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Tutorial - How I finish the bottoms of my turned bowls

Started by CHARLIE, February 11, 2012, 02:31:48 PM

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CHARLIE

I had offered to help Patty resolve a problem she was having finishing a bowl by telling her how I did it. When I finally had some time, Patty asked me to post my explanation in case it might benefit others.  The method I use isn't the only method, but it has worked well for me for many years and I like it.
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Tutorial – Finishing the bottom of a bowl
By: Charles M. Cadenhead
February 10, 2012

I learned this technique from Allan Lacer, a nationally known woodturner who lives about 20 miles from me.  I learned this  technique in the mid 1990s when I took an "Introduction to Bowl Turning" class he taught at Woodcraft in Burnsville, Minnesota. This technique is easy to use and fast plus the lip of the bowl doesn't have to be even. That means it can be used on natural edged bowls that has bark along the rim. The technique has worked well for me ever since.




 
(1) You can make the tool easy enough.  It is basically a #2 Morse Taper with a collar screwed on that also has a set screw. A short shaft with a 3 inch pully attached on the end. Epoxy a piece of cabinet grade plywood to the pully and turn it true to about a 4 inch diameter. Glue on a rubber pad.  Note:  I also make an abbreviated, less permanent tool, based on this idea, from wood which I clamp into my 4 jaw chuck and use to finish bottoms of turned lidded boxes.




 
(2) Put the tool into the headstock of your lathe.




 
(3) Place your bowl over the tool so the pad rests on the bottom of the bowl and bring the tail center up to the tenon (Notice the wide tenon that was used to hold the bowl in my 4 jaw chuck.).  The bowl is now securely captured between the inside bottom and the outside bottom.  Note: When I'm roughing out the shape of my bowls and putting a tenon on it, I put the wood between the two centers.  That way, I have a center mark on the end of the tenon.




 
(4) Finish turn the bottom of the bowl and turn the tenon down to somewhere between 3/8 inch or ¼ inch diameter.  Whichever you are comfortable with.  Don't get it too thin that it might break.  Now sand the finished bottom.  Note:  I use a rounded edge with a slightly concave bottom, but you could also put a foot on the bottom too. This technique allows you to make any type of bottom you prefer.




 
(5) Remove the bowl from the lathe and place it upside down on some kind of pad. Here, I'm just using a washcloth.  Of course this only works if the lip of the bowl is even.  For natural edged bowls you'll have to set it over something to keep the edge from hitting the workbench.  Lightly chisel off the tenon (nub).  Don't chisel flush with the bottom but leave the nub a little proud so that if you get any tearout, it won't go into the bottom of the bowl. Note: A sharp chisel and light taps with your wood mallet always does a better job.  You can also use your pocket knife to remove the nub.




 
(6) Sand the rest of the nub flush with the rest of the bottom.  Keep feeling the bottom with your finger and make sure that there is an even concave surface. Usually you can't see a slight bump in the center, but you sure can feel it.  Once you've finished sanding it, you are ready to apply your finish.  Note: I use a piece of 180 grit sandpaper to sand the bottom down to a consistent concave shape. I then progress to 600 grit sandpaper before applying a finish.

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Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Patty

 8)  Thanks for posting this Charlie! I was hoping you would ....the tutorial was very well done.

Your friend,
Pam  ;)
Women are Angels.
And when someone breaks our wings....
We simply continue to fly ........
on a broomstick.....
We are flexible like that.

CHARLIE

Thank you Patty.  I hope it addresses the problem you were having.  I think it does if I understood correctly.  I noticed I had typed in Pam instead of Patty. I had just gotten off the phone with a woman named Pam that I used to work with and I guess I had her name on my brain. My apologies.
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

jdtuttle

Thanks, I always struggled with that part of bowl turning. Now I just need to make that tool  ;)
jim
Have a great day

CHARLIE

Jim, there are other methods to finish the bottom of a bowl also but I find this method the easiest and quickest.  Its advantage is that the bowl is captured by pinching it at the bottom between the pad on the inside and the live center on the outside. It ain't going anywhere and there is no stress on the bowl rim or sides and as long as you don't pretend you are Hercules when cranking down on the live center you are A-OK.  The only other thing to watch out for is to not turn the tenon (nub) down too thin where it might break. If the nub breaks, the bowl is definitely coming off the lathe and damage will occur.  I Hope you give it a try.  Plus, I'll gladly try to answer any questions you might have.
 
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Lud

Simplicity mill, Ford 1957 Golden Jubilee 841 Powermaster, 40x60 bankbarn, left-handed

CHARLIE

Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Radar67

Charlie, do you ever have any problems with wobble with this method? What if the bottom of your bowl is a little "off" on the inside? I've always had issues getting everything lined back up if I remove my project from the lathe to reposition it (turn it around). Do you have any tips for that?
"A man's time is the most valuable gift he can give another." TOM

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CHARLIE

Radar67, when I'm roughing out the initial shape of a bowl, I put the chunk of wood between centers (the Drive Center at the Headstock and the Live Center at the Tail Piece).  This is when I turn a tenon on the bottom for my 4 jaw chuck (If you use a faceplate instead, turn a small tenon that will just fit into the center hole of the faceplate. This will help you center it when you take it off the faceplate).  The tenon will have a dimple where the Live Center was and the tenon is true to the dimple.  When you put the tenon in the 4 jaw chuck or on the faceplate, it is centered and when you turn the bowl, it remains centered to the tenon and the dimple in the tenon.

I'm not understanding having an uneven bottom to the bowl since you are creating the bottom while the wood is spinning, which I would think would make it all the same curve. However, if you put the bowl over the tool to finish the bottom and after tighting the Live Center in the original dimple in the center of the tenon and the bowl wobbles a little bit, then loosen the Live Center just a little. Just enough to allow you to reposition the padded disk inside the bowl. Then tighten up the Live Center again. Through trial and error, you should be able to get the bowl to spin true. I hope that helps. If I confused you, let me know and I'll try again. :)
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Mike Mills

Good looking jig.  Really helps when the item is deep or has a small diameter.

A key to preventing wobble after remounting is to do as shown and make the base about as wide as the foot.  I use about a 2" diameter and 4" diameter depending on the size of the base; this puts the major support at the outside edge of the cutting area.
Most of my items are more shallow so a piece of leather (or thin foam, etc) over the chuck jaws does the same thing.   On deeper items the bowl would hit the headstock before the friction chuck made contact with the bowl bottom.

As Charlie stated, the key to recentering is to leave that little dimple from the tailstock.

Left Coast Chris

Thanks Charlie,  another good tool for the tool box.  My current method is the use of the flat plate jaws with rubber pieces to grip the outside or inside lip of the bowl.  Very good and fast (maybe Im spoiled) but does exert tension or compression around the circumfrance of the bowl.   Your method is good for fragile work also.  --thanks--
Home built cantilever head, 24 HP honda mill, Case 580D, MF 135 and one Squirel Dog Jack Russel Mix -- Crickett

CHARLIE

Chris, I have a set of those flat plate jaws and hardly use them for a couple of reasons. First, it takes too much time to unscrew the jaws on my chuck and screw on the plates and then unscrew the rubber knobs and screw them back into the correct holes for the bowl.  Secondly, I have to be careful when clamping down on the rim of a bowl or expanding against the rim on the inside of the bowl. Too much pressure it will crack and not enough pressure it might come loose. The tool I'm using here is easy and all the pressure is against the bottom of the bowl.
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Lud

I built a set of those plates and used them a few times but they've set for the last few years.  So I'm glad I didn't buy them.

I do both internal and external grabs with the Supernova II chuck and push the limits of  minimal grab with spigots of an eighth inch and less.  Hardly anything to turn off.

What I don't get is the turner's tradition of trying to disguise how the bowl had been held to the lathe.  It's like a guild thing of being mysterious!  You sense it in a lot of the writings and it's bogus.  John Q doesn't perceive the issue at all, IMHO.  I'd be interested in your opinion tho, Charlie......

Simplicity mill, Ford 1957 Golden Jubilee 841 Powermaster, 40x60 bankbarn, left-handed

CHARLIE

Well I got opinions and I usually voice them. ;D  Actually, I think that removing the evidence of how a piece was attached to a lathe is a woodturners thing.  If you ever watch a woodturner pick up someone elses bowl, the first thing they do is look at the bottom. Then they'll run their fingers across the wood on the inside of the bowl.  If it's a lidded box, they'll check the bottom and the fit of the lid.  A person that is not a woodturner doesn't look for all that stuff. They either like it or don't.  So, I reckon woodturners turn for the approval of other woodturners. :)  A lot of it shows a turners skill but isn't very practical. Like a bowl with paper thin sides. 
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Lud

"Turn for other turners".  That makes sense tho I speculate it can be applied to any activity.  Cooks cook for other cooks.  Sawyers saw for other sawyers applies to the forum.  Seamstresses sew for other sewers.

Any craft learns from it's masters which are the folks with more experience.  When it's done with humility  and a sharing attitude, it's right and honorable.  When it's secretive and tricky  and cute for no purpose , it's bogus.

You got the Right Stuff,  Charlie,  and I like the way you share it. 8)
Simplicity mill, Ford 1957 Golden Jubilee 841 Powermaster, 40x60 bankbarn, left-handed

metalspinner

Charlie,
Your system is a lot less complicated than mine. I need to get set up like you. :)  For normal sized bowls your set-up  looks nice.

I've been using what I call a donut chuck for finishing bottoms. But it takes a few minutes to chuck up the bowl. The "dimple method" is used to center this, too.  Here's a pic so you can see what I mean...



 

I like the security of this method on large work.  But for smaller and lighter objects, I'll give your set-up a try.  Thanks for sharing. :)
I do what the little voices in my wife's head tell me to do.

Lud

I thought about this yesterday while I refurbished a trailer and it came to me that we all  know the phrase " tricks of the trade" and there's two sides to it.  The good "tricks" are the ones that your Dad and Grandpa showed you of how to do a job right and easier and you discover yourself when you solve a puzzle doing a job.  Bad "tricks" are the deceptions  of fake antiques, art fraud, and deceptive bowl bottoms! :D
Simplicity mill, Ford 1957 Golden Jubilee 841 Powermaster, 40x60 bankbarn, left-handed

CHARLIE

Well, I do get a kick out of someone, most usually not a woodturner, look at something I made and say, "How you do that?"  I'll usually tell them a tall story first and then tell them how I really did it.  The one that usually gets people are the "Inside/Out" turnings. They wonder how I hollowed out the inside. ;D 

Metal Spinner, I've seen those kind of clamps but have been too DanG lazy to make any, so I've never used 'em.  I know one thing though, that bowl ain't coming off the lathe.  :)  For big bowls, I'd probably use that idea. I just don't make real big bowls. 
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

Mike Mills

My only thought on finishing the bottom of a bowl is just pride in the entire item.
When building cabinets in my home I dovetailed the drawers.  Makes no difference; I could have just glued them and hammered in some nails.  I fairly sure no one knows the drawers in the bathrooms are dovetailed.  Except me.

CHARLIE

I agree with you Mike. Pride in your workmanship has a lot to do with it.
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

terrifictimbersllc

Quote from: CHARLIE on February 11, 2012, 02:31:48 PM


 
(1) You can make the tool easy enough.  It is basically a #2 Morse Taper with a collar screwed on that also has a set screw. A short shaft with a 3 inch pully attached on the end. Epoxy a piece of cabinet grade plywood to the pully and turn it true to about a 4 inch diameter. Glue on a rubber pad.  Note:  I also make an abbreviated, less permanent tool, based on this idea, from wood which I clamp into my 4 jaw chuck and use to finish bottoms of turned lidded boxes.




 

Charlie, anyone, where can I get such a threaded collar? I found #2 morse taper to 3/8-24, 1/2-20, or 5/8-16 thread mount at mcmaster carr.
DJ Hoover, Terrific Timbers LLC,  Mystic CT Woodmizer Million Board Foot Club member. 2019 LT70 Super Wide 55 Yanmar,  LogRite fetching arch, WM BMS250 sharpener/BMT250 setter.  2001 F350 7.3L PSD 6 spd manual ZF 4x4 Crew Cab Long Bed

CHARLIE

It's been about 14 years and my memory has failed me.  Try a machine supply store or something in that order.  I'll look at mine and see if it has a brand name on it.  I think it might be called a Rigid Shaft Coupler.
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

terrifictimbersllc

I realized I have a drill chuck on a #2 Morse taper.  My lathe headstock (Conover) is #3 and I also have a #3 to #2 sleeve reducer.  Put this together and I have a drill chuck  in my headstock that holds 1/2".    Now the problem is that the drill chuck/#2 morse taper has about 10 thousandths runout at the end of the #2 taper before it goes into the chuck.  The headstock with just the #3 to 2 sleeve reducer, only about 1 thousandths.  I hate wobble.   Separated the chuck from the #2 taper (it has a 33 Jacobs taper on the other end going into the chuck). To make things simpler and get a higher quality taper for the chuck, I ordered a #3 to 33 jacobs taper from McMaster Carr, to replace the sleeve and the (probably) imported #2 to 33 taper which was on the chuck (says "Gray Goose" on the chuck.  Also ordered a hardened steel 1/2 shaft .  Will get it tomorrow and if it works post a picture.   
DJ Hoover, Terrific Timbers LLC,  Mystic CT Woodmizer Million Board Foot Club member. 2019 LT70 Super Wide 55 Yanmar,  LogRite fetching arch, WM BMS250 sharpener/BMT250 setter.  2001 F350 7.3L PSD 6 spd manual ZF 4x4 Crew Cab Long Bed

CHARLIE

OK, I made a closer look at the tool and also did some Google searches.  It is a #2 Morse Taper End Mill Holder for a 5/8 inch shaft. The one I have is made by Poland but there are many brands out there.  I hope that helps. 
Charlie
"Everybody was gone when I arrived but I decided to stick around until I could figure out why I was there !"

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