Modified caliper for bowl bottoms

I have usually estimated bowl bottom thickness using a rod touching the
bottom and sighting across the rims, then holding the mark move it to
the outside and sight. I found I often missed the true thickness by 3/4
inch. If I took the bowl off the dovetail chuck and did a caliper
measurement from the base of the dovetail recess to the inside bottom of
the bowl, it often would not run true on rechucking.
On ABPW is a rough drawing of how I made a dedicated caliper. It
measures from the shoulder of the dovetail jaws but indicates the true
thickness of the bowl bottom to the dovetail recess, while leaving the
bowl on the chuck.
I should modify the instructions to cut off the nib and tip of the
straight leg first and check the measurement on the empty chuck. It may
be possible to trim both the bowl side and the back side of the straight
leg of the caliper to adjust for zero. I wound up taking too much off
the curved tip and had to epoxy a dowel tip on, but it works great for
me. It is easy to measure and tell how much more wood to take out
without making a flower pot with a hole in the bottom.
Reply to
Gerald Ross
If you have a longbed lathe and leave the tailstock in place while hollowing a bowl...
Before you mount the bowl, measure the distance from some reference point on the tailstock and the face of the jaws. Write it down. Now, when you want to know the thickness of the bottom of the bowl, measure again and subtract.
For those of us with shortbeds who take off the tailstock -- I put a mark or a piece of masking tape somewhere handy on the bed. Then you would put a square on the bed at the mark and measure from the square.
Bill
Reply to
Bill Rubenstein
I don't know how to find ABPW, to see your tool, but I have a simple way where you don't have to take the bowl off, and the parts easily fit into your pocket. Measure the distance from your headstock to your chuck jaws. In my case, it is 4 3/8 inches with both of my Vicmark chucks. Cut a cheater stick this length. Now, to find the bottom, measure from the headstock to the rim of the bowl, say 9 inches. Put the cheater stick on the tape at 9 inches. This would show 4 5/8 inches. This is the depth from the rim to your chuck jaws. Next measure from the rim to the bottom of the bowl. If you want a 1/2 inch thick bottom, you would want the tape to read 4 1/8 inches. You can do this while the lathe is running, but when measuring from the headstock, don't let the tape hit the bowl edge as this can break you tape. If the bottom of your bowl is fairly smooth, it is easy to get the inside measure. This same method can be used on natural edge bowls but you have to use a big square on the lathe bed because you can't sight along the rim of the bowl. > I have usually estimated bowl bottom thickness using a rod touching the > bottom and sighting across the rims, then holding the mark move it to > the outside and sight. I found I often missed the true thickness by 3/4 > inch. If I took the bowl off the dovetail chuck and did a caliper > measurement from the base of the dovetail recess to the inside bottom of > the bowl, it often would not run true on rechucking. > > On ABPW is a rough drawing of how I made a dedicated caliper. It > measures from the shoulder of the dovetail jaws but indicates the true > thickness of the bowl bottom to the dovetail recess, while leaving the > bowl on the chuck. > > I should modify the instructions to cut off the nib and tip of the > straight leg first and check the measurement on the empty chuck. It may > be possible to trim both the bowl side and the back side of the straight > leg of the caliper to adjust for zero. I wound up taking too much off > the curved tip and had to epoxy a dowel tip on, but it works great for > me. It is easy to measure and tell how much more wood to take out > without making a flower pot with a hole in the bottom. > -- > Gerald Ross > Cochran, GA > > A millennium is like a centennial, > only it has more legs. > > > > > >
Reply to
robo hippy
Nice Gerald. Personally I use a bent wire as well as a depth guage, but the calipers are good.
______ God bless and safe turning Darrell Feltmate Truro, NS, Canada
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> I have usually estimated bowl bottom thickness using a rod touching the > bottom and sighting across the rims, then holding the mark move it to > the outside and sight. I found I often missed the true thickness by 3/4 > inch. If I took the bowl off the dovetail chuck and did a caliper > measurement from the base of the dovetail recess to the inside bottom of > the bowl, it often would not run true on rechucking. > > On ABPW is a rough drawing of how I made a dedicated caliper. It > measures from the shoulder of the dovetail jaws but indicates the true > thickness of the bowl bottom to the dovetail recess, while leaving the > bowl on the chuck. > > I should modify the instructions to cut off the nib and tip of the > straight leg first and check the measurement on the empty chuck. It may > be possible to trim both the bowl side and the back side of the straight > leg of the caliper to adjust for zero. I wound up taking too much off > the curved tip and had to epoxy a dowel tip on, but it works great for > me. It is easy to measure and tell how much more wood to take out > without making a flower pot with a hole in the bottom. > -- > Gerald Ross > Cochran, GA > > A millennium is like a centennial, > only it has more legs. > > > > > >
Reply to
Darrell Feltmate
Bill, In that vein, carpenter square from ways to face of chuck, mark ink/scribe on way, carpenter square to face of work, measure in and compare to ink/scribe mark and there's no question of exact depth. If face mark is taped to way at the start then any probe compared from head mark to tape quickly gives result without moving tailstock (if sufficient opening). OMO YMMV TomNie
Reply to
Tom Nie
Just goes to show you there is more than one way to skin a cat. Or as my old pappy used to say, "Two heads are better than one, but then you'd have to buy another hat."
Reply to
Gerald Ross
I have a probe which I can insert in my tailstock, using the Morse taper. This has an adjustable laser mounted above it, which I train on the tip of the probe. Then, I move the probe to the bottom of the bowl, and the laser shows me, on the outside of the bowl, where the bottom is.
This probe can be replaced with a drill, so I can drill into a bowl blank and see, as I am drilling, how close I am to the bottom. Then, as I am hollowing the bowl, the hole tells me when to stop. The hole also makes it easier to hollow the bowl, for obvious reasons.
Reply to
Leo Lichtman
You don't happen to have any pictures do you?? ^^^^^^^^^^^^^^^^^ Not at the present time, but if I get a chance, I will take one, and send it to you. I don't have a website.
Reply to
Leo Lichtman
Reed.. Since you sent me that trick, I've sort of customized it for my use:
I used a 3" wide scrap of 1/4" plywood that is notched to sit square against the headstock and ends at the end of the chuck jaws... (assuming that I don't put the spigot jaws on)
It will stay in place by itself, unlike my original stick, so I can use a more conventional bowl depth gauge and use the plywood for the "bowl bottom"... Just easier for me and the type of turning that I do to have the measurement of the jaw ends an inch or so above the place where the stick went.. Mac
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Reply to
mac davis
On Sat, 09 Sep 2006 21:07:27 GMT, "Leo Lichtman" wrote:
I think his is a little bit less expensive, leo... *lol*
Your setup sounds a lot like the Oneway hollowing system?? Mac
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Reply to
mac davis
Thanks, I appreciate it. I don't have a web site either. It seems like every one else does.
Bruce
You don't happen to have any pictures do you??
Reply to
Bruce Ferguson
Hi Gerald
Like they say there's more than Oneway to etc. cat etc. (pun intended).
Over the years I have developed a simple way of measuring the bottom thickness left or the depth to which to drill, that fits the way I work.
If I don't forget I will lay my blank face down, straightedge on the top and measure between the straightedge and the table surface.
If I forget or forget the just measured measure,(does never happen) than I will, with the blank in the chuck take the straightedge and hold it to the back of the blank and measure from the straightedge to the top of the blank.
Than to drill for instance the center of a bowl blank I detract the tenon or recess measurement from the total and the wanted bottom thickness to get the depth to drill to.
Now when I get close to the final inside depth and form I will use my calipers, (mine are similar to yours, I got them at Lee Valley, I will measure the wall thickness going down to the bottom,
Then (this works with my Stronghold chuck almost always) I slip the straight leg down between the chuck jaws and measure the center part of the bowl bottom, with a recess I get the true thickness and with a tenon I have to detract its thickness to arrive to the thickness left for the bottom. Doing it this way I now NEVER make any funnels like that anymore, ya right, now I only do it when I rework the foot or the recess, just happened to me again yesterday DARN DARN DARN.
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Have fun and take care Leo Van Der Loo
> I have usually estimated bowl bottom thickness using a rod touching the > bottom and sighting across the rims, then holding the mark move it to > the outside and sight. I found I often missed the true thickness by 3/4 > inch. If I took the bowl off the dovetail chuck and did a caliper > measurement from the base of the dovetail recess to the inside bottom of > the bowl, it often would not run true on rechucking. > > On ABPW is a rough drawing of how I made a dedicated caliper. It > measures from the shoulder of the dovetail jaws but indicates the true > thickness of the bowl bottom to the dovetail recess, while leaving the > bowl on the chuck. > > I should modify the instructions to cut off the nib and tip of the > straight leg first and check the measurement on the empty chuck. It may > be possible to trim both the bowl side and the back side of the straight > leg of the caliper to adjust for zero. I wound up taking too much off > the curved tip and had to epoxy a dowel tip on, but it works great for > me. It is easy to measure and tell how much more wood to take out > without making a flower pot with a hole in the bottom. > -- > Gerald Ross > Cochran, GA > > A millennium is like a centennial, > only it has more legs. > > > > > >
Reply to
l.vanderloo

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