MASSIVE 2.5M x 4M BED - GANTRY DESIGN HELP NEEDED!!

**woodhouse** · 09-07-2015

No, that one the gantry is separate so the table can change size. We have no need for that so was planning on the rails being higher up but under the table

**Boyan Silyavski** · 09-07-2015

To say it better then, you will need to design a table with rails and gantry and then add separate bolt on working area which has to be higher and hide the rails. Otherwise you will be facing an impossible problem of aligning the rails.

Its up to you of course, but maybe for such a machinea separate working table is better idea, and all else modular design using RP, like heavy duty plasma tables.
Cause at the end of the day this is a production machine. Tomorrow you could decide you need 5 meters longer or sell to sb who need 1 meter longer, etc...

Adding then ATHC and plasma torch is all needed to convert it to plasma , and so on. means easier to sell if needed an upgrade.

Of course your priorities could be different.

Using ball srew and rotating ball nut on such a machine could make it very high value machine that can precisely cope with big stuff. Combine that with strong gantry and you will have a real beast

**woodhouse** · 09-07-2015

Thanks boyan.

Well that was my thinking too.
The project started out as just a nailgun bridge and was going to size components accordingly as the forces involved from the small nails is minimal and the there's no real deflection forces from the tool other than upwards.
Then I managed to acquire 55mm thk profile rails and carriages off an old machine which got me thinking why not design a more capable machine with a spindle.
Will enable us to do so much more!

**Boyan Silyavski** · 09-07-2015

ha ha, i see you finishing with 2 spindles and drilling head , so design the z cleverly, better oversize the z plate so you could fit this and that.

**woodhouse** · 09-07-2015

Haha you know me so well already!!

**woodhouse** · 09-07-2015

I know this is a very ambiguous question, but does anyone know the maximum horizontal force that can be expected from a spindle?
From this I can obviously work out the resulting force on the gantry rails for different designs and keep the gantries deflection below spec

**Boyan Silyavski** · 09-07-2015

Depends what spindle you are going to fit. 2.2-3kw water cooled or 10Hp and up using BT holders...

But you have it all wrong there. What would be the biggest longest tool you want to fit and desired deflection. Download HSM adviser it calculates tool deflection nicely.

Cause the tool will be the weak point there.

Also there is very nice stiffness calculator here in the forum. Thats what you need.

Dont worry about the bearings of the spindle, they will take much more than you could push them even routing aluminum.

**woodhouse** · 09-07-2015

Thanks boyan, you're being really constructive. I appreciate it.
It wasn't the actual tools deflection I was concerned about.
What I am trying to work out is obviously the gantry design.
Now I could go crazy and use a 500x500 square 10mm RHS and would be incredibly heavy but would do the job but waste a fortune trying to accommodate it.
To far the other way and my two 100x50s spaced apart 250mm would be much lighter but probably twist too much to be useable.
Add to the fact that on this build the rails will probably be spaced apart half the distance the spindle is from the bottom rail (eg 250mm apart rails, 500m from bottom rail to spindle)
Then the force on the bottom rail will be 3x that from the tool on the bottom rail and 2x in the opposite direction for the top.
Likewise any deflection in the gantry is magnified at the tool.

If I can work out the force produced by the tool then the gantry can be sized properly for them forces and not twist.
But that's the million dollar question

**Boyan Silyavski** · 09-07-2015

The key being here is how long the Z axis movement will be. That's how to start , then you will decide on the gantry box section. So how long the z axis movement down will be?