Replacing sprockets and counterweight chain.

[nervis1]

Anyone know this procedure? I dont find anything in the maint. manual.

I can't figure out how to get the sprockets off, as the weight must be up high to get at the chain links, the z axis servo has to come off to get to the front two sprockets. How do you hold that weight up while you do all of this?

[jwm1229]

If your machine is like our 4020 series machines there is a set of holes
in the side of the main mast. You raise the weight so the holes in the weight
line up with the holes in the mast and insert the shipping pins.

[nervis1]

OK so shipping pins in, raise z axis so there is slack in the chain, remove z axis servo motor and mount, replace sprocket and chain. Is that about it?

Is there any issues with removing the z axis motor when the machine is on? If I shut it down with the z axis off zero (head all the way up) all I have to do is a cold start right?

Are there any issues with having the z axis ball screw supoporting the weight of the whole z axis while I fiddle with the replacement parts?

[HuFlungDung]

Dave,
Once the pins are in, I would raise the Z even further, and place blocks underneath the head, on the table, and then slowly let the head come down on the stack of blocks. Then power off and do your work.

Otherwise, you will find out exactly how much weight that the counterweight was holding up

[jwm1229]

If you are going to remove the z motor you should rest the weight of the
head on a rack mount or a block, So the weight of the head is supported
like it was being shipped. If you dont the ball screw will turn and the head will drop.
After you reinstall the z motor you will need to reset the tool rack z position.

[nervis1]

Never considered that when I removed the z axis motor the whole thing would spin down.....whew....good thing I asked.


Thanks for the help guys.

[nervis1]

Got the job done today.

Here is what we (Fadal tech and I) did in case anyone wants to know.

Move head to put in shipping pins, one of these must go all the way through to avoid cocking the counterweight.

Move head up and block it so the chain is slack enough to move off of the sprockets.

Hit the E stop and turn it all off.

Remove the sheet metal around the head.

Remove and replace the back two sprockets.

Remove chain.

Remove z axis servo, keep the servo coupling from rotating so everything remains aligned.

Remove the z axis ball screw, two hex head bolts under the z axis bridge in the front, one bolt at the rear of the bridge on top.

Then 5 hex head bolts on the ball nut.

Remove the grease or oil zerk tube (quick connect type).


Remove and replace the front two sprockets.

Measure and cut chain to length, remove and replace chain.

Clean off all of the mating surfaces, ball nut to z axis head, z axis servo bridge to z axis head.

Put it all back together. Don't forget the grease or oil zerk fitting for the ball nut! make sure the ball screw nut is set in that there is not space between the z axis servo bridge and column when you tighten the bolts down, rotate screw to seat it.

turn on machine, e stop off, clear door, enter jog mode and move head up, remove blocking.

Align markers and cold start.

All done.

[Scott_bob]

What are some of your ideas on this subject:

What are some ways to minimize counterweight swing (and bumping inside the mast)?
The faster your machine the worse this is... Especially when peck drilling...
I really hate to hear the sound of that weight banging around in there. Theres gotta be an easy way to elimininate the swing without creating too much drag.

For instance I thought about attaching some guide rods say 3/8" diameter up and down the front and back. These would be flexible to the bumping force of the counter weight, and being round would not create much drag.

What do you think?

[nervis1]

I've never had the weight hit anything. I only have 400 ipm rapids and a standard 20" z though.

On some big machine with extended z moving 700ipm I could see how that thing might get swinging.

An easy way to dampen the swing would be to put a container of water attached to the top of the weight, say 2-3 gallons in a tupperware (half full to allow the water to slosh back and forth opposite to the swing of the weight) container zip tie it to the chain. Super cheap, and I bet it would stop the swinging. Maybe use a capful of bleach in the water to make sure it would not rot.

[TR MFG]

I tapped a hole in the bottom of the counter weight, ran a rubber strap from it to a tapped hole in the base. Worked great, no more banging around in the mast. i was later told that it voided the machines warranty, as did overriding the door interlocks.

[MidfieldJake]

I tapped a hole in the bottom of the counter weight, ran a rubber strap from it to a tapped hole in the base. Worked great, no more banging around in the mast. i was later told that it voided the machines warranty, as did overriding the door interlocks.

OH, so you're a "rebel" ??? LMAO