DIY donut chuck,reverse threaded wingnuts for safety?

[McAldo]

I was planning on making myself a compression chuck (wonder if that's the term) for turning away bowls' tenons.
Basically, a disk of plywood bolted to a faceplate, and a donut to trap the bowl, hold by six 4'' threaded rods locked by wing nuts.

For safety, protruding rods and wingnuts will go to the back of the chuck, and I'll make recesses on the front to keep the head of the rods flush with the donut.
However, that way the wingnuts will lock clockwise, the same direction the lathe spins, so I am worried they might unwind while turning, not exactly a cheerful perspective.
Is there an actual danger of this happening?

 

[AndyT]

I wouldn't have thought so, but to be extra sure, you could use two wingnuts on each bolt, one on either side of your back plate, and tighten them against each other.

 

[YewTube]

They will only try to unscrew if they are on the axis of rotation. They are not so they won't.

Bill

 

[paulm]

I use a similar setup of backing board, mine's held on a tenon in the chuck rather than on a faceplate but both will work fine, and moderate pressure from a cup or ordinary revolving centre in the tailstock to keep the bowl in position.

Works well. You need to keep the speed suitably low and use light cuts with a sharp gouge of course. Adding non-slip router type mat to the board may give added security although I haven't to date.

I think the donut approach may well be over-complex, time consuming and fiddly for most even rimmed bowls, but of course you need to take into account your own levels of experience, size of workpiece etc.

Cheers, Paul

 

[chipmunk]

I have a doughnut chuck and it works well. A doughnut chuck is certainly a cheap and cheerful way of turning away the chucking point on the bottom of the bowl fully without leaving a tailstock nib that needs cleaning up afterwards.

I use cheap closed cell foam camping mat between the wooden faces and the bowl I'm turning and find that the "spring" in the mat acts in the same way as spring-washers would to stop the wing-nuts coming undone. So, do not worry about that.

I would also use round headed M8 coach bolts (Screwfix or Toolstation) through a 9mm ply doughnut to avoid having to recess the bolt heads and lose strength or have to resort to thicker sheet material - but use whatever works for you. You also might find it useful to taper the hole on the inside edge (mine tapers over a good inch to almost nothing) so that you are not reaching too far through the plywood sheet to reach the outside face of the bowl.

As Paul says there are other ways of achieving the same outcome but, even though I have plenty of other options, I find that it's handy to keep the doughnut chuck for the odd "awkward" bowl.

HTH
Jon

 

[McAldo]

Thanks everybody, it's so great to get so much advice, and useful.

@ AndyT That makes sense, I didn't think about it, will give it a go.
@ YewTube thanks, good to know for the future too. I see what you mean I think, as the main vector is not along the axis of the lathe but 90 degree to it (sorry, badly phrased)
@ paulm Hi Paul, thanks. My current level is zero, pretty much, I have only three days turning under my belt, and mostly spindles with my skew for practise. I see your point that there are other, less complicated solutions. However, I have seen the doughnut chuck at a club demonstration from a professional, and was quite impressed because it seems it would contain the bowl in case of mishaps and would work quite well with irregular pieces. So, I was hoping it would be safer in case of bad catches, given at the moment I am always risking one
@ chipmunk Thanks for all the advice. I have gone for round heads for the bolt too, so perhaps I could avoid recessing. My choice of plywood is actually a bit thicker than what you describe, but if the whole thing turns up to be to heavy I have some thinner ply I could remake the front doughnut with. Tapering sound like a good idea, will do that, and the foam mat too, will look for some in shops (I suspect my wife wouldn't take well to find a doughnut shaped hole in her yoga mat)