Hello

[JoeHarris]

OK, so will whipping still be an issue with 2no. 1610 screws at 1500mm long - as they will still both sag? Jonathan have you drilled your housings with a holesaw? if so can you recommend a make, I bought some makita ones a while back and they are rubbish.

Also what are the implications when buying drivers if you are going to add another stepper into the mix later? (I was thinking of getting the electronics from http://www.diycnc.co.uk by the way)

I do want to be able to cut more than just ply! everything from aluminium/ply/mdf for furniture making to paper/card with a drag knife for architectural model making/graphics. not sure if I am being unrealistic as I am sure one machine can't properly fit all tasks?

Apologies for all the questions!

Joe

[JAZZCNC]

OK, so will whipping still be an issue with 2no. 1610 screws at 1500mm long - as they will still both sag?

They will just about be ok but will need very carefull alignment has any miss-alignment will be exagerated at high speeds and this is when whip will occur.

Jonathan have you drilled your housings with a holesaw? if so can you recommend a make, I bought some makita ones a while back and they are rubbish.

I have a Bosch quick realease hole saw and it's brilliant, not cheap but good.

Also what are the implications when buying drivers if you are going to add another stepper into the mix later? (I was thinking of getting the electronics from http://www.diycnc.co.uk by the way)

No problem adding at a later date but does need a bit of initial planning regards PSU to workout best way and reduce cost's further down the line.

Regards DIYCNC then personally I'd say no because he doesn't do any drives powerfull enough for what you'll need to get best performance.
My advice would be buy individual drives and pay the little extra and get 80V drives with 60-65v PSU this will give you the best performance for the 3nm motors your going to need to drive this machine.!

I do want to be able to cut more than just ply! everything from aluminium/ply/mdf for furniture making to paper/card with a drag knife for architectural model making/graphics. not sure if I am being unrealistic as I am sure one machine can't properly fit all tasks?

Then absolutly 110% go with twin screws from the get-go.!!

Apologies for all the questions!

No need thats the whole point and why where here.!!

[JoeHarris]

Then absolutly 110% go with twin screws from the get-go.!!

Just so I'm clear do you advocate one stepper driving the two x axis screws via a belt like the image attached

or two separate motors and drivers? if one is used presumably the motor needs to be more powerful?

[JAZZCNC]

Just so I'm clear do you advocate one stepper driving the two x axis screws via a belt like the image attached

or two separate motors and drivers? if one is used presumably the motor needs to be more powerful?

Personaly yes I prefer one motor using just the system you have drawn.
My machine is done this way and it completly eliminates some potential issue's that come with slaving motors together. I have used both methods and by far prefer this method.
It's not pritty and slightly more work intially but the peace of mind your not running out of sync and that if one motor stall and the other keeps going the machine not going to try and destroy it's self is well worth the trouble.
The cost is not much less due to belts/pulleys and has you say bigger motor and drive but again there's plus's in that it's less electrical components to intigrate and go wrong plus less Inputs/outputs required so more spare for other things like Probes, etc.

The other BIG differance comes when you you tune the motors.? When slaving motors you effectively have to leave a large safety margin regards motor tuning and velocity/accelleration than when using a single motor.
By the very nature of how steppers work and the fact they lose torque has RPM's rise then the chance of a stall increase's massively and on dualscrew setup stalling at high feeds can be devastating to the machine and your heart plus wallet.!! . . . . With single motor you can push the edge without fear of killing the machine or your self.

[JoeHarris]

Personaly yes I prefer one motor using just the system you have drawn.
My machine is done this way and it completly eliminates some potential issue's that come with slaving motors together. I have used both methods and by far prefer this method.

Thanks Jazz, that's very helpful. Do you have any pictures of your machines that have used this method or could you point me in the direction of other builds so I can get a better understanding of how this will work in practice.

Jonathan - if you are still keeping an eye on this thread - I have seen on other threads that you have successfully developed a rotating ballnut system. I was wondering if fixed ball screws held in tension along my x axis would make sense here as it would eliminate whip? Do you sell your spinning ball nut mounts?! :) presumably the arrangement shown in the previous post could be used to drive two ball nuts mounted on the y axis gantry?

Does anyone have any pictures of a good twin x-axis (fixed) ball screw mill?

[Jonathan]

Sorry for the late reply...

Jonathan - if you are still keeping an eye on this thread - I have seen on other threads that you have successfully developed a rotating ballnut system. I was wondering if fixed ball screws held in tension along my x axis would make sense here as it would eliminate whip? Do you sell your spinning ball nut mounts?! :) presumably the arrangement shown in the previous post could be used to drive two ball nuts mounted on the y axis gantry?

Tensioning the screw helps, but you need a lot of tension to make a significant difference to the stiffness and most CNC router frames are not strong enough to apply that much tension. On mine I had the ballscrew machined the same on both ends with a thread. Nut on one end clamps the screw and the other end can be used to tension it a bit. It works well...
I do sell the rotating ballnut mounts, 1500mm is about the threshold where I would say it's worth considering a rotating ballnut, fixed screw setup. You'd certainly get a higher feedrate, but the question is do you actually need it? If you're mainly cutting wood/plastics then you can certainly take advantage of higher feedrates, but if the machine is mainly cutting aluminium then the difference in overall machining time is extremely slight.

Jonathan have you drilled your housings with a holesaw?

No, I milled those housings and bored the hole for the ballnut in the lathe.