Diameter of dome

[damias]

Hello all, glad to of found this group. I have some basic questions.
I'm building a 25' 3v 5/9 greenhouse using the Fuller method for a
flat base (2x4). I'm planning on using 4x6 material for the base and
cutting it to mirror the first row of struts. I want the dome to sit
on the inner half of the 4x6 so that I can angle off the outside half
for runoff. My question is, with all the calculators I've seen (simply
different, domerama...) I'm wondering if when using 2x4, is the
diameter calculated from outside to outside of the 2x4, inside to
inside, or middle? I'd like to know so I can properly dig out the
trench foundation. The trench will be wider than the base respectfully
but I would like to be exact.

Also, on simply different, it offers the degree's for the faces. Am I
safe in assuming that these would be the bevel angles on the outside
of the struts for the covering?

Thank you.

[TaffGoch]

damias,

To start, we should make sure that we're working with the same geodesic subdivision.

You refer to the "Fuller" method, but I think that it is more-commonly known, today, as the Kruschke method (flat ground-level struts.)

See if these chord lengths match your design, for a 25' diameter dome (12.5' radials):

[damias]

Hmm, my values came up different.
a=4.121
b=4.779
c=5.269
d=5.513

I got the values from this website.

http://www.domerama.com/calculators/3v-geodesic-dome-calculator/3v-flat-base-815-kruschke-calculator/

Where do you get yours from?

>  damias; 3v, Kruschke.png
> 89KViewDownload

[TaffGoch]

Where you got your information is what I needed to know.

I'll look through my library, to find the origin of my numbers. (I can't immediately recall.)

I'll 3D-model your numbers, as well. Stay tuned...

-Taff

[Gerry in Quebec]

Damias,
Taff`s strut lengths for the Fuller-Kruschke version of the 3v icosa,
which are a bit longer than what you got from Domerama`s calculator,
are based on a floor radius of 12.5 feet. Domerama`s numbers are for a
spherical radius of 12.5 feet. The floor radius of the 4/9ths and
5/9ths versions of the Fuller-Kruschke layout is 98.22% of the
spherical radius.

When people talk about domes that aren't exact hemispheres, i.e.,
where the sphere is sliced above or below the equator, it's helpful to
distinguish between spherical radius and floor radius. The circle
passing through the footprint's vertices is a "lesser" circle, akin to
the Tropic of Capricorn or Tropic of Cancer in geography, while any
circle with a spherical radius is a "great" circle, like the Earth's
equator.

- Gerry in soggy Quebec

On May 3, 2:15 pm, damias <sebastianpilking...@yahoo.com> wrote:
> Hmm, my values came up different.
> a=4.121
> b=4.779
> c=5.269
> d=5.513
>
> I got the values from this website.
>

> http://www.domerama.com/calculators/3v-geodesic-dome-calculator/3v-fl...

>
> Where do you get yours from?
>
> On May 2, 12:47 pm, TaffGoch <taffg...@gmail.com> wrote:
>
>
>
> > damias,
>
> > To start, we should make sure that we're working with the same geodesic
> > subdivision.
>
> > You refer to the "Fuller" method, but I think that it is more-commonly
> > known, today, as the Kruschke method (flat ground-level struts.)
>
> > See if these chord lengths match your design, for a 25' diameter dome
> > (12.5' radials):
>
> >  damias; 3v, Kruschke.png

> > 89KViewDownload- Hide quoted text -
>
> - Show quoted text -

[TaffGoch]

Gerry,

You're right, even though that wasn't my intent. I thought that I had scaled the dome for a 12.5' radial. I, apparently, scaled from the wrong "centerpoint" (floor centerpoint, instead of sphere centerpoint.)

Corrected image attached.

_______________________

damias,

Now that our numbers match, I can model the lumber/timber geometry for your specific application. Note that the 12.5' radial can be applied to a vertex at the inside of the frame, outside vertex of frame, outside vertex of skin, etc. It's actually your choice.

To what vertex point do YOU, personally, want to apply the 12.5' radius?

-Taff

[damias]

Ok, let me see if I have this correct. The Fuller-Kruschke method
requires you to build more than a half sphere? If this is correct, I
would want the model for the spherical center point as I envisioned
the half sphere dome. And I suppose if I wanted a true 25' diameter
dome, I would want the measurements from the inside vertices of the
frame. Thanks so much for the clarification.

>  damias; 3v, Kruschke.png
> 77KViewDownload

[Blair Wolfram]

I'd like to jump in...
First I suggest you use the line measurement that is the exterior face of the strut as your diameter measurement. This is also the line which is the interior face of the exterior panel. If you use a 3v dome there isn't a true diameter as there are 15 foundation walls and no exact hub opposite points on a great circle, so the measurements are taken off a radius.
Any odd frequency dome can't be made into an exact half sphere. However any even frequency dome, kruschke's, fuller or any other can be made into a half sphere. The frequency times 3 is the fractional denominator for the profile of a dome. A 3 frequency dome is identified in 9ths. A half dome in 9ths would be 4.5/9th which is an improper fraction, and cant be done. (dont say it Gerry) A 4 frequency dome is expressed in 12ths, and 6/12 is a 4v half sphere. A 6 frequency dome is expressed in 18ths etc.

Sent from my iPhone

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[TaffGoch]

Using the former 3D model as a template, applying 2x4s (3-5/8"x1-5/8") to the surface, would look like this:

[TaffGoch]

The next question is...

What kind of joints/hubs to you foresee using at the vertices?

-Taff

[damias]

Ok, Im confused. From domerama, I thought I was getting the
measurements to build the domes base at the spherical radius, but
instead its giving me the measurements for the floor diameter instead?
I started out on simplydifferentlly.org to build the 3v 5/9 icoso and
understood that it wouldnt be flat, and was going to shim it. I then
came across domerama.com, and as I understood it, the Fuller-Kruschke
method would flatten the bottom. So does the F-K method require you to
build beyond the spherical radius? I agree with using the exterior
face of the strut for the diameter too, thanks.

Ok, maybe I'm getting ahead of myself. So with a 25' diameter 3v 5/9
dome at the spherical diameter, will produce a smaller floor diameter?
It doesn't look like it on the pictures, and I guess that is confusing
me.

On May 3, 3:36 pm, Blair Wolfram <thedome...@gmail.com> wrote:
> I'd like to jump in...
> First I suggest you use the line measurement that is the exterior face of the strut as your diameter measurement. This is also the line which is the interior face of the exterior panel. If you use a 3v dome there isn't a true diameter as there are 15 foundation walls and no exact hub opposite points on a great circle, so the measurements are taken off a radius.
>  Any odd frequency dome can't be made into an exact half sphere. However any even frequency dome, kruschke's, fuller or any other can be made into a half sphere. The frequency times 3 is the fractional denominator for the profile of a dome. A 3 frequency dome is identified in 9ths. A half dome in 9ths would be 4.5/9th which is an improper fraction, and cant be done. (dont say it Gerry) A 4 frequency dome is expressed in 12ths, and 6/12 is a 4v half sphere. A 6 frequency dome is expressed in 18ths etc.
>
> Sent from my iPhone
>

[damias]

I will be using the compound miter technique. Thanks

[TaffGoch]

The sphere center is elevated above the 5/9th's ground struts (5/9ths level) by 2.344906'

The footprint radius is, therefore, slightly less than 12.5', i.e.; 12.278087', to the vertices.

-Taff

[TaffGoch]

Depicting spherical center elevation:

[damias]

Ah, I see know, thanks.

On May 3, 4:44 pm, TaffGoch <taffg...@gmail.com> wrote:
> Depicting spherical center elevation:
>
>  damias; 3v, Kruschke; elevation.png
> 332KViewDownload

[TaffGoch]

Note that, when reference is made to the bottom struts being "flat on the ground," or "level," for a Kruschke method subdivision, they're talking about how other subdivision methods (for odd-frequencies,) producing results as depicted in the attached image.

This is a method-1 subdivision method, 3v example:

[Paul Kranz]

Damias:

 

The F-K dome lies flat both on the base of the five pentagons and at the row of triangles below it, because they have the same perimeter. Please find attached an example of a FK Dome profile attached. There is a difference between the floor radius and the sphere radius.

 

Paul sends...

[TaffGoch]

damias,

While the ground struts do, indeed, follow a circular path, on a flat plane, the struts will be tilted, since the 2x4 cross-section long-axis "points" at the sphere centerpoint. (See attached image.)

I just wanted to make sure that you knew about that characteristic.

-Taff

[damias]

So, is a dome size represented by its spherical diameter or its floor
diameter?

>  3v; method-1.png
> 58KViewDownload

[TaffGoch]

It can be either, which is why it was so important for me to establish the parameters you choose.

For calculating vertices, it's typical for the geodesic vertices to be based on the sphere diameter, rather than the footprint. To subsequently fit to a particular footprint, scaling adjustments are made.

-Taff

[Sergio Cohen Arazi]

Hello, 

this is still experimental (only sketchup test yet)  I´ll be talking in meters, sorry.

In  3V 5/9 standard, for example a 6 meters diameter dome. Only reducing 4cm the C struts descending from the B strut under the pentagon, gives me a flat base. The other two C´s at the base remaind unmodified. (this is at the bottom half hexagon)

I think in a real situation, with 2"x4" struts, using B´s instead of C´s on that position would make an almost unnoticed difference. Only a different triangle appears (a BBC instead of the BCC)

In my case, the flexibility of the steel of the hubs would hangle the angle differences.

I will try with "real" experience. 

Anyways I wouldn´t use a B, Y would use a  " - C " special strut with the correct length.

Hope its right!

Thanks

 

Sergio Cohen Arazi    sergio...@yahoo.com

Génesis Geodésica   Http://www.genesisgeodesica.com.ar  ARGENTINA

     Http://www.genesisgeodesica.com.br      BRAZIL    

Cel.(48) 964-30281
Ecovila Céu do Patriarca  Http://www.ecovila.org.br

Vargem Grande,Florianópolis.

Brazil

Génesis Geodésica Argentina
Ciudad de Mar del Plata

[Paul Kranz]

Sergio:

 

The 3V icosa only requires two different triangles-- one for the pentagon and one for the hexagon.

 

The Fuller-Krusche dome requires three different triangles-- one for the pentagon and two different "rotating" triangles for the hexagon.

 

The difference is that no profile of the 3V icosa produces a perimeter where the vertexes are planar. This accounts for the reason that the dome does not lie flat as does the F-K dome (Taff's comments on the tilt withstanding).

 

Some people find that using three different triangles for a 4/9ths 3V icosa creates an over-engineered structure, i.e. an uneconomical benefit-to-design ratio.

 

I tried building a 39-foot diameter 3V icosa garage with the 2-triangle method and where the vertexes of the center hexagons rose above the plane established by the vertexes of the pentagons, I just filled in the empty space. The structural engineer on the job insisted that the floating hexagon centers along the perimeter did not pose a significant effect on the overall integrity of the dome to warrant the third triangle.The building department bought it. The dome is attached.

 

This, of course, does not apply to the 5/9ths 3V icosa as the centers of the hexagons on the perimeter are actually below the plane established by the other vertexes at this profile.

 

We find then that we go from the 5/9ths 3V icosa (105 triangles; two shapes) to the F-K dome (105 triangles, three shapes) and to lose the non-planar perimeter, and then go to the 1/2 4V icosa (160 triangles, four shapes) to lose the tilt.

 

Count the cost.

 

Paul sends...

[damias]

So, would my original ABCD values be correct for 25' spherical
diameter from outside to outside of the frame? And the floor radius
would be 12.278087'?

> <sergio_co...@yahoo.com>wrote:

>
>
>
>
>
>
>
> > Hello,
> > this is still experimental (only sketchup test yet)  I´ll be talking in
> > meters, sorry.
>
> > In  3V 5/9 standard, for example a 6 meters diameter dome. Only reducing
> > 4cm the C struts descending from the B strut under the pentagon, gives me
> > a flat base. The other two C´s at the base remaind unmodified. (this is at
> > the bottom half hexagon)
>
> > I think in a real situation, with 2"x4" struts, using B´s instead of C´s
> > on that position would make an almost unnoticed difference. Only a
> > different triangle appears (a BBC instead of the BCC)
> > In my case, the flexibility of the steel of the hubs would hangle the
> > angle differences.
> > I will try with "real" experience.
> > Anyways I wouldn´t use a B, Y would use a  " - C " special strut with the
> > correct length.
> > Hope its right!
> > Thanks
>

> > Sergio Cohen Arazi    sergio_co...@yahoo.com
> > Génesis Geodésica   Http://www.genesisgeodesica.com.ar *ARGENTINA*
> >      Http://www.genesisgeodesica.com.br     *B**RAZIL*

> > Cel.(48) 964-30281
> > Ecovila Céu do Patriarca  Http://www.ecovila.org.br
> > Vargem Grande,Florianópolis.
> > Brazil
>
> > Génesis Geodésica Argentina
> > Ciudad de Mar del Plata
>
> >  --
> > 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, visithttp://groups.google.com/group/geodesichelp?hl=en
>
>
>

>  Picture 008.jpg
> 1236KViewDownload

[TaffGoch]

damais,

You can use those ABCD values, measured to the outside of the frame, if that's what you want.

In that case, the floor radius (also, to the outside of the frame) would, indeed, be 12.278'

-Taff

[Paul Kranz]

Damias:

 

According to my calculations, if the radius of the F-K sphere is R, then the radius of the floor at the 4/9ths and 5/9ths profiles is 0.981888852R.

 

Paul sends...

[Gerry in Quebec]

Hi Paul,
The floor radius is 0.982247 when the spherical radius (R) is 1. This
number is based on a truncation plane located at either 79.187683
degrees (4/9ths dome) or 100.81231554 degrees (5/9ths dome). If A is
the dome apex, and B is the spherical centre, and C is any of the 15
footprint vertices, then this truncation angle (often called theta) is
ABC. For this type of class I, 3v dome, no other pair of theta angles
puts all the footprint vertices in the same plane while maintaing
icosa symmetry. The sine of ABC is 0.982247.
Cheers,

- Gerry in Quebec
(working from what's gotta be the slowest dialup connection this side
of the equator)

On May 4, 4:59 pm, Paul Kranz <p...@revivetheflame.com> wrote:
> Damias:
>
> According to my calculations, if the radius of the F-K sphere is R, then
> the radius of the floor at the 4/9ths and 5/9ths profiles is 0.981888852R.
>
> Paul sends...
>

> > For more options, visithttp://groups.google.com/group/geodesichelp?hl=en- Hide quoted text -

[Bryan Lawson]

On 04/05/2012 23:05, Paul Kranz wrote:

...

> I tried building a 39-foot diameter 3V icosa garage with the 2-triangle
> method and where the vertexes of the center hexagons rose above the
> plane established by the vertexes of the pentagons, I just filled in the
> empty space. The structural engineer on the job insisted that the
> floating hexagon centers along the perimeter did not pose a significant
> effect on the overall integrity of the dome to warrant the third
> triangle.The building department bought it. The dome is attached.

That is your garage???

...

[Paul Kranz]

Gerry:

 

Thanks.

 

Paul sends...

[Paul Kranz]

Bryan:

 

Well, I designed it and supervised the construction, but I am not the owner. I did it for a friend. We put $4K into the shell, $4K into the foundation, $4K into the shingles and the tax collector promptly taxed it as a $48K structure. The owner was steaming mad!

 

However, I don't know which pic you are looking at!

 

Paul sends...

[Bryan Lawson]

Hi Paul,

I was just making a joke because you mentioned a garage and then said
dome attached. Clearly the attached pic was not a garage...

Bryan

[Paul Kranz]

Bryan:

My Google acount only allows me to see my attachments after I send them. I guess the one I sent does look like a pretty bad garage. Let's try the actual...

Paul sends...

Bryan

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[damias]

Gotcha, thanks for all the help peeps!

On May 4, 1:59 pm, Paul Kranz <p...@revivetheflame.com> wrote:
> Damias:
>
> According to my calculations, if the radius of the F-K sphere is R, then
> the radius of the floor at the 4/9ths and 5/9ths profiles is 0.981888852R.
>
> Paul sends...
>

[damias]

Gotcha. Would the face angles still be correct on of this website?

http://www.simplydifferently.org/Geodesic_Dome_Notes?page=3%234V%20Icosahedron%20Dome

On May 4, 1:59 pm, Paul Kranz <p...@revivetheflame.com> wrote:

> Damias:
>
> According to my calculations, if the radius of the F-K sphere is R, then
> the radius of the floor at the 4/9ths and 5/9ths profiles is 0.981888852R.
>
> Paul sends...
>

[Paul Kranz]

Damias:

 

Gerry corrects my calculation to 0.982247R.

 

Paul sends... 

[Gerry in Quebec]

Hi Damias,
The face angles given by the Simply Different website are for the more
conventional dome: class I, 3v icosa,, method 1, the one that doesn't
sit flat. For that geometry which involves just two triangle types --
AAB and CCB -- the angles seem to be correct, with a tiny variance
from the numbers I have on file.

For the class I, 3v icosa Fuller-Kruschke dome, there are 3 triangle
types: AAB, CCB and CCD. Here are the face angles in degrees:
AAB: 70.86, 54.57, 54.57
CCB: 53.94, 63.03, 63.03
CCD: 63.10, 58.45, 59.45

Cheers,
- Gerry in Quebec

On May 5, 4:17 pm, damias <sebastianpilking...@yahoo.com> wrote:
> Gotcha. Would the face angles still be correct on of this website?
>

> http://www.simplydifferently.org/Geodesic_Dome_Notes?page=3%234V%20Ic...
>

[damias]

Awesome, thanks everyone!

[TaffGoch]

damias,

Once you are set upon what design & size you want, I can model the 2x4 frame, to provide all the compound miter angles for the strut-end cuts.

-Taff

[damias]

Design-3v 5/9 F-K
Size 25' spherical diameter from outside to outside of the frame.

[TaffGoch]

Okay, I'll get started.

Are you still planning the use of a 4x6 base ring?

I can also provide the foundation (since you mentioned a trench,) if you would describe your proposal.

-Taff

[nuconz]

this has probably been covered in this forum, but how does a DIY builder
deal with some slick angle like 70.86 degrees and a strut length of 8.87
feet?

[damias]

Cool, the base ring will be 4x6 and will mirror the first floor from
the inside. I wanted to trim the outside of the first row after I get
a cover on, so I will be beveling the outside edge of the 4x6 up to
the trim (if that's possible to model :p). Otherwise a basic 4x6 ring
will do, thanks.

[TaffGoch]

Nick,

To be completely foolproof, I generally produce a paper template that
wraps around the end of the strut. SketchUp makes production of the
templates fairly straightforward.

Measuring the length, to the "pointy" end of the paper templates makes
that foolproof, as well.

-Taff
______________________

[damias]

For 70.86 degrees, I would round it to 70.9 and for 8.87 feet, you can
take the .87 and divide it by .0833 (1/12) which would be 10.4 inches.
I think that's how it works.

[damias]

Oh and the trench will be approx 7"x11" centering on the 4x6, and
filled with gravel.

On May 6, 3:16 pm, TaffGoch <taffg...@gmail.com> wrote:

[TaffGoch]

Got it....

[Gerry in Quebec]

Oops.... typo in the last line. The base angles of the CCD triangle
should both be listed as 58.45 degrees.
- Gerry

[nuconz]

i guess my point is that with a fractional degree cut required, how can
i make a 70.9 degree cut on a miter saw? i've never needed to even use
a 71 degree cut!

of course to convert .4" i see a table showing that it is about 13/32".
i don't measure or cut anything with wood in 1/32" and i try to avoid
1/16" measurements if possible. how much difference is there really
between 3/4" and 7/16"?

what i'm really asking is for those that actually build domes, the
professionals or the DIY carpenters, how are these done? it seems to me
that dome assembly might work out just fine until you get to the last
few triangles and at this point a couple of "adjustments" might be required.


thanks.

[Gerry in Quebec]

Taff,
Just a reminder, so you don't end up doing the same work twice. On
July 22, 2010, you did SketchUp models for Michael Goodhart's 25 foot
3v Kruschke greenhouse.
http://groups.google.com/group/geodesichelp/browse_thread/thread/185755d96621f957/7b7fd33bdd5d9396?q=greenhouse&lnk=nl&

That was for a 4/9ths not a 5/9ths dome, but it contains much of the
info Damias requires, espcially the compound angles for cutting the
strut ends for butted joints in a panel dome.

- Gerry

[damias]

Correction noted.

[damias]

These are the measurements I got for the struts. From what I've read,
these measurements have to be right on and my math has never been a
strong point. Can someone confirm these measurements?

a) 4.121= 4' 1 7/16"

b) 4.779= 4' 9 5/16"

c) 5.269= 5' 3 7/32"

d) 5.513= 5' 6 5/32"

[Hector Alfredo Hernández Hdez.]

METRIC SYSTEM allways is better


ALSO i am going to recomend DONT USE directly angles,

 instead of USE  Legs of corresponding right triangle

For example: If you need 45 grades use a=1, b=1

if you need 30 and 60 grades

use a=1 and b=srt(3)/2

en general if you need
Theta grades
use a=1   and  b=Tan (Theta)  obviusly other angle will be 90-theta

you can make TRIANGLES with photographic cardboard, and keep them jealously


Because you will obtain the TRUE ANGLE more accurate.



I hope this be usefull.

See you.

[TaffGoch]

damias,

I measured, from my SketchUp model, the following:

4.121331'

4.778627'

5.268610'

5.513204'

So, your numbers are correct.

___________________________

I'm still working on the model, to produce the 2x4 miters. I should be able to finish, this weekend.

Sorry for delays, but my wife's car "died" and can't be resurrected (for reasonable cost.) I've been shopping for a replacement used car. (Who can afford a new car, nowadays, anyway?)

-Taff

[TaffGoch]

If you wanted fractional inches:

4.121331' - 4' 1 15/32"
4.778627' - 4' 9 11/32"
5.268610' - 5' 3 7/32"
5.513204' - 5' 6 5/32"

You won't be able to measure and cut to 1/32" inch tolerance. For this size dome, 1/16" or 1/8" tolerance will likely be okay. Depending on the moisture of the wood, as it ages, it's going to shrink some, anayway.

-Taff

[damias]

Thanks Taff, no hurries on the model but I'm going to start cutting my
struts today. I have my angles for

a=9.49
b=11.02
c=12.16
d=12.74

and my pentagon arrow heads will be 54 degrees, hexagons 60 degrees.

So I should be able to start cutting. Can you elaborate a little on
what you were saying about the 1/32" tolerance. I'm not quite clear on
this. I see you changed my 16s to 32s, is that to be more accurate?

[TaffGoch]

I "measured" the lengths in SketchUp; once in decimal, and again, in fractions. SketchUp permits switching the form of the units. For the second set, I set SketchUp units to 1/32nds, so all measures came out in that fraction. I could have, just as easily, set to 1/16ths.

Note that the pent & hex angles won't be 54° and 60°. Those angles only apply to "flat" pent & hex geometries. Also note that the pent angles will all be the same, but the hex angles, generally, aren't. This will become evident, once I finish & provide the model. (This characteristic is what "defeats" a lot of tyro geodesic-dome builders.)

-Taff

[damias]

Ok, I guess I'll wait for the model before I start cutting my arrow
heads, thanks for the heads up.

Another thing, any thoughts on the door way? I was planning on framing
a rectangle in the hexagon between the pentagons.

[Gerry in Quebec]

Damais,
I believe Taff has just saved you a lot of frustration, time and money
by pointing out that those angles you mentioned won't be 54 and 60
degrees. You used the term "arrow head" in your most recent post. This
sounds familiar. Are you using information from a fellow named Kacper
who sells an e-book, with a title something like the Eden Revolution?
I know someone who tried to build a 2x4 dome using the info in that
book and it was a total failure. He experienced what Taff mentioned,
namely "flat" geometry. There are a few You Tube videos by people who
built domes using Kacper's numbers and method and the results looked
pretty good. I have no idea how they managed that.
- Gerry in Quebec

[Gerry in Quebec]

Damias,
Another comment on that question of angles. In Kacper's cutting
system, you stand the 2x4 on its narrow edge to make the cut using a
compound mitre saw. The mitre angle he uses for strut ends at 6-way
joints is 60 degrees. But to avoid "flat" vertex syndrome, those
angles should be greater than 60 degrees (so that the final "arrow
head" point is less than 60 degrees). But most compound mitre saws
won't cut an angle greater than 60 degrees. The Milwaukee and Bosch
12" saws, for example, have maximum mitre settings of 60 degrees.
However, it's possible to do the cuts on a radial arm saw, with the
2x4's wide side flat on the table.
- Gerry in Quebec

[damias]

Yes, I have been following Kacper most of the way but have "educated"
myself on other websites. Like you said, I'm glad Taff pointed that
out. It seemed so logical but now that I think about, if the joints
weren't flat, it seems it would increase the angle of cut. Maybe its
within tolerance?

[damias]

Damn, I bought the Milwaukee too...

[TaffGoch]

damias,

I've actually finished the strut modeling, but haven't done the foundation, nor have I measured all the angles. (The angles are "constructed," using SketchUp intersections, NOT by calculating and inputting angles.)

You should take special care to note that the cyan and purple struts are mirror images of each other. While they are, indeed, the same length (chord factor,) the angles of the end cuts are mirrored, and the struts are, therefore, NOT interchangeable. Because of this, there are not four strut definitions, but five. When you get to the stage of cutting, marking & assembly, take care!

___________________

I'll start measuring, this evening.

-Taff

[TaffGoch]

Also, of special note, you have to take care, when assembling, not to swap ends of most of the struts.

It should be readily obvious that the red struts are different at each end, and you have to make sure that the strut is oriented in the correct direction, when assembling.

This is true of all struts, except for the blue ones.

Organization and labeling will be a critical process, when building such a dome. (This is one advantage of metal-tube [conduit] domes, where you don't have to worry about strut orientation.)

-Taff

[TaffGoch]

damias,

Angles measured....

(SketchUp model also attached.)

I haven't, yet, done the foundation, but I should be able to get to it tomorrow.

[damias]

Gotcha. Can you think of any reason for me not to start cutting my
lengths?

[damias]

Ahhhh, replied before I saw the new post, thanks Taff!

[damias]

Damn, that 62.2 degree cut is buggin as my Milwaukee goes only to 60.
I wonder if I could put a 2.2 degree angle shim against the fence on
the miter to make a 62.2?

[Gerry in Quebec]

If you plan to cut struts on a compound mitre saw with the board
sitting on its narrow edge, following Kacper's method, you will need
to rotate Taff's angles 90 degrees.

> > > > -Taff- Hide quoted text -
>
> - Show quoted text -

[damias]

What?

[damias]

I haven't cut anything yet but I'm confused. Can you clarify?

On May 12, 12:47 pm, damias <sebastianpilking...@yahoo.com> wrote:

> > > > - Show quoted text - I haven't cut anything yet but this is confusing. Can you clarify?

[Gerry in Quebec]

Hi Damias,
I'm just saying that the angles Taff gave you are for a cutting
arrangement whereby the wide side of a strut (3.5") lies on the saw
table. If you wish to cut the struts using a compound mitre saw, with
the narrow edge (1.5") lying on the saw table, then the angles must be
recalculated to accommodate the 90 degree rotation. It would be good
for you to describe/confirm the cutting method you plan to use?
- Gerry

[TaffGoch]

Don't feel too bad, my compound miter saw only goes to 45°

It's much safer to keep lumber lying flat, but for a 2x4, I guess it shouldn't be too difficult to cut it, standing on edge. (I wouldn't want to try it with 2x6s.)

For the 2x4s, I'd make sure to use good clamping technique, rather than hand-holding against a fence -- not just for safety's sake, but to ensure accurate and reproducible angles.

________________________

Actually, my tablesaw has a large table surface, so I'd probably be using it, for 4-5' struts. With this many struts, I'd likely be using jigs, as well.

-Taff

[damias]

Ok, so I will be using a compound miter saw for the cuts and I haven't
had a problem doing this in practice. The only thing I'm concerned
about is getting the cuts over 60 degrees which I think I can simply
shim to get the extra degrees. I don't understand how the angles given
will be different? First I cut my 9.49 angle(as example) on the wide
side and then flip it up to the narrow and cut the arrowhead after
matching up the vertical angle to the first cut. Am I missing
something. What do you think of my shim idea to get the extra degrees?

[TaffGoch]

Uhm, two cuts?

With a COMPOUND miter saw, you should be making, at the same time, the radial cut (9.5°, for example) and the face-corner cut. You have two degree dials on a compound miter saw, after all.

Regarding shimming, I employ such techniques, on table, radial and miter saws, as it's a commonly-accepted practice, when the need arises.

-Taff

[TaffGoch]

I am assuming that you do, indeed, have a "compound" miter saw, not just a miter saw.

With the 2x4 laying on it's side, you "swing/rotate" the saw head around it's vertical axis (by the 9.5°,) and then, tilt/twist the saw head, rotating around it's horizontal axis.

_______________________

You may have, as do I, a "sliding" compound miter saw, that acts like a radial/miter saw combination.

Right?

[damias]

Yes, I do have a compound miter saw that slides. I tried to cut it the
way you said but my radial end cut is not coming out to 9.5. I set the
vert cut to 9.5 tilted left and swung the horz to 60 degrees and cut.
Then I set the vert the other way and flipped the strut around and
cut. My end result angle come to almost double the 9.5 angle. The only
way I can keep the 9.5 angle is to cut it on the horz first at 9.5,
turn it upwards, swing to 60 degrees, line the blade up with the first
cut (which comes out to more like 6 degrees on the vert) and cut. Then
flip the strut and line the blade up again and cut. The end result
always keeps the original angle of 9.5 where as when I try it your
way, it doesn't. I guess Im doing something wrong?

[damias]

The angle on the vert seems to increase as I swing it to 60 degrees.
For instance, If I cut the 9.5 radial on the horz and then flip it up
and match the vert with the cut, the vert reading comes to about 10
degrees and matches. But if I swing the horz to 60 degrees and line
the blade up again, its out. Whats the reason for this?

Im able to get a more accurate cut on the horz since its digital, as
the vert is not. I suppose this is why the are cutting the radial on
the horz first? It seems to work out for me this way but why cant I do
the compound miter cut w/o doing the radial cut on the horz?

[Gerry in Quebec]

Damias.

I ran Taff's Sketch-Up numbers through an Excel spreadsheet and they
were, of course, bang on... as expected. However, minor tweaking of
the angles (with zero loss of angular accuracy) results in 4 unique
struts rather than than the 5 in Taff's scenario. Cutting is faster
and simpler because there's only one type of C strut, not two.

In a few minutes, I'll post a jpg with all the angles. These angles
have been rotated 90 degrees so that you can stand the 2x4 on its
narrow edge (1.5"), as in the Kacper's cutting arrangement on a
compound mitre saw. As you mentioned earlier, Damias, you will need to
create a jig (or "shim") to be able to cut the extreme (60+) mitre
angles. The maximum is 62.9 degrees. With this setup, all the bevel
angles (i.e., saw tilt angles) are very small, around 5 or 6 degrees.
I'd appreciate some feedback on this.

- Gerry in Quebec

> > Right?- Hide quoted text -

[Blair Wolfram]

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

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[TaffGoch]

On Sun, May 13, 2012 at 1:49 PM, Blair Wolfram wrote:
>
> You know the first rule about using a sliding compound miter saw?

____________________________

Don't keep us guessing, Blair! I have no patience for guessing games :)

[TaffGoch]

The concept of a compound miter saw is fantastic -- being able to combine two angled cuts into one accurate cut.

That's the ideal theoretical concept, anyway. I'm repeatedly amazed at the number of reports I read (in Fine Homebuilding/Fine Woodworking magazines) that describe user issues with accuracy. Is it a deficiency in the saw, or the user?

I like my Craftsman compound miter saw (made by DeWalt, if I recall correctly.) I can, for example, swing the blade to 10°, then tilt to 30°, and the cut comes out just as I expected. Surely, the Craftsman/DeWalt sliding compound miter saw isn't radically different from other manufactures?

I know this isn't a woodworking forum, but has anyone else stories to tell?

I have enough trouble explaining how to cut the ends of struts, without saw design/application issues getting in the way.

-Taff

[Blair Wolfram]

Safety First.

--

[TaffGoch]

Anti-climactic

[Blair Wolfram]

Anti-climactic yes. Right up until the time when the saw running at 4600 rpm gets pinched in a loose 2"x6" strut, and a chunk of wood zips past your bean at 150 mph. Anti-climactic...not.

On Sun, May 13, 2012 at 4:15 PM, TaffGoch <taff...@gmail.com> wrote:

Anti-climactic

[TaffGoch]

I've been told that I've, so far, been lucky, as sooner-or-later, any woodworker, using stationary woodshop power equipment, will eventually get hurt -- potentially, badly.

-Taff

[Domerama]

Blair,

You have a point. And may I commend you on replying to this thread with the last 3 fingers on your remaining hand.:-)

But seriously, isn't there a more safe way to cut angles? It seems either method is pushing the abilities of what the blade can do. Would someone be better off with a radial or mitre saw?

And furthermore, would hubs be a safer and easier way to do this dome? I tend towards using a thick pipe to connect the struts, or something similar to what I attached as images?.

[Blair Wolfram]

The compound miter saw is designed for this work, so notwithstanding the whole power tool world, its safe to use these tools to cut compound angles in wood.

The weak link in the hub design you've shown is the tensional element on the connections. To test your hub, set your five lumber struts in the joist hangers and set it on the floor like a pyramid. Have Tiny the fork lift operator jump on the hub, and the assembly will come crashing to the floor.

I don't know which is safer to manufacture or build, but I've found hub designs to be more efficient and stronger than panel domes. I manufacture far more wood dome homes than steel dome homes, but I've found steel domes to be way stronger than wood, far easier to build, and less expensive. Yet there is a strong initial resistance by individuals against steel frame homes just from habit or tradition. As Spock would say, "It's illogical."

But don't misunderstand, almost any dome is better than every square home. If you are comfortable with a wood frame panel dome, get off the computer and start cutting lumber.

Blair

[Laurent Pilon]

You are correct by pointing out the tensional aspect, though I did not post the actual full construction which includes reinforcements between the struts. These are prototypes from a nameless source, but they look really nice in certain designs.

Just curious: the hubs you carry, what are the specs. as in what is the limit of how big a dome I could build with, let's say, 2X6 lumber?

[damias]

With this method I was able to cut them right. My task now is to make
a jib to make a cut more than 60 degrees. So , if I wanted 62.2
degrees, and I cut a shim 2.2 degrees and put the flat side against
the fence, would this work? Basically I'm moving the fence closer to
the blade. Does this work? How can I make sure my angles are right?
I'm ordering a protractor thingy now, but wont have it for some days.
Oh, and thanks for the model. Can this model be confirmed Taff?

On May 13, 12:26 pm, Gerry Toomey <toomey.ge...@gmail.com> wrote:
> Hi Damias, Taff et al,
> Here's a jpg showing the compound angles to cut struts for a 3v icosa
> dome (double-bevel system) based on the Fuller-Kruschke geometry. Note
> that this is an alternative to Taff's set of angles.
> - Gerry
>
>  Damias-3v-icosa-Fuller-Kruschke.jpg
> 149KViewDownload

[TaffGoch]

damias,

"Confirmed" ?

You could build a 2x4 model using struts that are limited to about a foot. That would confirm the SketchUp model angles, as well as your cutting accuracy/methodology.

(Personally, I use SketchUp to confirm. You can also open the SketchUp model and use the "Protractor" tool to measure/confirm the angles.)

-Taff

[Blair Wolfram]

Currently my dome hubs are designed to build up to 50' diameter domes. (more to come). You can use longer than 8' struts in a 4 frequency dome to build larger, but you will exponentially lose strength and performance by increasing the strut span. At 8' max strut length, my hubs are part of a dome system certified to withstand a MINIMUM of 150 mph winds and 110 pounds per sq. ft. snow. Engineering doesn't ever rate the maximum load a structure will take, but rather the minimums it is designed to hold. Some pictures of the hub are in the slow moving slide show on this home page:
http://www.hurricanedomes.com

The smallest lumber frame my hubs will accept is a 2"x8", and will accept up to 2"x12".

Blair

[TaffGoch]

For readers who aren't familiar with the Wolfram hub:

[damias]

How do I scales it down to a foot? I tried domerama but I think its in
meters?

[damias]

Heres what I got

a=1'
b=1'1 7/8"
c=1' 3 5/16"
d=1' 4 1/16"

Does this look right?

[TaffGoch]

damias,

I scaled it down, in SketchUp, such that the longest strut would be 12"

[TaffGoch]

damias,

Your numbers will work fine.