PDA

View Full Version : Segmented Turning Calculator



Blocklayer
9th Jan 2018, 08:27 PM
The other day someone asked me about a segmented turning calculator. But they got their email wrong so I can't reply to ask for details and help.
I'm not a woodturner, but going off the geometry, I've just put up a calculator on blocklayer.com

https://www.blocklayer.com/woodturning-segments.aspx

First go at it, so it probably needs some adjusting and additions or fixing.
Any suggestions from woodturners for additions, adjustments or fixing it appreciated.

427499

Oldgreybeard
10th Jan 2018, 09:21 AM
I just had a quick look at the calculator. A major problem appears with the use of whole numbers only.
I tried 10 segments and 12 segments and both yeilded the same error. The sum of the 3 internal dimensions (10 +59 +10 for 10 segments) does not equal the external dimension of 78. It is likely only a rounding error, but which is correct? - and indeed are any of them correct in terms of the precision required for quality segmented turning?

I am no expert in segmented turning, but an error of 1 mm would seem to result in a very open joint.

I would be interested to hear the opinions of someone with more knowledge and experience.

bob

Blocklayer
10th Jan 2018, 09:56 AM
Good point Bob, it doesn't look all that accurate when the measurements don't add up.
The rounding error happens a lot with length divisions not adding to the exact correct total.
It's easy to add more precision (I just changed it to 0.1mm), but results with too many decimal places (even 1) can annoy people also.
I've had plenty of people complain about using 0.1 mm, which is impractical to mark out for woodworking.
It's even worse with Imperial, where people don't like 1/32", and using ~1/8" or 1/4" really makes the multiple length division look bad.

So, as far as I can work out, the options are:
1: Add a note that measurements are rounded to the nearest mm
2: Display all measurements to a higher precision (can clutter it and makes it harder to read)
3: Add a Precision selector so the user can choose decimal places

Which would you choose?

Oldgreybeard
10th Jan 2018, 10:10 AM
The change which you just made looks OK to me - precision of 0.1mm. But if there are plenty of people who don't like even 1 decimal place, my suggestion would be to go for option 3 - a precision selector.

Bob

powderpost
10th Jan 2018, 11:02 PM
This type of calculation will only worl for segmented "bowls" with vertical sides, amd is useless for a vase or vessel with tapering sides. The correct mathematical calculation for the long side of a segment is "tan (angle of cut) x radius x 2. It is necessary to draw a plan and elevation of a segmented piece, to develop the information necessary.
I have done, some time back, a WIP to show how it is done.

Jim

powderpost
10th Jan 2018, 11:26 PM
Found it.... http://www.woodworkforums.com/f8/segmented-vase-174358

Jim