Finally settle design for board 3

I've just recieved a shipment of 100x1400x6 mm paulownia wood planks. Enough to make 10 cores.
I've been working up my ideas for 6mm cores Borkite style but need to rebuild my rocker table and trial-and-error a few things before I invest in the carbon to make this single decks.

So I'm going to stick to more convention design -

1. 2 x 6mm decks 1 wood, 1 klegecel.  
2. R180 Slow Epoxy from FGI
3. poured rails
4. 2 x 7oz e-glass top and bottom (less that usual 3 x 6 oz due to use of wood in core)
5. vac bagged

New things I'm going to try

1. Post cure at 50 C
2. use router to but chamfer of 60 degrees from vertical and 85 degres from vertical aroundupper deck tip and middle like the new North designs
3. Footstrap inserts all the way through the board to avoid any risk of delamination due to epoxy or sand in the inserts holes
4. re-instate the use of 0.75mm holes right through board to allow excess epoxy from underside to squeeze through to the upper deck and be wicked away through the bleeder material.

 Heres the compositied design.

Press used in North factory

I came across this picture of the press used by North. Presssure  = 170,000 pounds of pressure ( pressumable over the entire surface of the board).

Link to North site Which looks almost identical to the pnuematic presses used to make snowboards.
GrafSnowboards DIY site that used 6 bar (c. 90 psi)

However, I was under the impression that snowboards don't have concave so what does North kites do differently to their press that accomodates concave without the top part of mold causing dry spots in the middle of the board where the top surface bends over it?? Anyone know?

Cheers Matt

Humble beginnings

Tonight I printed of the 1:1 scale template for board #3 using the the grid overlay feature recently added to Board-off and it worked like a charm. The diamond shapes give you more than enough points of reference to position the A4 pages exactly right without the need for a straight edge to guide. Its only a minor success but a success none the less.
The pdf file contained the board template scaled up 125% and when I printed it I scaled it down to 81% so that the cut marks placed in the pdf by adobe acrobat reader x were visible inside the printable area and not in the margins where they are not printed. 125%*81% gave me the right amount of net scaling I needed. The need for greater than 100% net scaling may be due to my setup (printer etc) so check this for yourselves.

A4 pages stuck together into the 1:1 template from Board-off.



The annotations on the board with the 50mm diamond grid overlay showing.

I'm still waiting to hear back from Paulownia Paradise about transport costs for the wood core. As a back up I'll go with the light weight gaboon marine ply. Even though it comes in at 2x the weight, it is also substantially stronger. the strength to weight ratio is not as good as Paulownia but it is net stronger.

Lateral profiles of rocker table & Mega Clamp!

I've just uploaded another version of Board-Off that includes a new tab there the lateral profiles of the rocker table are generated. Previously the Rocker Jigs in Board-Off where for a rocker table design where the surface material is bent over a central and 2 side jigs that bend the right rocker and concave into the surface. The lateral jigs would be used perpendicular to these jigs to provide additional support to the surface to eliminate the chance of the surface being distorted.

Rocker Ribs plot

Why is this useful? A few different scenarios: i) You are trying to bend a core material that is stiffer than the surface material e.g a plywood core over a thinner ply surface or plexiglass/ perspex surface with just about anything. ii) If you are applying positive pressure to the surface of the board in addition to or in place of the vacuum. e.g. you a clamping the core onto the rocker table under a sheet of ply wood like when trying to clamp stiff core material or adding additional pressure to the surface to get greater than 1 atmosphere clamping pressure to squeeze out more excess resin; or (iii)Rather than deal wit #%@ing tackytape/table surface issues, you want to place the entire rocker table inside a bag and evacuate it. This would make the vacuum bag reusable and avoid the need to search endlessly for leaks every time you make a board.

THE MEGA CLAMP.

Part of the motivation for drawing these up is an idea I have been thinking about for working at greater than 1 atmosphere without having access to a pressure vessel.

The idea is use a deep layer of sand over the top of the vacuum bag set up and then use a layer of thick plywood over the sand that can then be clamped down to achieve much higher pressures. The idea of the sand is to allow the pressure applied by the plywood cover to be distributed evenly over the surface of the board ( and so avoid dry spots).

Practically, the sand could be placed inside a large bag to make handling easier and to prevent sand flowing away (indeed removes the need to have a retaining barrier around the top of the table to keep the sand in.

This idea is a variation on the 'Quickstep' process for creating high performance composites for aerospace industry. Here, they use a plastics 'bladder' over the top of the part and fill it with hot water. This provides both the heat and the pressure they need to do away with the need for an Autoclave.

The questions I haven't yet found answers for is how much pressure will lead to dry spots in the reinforcement and what resin/fibre ratio might be able to be achieved.

.... to be continued.

Board-Off Printing

I tried printing and sticking the tiled 1:1 plan together using the method described in the previous post. While it did work,  it was very tedious and getting the pages to align properly on both axes was very difficult. I ended up with quite an uneven surface and the final plan was not dead straight.

So, to make things a bit easier I've just added a switch to the OutlineParameters that lets you print a diagonal grid over the top of the baord plan so that you have multiple points and lines to get the pages aligned when you print off a tiled version of the 1:1 plans. The output looks like this and shoulb be much easier to sticky-tape together.



Board plan showing grid overlay to assist with physical compositing.

 This will be included in 1.3.10 that I'll post in the next few days.

Printing Board-off plans on standard printer

I've finally got a process down for printing Board-Off plans on a standard A4 laser printer at home. Its taken a while since trying rescale the charts to print from excel but now its a bit more stable. Its a 3 step process and uses 4 bits of software (freeware). Sounds a bit involved but the process is quick even if getting all the software is a bit tedious.

Software:

i) Board-Off design tool - get the latest version from this blog.
ii) A9CAD - free cad software that allows you to import the dxf files created by Board-Off
iii) CutePDF - a free tool that creates a virtual printer whose output is a pdf file. Use it just like a normal printer only it saves pdfs.
iii) Abode Acrobate Reader X (free version) - for splitting the 1:1 scale plan into A4 pages.

Steps:

i) Export you design and rocker/concave jigs as .dxf file from Board-Off.
ii) Open the file in A9CAD
iii) In A9CAD select print and configure the options highlighted below to the settings shown.



A9CAD print configuration for exporting 1:1 scale pdfs of board plans

 iv) save the pdf to a new folder for this board.
v) Open the pdf doc in Abode Acroba Reader X.
vi) Click on file->print and again select 'cutepdf' as the printer.
vii) Configure it as follows:
  a) select 'tile all pages'
  b) scale tile = 125% (the reason for this will be obvious soon)
  c) check 'cut marks' and 'labels' and be sure to say yes when it asks if you want the comments printed.
  d) click on page setup and make sure A4 is selected ( or letter if in US)
 viii) click print to save it as a pdf with the 1:1 scale pdf split into A4 pages.

So, at this point you have a pdf file that contains the 1:1 scale plan split into around 28 A4 pages (many of which are blank) but the plan has been scaled up to 125% of the original size because of item (b) in the previous steps. The reason for doing this is that the pages produced by tiling the oversized image include crop marks that show you where to cu tthe pages so that you can stick them together to get your full size plan. However, these crop marks appear in the margins of the page and so will not normally be printed. To ensure that crop marks are visible you must reduce the page size so that what would be in the margins will appear in the printable area of the page. This invovles scaling the page before you print it out.

As we scaled it up by 125% you need to reduce it to 80% when you print it out (80% = 1/125%). You many need to look in the advance settings for 'free scaling' if the page scaling option in the basic settings doesn't have an 80% option. Below is an example of the 'free scaling' option in the Brother 2040 that we have at home.



Free scaling printing option. USed becasue the page scaling on the basics tab only has 100% and 75% scaling option.

 The printed document should then be the right size. I found that I needed use 81% reduction because of the scaling 'rounding' that I mentioned in my previous post.

Printing Board-Off plans on desktop printer

I've just discovered (late arrival to the party!) that abode Acrobat Read X (freeware version) allows you to print oversized pdfs across multiple smaller pages. Even lets you set the overlap of the content on the 'tiles' so that its easier to crop and align the pages to stick the larger 'poster' back together.

To print the Board-Off plans I exported it to paper that is 24"x60" with 1 drawing unit = 1 mm. When I set the Tile Scaling to 101%, the x and y scaled printed at the center of the board were just about perfect. Same goes for teh rocker jigs

I tried it on the board off print for the board #3 and it chopped it into 24 pages although I found I had to select 'scale the Tiles' = 101% to get it right. Seems that either something gets lost in the conversion or the pdf output from A9CAD is off a bit. Not sure which but 101% did it.

FoxIT readers doesn't appear to have the same function.

Hope this helps

Getting a good bond to plastic

I came across this link to the West Systems site that shows some real data on the strength of adhesion to different plastics when the surface is prepared differently. The result for ABS was very suprising. Flame treating on its own actually reduced the strenght (v. small). Only when it was cleaned up with alcohol in conjunction with flame treating did the bod strength jump up. It was also interesting to see how the alcohol/flame increased the bond strength of ABS proportionally more than in other plastics where the roughing the surface and flaming had the biggest impact. Looks like ABS / epoxy bond is most affected by surface contamination.

http://www.westsystem.com/ss/gluing-plastic-with-g-flex-epoxy/