why do my bowls end up so shallow?

[andrew zukewycz]

i keep making these really nice bowls, no more lines in the bottom when im done since i got my grinding jig=sharp tools...

but i find myself using my scrapers more often than not...

i usually rough gouge the outside, then do the same with a smaller gouge to the inside, but then a scraper seems to give me the best results on the inside...

once im getting down to the final shape, i always make the base too thick, and the bowl too shallow...

heres a rather large bowl, that ended up too shallow
http://i92.photobucket.com/albums/l40/zuke83/woodturning/2008_1218woodturningsdec0016.jpg

ive had a bowl get too thin and break apart on me, is it that im afraid for them to be too thin, or is it the tool chatter towards the finished product? it allways seems to be hard to get the bowl deeper and deeper without causing too much thinning in the side walls...

is there a tool or technique im missing?

or is it just lack of experiance?

thx
zuke

[scott schmidt grasshopper]

you say you rough the outside then the inside,, hhm
most? would turn the outside with the peice held by a faceplate or chuck in a forstner hole on the inside ( top ) of the bowl . then finish cut the outside do everything and might include sanding it . then put a mortise (inny)in the bottom for a chuck or a tenon ( outy). I prefer the outy cause it means I dont have to account for the mortise cutoff after I hollow.
once you remount the bowl making sure it runs pretty close to true then start hollowing. I think you are perhaps not hollowing in stages which will allow your sides to start flexing. try steps in the process. 1 or 2 inches at a time leaving plenty of wood below the working level to hold the bowl steady . be sure to blend each stage as you get to final thickness. are you using calipers or a C shaped bent wire to gauge uniformity of wall thickness? I use two peices so I can tell if I am following the curve at say 1/2" thick and then to see if I am to final thickness of 1/4 to 3/8".
as for the scraper are you using it in shear cut mode? this will greatly reduce the forces and mellow out grabbing/ flexing the thinner wall.
when you get to the bottom if you have an inny ( mortise) then you can reverse the bowl on a jam chuck or donut chuck to remove the added @ 1/4" of bottom thickness or to cut off the tenon
good luck

[andrew zukewycz]

i normally use a 4blade and put a tennon while im between centers...

then with my tennon cut i use my jaws and rough the outside... then get near finish product on outside...

then i drill to my desired depth, and gouge out the insides... but its allways difficult to cut where the sidewall meets the bottom of the bowl and there allways seems to be a lot of chatter... i sharpen, then attempt again, still chatter...

once i get close enough to the look i think i like ( which allways ends up being too shallow off the lathe later!) i make a jam chuck and cut the tennon off and finish sanding/staining w/high friction bowl finish.

my technique is adding to the depth of the bowls? or my poor quality tools?

[alex carey]

this might all be good advise but i'd just chalk it up to lack of experience. When I first started I had the same problem. Just keep making bowls and don't worry about the finished product, take risks. If the bowl breaks or turns out bad you will still have learned something.

Keep turning

[neil mackay]

[this might all be good advise but i'd just chalk it up to lack of experience. When I first started I had the same problem. Just keep making bowls and don't worry about the finished product, take risks. If the bowl breaks or turns out bad you will still have learned something.



That pretty well sums it up, I think we all are guilty of doing this at some stage. Dont feel too bad just keep on turning, try using some cheap pine so there is no great loss to the pocket.

[Jeff Nicol]

Andrew, I think the fear of wrecking the bowl after all the work put into it is holding you back. The first thing I would get is a caliper to check the thickness of the bowl as you turn it. Also you could drill a hole to the depth you want to finish at and when you hit that depth you finish every thing to that. It takes some patience and no fear of failure as was already said.

Hope this helps,

Jeff

[Bernie Weishapl]

One thing I found that helped me when I first started is to use a curved tool rest on the inside of the bowl getting it as close to the work as possible. This will eliminate the tool hanging over the edge to far. I would also get you a figure 8 caliper with a big end and small end. Keep measuring the bottom and sides. Just keep at it. It will come and yes I do have several beautiful funnels on the shelf as reminders to take my time and measure.

[William Bachtel]

When it gets close to being too thin on the bottom, you will start to hear a different sound. You might try making a very thin plate, or bowl l/8 or thinner, this will show, that you can do it. Get the calibers. Out of several hundred bowls, I have gone thru only one., no take that back went thur the side of one too.

[George Guadiane]

All good ideas!
I have the same problem, STILL... I have started drilling the bottom (almost) "to depth." In that way, I already know where I want to end up and just work the inside profile to match the outside... For turning green and thin, all in one shot, I was taught to work from the top down in sections, about an inch at a time (someone MUST have a tutorial or video on the technique), and don't plan on going back to the to the previous section, except to "blend" the previous section to the current one. I don't see why that method wouldn't work for thicker turnings as well, and it would be good practice for when you fell confident enough to go for super thin.
(JMThought)

[Curt Fuller]

Andrew I chuckled when I read your post. I have a bunch of bowls that are the same, thick bottomed shallow bowls. Here's my guess why. I used to get too anxious to get them done. I wanted to see what they looked like with finish on them. In fact I still have a tendency to do that. Also, I would get a nice looking, smooth surface inside the bowl and not want to mess it up so I'd quit before I had the actual shape and depth I really wanted. You just have to forego the temptation to quit before it's the shape and wall thickness you want. Don't take you're scraper out of the tool rack until you have the bowl you want. Then get it out and make those last few shear scrapes and call it done.

BTW, that's a nice looking bowl.

[Steve Schlumpf]

Andrew - nothing to add as far as advice - just wanted to say that I like the bowl! Good looking wood and finish! Form comes with time! Relax and have fun with it!

[David Christopher]

Andrew - nothing to add as far as advice - just wanted to say that I like the bowl! Good looking wood and finish! Form comes with time! Relax and have fun with it!

ditto what Steve said

[Brendan McAreavy]

Hi Andrew,

I know exactly what you are talking about because all my bowls had heavy bases at the start and were a lot more shallow than I thought. My problem was that I was overestimating the depth I had gone in the bowl and I was scared of going through the bottom. I think I was also having difficulty separating my awareness of the thickness of the finished wall at the top from my estimation of the thickness of the remaining bottom and that curve towards the base made me feel I was a lot closer to cutting through the wall than I was.

I got a piece of wood and rounded it to about 2 inches in diameter and then started hollowing the end with a gouge. I would work for a few minutes, estimate how far I had gone in and then stop the lathe and measure it. Every single estimation I made of the depth I had gone was about twice as far as the actual measurement. I did this a number of times and still I overestimated the depth. I think I was estimating the depth by the time I was working and thinking 'I must be rightly down by now'.

So, I made a depth measure (just a piece of wood wider than the bowl and a dowel pushed through a hole in the middle) and measure regularly. I measure wall thickness a lot too. I still find it hard to believe how little I have actually hollowed and I still get scared nearing the bottom but my bowls are a lot deeper and weigh a lot less.

[Thom Sturgill]

i usually rough gouge the outside, then do the same with a smaller gouge to the inside...


Do you have a curved tool rest? If not, then the tool overhang on the inside is much greater than than when turning the outside and the tool will tend to flex causing chatter. A thinner tool just makes that worse. Rather than using a smaller gouge, try grinding a secondary bevel rounding the 'heel' to reduce the amount of bevel rubbing.

Also, I would ditto the comment to use a stick across the bowl to measure from and measure the depth and compare that to the bowl height. That is what I had to do to get the bottoms deep enough.

[scott schmidt grasshopper]

a suggestion for a depth gauge. make up a block of wood (1x4?)that is the same distance away from the headstock as your chuck jaws are. then when you square off the rim you measure the height of the rim with the block and a tape measure ( say top of chuck 3.5 inches plus tape measure to rim of 3.25 inches) then I write this number on the edge of the bowl , subtract what I want to ending bottom thickness ( 3/8) so I know I need to be 3.125 ( 3-1/8) when I am done to depth . I can check this often and then take the center out almost to depth until I have the sides done and finish the inside bottom then . something I still have a problem with is getting the tenon off/ thinner before my green turned gets dried( 3/8 bottom thickness plus 1/4 in or more tenon depth) so after I finish the bowl I put the rest between the chuck and bowl and use a parting tool to reduce the bottom on the outside leaving a small ring tenon/ mortise. this helped keep green turned from cracking due to the extra tenon thickness

[Paul Douglass]

I use one of these. Got it from Bill Grumbines's DVD. Works great. Takes 10 minutes to build. Set the rods to the depth of the bowl, than sight down the two rods and you can see and mark on the outside how deep the bowl is. Works great.

[alex carey]

as far as a depth gauge goes, I just use a measuring tape and eye ball it. Might not work for you but so far has worked for me. Also I tap the wood with my knuckles and listen to it, with practice this will work for you.

[ROY DICK]

We have all been there. Use whatever measuring device works for you.
Close your eyes and use your fingers to check depth/thickness (thinless ?).You will be surprised that you can get real close.

Roy

[Ryan Baker]

There's a lot of good advice here about ways to measure the depth. If you find a method that works for you and use it frequently, you should know when you are to the depth you want and not have to worry about going too deep or end up stopping too soon.

As far as your chatter problems on the bottom, several things come to mind. One, as mentioned, is that too small a tool hanging out over the rest will tend to chatter and grab more. For that you could try a bigger tool or a curved rest.

When you go around the corner from the sides to the bottom, you are cutting into the end grain, which is a harder cut. That will make the gouge grab more too. Take lighter cuts. You may also be losing your bevel support when going around the corner, which will also cause grabbing. There are techniques for cutting smoother in such cases. You can also switch to a gouge with a much steeper bevel, like an 80 degree traditional grind, which is much easier to use in the bottom.

Keep practicing. You'll find a combination that works for you.

[Skip Spaulding]

Andrew, pretty bowl, thick and heavy make good "Utility Bowls", you can cut, chop and mash in them. They stay put and don't break! I found as my skill improved I make more "Salad Bowls", thinner, nicer shape etc. My wife tells me utility bowls also have a place!

[Kyle Iwamoto]

There are no mistakes. Just learning events. Keep cutting.
Even if the bowl catches and flies out, re-chuck it and turn the gouge out. All that meant was the bowl was too big anyways. Ashtrays are cool too....:)