Well, when it rains it pours!

[Dave's_Not_Here]

I was running a Coat of Arms project on a $50 piece of Curly Walnut. I walked away during the 3D Finishing pass and when I cam back, the Z Axis was going up then down then up then down and no Y Axis movement. There was also a long, beep cut halfway down the x Axis, right in the middle of the walnut, effectively ruining a $50 piece of wood.

It was making a bad noise around the Y Axis Servo, so I ended the program and shut everything off. I removed the cover to the Y Axis Servo/Ballscrew connection and the Ballscrew pulley dropped into my hands. I first thought a set screw had come loose, but that was not the case. It seems that the pulley had literally twisted the end right off of my Y Axes Ballscrew!!!Has anyone seen anything like this before, or have any ideas how this could happen...


I guess this is when you start touting the benefits of Rack & Pinion...

I will not know what the cost is to replace the ballscrew, but I have to seriously think about staying in this line of work, given all the problems I have had with a CNC router the is only 2 1/5 years old.

[Al_The_Man]

Never seen it on a ball screw, I have seen a motor shaft go like it that used solid coupling, is it possible the timing belt was over tensioned?
Apart from that, the only thing I can think is a over-hardened shaft.
Al.

[advt001]

Even though you probally wont get the factory to replace it, I would still raise h*ll.

[Dave's_Not_Here]

Never seen it on a ball screw, I have seen a motor shaft go like it that used solid coupling, is it possible the timing belt was over tensioned?
Apart from that, the only thing I can think is a over-hardened shaft.
Al.

Al,

Tension was set at the factory, so it's anyone's guess.

My vote is for the over-hardened shaft, as the break is as clean as a whistle, with no indication, to the naked eye, of twisting. I might send the trashed end, inside the pulley, someplace local to test the hardness. I wounder if Techno will stand behind a bad ball screw with less than 300 hours run-time.

Whatever caused the ball screw to snap, I wonder why the controller didn't fault out before snapping off the pulley end of the ball screw? It was a tapered .125 ball nose with a .0625 diameter end... I have had .25" end mills snap off and the Y axis never missed a beat. That's why I lean toward the hardening issue.

As a side note, the bearings run nice and smooth, so that was not an issue.

Guess it's not a good time for me to play the lottery...

[Dave's_Not_Here]

Even though you probally wont get the factory to replace it, I would still raise h*ll.

Maybe I will get lucky if the hardness test comes back in my favor, and they will take care of me.

Mike, from Techno, is doing an outstanding job of taking care of the last set of issues, and he is going to make things right on the servo issue too. We will be talking again on Monday, so I will run this latest issue by him. I have nothing but respect for Mike.

D

[Al_The_Man]

Whatever caused the ball screw to snap, I wonder why the controller didn't fault out before snapping off the pulley end of the ball screw?

The problem most likely was that the controller would have no indication, even with servo's with the encoder on the motor.
Al.

[Montabelli]

can you manually push your axis, will it move and spin what is left of your screw? I have seen machines stopped by having too much sawdust build up in the ball nut.

if it is clean and moves freely, obviously that wasn't the problem.

[Pplug]

Wow! Didn't you say the previous owner had had a problem with the x axis?

[Dave's_Not_Here]

can you manually push your axis, will it move and spin what is left of your screw? I have seen machines stopped by having too much sawdust build up in the ball nut.

if it is clean and moves freely, obviously that wasn't the problem.

It moves very easily. The bearings are excellent. The ball screw is fully encased in an aluminum extrusion, so I doubt that sawdust caused the failure.

I have contacted two or three companies that specialize in ball screw repair, including repairing broken journal ends. I am waiting to see what they say, but will most likely have to ship it to get a firm quote. One company offers a 3 year guarantee at cost of 40% of a new replacement... but it would be nice to have first hand knowledge of their work.

D

[Dave's_Not_Here]

Wow! Didn't you say the previous owner had had a problem with the x axis?

He bought a new 5' x 10' Techno after selling me the 4896. The 50120 he purchased, went stupid crazy and bent the X Axis ball screw and damaged the Z Axis big time... don't know what his final resolution was... it was definitely under warranty.

The only issue I have with the X Axis is the encoder connector on the servo only catches the first couple of threads on the two nuts, so it is also held down tight with a lot of strapping tape. I asked Techno about a replacement encoder cable with longer screw connectors, and they said that the current method of strapping tape should work fine....

D

[Al_The_Man]

The only issue I have with the X Axis is the encoder connector on the servo only catches the first couple of threads on the two nuts, so it is also held down tight with a lot of strapping tape. I asked Techno about a replacement encoder cable with longer screw connectors, and they said that the current method of strapping tape should work fine....
D

Sounds like a technical fix to me!
Al.

[Dave's_Not_Here]

Al,

Have you, or anyone you know, had any experience with repairing the journal end of a ball screw? There are several companies who have been making these repairs for a number of decades, so it must be some type of standard practice.

An $800 journal repair is better than a $2,500 ball screw... if it works.

D