Finger Caliper Adjustments??

[William Hutchinson]

I used my finger caliper to check the bottom depth of this bowl. How do you calibrate these things?:eek:

http://i3.photobucket.com/albums/y66/wlhutch/Turnings/toothin2.jpg

http://i3.photobucket.com/albums/y66/wlhutch/Turnings/toothin3.jpg

http://i3.photobucket.com/albums/y66/wlhutch/Turnings/toothinbottom.jpg

After the piece was ruined, the bottom became a test pallet for dye colors.

[Bob Vallaster]

Will,
The saying goes: There are those who have done it... and those who will. Congratulations on having undergone a rite of passage.
One way to cope is to drill a hole from the face side before you begin to hollow. Example: For a 4" thick block, you could drill a 3 1/2' deep hole and let the bottom of that hole be the depth limit for your hollowing. The 1/2" will probably wind up being further reduced when (inside) cleanup cuts take out the mark of the drill point and later cuts on the reversed bowl put a rim-and-relief for a bottom. Caution is the byword.
Another way is to make a cheap depth gage from a piece of flat stock and a 1/4" dowel that fits in a through-hole. The flat stock is placed on the rim and the dowel is pushed to the bottom of the hollow. Once you have plumbed the depth, remove the gage and view it against the profile of the roughed bowl. So long as the extended dowel does not reach your glueblock/faceplate/chuck, you have the (crudely) indicated bottom thickness.

BobV

[Tom Wilson66]

You know of course that any adjustments to a delicate instrument can have an affect on the measurements of that instrument. So when you trimmed your fingernails, you needed to recalibrate.:p

[John Keeton]

My first inclination would be to go with Tom's theory on the fingernails, but it is also possible you may have failed to account for that highly accurate "angle of view!" I find with my "set of calipers" that my years of training and experience come in to play when I mentally calculate the precise perpendicular view of the "read point" on the caliper.

Apparently, however, there are now more precise instruments available for this task!

[Fred Perreault]

Just an informal poll.... all of those that have NOT gone through the bottom of a turning, please sign in. I would suggest that this poll would produce a much smaller number than if it was asked... "how many HAVE gone through the bottom of a turning?". It is a lesson usually learned early, and more often than not on "Dang, that is my best piece yet!".
My lesson was learned on a small, locally found black cherry burl. I had a spinning spindle, sharp tools, and free wood. What the heck do ya need a ruler for.

[Roger Chandler]

Fred,

To date, I have not turned through the bottom.........no funnels yet........I say yet, because I understand that it is a most probable event for every turner.

I do use a high tech depth gauge though......it has an eraser on the end of it, so it is really high tech! For a deep hollowing job, something else would be needed.

Bob's suggestion on boring a hole in the center as a depth indicator is a good one, and I did turn with my Ellsworth tool without drilling a hole first, just to see if I could do it like he does, and it did work, so both can be done, but the drilling first is probably the most reliable if one does not want a funnel.

[Bernie Weishapl]

I use a figure 8 calipers I got from craft supply. I could never get my calibrated calipers to work.:mad:

[Terry Murphy]

Hey! I got one of those....

[David Woodruff]

I have three sizes of figure eight calipers and a few other homemade depth gauges. Be certain that where ever you are measuring is perpendicular to the measuring points. And yes I have still had a breakthrough, I think maybe the last one was 10 years ago and that measure twice thing came to mind. If I have a piece with waste block, face plate. I stand the entire piece on my drill press table, measure inside and out with steel rulers. Place one ruler horizontally across the opening. Take inside & outside measurements to the horizontal ruler. Subtract the two numbers. You now have a measurement that defines the bottom thickness + the waste block/face plate combo. Measure the waste block/face plate. Subtract then from the last measurement and that is the bottom thickness. A fat half inch and I am happy. Takes a lot longer to describe than to do it.