How to turn discs?

[bassmansimon]

Ok, so there is probably a simple technique I am missing here, but I cannot figure out how to turn a disc which is rounded on both sides.
Example of what I am talking about:
http://bungendorewoodworks.com.au/sites/default/files/styles/8c_square/public/field/e-sale-products/Bwwg-Disc-vases-12_0.jpg?itok=78rGNAFS

I can imagine the process for a clock version:
http://bungendorewoodworks.com.au/sites/default/files/styles/8c_square/public/field/e-sale-products/Bwwg-MiniDiscClocks-03.jpg?itok=Iddu9M9H

For the clock, I would personally:
- use a faceplate with very short screws (into what will be the back)
- turn the front
- drill a hole with forstner bit for the clock face
- sand & polish etc
- then turn around and hold it in a chuck in expansion mode in the clock hole, and turn, sand & polish the rear side.
- then cut the base off using a mitre saw / band saw etc, so that it sits flat.

Is there something fundamental I am missing, because this process would not work for the disc vase shown above.
Holding the entire job in cole jaws seems out of the question, because of the curve in the shape (I have some of these at home, and from memory the centre is about 5cm thick while the very edges might only be about 1cm thick).

Thanks in advance, Simon.

[Paul39]

For the disk vase I would.

Put a round disk in my chuck with sandpaper glued on the face.

Jam the blank centered between the disk and a ring live center with a point.

Make a spigot for the chuck to grab and turn, sand, and finish all but the spigot.

Turn around and grab the spigot in the chuck, turn, sand, and finish everything I can reach front and back.

Remove from chuck and make a spigot or recess in a piece of scrap, put that in chuck and make a hollow area so that the edge will bear on the oval piece about 1/2 to 2/3 the diameter of the oval piece. Sand the front of the fixture smooth and drape a couple layers of soft cloth over it.

Place the oval piece against the fixture and gently bring up the live center in the mark left in the center of the spigot. Pull out the cloth so there are no folds. Tighten the tailstock firmly.

Turn off all the spigot you can reach, sand, and finish.

Remove piece from lathe, place on folded up towel, chisel off nub, hand sand, and finish. Drill hole, cut off bottom, sand and finish.

A two inch disk on a soft pad run by an electric drill works nicely for taking down the nub. When you are almost down to the surrounding surface, a two inch disk on a firm backing - cardboard - round and round, back and forth, rotating the piece, blends nicely.

See photos for removing nub from bowl bottom.

[Sturdee]

Holding the entire job in cole jaws seems out of the question, because of the curve in the shape (I have some of these at home, and from memory the centre is about 5cm thick while the very edges might only be about 1cm thick).

Thanks in advance, Simon.

Simon, for reverse chucking of that kind of shape I use the V grip extensions (http://vermec.tripod.com/PDFs/Vermec_Bowl_Jaw_V-Grip_Extension_Set.pdf) for the cole jaws from Vermec.

Peter.

[NeilS]

cole jaws

+1

[TTIT]

I would turn down or glue a dovetail spigot on one side to hold with standard chuck jaws and then finish as much as possible of both sides from the one mounting. To remove the spigot, I know not everyone has one but it would be sooooo very easy on the vacuum chuck :B:U

[bassmansimon]

Simon, for reverse chucking of that kind of shape I use the V grip extensions (http://vermec.tripod.com/PDFs/Vermec_Bowl_Jaw_V-Grip_Extension_Set.pdf) for the cole jaws from Vermec.

Peter.

I couldn't open the link but looked them up online. They look perfect for the job, but oh wow super expensive for basically a set of long screws, washers and rubber.

[Beedeejay]

I couldn't open the link but looked them up online. They look perfect for the job, but oh wow super expensive for basically a set of long screws, washers and rubber.


Hey Bassman

Maybe something in this thread will help with DIY cheaper option.
http://www.woodworkforums.com/f8/bowl-jaw-extensions-172225/

Cheers Ben

[Paul39]

I couldn't open the link but looked them up online. They look perfect for the job, but oh wow super expensive for basically a set of long screws, washers and rubber.

Simon, I looked for and couldn't find or open the above.

A lot of expensive stuff can be built by having a catalog page and a trip to a hardware store. combing the aisles and / or asking, "do you have something like this", will often get the same thing made from a handful of unrelated bits, and a few hours of work at much less cost.

Any round bits can be turned and drilled on the lathe.

Edit: Wrote this before reading #7 above.

[Mobyturns]

If you are using flat boards near the thickness of the finished piece I prefer to use two temporary glue on chuck spigots (tenons) using hot melt glue. Requires two chuck & jaw sets plus a reversing mandrel though.

1. Glue on 1st tennon block one side & turn & finish the other.
2. Using a reversing mandrel and chuck position & glue on the 2nd glue block tennon to the finished side.
3. Reverse and use a "burn wire" to slice through the hot melt glue joint to recover the first glue block. I prefer to leave on the 1st & use it with tail stock support for as long as I can before removing.
4. Turn & finish the other side.
5. Part through 2nd waste block & remove remaining hot melt glue. It usually peels away easily from a finished surface.

I often use two glue blocks face to face - one in a nice hard material has the tennon, the other is softer and is a sacrificial waste block to be parted through. Another option is discs in aluminium machined with a tenon to suit your jawsets. Placing on an old electric clothes iron & heat will loosen the glue joint for removal.

If you are doing production runs TTIT's vacuum chuck is the only way to go. Be very very wary of techniques that some use to friction hold using tailstock force only to hold between jamb mandrels in the head & tailstocks or against the chuck jaw faces. One good catch or the tailstock working loose ever so slightly turns your piece into a flying discus.

ps there are various qualities in hot melt glue sticks. I prefer the Bostik glue sticks.

[bassmansimon]

Brilliant Thanks :p

[Sturdee]

They look perfect for the job, but oh wow super expensive for basically a set of long screws, washers and rubber.

They are indeed perfect for the job of holding odd size items, such as disks or bowls or boxes with fancy edging, and IMO the only safe way to secure them to finish the bottom as it uses the cole jaws in compression mode. It is also very quick and easy to use. All other methods described seem as make do and have inherent safety issues.

I'll admit that they are a tad expensive but what price do you put on safety? They are a damn sight cheaper then doctors and hospital costs if the make do method holding it fails and the disk flies into your face.


Peter.

[fubar]

heres carl jacobsens way Woodturning Projects small vase on the lathe in two parts - YouTube (http://www.youtube.com/watch?v=EK5es1c7M98)

[Mulgabill]

I would turn down or glue a dovetail spigot on one side to hold with standard chuck jaws and then finish as much as possible of both sides from the one mounting. To remove the spigot, I know not everyone has one but it would be sooooo very easy on the vacuum chuck :B:U
:2tsup:Yep! that's exactly what I do.

[turnerted]

I have made them as TTIT describes using a vacuum chuck but have also done it by glueing on a tennon with titebond, then truing up the blank and finishing off the first face. I then hotmelt glue on a tennon to the finished face using the live centre to align it. Turn the job over and shape the other face and remove the glued on tennon using tailstock support as long as possible.I then zap it in the microwave oven to remove the hotmelt glue tennon and clean off any residual glue wih turps.
Ted

[bassmansimon]

They are indeed perfect for the job of holding odd size items, such as disks or bowls or boxes with fancy edging, and IMO the only safe way to secure them to finish the bottom as it uses the cole jaws in compression mode. It is also very quick and easy to use. All other methods described seem as make do and have inherent safety issues.

I'll admit that they are a tad expensive but what price do you put on safety? They are a damn sight cheaper then doctors and hospital costs if the make do method holding it fails and the disk flies into your face.


Peter.

Thanks for your feedback. I take your point. Does anyone know if these Virmarc ones would fit into a set of Teknatool nova cole jaws? Wouldn't want to end up getting something that wouldn't fit

[Sturdee]

Does anyone know if these Vermec ones would fit into a set of Teknatool nova cole jaws? Wouldn't want to end up getting something that wouldn't fit

Don't know ad I have the Vicmarc Cole jaws into which they fit.

If you were closer you could come over and try them out on your jaws so instead I suggest that you enquire direct from Vermec by email. I found Enzo of Vermec very helpful in that regard.

Btw they make them themselves and are a quality machined product which fits and centres the bowl or disk perfectly.


Peter.