# Need suggestions on how to model bandsaw wheel distance

#1

I want to model a band saw to build. I know the length of the blade I want to use and I know the diameter of the wheels for the saw. I’m stuck trying to figure out the distance between the wheel centers and how to model the blade. Any help would be appreciated.

Mike White

#2

Hi Mike: I might be misunderstanding, but…
The blade typically will go around 1/2 of each wheel, or one entire wheel for the purposes of blade length. The front & back blade lengths between wheels are equal, and are also equal to the distance between axles. Sooo…
blade length = pi * wheel diameter + (2 * distance between axles).
OR
distance between axles = (blade length - (pi * wheel diameter))/2

Is that what you were hoping for?

#3

For the record, there are some bandsaws that use more than 2 wheels, with varying diameters. That will get a little messier, mathematically.

#4

You’re right. I should have specified my saw will only have two wheels. Thanks for the response.

Mike White

#5

I think that might be what I’m looking for. I’m checking it with the calculator. Looks like I may need to adjust the wheel diameters. Thanks for the reply.

Mike White

#6

Matthias has already made several, and he uses SketchUp for his drawings…
http://woodgears.ca/big_bandsaw/
The big one’s plans will be available in a few weeks…
His smaller/older one’s plans are available now -

#7

I’ve been following his band saw builds and I like them. I want to build a smaller version and also want to try to figure out some of this on my own. I may still end up buying his plans and reducing them to what I want. Thanks for the reply.

Mike White

#8

Your main issue will be how to cope with two wheels of different diameters.
Then to calculate the total perimeter - consisting of the two partial circumferences [NOT 1/2 unless their diameters are equal] and the two straight sections of the band.
Than needs some trigonometry.
Since there will always be some adjustment built-in between the two wheels’ axes it need not be exact, but of course it needs to be good-enough.

The yellow edges are ~ the total band length.
Note how SketchUp’s segmented circles prevent exact tangent snapping - here I used my tool ‘common-tangents’:
http://sketchucation.com/pluginstore?pln=TrueTangents

#9

I like that example. I can use that to draw my blade. Is it possible to use the tape measure tool to get the total length? I haven’t figured out how to measure anything except straight edges in Sketchup. Measuring an unknown arc would be helpful. I guess you can tell I’m a Sketchup noob? Thanks for the reply.

Mike White

#10

If you select the highlighted parts that form the band - i.e the two arcs and two straight edges, then Entity Info should report the total length of ‘edges’ selected…

#11

Thanks a lot. I’ve only used Entity Info to determine what layer the part is on. Now I have another use.

Mike White

#12

#13

Yeah. I’ve watched all of his band saw videos.

Mike White

#14

FWIW, I think you’ll want to make sure the wheels are the same diameter. It’ll be easier to make and keep the table square to the blade.

There’s a minimum radius that the blade can handle (depends on how thick the blade is) and you’ll have to find a good balance between throat depth and resaw capacity.

#15

If there are just two wheels and they are the same diameter [d]. then for a given band-length [b] the distance between those wheels’ centers [c], is found by calculation thus:

c = ( b - ( Π × d) ) / 2

Remember that there needs to be some ± vertical adjustment on the top-wheel’s axle to let you tension/loosen the band and allow for varying lengths and stretching etc…

#16

My plans are to build a small bench top saw. I know I can buy a cheap one, but I want to build it myself. My questions here are so I can learn more about using SketchUp. Thanks for all of the reply’s.

Mike White

#17

Hello Mike… You can also use “Entity Info” to change number of segments in circles.
Good luck with you project and Sketchup in the new year coming.

#18

So, would changing the number of segments to a higher number give me a smoother circle or arc?

Mike White

#19

Yes. It would give you a smoother circle or arc. There’s no need to go overboard, though. maybe use 48 or 96 segments. I prefer to use values that are divisible by 12. And make sure you drag out the radius of circles on axis.

#20

Had to find my old machine design text book aka 1959 edition which has a closed form solution for this static case. When you start the saw then conditions change but if you so desire the loads can be calculated in a closed form basis. You are building your so you may need that info also?
You can program this in EXCEL and make as many calculations as you please. Of course you get strange results if you set up a bad case
L= 2sqrt(C^2-(R-r)^2)+pi() (R+r)+2 * (R-r)* arsin((R-r)/C)
C= distance between wheels
R large wheel R
r small wheel r
Make sure the arsin is in rads
Note site was not showing * properly it appears I got it fixed.