JBEC router system UNDER THE BONNET

[Jonathan]

I agree that the ballnut mounts in particular look much too thin, and that for the amount this costs you should be getting proper linear guides not glorified skate bearings.

If you grab the spindle structure (not too hard in case you break it before you've bought it :) ) and put some pressure on the structure in all directions and see how it performs. What your doing essentially is simulating a cutting process where you are putting forces on the machine. The level of "play and delfection" will dictate the performance.

You will pull the machine off the table before you bend and flex the gantry structure with any significance on this platform.

No. If you clamp an indicator to the bed and touch it against the spindle or Z-axis and try what you suggest you'll see plenty of movement on the dial. I agree you probably wont see the deflection before pulling the machine off the table, but that's besides the point since the tolerances required for a good CNC router are well below the distances anyone can see. Can you see 0.1mm deflection?

If I was buying a CNC router I'd take a dial indicator, a force meter (e.g. cheap hanging scales would do) and a piece of string with me, then use them to do, at the very least, the following tests:

• Set the dial indicator up to measure the deflection in each axis and apply a suitable force, divide the two readings to find the stiffness of each axis and compare that to typical values or other machines.
• Use the indicator to check the backlash of each axis. For any machine that uses ballscrews and is set up correctly, the backlash should be less than about 0.05mm in X and Y. If Z uses rails with low preload, the backlash should be close to zero as gravity pre-loads the axis. If it isn't then that implies the rails and ballscrew could be misaligned.
• Again set the indicator parallel to each axis, and give each axis/slide/ballscrew a sharp tap. The indicator needle will oscillate and should return to zero (+-backlash). If it doesn't return to zero then something's loose or the ballscrews aren't mounted properly. If the indicator oscillates for a long time before returning, then I'd be concerned that the machine will resonate when cutting.
• With the indicator in the spindle, put a large mass on the machine bed (e.g. sit on it), and see how much the bed deflects.
• Mount indicator in spindle on L-shaped bar and use it to check the spindle is in tram. This is less significant than the other points, since you should be able to correct it without too much difficulty, however it's a good sign of how carefully the machine has been built

Feel free to post a video showing these tests, I expect you've already checked these things so it shouldn't be a problem?

[JAZZCNC]

If the indicator oscillates for a long time before returning, then I'd be concerned that the machine will resonate when cutting.

. . . Or you have a shitty cheap dial indicator. . .