About 2 years ago, I decided that I’d like to try my hand at CNC routing. There are loads
of Chinese made routers available on Ebay, but I wanted something a bit more capable. e.g. Able to machine aluminium.
I started my design using the excellent PTC Creo Elements Direct Drafting CAD package. This is a full blown CAD system, and simply the best in my opinion. There is a fantastic free version which has identical functionality and is great for producing 3D printable files.
Check it out at Creo Elements Direct Modelling Express.
My design is of the moving bed type. This results in a larger footprint, but it should be very sturdy. After finishing my design I published some pictures on CNC forums and asked for comments.
It was suggested that my design was loading the Y axis bearings incorrectly, so I redesigned the entire Y gantry to look like this:
The Y gantry is now a 555mm x 160mm x 45mm piece of aluminium. It is unlikely that it will flex!
The design is based around some 45mm extruded aluminium that was being thrown out at work and the lengths had been pre cut, so it was made around these dimensions. When complete, it will have a cutting volume of 60cm x 35cm x 15cm which is quite respectable.
I’m using SBR20 bearings throughout so it should be pretty tough. I got these from a Chinese supplier who was recommended on the excellent forum http://www.mycncuk.com.
The axes of the router slide around on 20mm bars known as linear bearings. These allow each axis to move forwards/right/up and backwards/left/down with no movement except in the direction of travel.
The axes are driven by ballscrews. A ballnut is driven along the ballscrew by the thread. This has a special never ending loop of ball bearings internally and does not suffer from backlash or wobble along the thread axis, that can happen with normal threaded rods and nuts.
The ballscrews have specially machined ends which fit into mount bearings at each end. These absorb the thrust of the axis and prevent it from damaging the drive motor and having undesired movement along the axis. The supplier was able to machine these onto the ballscrews for me.
The bearings turned up about 10 days after ordering them. The postman commented on their weight, and not in a positive way.