Servo Coupling?

[mniadna]

Anyone using the bellows style couplings on their machine?

[alex gitzel]

I have run across them on service calls what do you need to know?they seem to work ok but are pain to work with when you need to take the motor off.

[Neal]

The bellows couplers were used for a short time on the Fadal machines. They did not work out as hoped so they were abandoned inlieu of a superior style.

Neal

[Al_The_Man]

Generally I found they are OK for encoder, but I wouldn't use them for motor drive.
Just as if you use helical, use the aluminum for encoder but stainless for small motor drive applications.
Al.

[mniadna]

I think the majority of the backlash comes from the factory 2 finger couplers and nylon insert. My Haas has disk couplings which are zero backlash. I want zero backlash couplers on my Fadal as well. I can readily find the bellows style couplings in the configuration I would need. The disk couplers are harder to find. That being said... I am going to put the bellows couplers on the machine. I was just wondering how much this helps with the backlash, and how noisey they are. I think the bellows would resonate to some degree.

[alex gitzel]

Fadal now has zero backlash couplers in a 3pc.configuration 2)couplers+1)insert they are 4 lobe type that clamp on the screw and motor with no keys.I have updated many machines to this style and have had no issues,just do not make the screw too tight(i will send you the toruqe spec. if you go with them).the part #is mtr-0189 for most machines exept 6535 i think,let me know what type of machine and what motors are on it.the bellows are a real pain to work with and most machines have had them taken off long ago.I think they had some other issues but i will need to look at the bulletins.you should check the thrust bearings on the screw those are what usualy cause backlash in an axis.

[mniadna]

alex,
I did the bearings on all the axis. I even have 1 new screw.

[alex gitzel]

how much backlash do you have?if it is a boxway machine the gibs may be to tight/loose both will cause extra slop.the 2 lobe type you have now dont usualy give me too much trouble if the inserts are not all worn out,and the nylon ones are normaly ok.

[mniadna]

I just replaced the saddle turcite, table turcite, saddle strap turcite, table strap turcite. I bought new turcite table gibs and switched to bronze saddle gibs. Everything is adjusted correctly according to the Fadal manual. I realize this machine is still tight. Especially the new bronze gibs. I pulled one after I ran it back and forth and it wasn't touching evenly.
X 10,13,13
Y 25,32,23
Z 44
Z has a new screw. I think part of the problem with Z is the servo. Two of the brushes are wore really bad. They flop back and forth when the armature changes directions. The servo makes a slight "buzz" when this happens, until it settles. I'm getting my spare servo back from the motor shop tomorrow, so I will be able to swap the Z servo out. I might also just try putting new brushes in the servo, first.

[alex gitzel]

The best way to find where the backlash is coming from is to first put an indicator on the end of the screw and jog 1-2 clicks each way in .010 and get the reading,this is thrust bearing play and casting flex(more flex in y is normal because of the thin casting there).Then put the indicator on the table,saddle,and head to check x,y,z screws.place indicator tip on the angle part of the screw and jog each way one time to get the screw slop reading.then what ever is left from your total backlash is what is in the motor/coupler.the 2 lobe couplers are known to have the set screw loosen up sometimes,so retighten and add a second set screw to lock it.to check the inserts try swaping with another axis.the inserts should also be lubed with vasoline or something like it,and there should also be a gap between the insert and coupler(approx. .050).your z blacklash may also be from tight gibs sometimes you need to loosen them a bit and take a reading then tighten a bit at a time untill the backlash starts to rise that should be good,sometimes factory settings do not work because of the turcite not being even or worn in places.

[mniadna]

Well Z is definately toooo tight. I just swapped the servo, and grabbed ahold of the ball screw to spin it to bring the coupling set screw around to tighten it. I couldn't move it. Granted, the screw was full of oil, the head was at CS and I was all scrunched up on top of the machine, but I still should have been able to turn it. My manual said .0005" for the gibs. A newer version I downloaded said .0002" to .0003" for Turcite. I set them to .0005". I'm going to re-check the strap gibs. I think the whole "stick the shim in and pull" thing is a little wishy-washy to begin with...
One other thing I'm not clear on... My manual says to set the servo loop gain to 595. In the newer manual it says 302. I set mine to 302. The machine has the 1010-4 cards and metric screws. Is this correct?
I think I'm still going to buy the couplers.

[alex gitzel]

The 302 amp tune is for ac motors with axis software prior to ac-0017(the software chips are on the axis cards you will need to pull and check them).the ac motors with ac-0017 and newer software are tuned to 600.the dc motors are tuned to 595.the center gibs are good at .0005 the strap ones need to be played with,tighten untill you start getting some resistance on the top ones,(not very tight) they should be close with the shim setting unless a)the bootom ones are too far in or b) there is debris behind the head so it will not sit correctly.the bottom ones you should set last and use the shim because if you go untill you feel resistance they will most likely be to tight(these should be backed off while setting the top ones) and you should definetly be able to move the screw by hand.If you sweep the front to back tram you will see if the head is hanging.(be shure to check table flatness before tramming).