How much rigidity do I need

[peteeng]

Hi Hanermo - What I and others in the forum are trying to establish is a reasonable design deflection spec for a machine. We have the tools to design machines if we have the specs. So from your writing above and please correct as necessary...

Rough Process: place a tool in spindle or router and snug up. Use dial gauge at collet area as close to tool as possible. Push or pull here at 25kgf, what deflection will I get? also put spindle at mid span of gantry and full down Z, which should be worse case structural configuration.

Hobby machine 25kgf deflects >0.1mm plywood, plastics and foam
Good hobby machine 25kgf <0.1mm plywood, plastics, foam and aluminium
industrial machine 25kgf <0.01mm or 0.001mm? metals
precision machine 25kgf <0.001mm or 0.0001mm metals

Thanks Peter

I pick 25kgf as its easier to actually do. Nothing to do with actual tool force yet. The machine should have a linear response so if we have a tool load of 250kgf then we have 10x the noted deflection... Peter

[deadlykitten]

hello, i am not so much into building machines, but maybe this helps : https://www.makino.com/resources/con...ing-moment/392

so far i did not had time to apply & check what that video suggests, but, in short, it seems that BT cones are the most rigid for the "teoretical heavy specs", while other types are more rigid for the real, most common " cutting specs ", but, above this range, they start to deflect pretty fast; in other words, use the machine in a 'normal' manner, regardless of what shank type is there / kindly

[peteeng]

Hi Henry - Hows the project going? Looking back at your numbers the FEA model is 150lbf/0.001" this is 262N/um. Reading the thesis and reviewing Hanermo s input this is off the dial in terms of stiffness for machines so if the FE is true then you have a remarkable machine. 10-25N/um is a typical mill machine and a precision machine is 70N/um so get it going.... Peter

[peteeng]

Hi Henry - 150lbf/0.001" is not 262N/um sorry my maths was wrong. Its 22N/um which is still a very stiff machine. Any news on the machine? Peter