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FP4NC "Z" axis repairs (Noisy movement)

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Like to open by saying that this is a bit of a tale...took me several weeks to resolve the initial issue.
Trying to give the highlights here in the hopes that some of this might be of use to others.
If you are not of a sort to read through an extended post, my advice is to wait till it reaches conclusion and simply jump to the final bit and avid the drivel in between.

Further, the details here may be specific to the FP4NC's...There are detail differences to the smaller versions. (FP2NC,FP3NC)

"The Plot" ;
Number of weeks back, i returned to work after a weekend off...Turned on the control of my "non flip" FP4NC in preparation for the weeks work...lots of projects waiting.
Machine powered up fine..all seemed normal till it came time to move the slides around.....
To my dismay, moving the "Z" axis (vertical) was now uncomfortably noisy! Any movement made a LOUD rumbling sound...Rough and i could also feel the entire machine
vibrating with the move....Did not remember this condition when i shut the machine down the previous Friday...Somethings not right. The noise is bad enough that it makes me
believe that it is damaging something....Just have to solve this...it makes me quite uncomfortable!
Did a little testing. The noise was directly proportional to the speed of the slide movement. Move faster and the frequency of the noise went up...Sound was also somewhat different depending on
weather the slide was going up or down. Further the volume seemed to lessen as did the felt vibrations if the move was fast....

My first inclination was to jump toward the worst case...These machines have a tendency to have vertical way issues....My initial guess was that there was a failure of lube or it
swallowed some chips of swarf ...and there was some sort of stiction causing a judder in the movement.(stick slip). In hind sight that was not really the indication , as the
noise was consistent over the full length of the way surface, Looking back i think this would have been unlikely if the issue was with the sliding surfaces...
However, i spent several hours loosening the rear keeper plate gibs as well as backing out the side tapered gib for the vertical slides...Liberally applying way oil to all surfaces and testing
the movement...Result is that the noise was the same...no change.

OK so I feel a bit relieved...no issue with the gibs or ways....This is good, but i still have this noise.
A small voice in my head was telling me something that a "professional" Deckel guy had told me years back. "If you get a rumbling sound from the "Z" axis when moving its the thrust bearing on the screw...


Chapter One: "The Screw"
So seems like i need to do a major service on the elevating screw assembly and replace the thrust bearings...
I have been here before on my home FP3NC , and when i repaired the vertical ways some years back, so i had a pretty good idea of the steps required.

First off i removed both the side panels (hand wheels removed) I also removed the chip pan. This is not required, but it gives better access to the screw assembly and just makes the job easier.

Positioned the vertical slide (Z) almost all the way up, and set blocking under the slide , then used the MPG to lower the slide on to the block to take the load. This is critical....you must support the slide to
prevent it from falling down when the belt is removed from the axis servo. In normal use the servo holds the slide position through a magnetic brake that is released when power is applied....

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While i am here, i also unbolted the hand wheel mount for the "Z" axis and pulled it out...freeing the servo from the hand wheel drive shaft....The interlock switch and cables have enough slack to allow
this as shown...

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I removed the chip guard plate that fits on the "Z" slide and covers the upper way cover. (sorry no photo) Once this cover is removed it exposes a hole and rubber plug in the top surface of the
upper keeper plate gib.
Photo below shows the hole with plug removed. The hole allows access to a hidden Allen bolt below that secures the top of the screw to the vertical slide. This bolt is only removable by taking the
"X" slide off the machine.
The brass piece visible here is a formed sheet (springy) that helps apply better pressure to the way wiper . Pretty sure this is exclusive on the FP4NC's....

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The "X" slide is positioned to line up the hole with the bolt below....

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Once positioned correctly , an Allen wrench can be inserted and the bolt below can be loosened...Do not attempt to unscrew the bolt fully at this point (more on
this later). Simply unscrew the bolt several turns.

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Stay tuned...lots more to follow....Reached my photo limit for this post....
Cheers Ross
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
With the screw retaining bolt loose, its time to deal with the servo and its drive belt.
I removed the 4 flange bolts from the base of the servo to allow it to move enough so that the belt can be removed from the pulley on the bottom of the screw....
Bolts out, push the servo fully toward the machine frame...The servo is located by two pins sticking up from the machine where the servo mounts..The pins engage a slot that
locates the servo in one direction, but allows it to slide toward or away from the machine frame....The holes in the servo flange are large enough to allow for tightening the belt once it is fully on the pulleys.
Care must be used when installing the cog belt on assembly to be sure its engaged fully in the drive notches.....

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With the servo loose its time to get the belt off the screw pulley.....
Access is through a window on the side of the machine base.....Normally covered with a sheet metal cover that is held in place with snap in tabs....
If you look closely at the poor photo the cover is just seen toward the upper right laying on the base of the machine.

Be aware here that this is likely the nastiest part of your machine!!! Used way oil from the screw eventually finds its way into this space..that coupled with remnants of rubber off the belt and you have a slimy mess.

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Once the belt is off the screw pulley, its time to remove the assembly from the machine.
The screw base casting is held by 4 bolts through the base flange, along with two tapered dowels. Dowels are blind so they are provided with a thread to allow extraction....
These dowels are the only locating feature for the screw and are important for proper screw alignment.
Of the 4 bolts, 3 are counter bored Allens. One on the left side rear is an extended hex bolt that doubles as a limit stop for the slide....
In addition before removing the screw you need to retract teh spiral steel outer cover....With some effort its possible to pull the shield down and hold it compressed by fitting a 6mm bolt into a threaded hole in the screw
support .(provided for this very purpose)

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With the belt off and the cover pulled down, you can use your hands to turn the assembly and lower the screw....Remember that you did not fully unscrew the Allen bolt at the top . you
must loosen the bolt as you lower the screw....
The top of the screw is located by a key (pin) that prevents its rotation until it has been lowered enough to escape the pin and upper Allen bolt.

With the screw lowered you can then tip the top of the screw forward to clear the vertical casting (this is why you need the slide positioned high in its travel) ,then carefully lift the entire assembly out of the machine.
Use care here as the pulley has a retaining flange that can be damaged when lifting it out of the base clearance hole....

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Also visible here are the two catch trays (plastic) that are mounted below the box ways to catch the way lube run off...
These need to be removed prior to removing the screw assembly.....

Here is the entire screw assembly after removal....

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More to follow.....
Cheers Ross
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Photo above shows the elevating screw assembly. The lower portion (seen to the left) is stationary and is bolted to the machine base casting by a flange.

The thrust portion lives jsut above the right end (as shown) of the compressed spring cover(blued steel)
Above the step is an extension that rotates and holds the ball screw nut at the top.
There is a large ball bearing below the flange that takes the side thrust from the belt.
There is the cog pulley and as seen the screw (down) extends to the left....

Details:
Thrust bearing (left of the dark line) and retracted spring cover with the holding bolt.....

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Shot of the drive pulley...4 Allens in the pulley face pull up on a tapered collar that tightens up on the rotating portion of the assembly..sort of like a collet.
Allows securing the pulley drive to the assembly and positioning for good belt alignment...(up or down)

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Photo shows the bearings in the elevating assembly. Two ball bearings and a roller thrust bearing...
Of note here is that the thrust roller set is a full compliment setup...should be replaced by the same.

All the bearings were sourced locally with one exception....One side of the thrust bearing thrust face (the flat washer part) is Deckel specific....not a generic thrust plate.
one side is flat as one might expect, where the rollers run. But the opposite face has a locating shoulder that actually carries the bearing.

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I sent the special thrust bearing to my friend ,Jim Dour at Mega Cycle cams, and he lapped the flat face true on his "Lappmaster"..making it flat and smooth....
but i still needed to be sure that the refinished flat was still true to the original register step.

Some careful indicating showed that indeed the two surfaces were no longer planer...a problem that i needed to address....

Call for the Myford.....
So i fired up my little Myford grinder...set it up with a chuck in the work head.
Gripped a piece of stock in the chuck that had a tapped hole in its center.....
Ground a shoulder with a true face, done using the side of the wheel......

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Once that was done I setup the thrust bearing, seating the lapped flat face against the just ground face on the tool....The part was held using a washer and center bolt in the tool threads....

The step was then trued flat using the side of the wheel....

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Stay tuned...
Cheers Ross

...
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
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With the thrust bearing made flat, i tested for truth....no detectable run out as best i could gauge....ready fro assembly....

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The assembly is pretty straight forward from here...Replace the ball bearings and fit the thrust bearing....
You do need to set some slight preload on the thrust....accomplished with shims or as in my machine's case an adjusting nut.
Preload should be somewhere around 1-2 '# to rotate the assembly...Just need enough to assure that the thrust is in slight tension and has no slop....

Since i had all this apart, I opted to re-ball the screw.
Ordered a number of different sized balls form "BalTek" and i used the balls starting small and working up till i got a good feel for the fit. I am told that the sizes in the nut/ball assembly are near impossible to accurately gauge
in the normal shop environment, and that the most effective method of sizing the balls is to work up is very small increments till you get an assembly that has light resistance when fitted to the nut without preload.

I use grade 25 balls. That means they are round and sized within 25 millionths.....And i buy sizes for this screw at around .125"
Here is the size i ended up using.....

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The screws that Deckel used do not have external return circuits on the nuts, so the re-ball is a bit more tedious.
I apply a light coat of grease to the tracks inside the nut...then carefully place the balls into the tracks being careful to fully fill each ....
To fit the screw, I make a mandrel (delrin) that is the same OD as the minor diameter of the ball track in the screw.
The mandrel is longer than the nut and has a good square end.
Mandrel is carefully inserted into the ball loaded nut...which keeps the balls in heir tracks.....it will also tell you if you have too many balls in any track as it won't slide in.
I Start the screw into the nut and begin turning the nut to engage the balls, while keeping the mandrel butted to the end of the screw...as the screw starts i allow the mandrel to follow it and be eventually pushed
out of the nut...If there is any problem starting the screw, is reevaluate and start over....

Some shots of the screw....

Top end showing the collar held in place with snap ring and in that collar the notch for the key (pin) to prevent rotation. Bolts hold the nut to the top of the elevating assembly extension.
O ring is there to seal off the collar so that the pressure lube is directed down the screw...Also keeps coolant from above out....
Center threads for the retaining upper Allen bolt shown.

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Screw complete...oval on the side of the nut is milled window where the internal return ramp fits...Installed from inside the nut....
Also of note here is that the "Z" nut is one piece...has no ability to adjust for backlash.
The other ball screw nuts on the machine are made in two pieces...joined in the center using a cute little differential spline coupling that allows shifting one hut half from the other by small amount of rotation,
thereby working one half against the other and giving the nut preload...fully adjustable...

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Ok so i completed all the above repair work....installed all the parts and returned the machine to service, full of positive expectations....
To my surprise and grief...the original problem, the killer noise was still there....
Perhaps the tome and volume was a bit different, but i had not repaired the initial problem...Crap!

Signing out for now...but there is more. :sleepy:
Cheers Ross
 

rklopp

Diamond
Joined
Feb 27, 2001
Location
Redwood City, CA USA
FP4NC "Z" axis repairs (Noisy movement)

I am a bit confused. If the thrust bearing is preloaded, it must be preloaded against another bearing, or Deckel violated Newton’s laws. What is reacting the thrust bearing preload?


Sent from my iPhone using Tapatalk
 

TNB

Stainless
Joined
Aug 18, 2002
Location
France
Could it be a bi-directionnal thrust bearing with a main ring (the one with the locating shoulder) supporting two rows of balls ? One on the upper side, and one underneath.
 

Kees

Hot Rolled
Joined
Feb 2, 2007
Location
Netherlands
Mechanical wear does not come suddenly but electronics do. Turning off a perfektly working machine, switching it on and it has a defekt. So I would check the controller boards involved in moving the Z-axis first.
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Rich:
Thrust bearing is in opposition to the large deep groove bearing at the lower end of the assembly...just next to the drive pulley.

Kees:
Your observation is germane. Had trouble thinking electronics because of the severity of the noise and vibration....hard to believe anything electronic would cause this...
And to say that the machine was "perfect" when shut down might be a stretch...None of these machines at this age are "perfect"
Cheers Ross
 

J Geisler

Plastic
Joined
Aug 12, 2007
Location
Melbourne Australia
Hi Ross,

This is interesting and relevant to me as of last night...

Overview
I have just (this weekend just gone) had power board repaired on a 'dead in the water' FP3NC.
Came out of a university and in my estimation, presents well and hasn't been really worked that much as one would expect with that history.
Machine was acquired a while ago with the above fault existing in a non operational form.
Until it lit up and gave me a readout on the monitor I had no way of qualifying or checking the rest of the machine.
It now powers up and is happy in all modes.
The spindle gears all select when asked and it runs quiet thru all speeds and the tool release is working as it should.

My issue..
On to moving the slides via the electronic handwheel, all behave except the Z.
Your noisy Z description matches mine to the letter...!
I initially pulled down the sprung screw cover and simply inspected the condition of the screw, everything looked tidy and clean, nothing that would suggest a mechanical breakdown of the ball screw that would befit the 'noise'.
The sprung cover plate in the base was removed and the condition of the drive belt and pulleys is tip top.
My next thought was to prop the table and remove this drive belt and run the drive motor to start a process of elimination.
My question..
At any point, while having your belt removed, did you run the drive motor?

Best Regards
J Geisler
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
OK...So i intended to continue this saga some and detail some of my guesses at solving this problem.
The idea was to provide a bit of humor at my expense...having been led down the rabbit hole of looking for the issue when all along it was staring me right in the face.

Totally lost sight of "Occam's Razor"....lesson learned the hard way after a number of other repair tries finally went back to the basicsd with some encouragement from the helpful members of this board (thanks
Mudd and Colt45)

Turns out my issue was the servo tachometer!!!!!!!!!!!!!!
I know about these little devils..and that they can have issues from dirt and contamination...but never would have believed that the tach could have caused the severity of noise and vibration that
i was getting.....

My belief now in hindsight is that the tach was outputting a ragged signal and the servo was attempting to follow the uneven output, causing the motor to accel/deccel and hence the slide was doing the same...
giving the noise and vibration.....

So before doing any further disassembly, clean your "Z" tach....Simpler to do....Just need to remove the hand wheel gear box from the top of the servo...
Use clean wipes or cotton swabs and alcohol wipe the tach commutator while the seervo is in motion (mode 6 relatively low feed rate) Repeat till the wipe comes up clean...

As an aside, don't think you can just run the servo with the belt disconnected....control needs some feedback (scale) for any commanded move.
Cheers Ross
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Well to be precise the electronics were working perfectly....
The problem here was "electro -mechanical"...The solution was turning the commutator of the tach....(a mechanical solution)
But i understand you point....
Your idea that things that were working , then turned off and upon restart had problems would not indicate a mechanical problem...All i can say to that is you most likely have not spent much time around
old cars ...I see stuff like this on a regular basis....
Cheers Ross
 

J Geisler

Plastic
Joined
Aug 12, 2007
Location
Melbourne Australia
To follow up here...

Convinced it was an electrical issue my end, because as stated, all mechanical elements were presenting in tip top shape, I did turn my attention to that.
Nevertheless, it began with my question on this forum regarding running the drive without the belt.
To be specific, at that point, it was just a question, I didn't get ahead by trying first and asking later..
My concern was that it would send a conflicting signal to the scale but the actual table had not moved, causing a positional / scale / drive conflict...hence the hesitation.
On the basis of your post which highlighted your ultimate solution (of cleaning the tachogenerator commutator and brushes) I dismantled the Z axis handwheel drive and removed the housing containing the manual feed right angle gearbox that sits on the top of the tachogenerator which itself sits on top of the drive motor.
First impression was that it looked fairly tidy and clean.
As you did, I ran it in a slow feed and watched...the brushes did seem to reflect the action / noise of the table movement.
Removing the 2 screws that hold the housing that the carbon brushes are stationed in gave me full access to clean the commutator and the brushes.
The main point of my follow up is to mention that not a lot of build up came off the components that I cleaned with isopropyl and a white cloth.
HOWEVER, once reassembled, the issue was completely resolved!
Ostensibly, the small amount of carbon dust that was built up as residue had brought my machine to its knees..
If you had first heard the racket that it was producing, you definitely could've been forgiven for thinking it was a mechanical / slideway / ball-screw / preload issue.
So, many thanks to Ross for leading the way on this one (also, as suggested, to Mudd and Colt45) .

Quite relieved and satisfied this end.

Regards,
Jesse
 

Colt45

Hot Rolled
Joined
Nov 27, 2004
Location
SLC, UT
If it makes you guys feel any better-

Whenever I have a problem with one of my FP4Ncs (fairly rare event, but it happens occasionally), I tend to imagine the most complicated, expensive, difficult and time consuming repair possible and head directly there. 9 times out of ten, it ends up being something pretty simple, like replacing the batteries or cleaning the tachs in this story.


Overall, it seems the 35 year old electronics are the biggest weakness of these machines, yet they really aren't that difficult to keep going, (once you kind of know your way around) and the machines still deliver excellent performance. :cheers:
 

Kees

Hot Rolled
Joined
Feb 2, 2007
Location
Netherlands
All i can say to that is you most likely have not spent much time around
old cars

No I don't.But I do work a lot on older production-lines/machines in various branches of industry. Over the years I developed some kind of "feeling" in what direction the cause of an error/defekt could be found.
 

Fastguido

Aluminum
Joined
Nov 20, 2003
Location
Reno,Nevada USA
On my 2NC, if the machine sets for any length of time (like a month)I have to clean the "Z" tach, because of the noise. It is very weird, maybe mad that I am not using her. There will be no noise when I shut it off, come back a month later, Noise! I am starting think that the brushes are soft from age?, because of the amount of carbon on the tach from not much usage. I am using 99% isopropyl alcohol to clean the carbon off. Never a problem on the other axis's, always the "Z".
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
Fast:
If your machine has handwheels, there is grease or oil or both in the gear box above the tach...
Might look at the condition of the seal on the shaft...maybe it is hard and not sealing well enough and letting contamination form above enter.
Cheers Ross
 

Fastguido

Aluminum
Joined
Nov 20, 2003
Location
Reno,Nevada USA
Thanks Ross, I will check it out. I did clean off the universal joint thing above of grease to see if it was the cause, (Was thinking it was flinging off to the commutator below),but no did the same thing, so I relubed with very little grease. I will check out the seal in the gear box.
 

AlfaGTA

Diamond
Joined
Dec 13, 2002
Location
Benicia California USA
The "Z" is the only servo that sits vertical...having the Tach above the servo....
That "Z" lives is a harsh environment...lots of crud below...Oil and "goo" collect below the servo. Runoff from the "Z" axis ball screw and thrust....mix with dust off the drive belt and you get
some serious "YUK" down there....Need to clean this area out form time to time....
There is no real seal between teh bottom of the servo and the tach...Top servo bearing is (if original) a shielded bearing...I replace with sealed bearings...might help keep the "bad Vapors"
from getting through and settling on the tach...just a thought.

Side note...all the bearing replacement on my FP4NC's "Z" axis had one positive effect...Machine now moves smoother than i can remember and is much quieter than before the tach issue cropped up.
So there was some positive result from changing all the mechanical parts....

Cheers Ross
 








 
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