[peteeng]

Hi Jayne - If your keen have a look at this. The terminology has to do with the difference between the torque required to set the bolt and then restart the tightening or loosen the bolt. Since there is no preload in a pulley connection its not useful info in this application. But since you probably do up and undo bolts the terms would be useful for you. I tried to get the iso std but the sources wanted payment...

I prefer taperlocks and have used them up to dia600mm on mining equipment axles, brand name Ringfeder but they don't make small ones. The CPT pulley looked reasonable. Peter

https://ntrs.nasa.gov/api/citations/...0120015467.pdf

https://www.ringfeder.com/products/l...oads/rfn-7012/

[Zorbit]

I like the idea of having the motors tucked underneath, but there are disadvantages too. More cost, more failure points, more inertia, radial / side load on motor and ballscrew bearings. I think, overall, I'd mount the motors on the end of the screws.

[JayneV]

Hi everyone,

I have been thinking about my choice of using Nema 23 stepper motors. Without spending a whole lot extra, I can upgrade to Nema 34 motors. These motors are readily available with key slot shafts and the shaft also has a larger diameter at 14mm which should permit larger radial loads from tensioning the timing belt. I sent an email to stepper online asking for shaft loading specs. I also sent a message to Fred at BST asking if they can machine key sots in the ballscrew ends, I neglected to ask that question in the previous message to him.

[Zorbit]

Where is the "weak link" in your drive system ? Sooner or later something is going to jam, and something is going to break or stall. Better if the motor stalls.

My first CNC was a DIY conversion of a knee mill, with Nema 34 motors and 8.5A drivers. Belt driven screws, geared down 3:1 . When the inevitable collision happened the motor pulled the middle right out of the ball nut.

[JayneV]

Where is the "weak link" in your drive system ? Sooner or later something is going to jam, and something is going to break or stall. Better if the motor stalls.

My first CNC was a DIY conversion of a knee mill, with Nema 34 motors and 8.5A drivers. Belt driven screws, geared down 3:1 . When the inevitable collision happened the motor pulled the middle right out of the ball nut.

That’s a good point. I’m not really looking for more power out of the motors. I think 3Nm is a good match for my machine. The belt drive will be a 1:1 ratio. I’m a little concerned about the motor bearings prematurely wearing by being subjected to radial loads at or above their rated maximum due to the belt tension. Nema 34 motors have larger diameter shafts and bigger bearings with a higher load rating. Also, Nema34 motors are easy to find with key shafts, I haven’t found any Nema 23 with key shafts. I’m looking at 3.5Nm Nema 34 motors, so not too much more torque than the N23-3Nm. N34’s seem to maintain torque at higher speeds than N23’s. I haven’t made any decision yet, still weighing up the pros and cons of each. Thanks for your input. I’ll add your points into the mix.

[mactec54]

Where is the "weak link" in your drive system ? Sooner or later something is going to jam, and something is going to break or stall. Better if the motor stalls.

My first CNC was a DIY conversion of a knee mill, with Nema 34 motors and 8.5A drivers. Belt driven screws, geared down 3:1 . When the inevitable collision happened the motor pulled the middle right out of the ball nut.

With a poor system setup, things like this can happen, if the drives where set correctly, as soon as your machine stalls, the drive should create a fault, ( overload Fault ) and everything stops, with no damage done.

[JayneV]

With a poor system setup, things like this can happen, if the drives where set correctly, as soon as your machine stalls, the drive should create a fault, ( overload Fault ) and everything stops, with no damage done.

For the driver to recognise if the motor stalls, the steppers would need encoders wouldn’t they? Closed loop steppers are more expensive but I am considering using them. Servos would be even better but are too expensive, maybe they can be a future upgrade down the track.

[Zorbit]

For the driver to recognise if the motor stalls, the steppers would need encoders wouldn’t they? Closed loop steppers are more expensive but I am considering using them. Servos would be even better but are too expensive, maybe they can be a future upgrade down the track.

I think Mactec is referring to setting a current limit on the drive, although in practice it's not so simple. If I was designing a router now I'd be looking for a motor / ballscrew combo that was running at high enough speed to sound smooth at my most common feed rates, which depends on what you are cutting. So, for my 10x5 router the sweet spot should be at about 1500 - 2000 mm/min. Ideally the motors would be towards the top end rpm at that feed rate, so that as the x or y slow right down in a curve they will still be running fast enough to be smooth.

[peteeng]

Hi Jayne- I think N34s will lead to increased cost and less speed. On Scoot at the moment the drives are set to 1.2A and they are performing very well. When they hit something hard they stall so that's a good safety feature. I shall bump up the A's when cutting aluminium and when I start looking for more speed. But overall the N23 or N24 will be fine for your machine. I wouldn't be hung up on keyways either...that means something expensive will break vs the motor slipping in the inevitable crash one day....Peter

[mactec54]

For the driver to recognise if the motor stalls, the steppers would need encoders wouldn’t they? Closed loop steppers are more expensive but I am considering using them. Servos would be even better but are too expensive, maybe they can be a future upgrade down the track.

Any good Stepper Drive will have current limiting, where you can set the current, this will then stall the motor if you hit something if set correct, without damaging anything, if the Drive has over current protection even better

[mactec54]

I think Mactec is referring to setting a current limit on the drive, although in practice it's not so simple. If I was designing a router now I'd be looking for a motor / ballscrew combo that was running at high enough speed to sound smooth at my most common feed rates, which depends on what you are cutting. So, for my 10x5 router the sweet spot should be at about 1500 - 2000 mm/min. Ideally the motors would be towards the top end rpm at that feed rate, so that as the x or y slow right down in a curve they will still be running fast enough to be smooth.

2000mm/min would be to slow for most on a machine that size.

[Zorbit]

2000mm/min would be to slow for most on a machine that size.

Definitely, it depends on what you're cutting. When I was cutting 6mm marine ply at the boatyard I was running a lot faster. Now I'm cutting carbon fibre and GRP.

[JayneV]

Hi everyone,

Thank you for the great feedback. I haven’t really started looking at what features the stepper drivers have. I didn’t even know setting a current limit was an option. Learn something new every day! So far I have only been looking at the mechanical side of things and only looking at the physical size of the motor body and shaft to figure out fits and clearances of the parts. I better start reading up on the stepper drivers before going further.

[mactec54]

Hi everyone,

Thank you for the great feedback. I haven’t really started looking at what features the stepper drivers have. I didn’t even know setting a current limit was an option. Learn something new every day! So far I have only been looking at the mechanical side of things and only looking at the physical size of the motor body and shaft to figure out fits and clearances of the parts. I better start reading up on the stepper drivers before going further.

Leadshine Stepper Drives are one of the best out there, they have over voltage / over current Fault Protection. which can be wired in to the Estop circuit.

[peteeng]

Hi Jayne - To discuss the direct drive version a little more vs the belt drive. The belt is used to save space or address aesthetics. It definitely costs more then a coupling. There is dead space at the rear and front of a machine like yours due to the gantry and spindle geometry. If you run the rails to the rear and the front of the machine arbitrarily then the motor will stick out in a direct drive machine. But if you account for the fwd or rear dead space and adjust the gantry/spindle in relation to its bearings then the motors can live in the dead space and this won't affect your footprint or your working envelope. Plus as there are 2 motors driving the gantry you can use a small motor say a 70mm motor vs a 115mm long motor and that's enough to not have it stick out and minimise the visual impact of large motors. All decisions lead to a compromise... two 10mm pitch ballscrews with a smaller motor still gives you a very large cutting force. Peter

[JayneV]

Leadshine Stepper Drives are one of the best out there, they have over voltage / over current Fault Protection. which can be wired in to the Estop circuit.

Leadshine is one of the drivers I was going to read up on. BST also sells this, so may be able to get a better deal if I bundle it all together with the ret of the order. Thank you for the feedback

[JayneV]

Hi Jayne - To discuss the direct drive version a little more vs the belt drive. The belt is used to save space or address aesthetics. It definitely costs more then a coupling. There is dead space at the rear and front of a machine like yours due to the gantry and spindle geometry. If you run the rails to the rear and the front of the machine arbitrarily then the motor will stick out in a direct drive machine. But if you account for the fwd or rear dead space and adjust the gantry/spindle in relation to its bearings then the motors can live in the dead space and this won't affect your footprint or your working envelope. Plus as there are 2 motors driving the gantry you can use a small motor say a 70mm motor vs a 115mm long motor and that's enough to not have it stick out and minimise the visual impact of large motors. All decisions lead to a compromise... two 10mm pitch ballscrews with a smaller motor still gives you a very large cutting force. Peter

Hi Peter,

I have grown to like the belt drive arrangement, but doubt I could offer a good reason to justify the added complexity over the direct drive option. I guess I just like the look of it. lol I know what you are saying regarding the dead space at the front or back (or both) of the machine. As the machine is now, the spindle overhangs the front and the dead space is all at the back. Pushing the gantry further back relative to its bearings would reduce that rear dead space and also allow the motor to fit within the machine envelope at the back for a direct drive setup. However, I want to keep the ability for the spindle to reach beyond the front edge. It might be worth revisiting v10 again with a direct drive setup.

Attached are images of the gantry at its forward and rear limits in the current belt drive configuration. I have also attached two images with a motor mounted on the front and rear face for a direct drive setup. I'm not keen on front mounted motors, so that option is bottom of the list for now. I'll get to work on v10 again and see if it works for me.

[Zorbit]

Leadshine is one of the drivers I was going to read up on. BST also sells this, so may be able to get a better deal if I bundle it all together with the ret of the order. Thank you for the feedback

Leadshine are good enough that other Chinese companies counterfeit them.

[mactec54]

Hi Peter,

I have grown to like the belt drive arrangement, but doubt I could offer a good reason to justify the added complexity over the direct drive option. I guess I just like the look of it. lol I know what you are saying regarding the dead space at the front or back (or both) of the machine. As the machine is now, the spindle overhangs the front and the dead space is all at the back. Pushing the gantry further back relative to its bearings would reduce that rear dead space and also allow the motor to fit within the machine envelope at the back for a direct drive setup. However, I want to keep the ability for the spindle to reach beyond the front edge. It might be worth revisiting v10 again with a direct drive setup.

Attached are images of the gantry at its forward and rear limits in the current belt drive configuration. I have also attached two images with a motor mounted on the front and rear face for a direct drive setup. I'm not keen on front mounted motors, so that option is bottom of the list for now. I'll get to work on v10 again and see if it works for me.

You most likely won't have enough dead space, to fit the motor as a direct drive and fit inside, the machines max size, for travel you want the largest cutter you will use, to be able to clear the outside area of the Table / cut area, from this then you can workout the overall length of your machine, and then see what space you have at the back of the machine, in most cases there is not enough space to do this, unless you have a very large spacing between the Gantry Linear Bearings, and this then means a longer machine, for a wider Linear Bearing spacing.

[mactec54]

Leadshine are good enough that other Chinese companies counterfeit them.

Correct this is the case with most anything manufactured in China, one must be aware when buying anything like this to make sure it is from the manufacture.