Moving gantry and table on the same axis - why not?

[suicidal_orange]

I'm a complete newbie to this and in the first stages of planning a build (yes, it's that vague for now) I've had the thought that if the gantry and table both moved on the same axis the usable length could be (nearly?) doubled without increasing the footprint of the machine for storage, while keeping the moving parts shorter should mean it's more rigid. I'm only thinking of around 350x200x50mm so short means short compared to most of the monsters in the build logs here!

I guess there's a reason no-one does this, would anyone care to explain it please? Or if people do do this and the design/idea has a name I can search on that's just as good

[magicniner]

I'm guessing that it isn't done because it involves increased complexity and cost but if the table and gantry screws were driven by one drive system linked with toothed belts and pulleys of the appropriate ratios and directions then it could be done without any software integration of the two movements in the same axis.
Interesting thought!

[JAZZCNC]

This has been done before with Mach3. It's not massively complex but does require some special coding or formula's to be created I think.
I'll see if I can find a link to a thread of someone who's done it.

This is one way but I've seen better way using formulas in mach3 just cannot find it yet, but I will.
http://www.cnczone.com/forums/cnc-wo...ml#post1217301

[m_c]

If you design both drive systems to use a similar number of steps for full travel, just slave them, and adjust the steps per mm/inch to suit.

[suicidal_orange]

Great - it's not a crazy idea!

I need to research whether gearing, formulas or 'slaving' is the way to go as well as how much cost/complexity it will add. As if learning the basics wasn't mind-boggling enough...

Thanks all.