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How good/bad is your 3 jaw chuck
- Thread starter slow-poke
- Start date
I don't think a 6 jaw is necessarily more precise, maybe people think so cause they are more expensive? My understanding is that a 6 jaw is for holding thin wall items better with less chance of crushing or deforming the part. I haven't really checked my 3 jaw runout. Its from Grizzly and has the tongue and groove jaws that you can flip around or replace with soft jaws. I do think its not great, definitely get runout when rechucking a part, I just try not to do that on critical items. If its important to be properly concentric the 4 jaws comes out to play.
John Conroy
member
I hope this link works. This is the 3 jaw that came with my lathe.
johnconroy.smugmug.com
GH1440W Lathe - John Conroy
This video hosted by SmugMug; your photos and videos look better here.
Downwindtracker2
Super User
I think I remember reading anything under 3 thou was considered good. My unknown 8" om my lathe is a couple out. I wasn't too careful in my checking, either. . My guess it is an aftermarket. I can't see a BB 12" lathe coming with an 8" 3jaw chuck. It's overkill. I have a 6" Bison but I haven't done the backing plate yet.
I just recently checked my 3-jaw. It is the factory Grizzly that came with my lathe. It ran 0.0015 using a half inch ground bar. I'm VERY happy with that.
You can always regrind your jaws to improve your runout if you want. Just keep in mind that the runout will vary at various points along it's set diameter. In other words, it might be 1 thou using a 1/4 ground rod, 2 thou using a 1/2 rod, 1 thou using a 1" rod, 4 thou using a 1.5" rod, etc. That's because the runout depends on the accuracy of the scroll and the jaw teeth it engages in. If you decide to grind your jaws, pick a good OD to do it at and don't forget to use something to prestress the Jaws so they will see the same stress while grinding that they will see in use.
A few years ago I was planning to regrind the jaws on my 3jaw and built a toolpost grinder mostly for that purpose. I just assumed that a factory Grizzly chuck wouldn't be that good. Silly me didn't even check it first. I just assumed it had to be bad. After I finished the grinder, I checked my 3jaw to get a before number. I couldn't believe my eyes. Needless to say, I never used the grinder.
I don't think there is anything about a 6 jaw that inherently makes them any better than a 3 jaw. But most 6 jaws are a fair bit more money than the average 3 jaw, and therefore that premium might also allow the maker to make them slightly better. Just a theory.
Personally, I'd prolly be very happy with any 3 jaw with less than 5 thou of runout, and I'd be looking to regrind any chuck with more than 10 thou of runout.
That said, I don't really expect good runout from a 3 jaw. That's what 4 jaw chucks and collet chucks are for.
Last, but not least, it's good to remember that good parts depend on spindle runout, not chuck concentricity. You can make a great part that has excellent runout even with a really crappy 3 jaw because the part gets cut by the spindle precision not the jaw precision.
Hope that helps.
You can always regrind your jaws to improve your runout if you want. Just keep in mind that the runout will vary at various points along it's set diameter. In other words, it might be 1 thou using a 1/4 ground rod, 2 thou using a 1/2 rod, 1 thou using a 1" rod, 4 thou using a 1.5" rod, etc. That's because the runout depends on the accuracy of the scroll and the jaw teeth it engages in. If you decide to grind your jaws, pick a good OD to do it at and don't forget to use something to prestress the Jaws so they will see the same stress while grinding that they will see in use.
A few years ago I was planning to regrind the jaws on my 3jaw and built a toolpost grinder mostly for that purpose. I just assumed that a factory Grizzly chuck wouldn't be that good. Silly me didn't even check it first. I just assumed it had to be bad. After I finished the grinder, I checked my 3jaw to get a before number. I couldn't believe my eyes. Needless to say, I never used the grinder.
I don't think there is anything about a 6 jaw that inherently makes them any better than a 3 jaw. But most 6 jaws are a fair bit more money than the average 3 jaw, and therefore that premium might also allow the maker to make them slightly better. Just a theory.
Personally, I'd prolly be very happy with any 3 jaw with less than 5 thou of runout, and I'd be looking to regrind any chuck with more than 10 thou of runout.
That said, I don't really expect good runout from a 3 jaw. That's what 4 jaw chucks and collet chucks are for.
Last, but not least, it's good to remember that good parts depend on spindle runout, not chuck concentricity. You can make a great part that has excellent runout even with a really crappy 3 jaw because the part gets cut by the spindle precision not the jaw precision.
Hope that helps.
Chipper5783
Super User
Yeah, about 0.002”. I’ve recut the jaws on my original 8”-3J. It is pretty well right on. On a scroll chuck, the jaw position is determined by the face scroll, that scroll must have a little bit of clearance to the chuck body (if it didn’t, then it would not turn), where that clearance lands will introduce some variation in where your part ends up relative to the perfect center position. It is a common practice to dial in the part in your 3J, tap the part sideways as you snug the chuck (dial it in almost like you would a 4J independent chuck). Often you can get it pretty well perfect.
6J you ask? I have the Bison set tru offering, 6”. Obviously being set tru I can dial out the run out (also being a scroll chuck, there is the same issue with play in the scroll). Certainly, it is a very nice chuck, however I agree with the comments above about it not being really any more precise - sure it is good, but not magic. It is no better than the 60 year old Roem(?) that came with the lathe. I like the 6J, I use it about 25% of the time. Lots of times it is not the best option - it does not close down as far, the chuck jaws are physically larger (sometimes you can’t get into places), it just doesn’t feel like a heavy duty item. As others have said, it is good for thin wall items. I like it when holding a narrow part and maybe only 0.1” into the jaws - like just grabbing with a fingernail hold.
The 6J is great, sometimes it is just the ticket for a certain job - which is true for any of the various work holding options that you can tie onto the spindle.
6J you ask? I have the Bison set tru offering, 6”. Obviously being set tru I can dial out the run out (also being a scroll chuck, there is the same issue with play in the scroll). Certainly, it is a very nice chuck, however I agree with the comments above about it not being really any more precise - sure it is good, but not magic. It is no better than the 60 year old Roem(?) that came with the lathe. I like the 6J, I use it about 25% of the time. Lots of times it is not the best option - it does not close down as far, the chuck jaws are physically larger (sometimes you can’t get into places), it just doesn’t feel like a heavy duty item. As others have said, it is good for thin wall items. I like it when holding a narrow part and maybe only 0.1” into the jaws - like just grabbing with a fingernail hold.
The 6J is great, sometimes it is just the ticket for a certain job - which is true for any of the various work holding options that you can tie onto the spindle.
Perhaps you might allow one more comment from me.
In my opinion, the King of Chuck's is the Collet Chuck. Properly installed they produce great runout numbers, and do so across the full range of their capacity. Because they use collets for each size range, they also have premium grip, and don't suffer from thin wall distortion syndrome.
My collet chuck lives on my lathe far more than all my other chucks combined. I wouldn't be without it.
In my opinion, the King of Chuck's is the Collet Chuck. Properly installed they produce great runout numbers, and do so across the full range of their capacity. Because they use collets for each size range, they also have premium grip, and don't suffer from thin wall distortion syndrome.
My collet chuck lives on my lathe far more than all my other chucks combined. I wouldn't be without it.