I normally do not go to other plants to fix machines. But this customer was really in a bind and close to my house. In an hour he was back up and running. He was convinced he needed a new spindle. I think now he believes me when I tell him how important pull stud condition is.


Here you can see what is left with the holder.



This is the condition of the spindle taper. Very ugly



Here you can see my special carbide boring bar and diamond tipped insert. Boring bar looks round but has some reinforcement brazed in the back.



Here you can see the machine in action. I made a
program and very slowly kept on work shifting until it would cut.



Here you can see some sparks. Perfectly normal.


Here you can see the finished product. After the
boring bar I touched it a little with some paste
and normal paper.


When I was all done taking off all the garbage I tweaked in the taper by using some prussian blue and my taper test bar. Then I tweaked the program and ran the boring bar 4 times at identical start and stop points. Concentricity ended up better than I thought. 25 millionths at the top. .00015 at 8 inches down using the test bar. Normally I always have a tenth that is too stubborn to get ride of. Not bad for a hour. He almost cried when he saw the spindle. I think I have a customer for life.

fmari,

This is both pretty, and, to a lot of people, very useful. Clever approach, neat result. Bravo!

Thanks for sharing, especially with the pictures.

Jim

my pleasure, I really felt good helping out a fellow customer.

Very Very cool.
I Have thought about doing exactly what you did but I never had the guts to try it.


(I tweaked in the taper by using some prussian blue and my taper test bar.)

More info on the taper test bar please it may save my butt some day.

Also I hope the customer at least bought you a steak for dinner

G’day Frank.

Nice solution to a nasty problem. Do you go to any trouble to ensure that the tool point is at the 9 o’clock position, left hand top dead centre? Do you have to clock up the position of the bar or vee block?

I’m thinking about attempting this on one on my customers macjines. I normally pull them and send them out for grinding. But this spindle doesn’t warrant that.

Finally, is that a bar and tips your selling? I feel I need to invest in one.

Regards Phil.

Wow nice save !!!

Is a ceramic insert work or you need absolutly a daimond coated one ?

I never tried ceramic. My diamond works perfectly. Still looks like new and I only use this bar and insert for spindle repair. I have done this a couple times at my shop. As long as you take small passes the diamond looks like new even under a loop.

that's a great save. not that i'm paranoid now but how often should one change pull studs? maybe a guesstimation of toolchanges on a particular toolholder?

The best way is to keep track of amount of tool changes and amount of time a pull stud is in the spindle. Of coarse this is next to impossible.

Considering what damage can happen, if you are a full production machine shop I would say every year. I wont lie to you, this is a very very conservative figure. A broken pull stud can be so dangerous and violent it is better safe than sorry.

I plan on making pull studs in the near future. They will have some key features that will make them much stronger than normal. Once the product is launched you will know what I am talking about. With these new machines, higher rpms, higher clamping force, something has to be done. Pull studs are slowing people down in my opinion.

How much you figure you took out of the spindle to fox it?

Or fix it whichever you prefer.

I only took .001 per side of original material. The tool holder ended up sitting .005 deeper. He did not have to change the tool changer origin or anything like that.

Frank, it's nice to see others think outside the box and solve problems that stop some in their tracks.

Sometimes this scenario isn't the fault of the pull stud. What can happen is the draw bar doesn't clamp onto the pull stud properly to begin with, for example it may clamp too high on the pull stud. This leaves the tool holder free to bounce around in the spindle, which promptly breaks the pull stud whether it is a brand new premium one or an old cheap one.....You can usually tell if the pull stud was improperly clamped by examining the piece of pull stud which broke off. In either event, it is scary thinking about the possibilities when a tool holder exits the spindle at high rpm.

Occasionally I do some “manual” type machining on the CNC machines with the door open so I can see what is happening. But I always try to remember to close the doors before starting the spindle, just to make sure the tool is secure.

I think it is a good idea to regularly check for alignment problems with the tool holders and spindle during a tool change, and proper tool gripper function. As the machines are used and age things can and will change, maybe more often the machine just drops the tool completely, which is the lesser of two evils, but if it grabs the pull stud toward the end without seating the tool holder tightly into the spindle it is bad news.

How did you get a diamond insert to hold up on steel? Are you sure this is a diamond insert and not a PCBN? And if so, why not use a PCBN? I think it'd have been the better choice. Nice save though, bet that guy was following you around like a puppy dog.

We use diamond to cut Hardened tool steel. 58-60Rc. I have also seen diamond used to cut carbide.

Nice job Frank. It's always interesting to know what is possible. I never know when I'll have to McGyver a fix like that sometime

Did you remove the drawbar before doing the rebore?

NICE! I am surprised you only had to take.001, from the picture it looks like more. I don't think the 1/8" plastic doors on my Haas would withstand a 1/2" endmill at 10,000 RPM? I think the doors are just to protect you from coolant and make you feel better. I am curious how many here have had a pull stud snap?

The insert is CBN. All of the damage on the spindle was actually built up material from the damaged holder. That is why I only had to take off .001 original material. I did not have to modify the machine in any way. I did not remove the drawbar. I ran the spindle at 600 rpms and .5 inches per minute.

It is important that the spindle is always harder than the tool holder. Even if it just a point or two. Better to damage the holder than the spindle.

My concerns with doing it that way are these: #1 what if alignments are off. I see you could compensate for the head being tilted left or right by changing the angle, but what if it is shall we say hanging? So it would be out in Y. Also, doing it that way, if thee is any "funny " movement in either X or Z it's going to show up. Basically you will get a taper as good as the machine itself. Am I wrong?

Rocky,
I'd suggest that any sort of gross misalignment would quickly reveal itself as an incorrect taper angle. However, it should not be too difficult to use an edge finding technique to locate the insert, and from there, locate the table such that the insert is dead on the spindle axis centerline. Then, use a work offset to shift over by the amount of the gauge radius.

I grant that it would be nerve wracking to tickle a wee bit out of what looked like a good spindle, but if trying to rescue a disaster, then I'd have nothing to loose, so I'd try it

True, the taper will be only as good as the machine itself, but IIRC, the Haas encoder resolution is quite a bit better than .0001" per count, so this should permit motion that is smoother than .0001" rise over run, when executing a linear interpolation. In other words, the taper should be straight enough if tool deflection is non existent. I'm a little surprised that no hard spots would occur in a tool mishap, creating a slightly wavy taper condition after reboring, because I've never had a tool that did not deflect when going from soft to hard and back again.