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

[woodhouse]

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]

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.

[michaelw]

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

There are three maxima for the largest forces on tool tip :

(1) The thrust load provided by the ball screw et al . Stall torque of axis motor referred through drive mechanism and ball screw and corrected for any leverage effects .

May have components in more than one direction .

(2) The worst case cutting load . This is usually a max depth cut on one side of cutter only . Stall torque of drive motor referred through drive mechanism and any leverage effects .

May have components in more than one direction .

(3) Crash load . Can be estimated but if you design on (2) that is probably ok .

Simple quasi static loads are not the complete answer . Any cutting is unstable and vibration problems can be more troublesome than the simple loads .

Ned to consider masses , geometry and elastic stiffness of all components to make sense of this .

Generally apart from being just stiff a simple support structure needs to be relatively heavy to bring natural frequency of structure down into a safe zone .

Other methods are available to make lighter structures vibration insensitive .

Beam needs in any case to be stiff in three senses - vertical , horizontal and in twist .

Generally a beam structure which is of large cross section dimensions is desireable . A fabrication of relatively light sections at big spacings is a way to go .

Hollow sections may be filled with structural foam to aid damping and add a little stiffness .

An alternative way to go is to use space frames made of relatively light components arranged very much like a roof truss or lattice bridge .

An unorthodox alternative - which is already being used in some real machines - is to cast a hollow lintel in either concrete or epoxy concrete .

The above all assumes relatively slow movements of tool/table . If rapid moves are likely then there are further design considerations .

michaelw