Right, after finding out on this forum how hard it is to get welding/brazing gas in the UK, I've decided to switch to "plan B". Would it be possible to glue steel tubes into lugs using the sort of epoxy used for carbon fibre composites? I seem to recall hearing about aluminium tubing being used to build frames in this way before the advent of TIG welding. I can't think of any reason why it wouldn't work with steel as well (providing I'm not misremembering something), but I have a history of thinking things will work when actually there's a glaringly obvious reason why they won't, so I figured a second opinion would be useful.

Thanks in advance

Raleigh used glue in their Technium frames. They had some failures but there are still a lot out there. Specialized used glue in the CF Allez frames in the early nineties. The AL lugs failed before the glued joints.

I've wondered about this same thing, although my impulse would be to go with titanium tubes and stainless lugs.

I'm years from having any free time to try it (three small children), and so never asked the question, but I am intrigued.

Two issues:

- I thought I saw a post here saying that conventional lugs weren't deep enough for epoxy. There are listed strengths for epoxies, but I don't know how to compare to the strength of a braze.

- Surface prep is apparently critical in epoxying to metal, depending on the metal. More critical for aluminum, less for steel (assuming de-greasing, at least), medium for titanium. So, you might need to acid etch the areas to be joined shortly before bonding. See google books "Surface Treatment of materials for adhesion bonding"

I just got done building my first frame with steel and carbon. Wasn't quite as easy as I thought but its together. I basically made a whole steel frame and cut the center section out of the top and down tube to glue the carbon tubes in and then used a Taylor Carbon cross seat stay. I was happy with the way it turned out but it hasn't been ridden yet so we'll see. Its being painted right now for a customer and I am curious to see how it rides. If you want to check it out its on my blog https://meechcustombikes.blogspot.com/

If I had to choose between epoxy and a bad braze job, I would consider MAP gas in a hand held torch, or a propane system, before going off on a whole new technical angle. I buy epoxy by the 10 gallon pack, so I love the sticky stuff. It would still seem to me to be easier to find an alternative torch than to build an alternative lug system.

Isn't that really expensive?

There were some Rocky Mountain bikes that were made with steel lugs and aluminum tubes. They looked pretty nice and I see a few of the about town on a regular basis. The joins were glued (not sure with what though). Not sure the year and model of the bikes either.

The one thing that really catches the attention is the colors of the aluminum tubings next to the lugs. I have personally seen a purple one (a few times), a blue one (regularly) and a black one (once).

Just curious as to why it is so hard to get welding gas in the UK? There seems to be a fair number of frame builders from that area.

I used to race BMX with a set of answer alumalite forks. Aluminum tubes with sleeves epoxied into an aluminum crown.

Not terribly expensive. I use those little canisters for occasional plumbing and the cost is negligible. Having never tried brazing with one, I expect you`d use up quite a few over the course of a frame, so they`d add up, but that`s always the catch when you deal with "convenience" sizes of anything. For a single frame, MAPP would undoubtedly cost you less than tanks, regs, torch and tips for oxy/anything.

It's not actually that hard, but you can't buy the cylinders and get them refilled like you can in the US. You have to rent them, at a fairly high price, which is too expensive for a 17-year-old student like me. It's not hard to get welding gas in general over here, it's just hard for people in my particular situation.

By the way, on that carbon/steel frame you made, how far into the steel tubes did the carbon tubes actually extend?

I think this kind of thing was discussed on MTBR recently. I believe the consensus was that it could be done, but you want to be 100000% obsessive compulsive about cleaning both tubes, no touching it after cleaning, and do some serious research on what epoxy you use. Also, be careful with the epoxy fumes from that stuff!

That said, I bet if you asked around, you might be able to find someone with some O/A tanks who might take you under their wing. There is a subset of the population that loves passing on knowledge/skills if someone's willing to give it some real effort.

Cheers!

OK, here's an idea. The big problem is that the lugs might not be deep enough to give enough surface area for the glue, so what would happen if I glued the tubes into the lugs then put sort of "plaster casts" of carbon around the joints? Would that be any better?

I was told that 1 1/2" would be sufficient but I had more than that because on the top tube I went past the braze-on cable stops and on the down tube I had to cut it shorter in order for it all to fit. I was trying to leave them all the same length but the compound angles wouldn't allow it to go together so I just kept shortening until I could get it together.

I recall seeing a post in a similar thread that noted that as steel lugs are designed for brazing, there have more clearance than would be good for using epoxy......this allows for different frame angles and and gaps are filled during the brazing procdess.

the OP mentioned he is a student does that give you any access to a school shop or are there any co-op type shops around?

These are from a Raleigh Technium brochure - it shows very long internal lugs being used.

Man nothing screams "This bike is fast" Like a skinny MacGyver in running shorts.

" there have more clearance than would be good for using epoxy"

Epoxy loves big gaps, though obviously brazeable lugs are not designed for this purpose as you point out. Still, I wouldn't bat an eye at filling 1/4" gaps other than the obvious, but structurally the epoxy would be very happy.

Thanks for all the advice, people, I'll see what I can come up with by way of a bike!

I found an indication of how far to overlap tubes, from a LucasMilhaupt document on Brazing Joint Design. It gave a formula for how long the joint needed to be, based on the relative tensile strengths of the tubing material, and the shear strength of the filler material.

X = W*(D-W)*T / (C*L*D)

W = wall thickness of weaker member
D = diameter of lap area
T = Tensile strength of weaker memeber
L = shear strength of filler
C = "Joint integrety factor", suggested at 0.8

So, regular CP titanium is often listed at 345 MPa tensile, for T
W = 0.9 mm, D = 1.125*25.4 = 28.575 mm

L = 20 MPa is commonly listed for epoxy

X = W*(D-W)*T/(C*L*D)
X = 18.795 mm

So, the lug would need to be ~3/4" deep.

There are epoxies that advertise 60-80 MPa failure strength, but with yield strengths lower. (The Ti yield is also lower, more like 275 MPa). Using 3/2.5 Ti would take twice the overlap, to make the joint as strong as the tube, as it has > 600 Mpa tensile.

So, the good news for this approach is that we're not off by factors of 3-4. Deep lugs such as those meant for custom carving, and a good epoxy choice, might make this work out.

I Built alot of epoxy tubing frames but I use some very expensive epoxy, Hysol 9320 epoxy and I use a special prep inside the lugs for adhearsion, I work at an aerospace company so I have ways to get ahold of it.

Do you use standard tubes and lugs with your epoxy method?

Is your prep a mechanical roughening, or an acid wash/pickling/ type of chemical cleaning?

Thanks for posting, I'm delighted to hear that someone has done this.

I use exxon graftek lugs and I have the lugs epoxy primer etched on the inside of the lugs, they use a spray gun to put it on and it's done in our material processes lab. Our company built alot of the space station and that's how it was built.

I thought the problem in gluing metal tubes and lugs is that the epoxy is more rigid and brittle than the relatively flexible steel or aluminum tubes. Hence the occasional failure of those glued al. frames? The Alan frames used glue and screws in the joints, that may have stiffened the joint...

Or perhaps better epoxies are more compliant, like brazing filler?

Anyway, here is a video of Colnago gluing carbon tubes in carbon lugs: https://www.youtube.com/watch?v=MRt4p...layer_embedded. My guess is that carbon is generally stiffer, and perhaps has similar properties as epoxy?

I don't think so epoxy is hard but not hard like metals. On small sections my worry would be adhesion and differential expansion, on larger sections I wouldn't worry at all. Carbon is stiffer relative to the fiber reinforcements, the plastic around the carbon fiber is likely some kind of epoxy so there is compatability on expansion ratios and such. You can easily cut epoxy or carbon composites with metal hack saw, even one one made out of sheet metal, untempered. Epoxy hack saws would have little effect on metals.

Last thing last night I tripped over a 2 pack of epoxy in my bedroom. came right down with 200# + on the plastic gal of hardener. Lucky it didn blow up all over the place. Livin the life!