Z falls due to weight. Normal?

[ryan_slaback]

This may not be a problem at all but I thought I would ask as it seems like it would be. I am setting up my new shopbot in my school lab. I have installed the machine and it seems like it is ready to go. However, I am a bit concerned that the Z axis falls down due to gravity until it rests on the table. I see there are springs in the housing but they are not enough to hold the weight of the Z. I know that the manual cautions about moving the axis without power and I know some of the guys on the forums have said that moving motors manually has fried controllers so I wanted to get the ok before I fire it up and have the Z axis fall when the motor shuts down and fry a controller. So, is this normal? If not, what do I need to adjust?

[steve4460]

Ryan
I would call shopbot asap to get the right springs for your machine .

Bot on

[sawkerf]

That's certainly not normal, call Shopbot.

[paco]

Look like you've got the wrong springs for your spindle (you got a spindle right?!). Router and spindle installation don't use the same springs (bigger for spindle that is).

Until you get in touch with SB support about this (and you get the right one), try to remember to reach the spoilboard for the spindle to rest on when you turn off the control box so it doesn't fall from too high. You could use a block of some sort under the spring hook to rest on.

Or maybe it's not that at all and something is wrong with the way the springs are installed no matter if you have a router or spindle. They should hooked at the spring hook right above where the dust shoe is and at the top most of the Z on the two through bolts that are there just for this.

In all case, the right match of spring and correctly installed should prevent the Z from "falling" down like this.

[mikejohn]

I actually checked this after moving shops recently.
I was suprised to find that it zeroed out exactly at the same height as I had left it the night before.
This with a router, not a spindle.

.............Mike

[kerrazy]

Ryan, when you remove the load, (ie motors are off) from the z Axis, some movement is normal, 3-4 inches. I suspect this is occuring when you reset your control box, which in return removes energy from the Z motor, thus causing it too fall.
As you get used to the tool, you will see your actions and the routine you develop will see that this does not occur.

I know this does not make sense and it has in the past caused me confusion as well, during installs, but if you leave the controll box powered it does not allow the z axis to drop correct? Only when the Z motor is not energixed will it "fall". This being said, it will not consistently drop, only during machine control box power downs, when you hit reset and set your z again it will maintain its height fine.

Dale

[paul_z]

Ryan,

What type of bot do you have? I have a PRT Alpha with the PC router and my Z axis does not move at power off. I'd definately get in touch with shopbot (and please let us know what they say).

Paul Z

[mikejohn]

I can't agree with Dale that "some movement is normal,".
Others have posted about this before, and the majority of answers is that they have no movement (or very little).

However, if you have movement, and you are aware of it, I guess there is no big problem.
I am sure everyone z zeros before cutting, anyway.

...............Mike

[cnc_works]

When I put my 3hp spindle on, I was concerned I would have to get new springs because it just barely held its own when off. Touch it and down it would go. However, it has not caused any issues regarding lost z steps and is rock solid when powered up.

Donn

[odulfst]

only concern I would have is if it's over working the motor when pulling up. but I doubt it.

[scottcox]

I noticed with my 5hp spindle that upon power down, it would move toward the center of travel where the spring was relaxed. If it was low, it would spring up. If it was high, it would spring down.

I made a range mark on my Z, and now move it to that "at rest" position before power down. It's never errantly moved since.

[ryan_slaback]

Well to let you all know, it was indeed a problem with the setup of the machine. The Z was not in anyway supposed to move after the power was removed and especially not down. That is a broken cutter waiting to happen. As far as what the actual fix was I prefer not to say (it wasn't anything embarassing) but as Chris who helped me through it pointed out depending on which PRT you have etc the solution might be different and it is best just to call them and have them help work you through it. Basically what I wanted you guys to help me with was if this is normal or not. So if in the future someone reads this because they have the same problem, it is not normal. Call ShopBot