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Kerf Spacing Calculator for Bending Wood

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Kerf Spacing Calculator for Bending Wood

Postby Blocklayer » 11 Oct 2017, 10:40

I've just added a Kerf Spacing Calculator to blocklayer.com, that some of you may find useful.
It works out the geometric spacing of the cuts so when bent, the inside edges of the cuts join to create the curve.
The depth of the cuts (and remaining wood thickness for the bend) can't be calculated (that I can work out anyway). That seems to be the art of it. Depends on the wood and the dimensions. Trial and error?
But this will produce simple geometric diagrams, so you can see the wood and cuts both straight and bent, and drag sliders to animate angle, radius, cut width etc to see what changes.
It also creates a full scale template to mark out the cuts.
https://www.blocklayer.com/kerf-spacingeng.aspx (Imperial)
https://www.blocklayer.com/kerf-spacing.aspx (Metric)
It obviously can't be 100% accurate, but should give a pretty close idea of what sort of a bend you'll get for the entered dimensions.
If it needs editing, additions, fixing or you have any other ideas for improvements, please let me know.
Attachments
Kerf1.jpg
(29.98 KiB)
kerf2.jpg
(60.45 KiB)
Blocklayer
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Re: Kerf Spacing Calculator for Bending Wood

Postby 9fingers » 11 Oct 2017, 19:55

I entered my saw blade thickness which is 3.2 mm
A typical curve gave me cuts at 32 mm centres and 29 mm wood width
Obviously both cannot be true. So does your calculator give accurate centres and approximate wood width of the other way round?
Cheers
Bob
Information on induction motors here
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Email:motors@minchin.org.uk
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Re: Kerf Spacing Calculator for Bending Wood

Postby Blocklayer » 15 Dec 2017, 23:34

Good point Bob. It looks confusing.
It just rounds the measurements to the nearest mm.
Now it shows measurements (in the top label only) to 0.1 mm, but that can annoy people also.
Obviously the diagrams and running measurement list show measurements rounded to the mm.
Having all measurements to 0.1 of a mm just clutters things and makes it more difficult to read and use.
Do you think a label saying ~ 'Measurements rounded to nearest mm' would be a good idea?
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Re: Kerf Spacing Calculator for Bending Wood

Postby 9fingers » 16 Dec 2017, 11:31

Hi Greg,

Thanks for your reply and looking into this. As an engineer with OCD tendencies(!) I much prefer the label now it is consistent.
The graphic below still raises the query in my mind and possibly others.

Maybe you could either state that the kerf positions are rounded to the nearest mm as in practise their exact position is not that critical and the comment would resolve the issue for users.

I'm quite intrigued by this method and really must get round to trying it out.

Cheers

Bob
Information on induction motors here
https://drive.google.com/file/d/1dBTVXx ... sp=sharing
Email:motors@minchin.org.uk
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Re: Kerf Spacing Calculator for Bending Wood

Postby Dave R » 16 Dec 2017, 20:45

Interesting calculator. I've always done it by hand by taking the difference between the outer length and inner length and dividing it by the saw kerf width to get the number of cuts I'll need.
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Re: Kerf Spacing Calculator for Bending Wood

Postby 9fingers » 16 Dec 2017, 23:51

Dave R wrote:Interesting calculator. I've always done it by hand by taking the difference between the outer length and inner length and dividing it by the saw kerf width to get the number of cuts I'll need.


This is the way I would approach it too.

The rather curious thing is that the number of cuts is solely defined by the width of the kerf and the depth of the cut. It has no dependency on the radius of the bend required. I derived this mathematically and thought that I must have made a mistake in my working. However a spreadsheet confirmed that it really is true.

To illustrate this easily, take Greg's calculator and put in some typical values for radius, kerf and wood thickness and minimum thickness and press calculate.
Then move the radius slider along from one extreme to the other and you see the number of cuts remains UNCHANGED!

I bet that you would not have expected that!

The radius created is a function of the length between cuts alone.

Bob

Having fun with maths on a Saturday evening
Information on induction motors here
https://drive.google.com/file/d/1dBTVXx ... sp=sharing
Email:motors@minchin.org.uk
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Re: Kerf Spacing Calculator for Bending Wood

Postby 9fingers » 17 Dec 2017, 11:11

For anyone struggling with this concept, think of the compressed kerf cuts as each contributing a few degrees of the bend at the centre of the radius and the material between the points where the kerf closes as contributing to the length of the arc and hence its radius.
The two effects are not related.

Bob
Information on induction motors here
https://drive.google.com/file/d/1dBTVXx ... sp=sharing
Email:motors@minchin.org.uk
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