Spindle runout - do pull studs matter?

[pjensen]

Ok, this one was a bit weird. I am measuring the run-out of my collet holders with a dial test indicator. I'm measuring the collet holding surface, so no collet is in the holder, just the inside surface of the tool holder. Note that inside the spindle itself I measure less than a tenth of runout.

I'm getting anywhere from 0.0002" to 0.002", but usually around 0.0005" of total runout. The thing is, it seems to matter which way the tool holder is put in the spindle. If I measure, say 5 tenths on a given tool holder, I can take that holder out of the spindle, rotate it 180 degrees, put it in, and then measure 1.5 thou.. I rotate it back 180 degrees, and I'm repeatable, back to 5 tenths.

After some playing, and cleaning everything in site, I discovered that the pull stud seems to effect things. The same tool holder with a different brand pull stud can have a very different runout. (by the way, I'm being careful to tighten them down and make sure they are clean)

I have pull studs from different companies, and I don't even know which comes from where anymore, because I didn't think they really mattered, so long as the tool stayed in. Apparently, not true.

Does anyone have any idea of what is going on here? I don't know what's going on with the geometry that can cause a 180 degree rotation of the tool to make a difference (it should be symetric!). And if I measure the pull studs, they seem as identical as I can measure, but the differences are repeatable, so something's going on.

Any ideas?

[Neal]

Some possibilities are:
1. Conatamination in side the spindle--dirt, embeded chips, dings
2. Chips or dings on the tool holder taper
3. excessively grooved pull studs
4. Weak bellville washers not applying enough retention pressure.
5. A bad tool holder. re-test with a different holder.
Neal

[JimBoyce]

PJensen,
I read an article in MMS about the thread of the pull stud, if tightened excessively, expanding the small part of the taper on a holder. This may cause the holder not to contact the spindle on the large part of the tapor. Try checking a holder with a pull stud hand tight (obviously do not run it like that).

[Andre' B]

Originally Posted by JimBoyce PJensen, I read an article in MMS about the thread of the pull stud, if tightened excessively, expanding the small part of the taper on a holder. This may cause the holder not to contact the spindle on the large part of the tapor. Try checking a holder with a pull stud hand tight (obviously do not run it like that).

I remember that but cannot find it. As I remember someone (HPI ??) had used the data to design a pull stud that reduced the effect but even then the recomended torque was less then you would think safe.

[Boots]

Not all pull studs are =. You have to make sure you use all the same type. If you are getting different readings,like you said, swaping the tool 180 deg. then there must be debris in the taper of the spindle. If you can move the tool holder (front to back of machine) with your hand while watching the indicator then it probably verifies debris or a ding etc. on the spindle taper.

[pjensen]

Thanks for the suggestions. For the record, I see the change in runnout when rotating 180 degrees on all of my tool holders (of various make). I think that rules out any problem with the tool holder, and leaves something going on with the spindle.

I don't get any deflection if I grab the tool holder while in the spindle and pull with my hand. I've cleaned the spindle out a few times, using a green mesh "brillo-pad" type thing. All the pull studs are nearly new (I've had this particular machine for less than a year, so all tooling and pull studs are less than a year old).

Hadn't thought about over-tightening being a problem. I'll try again with a hand-tightened pull stud, and let you know if I get any results from that.

My fear is that the draw-bar is not pulling enough, and I'll have to go another round with the belville washers - although I still don't quite understand how this would result in the asymetry... a weak drawbar should be weak in either orientation, and it's tight enough that I can't move anything even a tenth when pulling hard on the tool holder when it's in the spindle.

I'll keep looking - thanks for all the suggestions so far!

Cheers,

-Peter

[alex gitzel]

make sure the end of the drawbar is even,i have seen them streched around the thinner parts where the bearings go,also check the drawbar collet (or floater as it has been called) and see if it is damaged.i have also seen too many washers put in and the drawbar is not able to come down all the way and grabs the pull stud on the side and will not fully engage the taper,and sometimes they are able to run like this without it being noticed untill the drawbar or collet gets damaged,do not put in more that 1 washer above the top of the spindle pocket that is all that will fit properly(this comes from much trial and error on my part)it does not matter what the paperwork from fadal has for the amount of washers,different setups reqiure different amounts that are not listed but the 1 above always works.

[pjensen]

Ok, I'll take apart the drawbar and look for problems. Finger-tightening the pull-stud made no apparent difference. I'll let you know how it goes.

Thanks,

-Peter

[Delw]

Before you worry too much, about the movement when grabbing the tool holder and moving it, check your z axis head to see how loose that is also. the gibbs might need to be snugged up.
That usually doesnt effect rotaion but I noticed you said you shook it by your hand.

On tool holders some of them are pretty bad and not round. I bought a bunch of them from usshoptool and had nothing but vibration and chatter problems. I bought kenmetal ones with studs and I havent had a problem sence.

[pjensen]

Delw, I must have mis-typed. I meant to say that, when I tried to shake/push/pull the tool holder by hand, I could NOT measure any deflection. The toolholder and the entire Z column seem to be firmly in place as they should be.

My tool holders are from Glacern Machine Tools, Maritool, and a few from eBay. I get this problem with pretty much all of them, although it varies a bit from tool holder to tool holder. Has anyone had any trouble with Glacern or Maritool tool holders? (I won't ask about the eBay ones ;-)

Thanks,

-Peter

[Andy Fritz]

Peter,

Did you find out what was causing this problem?

Andy

[pjensen]

I haven't found the source of the problem. I went through all my tool holders and marked the orientation that results in the least runout on each. Now, when I use the tool holders, I make sure to keep that orientation. On most tool holders, that results in a reasonably small runout (usually around 0.0005 or so).

Compared to newer machines (mine is from 1985), this machine has a very primitive draw-bar mechanism. I'm going to chalk up the problem to a design flaw.

For example, I can't put any more or less spring washers in, otherwise it doesn't work at all. There is no separate floater to check, an there are only 3 ball bearings that grab the pull stud. I completely dismantled the drawbar and cleaned/checked everything, but it made no difference.

I'd still be interested in any suggestions, but for now I'm making chips ok by watching which way I put in each tool-holder.

Cheers,

-Peter