One of my favourite dome designs is the 3v or 3 frequency dome, it is very easy to build being only slightly more complex than a 2v design but looks much nicer and has smaller panels. I find that 2v designs are very limited because you have no way to build a door into the dome without destroying the design. 3v domes however are pretty easy to customise for door openings and with only two different shaped panels are a peace of cake to build, but there''s a problem...A 3v geodesic dome doesn''t sit flat on the ground! This can really be a pain, and changing the bottom angles starts to get complex. You can get away with it if you build a stressed skin dome because the dome will flex and although it ends up slightly distorted it will sit flat on the ground. So is it time to go up to a 4v design?
[ Comments 14 ]
There is more work involved in a 4v than just truncating a 3v if the main goal is to get a flat base.
A 4v uses 6 different struts as standard, a flat based 3v would require just 5.
The 4v design does give a nice looking dome though :))
I havn't ventured into 4v dome building yet, I am tempted though. Would you say it's easyer to fit doors and windows into a 3v or 4v dome?
I think you would need to be building a real big dome to justify going to 4v...what do you think?
I find the door is usually the "bone of contention" especially with smaller sized domes..they`re never tall enough, LOL. The 3v 3/8 is a pain, 5/8 is ok if the dome is at least 5m or more in diameter. The higher the frequency the smaller the door gets if the dome diameter remains the same. 20ft (6m) is a reasonable minimum size for a 4v hemisphere, the struts being around 1m long.
Smaller diameters (4m) can use a 7/12 format instead of a hemisphere to increase the height.
The door is still a pain :)
One you have made a 3v (3/8) dome how difficult is it to add a flat base. Like on Colin's sons dome? (sadly I have only just realised that 3v does not have flat bed!! And have cut all wood to length). Is it just a matter of having 30 extra struts - cut to appropriate lengths - and then hubs with slightly different angles. I have used the dowel screw method. Also I am confused about how you work out spacing between the holes on the hubs. Help much appreciated.
It`s dob-able. The cheapest way is to alter the dome to a 5/8 if it`s possible from the added height point of view? How big is the diameter? Adding struts is perhaps just as expensive as replacing the ones needed to give a flat base. The 3v is quite forgiving of hub angles, you`ll only be about 4 degrees out at the most, using pure hexagon and pentagon spacings,there will be enough play in the holes to account for at least that much tolerance.
So does a 5/8 have a flat base? The diametre is 7.2 Mtres.
Thats a nice size dome.
A 5/8 doesn`t naturally have a flat base as a 3v can`t be equally divided in half ;)
To convert the 3/8 to a flat base would entail altering the bottom row of triangles. Having the pentagons on the bottom row makes things a bit more complex (A,B and C struts to adjust).
The 5/8 retains all the stuts you have now and adds a further 45 to make a new bottom row which has the lengths adjusted to make it flat (just B and C struts).
Being a sizable dome already, you may not want to increase the height from ~3m (10ft) to ~4.23m (almost 14ft). It would provide nice headroom near the perimeter.
A base hexagon with 6 struts removed gives you about 2.4m (8ft) of height for a door. Almost large enough for a 2nd floor :)
Can you give me the actual cut lengths for your A,B,C struts? They should be around 1255mm,1453mm and 1485mm (minus the hubs)
The hub diameter would also be useful to know :)
It looks like you`ll need 10 new struts to modify the 3/8 to a flat base. (longer ones than any you have already)
The other 20 struts can be recycled from your existing ones as they are longer than required.
Struts: 125 cm 145 cm 148cm. Hubs 3 inch diametre - 1.5 inch face. Approx = 25mm of thread on the ends of strut. Used m6. I have ordered extra wood for a 5/8 - on the basis of that it is said to be more pleasant aesthetically. The height is no problem = except that it will cost me more Army Tarps to cover. What then are the B and C lengths to to make this flat base? And thankyou for your support.
I tend to work to the nearest mm, that 0.5cm tolerance could add up to a 3" (75mm) error over 15 struts instead of 5/8" (15mm) :)
M6 is a little small for a dome that size, M8 or M10 would be better.
Here are the actual lengths to cut the struts,they take into account the 76mm dia (3")hubs and are measured along the outside edge from point to point (ie: the longest part of the strut)
The colour coded layout diagram, showing the locations for all the struts : xxx.nurl.us/6qr
(change x to w)
The basic 3v 3/8 requires:
Red: 30 struts at 1177mm, 10 deg end angle.
Blue: 40 struts at 1375mm, 12 deg end angle.
Mauve: 50 struts at 1407mm, 12 deg end angle.
The additional 45 struts for the 3v 5/8 flat base modification:
Blue: 15 struts at 1375mm, 12 deg end angle.
Mauve: 10 struts at 1407mm, 12 deg end angle.
Green: 10 struts at 1391mm, 12 deg end angle.
Grey: 10 struts at 1423mm, 12 deg end angle.
The base circle dia will be about 16mm less than calculated due to the flat faces of the hubs.(a circle with 15 flat spots ;)
The base hubs will fit inside a 7070mm diameter (3535mm radius) foundation circle.
Don`t forget to fit a cargo net in the top part of the new 5/8.. the ultimate hammock :)
I realise now that I should not have used cm measurements. I did not use mm in the calculator on this site = insted put in 3.6 thinking in mtrs. People be aware.
But do i need to modify all of the previous struts.
Is there a workaround?
At present my setup:
A Struts should be 1254.79 (yet I have 1250
C structs 1484.54 (rounded to 1480)
Fortunately I have not cut the b struts yet - but these could be cut to 1447).
Would this be approximate enough not to rehash the poles?
I assume it works as a ratio. So it would be very approximate. But not as intense as .5 cm
If so what whould be the lengths of the bottom row be?
Did you make adjusments to the strut lengths to account for the hubs?
If you have "A" struts (coded Red on my layout) already cut to 1250mm and "C" struts (coded Mauve)already cut to 1480mm, you have the opportunity to shorten them to 1177mm and 1407mm respectively.
The "B" struts (coded Blue) which are yet to be cut would be 1375mm.
The alternative is to take the struts you have already cut as a yardstick and modify the lengths of the base row to reflect the same difference to keep things on track. If you use one format for A and C (precut) struts and another for the B struts you could end up with all sorts of problems ;)
I just thought i`d mention that Paul`s (site admin) and my colour coding/lettering system is somewhat different ..so don`t mix and match or you`ll be all over the place. Check and double check everything before firing up the saw.
There is the small error regarding the end angles on the 3v calculator page.
The pentagon inner struts need to have 10 degree end angles. Paul colour codes them as Red and letters them as "B" struts.
(I also code them Red BUT letter them as "A" struts.. confusing or what LOL)
The calculator page has the "A" and "B" strut end angles transposed. Which means 12 degree angles on the 30 inner pent struts and 10 degree angles on the hexagon and pentagon perimeter struts..it should be the other way around. The "C" struts are ok at 12 degrees :)
I did mention it to Paul but i know he`s been real busy of late so perhaps hasn`t had time to alter it. If you`ve already cut the stuts don`t worry.. 2 degrees isn`t much :)
has anyone got any resources on putting a dooor into a 3v?