John in CR's monocoque composite frame build log

[Gordo]

John;
I haven't read the entire post but from what I have read, I did not see the recommendation to dimple or drill the area of the original frame where you intend to use a composite connection. Doing this will increase the strength of the connection substantially.

 

[John in CR]

I'm interested in ease of a good finish. Would molding the composite structure into a thin sheet of aluminum held to the curve I want with a temporary frame be a bad idea, leaving the aluminum as the exterior skin? Or should I just use sheet metal as a mold by polishing it smooth and coating the inside with mold release, and then give it a good gelcoat before starting with the epoxy and cloth layers on the inside?

I don't think coating with gelcoat will be very easy to do in a narrow/deep box with lots of corners? You're probably going to have to do some bondo work & painting it or use some stick-on material like that 3M simulated carbon fiber.

Applying gel coat first before glassing, so you pull a finished item out of the mold, is only something I've heard of, never done. I'd think it would be easier than laying up the glass though, since I can just paint it on. This is such an easy form with an easy to remove one-off mold that even just going straight to cloth layup should give me a pretty good finish. If I need much more than trimming the edges and a bit of sanding, then I screwed something up. Bondo is not in my vocabulary at this point. LOL.

I even want to sanding as much as possible. That's why I'd like to lay up and bond to a thin sheet of AL if it's reasonable. Then all I need is paint to finish, or polish it and apply lacquer to stay au naturale, which would be cool if I did it for the whole bike, though the way I am about washing vehicles a flat brownish grey finish may be best.

John

 

[John in CR]

John;
I haven't read the entire post but from what I have read, I did not see the recommendation to dimple or drill the area of the original frame where you intend to use a composite connection. Doing this will increase the strength of the connection substantially.

That's something I've not heard of. I thought just a rough sanding with a large grit was all I needed for a good epoxy bond. I'll wrap wetted material all the way around the original metal, so that bond isn't a big concern.

 

[Jeremy Harris]

True, the foam would be the perfect solution if I can get the right amount. It really makes me want to hack that downtube open, so I can get in there and see what I'm doing to make sure I get it done correctly. Then could either make a thick carbon fiber and glass ring as the reinforcement and save my ceramic for another time, or use a lot less and easily cast a ceramic donut instead a full plug.

Another advantage of doing the big cut is that I feel like it forces me to use carbon fiber, so I can do a stronger and lighter structure.

Here's a drawing of a cutaway view for what I had in mind, not to scale on the layer thicknesses. Note that I will use epoxy resin, not poly.

My worry with making a big cut in the tube is that the top and bottom of that tube are taking the headset moments - normal loads put the top face of the tube in compression and the bottom in tension (they try to twist the headset anticlockwise in the sense of your photos) and bump loads that tend to push the front wheel back do the opposite, putting the top surface of the tube in tension and the bottom in compression.

The least stressed parts of this tube are the sides, in fact you could drill fairly large holes in the sides and only have a minimal effect on strength. Is there a way that you could cut holes in the sides to access the area where you want to put the plug and keep the top and bottom face of that tube intact?

As Gordo has said, getting a good key for the epoxy is vital. Epoxy doesn't chemically bond to aluminium alloy at all, so the connection will be purely mechanical. Getting a good key, but without weakening the structure, will be essential.

Jeremy

 

[John in CR]

Thanks Jeremy,

I got it now, the epoxy needs some holes for a good mechanical bond since it doesn't really bond with metal like with wood or fiberglass. That means an AL skin is out too.

After drawing up what the bike would look like with 20" wheels, I may not hack into the bike at all and use the tremendous amount of space available under the downtube for batteries. I need to get some 20's with the right kind of hubs and see if the saddle is low enough.

In the meantime, I figured out how I can get the right back fill and do my reinforcing plug. I'll use 2 holes, one at the bottom and one at the top of the reinforcing area. The lower one I can use to see my fill level for foam or whatever that I insert through the larger top hole. When I pore the ceramic, I'll cover the lower hole with plastic and tape it securely. Ill hold the tube at an angle as I fill it, so I can fit more than enough to cover the top hole too. Seal it and tilt the tube vertical for curing. The holes will be sealed by the ceramic and with a little luck they'll be smooth and flush with the alloy tube, so no weak point from the holes and an incompressible tube at what was the weakened point. Even if I had to re-weld at some point, my plug would remain intact due to a 4000°F thermal limit for that ceramic.

I still need to get a motor solution going on this bike and the tube repair done and see how it works with 20" wheels. Then I can quickly go to about 1kwh below the downtube and 1-2kwh above it with storage room to spare in a form something like this:

 

[Gordo]

John;
I haven't read the entire post but from what I have read, I did not see the recommendation to dimple or drill the area of the original frame where you intend to use a composite connection. Doing this will increase the strength of the connection substantially.

That's something I've not heard of. I thought just a rough sanding with a large grit was all I needed for a good epoxy bond. I'll wrap wetted material all the way around the original metal, so that bond isn't a big concern.

A couple of more tricks. Don't waste money on "mold release wax" just 2 coats of floor wax, buffed by hand to a nice shine. Cloth will print through the GelCoat, but it looks neat if you start with one whole piece of material, so who cares. If you want to get away from the fabric print, you need 1.5oz matt for the first layer, then cloth, then roven for strength. One must not confuse hi-tec expensive epoxy that the aircraft industry uses to bond AL wing skins, with the stuff we get in a hardware store. As soon as your laminate sets up, trim all the edges with a razor knife. It will cut like cheese. Cut with the pressure towards the mold, not breaking it away from the mold. If you wait too long, you have to cut it with a saw and you get the glasbestoses dust everywhere.

I often wonder why I haven't died from all the gasoline, acetone, reducer, ethanol I washed my hands in and all the fumes and dust I have breathed? Most of my friends who practiced the same stupidity began to die off in their late 30's. I guess is was not bad to wash your hands in the 97.5% ethanol because drinking it did not kill us either.

 

[Jeremy Harris]

I often wonder why I haven't died from all the gasoline, acetone, reducer, ethanol I washed my hands in and all the fumes and dust I have breathed? Most of my friends who practiced the same stupidity began to die off in their late 30's. I guess is was not bad to wash your hands in the 97.5% ethanol because drinking it did not kill use either.

Me too. I used to regularly wash my hands in either acetone or MEK........

BTW, I now use ordinary industrial vinegar to clean up epoxy. It works a treat and doesn't take all the oils out of your hands the way that isopropyl alcohol does. It does sting like hell if you have any cuts or grazes though.

Jeremy

 

[AussieJester]

Discount Dolce&Gabbana clothing,shoes,handbags,watches retail and outlet
Dolce&Gabbana is a rather young Italian luxury fashion company.In 1982 Demenico Dolce met Stefano Gabbana,founded a small duo studio,which was the predecessor of Dolce & Gabbana.But it was didn't known to public until 1985 Milano Colleziono Fashion Show.At that show,they published their first Dolce&Gabbana women's clothing,won wide praise,dolce and gabbana men sneakers,and considered to be talented.After the next years,Dolce Gabbana Clothes,Dolce & Gabbana concentrated on women's ready-to-wear.By 1993,a big chance occurs to it.Madonna ordered over 1500 costumes for her world tour.This deal brought it a lot of worldly fame.After that Dolce&Gabbana dabbled in other fields,Dolce Gabanna shoes,belt,handbags,Dolce Gabbana Hats,D&G sunglasses,scarf,purses and Dolce&Gabbana watch.But its most famous products is still D&G clothing,its black color,geometric shape and inspiring fashion are key features,which is popular by sef-confident social women,like Whitney Houston,Alexandra Burke,dolce and gabbana sneakers,Madonna Louise Ciccone.

Awsome post ... might have to grabz me a pair of 'dem 'D&G men shoes '

KiM

 

[katou]

The active ingredient in vinegar is acetic acid, (which I'm sure you know).

What is the percentage in your "industrial grade" stuff? Here I think ours is 10% from the grocery store.

I buy it for concrete work, the alkalinity of the cement makes your hands hard to clean. A quick wash in vinegar, the alkalinity is neutralized and then wash as normal.

I'm interested in anything that keeps my hands free of paint thinner/acetone/MEK. I've done all that, and I don't like the way it dries out my hands. (I have very delicate skin you know)

Katou

 

[Jeremy Harris]

The active ingredient in vinegar is acetic acid, (which I'm sure you know).

What is the percentage in your "industrial grade" stuff? Here I think ours is 10% from the grocery store.

I buy it for concrete work, the alkalinity of the cement makes your hands hard to clean. A quick wash in vinegar, the alkalinity is neutralized and then wash as normal.

I'm interested in anything that keeps my hands free of paint thinner/acetone/MEK. I've done all that, and I don't like the way it dries out my hands. (I have very delicate skin you know)

Katou

I'm not sure, to be honest. I get it from a local place that sells composite supplies, it's smells like vinegar, but is clear and seems to be stronger, so I'm guessing that it's dilute acetic acid, but the dilution isn't specified. It's nice and cheap as a clean up agent, plus I'm pretty sure that it isn't too harmful to the environment, which makes it OK in my book.

Jeremy

 

[Hillhater]

In Australia it called white vinegar.. available in every supermarket and used for all general cleaning and even jellyfish sting relief
!

 

[John in CR]

I thought you guys lived in developed countries. I've bought the stuff, and here it's called acido acetico (acetic acid in spanish) and the % dilution is stated right on the container. It's good to know though, because I'm sure it's a lot safer than the xylene I was given as a teen to remove some industrial paint. It sure worked well, but it's probably good that job was very temporary.