Mechanical backlash causes and solutions - vf0e

M K · Nov 23, 2020

Hi

I have a 2000 haas vf0e and I’m trying to gauge info on bringing it back into spec with tolerances

I’ve owned it around 15 months and it’s a good machine but although the electronic back lash is acceptable, between 2 & 5 microns in X & Y, the mechanical slop Is quite bad!

My cause for concern is recently is started to wonder off of its datum when I set say g54 x0 y0, on a Piece in a Collet block then run 8 parts for example, if I then check the g54 with a dial indicator and gauge pin the g54 is now off in X normally by around 0.02mm or 0.03mm and
In Y about 0.010mm

If I put a dial indicator and mag base on the table and zero off the spindle collar then grab the table to try and move it I can move it approx 50 microns (0.050mm)in Y + & -, and in the X axis I can move it approx 20 microns (0.020mm) in + & -,

I believe anything over 0.005mm is out of spec

Now I know they are old worn machines now but what is the most likely cause for this mechanical slop?

Would it be best to replace both X & Y ball screws nuts and
Thrust bearings? And the oil lube lines whilst I’m in there,

Any idea if the parts are still available? I’m in the UK

Thanks
Marc

Milland · Nov 23, 2020

I haven't done it myself, but you could try pulling the way covers to expose the ballscrews, then push the tables while having a test indicator needle on the ballscrew thread (as high on the profile is will be reliably in contact) and look for excess motion there. That would be for the thrust bearing looseness, which is more likely IMO than ballscrew nut movement.

But if the screws don't move, then it's either the ball nut or the mounting bolts that hold it to the table.

In some odd situations you could have really worn linear ways causing excess motion, but that would tend to be lateral to the screws themselves and pretty easy to notice.

countryguy · Nov 23, 2020

Hi MK,
There is a lot of good information in the archives here for the items your mentioning. Definitely worth wading around the archives of this forum before getting into the tools-in-hand mode IMO. Essentially, we did 2 of the 3 on our 98 VF/4. The thrust bearings and the end-screw mount bearing. (it was $10). Plus the I did the flow restrictors. My posts are in here and I reference all the docs I used. The screw nuts were not needed on mine and I'm not sure we could have done it anyway, Upon our efforts and completion, we put our X backlash mechanical at a lonely ten. (.0001) We're about 2 Y and 1 for Z. Overall, the process is not to hard at all.

tip: w/ the way covers off.... do the wiper rubber replace if needed IMO. We pulled all the rust off and greased and put in the w/ new rubber. While in bowels of your beast- Check the oil lines for rub wear and clean the switches for home. (we did all these)

Hope this helps some..

BGL · Nov 24, 2020

As countryguy said, #1 suspect are thrust bearings.

countryguy · Nov 24, 2020

Our thrust bearing came out and felt like a worn lawnmower wheel! It was bad! . The cost was $350 US if I recall. No core charge.

Delw · Nov 24, 2020

as others have said thrust bearings. thrust bearings are like trailer bearings they very rarely get checked or replaced. it will clean up most of your issue if not all. balls screws and nuts do go bad however.

M K · Nov 24, 2020

Thanks for all the reply’s

So are the thrust washers on the servo motor side?

Is there a guide anywhere to checking and changing them?

Thanks
Marc

countryguy · Nov 25, 2020

Find my posts from a few months ago... it's all in there is the best way to proceed.
Plus the Haas DIY site has instructions (which I have the links too in that post). Thjere are a lot of others too.
Use the search Forum feature and do Haas Thrust Washer. It's more a unit than a washer. :-)

M K said:
Thanks for all the reply’s

So are the thrust washers on the servo motor side?

Is there a guide anywhere to checking and changing them?

Thanks
Marc

M K · Nov 27, 2020

Thanks

I searched some old post for the info,

I have removed all the covers on the X axis and got to the thrust bearing nut and I managed to tighten it another 1/3 or a turn! The ballscrew still turns freely by hand so it’s not too tight but in doing so I have kinked the flex pack in the couple a bit

Here’s photos of the flex pack shims before and after tightening

I ran out of time to test if this helped the mechanical back lash in x or has now made it worse so will check today

I am also waiting on Haas uk to come pack with a price for the bearing kits and new flex couplers

I done a 12” sweep test on the table to check my issue as someone said the head could be wonky but on a 12” sweep, indicator base mounted to spindle nose it’s maximum of 0.0127 for I think is great for such an old machine

I want to check the Oiler’s too as mentioned while in there, is there a way to directly activate the pump so you can see the oil coming through the lines?

Thanks
Marc

BGL · Nov 27, 2020

Simply tightening may fix the symptom, certainly worth verifying but do not consider it done.

Disassemble, clean and inspect the thrust bearing pack. If you have the needle bearing type its a simple task, something like $20, two washers and the bearing.
The later models are preset bearing packs and to my knowledge not an easy item to service but they are alleged to be maintenance free. It will be obvious once apart what type you have. If you can afford it the newer type are worth the investment. I'm cheap and only put one on the Z axis.

If you do not have them you should invest in a pair of hook spanner wrenches - worth every penny. 32mm I believe?

DO NOT loosen the four flex coupling bolts! There is no need to.

Referencing your picture.
Sequence:
- Loosen coupling split nut bolt. [To the right, yellow paint marked one, clue it may not have been apart since new]
- Remove four bolts holding servo
- Pull out servo [mind the key!]
- Make a note of the couplings axial position from the left [just to be sure]
- Loosen split clamp bolt on ball screw, pull off [mind the key!]
- Loosen locknuts and remove
- Remove four bolts to thrust pack
- Pull out, keep track of the parts order
- Wash parts in solvent and inspect
- Lube with fresh grease and reassemble [new bolts, blue loctite on split collar bolts]

EDIT: Looking again you can likely just loosen the bolt to the split clamp on the left, remove servo bolts and pull the servo with the coupling in place.

If the later style ball bearing pair all you can do is check condition. I believe they are sealed bearings. Best case they are fine and only needed an adjustment.
Kind of a long way to find out but now you know what they are and what to do.

Reassemble with locknuts just snug, attach coupling on with key to use as knob. Use indicator on the end while push pull on the table. You should be able to get zero but smooth rotation. Just a touch tighter and your good. Use careful judgement. Too tight is obvious.

There is a procedure for setting the parameters for backlash - worth the time once you have done this to the three axis. Do you have a service manual?

Getting the servo back in without loosing the key can be a pain without help. I radiused the leading and a drop of superglue to hold in place.

Disclosure - This is all from memory so stare at it a bit before taking it word for word.

Oiler - Just pull up on the knob on the reservoir, Depending on the position of the cam this can be a long or short motion. Note pressure on gauge, It should go up to I believe 60? and slowly drop. This age a machine I would definitely R&R the filter and clean out the reservoir. I replaced my way lube with 10w 30 mobil one a while back and have no regrets. Mobil one will not have the wax buildup way lube has.

Hope this helps - good luck!

Milland · Nov 27, 2020

You really should verify that not only is your Bijur building pressure at the tank manifold, but that the hoses and and any restrictors are in good shape and not plugged or cracked.

I had a cracked nylon line for my "Y" lube in an older VF-2, but fortunately it didn't seem to have been like that for enough to have starved the bearings for too long.

M K · Nov 27, 2020

Hi

Thanks for the reply’s

The bijur reaches 60psi pressure, I removed and cleaned off the filter as I don’t have a new 1 yet, the lines and system seems to be working fine.

After
Tightening up the split nuts all round on the thrust bearings or bearing packs (still not sure which I have) I put a round mag base on the table and indicated to less that 0.0127mm, I set g54 to zero and user position to zero

I then hit g28 home and then mdi g54, G0 x0. Y0. And did this several times eventually stopping at g54 and the
Jogging back down to z 0. The result is almost perfect but I still have an issue

If I then put a mag base on the table and zero to the spindle column then Set the jog Handwheel to 0.1mm and jog the Y axis 0.3 then the dial shows 0.36mm !!! If I do 6 clicks it should be at 0.6mm but it shows 0.7mm

So if I’m seeing backlash error here why don’t I see it when I clock a test piece and rapid the table back to home then back to g54?

Am I missing something?

M K · Nov 27, 2020

I also got a Price from Haas UK

They don’t sell the thrust washer sets now, they are the prepacked seal kit type,

For 2 bearing packs
2 support bearings
2 flex couplers

£1230 + vat

If the ballscrew & nuts are bad it’s another £2550 + vat but if I did need them I’d get them from a specialist elsewhere

M K · Nov 27, 2020

I downloaded the service manual but it doesn’t say how to adjust the backlash

Do anybody have a link to how

Thanks
Marc

BGL · Nov 29, 2020

"So if I’m seeing backlash error here why don’t I see it when I clock a test piece and rapid the table back to home then back to g54?"

A commanded movement uses the backlash compensation from the parameter for each axis. Parameters 13, 27, and 41.

Chapter 3.3 page 13.
https://staging-diy.haascnc.com/sit...6-7045_English_November_26_1993.pdf?0=%3F2340

There is a difference between backlash with power on and power off. Try it and see, the axis load will increase as you push against it. Get the axis backlash the best you can with power off then use the parameters. It can be tedious as there is a tipping point, creep up to it then back off. There is a reason it's called 'Compensation'.
A combination of mechanical adjustment and parameters settings gets the machine to its best.

In your case I would not invest in parts until physically inspecting and tuning is exhausted. If you have the flat roller washers in your machine and they need replacing, any competent bearing supply house will have them, I got mine from McMaster-Carr.

<Pause to reread original post>

Wait a millimeter!
You said 0.005mm is out of spec. Here is what peeves me off! Mixed units. Not your fault. 0.005mm = 0.000197".

Allow me to set you right. It is a twenty year old Haas machine tool. It's like saying your 1980 MG Triumph Spitfire uses more oil than your 1990 Acura.

Put the covers back on. Put the indicator away - make parts. If they don't meet your tolerances make other compensation such as tooling, tool path, workholding.

magno_grail · Nov 30, 2020

If you still have the needle thrust bearings it is worthwhile to replace them with the double angular contact setup of the later machines. On my '91 the needle desintegrated and the cage was wearing through the ball screw shaft.
The angular contact set is expensive because they are ground as a pair for a predetermined preload. The backlash parameter will be less with the angular contact bearings.

M K · Dec 1, 2020

Thanks for the reply’s

I never said I was chasing the 0.005mm tolerance, I just said the Haas book says anything over this is out of tolerance meaning when new,

I think the machine has the new sealed bearing units but I can’t be sure till they are removed,

The new style bearing Packs Are £355 each

As I’m not 100% sure where the main problems lie I have a cnc repair company coming in tomorrow to do a full ball bar test on the machine and parameters tune up so I know exactly what needs replacing and what doesn’t

Thanks
Marc

BGL · Dec 5, 2020

Marc,
No, my apologies - It was entirely me! My fractional trained brain... more like fractured most times. What I read and understood was clouded by conversion between units.

What you are doing is worth the effort. Took me over 30 hours to refresh the thrust bearings, adjust backlash and tram the spindle. My Berta does as well, actually better than the seven year old VF2 at paying job.

Good luck!

M K · Dec 6, 2020

Well the ball bar test never got done as even though I specifically booked one they turned up without 1 so I refused to pay and that was that,

I know the X axis ballscrew is the worst part and noisy too so I bit the bullet and ordered a new ball screw assembly and main and support bearings along with a new coupler at a cost of £2211.00

I also then decided to buy new bearings for the Y axis for another £370.00 as the blaascrew and nut seems very good still

I am also going to change the Z axis bearings for another £370

Then get the machine all buttoned up again and have a proper company coming in to ball bar test, adjust all parameters and then re run the test

So it’s about £2600 without the vat but it’s my only machine and it needs to be as good as it can be so worth spending the money I think

Thanks
Marc

Mechanical backlash causes and solutions - vf0e

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