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Thread: Z axis gib adjustment or???

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    Default Z axis gib adjustment or???

    Hi Guys,

    Sorry about this super long post, but I tried to send this to Gary at Fadal and it bounced back as he is likely not there anymore. Rather than retyping I thought I'd paste it in here and see if anyone can give me some hints.

    Cheers,

    Andy

    -------------------------------------------------------------------
    Hi Gary,

    I am not sure you are still around at Fadal, but let’s see!

    A while back I bought a new AMP-0021 for the Z axis on my 4020HT. You coached me along with the tuning and it has been working.

    However fairly soon I started to get motor overload alarms on rapid moves which I never had before while running the Z from the A axis amp which is an after market amp for smaller motors. Anyway I just dropped the rapids to 50% and had no further problems. Gradually I noticed the head getting “floppier” meaning vibrating at direction changes and making thumping sounds when jogging with the mpg in the fast setting. Also very noticeable during peck drilling.

    A few weeks ago I started setting up a job which required to drill a very precise 0,82 mm diameter orifice exactly centered in a tapped hole and I started worrying about getting the orifice elongated in the Y direction due to the flex in the head. I ordered some .001” shim stock and tried to follow the directions for adjusting the head gibs and gib/strap assemblies. At first I couldn’t measure any sideways play in the X direction despite using a serious pry bar. Also I wasn’t too sure about where to place it on the top of the head to adjust the top gib. I thought I would just leave it and check the gib/strap assys as I had noticed most play in the Y direction. The manual talks abut loosening all four adjustment screws and then sliding in the shim stock. This was not possible anywhere, so I loosened them all the way until the threads bottomed out. Only by putting my whole body weight on the head could I slide in the shims between the column ways and the head. After this I followed the manual, tightened both top screws until I could not pull out the shims, reversed until I could pull them out and tightened a full turn each CCW. For the bottom there was no way to slide the shims in so I had to pull the gibs completely out. I cleaned the gibs and one of the trucite laminations fell off. Still it didn’t look bad so I just figured it would stay in place due to the rough grinding pattern on the steel. After sliding the shim stock in first I could wiggle the gibs back in and followed the same procedure as for the top gibs. I noticed that it was very difficult to find a definite point where the shims was pinched. Maybe the trucite pads are a bit soft and more worn on the short ends so the pinching point comes gradually as more surface compress the shim. Anyway I followed the manual, but after the final one turn CCW I noticed the gibs was still so loose I could wiggle them side ways with my fingers.

    After this I ran the head up and down a few times but didn’t really see a big improvement in rigidity. I tried a tool change and now I got over load alarms halfway through the down stroke when the head rapids down to pick the new tool. I reset and tried a few more times and always the same. I tried a few rapid moves up and down with MDI to get a consistent rapid feed rate and there was no way I could use 100% speed. I tried 50% and this worked, but on every downward move I saw the following error double from the nominal for a second or so just in the beginning of the move. On the upwards move it is much more smooth and starts with a split second lower following error which quickly goes up to the nominal. So this looks like a stick slip problem. I tried to adjust the two top and bottom gibs which controls slop in the X direction. The only way I could get the indicator to show some movement was with one guy pushing the pry bar using he doorway for leverage and pushing as hard as he could while I looked at the indicator. This way we could just about create a .0002 - .0005 play but it varied a lot.

    So I tightened a bit until we had it between nothing and .0003. Again lots of variation between trials. The top was nearly impossible to get an indicator movement on, but I think this is because it is much more difficult to get sufficient leverage with the pry bar. Eventually we had to place the bar between the column way and the spindle motor chassi as the head has too much cooling lines and wiring.

    Sorry about this long story, but should it really bee this hard to get the head to deflect? As this adjustment did noting to solve the problem I tried to alternate between loosening the top and loosening the bottom gibs just to see it it made any difference and it did not.

    I had a quick look at the back lash and it is the worst I have ever seen! It is 0.0066, which means it cant even be compensated. The highest BL comp seems to be 0.0063 but if I use that I get an over load alarm just by moving the MPG one pulse. I think this is because the resolver see the position deviation. I tried to increase the over load setting in the parameter to 4 instead of the default 2. I also dropped the rapid from 500 IPM to 400 IPM and with this I no longer got the alarm, but moving the Z in the minus direction only one pulse makes the head drop half an inch and swing back up. Moving in the plus direction works like normal though.

    I should ad that I had a brand new Z ball screw and ball nut installed when I bought the machine and it doesn’t have more than around 300 hrs use. I have checked a few forums and most suggest the weakest part is usually the thrust bearings. Are those the same as ball nuts? Apparently they can go bad quickly if the seals are bad and the dow frost leaks out on them.

    Is it normal that a healthy Fadal makes these thumping sound on quick rapid moves like when peck drilling? I have an old Hitachi Seiki here with a bad ball nut in the X and it also makes a thumping sound after a rapid direction change. The z is smooth and makes no sound at all when peck drilling.

    I tried to just move the head down to around 10” from the table and used a big pry bar between the table and head. The indicator showed a 20 micron lift when I pushed as hard as I could. Is this bad or normal? Maybe this is just the defection of the head chassi or the whole column?

    With the over load parameter set to 3 I can now do the tool change with out alarm but each time the head changes direction from up to down it seems to over shoot about half and inch. It decelerates and completes the tool change but I worry about peck drilling my orifice as each peck is only 0,8 mm.

    If I put some MDI rapid moves in the MDI I can use 100% rapid (400 IPM) without overload. It works fine in the plus direction but on the minus travel it starts out at full speed and the following error shoots up over 2500. after a second it drops the rapid move to 50% speed and completes it with out alarm.

    Any ideas what to do?

    All the best,

    Andy

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  2. #2
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    Default gibs

    The center gibs are way too tight they should be set to where they move to when the pressure is off of them,so loosen both set the indicator pry on the atc side,then take the bar out and set 0 on the ind. then pry the other side,thake the bar out and look at the reading.thighten the gib untill you are at .0003 away from 0.then recheck it.the strap gibs are set with the shim.you should replace the gibs w/bad turcite.it would be a very good idea to replace all 6 gibs,screws,and the fingers(if bent or stressed)the gibs have the size marked on the side they are ordered like this length+thickness,so a 5''x.545 gib is a (gib-5545).the gibs tend to get the threads streched if over thightened or worn and may be getting tighter/looser with up and down movement causing binding and looseness depending on direction of movement.also you should line up the screw after the gibs are set.jog the head up as far as you can and still get at the 3/4''hex bolts.take the motor off(be sure to mark the coupler before taking the motor off as it must go back in the same so cold start will not be off.)then loosen the bearing block bolts it will line itself up then retighten the bolts.



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    Default

    Hi Alex,

    Thanks for your explanation. Just one thing about the pry bar; When you do this do you push all you can? I have seen posts about using a 2 x 4 block as a pry bar. If I did this I wouldnt be able to move the head at all. I am using a 5 foot bar and push it with all I've got. I am just trying to figure out if what I see is head movement or flex in the column.

    Since the first post I have tried to change the bottom gib/stap adjustment all the way from completely loose to so tight I can just about move the gibs side ways a little with my finger. No matter how these are set it doesnt make any difference.
    Using 400IPM and 100% rapid allways works fine in the plus direction. Going from CS position to Z-8" has the effect of fast movement for a half second or so until the following error peaks at around 7000 and then drops to 670 as the move completes at 50% speed.

    I will order some gibs. In your opinion are bronze better than the turcite?
    Unfotunately I am in Thailand so it will take some time to get here. Meanwhile I will experiment with what I have.

    Regarding the back lash; Do you think that the weight reduction from removing the head cover would be enough to cause it?

    Andy



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    Default gibs

    I use a 36'' prybar and push on it a good amount but not all i got.the idea is just to move the slop in the gib from one side to the other.put the indicator on the way and the tip near the pry point on the head on the right side.what you are looking for is what the reading is with no prybar pressure just where it moved to.if there is no movement the center and/or strap gibs are too tight or the screw is not straight and is binding.if you are having trouble getting the shims in or the gibs tight enough on the top to grab the shims there may be dirt between the head and the ways,i have had this happen a few times and you can clean it out buy loosening the straps and prying the head away from the way a bit so you can spray solvent and get metal strapping stock in if nessesary to lossen the dirt.and also check to see if the turcite on the head is worn evenly.the backlash you are seeing is because the gibs are too tight and or the screw is not square,the bearing block can flex that much with the head bound up.with the gibs loose check the end of the screw w/indicator there should be less than .002 play and under .001 w/new bearings(you did replace the screw+bearing block assy. right?).the gibs when set properly will not be much tighter that you could go with a nutdriver type screwdriver.you must be able to take your hand and turn the screw just by grabing it.(put the e-stop on and try).if you can turn it it is too tight,the slop you are seeing while machining is from the bad gibs w/the turcite off.the bronze gibs are better and is what i use.



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    Alex,

    Regarding the screw alignment, should it also be aligned on the bottom?
    If so, how?

    Andy



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    Default screws

    if there is a block on the bottom loosen it and bring the head down as far as you can and then tighten.most 4020's dont have bottom blocks but some do.those bearings are usualy pretty loose and have room to play with.



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    Thanks Alex,

    What I have done so far is loosened the top and bottom gibs controlling play in the X direction. I tried to gradually loosen and testing the rapid moves to see if it made any difference and even with the gibs removed it made no difference.
    Before I did this I tried moving the screw by hand and it worked at least in the Z - direction. I tried with the head high, mid and low to see if there was any position which seemed tighter. High and low seemed tighter and I could only move in Z-, not Z+. This would appear normal as there is more flex in the screw in the middle. Exactly how easy or hard it should be to move by hand I dont know.

    Next I loosened the top gib/strap gibs really a lot and this made it possible to rapid up and down. I still get more following error on the downward moves but now it peaks at 2500 rather than 6500 like before. Also the control does now keep the 100% speed. Before it dropped it to 50% after the following error peak.

    After loosening the top gib/strap gibs I also tried moving the screw by hand again and it felt a little easier. I do however, notice a clear gap which may be the backlash? It is hard to say but it feels and sounds like there is play in the top somewhere. Maybe it is between the screw and the coupling or between the motor and coupling. I will try with an indicator as this would show if the play is in the ball nut or coupling.

    Ok, so since the only adjustment I felt I had nailed was the top gib/strap gibs and that setting obviously dont work I am now thinking I should really just do all gib adjustments as per Fadal guidlines as well as checking the ball screw alignment. The ball screw look brand new (and it is more or less) and the gibs I have removed also looks good. The threads in all adjustment screws has zero play.

    Regarding gib adjustment (all of them) and ball screw alignment, which order is best? Assume everything is off by miles! The Fadal manual starts with the two gibs for play in X and next the top gibs in the Y direction and finally the bottom gibs in the Y direction. There is no mention of ball screw alignment.

    Is it maybe a matter of just doing one, then the next, goa back and check the first, readjust, check the next and so fourth until everything is to spec?

    If I want to remove the strap assys do I have to block the head to prevent the weight to bend the screw?

    Andy



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    Default Wayliube flush pump

    Oh, one more thing;

    I have been using an hydralic fluid as waylube. I know this is not recommended, but I have been using it on all machines for years and it works great, but a bit wasteful. Now I have finally got hold of a stock of Mobil Vactra Oil #2, which is supposed to be good stuff and i want to see if this helps. Is there any make shift way to flush out the old lube from the system with out a flush pump?
    The manual says to work the axis while flushing with Kerosene. I have the Kerosene so would it not be the same if I just dump the old oil from the Bijour pump, fill it with Kerosene and run work the axis? I could hit the test button on the PDI lots of times to speed up the process.

    If the above is a bad idea I guess I could build a fluid reservoir, put a gauge on it and pressurize the top with regulated air to get the recommended 180 PSI.

    Andy



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    Default gibs

    I have not heard of useing hyd. fluid as way lube before so i dont know what if any damage may have been done to the turcite,block the head and take a strap off ,loosen z bearing block bolts and have a look at the turcite on the head.dont use the kerosene just clean out the pump at run waylube through,it will work itself through.keep pumping untill the way lube comes out .this may solve the whole issue as i am not sure how much the hyd. fluid this effecting the system.you should check the chain+sprocket system for the counterweight,make sure the sprocket beaings are good and moving free.mic. up the ways at different spots up+down the coulum and see if there is any uneven wear,if there is set the gibs in the largest spot.if you can get a dc clamp on amp meter you can test the brown wire from the amp for exess amp draw in different areas.the screw should be able to be turned with one hand in both +/- directions.you should also try swaping amps with x axis and retune,you may also have to swap motors to test and rule them out.check the amp chassis capactitor for dc voltage should be 120vdc+.go through the troubleshooting checklist and let me know if you still have not found the issue.



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    Default

    Hydraylic fuild is WAAAY to light a viscocity to use as way lube. Definately use an
    ISO 68 like Vactra #2 or simalar.

    Neal



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    Alex,

    I ran a 50/50 cocktail of Vactra 2 and hydraulic oil in a little mixer to check for foaming and after the air bubbles were gone I could not see any problems. So I just cleaned the pump and filter and filled with Vactra 2.

    I tried to follow the gib adjustment procedure from the pdfs you sent, but no joy, I started with the gib/strap gibs, but rather than doing the one turn CCW after the shim pulled out I just left them as to have a slightly loose starting point for the pry bar gibs. Then I started with the top gib as per the instructions, put it at 0,0005 play. What I notice straigt away is that I am getting random readings again. After hours of fiddling I got 0,0005 after three tests. Then when I put the indicator on the lower right side of the head and pry there is zero movement. I think the initial 0,0005 setting on the top really fights the ballscrew and the force of the screw combined with the friction from the top setting makes it impossible to set the bottom gib.

    I would think it is not a good idea to try to align the screw until a reasonable gib adjustment is made?

    As I at one point had both top and bottom gibs out for cleaning I noticed that the natural resting position of the head was in such a way that the top gib would just slide in and the bottom gib had to be tapped in. Is there a way to shift the position of the ballnut holder in the X direction so that the natural resting position of the head is more in line with the column ways? Should I shim it one one side?

    Andy



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    Default gibs

    I think the screw is the problem,i think it is not straight and is causing the whole issue.I have never had trouble setting the gibs like you are describing.do this make sure the counterweight is even and not bound on one side just to rule it out.loosen the bolts for the ballnut and the bearing block if you block the head you can take the screw assy. out pretty easy and make sure all the mounting surfaces are clean as there may be chips not letting it line up.the screw and bearing block come out as 1pc. and just take the 4 motor bolts out and pull the motor and rest it over the chains it you can leave the wires on.snug up all the gibs tight then put the screw back in and put in all the bolts loosely the ball nut get tightend first then the bearing block.with all the gibs tight the screw should be straight make sure the gibs are tight before blocking the head so it will not deflect with the gibs tight the head should not even move put blocks in loosely for safety if it moves.after the screw is in loosen the gibs up and then reset them.while it is apart you may want to check the turcite on the head.when the gibs are done move the head up and crack the bearing block bolts loose then tighten to make sure the block is in line.make sure the way oil is worked in first.



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