Can this chuck be improved?

[rock_breaker]

I have a no name, no marks, 6.25" D1-3three jaw scroll chuck that the TIR is 0.019". When mounting I can get a 0.006" feeler gage between the spindle and chuck in one place on each of the three mounting positions, the rest will not pass the feeler gage. Using a dial indicator on the back of the chuck the runout is 0.004" when the jaws are clamped on a 1.00" X 10" steel test bar that is within 0.0015" end to end on centers. The taper on the spindle has 0.000" runout. The tapered face on the chuck that fits on the spindle taper is estimated to be less than 1/16" wide. At first glance it looks like there is no taper at all but it does have a very small width of taper. My questions are should this area be wider? If it should be wider, if so how wide? If any machining is done is lay out dye the only way to know if the two tapers are in full contact. All help will be apriceated.
Ray

 

[mmcmdl]

Read the other thread on the subject , it's on here now . Use prussian blue , not layout die . Your taper diameter sounds like it is a tad small , polish it out . Then blue the spindle face , it should transfer to the chuck . That is assuming your locking pins are correctly in .

Why is it acceptable

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www.hobby-machinist.com

 

[extropic]

I'm wondering if yours is a flat back chuck mounted on D1-3 plate. Or, is the D1-3 integral to the chuck body? Pictures?
I'm assuming that you have other chucks/face-plates that mount well so the spindle nose taper is expected to be free of damage that would prevent a good mate.
I would remove the cam lock pins from the chuck. Then blue the spindle nose (Prussian Blue, not layout die) and mate the chuck with the spindle using as "straight on" a motion as possible plus a little (±5°) rotation of the chuck on the spindle. Blue will transfer to the chuck taper showing the contact.
While you have the spindle nose exposed, check the runout of the flat face with a .0001" indicator (just so we're sure it's OK). Because the cam-lock holes take up so much of the flat surface area, I suggest lightly going over the flat surface with a fine hard stone looking for high spots.
Let us know what you find.

 

[mmcmdl]

If it should be wider, if so how wide? If any machining is done is lay out dye the only way to know if the two tapers are in full contact

Think of the " taper " as a register diameter . The taper in the chuck HAS TO BE LARGER than the spindle taper . If it isn't larger , how is the chuck suppose to seat face to face with the spindle ? This is not rocket science , just simple mechanics . Yes , theorecticly it would be perfect if the taper had full contact and the chuck was seated true , but it's not needed . A thou over gets you a small amount of runout , but a lot less headaches .

 

[mikey]

Ray, I find it odd that there is only a 1/16" contact patch in the back of the chuck. If this is true then that taper is not correctly ground. The camlock spindle taper is 7 degrees, 7 minutes, 30 seconds and the chuck taper should match that. Moreover, the chuck taper should be deeper than the spindle taper is long so that the back of the chuck touches the face of the spindle when the chuck is locked down. If all of this is not true then the problem is the chuck. You can check it with Prussian Blue as Dave said.

The other thing is that checking the run out on the back or front or side surfaces of the chuck gives you no useful information. It does not necessarily reflect the accuracy of the chuck. While we are on the subject of scroll chuck accuracy, the only realistic measure of accuracy is how it turns a work piece the first time. That is, if you take a piece of stock, say a 4" long piece of unturned 6061 and chucked it and turned it, what is the run out on the piece while it is still in place in the chuck. It should be zero and if it is not then you have a problem with the jaws or jaw guides. All scroll chucks should work this way.

Chucking up a test bar in a scroll chuck will always show run out, and the amount will vary with the diameter of the bar.

So, I suggest you remove the pins in back of the chuck and check the contact patch with Prussian Blue. If it is proper and adequate, meaning there is full contact and the chuck seats flat on the spindle face, then the fit is okay. Reinstall the studs and check for fit. There should be no gap between the spindle face and the back of the chuck. If there is then one of the studs is either not adjusted properly or there may be some damage to one of the cams in the spindle. It may require switching the stud positions to get a proper fit but if you can find it, mark the chuck to align with the mark on your spindle so you can reinstall the chuck the same way every time.

 

[Tozguy]

So, I suggest you remove the pins in back of the chuck and check the contact patch with Prussian Blue. If it is proper and adequate, meaning there is full contact and the chuck seats flat on the spindle face, then the fit is okay. Reinstall the studs and check for fit. There should be no gap between the spindle face and the back of the chuck. If there is then one of the studs is either not adjusted properly or there may be some damage to one of the cams in the spindle. It may require switching the stud positions to get a proper fit but if you can find it, mark the chuck to align with the mark on your spindle so you can reinstall the chuck the same way every time.

Mikey, are you suggesting that by removing the pins and holding the chuck on the spindle by hand that we can determine if the fit is OK?
What if the nose taper fit is too tight and prevents the chuck from seating to full contact using hand pressure? Is the objective to overcome this by adjusting/switching the pins?

 

[T Bredehoft]

What if the nose taper fit is too tight

I think that's what Mikey is trying to determine, whether or not the pins are causing the problem.

It's possible that the chuck and the mounting plate were not made for each other, too.

 

[mikey]

Mikey, are you suggesting that by removing the pins and holding the chuck on the spindle by hand that we can determine if the fit is OK?
What if the nose taper fit is too tight and prevents the chuck from seating to full contact using hand pressure? Is the objective to overcome this by adjusting/switching the pins?

I'm actually trying to determine where the problem is. I've not seen a chuck with a 1/16" contact patch so I am asking Ray to confirm. I also want to know if the chuck seats without the studs in place. If it does, then we have an issue with the studs or spindle cams. If it doesn't then the Prussian Blue may tells us why; it may be that the taper is improperly ground. Then we need to know if its the studs or the cams and then figure out if one or more than one is the problem.

Like all machine-related issues, you gotta make a diagnosis before you can fix it.

 

[Tozguy]

Understood that we are in the diagnostic phase. By my questions I am wanting to confirm my understanding of what you have written. This is what I understand. The D1-3 spindle nose spec for protrusion is 7/16'' so if the nose only goes 1/16 into the chuck then there must be a problem somewhere.

If the pins are removed and the chuck held up on the spindle it would show if there is a problem with the size of the internal taper.

The cams and studs can be checked for operation by simply turning the cam in its socket with a pin in position. Rotation of the cam will show the stud move in and out of the spindle. It should be obvious if something is off and what needs fixing.

Then there is installing and adjusting the studs to the right protrusion.

 

[mikey]

I've seen camlock spindle cams that were somehow chewed up. I don't know how that can happen but I do know that the issue can be the chuck, a damaged spindle taper, bad studs or bad spindle cams. We just have to sort out which it is.