Why is it acceptable

The OD is irrelevant. The back being out could point to a bigger problem. Mount the chuck on the the spindle in whatever configuration gives you the best possible readings. Then chuck a piece of round stock and indicate it as close to zero as you can up close to the chuck. Then check it several inches away from the chuck. If the two readings are significantly different, the chuck is not mounting square to the spindle.

From the picture, I don't think you have a removable backing plate. I don't know what the cap screws are for, but they don't look big enough to be mounting bolts, and a backing plate would not be cut away to match the chuck casting.
 
Tooling can be expensive. My Bison 4 jaw was about $1,000. That was a super deal.
Starting to think I may be going that direction soon. I dont mind paying more for nicer stuff but when a reputable vendor doesnt list that modifications are needed on certain products I'd like to think modifications wouldn't be needed. Idk maybe the chuck will turn fine with the setting I've dialed in on. Just makes me nervous taking a cut with any kind of wobble at all. My eyes are playing tricks on me all I've seen is wobble sincee got off work yesterday. Probably need to take a step back for a moment.
 
The OD is irrelevant. The back being out could point to a bigger problem. Mount the chuck on the the spindle in whatever configuration gives you the best possible readings. Then chuck a piece of round stock and indicate it as close to zero as you can up close to the chuck. Then check it several inches away from the chuck. If the two readings are significantly different, the chuck is not mounting square to the spindle.

From the picture, I don't think you have a removable backing plate. I don't know what the cap screws are for, but they don't look big enough to be mounting bolts, and a backing plate would not be cut away to match the chuck casting.
Thanks for your kind reply. I didnt think it had a backplate but the vendor rep told me to remove the backplate while I'm tuning in the chuck lol. That could have turned out ugly if i went prying on that thing.

I'm going to check a piece of stock as you instructed. Makes sense. Much appreciated.
 
Can you post some pics of the backplate?


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The screws you marked are to lock the studs for the jaws to the chuck. I have a chuck similar in design except is flat on the backside. The mounting studs are threaded directly to the back of chuck. Your picture looks like there is a ring plus the chuck?
After looking at the second pic it is definately one piece.
 
Wow. Wasnt expecting so many replies, that's awesome. That was my first post but I've been lurking on the forums for months now and I really do appreciate all the info one can learn places like this. Truly amazing.

My apologies for the confusion. Honestly guys the 4 jaw came with the studs not installed so i read the manual and was able to get them to seat just fine. Let me explain all I've tried as far as the studs are concerned.

First I hand tightened them down to bottom out in the hole then roated them to where they aligned with cap screw and that was a no go for camlock engagement. Then I backed them out one full turn from from that position and no engagement(yes I have the 3 studs as well as the 3 locks on the spindle numbered) no matter how I clocked them there was no engagement. Next I went two full turns and I get no engagement however I clock them. At 3 full turns i get proper engagement with the camlocks and there's no light between the spindle and the chuck. But all of the locks are at different positions within the V two are pretty close but one is obviously off. With that setup no matter how I clock them I get runout along the side of the chuck of about .0025" and the back I get about .013-.020"runout yet the back is fully seated on the spindle or at least I cant see a gap or light when I shine from opposite side. Not to mention the wobble I get when I actually run the spindle. So I back them all out 4 full turns and they all fall between 6-12 and the other is close to 6-12. I even had the two that engage at 3 full turns nicely set at 3 full turns and then I'd set the one that's off at 2 turns and it engages but still has a wobble, then I'd set it at 4turns and it would spin to 6-12 position. I've pretty much rotated studs and clocked it every which way I can imagine while it still engages and well nothing... but wobble

Ok I went through to double check all the stud heights and clocking each.
- First I put studs at the first available setting that matches with the cap screw hole I will refer to it as setting 0. None of the studs would engage.
-next I put them all 1 full turn out from setting 0 I'll call that setting 1. None of them engaged
-next I tried setting 2 and with all 3 studs number stud 3 was able to engage with all 3 locks at the spindle somewhat but the other two could not
not
- tried them all at setting 3 and clocked all 3 ways but could not get rid of wobble.
wobble.
- then put stud 3 back to setting 2 and left studs 1an 2 at setting 3 and I was getting better readings. I found the studs had the hest readings when seated with the corresponding number on the spindle coincidentally. 1at1 2at 3at3 I was able to get a reading of .0005" on the side of chuck and .004" at the back of the chuck. Manual states you want a runout of -=<.025mm or .00098". I ran the machine and it seemed better but I feel like I saw a bit of wobble but it seemed to be less noticeable at a higher speed.
-next I tried studs 1an 2 at setting 4 and neither would engage at any position on clock
then to be extra I put studs
-then to be extra I put studs 1 and 2 back to setting 3 and tried stud 3 at all positions on the spindle and it would spin past the v's just like studs 1 and 2 did

I think it's safe to assume I'm tuned the best this thing is going to get at this point.

Is the only way to find out to take a cut? I mean it's hard for me to seem wobble at this point but I think I see a bit at lower speeds. The vendor rep told me the dial indicator reading on the od of chuck and the back don't matter. But the manual for the chuck being sold under vendors name that was apparently written by the vendor or specifically for them states otherwise the way I'm visualizing it the indicator would pick up wobble from the back for sure. If the numbers do matter is the od being out .0005 and the back being out .0045 acceptable?View attachment 314138

I've attached a picture because I'm wondering if this style chuck has a removable backplate and if the cap screws I circled would have anything to do with the alignment?

Sorry my post are so long I'm obviously not the most concise.

Kind regards, thanks
Welcome to the H-M play pen. You will always get help here in some way.
 
OK its a direct mount chuck, no backplate as Cadillac said.
I agree with the idea that there should be no visible wobble when the chuck is mounted to the spindle. It might not be a deal breaker but it certainly is irritating.
How easily does the chuck come off the spindle after it was fully tightened on the spindle? My concern is that the tapered recess in the back of the chuck might be too small and prevents full contact of the flat surfaces that are all important. Maybe remove the three studs and hold the chuck on the spindle to see how tight the taper is.
I would not take a skim cut anywhere on the outside of the chuck but I would certainly relieve the tapered recess in the back of the chuck by hand with wet/dry sandpaper if it is too tight.
 
By changing the order of the studs and getting different results, it is evident to me that the counterbore on the chuck is slightly smaller than the spindle nose and not drawing up truly square. It may look like it's drawing up tight, but when you re- arrange things and get different numbers, it tells me that it is not bottoming out. I would open up the tapered counterbore on the chuck slightly with some emory cloth, and check it with some bluing. Once it bottoms out, the run out on the back of the chuck should be .000.
 
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