Discussion in 'General Woodturning Discussion' started by Johnturner, Jul 30, 2019.
What is the best way to turn the bottom off a bowl with uneven sides? Please see obligatory picture.
In this order, 1 being best...
1. Vacuum chuck
2. Jam chuck
9. Chisel it off
I made vacuum chucks from PVC (2" up thru 6") and padded with closed cell foam for vacuum. These will also work as a jam chuck, though pushing on tailstock can wear out the foam easier. Aside from that, just make up some blocks to mount in your chuck, put a slight radius on them...you ideally want curve to mimic surface they'll be against inside your bowl...I put some 1/16 or 1/8 craft foam to help hold and prevent damage.
Here’s some pics.
I like to have a diam of contact at least 1/2 the diam of what I’m turning. Ideally with jam chuck, match curve if you can to give most holding power.
Place your piece on.
Or use vacuum chuck with pump or without
Turn till youve got a small ‘nubbin’ to remove with chisel if vacuum not used.
Oh...forgot to mention...it can be difficult to move into that jam chuck or vacuum chuck mode without inducing 'wobble'. When using vacuum, an adapter can be screwed into the chuck and has a fixed (or rotating) #2 taper on other end that you stick in tailstock. Then you can bring the bowl up to the vac or jam chuck aligned squarely before removing it from the chuck. If that doesn't make sense, i'll try to get a pic or find a vid on it.
John, I'm gonna sound pretty biased herewith my reply. The only tool that will effectively assist you in removing a tenon or cleaning up a bottom is my invention, the Tail Stock Steady. It is a pair of wheels with a MT2 arbor that fits into the tail stock quill. If you were to visit my website in my signature line, you can see what it is. You can also check out my youtube channel, "Nubsnstubs", and see more videos. Sorry that I can't give you a particular name of one of my vids, but there is one for removing a tenon on a natural edge piece.
In Tim's reply, the first picture shows what you could make to use with my TSS. I usually make mine the same OD as the ID as my piece. I then bring up my tail stock, remove the tenon or clean up the bottom until I have a nub about 3/4" OD. I don't know if all banjos do this, but when I lock mine down, it creeps forward just a bit. So, I bring up the tool rest until it's tight against my piece, then lock it. Next is to pull the tail stock away, and insert my TSS. The tail stock is brought up against the piece, pressure applied, tool rest loosened, brought up to working height, and remove the nub and finish off the bottom. For the last 2 years I've been decorating all my bottoms, including putting finials in then when I have a foot over 1" tall.
Several people here have one. I don't know if they are using them, but it works like I indicated. Cleaning up the bottom is also done completely between centers, which is a lot safer than any of the other holding devices on the current market. Like I said, I'm a tad biased on bottom cleaning tools...... Mine's the best.............. Jerry (in Tucson)
Looks like an interesting tool to hold the piece with tailstock. What’s the smallest diameter it can push against?
Tim, I believe the smallest OD I've turned with the TSS was 1" OD, possibly 7/8". It scared the hell out of me at the time, but you have to know the limits of the tools you invent. That was about 4, maybe 5 years ago. If I could find it, I'd take a picture. It's possible I was showing it to someone, said they "liked it", and then gave it to them/him or her. don't sell my show stuff, ususlly give it away. ,............... Jerry (in Tucson)
While I haven't had opportunity to use it a lot, the few times I have used it, I've been very impressed with Jerry's Tailstock Steady.
This comment here kinda concerned me however!! The mental image simply will not go away!!!
Pretty amazing little device honestly, design is simple and easy to work with, and the flexibility in adjustment affords a pretty wide range to work in. When opened up on fat bottomed bowls, it allows lots of room to get in their and massage things!
One more vote for Jam Chuck.
Here's another way to do it. I have turned several cylinders, with a slightly domed end, of various lengths and widths that have a tenon that can be held in a chuck. I mount a cylinder in the chuck, take a couple of rubber pieces, about 3"-4" square and put them in the bowl between the cylinder and the bowl. I always start bowls between centers so I have a registration point on the bottom of the bowl. I bring up the tailstock with a cone center and put the center of the cone into the registration point and tighten it down. I turn the lathe on at a slow speed to make sure the bowl is running true. If it's not running true, I loosen up the tailstock and move the bowl on the rubber pads, tighten it back up and check it again. Once the bowl is running true, I turn away the tenon on the bottom of the bowl, leaving a small, inverted pyramid with about a 1/8" top connecting it to the bowl. I take the bowl off of the lathe and use a chisel to cut the pyramid off of the bowl. Keep the lathe speed down as you're turning off the tenon and a sharp gouge is a big help. As you get the tenon turned down and start turning the inverted pyramid, stop and check it for cracks and splits, indicating wood failure. You can also put some CA on the inverted pyramid to help keep it from breaking. There have been instances where the pyramid has broken and the bowl starts bouncing around on the lathe. If you're turning at a slow speed as recommended, there shouldn't be any damage to the bowl. If I have any doubts about the pyramid, I leave it thicker than usual and use a chisel to cut it off.
I am going to +1 for Jerry's Tailstock Steady. I brought one home to Australia and it is the single best bit of gear I have. I have been planning to do a feature on it but I am a bit incapacitated at present, so very little turning, but I will do it. You certainly can't go wrong buying one of them.
Guess I am old school. I prefer a friction drive (many folks now call a friction drive a jam chuck which is completely different).
I always leave a nub with the center point on the base whether it is a tenon or recess.
A jam chuck by old school (Raffan, Batty, Stubbs, etc) is made by cutting a waste block which the item will fit over (or in) tightly enough to not need tailstock support. I have never made one because almost by default you have to turn a new one for each item. Chucks hold items without tailstock support.
Some folks turn friction drives to match the curve of the bowl; again this may require turning a new one for each item.
I turn my friction drives with a flat or slightly concave bottom. A 4" diameter drive will give 12+" of contact. Basically the same as Tim Carter described except for the end. By driving with the edge of the friction drive the item is self centering using the divot with tailstock support. As to size I try to match the diameter of the base, sorta. So a 12" bowl with a 4" base I would use a friction drive about 4". This places the support where the cuts are being made.
Most of the time the fricton drive can be held in a scroll chuck but some folks mount them on faceplates.
Sometimes if the item is very small it will not fit over the chuck and sometimes if it is too deep it will hit the headstock. For these cases just make the friction drive longer.
I like the idea of the TSS but am wondering how to use it with a bowl with uneven sides??
John, you make a jamb chuck, or Plug is what I call them. It's a snug fit and touches at the inside bottom. The natural edge rim straddles the plug at the rim of the work piece. Bring up the tailstock with live center until it's seated into the dimple made during the roughing stage. The tenon is turned into a small nub about 5/8". My live center nose is that size, so I use it as my guide. Like I said in my reply above, my tool rest creeps a little when being tightened, so I use that to hold the piece in place until I remove the live center and insert the Tail Stock Steady. Then I, (for you, Rocky), clean up my bottom safely between centers. It's the best thing I've seen( I invented it) since you don't have to have super clean wood( no cracks), don't have those nubs sticking out that's on a couple other commercial holding tools, and the whole bottom is easily accessed. Go to my website and look for a video I made removing the tenon on a natural edge.
The video below shows how I did a natural edge tenon removal.
Here is another. .......... Jerry
I use the tailstock steady for every bowl I make now.
With the uneven rims - a jam chuck works best for me, some learning curve on positioning and keeping it there— light cuts.
In a pinch, I have used a Dremel with a router bit — but that soon turns into an exercise of patience and inventing new expletives during that process.
John, I brought a Tailstock Steady to the last open turning we had at Middlesex (about 18 months ago?) If I remember I'll bring it to the next club meeting and you can see what Jerry is talking about first-hand.