ballscrew z axis

[cxixer]

Ok, this may be a stupid question, but I'm confused. A ballscrew moves very easily, I just got one in for my z axis, the rest of the router is R&P. The slightest bit of force moves the nut down the screw, it's very cool actually.

Right now I have a 1/2-10 acme screw on the z axis. I am in the habit of getting my piece cut, letting the router move itself back to 0,0,1" and shutting off the control box/stepper motors. In its current setup, the router sits there, the acme screw makes it stay put. If I put a ballscrew on it, and shut down the steppers with the router at 1" on the z, it will come crashing down...

So... how do you prevent this? I guess you could zero out the z every time, but without taking the bit out each time, the router would just be resting on the bit... that can't be good for it...

What do others do with this situation?

[One of Many]

A couple solutions to consider.

Industrial machines use a spring set break to hold the Z axis in idle.

Counter balance the z axis weight?

In shut down mode, have a relay disconnect the motor from the drive and short the stepper coils to each other?

DC

[cxixer]

Originally Posted by One of Many A couple solutions to consider. Industrial machines use a spring set break to hold the Z axis in idle. Counter balance the z axis weight? In shut down mode, have a relay disconnect the motor from the drive and short the stepper coils to each other? DC

This spring set break sounds interesting. Do you have any more info on this? An example maybe? I've never actually seen this delt with here on the zone, and its hard to search for 'z axis' when you can't search for 'z'.

[One of Many]

This will give you the concept. You can find them on various electromechanical scrap equipment. Finding the right voltage and size might prove a challenge.

Warner Spring set Brake

These are electrically released with an electromagnet. Others may be pneumatically operated.

DC

[cxixer]

Looks interesting, complicated, and quite possibly expensive. I may look into this tonight. Any other suggestions?

How would the counter balance work? I'm picturing a pully system with a weight... but this would swing all over the place, even if you had it secured, I can't imagine it would be perfect 100% of the time, due to differences in friction of the linear bearings at different spots, if the weight was secured too tightly, etc. I can see problems with that in my head... maybe I'm thinking of a different type of counter weight?

[One of Many]

Some builders use adjustable pressure gas struts, but I have seen them leak off and become worthless. Heck, I have used small air cylinders with a regulator. That works fine if you don't mind it coming to rest without air.

You could fab up a cheezy spring set brake, created out of a pull solenoid and a spring set shoe or disc brake style on the Z pulley somewhere. As long as the drive is enabled, the solenoid will be too. When the drive and solenoid drops out, the springs take over and grab the Z. Keep it simple with the concept and be creative!

DC

[cxixer]

Originally Posted by One of Many Some builders use adjustable pressure gas struts, but I have seen them leak off and become worthless. Heck, I have used small air cylinders with a regulator. That works fine if you don't mind it coming to rest without air. You could fab up a cheezy spring set brake, created out of a pull solenoid and a spring set shoe or disc brake style on the Z pulley somewhere. As long as the drive is enabled, the solenoid will be too. When the drive and solenoid drops out, the springs take over and grab the Z. Keep it simple with the concept and be creative! DC

Thats what I'm thinking. I will give this some thought. Hopefully after the upgrades I will remember to update my build thread... This info may be helpful to someone else in the future.

[One of Many]

One last thought to convey.

If there is still some slight drift after releasing the stepper, this could upset the Z reference setting. Moreover, if there were a need to restart after this condition, the Z reference should be double checked if no feedback is utilized to restore it.

DC

[cxixer]

I don't know how others do it, I'm self taught, never working for someone else to learn the art of cnc'ing... but the exact z reference does not bother me. I zero the z on the top or bottom of each new part. I would like to add that neat zeroing jig I saw on a video from joe. Either way, I'm not worried about keeping the exact place so much as the router not crashing down into the table when the stepper holding torque is switched off... So this is ok. Feel free to send over any other afterthoughts. I will likely be getting back to working on this topic tonight or tomorrow with some ideas.

[One of Many]

Point being if you are in the middle of a project, kill the drives for dinner... realize you wanted to do another section....what ever. Going back at it, the Z axis reference may be lost in the process.

More of a forewarning, but you'd find out eventually!

DC

[cxixer]

Originally Posted by One of Many Point being if you are in the middle of a project, kill the drives for dinner... realize you wanted to do another section....what ever. Going back at it, the Z axis reference may be lost in the process. More of a forewarning, but you'd find out eventually! DC

Point taken. Good advice for anyone. I am thinking of a simple diy version of that brake as you suggested, but to keep any accuracy at all it would have to engage instantaneously. Perhaps a shut down cycle instead? Something that engages the break just before powering down the rest? Or a well placed capacitor?

[One of Many]

I had pondered that lead lag issue also.

Typically the drive power output dissipates a bit slower so the spring set brake should be fairly rapid. Secondarily on power up, the drive output may not initialize as quickly so the brake should stay engaged a bit longer?

Play with it and see if it becomes an issue before you try to resolve something that may just take care of itself. The forewarning applies until proven otherwise? LOL!

DC