Browsing through the net for custom bamboo bikes I noticed that people use either carbon twine or ramp, compressed hemp fibers. Is there any compelling reason not to use (compressed) hemp twine for this method of construction? Just curious thanks in advance

Because there are better and stronger materials out there. Once you encapsulate the hemp fiber in polyester resin, you've just robbed any attempt at recycling-- so why not go ahead and use carbon tape?

If you HAVE to use hemp, I'd suggest a nice hemp linen instead of twine. It's going to finish up much more nicely, and if you cut it on the bias it will be much stronger as well.

I think the joint strength depends on the Carbon Fiber, Epoxy matrix.
maybe finish off a decorative layer of natural fiber on top ?

In my frames I think that dealing with hemp fibers was easier than dealing with twine. It finishes easier, there are less voids and pockets of resin, it compresses better (which means more excess resin is removed--fiber is strong, resin is brittle) and since one has complete control of the fibers' orientation I believe it produces a stronger lug.

The hemp looks better - if you are seeking that warm and fuzzy 'green' all natural look.

Don't use polyester resin.

What resin are you guys using? In my boatbuilding work I've had great luck with T-88 and RAKA products. T-88's probably the most flexible epoxy out there.

3M Scotch Weld to tack the frame together, and West Systems 105 for wetting out the hemp.

Are you happy with the WEST System? I know plenty of guys who swear by it and a couple who swear at it.

I have had good luck using "Manila Hemp" rope which has been soaked and untwisted. That's the material used to make typical "Hemp" rope which you can find nearly anywhere. It's actually "Abaca" or banana leaf fibre. It's very strong and has the required "green" look with small dark flecks and streaks mixed in.
I have experimented with various epoxies and all seem to work pretty well. There is quite alot of similarities across the types offered by various companies.
I really liked the MAS resin. Good price and seemed virtually odorless and free of "fumes".
I'm actually really interested in trying some Poly Epoxy from Aircraft Spruce. It is fully twice as strong in every way above all the other types of Epoxy out there.
It makes sense to me that the apparent drawbacks of natural fibre breaking down over time (as demonstrated by the bamboo bike studio) could be offset by doubling the matrix binder strength.

Sorry for the late response, the thread slipped by me.
I really like West Systems. I've had no problems at all with it.

"Are you happy with the WEST System? I know plenty of guys who swear by it and a couple who swear at it."

It is my favorite hands down. Last summer I used both WEST and MAS. I preferred the WEST. I thought the MAS was far from odorless, and the odor was gross chemical. I like the smell of WEST, which is probably a bad thing. WEST is just very high performance, it is not the easiest to wet out fabric with, but it plays best with wood. The fabric problems are with the heavy knits. While the problems exist with lighter cloth they are totally manageable.

WEST was more expensive for a long time, particularly when people doing boat sized projects passed on the project discounts that were substantial. These days the costs are pretty competitive with brands like System 3, the cheapo RAKA of an earlier time, being more expensive. West price is the same or lower than the 70s. I know guys who hate WEST, it seems for the cost only. I have a friend who is doing a large catamaran, who did everything to avoid using WEST, and made himself sick with all kinds of discount brands (not that WEST is a picnic if you get yourself saturated in the stuff). He is now a WEST proponent. Drives me crazy. All that said there are a lot of projects or steps within a project where you can easily get away with any of the semi credible brands, and there can be advantages to other brands like longer pot life, or easier wet-out.

The other thing one hears against WEST is that it is hard and cracks So other brands market themselves on flexibility, which is normally a big negative, like wanting soft cement in a fero cement structure.

Hm I'd rather not taking any chances with the stuff holding my bike together i wonder how they did it on those earlier bikes, before the advent of epoxy.

None of the common resins are going to make a bike prone to failure if they are used properly.
I'm not sure where WEST gets a reputation for brittleness. You can add a bit of G/flex to your mix if you want a bit of flexibility anyway.
I had a pot of WEST set up in minutes from mixing too much at once and I could hit the chunk of Epoxy with a hammer without being able to crack it. Mix in some fibers and it's practically indestructible.
There is a demonstration with someone trying to crack a piece of homemade micarta made with WEST and denim. It is seriously strong stuff.
There were other pretty good glues before the advent of Epoxy. Some of them are still in use.
I have an ancient set of golf clubs with hickory handles inserted into the metal heads and the joint is seamless with no signs of separation. I would imagine original bamboo bikes had the bamboo inserted into the metal lugs in a similar manner.

On the Calfee site they say the thermal expansion properties of bamboo and carbon fiber are different, resulting in eventual de-adhesion, so they switched to hemp; presumably no expansion issues.

I wonder about that. I've ridden a carbon wrapped bike through hot and cold extremes for years.
I wonder if Calfee is curing his bamboo long enough and sealing it adequately. When natural material cures it tend to continuously shrink through each cycle of dampness and dryness.
That's why tool handles eventually loosen despite being dried adequately before intial installation.
Yoiu can get bamboo or wood "dry" quickly and it will still shrink gradually over time.
If Calfee only treats the bamboo with satin polyurethane then that's not nearly enough to slow the moisture cycling to negligeable amounts.
Things like this are why old time craftsmen working with natural material demanded that it be cured rather than just dried.

I think the reason that WEST is accused of hardness is because they made a big deal about it, and it is one thing that can be hard to get out of cheap epoxy. So their competitors cleverly turned it against them. The hardness WEST has is not required in every case, but I don't know of any to many cases where it is a problem.

I doubt the calfee thing makes much sense either, at least for bridging the parts. In that case the tow is linear and will move in and out with expansion and contraction of the materials. One thing about bamboo is that as wonderful as it is, it is still grass, not say, carbon fiber. So in theory something of a similar set of properties, say hemp, should be able to get the job done also, and if so, why bother with carbon. I made some fenders of bamboo, and because of the watery environment I finished them with WEST epoxy. They looked great, not always the case when epoxy is used in the top coat. The epoxy was a very good fit with the bamboo, sank in just the right amount, etc... Therefore I would finish the frame with epoxy, and that would eliminate the expansion and contraction problem.

I have been gathering parts for a Bamboo bike frame an have been considering West system but the cost is close to $100 once I buy the pumps and extras.
I was thinking of using this stuff off eBay as it looks pretty good and is supposed to be very good a wetting carbon fiber.
https://cgi.ebay.com/Premium-Epoxy-Ki...item4cf5ecda40

any thoughts on this epoxy?