routercnc

23-08-2010, 09:51 PM

For those interested, I thought I'd post my updated stiffness calculation spreadsheet in a new post. This spreadsheet is intended for a typical moving gantry cnc routing machine, and may help with the design of the basic structure. X axis is the long axis which the gantry jogs along. Y axis is spanned by the gantry, and Z axis is up and down.

General process is:

step1. Select 'gantry top' tab and study diagram

step2. Enter required load, material and other data

step3. For your chosen section(s), enter geometry (e.g. RHS, tube)

step4. The deflection calculations are then shown below

step5. You can then select one of these sections to be used in the tool deflection graph

Repeat the above for 'gantry sides' tab

Finally, in the 'tool error' tab, enter the required accuracy and the section results selected in step 5 from the previous tabs are shown as an ellipse for the X and Y deflections. Z direction is just a bar graph. You may wish to add a safety factor to the required accuracy figures to account for parts of the machine not modelled.

New features in version 7 are:

Stiffness approximations of commercial ali profiles (e.g. Hepco)*

I value calculations for arbitrary shapes, not just RHS, round etc. This is a standalone calc and gives vertical bending deflection only.

Gantry top bending in the X direction (previously ignored)

Visual tool deflection error graph vs requirement

Usual disclaimers apply.

* method used is to create an RHS section with similar properties

General process is:

step1. Select 'gantry top' tab and study diagram

step2. Enter required load, material and other data

step3. For your chosen section(s), enter geometry (e.g. RHS, tube)

step4. The deflection calculations are then shown below

step5. You can then select one of these sections to be used in the tool deflection graph

Repeat the above for 'gantry sides' tab

Finally, in the 'tool error' tab, enter the required accuracy and the section results selected in step 5 from the previous tabs are shown as an ellipse for the X and Y deflections. Z direction is just a bar graph. You may wish to add a safety factor to the required accuracy figures to account for parts of the machine not modelled.

New features in version 7 are:

Stiffness approximations of commercial ali profiles (e.g. Hepco)*

I value calculations for arbitrary shapes, not just RHS, round etc. This is a standalone calc and gives vertical bending deflection only.

Gantry top bending in the X direction (previously ignored)

Visual tool deflection error graph vs requirement

Usual disclaimers apply.

* method used is to create an RHS section with similar properties