Movement when pressing

[Richuk]

I'm wondering whether the compressor is partly responsible for way the carbon fibre has moved. The size of the bladder means that it is only partially inflated before the motor kicks in. When it does kick it, the needle rocks back and forth as the air is pumped in. If the air hose remains attached, is the fire hose, which remains linked, being forced to act like a diaphram?

[Alex13]

It could also be a result of excess epoxy being forced out the sides under pressure, taking parts of the carbon with it.

An interesting problem though, most people wouldn't see it due to topsheets and base material.

[Head Monkey]

Alex is right, its the epoxy flowing. Add a few drops of color to a test layup sometime... it looks cool, and it's informative.

[Alex13]

Any suggestions on how to prevent it Mike? Use less epoxy, I guess?

[falls]

I'm with alex and head monkey. I think it's particularly a problem when you use a really viscous epoxy (?) as when thick epoxy sludges outwards it has more force behind it to push your strips out too. whereas runny epoxy just flows out the side like water.
Maybe get carbon unidirection tape instead of rovings? The tape is kind of stitched together regularly so it would be less prone to pushing outwards.
http://www.carbonfiber.com.au/category4_1.htm
Aussie carbon suppliers.
It's interesting in your picture rich that you can see the rovings closest to camera bowed out to the left and that is where the big pool of epoxy also pressed out to!

[twizzstyle]

You'll have a damn hard time preventing this. Even the pros get this, see the K2 Pep Fujas...



If you really want the carbon to be in perfectly straight lines you're only real option is to precure strips of it.

[Richuk]

Thanks for this guys, it's all making sense now.

The rows were cheap and got me moving while I found tape. When I use them again, I had thought about routing a very shallow channel in the future?

I'm using medium viscosity ... but I'm a bit slow laying up at the moment.

Cheers fella's

[falls]

Good picture twizz
I reckon nearly all carbon rovings end up like that, it's just without a clear top sheet you never see them.
In the end effectively with a bit of waviness they are still running longitudinally and providing stifness.
If you have a clear topsheet just call it "carbon wave technology" and espouse the increases of longitudinal rigidity and pop with this patent pending pattern of placement of carbon. I wouldn't worry about the router groove.

[Head Monkey]

Ya, no great way around this. Try to put the minimum of epoxy on that layer will help, but it will likely still move a bit. Only other option is to precure under a bit of tension...

[sammer]

This might sound like a lot of work but...
What about using a needle and thread to stitch it into place on your triax?
Just a thought.

sam

[Richuk]

Now that's an idea!

Here's a few photo's to show what I'm thinking. Photobucket will rotate these at some point ...

The kevlar tape on the left was laid on the fibreglass - it moved with the epoxy



The carbon tape, which was wet, was laid on a dry core - cohesion?



So, I laid the kevlar on the core



Ditto with carbon fibre



Although this is a really small sample, I'm left thinking that the cohesive effects of laying wet materials on a dry core will stabilise the materials and reduce movement.

Hope this info is helpful.

[dorabito]

why don´t you use a little bit of superglue (like with the edges) to make sure it doesn´t happen?

[Richuk]

Hi Dorabito,

Sure, that's a good idea, but it adds a job to the process : ( I'm thinking that I will slow the rate at which the pressure is applied and minimise any residual effect