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KBC 6IN. 4-JAW INDEPENDENT LATHE CHUCK

Phaneron

Phaneron

Scott
I have a brand new, never used 4 jaw chuck with accessories. It came with an older lathe I now have since sold. I plan to buy a direct mount D1-3 4 jaw for my current lathe instead of using this plain back with an adapter. Asking $120, will ship at buyers expense. Located in SE Calgary, Alberta.

Link to product which was bought from KBC Tools; https://www.kbctools.ca/itemdetail/6-318-004

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You guys with naked rotary tables should consider this. A 4J is a lot more versatile & useful (accurate) than a 3J in this application. Even if it never sees a lathe.
Some pics of my 5" on self made back plate. The plate allowed me a lip to screw into T-slot. But I've also seen (gasp) straight holes through the body into T-slots in case of 6" chuck on 6" RT platten. Something you cant do on 3J scroll due to the scroll.
 

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Do not forget to grind the chuck if you expect any kind of accuracy from it. It is standard Chinese chuck I have few of these - cheap to buy BUT very inaccurate out of the box.
 
I bought a a 3J & 4J Gator a while back (pictured). So called copy of Bison, dimensionally at least. The jaws & body were actually very good, quite accurate. But the 4J scroll wheels was so-so machining. Fortunately it was in the domain of handwork to stone raised burrs & bit of lapping on the shaft. But the thing is you just don't know until you get it. Some offshore tooling is crappy & some is not bad at all. I just find it odd where they cut corners. Like sometimes not even complicated parts, but integral to the fit or the mechanism action itself. For a few dollars more it could be great. Especially if it involves hand work or inspection or cleaning. One would think lower labor costs would work to their advantage in that regard. Oh well. All we can do is vote with our credit card.
 
This is not a copy of Bison - it is the cheapest one you can get. I own this, the 8in and 10in versions. It is amazing you can get it for so little $.

The main problem is that the jaws need to be ground - without grinding part wobbles in them.

I got a small 5" 6 jaw. Initial was a whopping 6 thou+ runout. That is a lot for a new chuck. After grinding it is 1.5 thou. Not bad. I have a 40 year old Bison 3 jaw used in High School. It has 1.5 thou runout.

Using the cheap Chinese chuck without grinding == scrapped parts. You indicate 0 rounout in one place and it is +- 5 thou few inches further.

I have way too many chucks now for my little D1-3 lathe. I am making a backplate for a Japanese 8" 4 jaw to complement ground 6" Chinese chuck for that lathe. I do not trust the Chinese 4 jaw to be too good in flatness department.
 
I think I have a video somewhere of one of my chucks pre-grind and can show clearly it is crap. You motivated me to do another you tube video. I have now close to a dozen Chinese chucks and none were good from the start - especially problematic are the 4 jaw chucks.

Note your Chinese chuck is not the usual stuff - it is Atlas branded. Some of my best general purpose drill bits are made in China by DeWalt.

Note that someone made a video of the 6 jaw I have with a 1.5 runout which made me buy it - needless to say I was a bit surprised when it came and it had 4x+ as much runout... but I ground it and long and behold it is now 1.5. Strange stuff.
 
Hmm, never thought of that - I guess depends on size/ type - I can grind 4 jaws easier on a mill and done it few times. At least size 6" as I think I have a stone just small enough to go through the hole.

For 6 jaw I ground I used some rubber spaces to lock the chuck in and an air die grinder with a lot of praying and zip ties - well it worked but I did not film it as I thought it was way, way too "amateurish". I was also unsure of the results - my main idea was that I cannot make it much worse.

I am unsure - for 4 jaw say $50? Standard 4 jaw not some kind of dependent jaws chuck. The jaws as ground will be best for the diameter of the stone and they will have a little rounding in them corresponding to the diameter of the stone.

The main idea is to lock the jaw(s) you are grinding in position whereas the put pressure as if they were grabbing the peace of work material. With independent jaw chucks you can lock the jaw against one another, with dependent jaws you need to get inventive, spacers between jaws - if jaws are removable pp put stuff in the screw holes and put pressure on custom made ring.

You can grind 3 jaw putting pressure away from the work peace (easier to do) but results will not be as great unless your chuck jaws are very, very tight in the groves and there is almost no slop - unlikely in Chinese chuck or even well used western chuck.
 
Hmmm I was thinking about grinding them to the same dimension on my surface grinder.
 
I had a similar thought about putting my TPG to work but I have enough trouble getting to my own projects LoL & have yet to attempt a jaw re-grind myself.

My gut feel is that the jaw locking procedure is important & some techniques or tools may be better than others. In other words experience is required. For example I can envision a clapped out chuck where the scroll/jaw threads are loosey goosey in certain wear areas so backlash is not fully removed with jaw wedges in place as though it was clamped on a bar. I've seen the wedges people use. I've also heard some jaws have relief on the back portion where you can clamp down on stock but grind the front business end. My chucks don't seem to have this feature. I think (hope) you could get it to within a thou with grinding & maybe that's good enough if you are dealing with 5 thou. It would only be dead true on the grinders own lathe but I guess if was going from grinders D1-4 spindle to customers D1-4 one would expect not too much deviation just like factory tolerances. Sounds like Tom has enough practice chucks to get the technique down pat HaHa. I think it would be a great service. TPGs are expensive. & take some time to set up & knock down.
 
I can also grind them on my surface grinder but I would first need to make sure the magnetic chuck is very flat - still didn't do that.

I wonder how much it is off anyways - I guess I could check on surface plate.

On my surface grinder I could do the 6" and 8" - 10" is to wide to do in 1 pass.

What is acceptable flatness of a chuck anyways? 1 thou? There does not seem to be too much discussion about this or concern online.

Related to it problem is holding item on the inverted jaws and using jaws as flat surface - how accurate is that given that jaws all lift?

As usual if you go deeper into any machining topic you can write a book about it.
 
As reminder, OP was listing 4J independent chuck. I'm not sure how you regrind those. Same wedge procedure? I guess you could true the jaw surface meaning make it perpendicular to spindle axis but seems like you would have more variables to set up on a (non-scroll) 4J to set up beforehand
 
PeterT said:
As reminder, OP was listing 4J independent chuck. I'm not sure how you regrind those. Same wedge procedure? I guess you could true the jaw surface meaning make it perpendicular to spindle axis but seems like you would have more variables to set up on a (non-scroll) 4J to set up beforehand
Click to expand...

Grinding 4J is easier for me - you can lock jaws against each other and grind 1 jaw at a time. The problem with a 4j jaws is that they hold items bell-mouth - allow work piece to wobble. Your goal in grinding is to make the jaw surface straight not wavy in respect to the clamping tension.

Imagine jaws as they move closer and clamp on work piece - they move up a little, workpiece is actually just held by bottom part of the jaw in just a small area which is different for each one of the 4 jaws. Your workpiece will be off just a bit towards the jaws with least engagement.

If your jaws are ground with respect to clamping pressure to say less then 1thou then such uneven grabbing is far less then 1thou say just 2 or 3 tenths or less - a lot here can now be taken up with the jaws simply biting into the workpiece or the wobble from say 3 tenths at 5" out will be just +-1 thou - which can be acceptable for application vs. say +-10 thou that I sometimes got (!)
 
I don't get what you mean Tom. How do you lock opposing jaws as though they are clamping stock so you can re-grind the jaw ID

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