PDA

View Full Version : Belts or Balls getting me Screwed up! Help I need advice Please.



longy
10-04-2014, 10:50 PM
Hi everyone, Iíve had a major change of plan from my original design build. Itís sort of grown a tad from the original X at 700mm to 1500mm so that I can drop a quarter sheet of plywood or phenolic ( high pressure laminate ) which will save me having to do tile the cuts on lots of jobs. I also want to be able to engrave a standard door or a lump of 4Ē / 6Ē thick oak post.

Iím still working on the design at the moment but getting my head screwed up as to do I use belts or ball screws or both. Could I use belts to drive both the Y axis ball screws and use just one motor instead of synchronising 2 motors ? I was looking at using nema 23 - 425 Oz-in motors.

12035

For the spindle I will be using an 1/2Ē router until I have enough funds to add a water cooled spindle. Iíve done a plan view so you can get an idea of what I would like to build, all steel framed and using SBR20ís for all the rails. X axis I was going to make up a lattice frame from aluminium extrusion and then laminate (epoxy) 2 sheets of 6 or 8mm plate to both sides, not sure how deep to make the beam but 6Ē or 8Ē (150 / 200mm)

As I want to be able to pass materials under the Y axis beams I was thinking of using 80x80x6mm with 50x50x3mm for the main frame, but might need to beef up the corners as this cnc will be floating on 4 corners. I welcome your input and wonít take offence but I may take the gate LOL

Lets me have your ideas as itís easier to to make changes at the design stage and a lot less expensive. Failure to prepare is to prepare to Fail.

Mike :topsy_turvy:

JAZZCNC
11-04-2014, 01:43 AM
First you'll get a stronger machine if you build it long and narrow rather than wide and short. It would also be easier to join ballscrews with a timing belt and use one motor and have the advantage of keeping screws in sync. Don't bother with timing belts only as they cost nearly as much as ballscrews by time you have bought belt and pulleys etc.
Also the ballscrews want to be 10mm pitch not 5mm if you planning on mainly cutting wood, if you need higher resolution then just put a ratio on the screws.

Ger21
11-04-2014, 03:07 AM
Also, the 425oz Nema 23 motors are about the worst choice in Nema 23 motors. They have very high inductance, which results in very low torque at higher rpm's.

Jonathan
11-04-2014, 11:48 AM
Also, the 425oz Nema 23 motors are about the worst choice in Nema 23 motors. They have very high inductance, which results in very low torque at higher rpm's.

The ones people like to call 'nema 24' sometimes don't, for example:
Nema23 Stepper Motor 3.1Nm (http://www.cnc4you.co.uk/index.php?route=product/product&path=83_84&product_id=362)

(Mike: Don't take that as a recommendation yet - it may well be the motor you require, but you need to do more of the design before selecting motors)

Ger21
11-04-2014, 01:07 PM
That's not a 425oz motor, it's 439. The OP said 425, so I don't think he's referring to that motor. All the 425oz motors I've ever seen are high inductance.

Jonathan
11-04-2014, 02:10 PM
That's not a 425oz motor, it's 439. The OP said 425, so I don't think he's referring to that motor. All the 425oz motors I've ever seen are high inductance.

The motor I linked to and the following one are probably the most popular ones on this forum:

SY60STH88-3008BF (http://www.zappautomation.co.uk/en/nema-23-stepper-motors/380-sy60sth88-3008bf-nema-24-stepper-motor.html)

That's 3Nm, so 424.8oz-in and 3.2mH... close enough for you?

I've measured the inducance of both motors and it does match the rating, within a reasonable tolerance.

longy
11-04-2014, 03:36 PM
First you'll get a stronger machine if you build it long and narrow rather than wide and short. It would also be easier to join ballscrews with a timing belt and use one motor and have the advantage of keeping screws in sync. Don't bother with timing belts only as they cost nearly as much as ballscrews by time you have bought belt and pulleys etc.
Also the ballscrews want to be 10mm pitch not 5mm if you planning on mainly cutting wood, if you need higher resolution then just put a ratio on the screws.

Thanks for your input Jazz, I had looked at doing it the way you suggested and may well go back to longer / narrower machine. Ball screw pitch I'm not sure what you mean by "ratio on the screws" I do need to have the higher resolution as the laminate I want to cut needs a high tolerance. It's harder than a lot of allies to cut / drill, so do you think I would be better using the 1605 bs ? I'm going take what you've said about the machines orientation and work on another plan, I do know I can rename the axis x & y to fit my machine.


The motor I linked to and the following one are probably the most popular ones on this forum:

SY60STH88-3008BF (http://www.zappautomation.co.uk/en/nema-23-stepper-motors/380-sy60sth88-3008bf-nema-24-stepper-motor.html)

That's 3Nm, so 424.8oz-in and 3.2mH... close enough for you?

I've measured the inducance of both motors and it does match the rating, within a reasonable tolerance.

Thanks Jonathan for the links to the motors. I've read your build logs with great interest well done. These are the motors / drive kit that I have been looking at „ÄźGermany Ship„ÄĎ4Axis Nema23 stepper motor 425oz-in Dual & Driver CNC control kit | eBay (http://www.ebay.co.uk/itm/271448501320) and within my budget, your views are welcome on the kit. I'm keeping well away from those 268 drivers offered with some kits.

Thanks to all for your valued input.

Mike :smile:

Ger21
11-04-2014, 04:11 PM
Virtually all of the 425oz motors available in the US and through Ebay (from China) are high inductance. The ones you linked to are not commonly available over here. So just make sure you know what you're getting.

longy
11-04-2014, 04:17 PM
Virtually all of the 425oz motors available in the US and through Ebay (from China) are high inductance. The ones you linked to are not commonly available over here. So just make sure you know what you're getting.

Thanks Gerry, I've not ordered any motors yet, but I will hopefully make sure I get the rights ones.
Mike

Ger21
11-04-2014, 11:00 PM
These are the motors / drive kit that I have been looking at „€źGermany Ship„€‘4Axis Nema23 stepper motor 425oz-in Dual & Driver CNC control kit | eBay (http://www.ebay.co.uk/itm/271448501320) and within my budget, your views are welcome on the kit. I'm keeping well away from those 268 drivers offered with some kits.


Yes, those are the high inductance motors I'm talking about. They'd need close to 100V to get the best performance out of them, but they give you a 36V supply.

But listen to what Jonathan said. You shouldn't just arbitrarily choose motors and drives. They need to match your choice of screws, and the machine to get the best performance from them. In some situations, motors half the size will easily outperform larger, high inductance motors.

longy
12-04-2014, 12:11 AM
Thanks Gerry, I will listen to Jonathan is saying and I will keep working on a new design and then ask for help in choosing screws, motors and drives once I've sorted how to have part of the bed removable so I can add a 4th axis at a later date. Still looking at the build logs and other stuff to aid in the overall design.
Mike

longy
14-04-2014, 08:23 PM
Hi everyone, I've had a play around with the design and changed the orientation round. It won't be a problem working over the side rails and as Jazz said it will make the machine stronger. Going to order the rails from china as I don't mind waiting a few weeks as I have lot of other things to do.

I would like your views on the ball screws to use ? so I can order these as well. I'm mainly going to be cutting and engraving wood and phenolic (laminate) and some plastics. Next will be the motors and drivers but not in a rush at the moment due to a lack of funds.

Your help will be much appreciated in getting the right ball screws.
TiA Mike

12056

JAZZCNC
14-04-2014, 11:09 PM
Your help will be much appreciated in getting the right ball screws.

You want 10mm pitch for X & Y axis 5mm for Z axis. Now personally I'd go for 20mm diameter at this length and sacrifice a little acceleration/speed in favor of reducing potential for whip compared to 16mm diameter.

Now the ratio I was talking about before comes from how you attach the motors to the ballscrews.? I always connect the ballscrews to the motors with Timing belts & pulleys. Doing this reduces affects of resonance on the motors and gives smoother running motors but it also allows a Ratio to be applied if needed.
This ratio can be applied both ways to either give Higher resolution and boost torque but at the cost of Speed or increase speed at the expense of torque and Resolution. Now in practice 10mm pitch with a 1:1 ratio works great for anything but fine engraving or work that requires high resolution. But if needed then a quick pulley change to 2:1 and you instanly get higher resolution.!

Can I also suggest you price up Profiled linear rails from Chai before buying the Round type.? . . . I think you may get a pleasant surprise.!
Even the cheap range of profiled linear rails blows the round type out the water and the slight difference is money well spent.

longy
15-04-2014, 02:10 PM
Thanks very much for your input JAZZCNC, I'm busy pricing up 2010 end machined ball screws and getting even more confused with this end machining terms like " MPF, IDE, FUS, WFR, WWF, DGK, MPH" no idea what it means. Could I use 2010 on the X axis (1500) and drop down to 1610 for the Y axis ? Would this cause problem setting the machine up ?

As for the profiled linear rails I can't find the lengths I need on ebay and uk supplier prices put it well out of my limited budget, looks as if I will have to go with supported round rails.

Mike

JAZZCNC
15-04-2014, 02:52 PM
No need to get confuddled it's not rocket science really. The letters will correspond the Ballnut type. You just want standard flanged ballnut.

Regards dropping the diameter for Y axis then it won't affect setting up at all. What the larger diameter tends to do is reduce the acceleration and overall rapid speed you can tune the motors to, inertia and all that, but in practice with 10mm pitch and slaved 3Nm motors you have more than enough power in reserve and will still get perfectly acceptable feeds/accel that excede what you'll ever need for cutting. Whip is something you want to avoid at all costs and your in the region of where it can happen and for the little difference I won't take the risk.

Regards the Profiled linear rail and Ballscrews for that matter then Give Chai at lineramotionbearings a email with the sizes you need, give him total length of screws including the machining, ask for them machined and he will give you a price.
I don't think he shows profiled linear rails on his Ebay site but he does supply them, I've had loads of them now and they are fine.

I'll PM you his email.

longy
15-04-2014, 03:46 PM
Thanks JAZZCNC, I'm easily confuddled these days I just put it down to my age LOL. I'll go with the 20mm ball screws for the longer X axis so it reduces any whip in the ball screws. This might be a daft question but how do you work out the length for the ball screws ? against the linear rail travel length taking into account for the mounting blocks BK15 / BF15 and the ball nut and mount. Thanks Dean for the PM very much appreciated.
Mike