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Danosa Danopren TR


oipigface

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Anyone know if this is suitable for vacuum bagging? It’s an extruded polyurethane foam similar to Styrofoam. Compressive strength is >300kPa. Density 30kg/m2. Sounds all right to me, (stronger and lighter than Styrofoam) but I’d like to know if anyone has any experience with it.

https://insulation4less.co.uk/products/danosa-danopren-tr-xps-insulation-all-sizes?variant=31683097100341&utm_campaign=I4L&utm_source=google&utm_medium=shopping&gclid=CjwKCAiAlNf-BRB_EiwA2osbxQ2isdR5m4tvuzp9cYQxIs39P4e_eLK2V9ARDAQ5ZaOqATRm7U4k5BoCIZMQAvD_BwE

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Never used it, I just LOVE the delivery prices. Was that £50 or £65 per order?

https://insulation4less.co.uk/products/danosa-danopren-tr-xps-insulation-all-sizes?variant=31683097100341&utm_campaign=I4L&utm_source=google&utm_medium=shopping&gclid=CjwKCAiAlNf-BRB_EiwA2osbxQ2isdR5m4tvuzp9cYQxIs39P4e_eLK2V9ARDAQ5ZaOqATRm7U4k5BoCIZMQAvD_BwE

We used to use Dow Styrofoam I.B. decades ago, 75mm thick, from Sheffield Insulations. I think it was about 30kgm-3. How about this:

https://www.ebay.co.uk/itm/281090056474

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I hadn’t noticed that, Graham! I would have done once I started to order it. It’s £65 ‘additional charge’ for a Danosa product even if delivery is free! You have to buy £500 worth before VAT to qualify for free delivery. If you just want one pack they want £30 (price), £65 (additional charge)  and £50 (delivery). Price and delivery attract VAT. They don’t say whether the additional charge does or not.

The one you picked out from ebay looks OK, but a bit of a f a g having to cut it down from 200mm thick. I found this one, which looks like the right kind of stuff. £16 for a 2x4 foot sheet 50mm thick. No delivery charge. Do the specs vary a lot, or is blue XPS pretty uniform in quality?

https://www.ebay.co.uk/itm/XPS-Insulation-Boards-Floor-Underlay-Panels-for-Electric-Underfloor-Heating/153630539630?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20160323102634%26meid%3Df188c0764ea44dad945b07d5583373fc%26pid%3D100623%26rk%3D3%26rkt%3D5%26mehot%3Dpp%26sd%3D281090056474%26itm%3D153630539630%26pmt%3D0%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic&_trksid=p2047675.c100623.m-1

 

 

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The first line in the description of the above Ebay link is:

"*Please note - Not Suitable for Crafting / Model Making / Hobby purposes. Colour may vary."

but it doesn't say why - perhaps because it's recycled and has lumps in it which would catch on a hot wire?

 

AJH

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11 hours ago, AJH said:

The first line in the description of the above Ebay link is:

"*Please note - Not Suitable for Crafting / Model Making / Hobby purposes. Colour may vary."

but it doesn't say why - perhaps because it's recycled and has lumps in it which would catch on a hot wire?

 

I think it means it may be blue or grey. I have seen green, orange, cream in parts of Europe.

The chunk I bought is great and seems perfect.

Favonius.com

 

 

foamblock.jpg

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I think you guys are at cross purposes. AJH.is talking about the URL I found, Graham’s talking about his. I take it from your second post Graham that you’ve given the blue/grey stuff a try and found it suitable for purpose? If so, that’s good enough for me!

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  • 1 month later...

Six or seven weeks later, I can report that in the last half hour, I successfully cut my first usable tailplane blank. I bought two 2'x4'x8" blocks of the grey foam that Graham recommended which arrived a couple of days before Christmas. The last month has been filled with design, redesign and tweaking the necessary equipment. I now have built three bows: 300mm, 600mm and 1000mm and an 800mm static wire, which fits onto my bench and can be used to cut larger pieces. The static wire was originally the 1000mm bow fixed upside down, but it proved not to be robust enough and I designed some beefier supports.

I discovered that the original static wire was not up to the job by trying to turn one of my blocks into two 2'x4'x4" ones. That was about three weeks ago, and almost everything about the cut was wrong: the wire wasn't tensioned enough; it wasn't hot enough; and I found a lot of difficulty pushing the original block through by hand at an acceptably steady speed. Still, I did finish up with two still usable blocks of foam, and with a wiser head on my shoulders.

I finished the redesigned static wire this afternoon and decided to have a go. I wanted to cut a few tailplane blanks 16.5"x6"x0.75". I started by straightening up one of the 2' edges of the block. I used a technique learned from Phil Barnes' video on vacuum bagging, which involves just dropping a bow onto the foam and allowing gravity to take over. Barnes makes it look easy, but it isn't quite as easy as it seems. Just starting in the right place is harder than it looks! My second cut was better than the first. It yielded a more or less rectangular block 2'x6"x4", which I shortened with the bow to 16.5" long. I then used the static wire to cut a 3/4" thick slice from this. 

I think next I'll try adapting the gravity feed system I built last year to draw blocks through the static wire at a more constant speed. 

Thanks to all for advice on various aspects of this project. It seems like a lot of effort for a tailplane, but other projects will beckon!

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Gravity feed system is up and working. I now have 5 usable tailplane blanks! Here they are in order of production. At the top is yesterday's effort. The others were all done using  the gravity feed. I used a similar setup to the system they are reputed to have used to get the stones for Stonehenge to Wiltshire from Wales, only I used a milk bottle with water in it to do the job of the hunky stone age workers. Four pieces of epoxy glass rod for rollers under the foam, a brick on top with a rope attached to it, and a system of pulleys leading to the milk bottle. Fairly pleased with this, but it seemed occasionally to hesitate as if there was some variability in the system's friction. 

thumbnail_77200FB0-A8A6-4B92-93E1-D878E2DDC062.thumb.jpg.a9438f0641d273ca5eeff578b1adbcfb.jpg

 

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Been busy the last couple of months building my new garage/workshop so just catching up on the chatter here.

Ref to original posting:

A cautionary note about PU foams. Definitely not recommended for heat cutting as above a certain temp’ it produces nasty fumes. At normal melt temps it’s okay but typically, hot wires are not well controlled. I used to injection mould PU and we had to be careful that during a purge of PU when changing to a plastic of higher moulding temperature, that the PU wasn’t heated above a safe temperature.

Neil P

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I would keep it below 230 deg.

There are so many chemical varieties of PU, with and without fire resisting additives, it is impossible to predict what may be produced without knowing the exact composition. Also that knowledge is way beyond my level! Just to say, Hydrogen cyanide and Amines are likely to be produced on burning PU.

Safety would err on the side of using other than PU foams. Having said that, PU foam blocks are easy to shape and sand with saws and abrasive tools. I used to do that for land yacht hulls years ago.

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  • 2 weeks later...

Big day today! Finished building a machine to cut tapered wing and tailplane cores. I also cut my first half tailplane core. It’s too imperfect to be really proud of, so I won’t embarrass myself by showing you a photo, even though I’m generally pleased with the surface finish, so I think I got the temperature right at last. The core is 15” long, 5.75” HT14 at the root, and 4” HT12 at the tip, with the TE at right angles to the chord. 

 I had two problems: the first was caused by the wire getting snagged on the template at the tip LE where the transition from profile to exit ramp is. I’ve rounded it off a little with a file, so it shouldn’t be a problem again. The second problem I don’t think I understand. The wire seems to be sagging between the templates, so (for instance) the core TE is 2.5 or 3 mm thicker at the centre than at the ends. Tomorrow I’m going to try cutting another with the wire tension cranked up a bit, but if there are any other solutions you can suggest, I’d like to hear them.

The machine is based on a design from the Charles River Soarers website centred on a pivoted drop bar. As the bar drops, cord  ends attached close to the pivot are pulled down a shorter distance than those farther away. The cords run through a pulley system so their other ends can be hooked onto a cutting bow. With templates attached to the ends of a foam blank, the machine will pull the wire through the foam at one end faster than the other, producing a tapered planform, and if the bow is weighty enough, the wire will rest on the templates and produce a cut with the same shape.


http://charlesriverrc.org/articles/tools/brengmancutter.htm

 

 

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Another big day. Finished building the machine for cutting tapered surfaces on Friday. Tried to use it yesterday, which was mostly frustration/learning. Then today I ran off four tailplane halves, which are of consistent enough shape and quality to be used in the next stage of the project. They are 15” long, with 5.75” HT14 section at the root and 4” HT12 at the tip. I managed to spoil one of them a little when the bow got out of hand at the end of the cut, but the damage is repairable, and I learned the value of long leadouts on the templates.

I started with 18 blanks, I’ve got 4 left, and 4 turned into tailplanes. So wastage yesterday was 100%, today 0%, overall 72% and falling.

14054117-C167-48DB-AACA-565CF125D5D2.thumb.jpeg.4a33fb9d7315c72b5f0d428e1ec1322e.jpeg

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3BBF974D-6C53-4A70-890A-7D6A3D1C448A.thumb.jpeg.8516f207a0d790d1b20d8ff8d2622dc6.jpeg

73387698-2EF0-4586-A026-638893A432AA.thumb.jpeg.5383ba0a9812c9e3466a050314dc495d.jpeg

 

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  • 1 year later...

…..and over a year later……I’ve actually started vacuum bagging the cores. My first effort came out of the bag about 10 minutes ago. It is a test piece made from half of one of the cores I judged not up to scratch to be used as a tailplane. It’s a tapered wing section with a span and mean chord of 120mm. I’m sure it will look better when it’s been cleaned up, but I’m really quite pleased with it. Despite its appearance, it is nice and stiff, and I’m beginning to think that the effort I’ve been putting into fitting the real thing with a spar may have been a bit of a waste (except that it will help when I try to finish a wing).

I have several questions to ask those of you who know about this sort of thing:

i) What exactly is meant by ‘mylar’ in discussions of vacuum bagging. I used some mylar drafting film that I’ve had for several years. It has a matte finish which isn’t really what is needed for a nice shiny finished product! I don’t know what weight it is, but I suspect it is too thin for this application. This is mainly because it tended to crease easily when I was applying the wax to it, and the creases appear as visible marks on the finished surface.

ii) What wax is best to use? I used a spray release agent ‘Alchemie R5’ mainly because I’ve got plenty of it, and thought it would be easier to apply than the car wax that I’ve also got in stock. Despite a lot elbow grease being applied as well, the spray pattern can still be seen on the finished surface. So I’ll maybe try AutoGlim for my next effort.

iii) The hot wire leaves a larger gap between core and bed when it goes around a sharp curve. On this test piece, this gap at the LE has been largely filled with epoxy. This might be OK after I’ve rubbed the thing down a little, but I was wondering if, rather than use separate pieces of cloth and mylar top and bottom, I shouldn’t have used a single piece wrapped around the LE? Advice welcome.

Here’s a couple of photos:

image.thumb.jpg.99bc235de1a40b9e0267eed51d3473b4.jpg

The section is symmetrical and looks pretty accurate to me. The piece is also straight and flat. I bagged it inside the foam beds, which I imagine helps prevent bends and twists occurring. I have seen several videos in which people don’t use the beds. Is there any advantage in this?

image.thumb.jpg.384d403e4406f3a6d7529c118897cf94.jpg

This is the lower surface. The core is made from black foam, which I thought I could turn white by putting a piece of printer paper over it. (Suggested by a guy on Youtube, who to be fair was using blue foam.) It has wound up as a not unpleasant shade of grey! Anyone got a better idea that doesn’t involve paint? The layup on this side was (from outside in): Mylar, wax, epoxy L285, 48g glass cloth, epoxy, paper, epoxy, core. 

image.thumb.jpg.934e064b175d510b49629f37ede49507.jpg
 

Top surface is much the same layup with a piece of printed silk chiffon between glass cloth and paper. The colours of the print on the chiffon have been muddied by the black core. You can also see the rattiness of the LE at the bottom of the picture.

I mixed up 28g of L285 laminating epoxy which I rolled on with a small B&Q disposable roller. I used most of this up, but there are places where the chiffon looks a little dry, so maybe I should have been a bit more generous. The piece was in the hot box under vacuum for 3 hours. Then I switched the heat off. I switched the vacuum off at the end of the snooker, which was another 4 hours, and then left it overnight.

I’m really quite happy with how this turned out, but there are still many things I could have done better. Your help will be much appreciated.

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Some more pictures. These were taken after tidying the edges and dewaxing the surfaces. My previous comments still stand, but it has now become apparent that at the leading edge the various bits of cloth have not adhered to the core at all (Photo 1). They have curled around to follow the surface of the beds instead, leaving a void between them (Photo 2). I could fill this with epoxy and microballoons and then sand it to shape, but I’d rather not have to. 
I’m a bit proud of the trailing edge! (Photo 3).

0285305B-5219-4C35-B965-2F758F3FFA07.thumb.jpeg.750108a7bc19ed7336b3db3abdc742b6.jpeg

 

C460EC28-6BDE-41DE-A1F3-EC958E799E13.thumb.jpeg.12474bcea6217c47f1322e9dfc1b17f5.jpeg

 

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