Modified caliper for bowl bottoms

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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

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Re: Modified caliper for bowl bottoms
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

Gerald Ross wrote:
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Re: Modified caliper for bowl bottoms
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

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Re: Modified caliper for bowl bottoms
Tom Nie wrote:
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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."

--  
Gerald Ross
Cochran, GA

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Re: Modified caliper for bowl bottoms
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.
Gerald Ross wrote:
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Re: Modified caliper for bowl bottoms

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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

https://home.comcast.net/~mac.davis
https://home.comcast.net/~mac.davis/wood_stuff.htm

Re: Modified caliper for bowl bottoms
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
www.aroundthewoods.com
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Re: Modified caliper for bowl bottoms
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.  



Re: Modified caliper for bowl bottoms
Leo Lichtman wrote:
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Wow!

--  
Gerald Ross
Cochran, GA

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Re: Modified caliper for bowl bottoms
You don't happen to have any pictures do you??

Bruce

Leo Lichtman wrote:
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Re: Modified caliper for bowl bottoms

"Bruce Ferguson" wrote:   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.  



Re: Modified caliper for bowl bottoms
Thanks, I appreciate it.  I don't have a web site either.  It seems like  
every one else does.

Bruce

Leo Lichtman wrote:
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Re: Modified caliper for bowl bottoms
wrote:

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I think his is a little bit less expensive, leo... *lol*

Your setup sounds a lot like the Oneway hollowing system??
Mac

https://home.comcast.net/~mac.davis
https://home.comcast.net/~mac.davis/wood_stuff.htm

Re: Modified caliper for bowl bottoms
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.

http://homepage.mac.com/l.vanderloo/PhotoAlbum28.html

Have fun and take care
Leo Van Der Loo



Gerald Ross wrote:
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