HF Bottoms

[Mark P. Brown]

Hi all. I have a problem/question about turning hollow forms. I have turned a few for practice with junk wood I have picked up.
I set the block between centers and round it and set a tennon on it then lock it in the cullet chuck. After I square off the end I turn to shape then hollow.
Now here’s the problem I turn through the tennon and release the HF. When I turn the HF back around and reset on the jaws of the chuck to turn and smooth the bottom the HF either cracks and flies off (exciting) or just slips off and flies (exciting) the landing is always on a solid surface so a lot more sanding is needed on the ones that don't crack.
I do not have the funds for a vacuum chuck (looking at making one) but until I do build one what is the proper way to hold the HF to finish the bottom.
Mark

[Gary Conklin]

http://www.laymar-crafts.co.uk/tip38.htm

[Steve Schlumpf]

Mark - I have a vacuum chuck but find that I use a donut chuck for most of my hollow forms either because they have voids in them or are thin enough that the vacuum could cause a problem. There are many simple ways to make your own donut chuck but this version by Art Liestman is one of the best. http://azwoodturners.org/DoughnutChuck.pdf

[Ken Fitzgerald]

I don't have a vacuum chuck. I use a donut chuck. When I do natural edge bowls, I have some foam insulation that I 've turned to a cone shaped cylinder. I place the NE over the insulation and trap it using the donut. The cylinder holds the edges of the NE away from the base plate of the donut chuck and prevents the edges from damage.

[Curt Fuller]

I don't have a hollowform in progress but I took a couple pictures of a finished one to try an explain how I do it. I'm not sure if this is called jam chucking or friction chucking but here goes. I have a collection of tapered pieces in different sizes that are turned endgrain and fit in my chuck, similar to the first picture. I slide the opening of the hollowform over the taper, and use the dimple in the tenon to line up the tailstock so it's centered between the two, like in the second picture. It doesn't take much pressure on the tailstock to keep it from slipping, too much pressure could crack the opening. Then you can turn away most of the tenon leaving about a 1/4" nub. You can then carve and/or sand that away.

[Curt Fuller]

I use a similar process for turning bottoms of bowls. Instead of the tapered piece I use a piece that is slightly convex or dome shaped in the chuck, like the first pic. I use a piece of non-skid rug backing against it, like the second pic. I then hold the inside of the bowl against that and center it with the dimple in the tenon, and turn away the tenon and finish off the bottom of the bowl. Again, it leaves a 1/4" nub that is sanded or carved away. This works really well on natural edged bowls that don't have a flat top edge.

Don't look at my messy lathe.

[Bernie Weishapl]

Mark I guess I am not getting how you reverse the HF. Could you post some pictures? I use a donut chuck and have been going to get a vacuum chuck setup together but the donut chuck works so well and cost about $12 to build.

[Mark Hubl]

For odd pieces I will create jamb chucks like Curt described. For most I use my small donut chuck.

[Jeff Nicol]

It sounds like you are trying to hold the piece with just the chuck, and if that is the case you need to bring the tailstock up to hold it while finishing the bottom. There willl be a little nub left that can be pared away with a chisel,gouge or just sanded off to finish the piece. This is what I pretty much do all the time as I am always in a hurry and setting up the vacuum or a donut chuck just seem to take to long unless it is a must for the piece. All of the other replies address all the different solutions I use too.

Good luck,

Jeff

[Ben Brown27]

Another vote for doughnut chucks and jam chucks. I made my doughnut chuck in about 30 minutes one afternoon, and it makes finishing the bottoms of many items so much easier. When I don't feel like getting out the doughnut, I just make a quick jam chuck or grab one of the ones I have laying around.

[Mark P. Brown]

Thanks for the help. I went to a few stores after looking at the donut chuck and got the materials to put it togather. I am thinking about making a disk of 2" maple to fit the collet chuck and mounting the back plate of the donut chuck to it for a faster change out after I part off the HF. Will this work or is it better to use a face plate?
Thanks again for all the help.
Mark

[Harlan Coverdale]

I am thinking about making a disk of 2" maple to fit the collet chuck and mounting the back plate of the donut chuck to it for a faster change out after I part off the HF. Will this work or is it better to use a face plate?
Thanks again for all the help.
Mark

It'll work, and I think a number of folks use that method, but I prefer to have a dedicated face plate that's always attached to the donut chuck.