Carbon Boom Design

olivers

Member
122
0
wind_apparent said:
Has anyone tried using floresent light tubes as mandrels? was thinking you could tape the tube with flashbreaker, lay up, cure, then blow up the bulb and pull the mess out.
Yes yes yes, a body of mine or I did that exact thing. If I remember, we ended up with a lot of the broken glass still glued to the wall. Not a bad low tech method if you properly wax/pva the bulb.
Mylar film (from TAP Plastics et al) works well between the mandrel and the layup. You need to tape it in place initially, then remove the tape as you slip some biaxial braiding down it.

You can also coat the mandrel with wax before wrapping with mylar for added piece of mind.

I've used this technique for carbon tiller extensions. The mandrel for those was delrin rod, also sourced from Tap Plastics. The carbon braided sleeving came from Soller Composites.

 

luminary

Anarchist
718
59
wind_apparent said:
Has anyone tried using floresent light tubes as mandrels? was thinking you could tape the tube with flashbreaker, lay up, cure, then blow up the bulb and pull the mess out.
Someone described it recently (thought it was earlier in this thread!) said it wasnt that great and the glass didnt release that well. Do a search through the forums.

 
That should go alright. Of course you're smart enough to check on the dimensions of your mandrel versus your class rules.... Will you be vacuum bagging the part? What laminate schedule are you going to use? Aluminum makes a great mandrel as its coefficient of thermal expansion is high. If you can make a hot box for the part to cure it in it will be easier to remove the part from the mandrel upon cooling. Good luck, let us know how it turns out

 

sadolph

Super Anarchist
1,903
1
Ottawa, Canada
I like that concept...laminate the boom in August, and extract the mandrel in February. let mother nature help a little on the thermal contraction side.

 

Phil S

Super Anarchist
2,606
233
Sydney
With the discovery that my alloy boom is bent, the emphasis has gone on making a new carbon boom. I have an old keelboat boom for a mandrell and once it's smooth and true I will cover it with packing tape and wax then lay up the first layer
By no means put tape on the mandrel. It will prevent you releasing the work. The tape tends to roll up into balls as you try to pull the boom off. It will start to move then lock up. Especially if you use any heat to cure the resin.

Using any old piece of alloy is asking for problems as any dints rivet holes or wear areas will cause problems on removal.

You need two sliding interfaces, both greased. Even some waxes ball up so avoid them unless you get expert advice.

lubricate the mandrel with vaceline, wrap it in mylar or some sort of plastic sheet which is stable beyond the cure temperature, Twice around so no resin gets into the mandrel. Them lubricate the outside of that. Only tape the plastic to the mandrel outside the limits of the work,

With two sliding surfaces you get double the chance of getting it off. which is still not 100% a certainty.

Refer to my post long ago on first few pages. I still only laminate small tubular parts and consider it better value to buy big items.

 
good point onthe tape although it is likely that once the first layer is done i will cut it to remove it as the mandrel is not round

overall the cost will be about the same as a bought one but the experience will be worth it and i needed carbon for other jobs anyway

 

usa7776

Member
180
0
I am late to this discussion, but what about a loss(loss or lost) foam process?

I was thinking about making a jig for a boom that is in the shape of a x, then gluing foam to it and shaping that foam. do the layup against the foam and then use solvents to melt the foam.

the thing could be hung vertically from a tree and vac bagged. the vertical hanging would help keep it straight.

 

iqcraig

Member
On a related but separate note:

I am trying to reinforce my boom around the vang location. Another fleet member with the same boom broke his, so this is a precautionary measure. Who has some ideas for how to lay up some more carbon around the outside of my boom? I would like this to looks somewhat professional, but strength is the priority.

Thanks for any/all advise.

 

usa7606

Member
195
0
On a related but separate note:

I am trying to reinforce my boom around the vang location. Another fleet member with the same boom broke his, so this is a precautionary measure. Who has some ideas for how to lay up some more carbon around the outside of my boom? I would like this to looks somewhat professional, but strength is the priority.

Thanks for any/all advise.
I did that for the white carbon boom I have because I was worried about it breaking also. I used 5.7 oz cloth and made my reinforcement about 18 inches long, probably wrapped it about 5 times around the boom. The piece of cloth is shaped like a trapezoid so that on the ends of the reinforcement it is tapered to avoid any point loading. One thing that helps is to tack the end of the cloth to the boom with 5 minute epoxy or superglue so that you can wrap it tightly and not have it slip. I'm not sure what the best way to consolidate it is. I taped it but it didn't come out that well.

 

usa7776

Member
180
0
On a related but separate note:

I am trying to reinforce my boom around the vang location. Another fleet member with the same boom broke his, so this is a precautionary measure. Who has some ideas for how to lay up some more carbon around the outside of my boom? I would like this to looks somewhat professional, but strength is the priority.

Thanks for any/all advise.

...did the boom fail on the top side or the bottom side first? If the top, you could probably make a carbon 1/2 sleave on a piece of pcv equal to the boom diam, vac bag it and then epoxy it to the boom. If the bottom side gave out first, I would probably do a bunch of Uni directional stuff going lengthwise on the bottom.

My thinking for the different layups was a top side failure is a point load compression issue, a bottom side failure is a tension issue.

 

iqcraig

Member
So I liked the idea of molding a separate plate and then bonding it to the top of the section. JB's boom appeared to fail by a combination of crushing(vang strop tightening around the section) as well as bending/compression failure at the top of the section. With bonding a reinforcement plate on as a separate piece, I can make the part look a bit more professional as opposed to trying to bond the carbon directly onto the tube. Will bonding a separate piece have a significant strength impact or is it a novelty in comparison to adding several full wraps around?

Using JB's broken tube as a mandrel, I wrapped it with packing tape and coated that with mclube as a mold release. I laid up a 4 layer laminate(8 oz carbon-5 oz kevlar-9 oz glass-8 oz carbon) and vaccum bagged it to consolidate. Everything un-molded nicely and I trimmed and sanded the part to shape. I think I should have added a few more layers, but I am not sure. The part is pretty stiff in bending but since it is not a full round it is not fully rigid(can be twisted).

What do you guys thing about sanding the mating surfaces and bonding this to the boom as shown? I was thinking of using epoxy and filler, but perhaps something like plexus(hate the mess) is a better move? Please let me know what you guys think. I am also going to make a new boom strop that doesn't tighten around the boom when loaded. This should relieve the "crushing" component that appeared to play a role in JB's failure.

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usa7776

Member
180
0
Looks like you did a great job!. Very clean looking part.

I personally would do the epoxy and colloidal, but only because that is the only stuff I have used.

i am a little surprised some of these boom manufacturers are not putting webs inside the booms where the vangs go for added stiffness.

 

usa7606

Member
195
0
Would it beneficial to put cloth around the entire boom in that area to keep the unidirectional fiber from splitting? That could have led to the failure on the other boom. You could overlap the cloth on top where the plate would cover it up.

 
Hi

It would be best to use a structural adhesive, as you say one of the plexus glues- there are a few different ones but I think they are all methalacrelate (got that spelling wrong). You could also use some thing like 3m's 9323 which is a epoxy adhesive, but then its probably fine to use laminating epoxy with fillers as the glue joint is not under a high load, as I have done when nothing else is avalable, and never had a problem.

Hope it all goes well, looks like you are making a neat start

Alistair

ps you did not need to release the packing tape, the epoxy will not stick to it

 
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was talking to a boatbuilder the other day who suggested wrapping the mandrel in paper so that the paper is about 1 or 2 mm thick then wrapping in plastic film. The idea being that when the carbon shrinks it crushes the paper. Pulling the mandrel out at about the 24 hr mark. as the mandrel is pulled out the paper unravels and is then pulled out after.

Any thoughts/has anyone tried this

 

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