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Tool holders fretting from light cuts and Belleville washer replacement

Mr.Chipeater

Aluminum
Joined
Apr 20, 2021
Running a new production job on a Mori Seiki Duravertical 5100 cutting low carbon steel plate with a 1/2in 5 flute end mill.

I'm taking a modest cut (8500 rpm .002ipt .05 WOC) and noticed after a dozen parts or so that the end mill was making a lot of low end vibration and noise. I inspected the tool but it still looked brand new. After pulling the holder out, I was shocked to see what looks like fretting to me on the taper.

The spindle is not even at 30% load so I'm surprised to see it but after thinking about it, I'm starting to suspect the drawbar force is low and the washers need to be replaced which brought up a couple questions.

1) What are the odds do you think my issue is caused by low drawbar force? (everything else is solid, work holding, program, etc)
2)The machine is nearly 15 years old but the drawbar force has never been checked to my knowledge. The machine has really low hours for its age but what is the expected replacement interval for the washers?
3) Anyone have experience replacing the washers in a Mori? How difficult/long of a process is it? Can it be done without having to realign the ATC arm?

A drawbar force gage is $700 which is the most logical thing to buy to verify but if replacing the washers is simple enough then I'd rather save the money and just replace the old washer to see if that fixes my problem.

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You will want the force gage even if you change the washers.

That is how you know how tight you need to tighten the washers up.

Another place to look is the collet inside the drawbar, assuming mori seiki used that type of tool retention. Some designs have a thread-in collet that is on the end of the bar. Those replaceable collets can wear and cause low clamping pressure. The collet can usually be removed from the taper side of the spindle.

Other drawbar designs can utilize balls in a taper. That type requires you to remove the whole drawbar from the spindle.


No matter what, though, get the gage.
 
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Go to Haas Tooling. They have the ISO40 drawbar force gauge for $346. It's backordered right now.

I don't have theirs but, I do have one. I checked my own Haas and found it dead in the center of the range specified in their documentation. I also checked a friend's VF-5. It also was dead in the middle of the specified range. The point being that having the tool means you can check that box and move to the next problem.

Next culprit: are you torquing the pull studs? After buying a pull-stud socket, I discovered I had been over-torquing studs. Excessive torque causes the top of the taper to swell slightly. That can cause the holder to mate tight up at the top and leave the bottom in looser contact. That's obviously the opposite of what we want. I'd buy a socket, check the manufacturer-recommended torque values of your holders and stick to that.
 
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Last time I tried to buy them, Mori was no longer selling the collets or washers separately. You now have to buy the entire drawbar assembly.

Also, if I may offer a piece of advice that you didn't ask for. Get rid of those US Shop Tools pull studs. In the picture on the left, that line that you see right at the 'T' of USST is the mismatch from the radius side near the holder to the 90° shoulder. That stress riser is exactly where they break. Cost us $30k to replace a spindle on a 5-axis Mori because of one of those failing (cracked right through the taper). On the flip side, we had saved $10 on the stud.
 
Last time I tried to buy them, Mori was no longer selling the collets or washers separately. You now have to buy the entire drawbar assembly.

Also, if I may offer a piece of advice that you didn't ask for. Get rid of those US Shop Tools pull studs. In the picture on the left, that line that you see right at the 'T' of USST is the mismatch from the radius side near the holder to the 90° shoulder. That stress riser is exactly where they break. Cost us $30k to replace a spindle on a 5-axis Mori because of one of those failing (cracked right through the taper). On the flip side, we had saved $10 on the stud.
I appreciate the heads up. The pulls studs are quite old as well and deserve to be replaced. Thoughts of destroying the spindle is just the motivation I need to get off my butt and finally do it!

How much did the drawbar assembly cost you? I'd imagine the washers must be a common item if I could match them.
 
No sign of bulged tapers, but there isn't ant contact with the spindle there anyway. From that much fretting it looks like you have spindle taper issues too.
 
Thanks for all the feedback. I looked into the pull stud bulging the taper as I've never heard about that before and sure enough, our CMM could pickup the form difference between a really tight stud and no stud. Form difference was about .0002" and the taper angle shifted .04 degrees near the pull stud.

I bought a brand new holder to replace the fretted one and blue'd up a couple to check the spindle taper fit. @DavidScott was exactly right, there's no contact near the stud. Also I'm no blue wizard but it looks acceptable to me. What do you all think?
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I wipe a narrow stripe of ink on the taper making it so thin that it's basically transparent. Then I mate the pieces and rotate the male a full turn relative to the female.
 
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Thats to much blue to tell. Its hard to see blue on a black toolholder, so put a faint amount on the toolholder and see what the transfer to the spindle looks like.
 
Went through a similar issue on our HURCO VM10i recently. It's only a few years old so was surprised the drawbar force was on the low side although still in spec. I decided to change them anyway. It was easy enough and while your machine is different I would imagine the process would be fairly similar. I've linked to the thread below.

It didn't really help much (slight improvement but still does it with larger tools) so I've decided that the machine is probably just not up to the job of using large tools that stick out of the spindle significantly.

 
The drawbar is a little involved but not crazy. Getting it out isnt too bad, assuming you can do it in the machine, ive only ever done it with the spindle out. Non standard bellevilles size and oem only grippers leaves you few options. I also believe you have to buy as an assembly.



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