stronger BMX frame- cheap or expensive?

[HeadSmess]

its fine to braze, use lpg/oxy to keep the temps down.

cleanliness and proper fitting of all joins. surface area. just like glue. avoid butt joins. lap lap lap

its hard because you dont get to "hold, close eyes and squeeze"

as long as you keep it below 950c or so, everythings good... the temp it loses its magnetism and goes into the first phase change in hardening/annealing... well over any tempering temps but let it cool slowly.

metallurgy is complicated


silver solder is better, but takes even more effort to get right. real silver, not plumber/electrical muck. melts at around 600c. barely glowing dull red

blue/white smoke on brass, and yellow smoke on silver, are signs of overheating.


looked at bits i got. other than the shroud and fan, most everything is junk. i wrote it off years ago and left everything in a pretty lousy shed...

seriously, the cost of repairing the epitrochoid is prohibitive. remove chrome, weld up chipped spots, rechrome, regrind...nope. its not just the rotor, its everything. sideplates are pitted too from corrosion.

better off cutting it up and making one of those "cut away" displays

 

[keatonx]

its fine to braze, use lpg/oxy to keep the temps down.

cleanliness and proper fitting of all joins. surface area. just like glue. avoid butt joins. lap lap lap

its hard because you dont get to "hold, close eyes and squeeze"

as long as you keep it below 950c or so, everythings good... the temp it loses its magnetism and goes into the first phase change in hardening/annealing... well over any tempering temps but let it cool slowly.

metallurgy is complicated


silver solder is better, but takes even more effort to get right. real silver, not plumber/electrical muck. melts at around 600c. barely glowing dull red

For whatever reason I find brazing pretty easy and more fun than mig.

I always end up having to aim the tip of the flame right at the bronze rod for a few seconds to get it to melt tho. Maybe because I'm using thick 3/32" rods and a cheap $70 bernzomatic oxy/mapp rig. Bottles of oxy are super expensive and the torch flashes back constantly if the head gets a tiny bit of dirt into it, but it does the job.

I've tried those nickel silver brazing rods too. They're supposed to be stronger (85000psi tensile vs 60000psi). The ones I had melted at around the same temp as the bronze rods. I can braze with them fine, but when the pool cools it always ends up looking super ugly and rough. Like it will dry with a sandy looking finish. But they hold fine.

Thx for looking for the parts

 

[keatonx]

Ok, the bikes in the final assembly phase, but before I braze on the motor mounts, I need to make sure my bike is fine. What I got is an old 90's huffy flatbed with a standing pad. Here's a pic of the frame-
The welds look pretty good for the most part, but there's a few spots where they're sorta uneven (look at the pics of the seatstay-top tube junction).View attachment 51267View attachment 51268small little dent in the stay that's probably supposed to be there for chain room, since it's on the inside where it's protected.




And inside the headtube- (seamed)

Rear dropouts are really thick (3/16-1/4"), but only welded on one side (easy fix).
It has a chromoly downtube, but the rest is hi-tensile.
The only thing I'm worried about is it being a flatland frame (weak).
When I first got the bike I noticed it was really light, but all I can compare to is my tank haro F3 (which is 36lbs stock and about 40 lbs if I include the heavy steel pegs I have on it) I weighed the frame by itself (with the seat removed but the seat tube was stuck in; I'll be cutting it off and putting a smaller one inside it) and it was 6.6-6.8lbs, which is heavy but the standing pad probably adds on a lot of weight. It also has a massive wheelbase (i could tell just by looking at the bike. I measured it and it was even more than my haro F3 (Street/park bike). It also came with a gyro (knockoff)

Here's a quick mock-up of how everything will be mounted-

The way I'm mounting everything will mean the only place with a lot of extra force will be the motor pulling the chainstay into the bottom bracket under hard acceleration.(I'm gonna reinforce this area alot)

The bike could have been ridden pretty hard because it had a bent crank arm, but it also has no dents (minus that one on the INSIDE
Of the chain stay, which is probably for chain clearance).

So does this sound strong enough? Keep in mind I'll be putting gussets/reinforcements on ALL of the highly stressed areas (bb, gussets/bridge on the headtube junction, reinforcing chain stay (a lot) and seatstay.
And all of my riding will be done on paved roads, so no big bumps or anything.

 

[HeadSmess]

dropouts are invariably brazed. same for any lil mounts like the kickstand mount thingy. dont try welding, you make a mess!


other than ground clearance, i aint complaining...

 

[IbedaYank]

dropouts are invariably brazed. same for any lil mounts like the kickstand mount thingy. dont try welding, you make a mess!


other than ground clearance, i aint complaining...

post 44 second picture down... clearly show dropouts with just one side WELDED

 

[HeadSmess]

post 44 second picture down... clearly show dropouts with just one side WELDED

post #44, 6th picture down, inside shot of dropout, devoid of paint, with slight brassy tinge....

second picture down...thats one neat weld if it is

ill let the OWNER make the call on this one. just speaking from experience

a file and application of heat will do it...

 

[IbedaYank]

and here I thought the capillary action of using a lug is what gave brazing it's strength.
Not a butt joint. I guess all the books for bicycle frame building are wrong.

 

[IbedaYank]

welcome to the wonders of a TIGWELDER
http://www.flickr.com/photos/44bikes/9903200905/
his company site..
http://www.44bikes.com/

 

[IbedaYank]

if it is a huffy flatbed it will have a chromed frame.
Chrome and welding/brazing/silversolder do not mix as there is a copper layer under the chrome

Going to need a painted frame not chromed
http://bmxmuseum.com/bikes/huffy/54161/1

 

[keatonx]

The dropouts are welded, the brassy tinge is just remanants of paint that I'm still stripping off (someone painted over the chrome frame). And I know brazing on the chrome probably won't be ideal, I was gonna file it to bare steel anyways