[How-To] Indicating a 3 jaw independant chuck

[682bear]

In response to a question that I was asked on the 'what did you buy today' thread, I decided to do a pictorial thread on indicating a 3 jaw independant scroll chuck. The reason for this thread is both to keep form hijacking the other thread too much, and also to make this easier to find if someone else needs it in the future.

To begin, a 3 jaw independant scroll chuck is like a standard 3 jaw, it has a scroll which moves all 3 jaws together and keeps them somewhat centered, but the jaws are 2 piece jaws, making them independantly adjustable. My Rohm chuck is older and has some wear, so it will only repeat within about .005-.007 using the scroll to tighten.



First, I put the part in and tighten using the scroll...



Next, I put the indicator on the part. I use a travel indicator mounted on a magnetic base that I just stick to the side of the QCTP.



I rotate the chuck and stop with the indicator even with all 3 jaws and note the readings. Here, jaw #1 is at 0.000...



Jaw 2 is at 0.010...



And jaw 3 is at 0.004...



Now, I go to the lowest jaw (#1) and loosen the adjuster on that jaw about ⅓ of the runout (0.003)...



Now I check all 3 jaws again. #1 is at 0.003, #2 is at 0.009, # 3 is at 0.001.

Now I will go to the high point, (jaw #2) and tighten it about ⅓ of the runout (0.003).

Now jaw #1 is at 0.007, #2 is 0.006, #3 is 0.001. I'll go to the low point (#3) and loosen it about 0.003.

I will continue to alternate between the high point and low point, tightening and loosening as necessary until I get it running as close as I need it.

If you turn the scroll at all during this process, you will probably have to start over... do all the adjusting with the jaw adjustments.

I can usually get it within a half thousandth of an inch in a minute... 2 minutes tops... but I've been doing this for a couple of years

Finished...

Jaw #1...



Jaw #2...



Jaw #3...



It's really simple and quick once you get used to it. I hope this helps someone...

-Bear

 

[markba633csi]

I want one of those for Christmas, Santa!
-M

 

[Mitch Alsup]

How is this usefully faster than putting the 4-jaw on the spindle ?

 

[tjb]

Nice explanation, Bear. Thanks for posting.

Regards

 

[Masterjuggler]

I'd love to have that but in 4-jaw form for holding square stock. I switch out chucks constantly between my scrolled 3-jaw and independent 4-jaw.

 

[682bear]

How is this usefully faster than putting the 4-jaw on the spindle ?

It may or may not be faster than a 4 jaw depending on how accustomed you are to indicating with the 4 jaw...

The reason I prefer this over the 4 jaw is because you can move all the jaws with one scroll pinion... and once it is tight, it is within a few thousandths already.

With a 4 jaw, I have to move from one jaw to the next- to the next- to the next... etc just to get it tight, then it is generally running out a LOT more than a few thousandths. I can zero this chuck much quicker than a 4 jaw... but then I rarely use my 4 jaw, usually only when I have to hold something that isn't round or when I need to machine off-center... also, if I go from working on a ½ inch part to a 2 inch part, Its much quicker to just use one pinion to move all the jaws rather than 4 pinions.

I prefer the 3 jaw with the independant jaws...

-Bear

 

[682bear]

I'd love to have that but in 4-jaw form for holding square stock. I switch out chucks constantly between my scrolled 3-jaw and independent 4-jaw.

I haven't seen one like it with 4 jaws, somebody may make one, IDK... from what I've seen, 4 jaw scroll chucks are uncommon, and I've really never looked at them close enough to notice whether any have the adjustable jaws.

I would guess that if you found one, it might be pricey...

-Bear

 

[mksj]

They make them in both a 3 Jaw and 4 Jaw configuration called combination chucks. They are a lot quicker for getting parts in and out and then tweaking the individual jaws to zero the TIR. Works well for stock that is rough or there is a mismatch or off center hole. Downside is that they are heavier, I have the Bison 4J 8" combination and with back plate it is around 85 lbs. The 4J is a bit easier to dial in with opposing jaws, the 3J combination is very uncommon, but Bison recently came out with a new series of of 3J combo's. They are pricey new, but I use my 8" 4J combination a lot more than my 3J scroll.

Combined Chucks - BISON-BIAL S.A.

www.bison-bial.com

 

[682bear]

They make them in both a 3 Jaw and 4 Jaw configuration called combination chucks. They are a lot quicker for getting parts in and out and then tweaking the individual jaws to zero the TIR. Works well for stock that is rough or there is a mismatch or off center hole. Downside is that they are heavier, I have the Bison 4J 8" combination and with back plate it is around 85 lbs. The 4J is a bit easier to dial in with opposing jaws, the 3J combination is very uncommon, but Bison recently came out with a new series of of 3J combo's. They are pricey new, but I use my 8" 4J combination a lot more than my 3J scroll.

Combined Chucks - BISON-BIAL S.A.

www.bison-bial.com

They are heavy... I actually have 2 of them, a 9" Union and the 10" Rohm. I haven't weighed either one, but I don't think either one is as heavy as yours... I would guess the Rohm is close, though. I may need to bring the bathroom scales down to the basement... I might be surprised...

Thats good to know about the 4j... I'm sure it would be a little easier to indicate...

-Bear

 

[mikey]

Mark, Bear, I think these chucks are very cool. However, when I first heard of them from Mark, I took a long look at them and decided for myself, they were not worth the cost. I do not own one so my comments are coming from ignorance but it seems to me that a 3 jaw, when used for a first op, would not need adjusting. For a second op, a 4 jaw is faster and should hold more solidly given that the part is held by tension of the screws for each jaw vs a scroll. I can see how putting the part in the chuck would be faster with a scroll but for the rest of it I just don't see the advantage, especially in light of how much they cost.

I can see one if you are trying to avoid having to switch out chucks or if you are dialing the chuck in to make a production run on some nominal stock of the same size but in a hobby shop, these are non-issues.

Again, I am speaking from ignorance. Is my logic off?