How much deflection to expect...

[Wal]

>And Anygood for what.?

Ah, sorry Jazz, was being a bit vague there - just ballpark any good for cutting alu plate. I'm not too bothered about crazy feed-rates and am happy with smaller step-overs. Reassuring to hear that it's a good starting point!

One more question, the pillow blocks which house the bearings that ride on the rails - they have grub-screws that you can tighten to get a snug fit between the bearings and the rails - how tight do you go with these? Just a nip front and side?

Wal.

[JAZZCNC]

One more question, the pillow blocks which house the bearings that ride on the rails - they have grub-screws that you can tighten to get a snug fit between the bearings and the rails - how tight do you go with these? Just a nip front and side?

It's a feel thing but basically until they have a slight resistance with no play.!!. . . Thou if your planning on cutting Ali then you'd be better cutting your losses now at this stage before going further and buy some profiled linear rails. These rails are not really upto it and will need constant adjustment if you want any thing like decent accuracy.

[Wal]

Thou if your planning on cutting Ali then you'd be better cutting your losses now at this stage before going further and buy some profiled linear rails.

I hear ya Jazz, it's a well known fact that the profile rails are the way to go for superior rigidity, but I think to swap out at this stage would mean too much heartache, ball-ache and expense on what was always going to be a learner build. I may as well build another machine, which I have every intention of doing..!

While I'd like to 'precisely' cut ali on this, think more ornamental than super high precision...

Wal.

[Jonathan]

You'll be fine with those rails to start with. I'm not saying the rails aren't important, but it's the whole picture not just the rails that affects the overall stiffness and the rest of your design looks pretty strong (as it's a fixed gantry) so you'll get away with it. For example, I cut plenty of aluminium on my machine before changing the Z-axis rails to profile rails and didn't notice much difference from the profile rails as the weakest point lies elsewhere.

[routercnc]

You can look at it another way which is if the machine stiffness is 1000N/mm, and you are cutting aluminium (guide figure 50N load), then you would see 0.05mm deflection at the tool (50/1000). This assumes a rigid tool (as your data was from the collet), and ignores resonances which would add slightly to the deflection in a difficult to calculate way.

If you can't be bothered with the maths - I just checked our kitchen scales (the flat digital type) and they go up to 5kg (50N). So if you have something similar handy use them to push against the collet until they read 5kg. If the DTI reads less than 0.05mm you are in business (>1000N/mm).