[ecurb5]

I'm finishing up my cncrp48x96 build, have a spindle on it now. The spindle is heavy enough that when shutting down the machine that the nema 23 motor with the 5 start acme lead screw that comes with the kit, drops. Is this normal? Is there something I can do to make it not drop when the power is removed?

Thanks,

Bruce

[xjdubber]

You can put a brake on the z-axis preventing it from dropping, depending on setup, yes this is normal.

[ger21]

You can also counterbalance it or put a spring on it to support some of the weight.

[lx007]

I use the same Z axis. I added a 25 pound gas spring to my Z axis after replacing a Hitachi router with a Colombo spindle. It works great, not only preventing the axis from dropping when powered off, but it also reduces the load on the Z stepper motor.

[ecurb5]

I use the same Z axis. I added a 25 pound gas spring to my Z axis after replacing a Hitachi router with a Colombo spindle. It works great, not only preventing the axis from dropping when powered off, but it also reduces the load on the Z stepper motor.

That sounds like a great and simple solution, sorta like the way a tailgate works on a minivan. Can you post a picture of it?

[lx007]

I ended up using this 20 pound spring from McMaster-Carr. To determine the spring force needed, I placed a digital scale under the spindle, then powered off the steppers. I repeated this several times, with numbers ranging from 14 - 18 lbs, so that's why I chose a 20 pound spring. The main reason I went with a spring instead of a brake is because the Colombo spindle weights 20 lbs by itself, and the spring takes a big burden off of the stepper.
Attachment 203734

[ecurb5]

That looks like a very well executed install of that gas spring. Looks like it should be a standard component of that z-axis kit.

Thanks for the info/help. :cheers:

[expo123]

lx007

Would you mind posting the McMaster Carr part number for the spring you used? These are "close-assist" gas springs, correct?

Thanks
andy

[ecurb5]

lx007

Would you mind posting the McMaster Carr part number for the spring you used? These are "close-assist" gas springs, correct?

Thanks
andy

In post #6, he has a link to the McMaster Carr page with the part.

Edit:
And, they are "open-assist". Look at the pic, it's set up to unload some of the weight by "pushing" the z-axis up.

[mmoe]

If you have a decent air supply, you can also use a pneumatic cylinder, which allows you to adjust the degree of assist by varying the air pressure to the cylinder. Ideally, whatever you do should only counter the actual weight. It's just as bad for the lead screw to be forcing the head down as it is to be fighting gravity going up. It should be in balance so that it's the same effort for the motor either way or you will get unnecessary wear on the lead screw.

[expo123]

Thanks... my apologies... I saw that there was a link there, just had it in my mind that it was one of those random advertisements that get sprinkled about these days.

andy

[ecurb5]

Yep, that's exactly what I'm after, balancing the up vs down force.

[district7]

Open assist springs are what you want if you mount the spring at the bottom of the z plate and to the top of the z rail. If it is mounted backwards it will drive force down. This post didn't have that information directly detailed and it may help someone else.

[H33t]

Hello guys, read all the posts, great advice. im pretty new to this cnc mechanics. I have been getting a z error when i power down but didnt think anything of it, cause i couldn't see anything physically moving, But the last time i used my machine it dropped in the middle of a toolpath. so i brought my spindle up and powered down, then noticed that the spindle was dropping alot this time. so i would wondering if they are both connected somehow.

[ecurb5]

After some time with that McMaster gas spring installed, the Z axis started acting up, loosing steps and sounding like it was binding or something. Figured out that the gas spring doesn't like fast tiny movements when compressed. Will be looking into the steel spring solution now.

[jbar]

After some time with that McMaster gas spring installed, the Z axis started acting up, loosing steps and sounding like it was binding or something. Figured out that the gas spring doesn't like fast tiny movements when compressed. Will be looking into the steel spring solution now.

Did you switch to a steel spring or find another solution?

[ecurb5]

Did you switch to a steel spring or find another solution?

I haven't done anything with it since, so the stepper is just working with the load. And when I go to turn it off, I'll put the gas shock I bought on as a "kick-stand" to keep it from falling.

[jbar]

I haven't done anything with it since, so the stepper is just working with the load. And when I go to turn it off, I'll put the gas shock I bought on as a "kick-stand" to keep it from falling.

I've learned having the gibs properly adjusted makes a big difference. I'm considering doing away with the gibs and installing linear rails on the Z axis. Problem is you need a mill to mill the dovetails off the column....it's a chicken or egg thing.

[Goonk]

I just went through this on my STD 2448. I adjusted it too much and busted a bearing! So, I created a "Park" script that carries it to the far end of the machine and I place a couple of pieces of 2x4 under it so that it rests on those if/when it drops. Mine doesn't drop every time. I figure that's a good sign - I'm right at the line of enough vs too much. I also created a script that zeros the Z against the limit and I run that every time I power up.

Still figuring this stuff out....

Tony

[ecurb5]

Open assist springs are what you want if you mount the spring at the bottom of the z plate and to the top of the z rail. If it is mounted backwards it will drive force down. This post didn't have that information directly detailed and it may help someone else.

By open assist spring, do you mean something like this: https://www.mcmaster.com/#9293k25/=170uxr6 ?