Are taper lock pulleys a good choice for ball screws?

[JeffZ]

I'm currently trying to figure out what the best way to install a HTD 5m pulley onto a 2010 ball screw is.
It will be driven by a 4.5Nm stepper motor through a closed loop timing belt.
This is what I have in mind:


One option would be to have the fixed end of the ball screw machined, either flat (into a d shaft), or into a keyway. This would accept standard AF/BF style pulleys with grub screws. However, I imagine that the loads of a Nema 34 motor are too high for a d shaft setup, and I'm not sure if keyway machining is a reasonable request.

During my research I've also come across taper lock pulleys. At first glance, they seem to be exactly what I need and don't require special ball screw end machining.
From what I've read, their disadvantage is that taper pulleys are large (start at 32 teeth) and heavy (steel).
My design can easily accommodate for the size, and I can't really imagine the weight of the pulley being an issue.



Unfortunately, I cannot find much information on people using them with ball screws.
Do you think that in my use case, taper lock pulleys are a good choice?

Thanks,
Jeff

[Muzzer]

I've used taperlock pulleys wherever possible, as they are much more secure and concentric than keys and grub screws and are often seen on professional machines. As you say, the main disadvantage is the size. All 3 of my machines have them where space permits and my Shizuoka came with them from the factory. I've used keys and grubs where space is tight (lathe cross slide and Bridgeport Z axis) and those don't feel as secure in my mind.

[JeffZ]

That's a relief, taper lock pulleys it is then.
Thank you!

[JAZZCNC]

That's a relief, taper lock pulleys it is then.
Thank you!

Wait there's a big difference between a router and a milling machine so it's not that simple.!

The milling machine is often rotating the ball-screw much slower with a lower pitch ball-screw. A router is using a high pitch and spinning the screw upto twice the speed and often much longer length (heavier) screws so the inertia becomes more of an issue. Also, servo's or steppers change the outcome. I've got a feeling muzzer is using servo's which have much higher torque than steppers.!

The weight of the pulley and the effect of inertia DOES affect the machine negatively in some circumstances ie: 3D where you are accelerating and de-accelerating quickly with lots of direction changes. Rapid positioning like when drilling lots of holes over a large area where you need to accelerate hard and then slow down between holes.!

All these kinds of operations are affected by the diameter and length of the screw which play a big part in the effect inertia has on the system, so any extra weight you add will only affect this negatively. If you plan to operate at high feed rates or do lots of 2.5/3D work then think carefully about any extra weight you add.

If the screws are long and the gantry heavy then 4.5Nm isn't a massive amount of torque if rotating the screws at higher RPM's.!

[JeffZ]

Wait there's a big difference between a router and a milling machine so it's not that simple.!

The milling machine is often rotating the ball-screw much slower with a lower pitch ball-screw. A router is using a high pitch and spinning the screw upto twice the speed and often much longer length (heavier) screws so the inertia becomes more of an issue. Also, servo's or steppers change the outcome. I've got a feeling muzzer is using servo's which have much higher torque than steppers.!

The weight of the pulley and the effect of inertia DOES affect the machine negatively in some circumstances ie: 3D where you are accelerating and de-accelerating quickly with lots of direction changes. Rapid positioning like when drilling lots of holes over a large area where you need to accelerate hard and then slow down between holes.!

All these kinds of operations are affected by the diameter and length of the screw which play a big part in the effect inertia has on the system, so any extra weight you add will only affect this negatively. If you plan to operate at high feed rates or do lots of 2.5/3D work then think carefully about any extra weight you add.

If the screws are long and the gantry heavy then 4.5Nm isn't a massive amount of torque if rotating the screws at higher RPM's.!

Thank you, definitely appreciate all the information.
This is for a diy router milling machine. I'm still in the initial design phase, so I have not ordered any parts yet.
Right now I'm planning for Nema 34 size motors, but that 4.5Nm figure (or motor type) is not final.
I'll figure this out once the dimensions of the machine are locked in.

I got curious and checked the mass of a 36T htd 5m taper lock pulley, and they are listed at 450g.
Definitely more than I was expecting.

I'll be sure to post my design and ask for critique and comments before ordering any parts.

[dazp1976]

Wait there's a big difference between a router and a milling machine so it's not that simple.!

The milling machine is often rotating the ball-screw much slower with a lower pitch ball-screw. A router is using a high pitch and spinning the screw upto twice the speed and often much longer length (heavier) screws so the inertia becomes more of an issue. Also, servo's or steppers change the outcome. I've got a feeling muzzer is using servo's which have much higher torque than steppers.!

The weight of the pulley and the effect of inertia DOES affect the machine negatively in some circumstances ie: 3D where you are accelerating and de-accelerating quickly with lots of direction changes. Rapid positioning like when drilling lots of holes over a large area where you need to accelerate hard and then slow down between holes.!

All these kinds of operations are affected by the diameter and length of the screw which play a big part in the effect inertia has on the system, so any extra weight you add will only affect this negatively. If you plan to operate at high feed rates or do lots of 2.5/3D work then think carefully about any extra weight you add.

If the screws are long and the gantry heavy then 4.5Nm isn't a massive amount of torque if rotating the screws at higher RPM's.!

I've got a 112mm taper lock and it is weighty.
It's for the 1.8kw servo that's going to be for a mill spindle.
Wouldn't fancy that on a ball screw!!!.
Going to have a go at lightening it with pockets (sort of trivial persuit segments) not cutting all the way through.

[JeffZ]

I did some more research and came across these types of clamping pulleys:


What are your thoughts on these?

[JAZZCNC]

This is for a diy router milling machine. I'm still in the initial design phase, so I have not ordered any parts yet.

Well, that's a good thing you haven't ordered anything yet because you need to decide if it's a Router or a Milling machine because when it comes to component choice's they are very different, and getting it wrong will impact either machine negatively.

Right now I'm planning for Nema 34 size motors, but that 4.5Nm figure (or motor type) is not final.
I'll figure this out once the dimensions of the machine are locked in.

Again be careful because bigger isn't always better.! . . For instance, Nema 34's, even smaller Nm ratings are often wrong for a Router unless they have high voltage drives because they cannot reach the RPMs before torque drops away. 99% of the time you'll find the same Nm rating or lower NEMA 23 or 24 will outperform the NEMA 34 given the same voltage. This is mostly down to the inductance of the smaller motor being much lower which allows higher torque/rpm's.

Also, look at Closed-loop motors/drives for both machine types as they are much better than standard stepper systems.

I'll be sure to post my design and ask for critique and comments before ordering any parts.

A wise choice and the right approach.

[Muzzer]

I've got a feeling muzzer is using servo's which have much higher torque than steppers.!

Yes, my machines are a 3.5 tonne Shizuoka, a 1 tonne Bridgeport milling machines and a Colchester lathe. The ballscrews are mostly 32mm and 25mm and they all have servos, so as Jazz says, the application is a key part of the decision.

Personally I wouldn't consider the additional moment of inertia of a taperlock pulley to be a massive concern if you have a long 20 or 25mm ballscrew but if you have steppers, I guess you may struggle with speed and response as it is. Without a high drive (power supply) voltage, the torque output of steppers quickly tails off, so the headline torque figure may be misleading. If you are still deciding what to use on the motor front, this may be a good time to consider something better and Jazz has good experience you can learn from on that front.

[dazp1976]

Nema 34's, even smaller Nm ratings are often wrong for a Router unless they have high voltage drives because they cannot reach the RPMs before torque drops away. 99% of the time you'll find the same Nm rating or lower NEMA 23 or 24 will outperform the NEMA 34 given the same voltage. This is mostly down to the inductance of the smaller motor being much lower which allows higher torque/rpm's.

A wise choice and the right approach.

Even with motors of near the same inductance is proven.

Results using 60V on a G0704 sized mill, all driver settings identical, X & Y axis:

Nema34, 1080oz (7nm and change) 3.5mh inductance:
Loud, bad resonance, max velocity 2000mm/min, stalls thereafter, Inertia causes 0.2mm overshoots at stop.

Nema24, 566oz (4nm) 3mh inductance:
Near silent, max velocity can exceed 3000mm/min, stops dead, accels like a rocket.

Still have a 1080oz on Z, (2000 is quick enough there). Might need it for my spindles new servo motor (7kg weight)
Upping the power to 72V, might change driver to a stepperonline 100vdc input one (psu can go to 80).


Nema 34 1600oz (12nm) YES I was one of those newbies
Thrown straight in the bin. Too embarassed to mug it off onto someone else!