Here are a couple of tables that might be of some interest. The tables show the maximum radius of dome that can be cut from standard timber lengths with the aim of keeping waste to a minimum.
2v and 3v (3/8th or 5/8th) are included and all lengths are related to hub and strut domes which use 75mm diameter tubular hubs.
If you need a different stock timber length or hub diameter calculated..let me know :)
[ Comments 13 ]
Nice table Colin, How many struts can you get from one 2.4m piece of timber?
Could be an idea to add total lengths required, then all you need is to add in the cost per length to get totsl strut costs. I'm hoping to get round to building a greenhouse using slate lath struts covered with polly tunnel film (maybe back end of this year) a cost calculator would be quite handy.
I`ll post a cutting plan which will show you exactly how to cut the stock lengths to get all the required struts with the correct angles, minimal waste and no chance of getting it wrong :)
Use the table to decide on the stock timber length which gives the desired dome size. A 3v 3/8 will require a total of 40 stock lengths of timber and the 3v 5/8 will need 55 lengths (always add a few extra tho). The cutting plan is exactly the same regardless of the actual lengths :)
The largest 3v 5/8 from 2.4m timber is 2.13m radius, the base radius will be 2.096m and an overall height of 2.5m
In a nutshell..exactly the same size as my old timber dome :)
I was in two minds about the 2v table, there are two possible routes.
The 2v table i posted above uses 33 stock lengths and gears the max dome size to a "BB" cutting length (just 3 stock lengths involved)). With hindsight it would be better to gear the max dome size to the "AB" cutting length (30 stock lengths involved). This will oncrease the size of some and minimise waste from 30 stock lengths..it will mean the stock length won`t be long enough to accomodate the odd 5 "B" struts so you`d need to use 35 stock lengths instead of 33. On the brightside those odd 5 lengths would only need to be slightly longer than the B strut length not necessarily a full stock length like the rest :)
I hope that makes sense hehe
Here`s the alternative 2v table, effectively it uses 30 stock lengths for the 30x A struts and 30x B struts. You will need to get 5 more B struts from somewhere..be aware you won`t get 2x B struts out of the same stock timber length, worst case scenerio is 1x B strut per length (wastage) but 35 lengths versus 33 lengths is not such a bad tradeoff.
As promised here`s the 3v timber cutting plan.
It assumes you are right handed and have a mitre saw (maual or electric)ideally fixed to a bench with a fence and some form of length stop (end stop)to set the various strut lengths..a block of wood and a G-clamp works well enough. The pic should explain the procedure but in summary, 1:Take 30 lengths of timber and cut a 10 deg angle off close to the end. 2:Set the "end stop" for the "A" strut length and cut 30 "A" struts from those 30 lengths.. setting aside the long offcuts as you go.
3:Reset the mitre saw angle to 12 degrees and replace the unwanted 10 degree angle on the end of the 30 long offcuts with a 12 degree angle. At this point you take your remaining full timber lengths (10 or 25) and do the same to them. 4:Reset the "end stop" for the "B" stut length and cut 30 plus either 10 or 25 "B" struts depending whether its a 3/8 or 5/8 some. 5:Finally you reset the "end stop" for the "C" strut length and cut 1x C strut from the 30 short offcuts and 2x C from each of the remaining long offcuts.(just rotate the timber after a cut and push it back upto the "end stop" ready for the next cut). Note that the long edge of the strut must be against the fence when cutting or it will all go pear-shaped pretty quick.
If you follow the instructions precisely and work methodically.. its a piece of cake :)
Almost forgot, the actual strut length is measured along the long (top) side of the strut from point to point. Finally, just to clarify: 30 lengths are cut "ABC" and the rest (10 or 25 lengths) are cut "BCC". Resulting in 30A,30B,30C + 10/25B + 20/50C = 30A, 40/55B & 50/80C.
Sorry for the longwinded posts,but hopefully you can follow it all ok. I could have cut the struts for half a dozen 5/8 domes in the time its taken :)
To help with the costing exercise here`s a 3v 5/8 with 75mm diameter hubs as an example:
A reasonably sturdy greenhouse the size of the one above using 3x2 timber including covering,hub caps and clamping strips etc would probably cost in the region of £400 for materials. Its surprising how all the small things can add up.
i was just working out 2.6m Radius dome using the calculator tool and using your timber/length chart.<<>>If the calculations come out as:<<>>Radius - 2600<>Strut A - 906.24<>Strut B - 1049.23 <> Strut C - 1072.16
<<>>If i add them together it comes at that i need a stock length of 3027.63
Sorry bout the dodgy <<>>> symbols i thought i remebered reading somewhere they start new lines and paragraphes.
If you take the hub diameter into account the struts will need to be slightly shorter.If you cut accurately and the timber is of reasonable non mashed quality at the ends you can also use the 16/18deg end angles to shave a bit more off the overall timber lengths
Hi! I am trying to do it without hubs. Just timber! Then, there is a tricky problem with A struts coming into B struts. My As cut at 60º head with 10º base angle don't fit properly on the 60º head 11,6º base angle of the B. And then, the problem goes to fit them perfectly when forming the pentagone in the dome.The lengths are correct from vertex to vertex, all cut to the millimiter, though model being 1,2m in diameter with 20*20 mm sticks. Don't want to go on the lumber before being certain! Any suggestions?