3 Axis CNC router

[JAZZCNC]

Hi Joe,
I wonder if that long unsupported run of belt would flap and vibrate around. Do you think it would be in perfect syncrony on each ballscrew? Also, a single motor would need to be more powerful than 2 singles.

Yes and No. Yes it needs a some support in the middle to stop flap. Does it keep perfect sync.? Yes it does.

On my new machine (not CSMIO) I am going with 2 motors and 2 short belts, then one long slave belt between them which mostly does nothing unless there is a problem.

Not so sure that will work has good you expect.? While in theory it will help keep screws in sync I'm not sure about the conflicts you might get if one motor starts missing steps. You'll have one motor fighting the other and because the Motors are connected directly to the screw I think you'll still get racking because the motors torque will force racking or affect the other motor and cause stalling etc.?
Also Don't see the point in taking the conflict risks when you still have the same belt setup.?

Edit: Then you have the affect of extra inertia of 4 pulleys on screws. It will affect performance.!

One thing for sure if you do this then make sure you have good drives because it will do funky things to the resonance and the drives will need to able to deal with it.!

Would CSMIO let you feed step/dir signals into 2 drives? Is that acceptable? I know you can't 'slave' home in the traditional sense with that suggestion, but with a link belt you wouldn't have to.

Bad idea with any controller but this isn't needed anyway the IP-M does allow slaving just doesn't independantly home each Axis.

I was going to up the motor to a nema 34 12nm beast. This is a similar size belt to Dean's first machine I think? He had an idler part way along not at one end. If I get flapping I could add one in the same way. I understood that the ip-m just did not allow proper slaving...

12Nm is way to Big Joe and will affect performance. 6 or 8Nm will be more than enough. Try to find motor with lowest inductance possible and use plenty of volts.

[JoeHarris]

The revised plan for the twin ball screws is to drive them from one motor with a long belt as shown in the image. The plan is two use two idler pulleys one of which will be fixed. I have been advised by one of the guys at beltingonline to support the long length of belt on sheets of UHMWPE which will not wear and is self lubricating. I will fix this to some lengths of steel angle I have left over. I should get the recommended 5 tooth engagement on all pulleys. I have allowed long enough slots for the motor mounts to use a smaller pulley if i want to change to 1:1 ratio. What do you think?

[njhussey]

Joe, I'd put a plate over the square steel section your rails are moumted on, move the top pulley to the right and move the other pulley next to it. That way you'll have more teeth in contact with the ball screw pulley.

[JoeHarris]

Joe, I'd put a plate over the square steel section your rails are moumted on, move the top pulley to the right and move the other pulley next to it. That way you'll have more teeth in contact with the ball screw pulley.

Yeah that's quite a nice idea. I think I might be too tight for space to get a good depth to tap for the idlers. I could certainly pull the lower left one up though which will improve things. This was a quick and dirty to test. I still need to draw a nema 34 as this is still based on the smaller nema 23 frame. Going from 56 to 86mm will change the setting out quite a bit...

Also any ideas why the SY85STH118-6004B Nema 34 Stepper motor from Zapp costs £94 and the cnc4you 86HS115-4208 8.7Nm Nema 34 Stepper Motor costs £71? Same size and torque and Inductance is the same...

[JoeHarris]

More or less complete design for the single motor, long belt method.
The idlers are both fixed and made from standard skate bearings spaced in the middle with a washer and edged with two penny washers to provide flanges - these will be mounted on a M8x40 bolt taped into the aluminum plate and stood off with a stack of washers. I can adjust the height of the whole motor assembly if necessary and fine adjustment can be made by raising or lowering the motor on 10mm slotted mounts, this was the max I could achieve with the large circular projection (which I assume houses the bearings) at the center of the motor.

Both lengths of the long belt (top and bottom) are supported on UHMWPE (blue stips on the image below) which will be bolted down to steel angle which in turn will be welded or bolted to the frame with strips of 90x6mm flat bar. This support framework can then double up as the framework for a belt cover.



The motor this is all based on is the cnc4you 86HS115-4208 8.7Nm Nema 34 Stepper Motor as highlighted on the data sheet below:

[njhussey]

I'd still put the top idler on the end of the square section (with a suitable thick plate welded/bolted in) and move the lower idler to the first idler's position.....

[JoeHarris]

I'd still put the top idler on the end of the square section (with a suitable thick plate welded/bolted in) and move the lower idler to the first idler's position.....

Like the blue lines in this?:

[JoeHarris]

I like the idea but it's a pain to implement. I only have a few mm of space:

[njhussey]

Like this....excuse the freehand scribble!!



Edit...Hah just seen the lines you drew....need to open my eyes!! Yes like that, will give much more teeth in contact, I know 5 is the min but I always think the more the merrier!!

[JoeHarris]

[QUOTE=njhussey;76714]Like this....excuse the freehand scribble!!

Yes, sorry that's what the really faint blue lines were supposed to show!!!