Machining tolerances/truing up a chuck and realistic expectations

[Roger Chandler]

Drawing from memory here, over the last year I recall some threads on chucks/jaws not running true, and some of that discussion came up also on threads related to lathes/spindles/manufacturing tolerances.

Currently, I have 8 chucks. 5 Teknatool and 3 Hurricane HTC models. I have had the SuperNova2's for years now. A couple months ago, I purchased a new set of bowl jaws [4" outside diameter-3" + inside diameter dovetail jaws] and put them on one of my SuperNova2 chuck bodies. I noticed a good bit of runout, where with the other jaws on the chuck it had run true.....obvious to me it was the new jaw set.

I actually used this set of jaws on a cherry burl I purchased from a turner at the Virginia Symposium back last November, and found a hidden branch inside the burl, all rotted out, which left me a hole right in the middle of that 15" burl that was over 2" in diameter, and went about 10" across, and made the thing structurally a failure where it was located......that was $25 down the tubes!

I noticed the jaws were giving me more runout than I thought was acceptable, so today, I put that chuck on the lathe, and took my Serious Toolworks Ultimate Gouge to the jaws to true them up. I thought that particular gouge would be best because the hardness of the metal on that gouge is 68 to 70 on the Rockwell scale, just below the carbides. That gouge peeled off tiny curls of metal and allowed me to true up the jaws and make a much improved situation.

I could tell that whoever cut those jaws into the 4 sections did a fairly sloppy job, as two of them sat a bit proud of the other two jaws. I am a firm believer that even in the same brand, that one can detect differences in the tolerances at times from one run of manufacturing to another. I am a guy that likes precision, and I am sure that many other turners on this forum are like me, in that they want to have a quality product when they drop the hard earned $$$ for a piece of equipment.......even an accessory like a 4-jaw chuck.

I would encourage turners who have runout in their chuck to examine them carefully, and see if it is the jaws that are the problem, or the seating of the insert that is causing it. If it is the jaws, then a good carbide tool, or even a good quality gouge can help you true up a jaw set if you are so inclined. I ran the lathe at about 500 rpm, and VERY CAREFULLY put tool to the face, inside and outside of the jaws and took tiny metal shavings off the jaws until it ran true. It was a bumpy start for sure, but got better as I went. Safety shield is so important as well as protective gloves........those little metal shards can penetrate skin or eyes and can be like a difficult splinter, which can cause pain and be hard to remove, so SAFETY FIRST! I hope this helps some folks out there who are not happy with runout in their chuck jaws.

[Roger Chandler]

BTW, the "realistic expectations" part of this is that we should pretty much expect that if it was made in China, it might not be machined to exacting standards, so we might just have to make some adjustments!

[Michael Mills]

Rather odd situation since the other jaws were fine.
Were the jaws proud as to the top edge or as to the circumference?
Sometimes the ring on the back that seats has a small burr, Teknatool suggest if it is too tight to use a block of wood to tamp it down. This would be when the top of the jaws were not flat.
I do assume you installed the jaws in the correct order. If not then they may not be true in circumference. Even if the billet was split apart just a little off (maybe one angle 89 and the other 91) when placed in order they would still form a perfect circle.
Did you, as per instructions, install the jaws finger tight then back off 1/4 turn? Then you scroll in for the jaws to align and retighten. If tightened not in alignment then you may not be able for "force" them into alignment. Even with the jaws slightly loose I had to use a rubber mallet on one set to get them to slide around and align.

I have thought of changing the spigot on my 35mm bowl jaws. Glad to know it worked but I think I will invest the 2-3$ for a metal working carbide cutter.

[Roger Chandler]

These jaws were a bit sloppy. the outside circumfrence was off, as well as the inside, and the cut where the jaws were divided into 4 sections was off on one of the passes....it was not square, but a bit angular where those two sections come together, only leaving it to touch on the inside points of the jaws. Visible to the eye, but not bad enough to send back after these months. In contrast, my last chuck was another Hurricane HTC 100, which runs true. I think this is the difference in manufacturing runs from the time my chuck was purchased some years ago, and the jaws which were likely manufactured in 2015 or 2016.

The jaws were certainly installed correctly.

[Doug Rasmussen]

How were the jaws held rigidly when you "machined" them?

On metal lathe chucks there are special fixtures to hold the jaws under pressure when you machine them. When machining the inside of the jaws the fixture holds them as if they were holding something tightly in the jaws. Likewise when machining the outside of the jaws.

http://www.taiki-jaws.com/15-jaws_bo...es_3_jaws.html

That fixture is one for power chucks where the jaws have a bolt mount on them.


It's very important to have the jaws under pressure when truing them, especially on basically low precision like wood chucks.

[Roger Chandler]

I just had the jaws tight against one another in the fully closed position.

[Tony De Masi]

Well Roger you certainly took a very different road than I would have. Mine would have been sent back for a new set that would hopefully be better spec'd.

If you need more cherry burl you know where you can get some right?

[Roger Chandler]

Well Roger you certainly took a very different road than I would have. Mine would have been sent back for a new set that would hopefully be better spec'd.

If you need more cherry burl you know where you can get some right?

I appreciate your generosity Tony! I am sure you know where that burl came from!

[Tony De Masi]

I can probably guess Roger. And I'm feeling well enough now that I can probably help load you up too.

[Roger Chandler]

I can probably guess Roger. And I'm feeling well enough now that I can probably help load you up too.

You & that Kabota, no doubt! I might take you up on something in the future Tony. I have a particular form I want to do with some burl figure, so I will need to email a pic or something to see if you might have something suitable. Stay tuned! I much appreciate your friendship!

[Adam Petersen]

I'm with Tony on that, I would have sent them back. That being said, it was an interesting solution. How did the gouge hold up?

[Doug Rasmussen]

I just had the jaws tight against one another in the fully closed position.

Hmmmm....okay, you machined the outside of the jaws with them tightened in the closed position.

You'll have to make a judgement if it helps on accuracy. It might, but generally that's not the recommended way to do it and could make accuracy worse.

[Roger Chandler]

I'm with Tony on that, I would have sent them back. That being said, it was an interesting solution. How did the gouge hold up?

The Serious Toolworks Ultimate Gouge did great! All I had to do was refresh the edge on my CBN wheel as per usual sharpening.

[Roger Chandler]

Hmmmm....okay, you machined the outside of the jaws with them tightened in the closed position.

You'll have to make a judgement if it helps on accuracy. It might, but generally that's not the recommended way to do it and could make accuracy worse.

It definitely helped...it runs true now! I realize it is not a metal lathe, but it was a well considered calcuation that proved out in the results. Disclaimer here.....others who attempt may find their milage may vary! BTW, I read somewhere recently that Stuart Batty trues up the jaws on new chucks, and some other well known turners as well.

[Trevor Mills]

I checked my chucks a few weeks ago . My Oneway Stronghold were good but I trued up a set of Nova jaws because I was getting a bit of wobble when I reversed to do the inside of a platter.
I used a scraper and didn't take much metal off, but it definitely made a difference. I'll attach a couple of jpgs.