Can only work out the deflection if you know the force, which obviously depends on what you're cutting and how you're cutting it. It's more meaningful to calculate the stiffness. You can do either with the spreadsheets that have been posted on this forum years ago...

Quote Originally Posted by John S View Post
The whole thing is crap, it's slow, max speed is 3.2 furlongs per fortnight
So 32mm/min .. that's about what my mill did when I first converted it using an old unipolar stepper driver!

Quote Originally Posted by John S View Post
Thing is it does the job which is engraving gauges. If i posted this as a build on this forum I'd get shot down in flames but this is an example of the work.
I certainly wouldn't do any shooting there, as an engraving machine is the right application for unsupported rails. The obvious reason is the cutting forces are low, so the appropriate size unsupported rail isn't too large. As soon as you require a bit better material removal rate, the required unsupported rails size is so large that it's much more economical to use supported rails. The problem is all too often people post a design with unsupported rails and expect it to work well at much more demanding tasks.

When someone (who will remain nameless) posts a machine with unsupported rails and calls it 'something more rigid that also has good performance' or says it 'will cut through a range of materials with ease and no chatter or wobble to be found', then then they really are asking for it.