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Bowl depth
- Thread starter Heath Warren
- Start date
You could consider some of the alternative gauges that Doc Green has documented on his website in the Gauges section of his Articles webpage.
I would love to say that I have never had the inside diameter exceed the outside diameter, but that wouldn't be accurate.
Good luck!
I would love to say that I have never had the inside diameter exceed the outside diameter, but that wouldn't be accurate.
Good luck!
Thanks. I’ll check it out. This was the first time it happened. I’m sure it won’t be the last
I mounted a drill bit in a handle (sorry - no picture at the moment). (See Richard Raffan's or Tomislav's youtube videos.) Measure on the outside of the bowl, and mark the drill bit with a sharpie. Then using the lathe, drill down to the sharpie line. That is the depth to hollow out your bowl. In 3 years of turning, only went through the bottom once - and that was more on the side because I wasn't paying attention. I have had many very thin bottoms due to not estimating the depth very well. Also look at Sam Angelo's youtube for his shop-made depth gauge.
I span a ruler across the rim and use a second ruler or calipers to measure from the edge of the first ruler to the bottom.
Dave Landers
Beta Tester
My favorite calipers are my "Digital" ones (digits == fingers!)
When those aren't good enough I usually reach for my homemade bent-wire calipers.
Bend a stiff wire (like1/8" diameter) so it'll get to wherever you need it. A sorta "D" shape usually is pretty good. If you're aiming (for example) to get a 1/4" wall, and you set the gap in the wire at 1/2" - then when the wire gap is 1/4" (between wire and outer bowl wall), you're there. I think it works better than setting the wire gap at exactly what you're aiming for, because you can judge progress and how far you have to go.
The other thing I do with bowls is to first get a consistent but thick wall. Thick so there's still wood to work with to get it consistent without risking going too thin. Then, always take off a consistent depth of cut (watch the "shelf" created by the gouge). As an example, make a consistent wall thickness of 3/4", all the way down. Then take passes removing consistently 1/8" each time. 4 passes and you're at 1/4". If your passes were consistent, there's no way to break thru the bottom.
(Wall thickness examples are not recommendations for bowl walls, just convenient numbers to work with).
When those aren't good enough I usually reach for my homemade bent-wire calipers.
Bend a stiff wire (like1/8" diameter) so it'll get to wherever you need it. A sorta "D" shape usually is pretty good. If you're aiming (for example) to get a 1/4" wall, and you set the gap in the wire at 1/2" - then when the wire gap is 1/4" (between wire and outer bowl wall), you're there. I think it works better than setting the wire gap at exactly what you're aiming for, because you can judge progress and how far you have to go.
The other thing I do with bowls is to first get a consistent but thick wall. Thick so there's still wood to work with to get it consistent without risking going too thin. Then, always take off a consistent depth of cut (watch the "shelf" created by the gouge). As an example, make a consistent wall thickness of 3/4", all the way down. Then take passes removing consistently 1/8" each time. 4 passes and you're at 1/4". If your passes were consistent, there's no way to break thru the bottom.
(Wall thickness examples are not recommendations for bowl walls, just convenient numbers to work with).
I made several slide wire thickness gauges with parts from Menards like in the picture, but I needed something to do depth holes more easily. I made one of the Richard Raffan wood handled drill tools and it works ok. I saw someone online make a simple depth hole gauge using a Jacobs chuck. I made one for my son using the chuck I got from Amazon for about $10. I added a handle and the beauty is you can use any bit you want and like Richard does with his tool you can adjust the length of the bit in the chuck to your desired depth and then drill in to the end of the chuck. Except for the bit and my time I have 10-12 dollars in this tool.
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Well, this is my method:
View: https://www.youtube.com/watch?v=0Ov5m50NXJ8
I never drill out my bowls since that only gets me close, but not exact. You can measure the inside and site along the rim for the measure and then put that on the outside, which again gets you "close" but not exact. My method gets you pretty exact. I guess the only other method would be if there is air in between your grip on the tenon and you can slip a caliper in the gap. I do use a recess, always.
robo hippy
I never drill out my bowls since that only gets me close, but not exact. You can measure the inside and site along the rim for the measure and then put that on the outside, which again gets you "close" but not exact. My method gets you pretty exact. I guess the only other method would be if there is air in between your grip on the tenon and you can slip a caliper in the gap. I do use a recess, always.
robo hippy
I mount drill bits in handles too - made these long ago, used drill stop collars to set the depth. The bit diameter, of course, doesn't matter. The outside is completely shaped first then the depth hole drilled.
Allow a "little bit" extra. Turn the wood, press the drill still it stops. Hollowing to the hole gets me the right depth as long as I keep the shape in mind. Once hollowed in the center, I have several specialized calipers to test the thickness while shaping the inside towards the wall and bottom.
The stop collars are nice because I don't have to watch the bit carefully and try to remember which Sharpie line is the the right one!
These are for small things but could use longer bits for deeper. I usually use longer taper shank bits directly in the tailstock MT and marked with a Sharpie (or a piece of tape) to drill deeper holes. The longer bits (up to 1" in dia") fit the 2MT, the smaller need a #1 to #2MT adapter.
(These are my favorite bits for drilling almost anything on the lathe). I started with several, now have most sizes. Using these I usually mark the depth with a bit of my favorite tape, Scotch #2026. (Hard to function without it.)
JKJ
Good idea. I’m going to do that.
I use a pencil, or a chuck key. Simply place it in the bottom of the bowl then sight the depth.
Dave Landers
Beta Tester
I have o-rings on my depth drills
Hollow-Pro Caliper
Designed by Mike Jackofsky, the precision made Hollow-Pro Caliper combines steel and aluminum for maximum strength while maintaining a comfortable light working weight and is designed to indicate the wall thickness of hollow forms, vessels, bowls and platters by transferring the measurement from...
woodturnerscatalog.com
Simon Hope Measuring Caliper
Never go through the bottom of a bowl again! Caliper made from stainless steel. Available in 10" and 16" Lengths. CNC routed numbers that wont wear out.
blackforestwood.com
Congratulations on making your first funnel! It's a rite of passage. Some of us have been through the rite multiple times.
I've tried a variety of methods, and there are some pretty good gadgets available, but the one that works for me and my clumsy fingers is below. Somebody else figured this out and I just copied. It worked wonderfully on boxes, so I made a bigger one for bowls. Some versions have a screw to hold the sliding rod in place, but I find I can hold the measurement without a screw.
The gauge is used while the bowl is still in the chuck, but I don't have a blank with a tenon available. The process is to span the sides, slide the rod to the bottom of the bowl, take the gauge out, put the rod along the side with the cross piece on the rim and sight down on the end of the rod.
I've tried a variety of methods, and there are some pretty good gadgets available, but the one that works for me and my clumsy fingers is below. Somebody else figured this out and I just copied. It worked wonderfully on boxes, so I made a bigger one for bowls. Some versions have a screw to hold the sliding rod in place, but I find I can hold the measurement without a screw.
The gauge is used while the bowl is still in the chuck, but I don't have a blank with a tenon available. The process is to span the sides, slide the rod to the bottom of the bowl, take the gauge out, put the rod along the side with the cross piece on the rim and sight down on the end of the rod.
I use a variation of what Reed Gray shows in his video in Post #8. I started doing this when I was making a lot of natural edge bowls. The uneven rim on NE bowls makes some of the more common depth gauges less useful or at least trickier to use.
The key point is to know the distance from the headstock to the face of the jaws for each chuck. The face of the jaws is also the bottom outside of the bowl.
I measure that distance and write it on each chuck. To check my bowl depth I put the end of the shorter leg of a framing square against the headstock with the longer leg of the square standing vertically, aligned with the center of the bowl. Measure the distance from the framing square vertical leg to the inside bottom of the bowl. Do some math to get the thickness of the bottom of the bowl.
An example, with made up numbers:
Math can be challenging when fractions are involved. What I actually do is to subtract the distance from the headstock to the jaw face from 14" and write that on my chuck. So if the distance is 9 5/8", I write 4 3/8" on the chuck. When I measure, if the distance is greater than 4 3/8", I've already made a funnel. If it's less, you can see right on the tape measure how much room you have left before you hit 4 3/8". That the bottom thickness.
Hope this makes sense and is helpful.
The key point is to know the distance from the headstock to the face of the jaws for each chuck. The face of the jaws is also the bottom outside of the bowl.
I measure that distance and write it on each chuck. To check my bowl depth I put the end of the shorter leg of a framing square against the headstock with the longer leg of the square standing vertically, aligned with the center of the bowl. Measure the distance from the framing square vertical leg to the inside bottom of the bowl. Do some math to get the thickness of the bottom of the bowl.
An example, with made up numbers:
- 10" from headstock to face of jaws
- 3.5" from framing square vertical leg to center inside bottom of bowl
- 14" (from headstock to inside of framing square vertical leg) - 10" (from headstock to chuck jaw face) - 3.5" (from framing square vertical leg to bowl inside bottom) = 0.5" thickness on bottom of the bowl
Math can be challenging when fractions are involved. What I actually do is to subtract the distance from the headstock to the jaw face from 14" and write that on my chuck. So if the distance is 9 5/8", I write 4 3/8" on the chuck. When I measure, if the distance is greater than 4 3/8", I've already made a funnel. If it's less, you can see right on the tape measure how much room you have left before you hit 4 3/8". That the bottom thickness.
Hope this makes sense and is helpful.
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That’s what Mike Jackofsky does.
@robo hippy (post #8) & @Dave Bunge (#15), good ideas. And these methods will work independent of the height of the bowl and with either tenon or recess.
Using millimeters would greatly simplify the calculations.
I totally agree and almost wrote that in my original post.
I'm comfortable with English units and fractions and have a more intuitive feel for dimensions using them. I did get a 3D printer recently and everything in the 3D printing world seems to be in metric so I'm getting reacquainted with the advantages of the metric system. I recently ordered a pure metric tape measure from Amazon to use in the shop: https://www.amazon.com/Fastcap-PMMR...s=hi&sprefix=fastcap+true+32,tools,158&sr=1-1
Another reason I don't use a drill bit for depth is that I core any bowl blanks that are worth saving. Never take that last little bowl though, had way too many of them hanging out around the shop unfinished.....
robo hippy
robo hippy