[Marne]

Good Day All.

I have a multi part question. I'm in the process of planning a steel rectangular tubing CNC Router and have a couple of questions regarding the weight that the Ball screws and linear Guides can Cary/move?
I'm using Nema34 motors and 25mm ball screws and linear guides for all axis.

The question is that I'm thinking of experimenting with backfilling the tubular structure with Epoxy Granite or similar product to give greater rigidity as well as vibration dampening but im worried that
the ball-screws and linear guides wont be able to handle the weight.

Has anybody got a rough idea about this or should I be fine ?? (running the Ball screws with nema34 motors?)

Thank you in advance

Kind regards
Marne

[ger21]

What linear guides are you using, and how big is the machine? What size tubing?
From what I've read, the inertia of the 25mm screw will have a larger affect than the extra weight if the epoxy granite.

[slopecarver]

If at all possible increase the outer dimensions of the tubing before adding epoxy granite. You can manage vibrations at a later date but if you make the structure stiff enough you may be able to increase the natural frequency of the gantry above frequencies that affect the operation. It is also easier to damp out high frequency vibrations with something like dynamat. Can you provide pictures/a model/a sketch of the router configuration along with the dimensions of the tube you intend to use?

[Marne]

Thank you for the replies so far.
Im using 25mm linear guides and bearing blocks. x 4 on every axis.
The steel structure i will be using is 120 x 60 x 2.5wall and the connecter plates will be 8mm steel.
The machine will be a standard half sheet machine to cut 2.4m x 1.2m. I would like the machine to be rigid enough to cut Alllie.

The epoxy granite will be an experiment but the machine will be made without the filler first. My worry is if i decide to go that way will the motors and linear guides be able to drive the gantry?

Also im worried that the hollow tubing will increase the vibration and cause chatter.

[ger21]

I'd go with a heavier wall tube.

[CarveOne]

So would I. Thicker wall tubing will be less expensive than epoxy granite for any but the smaller machines. And not nearly as much mess to work with. Epoxy is not cheap.

[wizard]

Thank you for the replies so far.
Im using 25mm linear guides and bearing blocks. x 4 on every axis.

That still doesn't tell us what type of guides. In any event you really don't need to ask us and the manufactures web sites generally have all the design information you need.

The steel structure i will be using is 120 x 60 x 2.5wall and the connecter plates will be 8mm steel.

That is a very small (extremely) small cross section for the span you are talking about. I'd sit back and seriously think about just what you need and want to accomplish but I would''t recommend that size of a beam even for wood working. At the very least square up the beam.

The machine will be a standard half sheet machine to cut 2.4m x 1.2m. I would like the machine to be rigid enough to cut Alllie.

I don't now who Alllie is nor why you want to cut here up but if you intend to cut metal with this machine, specifically Aluminum then you need to consider a far more robust structure than you would for wood.

The epoxy granite will be an experiment but the machine will be made without the filler first. My worry is if i decide to go that way will the motors and linear guides be able to drive the gantry?

If they can't then up grade. I have nothing against a heavy beam but realize that you don't need to fill a large beam completely to get a damping effect. There is a paper floating about the net that goes into great detail about what is required to fill steel tubing to enhance its mechanical properties. If I remember correctly the paper was titled Rapid Machine Design by a guy named Bamburg. An excessively heavy beam can impact machine dynamics so there are trade offs to be made.

Also im worried that the hollow tubing will increase the vibration and cause chatter.

It certainly could especially if you are real thin with the tubing wall thickness. A lot can be accomplished by making sure the tube is reasonably thick for the use.