It's begun....

[Washout]

Hi JCB

Thanks for commenting.

I'm by no means an expert, so I'll defer to one of the J's on this, but my reasoning was that when the cutter is moving through material in the X-Axis (either towards or away from the camera in that shot), then the leverage force would be at the cutter opposite to direction of travel.

The fulcrum point would therefore be at the lower Y axis bearing and would be trying to deflect the upper bearing mounting point (or the top of the gantry). As the distance between the lower bearing and the cutter tip is going to be considerably shorter than the distance between the lower and upper bearing point (the other side of the fulcrum), then the deflection should be minimal/reduced.

Of course the forces may cause the gantry mounting brackets to flex, but I have yet to see any by leaning into the gantry at the top - I wish the same could be said for the yaw in the gantry, due to only having one X-axis ballscrew however, but this is to be shortly remedied :)

At least that's the theory ;-)

[Washout]

Hi All,

A bit of an update and hopefully if I can work it out a vid to follow:

Its fun to be back on the learning curve and earlier in the week I retrofitted my second X Axis ballscrew. The ballscrew itself was not much of an issue, but I had some "fun" getting the pulley onto the back of the stepper motor and not wobbling about.


Anyway after doing that it was obvious I have some slack in my drive belt, which needs taking up so just for testing purposes I found something "suitable" to take some of the slack out it (see pic). I then ran a few full speed jogs around the table and all seemed well, but there's a few things I need to do:


1. Add some support to the 2nd ballscrew where it extends to the same length as the stepper motor (there's some flex in there when the axis changes direction) - a suitable bearing has been ordered.
2. Add a proper 3rd pulley to provide belt tension rather than the hasty affair you can see in the pic, although I'm not sure how much play should be in the belt - parts ordered anyway


After that I decided to push my luck, being an impatient bugger, and run a short job "cutting air", just to see how it goes. That ran OK from start to finish, which was nice although you'll hear that the belt (or maybe ballscrew alignment) is out if I can get the vid posted. The job is a 3D roughing operation from Cut3D that took ~15 minutes and I also ran the other "side" of it, which also completed OK (~15 minutes).


Flush with success I loaded up a longer job (50+ minutes) and ran that. Again all was well for 20 minutes or so, but I noticed that heat was building up in the X Axis stepper motor. Then all of a sudden during a longish X Axis run (@1200 mm/min) the stepper made what can only be described as a "graunching" sound, like it had met sudden resistance and I hit the feedhold and then the estop. After that I checked that the x axis could be moved by hand (as the motors were no longer "holding position" in the e-stop state) and it could.


I'm assuming therefore that my gantry hadn't crabbed and bound up due to the ballscrews getting out of sync, but I could be wrong as hitting the estop could have "relaxed" the binding. Also I noticed that the stepper motor was hot to the touch i.e. hot radiator temps, but I'm not sure what behaviour an over heating stepper usually exhibits and whether the stepper (3Nm SY60 Nema 23) is maybe not man enough to drive 2 ballscrews?


Anyway once I get the other parts I'll tidy up the belt and pulley arrangement and then work out next steps, which I guess might mean getting and then trying to fit a larger stepper on that axis (the other two axis motors were cold/barely warm)? Perhaps Nema 34?


Later


Chris

[Washout]

And hopefully here's the video:

[JAZZCNC]

What voltage are you running those steppers at.?
How are motors wired, Series or parallel.?

Regards heat then steppers do get Hot can you hold your hand on them for a minute without burning you.? If so then they'll be fine. They can take much higher heat and still work ok it just shortens there life.! . . They would have to be very very hot to lockup.

Your problem will almost certainly be coming from that belt setup causing misalignment and binding. Being honest now your always going to struggle with that long extension like that on ball-screw without some proper sturdy support or holding fixture. Even then it will need to be aligned spot on.
I'd seriously look at running 2 motors . . or . . Dumping the existing motor bracket then have 2 pulleys on one screw with belt on one across to other with shorter belt on other pulley to motor. This way you could apply some gearing and keep the Nema 23 which should do this job ok provided you have decent amount of volts.

That size machine with 2 x 3Nm motors running decent volts even with 5mm pitch screws should be running easily 6mtr/min at minimum.
I built a very similar machine with probably heavier gantry for Michael Marino running 5mm pitch screws with 2 x 3nm motors on AM882 drives with approx 70Vdc and I'm pretty sure he's had it up in the dizzy heights of 16-17mtr/min when pushing for it's limits.!! . . . Sure he's regularly running it around 8-9mtr/min with high acceleration.!!

IMO dump that belt setup you have now it's a serious bottle neck.!! . . . .Use belts by all means but needs to be better setup than that.!!

[Washout]

Point taken - I knew I was pushing my luck running it like that, but was eager to get some movement after the machine had been dormant for so long.

I'm running the motors in bipolar parallel and the drivers are PM752's and IIRC the PSU (Zapp PS806-5) produces 68V.

Funnily enough I have ordered another stepper (wanted a spare and could always use it for 4th axis assuming I can get the 3 running first), so I could cut the extension down and run 2 motors - would I need another driver or wire them both in parallel off of the same X axis driver? I also thought running 2 motors was a bit risky if one starts losing steps for some reason?

I could also go the two belt method you suggest - I have a 3rd pulley coming also, which I was going to use for tensioning. The problem I foresee with that is finding the right length belts will likely mean some kind of custom motor mounting plate, which I'm not setup yet to make - if only I had a CNC machine ;)

Good to know that the heat isn't immediately fatal to the drives, thanks for that.

I'll have a think over the weekend and see which option for "sorting" out the drive to the second ballscrew I should go for (read easiest).

8-9 m/min sounds scary enough, let alone 16-17.........

[JAZZCNC]

Funnily enough I have ordered another stepper (wanted a spare and could always use it for 4th axis assuming I can get the 3 running first), so I could cut the extension down and run 2 motors - would I need another driver or wire them both in parallel off of the same X axis driver? I also thought running 2 motors was a bit risky if one starts losing steps for some reason?

2 x motors will be your easiest route with how it's setup already.

Most common cause of missed steps is motors being tuned too high with folks trying to have both Acceleration and velocity too high.
If you keep tuning to sensible speeds then you generally won't have a problem, only other time you can run into issues is if your running very long jobs like large 3D work that can have cycle times well in excess of 20hrs. Because 3D work is usually lots of small fast moves and higher accelerations are often used then steps can get missed over time period.

Keep sensible motor tuning and you'll be fine with slaved motors but unfortunately you'll need another drive.

Run 2 x motors and with 68V you'll easily see 6mtr/min with good Acceleration without any issues provided everything is aligned properly.

[Washout]

Thanks as ever Dean,

I could probably do with another Driver in any case, so will add that to my order with Zapp - will have to see if the 806-5 transformer will be good for a 4th Driver or I'll have to get another of those as well (4th Axis would have needed it anyway I expect).

I did a bit of tinkering over the weekend and one of the x axis ballscrews was out of alignment, so have also rectified that whilst waiting for parts.

More as I work on it.....


Chris

[JAZZCNC]

I could probably do with another Driver in any case, so will add that to my order with Zapp - will have to see if the 806-5 transformer will be good for a 4th Driver or I'll have to get another of those as well (4th Axis would have needed it anyway I expect).

Erm . . well 6A is low for 4 drives and personally I would.!! . . . But worth trying first and will probably only cause you problems if pushing hard.

Being honest with you and Gary probably won't thank me for this.! . . Instead of buying another then I'd build one to suit your requirements exactly. It will be cheaper, take just the same room in control box has the one you have now. If you need the 5V then buy a cheap linear supply for £5.
If you then sell the existing 806-5 it will end up costing you next to nothing.!!

[m.marino]

JAZZ, Not quite that fast but have gotten it up to 12.5m/min rapids with an acceleration of 1.5m/sec^2. These days I am running it most the time at rapids of 7m/min on the x and y axis and 5.2m/min on the z axis with a acceleration of 1m/sec^2. Which with the mentioned motors and drivers and a well set up CV mode gives me cutting speeds possible of 4.8m/min with a 4mm Single Flute Lapped end mill with a 6mm shank. As JAZZ asked what voltage are you running at. I could run in crazy land IF I moved acceleration down to about 500mm/sec^2 but let me tell you 12.5m/min gets scary on my machine. -Michael

[Washout]

Hi Michael

Sorry I missed your reply - I'm pretty sure I'm running the steppers at 68V (that's the output voltage of the PSU).

Those are some pretty hairy speeds you're getting on your machine and I'll be very happy to get near that.

I also had some bits arrive today:

a. some components to brace and tension the belt between the two ballscrews (and support the "wobbly " extension. I had ordered these anyway so will try them out, as I redid the second ballscrew alignment and I must have missed a step in my haste and it was well out (2mm or more). Chances are that's where my overheating stepper was coming from and gantry binding.
b. Also a spare M752 came from ebay (China), so will use that as plan b, should a. above not work out. I'll also likely need a custom motor mount as the T-slots don't line up with the mounting bolts on that side of the machine.

More as I get on with stuff.....


Chris