finishing bowl bottom

[Brandon Speaks]

I am newer at bowl turning, have finished 5 reasonable bowls and have several blanks that I got wet and roughed and are drying.

The part that I have been least satisfied with in my finished bowls is the foot whether tenon or recess my chuck jaws have left a mark. What I have tried to do is turn the whole outside screwed to the face plate including finishing. Then turn it around, chuck it, and do the inside. My G3 has left marks either way though, it is more noticeable with a tenon, but either way they are there.

My conclusion is that I need to be able to flip it again and make a final cut on the bottom, this will also be relevant with finishing a roughed out blank I guess.

So...... what is the best way to do this. I think a vacuum chuck is out of budget for now so I believe I am left with cole jaws, a longworth chuck, or a jam chuck. Longworth seems easier to use than cole, and to be honest I am not really sure how a jam chuck works, I have watched a video or 2 on youtube but it seems rather difficult.

What do you all recommend?

[Prashun Patel]

i prefer a tenon to a recess for this reason. when i am finished with the inside, I flip it around and use a jam chuck and use a live center against the tenon. This allows me to remove the black marks from the chuck, smooth up the transition to the bowl, and finish the bottom of the foot. Of course, since the live center is against the bottom, you cannot get closer than about 3/8 inch to the tip. This leaves a nub. I then take the bowl to the bench and use a router plane to finish the bottom. If you don't have one, you can just use a sharp chisel, then sand any rough marks off.

The bowl will want to move on the bench, so I butt it up to dogs or a bench stop, and line the bench with a shelf liner or carpet. This provides just enough traction to allow you to do the clean up.

[Larry Matchett]

The above method works with both tenon and recess. When you make your recess or tenon be sure to use the tailstock. That way you have a reference point when you turn it around. I just put a piece of foam on the chuck. Makes a good enough jam chuck to finish off the bottom. Not a good idea to use the tenon as the foot of the bowl or a recess either for that matter. Usually the wrong size for the bowl. Think rule of thirds.

[Prashun Patel]

I don't have a way to clean the recess with The tailstock engaged. It requires a hook type tool that I don't have.

I disagree about the tenon not being the right size for the bowl. It depends on the shape of the bowl. I like feet. I usually alter the sweep of the bottom of the bowl to match the tenon.

[Steve Mawson]

If you can find a video by Bill Grumbine on bowl turning, he does a good job explaining how to remove the tenon without a vacuum system. Might be one on you tube.

[Brice Rogers]

On the larger platters and bowls, when I want to clean up the foot (usually a mortise/recess), I will stick it on a large $10 face plate. Let me explain my "faceplate". It is a round piece of pine that I bought at home despot - - probably 18-20" in diameter. I glued on a 4x4x2" block that I threaded with a beall tap. I also trued it up and drew a bunch of concentric lines with an ink pen. Then I place the bowl or large platter on it and line it up to one of the sets of rings. Then I take 4 blocks of wood - - perhaps 1" x 2" x 1" and carefully set them about 90 degrees apart. I try to keep the original center point and use that to re-align everything. How accurate can I get to being perfectly on center? Well, about as accurate as I want. I can sand off some blocks and shim some others. So, I can center it as well as I can see. Perhaps 0.010 or so, without difficulty. I typically use a live center to keep the platter from coming out. But I have also secured with hot glue. If I'm using hot glue, it is easiest to put masking tape on the platter to simplify separating it. I don't take heavy cuts - - but I'm only turning off part of the recess or turning off the tenon. It works well.

[Brice Rogers]

Part 2:
On the smaller bowls or plates, I can do the same thing. But, I am more likely to use the Cole jaws that came as part of the chuck "kit" that I bought from Griz. for about $225. I think that they go up to around 12". But, I have also turned using a jam chuck. The jamb chuck is just a piece of wood that is turned approximate the outer edge of the inside of the bowl or plate. With a jam chuck I would advise using a live center though. BUT...when I needed to get to the very center of the mortise or tenon, I have sometimes used filament tape and stretch-wrap to hold things in place. If you take light and careful cuts it works.

[Doug W Swanson]

Me yourself a donut chuck. They hold the bowls better than Cole jaws or longworth chucks. I either use the donut chuck or a jamb chuck. The jamb chuck is simple but you need to take light cuts as you remove the tenon. Get the tenon down as small as you can and sand the nub off.

[Doug W Swanson]

Brandon, I also see that you are from Forest Lake. I live just down the road in Vadnais Heights (near 694 and 35E). If you haven't already you should join the Minnesota Woodturners Association. It's $35 a year and they have monthly meeting, turning classes and a few times a year will get professional turners in for classes. It's a great club and the membership even gets you discounts at Rockler and a Woodcraft.

[Prashun Patel]

Doug, thanks for reminding me about doughnut chucks. Going to make one for myself!

Prashun

[Grant Wilkinson]

I'm with Doug on donut chucks. They are inexpensive to make and hold very securely. I have one base and several "donuts", each with a different diameter hole.

[John Keeton]

Brandon, there is one other option depending on the size of your bowl and base. You could mount the blank on your chuck with a worm screw, use tailstock pressure with the cone and small center point removed from the tailstock to reduce imprint on the base. Establish the foot or base and shape the exterior of the bowl, then make a finish cut to establish a slightly concave base, remove the tailstock and form a decorative recess similar to the one shown below.

Make the recess just barely larger than your jaws (the one shown is for 50 mm jaws.) When you reverse the blank, do not over tighten the chuck in expansion mode. The "bead" is the outer edge of the recess and it is undercut with a scraper tip ground for that purpose. The chuck jaws fit nicely into the undercut and do not mar the bead. The recess is probably 3/16" deep. All finish work, including sanding, is done to the foot/base prior to reversing to hollow the bowl.

I use this method for turning large platters, such as the one shown, and find that it doesn't take an extreme amount of expansion pressure to hold the blank. There is one caution - you must have at least an inch of material surrounding the recess. Otherwise, you risk breakout upon expansion. I would also suggest using tailstock pressure as long as possible when removing material from the interior of the bowl.

[carl mesaros]

I

My conclusion is that I need to be able to flip it again and make a final cut on the bottom, this will also be relevant with finishing a roughed out blank I guess.

So...... what is the best way to do this. I think a vacuum chuck is out of budget for now so I believe I am left with cole jaws, a longworth chuck, or a jam chuck. Longworth seems easier to use than cole, and to be honest I am not really sure how a jam chuck works, I have watched a video or 2 on youtube but it seems rather difficult.

What do you all recommend?

You mentioned the Longworth chuck as a possibility. I have one and used it successfully on quite a few bowls. If I remember correctly it was around $300.00, which is more than the Holdfast vacuum system I now use. I haven't even thought about the Longworth since going with the Holdfast.

[John K Jordan]

Brandon,

I've done it several ways. One is to make something to hold in the chuck and press against the inside of the bowl (a jam chuck to fit or a simple surface to press with), then press the tenon tightly with the tailstock, turn away most of the tenon (light cuts) and finish the center by hand. I often turn some detail for interest. Some people simply use a 2" sanding pad on a drill to sand the bottom smooth and maybe a little dished (sometimes even off the lathe). I prefer to smooth with small curved hand scrapers, on and off the lathe. Here are some bottom treatments done by supporting with the tailstock as long as possible:

bottom_IMG_5346.jpg bottom_PC141201.jpg cedar_bowl.jpg

Note that when I support with the tailstock I often don't press with the point of a live center but with a piece of wood which I can cut into as needed.

I do some bases with a 2" recess and leave the recess in the bottom, adding some detail in the base to draw the eye away from the recess. I do all this before reversing. These are some shallow squarish platter/bowls and a couple of conventional platters done this way. On the last one the recess is actually the three smaller triangles - plenty enough wood to hold the platter.

penta_plates_comp_small.jpg bottom_IMG_4687.jpg bottom_IMG_4749.jpg bottom_PC012804_e.jpg

A vacuum chuck does make some things easier. You can make most of the parts and buy an inexpensive used vacuum pump.

If the bowl is small enough I use Cole jaws in a chuck. You can also fasten a flat piece of plywood to a face plate, perhaps turn a groove for the lip of the bowl to sit in, then hold the bowl on with tape to finish and detail the bottom.

JKJ

[Leo Van Der Loo]

Brandon I have shown this here before, if you don’t have the Jumbo jaws, as I use those most often.

I mount a disk on a faceplate and turn a shallow recess where the bowl will fit into, so it can not slide around, I screw then half a dozen frogs down onto the disk holding the bowl down, finish turn the foot, sand and done.
shallow recess.jpg fingers to clamp the piece down.jpg recess finished.jpg

I use my Jumbo jaws most often, and depending the shape of the bowl I will hold it with the Jumbo jaws buttons on the outside or inside of the bowl, when needing to have he hold higher I will stack the buttons as in the last picture here.

outside hold.jpg inside hold.jpg double stacked buttons.jpg