Floating Z axis - How much down pressure ?

[AndrewMawson]

I'm using a cnc plasma table that I bought from a chap who built it himself. It has a floating head, where the 'floaty bit' runs on a short single length of HiWin rail. I'm reviewing the design as there's a bit of wobble in it - I may reconstruct it with two bits of rail.

But doing this I thought I'd measure the down force exerted by the floating head and was surprised that it's as much as 1.5 kg. This struck me as quite a lot but I have no experience to compare it to. There is a balancing spring, and it would be fairly easy to re-jig it to adjust the force so I'd much appreciate it if any readers know what sort of pressure their set up exerts could let me know.

[chasxjs]

I have never measured mine. But, I would guess it's not more than 2-3 ounces.

[exapprentice]

Hi Andrew

I don't think there is any precise answer to your question regarding your set up

But I would recommend just enough to lighten the load but not to much that it makes the movement sluggish or bouncy and not repeatable, you need to factor in your feed rates and acceleration when doing the final tuning of the spring assist

If you are going to cutting thinner materials, the less force to raise the z during touch off the better but again not at the cost of repeat-ability or the creation of bounce

[Rodw]

Before you worry too much, check the mounting bolts that hold the linear rail on are tight. There should not be any play in a Hiwin rail. Your 1.5 kg is about right. I tested my gravity floating rail setup when I first made it and it needed over 1 kg to overcome the static forces.