Truing up recesses - Doughnut chuck?

[howlingbaboon]

Hi All,
The first 4 big Alder bowls that I green-turned back in the spring have now dried out and faster than I was expecting without any cracks (other than some tiny ones in the small branch knots. I mounted them originally to our old Sorby Precision Chuck with a recess. Now I'm interested in the best way to true up these recesses so I can finish them.

With a jam chuck, I think it might be awkward to get the tools in because the tail-stock will be in the way (I've had this problem before). I was thinking of making a doughnut chuck. I've seen that people use this to finish off the base of bowls and remove tenons. I can't see any reason why this wouldn't be good for truing up the base and recess. What do you think? One of the bowls is a natural edge, would a doughnut also work for that? I like the look of the Longworth Chuck but not sure it's going to work with the NE bowl.

[Bryan Milham]

I've no idea what size the bowls you have made are.

My favourite method is to glue 75mm of Kingspan Insulation (find a building site and go skip diving) onto a disk of wood, roughly skim it to the right shape and then put the bowl over it and bring up the tailstock.

It compresses fairly easily to the internal shape of the bowl, even if it's out of round.

Then, using gentle cuts, reshape the recess with a skew on it's side.

[howlingbaboon]

Wow! That's a new one! Will have to give that a go at some point. The bowls are about 12/13" diameter. I'll have to take some pics. The recesses are the biggest the chuck will take, well the biggest jaws anyway, there is a small range.

 I've also seen custom made recess tools that get round the corner with the tailstock in place. I Don't have any spare steel however or I might make one.

Damn I was meant to measure up the hole sizes on the face-plate while in the workshop this evening. Anyone know if they are standard and if so what they are. Just so I can order in the bolts to fix the doughnut to.

[Bryan Milham]

Not sure it's that different.

Some people use a scrap blank and rough turn a shape to approximately fit inside the bowl to be reversed. Then cover it in Router Mat, kitchen paper towel etc., to take up the slack.

I came across the Kingspan/Celtex insulation one day and acquired a piece thinking it may have a use, even though I could net see what at the time.

Since then I've found several uses for it, but this one seemed to answer you request for an idea on reversing a bowl.

Other uses are Goblet reversing, pincushion filling, small items can be pressed into it etc..

As a separate thought, if your bowls are 12/13" diameter, the Doughnut chuck would need to be 16" or more in diameter to accommodate it. And it would not be able to hold Natural Edged bowls easily, if at all.

[howlingbaboon]

Do you tend to use a tenon or a recess then? I gather it's easier to true up a tenon as you can access it from the side without the tailstock getting in the way. I've only been shown how to do it with a recess, I'm not sure if the chuck we have works for tenons. I'll have to have another look.

I was just reading this: http://www.ptwoodturners.org/Tips%20and%20Handouts/Methods%20and%20Jigs%20for%20Reverse%20Turning%20Bowls.pdf

As crude as it looks, I think the tape chuck might just solve my problem of the tailstock. Any experience with this method? Is there a good method for remounting a NE bowl without the tail-stock? Sorry I know I've got a lot of questions, I've not remounted and finished a green turned bowl yet and I really want to get it right.

[Bryan Milham]

All of the methods shown in that linked document would work. Some do however appear to be more safe than others.

You need to temper each of them with the requirement of the bowl you wish to re-chuck. A small bowl, you would get away with taping it as shown in the document, A large bowl would be very unsafe to try and hold that way.

The issue is the rotational speed of the lathe to achieve a smooth cut with the tool, too fast and their is a strong chance of the tape not holding and the bowl flying free, even on small bowls I would strongly recommend bringing up the tailstock to provide support and hold the bowl in place.

Is your issue the need to prevent the point of the centre creating a mark in the foot. If so turn a small piece of wood to fit over the point and give you a flat to press against the wood. Or if you have the hollow live centre used by pen-turners (sorry I don't know how it is properly called) that has a flat end that would provide support without causing a mark.

Is there any chance of a couple of images of the bowl and foot so we can look at them and provide better information based upon the actual work?

[howlingbaboon]

I'll bear that safety advice in mind, cheers for that. If I go down that route I'll use some incredibly strong glass strapping tape. The issue is about the tailstock being in the way and preventing the tools from accessing the dovetail sides of the recess. I'm guessing this might be why using a tenon seems more popular...? I'll add some pics when I get the chance, but away for a few days.

Just to clarify, I usually use a skew to cut the dovetail of the recess. This requires the handle to be facing slightly behind the lathe but exactly where my tailstock sits. Open to any other methods though.

[Bryan Milham]

Have you considered using an old woodworking chisel and grinding it into a dovetail recess scraper. You can arrange the necessary angles for it to be leaning away from the tailstock.

I pick them up in car boot sales and use them to make all sorts of tools.

[howlingbaboon]

Yes, I think I'll do that as soon as I've a suitable old tool to use. We've got shop inside a huge antique centre here. They have no end of old chisels so I'll pick one up next time I make it in there. They never seem to have any turning tools though alas. I saw a video of Mark Siley where he whipped up a tool like this in less than a minute. Does it not matter if it's not HSS then? We've got a ruby grinding wheel and a standard grey one. Am I alright using edge of the grindstones then for making tools?

[bodrighywood]

Older turning tools are carbon steel and so tend to be more brittle than HSS steel, using old woodworking chisels etc is fine as long as you remember that they are much more brittle and so shouldn't be used with a big overhang on the tool rest. Some such as old files are far too brittle and can snap easily. Some things such as drills, allen keys and spanners which all have tension on them in normal use are also OK for various specialised tools. Just always remember that overhang should be kept to a minimum.

Petye

[The Bowler Hatted Turner]

As the H&S chap I have to tell you that you shouldn't grind on the sides of the grinding wheels, they are not designed for that. If you took lessons from an experienced turner all of the information you are looking for would be given to you, along with (hopefully) all the do's and don't's safety wise.

[bodrighywood]

As the H&S chap I have to tell you that you shouldn't grind on the sides of the grinding wheels, they are not designed for that. If you took lessons from an experienced turner all of the information you are looking for would be given to you, along with (hopefully) all the do's and don't's safety wise.

Second this as I have seen the wheel shatter with someone doing this. Not a nice thing to happen.

Pete

[Bryan Milham]

Taking my comment about the safety of fixing a part turned bowl by use of tape, and John's comment about the use of grinders, I think it a good time to remind you and other reader's of this thread that wood turning is almost exclusively a solo hobby.

It is beholden on each of us to consider the safety implications of what we are doing at each step. If an accident happens there is unlikely to be someone that would see it and be able to come to your immediate assistance.

We are responsible of our safety above all else.

[howlingbaboon]

Thanks for all the advice guys. Safety is important. Just for clarification and for others who may be reading, the advice not to use the sides of the grinding wheel, does that include the edges/corners? (as in edges of the usual curved grinding face, where it meets the flat side face).

[Bryan Milham]

I will stand to be corrected by John (BHT) but I do use the corners of my wheels as it is the only way to grind internal angles. But please do not apply sideways pressure to the wheel.