Effect of Forces on Gantry Cross-Sections?

**JAZZCNC** · 06-08-2012

Originally Posted by WandrinAndy

Thanks Jazz and apologies for doubting your interpretation Adil. Afraid I still have nagging doubts though about the vertical strength of those sections lying flat like that, and reckon there must be extra sag in the middle when compared to the GREEN design.

Obviously there will be some tiny tiny difference but when you have some profile in your hands you'll realise why it's not a problem.!! . . . . The difference you would struggle to measure with a dial gauge and I'm 99.9% sure you have far more pressing problems ahead to overcome than if the profile sag's 0.001mm more than 45x45.??
The extra lateral strength and rigidity the extra bolting into gantry sides allows will far far outway the very very minute difference any sag will make.

**JAZZCNC** · 07-08-2012

I've built machines using the green design and please believe me you have nothing to fear the strength is easily over the top for anything but steel or harder.

If you use Bk/BF blocks then they line straight up with slots so easy fitting. It offers good strong attachment to gantry sides.
Yes it places the ball-screw slightly further back than what's considered ideal but again it's nothing and doesn't make any difference to how machine performs. The positive is the screw is away from the firing line and protected.

Not trying to sell it to you but I know it works with no detrimental side affects and plenty of positives.!!

**WandrinAndy** · 07-08-2012

Originally Posted by JAZZCNC

Not trying to sell it to you but I know it works with no detrimental side affects and plenty of positives.!!

Well, you have sold GREEN to me Jazz... even without trying! I have updated my design and am moving on, although I'm still curious about how the thicker-walled box sections compare, and the effect this may have on the machine.

For instance if Jonathan were to build a new machine and dosh wasn't a limitation, I wonder if he would still use box section, what size it would be, and why?

Thanks for the ideas guys.

**JAZZCNC** · 07-08-2012

Originally Posted by WandrinAndy

For instance if Jonathan were to build a new machine and dosh wasn't a limitation, I wonder if he would still use box section, what size it would be, and why?

If NO DOSH limit then I'm 99.9% confident he wouldn't and it would be a hefty lump of ground cast Iron or some fancy composite affair.!!

Can't hide from the fact box section sings like a canary and resonance and vibration are to be avoided so density wins every time, that's why cast iron's used so much.

This is the kind of thing you'd buy(New) if Dosh no limit.!!! . . . .
Here's the Y Axis carriage(pic1) which carries the Z axis(pic2) of my future 5 axis toy(Doubt I'll touch it this year thou.!).!! . . . It's one big cast iron lump with a counter balanced Z axis which is very long lump of cast and ground aluminium that runs along the roof of the main machine frame which is one big structure of steel and ground cast Iron.. . . Very very very strong and heavy 3.8ton the frame weighs.!!