Please explain the reason for having a thrust washer.

[slickrick]

I am not really sure what the reason for having a thrust washer like the one sold on CNCRouterparts.

http://www.cncrouterparts.com/

http://www.cncrouterparts.com/parts.html

Could the stepper motor just be connected directly to the screw without the thrust washers? What do they do exactly?

[Al_The_Man]

In this case it is to complete the needle thrust bearing, you will notice there is one either side of the both bearings.
A typical set up would be a motor to coupling driving a ballscrew, the screw may be mounted with a bearing at each end, one end typically can have a normal raidial bearing, the opposite end would have a thrust bearing to take up any axial movement of the screw and eliminate backlash.
This often is composed of two thrust bearings back to back and is adjusted with the a thrust nut and thrust washers.
Then it is not necessary for there to be a tight axial coupling between motor and ballscrew, which spider couplings especially are not capable of.
Al..

[slickrick]

Thanks, I guess I get it.

They basically take up any backlash that may happen at the connection between the Stepper and the drive screw?

[Al_The_Man]

Thrust washers/bearing in this application are usually used to prevent axial movement of the Ballscrew itself in order to avoid backlash in these items only, regardless of the type of coupling.
Al.

[neilw20]

The ball screw is an inclined plane wrapped around a cylinder.
The inclined plane multiplies the force created by the torque. It is a ramp.
It translates rotary motion into linear motion.
The mounting bolts on the stepper transmit the rotary force (torque) to the frame.
The linear motion (force) which moves the table, or whatever has to have something to react against.
The stepper motor is not designed for thrust, hence the thrust bearings.
Because the thrust can be in both directions 2 thrust bearings are required.

[slickrick]

Originally Posted by neilw20 [The Ball Screw] translates rotary motion into linear motion. The stepper motor is not designed for thrust, hence the thrust bearings. Because the thrust can be in both directions 2 thrust bearings are required.

I think I understand what it takes care of, but not necessarily why the problem is there with the right setup.

I understand that the thrust washers and thrust needle bearing will keep the screw from having any backlash when it changes direction at the point where the bearings are located, but I guess what I don't see is why there would be any backlash there in the first place with the correct connection to the stepper.

Is there really backlash created between the rotating stepper shaft and the thrusting ball screw?

Sorry for the lengthy questions, I'm pretty mechanical and understand things pretty easily, but I guess I am just not seeing why there would be backlash here.

[joeybagadonuts]

Stepper motor bearings are designed for radial loads, they can not control the thrust forces generated by the ball screw.

Without thrust bearings the ballscrew would shift back and forth.

JoeyB

[Mr.Chips]

Nice parts becoming available. Modular really good for the builder isn't able to make thses parts themselves.

Did I say Sliced Bread!

[joeybagadonuts]

Axial load is any load that is parallel to the axis of rotation of the bearing. Radial load is any load that is perpendicular to the axis of rotation.



P.S. this is not a donut.

JoeyB

[gandalf1]

My understanding of Backlash is more about the clearance between the screw and nut thread flanks or clearance between gear teeth whereas the thrust washers control the end float of the screw or shaft as well as absorbing the end loadings on the screw. It follows therefore that a thrust bearing needs to be each side of a fixed position that the screw passes through to absorb the load in both directions. Of course a double row annular contact ball bearing will do this in a single unit positively contained in a substantial part of the machine and with the screw fixed so it cannot move axially withing the bearing inner.
John (UK)

[Oldmanandhistoy]

Originally Posted by joeybagadonuts P.S. this is not a donut. JoeyB

PMSL

[slickrick]

Originally Posted by joeybagadonuts Stepper motor bearings are designed for radial loads, they can not control the thrust forces generated by the ball screw. Without thrust bearings the ballscrew would shift back and forth. JoeyB

I was thinking about this today at work.

Since the steppers are designed for radial loads, does the shifting originate from the stepper? To me that seems feasable. Honestly, I cannot think of any other place that would create axial movement at this point.