Turret spindle repair

Spruewell · Jul 26, 2019

I am working on repairing the upper turret on my Miyano KNC-45. It has been having trouble indexing since I got it almost 3 years ago. The solution at the time was to not index it. Faced with a little down time, I decided to get into it and revive the upper turret. I quickly found that it had lost a bearing at the rear of the turret spindle. I managed to find replacement bearings and began to take it apart. Unfortunately the bearings ran directly on the turret spindle and ended up destroying the bearing surface on it.

Now I am looking for ways to repair the shaft as I am not sure if They are still available from the manufacturer. If they are, I don’t know that I can afford it.

If you know of any shops that can do this sort of repair, I could use some contact information

Thank you

RJT · Jul 26, 2019

Don't know anyone out your way, but turn down the damaged part, press on a hard sleeve (assuming this part is heat treated), grind at assembly seems like a pretty ordinary repair that lots of shops could do.

Richard King · Jul 26, 2019

Did you mike it? How bad is it? It might be the same size but scratched and if that's the case you might be able to put on a new bearing and not do anything accept cleaning with some steel wool. if it is a few tenths low, you could use some loc-tite. Was the bearing permanently greased or is it oiled? If it is bad then you will have to grind it down to clean up and then have it nickle chromed and reground in that spot. I found this place and it looks like they are expert at grinding and chroming EC GRINDING - Quality Hard Chrome and Grinding Craftsmanship Guaranteed

Spruewell · Jul 27, 2019

Thank you Mr. King, I’ll check them out. The shaft is supposed to be 40mm there and the thread in front of it is 40mm as well, so turning it down and pressing on a hard sleeve is not really a viable option for me. I haven’t put a micrometer to it yet, but I can see there is definitely a reduction in the diameter and it’s in rough enough condition that the new bearing will have little hope of survival. It also has an internal through shaft to drive the live tooling that I will have to remove before It can be rebuilt.

toolnuts · Jul 27, 2019

Hi,

There are several ways to fix the shaft:

1) spray metal, and grind the new surface.

2) hard chrome, and grind the new surface.
On the hard chrome method the other surfaces will
have to be masked off, and some chrome shops won't
do that.

There are spot chroming kits for DIY'ers, but I
don't know how well they work.

Good luck,

Paul

Spruewell · Jul 27, 2019

I do have a eutectic spray metal torch set and materials. However since I rarely use it, and the fact that it is in close proximity to those threads, I’m not sure if I want to tackle that project on my own. It seems a project best left to someone who does it all the time.

Richard King · Jul 28, 2019

I owned one years ago and took a class on how to use it. I tried it a few times and it failed to so I never used it. Now that was 35 years ago, so maybe technologies have changed

Ziggy2 · Jul 28, 2019

Spruewell said:
I do have a eutectic spray metal torch set and materials. However since I rarely use it, and the fact that it is in close proximity to those threads, I’m not sure if I want to tackle that project on my own. It seems a project best left to someone who does it all the time.

I have a question on this. Since this is a turret with a curvic coupling for positioning and locking in on an index, does the failed bearing actually slide on the shaft?

Either the bearing is locked into the turret housing and the shaft slides in the bearing journal or else the shaft bearing assembly must slide in the bearing holder.

This is likely one of those things in which the shaft is good enough as the curvic coupling is what is actually doing all of the positioning and locking.

Spruewell · Jul 29, 2019

It has 3 bearings on the shaft. One needle bearing at the front which is mounted in the turret housing and also allows the shaft to slide axially during indexing. The other two are combination needle bearing and thrust bearing. They are stationary along the axis and oppose each other. They are inside a hollow hydraulic cylinder which moves back and forth to engage and dis-engage the curvic. the forward mounted one is located by a step on the shaft and the rear one is held in place with a spanner nut and star washer. If these are not positioned correctly, either the curvic will not fully engage/disengage or it will allow excessive travel of the hydraulic cylinder, damaging the alignment pin which prevents the cylinder from rotating. If the bearing surfaces are not concentric with each other, it can cause binding (which was part of the problem I’m trying to fix) and premature failure of the bearings. I will try and post a picture of the break-down shown in the parts book.

Spruewell · Jul 29, 2019

These are the pages from the manual with the assembly breakdown:

There is of course more to the mechanism, but the rest seems to be in good enough shape that I'm going to leave it together.

Ziggy2 · Jul 29, 2019

Spruewell said:
It has 3 bearings on the shaft. One needle bearing at the front which is mounted in the turret housing and also allows the shaft to slide axially during indexing. The other two are combination needle bearing and thrust bearing. They are stationary along the axis and oppose each other. They are inside a hollow hydraulic cylinder which moves back and forth to engage and dis-engage the curvic. the forward mounted one is located by a step on the shaft and the rear one is held in place with a spanner nut and star washer. If these are not positioned correctly, either the curvic will not fully engage/disengage or it will allow excessive travel of the hydraulic cylinder, damaging the alignment pin which prevents the cylinder from rotating. If the bearing surfaces are not concentric with each other, it can cause binding (which was part of the problem I’m trying to fix) and premature failure of the bearings. I will try and post a picture of the break-down shown in the parts book.

This limits your repair options. Hard chroming and grinding to size is the only viable option.

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