[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]

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]

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]

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

[cxixer]

It does seem like I will have to build on a small manual holding device that I can just push over to let the router set on while the power is off for now... and then work out the details of this brake later. I will just add in some extra room for modifications later. This brake could also attach onto the other end of the stepper motor shaft.

[One of Many]

Sure, that'll work in a pinch.

As long as you don't forget it is engaged on startup.

Micro-switch fail safe? Heheh!

DC

[cxixer]

As long as you don't forget it is engaged on startup.

DC

That could be an interesting experience. I am trying to make this upgrade a couple weekend project... but it keeps turning into more projects, like the zeroing plate, and now this... wonder whats next that I havn't thought of. I'm going to try to gather all my parts, have things machined, and assemble what I can before I actually dismantle the router so I have as little downtime as possible.

[One of Many]

We have a Bridgeport VMC that will drop .05-.07 when the power is lost. This has become a grave concern in terms of the .010 thin edge taper parts we cut on a $10k 4th axis vacuum sine plate. Under a power outage and a few operator oops's, we have had to repair sections of the surface. So don't feel alone in your quest!


Some industrial machines(routers) have a macro call "Park". This allows the operator to place the machine in a shut down position out of the way. Z up, XY wherever designated. A block of wood under the Z might suffice for the time being.

Sounds like you have some planning and engineering to do......

Best wishes,

DC

[cxixer]

Found a commercial solution... http://news.thomasnet.com/fullstory/481682

Back to diy, though... Having trouble finding a solenoid for this purpose. Any round sping solenoids seem to be very expensive. I've been looking for linear pull solenoids, a solution to maybe push two arms toward the ballscrew at a certain point with grips that hold the screw in place. Or a round clamp in which the solenoid would close it around the screw (think worm-style hose clamp).

How do you calculate the clamping force needed and how that translates into the solenoid force needed?

Or even a manual 'clamp' style brake would work for me. It would keep the screw stationary, you just have one extra step involved in starting and stopping your routing. I would like to find something already engineered instead of starting from scratch, but either way.

[One of Many]

The solenoid only needs to overcome the springs. The spring force holds the brake against the object trying to rotate. This can be gained directly or mechanical advantage. Visualize it and bring it into reality!

I'd start with maybe a v-pulley or disk on that unused motor shaft. Find out how much force it takes to hold it by hand, then size everything accordingly. You are only trying to keep if from rotating, not stop a truck.

A de-sta-co clamp could be a temporary cheap option?

DC

[cxixer]

Here's what I'm thinking. It sure does have to overcome the spring only, but the spring has to be strong enough to make the shaft stay in place. The ballscrew is sitting on the kitchen counter right now, so I held it up and tried to see how much finger pressure was needed to stop the screw from moving, even though I wasn't putting that much force on the nut it still took quite a bit of finger pressure to stop the screw completely. I don't know what this translates into actual numbers...

Now the clamping force needed could be reduced by using some friction, rubber stoppers and such, and some lever action.

Something worked out of a design like this maybe:

[One of Many]

The further out away from a shaft, the less pressure it will take to hold the shaft still. Exponentially to some extent?

I'd be inclind to put it all together and check real world circumstances, seeking a convenient point that would offer the least amount of pressure to stop shaft rotation per the application.

DC