Finishing the bottoms of Hollow Forms

[Prashun Patel]

Yet another HF question:

The swing on my lathe is 12.5".
My HF is about 11". I'm stuck as to how to finish turn the bottom now.

The opening is too small to accept a jam chuck.
I've never used a donut chuck, but I don't think I have the clearance for one.

I've heard about Kirsten chucks or reverse chucky's but is there a simpler (read home made) solution?

My plan B is to finish off the lathe with an angle grinder and ROS, but that's so barbaric!!!

Any help (as always) appreciated.

[Roger Chandler]

Yet another HF question:

The swing on my lathe is 12.5".
My HF is about 11". I'm stuck as to how to finish turn the bottom now.

The opening is too small to accept a jam chuck.
I've never used a donut chuck, but I don't think I have the clearance for one.

I've heard about Kirsten chucks or reverse chucky's but is there a simpler (read home made) solution?

My plan B is to finish off the lathe with an angle grinder and ROS, but that's so barbaric!!!

Any help (as always) appreciated.

Prashun,

I think you can use a jam chuck........just have to configure it the correct way. For instance if your opening is 3/4 of an inch, then you could turn the end of a piece of wood to fit that diameter opening with a larger lip on it, say 1 inch...[think steps].....the part of the jam chuck that would fit in your scroll chuck could be 2.25 inches and taper down to the correct size........ turn a wooden cover for your live center in the tail stock and make a 1/2" diameter flat face........bring it up to the bottom with enough pressure to hold your hollow form on the jam chuck, and turn down the tenon and bring the tenon to a nib, where you can just cut it off with a sharp chisel, and sand it flush.

Most things can be finished off with a jam chuck, but one has to configure the jam chuck to meet the individual piece.....I hope this helps...........a picture would assist us in helping you in case there is some unusual issue with this particular piece.

[John Keeton]

Prashun, I do similar to what Roger suggests, except that I use a tapered jam that will fit in the mouth of the form with enough friction to drive the piece for light cuts on the base. I just bring up the tailstock to the center of the tenon, which was marked by the tailstock when I formed the tenon. Seems to work fine for me, and in fact, is the way I finished the bottom of the last blue piece.

[Prashun Patel]

I thought about turning a 'cone' jam chuck (or Roger's stepped chuck) but I was afraid that I'd rupture the lip/shoulder. The mouth just seems kind of delicate, no? I'll post pix tonight. My mouth's about 2" wide. Small for me.

[Jim Burr]

Remember Prashun, you are only gong to use light pressure to make contact with the jamb chuck. Also, the use of a pad of some type, I use shelf liner, will offer traction and padding. Getting the cone as small as possible is the trick. A sharp chisel and sandpaper are all that is needed after that.

[John Keeton]

How deep is the form? Why couldn't you turn a 1.75" jam to sit on the bottom of the form? Spot glue a piece of drawer liner on it for friction and it should be sufficient to drive the piece with light pressure from the tailstock.

[Prashun Patel]

Oh, I see. The jam chuck is a spindle that goes all the way to the base. Seems like it'll be hard to keep the form concentric without making a cone for the mouth. I don't have confidence that my mouth is perfectly concentric anyway.


Anyway, I'll give this method a shot.

[John Spitters]

With the last piece that I did I used one of my vacuum chucks as a jamb chuck, ( obviously I couldn't use the vacuum system ) then brought up the tailstock using the original center mark from when I roughed the piece between centers and formed the tenon for mounting.

John

[Steve Schlumpf]

Prashun - I agree with the use of a jam chuck in this instance but caution you when you apply tailstock pressure if using a cone.

Without knowing the shape of your HF... it is hard to suggest options for use as a jam. John Spitters has the best suggestion, in my opinion, and follows what I normally do when I use my donut chuck. All you want to do is apply enough pressure so that the HF can be driven. You can do that by using a faceplate with a thick piece of styrofoam attached (think double sticky tape). You remove the center of the foam (creating a donut) so that the foam supports the shoulder area of your HF instead of stressing the mouth/lip region. Again... using the tailstock to apply enough pressure to turn the form without slipping... remove as much tenon as needed so can finish once removed from the lathe.

Good luck!!

[Eric Holmquist]

A reverse chuck is an easy home made thing

I just took a piece of 1/2" steel rod and turned a cone that slipped over it.
I picked up a 1/2" drill stop from HF and used it as a backstop for the cone.
I turned a small foot that fit over the end of the rod, apply some PSA sand paper, and use that as a drive center.

Hold the 1/2" rod in a a chuck and using a dimple on the base of the HF to center the piece, pinch the base between the live center and the PSA foot at the end of the rod. Bring up the cone to center the mouth of the HF and use the drill stop to hold it in place. For under $10 you can make a reverse chuck like this.

[Jamie Donaldson]

Its very simple and safe to make a jam chuck that matches the shape of the top/shoulders of the vessel, not applying pressure as a cone shape would to the opening of the vessel. A cone that is a loose fit to the opening will assist in alignment, but slight pressure with padding to the top the vessel body is less disaster prone! Over the years a turner builds up a collection of different sizes and shapes of jam chucks, making future selection much more convenient.

[Eric Gourieux]

Prashun,
As you can tell, there are as many ways to turn the bottom of a HF as there are turners. I prefer to use a donut chuck. If the HF will clear the ways of your lathe, a donut chuck will easily clear. I have 8 or 10 different sizes of "donuts" to fit various bottoms. I use a cone shaped insert to support the headstock end of the HF, which distributes the pressure on the OUTSIDE of the HF. With the donut chuck, you can access the entire bottom, which I prefer over the tailstock support used with a jam chuck.

That's just my take on it. If you are interested, I could post pics of my setup. I look forward to your pics. That will help.

[Baxter Smith]

You have been given lots of good options depending on the shape of your form and what you want to try. I took a couple of cell phone pics earlier in the day to give you an idea of something you might make somewhere down the road. Its pretty much the same thing that Eric H described except I happened to have a 3/4" rod on hand.
232142
There is a piece of velcro on the end that I stick a small piece of sandpaper to. Used a whole disc this time so it would be visible. I made it for truing up the bottoms of once turned vase shaped hollowforms. I am using pin jaws to hold what remains of the tenon I used to turn it with. The point of a live center could do the same thing in applying pressure against the sandpaper at the bottom of the form. I add some shelf liner around the cone but didn't for the picture. Almost all the pressure is against the bottom and the cone just helps hold it steady.
232143

[Bernie Weishapl]

Prashun I also use a donut chuck. I made one out of scrap plywood. I use it on my Jet 1220 which has a 12" swing. Like Eric I made several different donuts for mine also. On the donuts I use shelf liner so it wouldn't marr the finish.

[Tony Pridmore]

I use something similar to what Eric and Baxter described. My setup is a section of 3/4-10 threaded rod that is held at the headstock with pin jaws. The tailstock side has a piece of wood on it that's been drilled and tapped. The other end of the wooden block is rounded off and has a dimple dished out to fit over any small nub that may remain in the bottom of the vessel. The dimple also helps align the rod using the live center point before the hollow form is put on. A thin piece of closed-cell foam is placed between the wooden block and bottom of vessel. The cone from a Oneway live center is used to center and support the vessel opening. Soon I plan to make a cone from wood so it can be left on the rig.

[Thomas Canfield]

I have a jamb chuck from Don Pencil similar to what Baxter showed. I can make a piece to fit at top of hollow form and use a 1" x 1/4" shaft sanding disk on end of shaft into bottom, and then bring up live center to tenon. I think that it important to have contact at bottom (or close to bottom) and support at neck to hold the piece while removing the tenon to reduce risk of having piece move when tenon is reduced to small section.

You can also just use a wooden rod jammed to bottom and then wrap something like paper towels at neck for support at neck, and I have done that on small hole pieces.

[Prashun Patel]

Wow, so much great information here. I'll be making both a donut chuck and a tapered-threaded-rod-style chuck for future HF's. For this one, I found a simple spindle worked pretty well. I turned a tenon for the scroll chuck. There's some play in the mouth but it does not seem to affect the spin.

I still have some sanding to do on the bottom. I'll probably keep a tiny foot.

[Prashun Patel]

Finished finally. Thanks for the help...

http://www.sawmillcreek.org/showthread.php?186921-Walnut-HF&p=1931484#post1931484 (http://www.sawmillcreek.org/showthread.php?186921-Walnut-HF&p=1931484#post1931484)