View Full Version : A concept design for a cnc machine

07-12-2012, 05:57 PM
Hi all

If anyone could point out any flaws in this design please let me know.

The idea is to sync up 2 motors per axis except for Z. (EvoDrive ST-23 looks very interesting for the job). Reduce weight and stress on rails and leadscrews by offloading it length wise onto the side supports which might have its own rail system as well. The end holders for the rail and leadscrews use a solid slab of aluminium while retaining its accuracy under compression of the cross supports (they can never sag at all as the cross extrusion maintains vertical accuracy even if the bolts are not aligned correctly). These use 4 x m6 bolts. All structural key points are using 45 degree or L brackets for additional rigidity. The bed allows 600 x 450 and around 150mm Z height. I will redesign the Z axis to protect the rails and leadscrews from dust and wot not. The unit has enough room for surrounding clamps and a decent size bed for most people. Past the Y support I think the Z height could be increased to allow for a 4th axis at 200mm diameter (inner Z axis rail is 300mm with 80mm Spindle carriage support).

I think there are many options to include a gear reducer for 10mm leadscrew with some kind of pulley system. (2:1). A replacement of the gear to 1:1 for 10mm usage vs 5mm depending on material (as advised by jazzcnc)



Would like to hear your thoughts on this



07-12-2012, 07:16 PM
You should increase the spacing of the Y-axis rails to reduce the force on each and thus minimise deflection of the tool parallel to X. It would be good to increase the bearing block spacing on Y for the same reason.

It may be difficult to align the Y-axis rails since the spacing is defined by the width of the machine frame, so if that is not cut extremely accurately it will not be parallel. You've not got any way to adjust the spacing. That's why most people mount them the same way up, not facing, on X, although if you can keep the same orientation the average stiffness will be greater.

Also I think you can get the X ballscrews slightly closer to the X-rails. That's not going to make a huge difference, but if you can there's no reason not to.

Hard to tell from the images, but is how far the spindle sticks out limiting the travel on X?

07-12-2012, 07:34 PM
150mm for the spindle holder from the back extrusion support. The actual working area is mentioned and this has been taken into account. I think the Y support needs to be increased with 2 x extrusions or something else to support the Z. At the moment those rails are a little close (80mm) back support is not alot.

07-12-2012, 09:40 PM
The company that will cut it have an accuracy of 0.1mm in cutting the extrusions. Is that good enough?