8x4 Wall Mounted; Upright ply cutter

[EddyCurrent]

Edit: written before Earle's last post but posted after it.

Not that it matters but here's what I think.
If you look at Matt's first build log; http://www.mycncuk.com/threads/5174-...6501#post36501
you will see he has been through the techno crap stages like everyone else. Now he's in a position to make it look easy becasue of that experience and the other builds he did.
But New builders and lurkers I feel you need to be aware that this machine was build by someone who made it look easy, not because he cut out the techno crap but because he was experienced.

[JAZZCNC]

But New builders and lurkers I feel you need to be aware that this machine was build by someone who made it look easy, not because he cut out the techno crap but because he was experienced.

NO it was made to look easy because he has experienced just enough to know how much Crap to cut so could achieve the intended purpose.!!

One other point I'd like to make is that this quick build and getting away with lesser accurecy build level was largely due to components used like round linear rails and normally prohibitly expansive rotating ballnuts.!!. . It would be a very differant story if profiled linear rails and conventional ballnut had been used.

Again I'll Say it for clarity I'm Not having a Dig at Matt (or anyone really) in anyway shape or form he's done a great job. Just stated what I wrote for sake of others as usual.!

[charlieuk]

Whats the advantage/disadvantage of rotating the ball nut rather than the screw? why did you choose to do it this way? Are there any more pictures of how you did it

[JAZZCNC]

Whats the advantage/disadvantage of rotating the ball nut rather than the screw? why did you choose to do it this way? Are there any more pictures of how you did it

The advantages are that only the ballnut is rotating so you don't get screw whip that can be common on long screws. Also the rotating mass is much less so smaller motors/drives can be used, alsoon a lesser note there's some speed advantage.

Problem or should say disadvantage with them is the cost if you try to buy the real thing.? They are silly money. This design is Jonathans and they where made by him just search the forum for rotating ballnut and you'll see he's posted the design.

While DIY you still need to be pretty well tooled up and know your way around a lathe and able to work to good tolerences and still there is a cost involved compared to normal setup that IMO negates the cost saving of being able to use smaller motors/drives.
So the real advantage IMO is that you take away the risk of whip/resonance etc that comes with long screws. I'd certainly use it over other means like R&P for long machines but you do need to be proficeint with a lathe and engineering. Farming the work out to a engineering company would not cost effective as well IMO as there is a fair amount of time involved to make these.

[charlieuk]

Cheers jazz I will look into it more but like you say probably not cost effective unless you have a good lathe to hand

[Jonathan]

Just to be clear, the rotating nut concept doesn't eliminate the problem of the screw resonating, it just raises the resonant frequency so you can go faster. The main reason the resonant frequency is raised is it enables you to mount the ends of the ball-screw more rigidly than with bearings, so for it to work well you need to make good strong mounts for both ends or the screw, with some adjustment in them to help with alignment.

The negative side is that to do a sufficiently accurate job of machining the mounts requires some care, so they take a long time to machine - at least with the equipment I have.

[charlieuk]

So it's posable to do a 8' ball screw with out a rotating but but you are just more limited with speeds?