Z Axis won't go all the way down!!!, Yikes!!!

[Chuck Keysor]

Hello Shopbot friends....

I have been cutting out 6 plastic bezels and suddenly my spindle won't plunge down all the way. (5 x 12 PRT alpha, 2004, 5hp Columbo spindle)

Yesterday, using scrap material, I cut out one part using first a 1/4th inch end mill, then cleaned up some tight corners with a 1/8th inch end mill. Everything was fine.

Today I nested the design to cut 6 pieces from the customer supplied ABS. All the cuts using the 1/4 inch end mill worked fine. I changed the collet and bit to use the same 1/8th inch end mill that I used yesterday, and then tried to use the C2 command to re-zero with the new bit....

I heard a funny sound, like an old coffee pot percolating, with some vibrating spring noise, and then got an error message on my screen, asking me if I should abort. I turned everything off, then back on and repeated the procedure, with the same results!

I turned off the Bot, unplugged the Z axis stepper motor cable, and tried to manually move the spindle down, and it would not go down as far as it should! There is 4.5 inches of rack left above the Z pinion when the spindle simply won't go any farther! I can't see any mechanical restrictions, and mind you, doing the exact same operation yesterday, I had NO problem.

The only thing different today, is that there are black chips of ABS all over (no dust collection). I looked at the clock, to call Shopbot, and it was a minute after 4pm Chicago time.... I called anyway, but got the message they are closed.... And my customer is coming at 5:30 to get his parts! Yikes..... What do I do? (I will copy this, and paste this message on the Shopbot help site.)

Thanks, Chuck

[Brady Watson]

Turn off the control box and push the Z all the way down as far as it will go by hand. See if it goes as far as you think it should.

-B

[Chuck Keysor]

Brady, I turned off the control box and disconnected the Z axis stepper cable, and pushed it down as far as it would go, and with the bit installed, the tip of the bit comes maybe to within .6 inches from the table top. It is in that condition that there is about 4.5" from the Z pinion, to the top of the Z rack.

IE, I can not push the spindle down as far as it should go, with the control box off, and the Z motor cable unplugged.

I got out my old chisels, and actually finished the parts by hand, and I just got done. So the immediate crisis is averted. But that still leaves me with an out of order Bot..... Thanks, Chuck

[Brady Watson]

I've seen this before on certain model tools where the Z doesn't touch the spoilboard with short tools. An easy remedy is to slap another sheet of 3/4" material on top of your existing layup and get all the way down. The other thing you can do is remove the stop bolt from the Z as long as you have enough rail and rack to go the distance.

Since this is a PRT, the Z should have 3 possible positions where the Z tower bolts to the Y car. It can be raised or lowered depending on your needs in 1.5 or 2" increments. Look on the 2x2 Z-tower tubes for the 5/8" holes I am referring to.

-B

[Chuck Keysor]

Thanks Brady. I'll play with this and see what works.....

My customer looked at my Z rack and pinion, and said, gee, there is a lot of grease in here, maybe there are hard chunks. I said this is all just soft grease, and it wouldn't block the motor. He picked out some of the goo from the rack and pinion, and we tried to zero the bit, and suddenly it zeroed. I feel I am on the very ragged edge of not working and he got lucky, as removing a little grease could not have jammed the Z servo.

He suggested that I remove the rack and pinion to carefully clean them. That didn't look very easy, without taking apart the Z-car and having to re-align my spindle. I can get in there somehow and clean out the grease and re-grease it. It can't hurt, but I don't think that is my problem.

Intuitively, the two springs on the Z car should only counter-act the weight of the spindle and the supporting mechanisms, so that they are effectively without weight, making it easy for the servo to move the Z car up and down. Yet when we had zeroed the bit successfully, I shut down the Bot's control box, and when the servo lost power, the spindle/Z car popped up maybe a full inch. This clearly showed that the springs had extended beyond their linear range, and were in fact exerting a significant upwards force, which is what had previously jammed the Z servo.


While I have never had this happen before, I have had a number of times where I have maxed out in the upwards range of travel in the Z axis, because I have thick material and a long bit. Though in those cases, I may have hit mechanical stops, as opposed to fighting the springs which I am doing in today's problem.......... Sorry, a bit of a digression.

Thanks, Chuck

[wayne_walker]

Chuck,

I have had an issue like you are describing.

You mentioned that you removed some of the excess grease and were able to get it to Z zero. There may of been a clump, lump, or whatever in the grease to cause it to stop the Z from going down.

I cut ABS plastic and use air blowing on the bit to keep it from melting back into the cut. I have had a chip get blown between the Z roller and the slide. This kept it from going all of the way down. It took me a couple of hours to finally determine the problem.

I am running a PRT with a PC router.

Hope this helps you out.

Wayne

[barrowj]

Chuck,

When I read your post mentioning the ABS and chips, my first thought was that a chip or chips has gotten in the grease and stuck in the rack. I would thoroughly clean the rack and pinion, even check the pinion to be sure it is not chipped. I have been cutting some acrylic and when I see the chips flying I thought of that. I have been really checking to be sure those chips don't get into places I can't reach and now I will be much more careful. Good Luck.

[Brady Watson]

Remove the top stop bolt & lift the entire t-rail and spindle straight up and out of the Z tower. Then clean away...

Cleaning that rack & keeping it properly lubed is normal maintenance on these machines. Do that first and see if it clears up.

-B

[Chuck Keysor]

Thanks Wayne, Joe and Brady. I guess my path is clear. I haven't gotten back to fix this, (because I have been painting by hand three 4 x 8 signs I carved, what a black hole of time....)

Brady, if I pull out the spindle, I'm going to have to re-plumb my spindle... I have only done this once, when I reassembled my Bot in my shop. It was a really long, tedious, and hard to do process. I finally got it right, as evidenced by the smooth cuts I get when resurfacing my spoilboard with my 2 1/2 Amana planing bit. But I'd love to avoid that if possible..... Isn't it possible to reach down in with brushes and degreaser to clean out the rack and pinion? Or am I confused because I am not clearly understanding or recalling?

Thanks, Chuck

[kerrazy]

Brady is correct,
You are simply going to remove the whole component by going up the rack and off.
You then clean your rack and don't grease it crazy heavy. It does not need it, all it does is allow chips and dust to stick and cause problems. A very thin coat is all that is required, it is better to do it more often than deal wit a damaged tool.

Then gently slide your spindle car back on and be careful to let the car engage on its own the pinion and z rack.
You should not have lost your plumb, as the spindle was never removed from the z car. Now of course a test with a thin surfacing or the old wrench in the collet trick will answer that real fast.

[Brady Watson]

Chuck,
There is no need to re-plumb your Z. Do not touch any of the V-roller bearings. Pull the t-rail and clean it properly. You can pull it out from the top, but you'll have to unbolt the lower spring perch from the bottom of the t-rail or from the bottom after pulling the springs off of the lower perch. Either case, you have to remove the stop bolt from the back side of the Z.

Squirting solvent in there is the diet coke version of proper maintenance on these machines...so I will not advise it. As a professional SB tech I would never do that sort of thing on a customer's machine. It would be disassembled, cleaned and lubed along with a pinion change. Same with my own tool - there are times when I cannot afford a breakdown or problem - so proper maintenance - which really isn't much on these tools - is in order to avoid shooting myself in the foot down the road.

Hook yourself up & do it right.

-B

[barrowj]

Just a quick question on this process since I have not done it to one with a Spindle, I have a 3hp Colombo and my question is with the weight, should I have help. Any other advise?

[Brady Watson]

A healthy man should be able to lift off any router or spindle on these tools. The Colombo 5hp is around 40#, the 3hp somewhere around 25#. Just watch your wires and strain relief when pulling out from the bottom. Have a block of wood or something available (a 6x6 is nice) for laying the spindle & t-rail on while servicing. While you're in there, scrape & clean the inside of the Z-tower near the pinion gear. Inspect & replace especially if you do a lot of 3D work.

Extra points cleaning the entire machine. Excess grease comes off with denatured alky (avoid acetone or MEK); a round fuzzy brush on the end of the shopvac for getting all the fine dust off; a brass el-cheapo wire brush for raking out the dust/grease that is hardened in the gears; automotive type instant detailer (Mothers, Maguires) is nice for wiping the whole machine down to make it look new again.

Motor shafts and pinions should not have a taffy-like sawdust grease donut slapping around on them...

CNCs aren't cheap. If you clean it once in a while, it'll make you feel good & the tool will run better with fresh lube and clean moving parts.

-B

[Chuck Keysor]

Hello Brady! Thanks for your detailed instructions, and I PLEDGE that I will remove the Z car assembly and clean it and inspect it! I'll do that next week, right after the election.

(I have gotten caught up in the elections, because a friend of mine is running for the Illinois House of Representatives. I made three 4 foot by 8 foot signs for him (another post). City inspectors called late yesterday, and made us move one sign back by THREE inches!)

Thanks again for the advise and encouragement, Chuck

[myxpykalix]

City inspectors called late yesterday, and made us move one sign back by THREE inches!)

They wouldn't feel as if they were doing their job unless they gave you a hard time....:mad: