router!

When building my cnc plasma cutter Found Here it occurred to me how useful a routing machine would be. My main idea was to use it for engineering plastics, but there are a whole range of materials than can be successfully cut using one of these machines.

I wanted a machine that would have a cutting envelope of 8' x 4' as this tends to be industry standard for many sheet materials. I set about researching existing products for ideas. I found the shopsabre range, which are an American machine. They run using ballscrews on each axis, which provides accurate and powerful linear motion.

The machine I will loosely base my build around is this one:

Straight away I noticed a few areas I'd like to do differently, but the concept as a whole looked good!

I was lucky enough to purchase a kit, which included all linear components as well as the spindle and many other bits and bobs! So I set about making the framework:

Assembled frame

Towards the start of the build the budget had to be suspended due to other financial commitments, which was hugely frustrating!! Never the less I carried on designing and drawing parts to be machined.

Some weeks later I was able to start ordering parts again and I began to make some progress:

Gantry fixed in place

Gantry detail

gantry rear, motor fixing

Some design changes:

After initial tests of the x axis with double ballscrews driven underneath the table, it was evident that the speed required to spin them fast enough to hit reasonable rapid movements far exceeded the maximum working velocity of these at this length. Therefore, a different approach was needed. The problem is that the longer the ballscrew is, the lower the maximum speed before vibration occurs. Once the maximum speed is exceeded the ballscrew tends to whip out in all directions, not dissimilar to a skipping rope type effect. In addition to these findings I concluded that the main framework was vulnerable to vibration, which wouldn't work well with the fast cutting speeds I hope for.

Items to address:

• Improve rigidity of main structure to eliminate resonance created by mechanical drive.
• Devise new linear driving method to overcome issues with rotating ballscrews at speed.
• Linear drive must be paralleled to prevent racking / distortion of moving gantry.
• Maintain minimal footprint of the machine to ensure a compact and efficient design.  

After much consideration, I decided that the most effective way of driving the x axis was by using the ballscrews I already had, but using them in the opposite configuration.... rotating the ballnut instead of the screw! Many of the top end machines use this method and although its more complex in terms of the mechanics its very effective when executed well. 

It was to the drawing board with my ideas to see how I could fit everything into my existing machine without too much chopping and changing. I think I have sussed out the layout, so have ordered the materials and sent out the drawings for my parts to be machined.. fingers crossed!!

Work on the z axis:

Amongst the confusion around the x axis I have also been working on the z axis. This has presented its own little worries, but I seemed to have ironed most of the creases out now:

Z axis, still a little bit of work needed, but mostly there.