[TrickyCNC]

is there a rule of thumb for machine size / gantry size or height etc in relation to the bearing spacing for the pair of bearings on each rail.

I have HWIN style rails with a pair of bearings spread 8" apart (outside to outside) I am noticing the gantry will move slightly in the direction of the rails, at the point where the bearings are mounted on the rails.

The movement will obviously be less, the further apart I space the bearings, at the expense of X Movement distance.

[louieatienza]

is there a rule of thumb for machine size / gantry size or height etc in relation to the bearing spacing for the pair of bearings on each rail.

I have HWIN style rails with a pair of bearings spread 8" apart (outside to outside) I am noticing the gantry will move slightly in the direction of the rails, at the point where the bearings are mounted on the rails.

The movement will obviously be less, the further apart I space the bearings, at the expense of X Movement distance.

I've pondered this as well, as my memory in physics hasn't served me as of late. But I would conjecture that there is an optimal spread for the bearing blocks, in relation to the distance between the rails. So if the rails were closer together, then the bearings blocks would by ratio be "father apart." Then there would be the optimum distance the rails could be close together, and still fight twisting of the gantry.

My gut feeling is that you might have to move the rails in closer together, but by how much I'm uncertain. I would check your mounting to make sure there is no flex there first...

[TrickyCNC]

I have my rails mounted under the bed (just an idea I had to stop dust ... keep the bed area accessible etc) )

This effectively makes the gantry twice as high, so when you look at the front of the table X is front to back, the gantry is left to right. The movement is a tipping motion of the gantry top back and forth. I am really impressed as to the rigidity of the gantry, made from 12mm MDF in a torsion box setup, but I had my doubts about the bearing setup as soon as I installed them.

This is just an experimental build so I can learn and see 1st hand how all this works, and what affects what. I'm using salvaged rails bearings screws and motors, which I am finding really limiting to how I wanted my machine to be.

I still want it to be usable though, I have the Z left to make, and I can start test cutting . I have all the electronics wired and ready to go.

I will use this to make another machine, as soon as it is capable

[louieatienza]

I have my rails mounted under the bed (just an idea I had to stop dust ... keep the bed area accessible etc) )

This effectively makes the gantry twice as high, so when you look at the front of the table X is front to back, the gantry is left to right. The movement is a tipping motion of the gantry top back and forth. I am really impressed as to the rigidity of the gantry, made from 12mm MDF in a torsion box setup, but I had my doubts about the bearing setup as soon as I installed them.

This is just an experimental build so I can learn and see 1st hand how all this works, and what affects what. I'm using salvaged rails bearings screws and motors, which I am finding really limiting to how I wanted my machine to be.

I still want it to be usable though, I have the Z left to make, and I can start test cutting . I have all the electronics wired and ready to go.

I will use this to make another machine, as soon as it is capable

The "under the bed" rail idea is actually used in many builds. The DataCut plans use it, as in the builds of MRM, Hack, and rodjava.

I'm using the idea in my current build as well. It's tough to find used or surplus stuff that's exactly the size you need, but I guess the hunt is part of the fun!

[TrickyCNC]

My surplus was donated by my dad.

He did a job for someone in a factory, and saw they were throwing them out. They looked 'useful' so he asked if he could have them .

I've just tried to get as much out of them as I could, hence trying to keep the bearings as close together as possible, without loosing out too to much movement and inaccuracy.