Why are bowls and hollow vessels turned in this sequence?

[Glen Blanchard]

For the sake of this discussion, let's assume that we are discussing turning dry wood. That is, there is no second turning.

It seems that most (if not all) the time when someone is making a bowl or a hollow vessel they contour the outside and then create a foot/tenon on the tailstock end. The piece is then reversed, chucked up in a scroll chuck and hollowed. As a last step, it is then reversed (again) and the bottom of the piece and the foot are refined.

Here is my question:

Why not contour the top 3/4 of the outside and do the hollowing and then reverse chuck (jam, vacuum, longworth, etc) to finish the bottom 1/4 and the foot? Doing it this way would eliminate one reversal. This could not be done between centers, but would require a glue block or something similar, but I don't know that I have ever seen it done in this fashion. Just wondering.

[John Keeton]

Glen, I am sure there will be many reasons given, but one might be the ability of a RH turner to cut 'downhill' on the lower portions first. I find it a bit more difficult to do the lower contour initial cuts from the headstock side.

[Brian Kent]

My novice answer - I need to start with a faceplate. If I was starting on the underside, I would lose some wood to the screw holes. I could do it if I used a glue block to start.

[Faust M. Ruggiero]

Glen,
I guess the simple answer is, "that's the work flow that we learned and it works". Turning the bowl onto a vacuum to remove the tenon is just no big deal.
Secondly, most of the time you start between centers, then form a tenon and mount in a chuck you will need to true the outside. Chucks rarely allow the bowl to turn exactly on the same center as is lived between centers. Not truing the outside after reversing the bowl would not allow you a smooth transition from the 3/4 you finished to the last 1/4 you did not.
faust

[Steve Schlumpf]

As someone who does hollow forms, it would be extremely hard to keep a consistent thickness while hollowing when there is no outside curve to gauge things by.

[Prashun Patel]

I'm going to give this a try. I've often thought that the outside form should follow the inside form on bowls - and not vice versa.

[Glen Blanchard]

As someone who does hollow forms, it would be extremely hard to keep a consistent thickness while hollowing when there is no outside curve to gauge things by.

This is exactly what my thought process was.

[Glen Blanchard]

I'm going to give this a try. I've often thought that the outside form should follow the inside form on bowls - and not vice versa.

Prashun - Aren't we doing exactly the opposite though when we hollow? We make the inside conform to the outside, no?

[Thomas Canfield]

It is hard to see the inside when you have a jam chuck stuck in the opening and then try to match the outside to the inside. Don't ask how I know from experience removing tenons on standard turned items.

[Wally Dickerman]

I do my HF's a bit differently than most....when starting with a dry piece of wood I rough turn first leaving the bottom 20% unfinished. When I do my hollowing, as I near the bottom portion I work on both the inside and outside. It takes experience to be able to picture in my mind what the final form will be.

I also do my finishing a bit different than most...I do my finishing while the piece is still mounted on the lathe. I've done hundreds of pieces that way and see no reason to change.

[Jeffrey J Smith]

For me, the outside of the piece establishes the form. I rough out to eliminate obvious defects from the timber, then contour the best form I can fashion from what's left. whether it's an open form or closed, owl or hollow form, the outside contour establishes the line of the interior.Personally, I'm thinking of the inside of the piece as I finish the outside. I'm looking for flowing curves that blend into each other. For bowls, the inside curve needs to flow seamlessly from rim to center and generally mimic the outside form.

I usually get everything except the foot and about 10% up from there done and sanded mostly to completion before reversing to hollow. Hollowing is a matter of following the curve of the side and establishing the bottom contour as an uninterrupted extension of the sides. At this point, I'll put on a single coat of the finish and very often if there are other pieces to complete, let it sit until the other pieces are ready to finsh the bottom. Then when I go to the vacuum chuck, I'll finish them all in one sitting.

Just seems efficient for me. If I've got a lot going, they'll sit for several daqys before I get to finishing.

[John Beaver]

Here's my opinion.



Why not contour the top 3/4 of the outside and do the hollowing and then reverse chuck (jam, vacuum, longworth, etc) to finish the bottom 1/4 and the foot? Doing it this way would eliminate one reversal. This could not be done between centers, but would require a glue block or something similar, but I don't know that I have ever seen it done in this fashion. Just wondering.

First off, as you said, you could not start between centers, which is the way I do all my vessels. This gives you the ability to adjust the form to the grain as you start turning your shape.

Secondly, for almost all your bowl shapes this would require turning downhill on the outside 3/4 which is riskier for tear-out.

Third, you would not have the outside profile finished so you could not be super accurate on your wall thickness for the bottom 1/4. Most likely you would probably end up with a bowl too thick or thin at the bottom.

As far as Prashun's idea, I have to disagree. The outside profile is the most visible and therefore the most critical and the one that should be done first. It would be very difficult to turn an interior first and end up with a nice curve on the outside - unless you aren't concerned with wall thickness, which you should be.

Lastly, it would seem prudent when starting a bowl between centers to have the base at the headstock end, and hence the tenon would have less chance for runout, however most lathes have more room at the tail stock end so you can access the bottom easier from that end.

[robert baccus]

I think we get too hung up on rules yeah. Principles work better for me as mine are very flexible. Just do what the situation or your likes at the moment call for. I start between centers, mostly HF, nicely contour the exterior, flat the base, glueblock, reverse to a single screw, mutilate the interior, sand, finish, reverse, cut off the GB and sign. But wood moves, even dry wood and even cast iron on bad days so It's okay to reverse 2-3 times a day if necessary Grrrrrr. Listen to Wally--them gray hairs came at a price.

[Lloyd Butler]

I would think it also depends on the finished shape and thickness of the top portion of the piece.

If you have a closed in piece, how do you hold it firm enough to cut away that extra material on the bottom. Sometimes it is tough enough to support the piece to lightly nibble away the little bit of a tenon you had.

The same goes or a thin walled piece. It is harder to hold on to it so that it is well supported so it does not break.

Lloyd

[Kyle Iwamoto]

In addition to all the above, I think if you form the outside first, the main thing is the blank gets balanced. If we turned the inside first, I would think you would always be limited to very low RPMs due to the blank being out of balance. A lot of times, speed is the best thing to get a smooth finish. Having a blank wobble around could also cause a lot of errors when cutting. The inside of a bowl is hard enough to cut smoothly in the first place.

Just my $0.02.

[Faust M. Ruggiero]

This is a good thread because it makes us think about our process and why. I answered the mechanical answer to this question yesterday. Here is an answer from a person who just enjoys turning. I use my current methods not because they are the fastest way since I am not a production turner. Even if I were, I would gain speed by the sheer repetition, not by skipping a step that would cause my work to be of lower quality. I enjoy the turning process and don't really rush it. Speed nor the shortest cut method is anywhere in my game plan. I even enjoy the sanding and finishing process. The process of taking a piece of wood from log to art form has so many steps and requires so much time that saving a few seconds means nothing to me.
However, I do thank you for provoking us to think about why we do the things we do. It's always important to look with fresh eyes.
faust

[Prashun Patel]

John, I'm sure most people see it as you do. However, I think the inside is more critical, because the entirety of the grain pattern is visible at once. On the outside, you see only a portion of the whole.

My comment about the outside following the inside is based more on form than grain, though. I find the hollowing motion on bowls more natural and fluid. For that reason, my interior curves tend to look better to my eye. Often, though, I have to alter it slightly to conform to the outside, or live with uneven wall thickness.

As for having to hollow at low rpms, one could first bring the outside to rough form, then hollow, then final turn the outside. The benefit to doing this would not be so much time saved; but would save having to re-center.

I also wonder what effect this would have on vibration around the rim when things get thin...

[Grant Wilkinson]

I'm something of a newbie, but I've done bowls both ways. The OP's proposal works for me if the blank is a glue up with a good flat surface to glue a waste block to. I glue the waste block to what will be the bottom of the bowl, mount a face plate to the waste block, turn the outside, hollow the inside,then reverse it to remove the waste block and finish turn the outside. I do more than 3/4 that the OP suggests because when I reverse it, my hold is not strong enough for anything other than very fine cuts to finish the bottom.
If I am starting with a dry log section, though, I do not have a flat surface to glue a waste block to, so I start between centers, and do the "two reversal" method.
Like Faust, I am not a production turner, and I'm in no big hurry to finish, so two reversals is no big deal.

[ron david]

on the little stuff there are various ways but when you get to a little larger pieces I just screw it to a faceplate and part it off when done
http://s908.beta.photobucket.com/user/padresag/library/turned%20work some of these are up to 2' tall
ron

[Jeff Nicol]

Well for me there is never a pre-determined shape, or form in mind when I mount a blank on the lathe. But some blanks that are tall or long they will most always be a vase or vessel/HF and flatter ones may become a bowl, HF, or closed form, and it all depends on what I find in the blank. I never worry about the direction of the grain, because I can always overcome whatever direction the grain is going with a little time and light finishing cuts prior to sanding. I do most always start by roughing the blank so it is turning smoothly, then I may create the basic form, create a tenon at the headstock end leaving enough extra wood that the tenon is not all that is at the bottom. This way I always have enough wood to hold on for reversing or to part of when a foot is detailed. Then depending on what the piece is that will determine how I will reverse chuck it to finish the bottoms.

So I agree with Kyle and just start and finish where I finish, but the outside is always done first and the inside is matched to that except with tall HF that need a little more weight in the base for stability.

Just keep turning and enjoy the outcome of each piece,

Jeff

[Robert Henrickson]

Many of the bowls I turn follow the 'classic' sequence, but some types may have the tenon on the inside of the bowl rather than on the base. Depends on the various characteristics of a given shape. Almost all bowls and plates I turn have tenons (some on waste blocks), and are finally reversed on a jam chuck to remove the tenon. Though I have a vacuum chuck, I don't use it.

[ron david]

on the little stuff there are various ways but when you get to a little larger pieces I just screw it to a faceplate and part it off when done
http://s908.beta.photobucket.com/user/padresag/library/turned%20work some of these are up to 2' tall
ron
when you have to use a faceplate
http://i908.photobucket.com/albums/ac281/padresag/wood/Image6_zps13e05fe7.jpg
http://i908.photobucket.com/albums/ac281/padresag/wood/Image7_zps075a6bf8.jpg
http://i908.photobucket.com/albums/ac281/padresag/wood/Image9_zps6adc48f8.jpg

http://i908.photobucket.com/albums/ac281/padresag/turned%20works/mapleburlhtvase2.jpg

http://i908.photobucket.com/albums/ac281/padresag/turned%20works/mapleburlhtvase.jpg
ron

[Prashun Patel]

Ok, so I tried it this weekend. I didn't like it. It is trickier to cut downhill on the outside. Very possible, but not comfortable.

The big reason I won't do this again (unless necessary) is because there's no way to mark the center of the bottom. This means when you go to flip the bowl to finish off the bottom, it's tricky (read hit or miss) to get the blank centered properly. This meant recutting the outside all the way up to get it to blend in properly. In the end, it did not save any effort for me.

[ron david]

a lot of times one will place it between centres to clean up for however you are going to mount it. that will mark your centres for later.
then you have to get trickier to cut downhill. always be sharp. you can always cut uphill or bring the tool back towards yourself on a shearing cut
ron