View Full Version : Construction Idea Discussion: Large Steel tubes + non shrink grout = win?

31-05-2016, 07:57 AM
Good day folks, I just had this idea today for in case I ever plan to build a 2nd machine in the far future, I wouldn't settle for a non rigid bad design, I would love to see myself do either a standard VMC column design or a gantry similar to hermle machines. ( in the far future that is )

my question to you is, how feasible do you think it is to gather a large amount of the largest tubes I can find and roughly weld the frame out of them, make internal channels in them and seal unwanted cavities and such. the purpose of that is to fill it with material such as grout or cement or epoxy or whichever is best to give it density and resonance/vibration dampening. but also I would like to try to make a mold out of wood of the desired shape of the frame from outside and be able to fill that mold with the same material filling the tubes so that way the steel is is engulfed in the material, then maybe heat the whole thing or add steel sheets to all sides to protect it?

then maybe scrape the surfaces to make them flat or do the favorite technique of this forum which is epoxy? I really don't have any experience in all that just throwing out ideas and hope somewhat it might work for whenever I would attempt this.

please enlighten me with your wisdom :p

31-05-2016, 01:37 PM
Hi Noplace,

You can weld large tubes together although you need to manage the distortion. Large tubes cost proportionately more so budget is the main 'feasibility' limit. Larger tubes are disproportionately stiffer than smaller tubes so a small increase in size gives more in stiffness. I've also seen some pretty large wall thicknesses used which although isn't the most efficient way to gain wholesale stiffness levels, it does help distribute any small / point loading forces such as locally where rails are mounted onto surfaces etc.

Anything which increases the weight of the bed or non-moving part is beneficial - assuming your floor / table can take the weight! Anything which increases the weight of the moving parts is subject to a study of the electronics required to drive it.

Filling the voids:
Cement is probably not wise as it contracts when set leaving a small gap all around.
Epoxy is possible although it will get hot in large quantities and would work out very expensive.
Kiln dried sand is cheap, easy to re-use, and provides good damping. This is probably your best bet.

Moulded design:
This is very possible and is what Chaz is looking to do (Thor, or should that be Zeus). Plenty of examples on YouTube etc of granite type designs.
The ones I've seen cast in some steel members leaving part of it sticking out. This forms the basis for attaching the rails. Milling, scraping or epoxy are then options for getting a datum surface.