Rechucking - arrrgh....

[Sebastiaan56]

Hi everyone,

I spent enough years in martial arts to learn that the dojo was where your character was developed. My shed is a bit like that as well. Here is a lidded bowl for my mum. New Guinea Rosewood from Anagote, EEE and Shellawax as usual.

The arrrgh comes from the lid. As you can see on the right hand side a difference in the height. The story is that the inside turned fine on the chuck but then I put on the cole jaws to finish the outside what was round, suddenly wasnt. This happens virtually every time I rechuck. Ive taken to ensuring that the bit I use to grip fits within the jaws and tightening so that it makes fingers white on the key. The chuck is a Technatool as are its accessories. The Cole jaws have a bit of slop when they are attached but I figured that this was intentional to absorb shocks.

Im willing to admit that I may have more to learn here, any rechucking tips out there?

Sebastiaan

[Cliff Rogers]

... New Guinea Rosewood from Anagote, EEE and Shellawax as usual...
I got some off a bloke in Cairns last year, it makes nice boxes

....... As you can see on the right hand side a difference in the height. ....
It doesn't show up in the photo, or, it might for you, but I can't see it.

.... Ive taken to ensuring that the bit I use to grip fits within the jaws and tightening so that it makes fingers white on the key. ....
That may be your problem, over thightening can distort the piece.
Try leaving a mark/dent for the centre & bring the tailstock up to the mark/dent for all but the very last bit of the reverse chucking.
It helps it get it central & it help to keep it in the jaws without over tightening. :2tsup:

[rsser]

Fingers white on the key? Sounds too much pressure to me. I tighten til there's no movement with a moderate tug on the piece, spin to see how true it runs, reposition to improve if necessary (it rarely runs fully true) and repeat.

The least pressure the better, consistent with holding for gentle cuts. If you want to go in harder use different chucking. Cole jaws are for finishing cuts IMO.

[DJ’s Timber]

You can rarely get pieces running spot on with cole jaws, you would have more luck with making the lid a jam fit on the box and finishing that way and then finish the box once the lid is finished.

Another option is to make a Longworth chuck, do a search on the forum. Would be a bit more solid as the face is one piece rather than 4 qtrs

[Alastair]

Hi Seb

Contrary to the popularly held view, I don't pathologically believe that one has to eliminate all evidence of chucking from the bottom of pieces. I use a shallow recess for chucking the base, (2-3mm) which I find gives ample holding power, particularly for 'cross grain' pieces like yours.

I don't have Cole jaws or Longworth, so proceed as follows:

For a piece like yours, with the grain running at rt angles to the lathe bed.....

Mount blank on screw chuck, in what will be base. Drill shallow hole, just long enough for screw.
Rough to round. Turn 50mm tenon on lid end. This could also be done between centres. rough out lid profile.
Reverse and grip by tenon. Use tailstock in screw hole, or spur centre hole, to centre in chuck. True up base, and turn recess for chuck, (55mm). Sand and finish bottom. Turn profile of base. Part off or saw off at lid line.
Hollow lid, and turn lip/recess. Sand and finish inside. Remove
Grip base by recess. Rough hollow to match outside profile. Turn matching lip/recess, checking with lid for tight press fit. Mating faces must be parallel, (ie no taper).
Jam fit lid, bring up tailstock for support. Refine outside curve, blending it with the bottom. Remove tailstock and finish top of lid, using light cuts. You can also use your left hand for support and security. Sand and finish outside. Remove lid.
Finish turn inside, sand and finish. Be gentle with mating surfaces, to get the fit you prefer.

regards

[OGYT]

Cheers, Seb. When I turn a tenon for chucking, I always have a center mark on it, left by the tailstock. I have a Longworth Chuck now, but when I used the Cole Jaws, I always brought up the tailstock for support, til I got it finished down to the nub. It helps the sloppy jaws to keep th' bowl centered. When you put knuckle-whitening pressure on the Cole Jaws, your bowl will give way a little bit grainwise, causing it to be off-center. You might try it this way so you won't need to tighten the pinion gears on your Nova 'til you warp things out of shape.

[soundman]

I think most of us have found that rechucking inaccuracies occur from time to time.
I try to arrange my work so that I don't remount un necesssarily, I will often take the job off the lathe chuck and all to avoid rechucking, when I'm waiting for finish or filler to dry.

When you do rechuck and expect inaccuracies, it is possible to arrange features so that the rechuck cuts arent obviously off.

If I'm turning a bowl with a foot I'll try to finish off the whole bowl final trim with it in one chuck position and sand and finish.
then flip it arround & trim of only one flat cut to remove the foot.
that way the slight misalignment isnt obvious.

The lid poses some problems if you want a smoth shape.
perhaps you could hard chuck it from the inside rather than cole jaws.

cheers

[BANNED]

Hello everyone

If you hadn't said anything Sebastiaan56, about the small imperfection, one wouldn't see anything wrong at all. I've tried to see it, but even with the zoom, I couldn't tell.
This is a good example, of how the mind works when one is a perfectionist. Regardless, if noticeable or not, it will be always a defected peace in the master's head. I know, "It needs one to know one", and I bet, there are a few of those in this forum. :brava

Thanks Alastair, for your explanation of your preferred method to turn such type of peace. "How many ways can you skin a cat?", is always handy to have more than one solution for the same problem, huh? I'm learning...! :2tsup:

Cheers
GV

[DJ’s Timber]

You guys need to get your eyes checked :o, nah only kidding :q

Think Sebastiaan is talking about the bit right next to the handle, I have circled it to point it out

[Sebastiaan56]

Many thanks for the feedback guys,

djstimber is right, that is the missing bit, it shows how out of round it was on the Cole Jaws. I sanded and sanded and thought I had it till the camera showed it in all of its glory. Its a wonderful device as there is so much mental effort that goes into each piece that I dont see the piece, just what I think I see. The story of life for you zen masters out there. Thats why I value the forum. There are very talented and experienced turners on the forum. Poor turning cant hide, that suits me as I can learn.

Alistair, Thanks for the head stretch, why do all chucking marks need to be removed? Thats like the gloss question. Gloss brought out the light in this timber, but other finishes... hmmm

Cliff and rsser, I have cracked a few pieces, but the lip on the lid id about 2mm. Using the base as a jam chuck sounds very sensible. There is some epoxy in this piece, partially from the timber, partially from the turner.

OGYT, I dont have a machine shop or the skills to make one, they do look great. Who makes them?

Nyodine, no point in not trying your best, whether its your tax return, practising kata, playing an instrument, relating to the people, surviving traffic, or facing a piece of timber on the lathe. A life half lived is, well, a half half lived. Yes, thats zen,

Sebastiaan

[DJ’s Timber]

OGYT, I dont have a machine shop or the skills to make one, they do look great. Who makes them?




You don't need a machine shop to make a Longworth Chuck, do a search here on the forum. Plenty of us have made them using scraps laying around

[Alastair]

Hi Seb

I seldom remove chuck recesses. I make them shallow, (2-3mm) in all but big bowls and soft/spalted timber, and have always turned them into a feature of the base, and part of my signature.

Where I am forced to use a deep recess, or a tenon for above reasons, or on parting off boxes turned "long grain", I will rechuck using a jam chuck, and clean up using sharp gouge, and light cuts, generally with left hand holding/rubbing on the piece for security.

[Wayne Blanch]

Hi Seb

I seldom remove chuck recesses. I make them shallow, (2-3mm) in all but big bowls and soft/spalted timber, and have always turned them into a feature of the base, and part of my signature.

Where I am forced to use a deep recess, or a tenon for above reasons, or on parting off boxes turned "long grain", I will rechuck using a jam chuck, and clean up using sharp gouge, and light cuts, generally with left hand holding/rubbing on the piece for security.


I do pretty much the same as you Alastair, but I often use a flat bit of MDF with concentric circles drawn on it as a locating guide and secure the item to this using Blu Tac. Then very carefully and with light cuts I remove the recess or tenon. Works for me and I have not had too many problems so far:oo:

[joe greiner]

Expanding a bit on soundman's remarks; although best to avoid re-chucking in the same orientation, when necessary I mark the workpiece to identify the chuck jaws' purchases. Although identical from outside appearances, manufacturing tolerance encourages the manufacturers to mark the jaw numbers for accurate assembly. When re-chucked this way, I get much less runout or eccentricity.

Joe

[hughie]

Think Sebastian is talking about the bit right next to the handle, I have circled it to point it out


Sebastian, I would say the that your problem is in the vertical plane rather one of eccentricity.
It can occur that the edge of the lid is not sitting flat on the Cole jaw base. If your jaws [ rubber bungs ] are like the one I bought from Teknatool. Then it is very easy to do.....been there done it :C

Anyway I tend to hand sand the effected area then wash it all out to a uniform surface with a inertia sander.

http://www.woodturnerscatalog.com/cgi-bin/shopper?preadd=action&key=300-1000

Then no one will ever notice, to find it you will have to carefully rub your finger tips over it.