How to find bevel angles for cutting compound angles

[Christoph J. WALTHER]

For constructing a wooden geodesic dome with struts joining in one place (no connector) they need to be cut with two compound angles at each side. The values for these angles (base angle as in fig. 2 and fig. 4 in the attached sketch and arrowhead angles, fig. 3) is not my problem as they can be found on a number of websites. However, cutting them with a miter saw requires a certain bevel angle so that with two cuts for the miter or arrowhead cuts the required base angle results. Does anyone know how to obtain (calculate or otherwise) these bevel angles to be set at the miter saw?

I know this a basically a question about using a miter saw and not specifically about geodesic domes, but in my case applies to it and maybe somebody has already solved it before and can share the solution. Any help, even hints pointing into the right direction, is greatly appreciated! TIA!!! 

[Paul Kranz]

Christoph:

 

I have had no luck using a mitre saw to cut the angle you are showing in the all-blue diagram. Rather a radial-arm saw seems indicated. Is there some reason you have to use a mitre saw? I feel you, man. It would be nice to do it with only a mitre saw, but the device you would have to create just to hold the attitude of the wood-- much less the actual correct angle-- for the mitre saw to correctly score the wood would give you far too unpredictable results and pose a major safety hazard.

 

Sorry about that.

 

But, if you do come up with something, I'm all ears.

 

Regards,

 

Paul sends...

[Gerry in Quebec]

Christoph,
In a separate message, I'll send a diagram and equation for finding
the bevel angle.

As far as I know, you cannot cut "arrowhead" struts for a dome on most
compound mitre saws. This is because the mitre angles you need to cut
are too large (some greater than 60 degrees) if you wish to cut the
struts standing on edge, that is, with the narrow face on the saw
table. And if you wish to cut the struts with the wide face flat on
the saw table, then the bevel setting angles you need to cut (greater
than 45 degrees) are too large for most compound mitre saws. A better
option is to use a radial arm saw which allows you to make very steep
bevel cuts. I have tried this and it works fine.

But if you really want to use a compound mitre saw to do the cuts, you
will probably need a dual-bevel model, that is, one that handles both
left and right tilting of the saw blade. For this to work you need a
jig. The jig is a rigid right triangle that allows you to position and
secure the strut so that its length is perpendicular to the fence.
With this arrangement the strut is cut standing on its narrow face.

Last May, Blair Wolfram, a carpenter and master dome builder,
described how to make and mount such a triangular jig on a compound
mitre saw. I've appended his original message to this post. (The
answer to his question at the end is "safety first".)

Can you tell me which websites provide the angles you mentioned? From
the terms you're using -- "base angle" and "arrowhead angles" --it
sounds like you've been using an e-book called the Eden Biodome
Revolution....Hmmmm.

Suggestion: Before you start cutting struts, make absolutely sure
you've got the correct "arrowhead" angles.

Good luck,

- Gerry in Quebec
P.S. Paul, I saw your post just after writing this!


Blair's post to Geodesic Help, May 13, 2012

"It's all about having the right tool for the job.

"Make if you can weld, or have made an aluminum triangle using 1.5" or
2"
aluminum angle. The triangle should be a right triangle, measure to
the
3-4-5 right triangle combination. I suggest a 25" x 20" x 15"
triangle
speed square and larger. I have Mikita and Hitachi sliding compound
miter
saws, and this will work on any saw with a rigid fence you can clamp.
Clamp the triangle to the fence on your miter saw. Run the material
and the
long edge of the right triangle perpendicular to the fence. Now your
saw
angle measure of 9 degrees will make a 9 degree cut. You can also make
the
sliver cuts past 60 degrees like any other cut. Each time you change
the
angle, the triangle will have to be moved and positioned so the saw
doesn't
nip off the inside corner of the triangle; set the two saw angles,
lock in
place, slide the triangle up so it just clears the blade, and clamp
in
place with at least two clamps. Once you measure and test the strut so
you
know it will fit, cut one side only on all 80 "C" struts, reset and
cut the
same material again for the other side of the compound. You'll reset
4
times for one strut. Make a table to support the material while
you're
cutting, now that it sits 90 degrees from where it sits along the
fence,
and its best if you make it so you can clamp the material to the
table.

"Cutting compound miters increases the potential for saw kickback if
the
material isn't supported and firmly in place. There is always a
temptation
to tape the saw blade guard up out of position so you can see and set
the
blade without having to hold the guard up.

"You know the first rule about using a sliding compound miter saw?

Blair"




On Mar 11, 9:00 pm, "Christoph J. WALTHER" <cjwalt...@gmail.com>
wrote:

>  Winkel.jpeg
> 83KViewDownload

[Gerry Toomey]

Christoph,

Diagram and equation attached. For the example you gave, the bevel angle is 8.4 degrees.

- Gerry in Quebec

[Daniel Larrauri]

Hi, my name is Daniel, I have a tutorial with how compound angles for v4 frequency without hubs.

Step by Step.

Visit:

Como Construir Un Domo Geodesico

or

Visit my product in Clickbank => Click Here!

Kind Regards!

Daniel

Regards

2013/3/12 Gerry Toomey <toomey...@gmail.com>

--
--
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en
 
---
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to geodesichelp...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

[TaffGoch]

Hey, Daniel,

I hope that your website is encouraging builders in all of South America, not just Uruguay. Good luck, and best wishes, on your commercial venture.

On the website, I did find the initial graphic to be distracting, because it appears to jump-around (and, it takes a LONG time to load.)

Might you find this enhanced version of the animation of beneficial use?

-Taff

[TaffGoch]

Oops, I overlooked an animation frame....

[Christoph J. WALTHER]

Gerry

Many thanks for the formula to calculate the bevel angels – it works! And yes, setting the saw correctly is crucial here. I've got a digital protractor with a 0.1° accuracy which is of great help to make sure I have set the bevel angle required. Only a slight deviation will result in a different base angle. So some test cuts to properly adjust the saw will be needed before the real cutting starts. And yes, for cutting angles which exceed the capabilities of the machine a workaround as described by Blair Wolfram will be needed. I've got a dual bevel sliding miter saw with a 12 inch blade which should allow me to do the cuts needed.

The the terms "base angle" and "arrowhead angles" I have picked up in this video here: https://www.youtube.com/watch?v=R31PlxhhBFg which seems compelling but suffers from omissions which are NOT pointed out so it becomes misleading. I assume this is because some commercialized instructions with restrictive terms of use are used in this case. I much more like to see as much information for building geodesic domes in the open so this concept with it's great potential for the 21st century can spread easily. In this sense I once more thank you for posting this crucial piece of information here so that it, hopefully, can be found by others looking for it.

Best Regards  – ChrisW

[Daniel Larrauri]

Hi TaffGoch, thanks for your message.

I know about the initial graphic, I will resize all the image...lot of work!

For others....

The "arrowhead angles" is an information in this product:

http://tinyurl.com/greenhousecheap

Kind Regards

2013/3/12 Christoph J. WALTHER <cjwa...@gmail.com>

--

[Thomas Lambert]

I'm sure you have already had the question answered. but due to the angle cut you need to set your saw at almost a 5 degree angle. the way I figured it out was to measure and mark the middle on top and bottom. then if you have a laser on you saw line it up. you will see you need to angle the blade a bit.

[norm...@gmail.com]

Can you guys work your magic for this method of joining?

(I borrowed pic from the Bucky Dome Restore thread, hope for educational purposes that's ok Blair)

Blair, what's the first rule of a sliding miter?  (haven't heard it)

[Paul Robinson]

Hi,

    That looks just like the method I use to build greenhouses, I have lots of videos showing how I make them here: https://www.youtube.com/user/pauly1060

It’s a pretty simple way to build, I use standard 2 x 2 or 3 x 2 cut down the middle with the bevel angle (half the dihedral angle) on one edge. here’s a diagram:

as long as you make all the triangles the same way you will get that need corner.

Cheers,

             Paul GD

 

-- 
-- 
You received this message because you are subscribed to the "Geodesic Help" Google Group
--
To unsubscribe from this group, send email to GeodesicHelp...@googlegroups.com
--
To post to this group, send email to geodes...@googlegroups.com
--
For more options, visit http://groups.google.com/group/geodesichelp?hl=en

--- 
You received this message because you are subscribed to the Google Groups "Geodesic Help Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email togeodesichelp...@googlegroups.com.

For more options, visit https://groups.google.com/d/optout.
<DSCN4597.jpg>

[norm...@gmail.com]

thanks, starting to watch your videos.