Wandering runout

[Spruewell]

Samchully 10” chuck in my Hyundai SKT28LM is having an issue with runout. However, it isn’t consistent. I’m running soft jaws and the runout is changing +/-.005 depending on how the chuck is oriented




It had runout when I first got it. I removed it, cleaned it and reinstalled it. It still had runout that I was never able to correct. I tore it down and reassembled it several times and even tried rearranging the jaws.

 

[Barbter]

To be clear....chuck body hasn't been removed from machine?
Jaws haven't been removed from chuck?
You're saying runout changes when operating?
If so, how often do you pump it with chuck grease?

 

[lobust]

What are you measuring the runout on? The chuck body or the workpiece?

 

[Spruewell]

Runout is in the workpiece. Any runout in the chuck body would remain consistent and be eliminated when I bored the soft jaws. It has been a while since it’s been greased. I’ll try that, but I’m a bit skeptical that would make such a big difference.

 

[mach ramsey mn]

How are you eliminating jaw movement when boring the jaws?

 

[Mud]

Do you mean it clamps the parts differently each time you clamp it? First thing I'd do it pull it apart and look it over and clean out the dirt. FWIW I grease mine pretty frequently, like 1X day or more.

 

[lobust]

Runout is in the workpiece. Any runout in the chuck body would remain consistent and be eliminated when I bored the soft jaws. It has been a while since it’s been greased. I’ll try that, but I’m a bit skeptical that would make such a big difference.

Do you have other power chucks that you are successfully boring soft jaws in, or is this your only one?

I ask because jaw boring method has a large impact on workpiece runout.

 

[mach ramsey mn]

If you chuck us worn out this is what you need:

Master Adjustable Jaw Boring Ring TL Type for 6", 8", and 10" dia. 3 Jaw Chucks

Master Adjustable Jaw Boring Ring TL The Master Jaw Boring Fixtures (TL Type) provides continuous adjustment for accurate jaw boring. Features :

www.mgworkholding.com

If you trying a disk on the master jaws you aren’t getting the right preload on your soft jaws, essentially boring them tapered when you hold your part out on the tips of the jaws. This style of boring ring loads the top of the jaws same as the part. The jaws will be almost square to the part when bored to size.

 

[Spruewell]

As you can see in the first picture, there is a step in the jaws. I put a bushing in the jaws to cut the step, then put a disk in the step to bore the ID. The part runs 1st op in the step, then turns around and goes in the ID bore for second op. I also bore the ID with a slight taper making the face of the jaws .001 - .002 undersized. I have used this method successfully on many sets of soft jaws.

The runout I’m seeing is changing from part to part. I’m pretty confident the chuck is clean internally as it hasn’t run more than a couple hundred hours since I took it apart and serviced it. I’ll try greasing it more frequently to see if that improves it. I’m wondering if there is a way to ship it back to Samchully to be reconditioned and checked to see if things are still within tolerance

 

[lobust]

Right, so next question is how do you measure the diameter you cut the jaws at?

Do you have a set of three point bore mics to measure it accurately?

When cutting soft jaws, size affects runout directly.

If the workpiece is smaller than the bored jaw diameter, it contacts on three lines along the centre of the jaws. This is very good for runout but not great for grip.

If the workpiece is bigger than the bored jaw diameter, it contacts along the edges of the jaws, which may or may not be perfectly true. This is very bad for runout, but better for grip.

A perfect match of workpiece diameter to jaw diameter is obviously ideal, but never really attainable in reality.

Summary, if your jaws are bored undersize relative to the part, you shouldn't expect good runout.

You also shouldn't need to add a taper if the jaws a preloaded when you bore them, especially if whatever they're preloaded on is near the top of the jaw (i.e. away from the chuck). Also, changing the pressure between boring the jaws and using them on the part can affect how they sit on the part and hence how true they run.

But I'm betting on the jaws being tapered and undersize being the reason why you can't get repeatable runout...

Also, you should grease daily, as others have noted already.

 

[mach ramsey mn]

So here is a thought, the draw tube is screwed into a wedge that is held centered with a bushing of some sort to keep the draw tube and the wedge centered. What if that bushing had excessive play and wherever the chuck cycled the wedge would fall to that position. This creating you inconsistent runout. I cannot see this bushing in the cutaway views on the Samchully drawings but you can on the Kitigawa chucks. Just a thought. Maybe you have to orient the spindle (if available) when you load a part to keep it consistent…

 

[lobust]

So here is a thought, the draw tube is screwed into a wedge that is held centered with a bushing of some sort to keep the draw tube and the wedge centered. What if that bushing had excessive play and wherever the chuck cycled the wedge would fall to that position. This creating you inconsistent runout. I cannot see this bushing in the cutaway views on the Samchully drawings but you can on the Kitigawa chucks. Just a thought. Maybe you have to orient the spindle (if available) when you load a part to keep it consistent…

Samchully chucks are carbon copy clones of Kitagawa AFAICT, although from my own experience with them (only two Samchully chucks and a dozen or so Kits, so maybe not the best sample data) they are tighter from the factory than Kit B series.

In most wedge chucks there is no bushing - the wedge block slides directly in the chuck body. I haven't been inside a huge variety of wedge chucks, but those I have been in, the master jaws and the wedge block don't have much lateral clearance, meaning that everything would have to be worn quite badly for the chuck to open and close off-centre. That's why wedge chucks tend to be fairly repeatable even when they're well used and loose.

One thing that can and does make them not repeat is lack of grease, if one or two jaws are tight from lack of grease or built up crud then it will drag and force the wedge assembly off-centre by however much slop is present.

 

[Barbter]

Right, so next question is how do you measure the diameter you cut the jaws at?

Do you have a set of three point bore mics to measure it accurately?

When cutting soft jaws, size affects runout directly.

If the workpiece is smaller than the bored jaw diameter, it contacts on three lines along the centre of the jaws. This is very good for runout but not great for grip.

If the workpiece is bigger than the bored jaw diameter, it contacts along the edges of the jaws, which may or may not be perfectly true. This is very bad for runout, but better for grip.

A perfect match of workpiece diameter to jaw diameter is obviously ideal, but never really attainable in reality.

Summary, if your jaws are bored undersize relative to the part, you shouldn't expect good runout.

You also shouldn't need to add a taper if the jaws a preloaded when you bore them, especially if whatever they're preloaded on is near the top of the jaw (i.e. away from the chuck). Also, changing the pressure between boring the jaws and using them on the part can affect how they sit on the part and hence how true they run.

But I'm betting on the jaws being tapered and undersize being the reason why you can't get repeatable runout...

Also, you should grease daily, as others have noted already.

+1.
Jaws to be bored "slightly" oversize at same pressure as job runs at.
Grease daily - there was a big thing in the UK a few years ago - Hardinge and XYZ machine tools sent out emails - grease daily with chuck grease.
Can't remember the exact stats now but apparently the holding grip can drop 25% easily within days of constant running and no greasing

 

[Mud]

And use the correct grease. It's like super viscous black moly grease

 

[mach ramsey mn]

To take out the slack?!?!?

 

[lobust]

To take out the slack?!?!?

To keep it inside the chuck when it's spinning!

 

[lobust]

And use the correct grease. It's like super viscous black moly grease

I use Fuchs Renolit Chuck Paste or Molykote TP42 - they're both a kind of off white colour and make WAY less mess in the machine compared to the moly types.

 

[Mud]

To take out the slack?!?!?

There's a great deal of pressure between he surfaces inside there, the heavy viscosity is to keep it from squeezing out I believe, and keep the surfaces lubed.

 

[Barbter]

To take out the slack?!?!?

Pump it more baby! It "fills" the wear
Stops the binding - makes the actuation work evenly and smoothly....

 

[Spruewell]

Greased the chuck. Re-bored the jaws. Still having a problem with runout. I put an indicator on the part and roll it around so the high side is up. Un-clamp and re-clamp. Now what was the high side is the low side. I tried this in multiple positions and keep getting similar results. It seems as if the center block has too much clearance, allowing it to "drop" in the chuck.