Chuck mishap

[Mobyturns]

I've been to the NZ Woodturning Symposium and while there came across this interesting item in "Creative Wood NZ" about a failure of a chuck back in March (June 2014 Wood Chat column on p13).

The author writes "I was turning a 80mm block of wood using the long jaws, which was originally designed to internally hold a bowl in expansion mode. I was turning the block down to size, all was well. I stopped to check progress then restarted. I brought up the tool to restart the cut then bang the tool flew out of my hands and skating down the workshop to the back wall. I thought the block had come out ........ Back to the lathe I realised the block was still in the chuck. That was a puzzle but it got worse , one of the jaws was missing and no trace of it, one screw was sitting the ways all alone & forlorn. ...... Checking the internal screws on the jaws I found all were loose. Now all the screws have been replaced......
I do realise I was very lucky to escape a serious injury."

(The missing jaw was latter found attached to the magnetic tool rack at the rear of the lathe.)

The type of chuck is not mentioned and it doesnt really matter however it would most likely be a Nova as Vicmarcs and others are scarce in NZ.

The article poses a couple of safety issues,

Was the jaw selection appropriate for the task?
How long had it been since the chuck was serviced or the jaw slide / jaw cap screw were checked for firmness?

It doesnt take very long to service a chuck; or to blow out the dust from the hex sockets in the cap screws and give them a quick nip up; or to change jaws if the jaws set is not suitable for the task. It also costs about $4 to replace the jaw slide cap screws.

Very simple regular maintenance may have prevented this dangerous occurance, so I hope it prompts a few of us to at least check the screws & jaws, or even better service a few chucks while having an ale.

[hughie]

This is definitely one of the dangers and given that many turners have little engineering experience I am surprised that we don't have a few more.
It could well be that this is part of the transition to Chinese manufacture of the chucks if it was Nova. . To date I have 7 or 8 Nova chucks for many years and have yet to have problem with them, but then they were all made in NZ.

But still you high light an area that is often over looked as we take chucks for granted most of the time, well I tend too anyway.

[Sawdust Maker]

Seems like the screws holding the jaws had worked loose or were't tight to start with

hmm wonder if the men's shed chucks need a bit of TLC

[chuck1]

Preventative matience being carried out often rather than seldom!

[bowl-basher]

Seems like the screws holding the jaws had worked loose or were't tight to start with

hmm wonder if the men's shed chucks need a bit of TLC

At our mens shed I have tried to introduce a program of checking all jaw screws before use also replaced the Nova screws with ones a MM longer this is a little more safety margin particular on the Coles jaws
Regards
Bowl-Basher

[Mobyturns]

At our mens shed I have tried to introduce a program of checking all jaw screws before use also replaced the Nova screws with ones a MM longer this is a little more safety margin particular on the Coles jaws
Regards
Bowl-Basher

Some cole jaw sets actually have another set of longer cap screws supplied with them.

[mick59wests]

after reading this post I checked the screws on the jaws that I always leave my standard 50mm chuck in.....and yes, a couple of screws were loose. This is not a cheap chuck (over $200) from the NZ mob but I am wondering where they were actually made (some investigation for me). Anyway, I am very glad for this thread as I may have had one of those accidents waiting to happen . Much appreciated Mobyturns
Mick

[robo hippy]

I have noticed that my jaw screws seem to work loose from time to time. Most of the time I discover it when reversing a bowl blank where I was sure I had done a perfect job on the recess so it would run true, but no matter how I wiggle it around, it still seems to have more run out than it should. I have no idea how this happens as I made sure all were tight when I first put them on.

robo hippy

[Mobyturns]

I have noticed that my jaw screws seem to work loose from time to time. Most of the time I discover it when reversing a bowl blank where I was sure I had done a perfect job on the recess so it would run true, but no matter how I wiggle it around, it still seems to have more run out than it should. I have no idea how this happens as I made sure all were tight when I first put them on.

robo hippy

Paul it is interesting that you have also made this observation about the movement of screws & slides. I guess most understand the lathe alignment, wood movement, wood compression, shape of tenon / recess etc have a bearing on the accuracy of the bowl reversing operation but few wood turners have any need to go past that. Do you use a reversing mandrel?

Now before others say this is rubbish it all depends upon the scale of the work. Large work it is not noticeable but on fine delicate work it is significant.

I believe the quality of the wood turners scroll chuck & whether it is generally machined to close tolerances in the slide ways, scroll etc has a fair bit to do with potential movement and whether the screws are firmed up or tight. When you run the chuck in one direction the backing slides are forced to one side of the chuck body, reverse the direction & they will move to the opposite side under the forces generated by the lathe rotation if they are sufficient to overcome the jaw slide friction etc. The jaw slides can move slightly in both radial & tangential directions in their ways each time you change a work piece, readjust the bowl in the chuck or reverse lathe direction or perhaps even when you change lathe speed if screws are not tight. It is insignificant on larger & thick walled work, however poor quality chucks just lead to more frustration on "accurate" work like very thin walled bowls etc.

I have a theory that when reversing a bowl, or reversing the direction or speed of the lathe, the backing slides move slightly in their "ways" for all chucks and add to the centering offsets (besides wood movement etc). Some of the cheaper generics move relatively significant amounts. I have noticed this because I do small (75 to 80 mm with a wall thickness < 2mm) laminated bowls where a centering shift of less than 0.25mm is very noticeable as it may become half the width of a veneer used in the bowl blank construction or makes the wall thickness vary significantly. My solution is that I attempt to turn both inside and outside profiles in one session on the one mount then use a jamb chuck to reverse and finish the bottom only.

This is also why I choose to use an ER collet chuck for delicate finials etc - no potential for jaw slide movement.

Loose cap screws in jaw sets are not only potentially dangerous but they also add to wood turners frustrations.