Time for a new Obs!

[SnakeyJ]

After wasting most of Friday afternoon in Visio, I've now decided it's time to try and teach myself sketchup.

Little to show so far, except the patio - which was the simplest part!

Hopefully I can gain some competence and increase the speed!

The aim is to be able to draw all of the ply components out, so that I can efficiently lay them out to minimise cutting waste.   Not that I intend to on this occassion, but presumably it's possible to produce some form of STL vector output for laser cutting?

[leelee970]

Good luck with the Obsy build, looking good so far Jake.

I have to admit I wished I had used slabs under mine. I've a problem with rats - although controllable.

Lee

[Gina]

SketchUp has quite a learning curve   I found the book "Google SketchUp 8 for Dummies" has a vast amount of information in it presented well and easy to understand.  Seems pretty much all of it applies to later versions too   I learned things from that that no amount of reading help files and Googling turned up

[SnakeyJ]

SketchUp has quite a learning curve   I found the book "Google SketchUp 8 for Dummies" has a vast amount of information in it presented well and easy to understand.  Seems pretty much all of it applies to later versions too   I learned things from that that no amount of reading help files and Googling turned up

The 'for dummies' bit sounds good    I've made slow progress, but have issues with objects auto linking together, then not being able to explode, ungroup or otherwise separate.    However, I have managed to model the pier and found an eq6 model on line, which should help with dimensioning.

[Gina]

Yes, I'm a Dummy at times

Do you mean you found a SketchUp EQ6 model online?  That's something I could do with

[SnakeyJ]

Yes, I'm a Dummy at times

Do you mean you found a SketchUp EQ6 model online? That's something I could do with

I just searched for eq6 in the sketchup gallery and downloaded the skp file.

[Gina]

Thank you very much

[SnakeyJ]

Further adventures in sketchup - definitely a growing love/hate relationship!

On a different subject, I'm looking for suggestions on cutting the curved sections of ply.    I will need to cut a lot of curved sections from 12mm ply and was originally thinking of making a trammel for my jigsaw.   However, my decent Metabo jigsaw has gone AWOL at work and I only have a cheap B&Q special.   Doing a little web research it seems most people are using routers and trammels to cut radius's from sheet timber - though I would have thought that this would be slower and more expensive in router bits due to the amount of glue.

Jigsaw of Router - what would you recommend for this?

[Tinker1947]

TCT Router bits will handle the glue ok, it just getting the router speed right, i use a lot of MDF 6mm to make profiles of a curve attach them with a headless pinner to the Ply, although some clamps would work ok, the idea is a guide bush attached to the router base this follows the profile of the MDF with the cutter sticking through the middle you then  cut a slot in the ply then lower the cutter and take another bite until your through, another piece of MDF on the scrap side of the Ply help stop the Router tipping, i have a picture showing a dovetail cutter this would be changed to a straight cutter but show the idea of how to do it...

[JamesF]

Have you worked out exactly what shape you need to cut?  I'm assuming it will be something like a tall isosceles triangle with bowed-out sides?  It might be easier to mark out and cut with a jigsaw than to make template or suitable size trammel for a router, though I'd have to admit that I'm not a huge fan of jigsaws.

James

[Tinker1947]

I have a couple of Jigsaws and there only any good if used free hand and not run round a jig, used with a jig the blade tends to bend in towards the under side of the jig......don't know if its just me and these are not cheap jigsaws....

[Gina]

I have that trouble too with jigsaws - why I bought a router

[SnakeyJ]

Thank you Tinker, James and Gina - excellent advice and much appreciated from this end.   I will go the router route and have just located a very good looking s/h Hitachi M12V, conveniently located on my route home.   It looks lightly used and the Japanese made version, but I will give it the once over for £ 60.      

However, must stress that tools are strictly outside the budget, which stands around £ 280 remaining!

Tinkers idea of making up templates in mdf and running around these sounds very practical and should save some time.

Subject to taking some final measurements, I have the following cut list:

Base:

Bottom ring, 8 x 90 degree circle sections, OR 1050mm, IR 1000mm in 9mm ply.

Top ring, 8 x 90 degree circle sections, OR 1050, IR 1000mm in 9mm ply.

Verticals, 8 x rectangles 1200mm x 50mm, in 9mm ply.

Dome:

Bottom ring, 8 x 90 degree circle sections, OR 1071mm, IR 1000mm in 9mm ply.

Skirt curved rectangles (run around outside of bottom ring) 3 x 140mm x 2440mm x 6mm ply (for a circumference of approx. 6.7m).

Dome aperture 8 x 90 degree circle sections, OR approx 1050mm,IR 1020mm in 9mm ply

Dome ribs, 6 x sub 90 degree arcs (to meet dome aperture)) , OR 1071, IR 1020 in 9mm ply.

Aperture ends (top and bottom), OR 1071mm IR 1020mm, arcs of approx 25 degrees or 500mm length.

This sounds like at least 32 curved pieces, which sounds like a lot of work and quite a lot of materials - I need to get this laid out so I have some idea of how many sheets will be needed.    I will also need to work out my method of fixing, but probably block (screwed and glued) and allow for materials for the shutter and door.   Hmm, budget now looking very thin.

[SnakeyJ]

The latest from Sketchup:

Slowly getting more acquainted with this, good job I've had a quite couple of days at work

[SnakeyJ]

I got out tonight and setup on the patio for a test run from the new site - not too shabby and the position gave much better clearance to the south.    Nice dark and clear conditions once the crescent moon and Venus had dipped below the horizon

[SnakeyJ]

Building on sketchup is a far cheaper hobby - I can do sectional views now!

Front Elevation looking North (NNW) - mount aligned approx north:

Left Elevation looking East (ENE):

This model is still very simple and does not show any of the shaped ply components (other than the dome skirt), but is useful for dimensioning and getting a feel for pier height.   Not sure if I'll attempt a more complex model, but now have the basic skills to muddle through in sketchup!

[Davey-T]

Looking good, hope you're going to do a little Jake in Sketch Up to put in it

Dave

[Gina]

:)  SketchUp takes a lot of learning but can be very satisfying   I think it's great software and it's FREE   I too use it to check dimensions (used it to design my observatory for instance) and also for designing models for 3D printing - an awsome combination that seems capable of absolutely anything (that will fit in the volume covered by the printer)

[SnakeyJ]

Looking good, hope you're going to do a little Jake in Sketch Up to put in it

Dave

I will look for a sketchup mini me - sort of tall, skinny and looking stressed!    My head is working overtime on how to skin and fix the ply to the curved walls.    I was thinking of lots of clamps, but currently toying with the idea of webbing straps to help pull everything together and hold it.     The long external butt joints between the 4mm ply sheets of the base will need special attention to get a good waterproof joint and I might have to use some epoxy here.

[Tinker1947]

One build on here used hardboard ( I think) pinned to battens, then fibre glassed the whole thing...

There is a ply that's very bendable not sure what name it goes under......

Found this link..

https://www.google.co.uk/search?q=elastic+plywood&espv=2&biw=1920&bih=1099&tbm=isch&tbo=u&source=univ&sa=X&ei=w4E3VcTcLYLDOeScgeAL&ved=0CCAQsAQ

[Gina]

Bendyply is what it's called but it only bends in one direction as I understand it, the other is the same as ordinary ply.  I've never used it but did some research when looking at materials for my mini obsy.   I don't know of anything that will bend in both directions other than one of the softer metals like aluminium or copper that can by hammered into shape. 

Another design I've seen for domes uses flat parts with either three or five sides and is called "geodesic" as I recall.  The pentagonal shapes hive a nicer result than triangles I gather but take more cutting.

[SnakeyJ]

One build on here used hardboard ( I think) pinned to battens, then fibre glassed the whole thing...

There is a ply that's very bendable not sure what name it goes under......

Found this link..

https://www.google.co.uk/search?q=elastic+plywood&espv=2&biw=1920&bih=1099&tbm=isch&tbo=u&source=univ&sa=X&ei=w4E3VcTcLYLDOeScgeAL&ved=0CCAQsAQ

I hadn't thought of hardboard, but there is some damp resistant that might do the job for the internal skin at least.   This is available in a 3mm thickness.     Butt joints would still need some reinforcement or overlap.   It's cheap enough that I could double skin the outside, with lots of waterproof glue to bond the sheets - just wondering about the weight now, as at some point I might need to have this lifted and moved (though a hiab should easily lift the whole obs over the fence from the sports field behind the house.   At least when the ground is dry!).

[SnakeyJ]

Bendyply is what it's called but it only bends in one direction as I understand it, the other is the same as ordinary ply.  I've never used it but did some research when looking at materials for my mini obsy.   I don't know of anything that will bend in both directions other than one of the softer metals like aluminium or copper that can by hammered into shape. 

Another design I've seen for domes uses flat parts with either three or five sides and is called "geodesic" as I recall.  The pentagonal shapes hive a nicer result than triangles I gather but take more cutting.

Thanks Gina, looking at the bendy ply I'm pretty sure that standard thin ply will take a bend radius of 1m to form a simple 2m cylinder.    I've seem much thicker ply used for skateboard ramps and similar, so must be possible.    I could also use fibreglass tape to reinforce the joint on the external side, which would not look too bad once it was all painted over.

The dome skin will be canvas or a rubber membrane stretched over the ply frame, so this should not be too hard to cover - keeping it water tight will be the trick!

[SnakeyJ]

I'm having a rethink on how to do the ply components to minimise wasteage and considering laminating these from thin strips of 4mm ply.    I would get a lot less wasteage, at the expense of time and glue and a little more sanding, but can layup all my 360 and 180 degree rings as single pieces.

To do this I would put down a couple of sheets of shutter board to cover the patio and cover this in plastic sheet.     I can then mark out my circles and curves and screw in blocks around the circumference to hold the outside of the curve.     A standard waterproof wood glue should be sufficient for the lamination and the spring in the ply should provide enough tension/pressure to hold the joints, though I could also rivet through.   I would just need to make a jig to accurately cut the strips at 15mm and 25mm widths from the ply sheets.

Anyone see any problems with this?

[SnakeyJ]

At times like this it's very handy to have a retired wooden boat builder in the family!  I've had a long and very useful chat this afternoon around the build and layup techniques for laminating the rings and frames.

Basically the method described above is ok, though the use of ply was discouraged due to the lack of core strength in thin ply and the costs.   Bob thought it was better to buy softwood timber and cut the lathes out with a table saw at between 1/4-1/2 thickness to meet the bend radius required.   He also suggested that I build up at least 6+ strips to give reduce the amount of spring back when I half and quarter the laminated circles.   The use of Gorilla glue was recommended as it will allow some slippage and time to get the layup right before it sets and it has good gap filling capabilities if my saw cuts are a little jagged.    Gloves recommended to avoid the black hands.

Bob also suggested I put toggle clamps on top of the outside blocks to prevent the lathes slipping out while being bent in to shape and to use blocks and wedges of the inside to add some internal pressure.

I've been down to the timber merchants this afternoon and arranged to borrow my brother's table top saw for cutting the lathes.   I'll do a little experimentation to test the best thickness for a 1m+ radius and to practice not chopping my fingers off