First Proper CNC Router

[routercnc]

My first ever machine had 4 posts like that and it took a while to get them all the same length. I didn't have a lathe back then. If they are out a bit the motor will be skewed and the belt won't run straight on the pulleys.

The other more popular option is to put the motor behind what is in your drawing the small orange box section, and run the belt horizontally out the back of the gantry, between the upper and lower beams. You just need a big L bracket to mount to and it is a bit more tucked out of the way.

For your other question - there are lots of pulley engagement formulae around but you can tell by looking that you are OK there with ~180 degree contact.

Make sure you have pulley / belt clearance should you ever want to do 1:2 instead of 1:1 to get more speed, and have adjustment in the motor plate to accommodate.


On the overall design it will work fine, but do think through if the underslung ballscrews will be easy to set up and align. Imagine that the base frame cross members (which the ballscrew blocks mount to) is not perfect, and end up on a different plane to the rails. It will tend to bind the ballscrew at some point and you will have to shim something in the system.
If you go the more traditional route with the ballscrews mounted down the side, driving the side members of the gantry directly (no underslung part), I think all the connections can be made with the appropriate 'slip plane' to get it aligned. This will quicker, cheaper and simpler to build and would be my preference.

Up to you but just make sure you can visualise the adjustment process for any scenario if it is not perfectly built.

If you are going underslung just to stiffen the gantry I'd put the efforts in on the gantry itself, e.g. plating across the back etc. (Not saying it needs further stiffening mind).