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flag Jump233PT
Posted: Apr 21, 2019 at 3:27 Quote
Compositepro wrote:
Jump233PT wrote:
SleepingAwake wrote:


I'm not sure what you mean with "polyurethane positive molding". Laminating onto a polyurethane foam core?

Other than that i really like to work with flax and there is actually some flax in this frame too. And in my albums you will find pictures of a full flax handlebar, which however was only the first prototype to check the mold dimensions and not strong enough for riding.

Yup using the PU foam core, now I am kind of suspicious of using flax to build a frame, I might use some carbon mid layer to reinforce but the main objective would be a 100% flax fs bike

When we used flax and hemp in bikes it was to control frequencies of vibrations in the layup , we also did the same thing in lemans and F1 in fact lots of the stuff from the days at Toyota F1 was reused in other Motorsport and road cars .

However many have poor stiffness characteristics as do lots of these newer super fibres and the flax would be structurally sound if used in enough quantity but would be well outside the "light" catagory your looking for in a bike you can make something stiff by using a bigger section and thicker wall however

I was thinking of using the bcomp power ribs to reinforce the main tubes (top and down tubes seat tube as well. Here is the link of it
http://www.bcomp.ch/en/products/powerribs
flag TyranT21
Posted: Apr 22, 2019 at 3:35 Quote
Organic fibres (hemp and flax) absorb a lot of resin making the parts very heavy. Another consideration is that it’s very hard to trim these parts and get a nice edge. Like Kevlar they always have fury edges whenever cut post cure and it’s very hard to get rid of it.
flag Jump233PT
Posted: Apr 22, 2019 at 14:36 Quote
Hi, so I found myself some setbacks and I would like to know if someone can help me out, so the main one is that on my design I am using a single pivot yoke driven suspension platform and I would like to hear some recommendations on cnc machinist in EU, the other setback's are the bb HT and dropouts as I am afraid of bonding metal the inserts and don't be as reliable as I would like to. Any further help is much appreciated!
flag SleepingAwake
Posted: Apr 23, 2019 at 0:46 Quote
TyranT21 wrote:
Organic fibres (hemp and flax) absorb a lot of resin making the parts very heavy. Another consideration is that it’s very hard to trim these parts and get a nice edge. Like Kevlar they always have fury edges whenever cut post cure and it’s very hard to get rid of it.

Are you referring to hand laminating? in that case i would agree, but with vacuum infusion or when pressing mechanically or in an autoclave i get a very reasonable fiber volume fraction. As for cutting, it does tend to get a little fuzzy but it doesn't delaminate as much as carbon and glass does. cutting with a metal blade, then a little sanding with fresh sand paper and you can actually polish the cut surface!

So flax has a very good stiffness to weight ratio, but ultimate strength is a little lower. furthermore it has very good damping properties. I built a lot of skis where i usually make a hybrid layup with flax and glass, flax diagonally to control the torsional stiffness and to calm the ski down which works amazingly well.

What metal are you trying to bond into the frame? Aluminum can be quite difficult, stainless is usually a little easier. But you always need to be careful with different CTE's and such. I would use a toughened bonding resin made for the job and making sure that i have like 0.3 to 0.5mm of a bond line with the toughened resin and not less...
flag Jump233PT
Posted: Apr 23, 2019 at 2:35 Quote
I would use steel or even titanium and wrap it on glass fiber so it doesn't corrode, the easiest way for the dropouts that I come to is to use the Santa Cruz 2018 dropout as I don't need to use inserts on the rear end and therefore making the rear end a bit lighter, might do the yoke with flax as well but it might be less stronger than alu.
Any recommendations on vacuum pump to resin infusion?
flag ChocolateNinja
Posted: May 8, 2019 at 20:40 Quote
I want to build a bike using 4130 steel. There is a local shop that sells it but the smallest wall thickness that they offer is 0.05xx inches for their chromoly tubing. Should I look elsewhere or is this an acceptable size? I have read that 0.03xx inches is better for bikes.
flag R-M-R
Posted: May 8, 2019 at 21:02 Quote
ChocolateNinja wrote:
I want to build a bike using 4130 steel. There is a local shop that sells it but the smallest wall thickness that they offer is 0.05xx inches for their chromoly tubing. Should I look elsewhere or is this an acceptable size? I have read that 0.03xx inches is better for bikes.

Conversion to SI:
0.05" = 1.27 mm
0.03" = 0.76 mm

The absolute thinnest road bike tubeset from Columbus is 0.5 mm at the ends and 0.38 mm in the middle. It takes a skilled welder to not cut through this tubing; it's not for novices!

Sounds like this is your first bike. Don't expect it to be a masterpiece. The 1.27 mm tubing will be a lot easier to work with. Heavy, but if this is a learning process, maybe it's better heavy than a complete failure.

Or maybe you're already an experienced welder, you just haven't done a bike. In that case, the thinner tubing should be sufficient if you're not going to be riding super hard on this bike, especially if the tubes have a decent diameter. If the bike is going to live a hard life and/or you plan to use a long fork, you probably want the thicker tubes, at least for the down tube.
flag shirk-007
O+
Posted: May 8, 2019 at 23:03 Quote
Oh man don't use 0.05.

Buy proper tubes from Nova cycles.

Or buy aircraft quality 0.035 from Aircraft Spruce or Wicks.
flag R-M-R
Posted: May 8, 2019 at 23:47 Quote
shirk-007 wrote:
Oh man don't use 0.05.

Buy proper tubes from Nova cycles.

Or buy aircraft quality 0.035 from Aircraft Spruce or Wicks.

0.035" = 0.89 mm. That's reasonable.

Butted tubing would halve the weight of the main tubes. Agree, worth it.
flag Tsoxbhk
Posted: May 9, 2019 at 7:22 Quote
I use straight gauge .035 all the time.
flag shirk-007
O+
Posted: May 9, 2019 at 9:28 Quote
My next frame is mostly straight gauge 0.035.

But you will need to buy some bike specific stuff so for a first frame just get tubes from Nova.
flag cedric-eveleigh
O+
Posted: May 9, 2019 at 14:03 Quote
@shirk-007 What do you mean by bike specific stuff?
flag Scotj009
O+
Posted: May 9, 2019 at 14:15 Quote
cedrico wrote:
@shirk-007 What do you mean by bike specific stuff?

If your building a frame or thinking about it and don't know what he means go back to the drawing board and maybe build a IKEA chest of draws first Razz
flag R-M-R
Posted: May 9, 2019 at 14:22 Quote
Scotj009 wrote:
cedrico wrote:
@shirk-007 What do you mean by bike specific stuff?

If your building a frame or thinking about it and don't know what he means go back to the drawing board and maybe build a IKEA chest of draws first Razz

Or, instead of being rude and unhelpful ...

Several companies make tube sets specifically for bikes. What makes them bike-specific is they're butted (thinner in the middle) and available in several lengths to ensure the thicker ends aren't longer than necessary.

If you're planning to use straight-walled tubes, then you'll be fine with almost any high strength, seamless steel with approximately the right diameter and thickness.
flag shirk-007
O+
Posted: May 9, 2019 at 15:29 Quote
*face palm* head tube, bb, seat tube.

If someone has the tooling to machine the above to the needed specs I'd really hope they also had enough knowledge to research what the appropriate sources for proper tubing.

If you can't then I'd agree you need to assemble a few more Ikea items before you've reached the level to build your own frame.

 


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