Heat Treating Aluminum Oven Costs ???

[damcard]

I have been frustrated with my current frame. The quality just isn't there. For example, the bottom bracket is not even close to parallel to the jack shaft. I may ditch it all together and move toward a custom frame. I have been pricing out how much it would be to anneal and then heat treat 6061. A local place here in San Antonio would charge me $300 or so for the annealing and another $300 for the hardening of a frame. Can anyone tell me how that compares to facilities in their area?

One note, their oven has room to do around 6 frames at a time and it would cost the same. So, if I did a second run later doing 6 frames, it would be about $100 per frame for the heat treating. -David.

 

[amberwolf]

Any particular reason to use Al instead of Cromoly? Good steel that's thin could be similar in weight and strength to Al, without having to go thru that kind of expense. I doubt you'd save enough weight on the bike with Al to justify the extra cost, unless you're making it for racing under human power only.

Also easier to re-heat-treat steel vs Al, since it doesn't conduct heat as well as Al so you can re-treat it "locally" at the joins, vs over the whole frame, if you actually needed to do that.

 

[vanilla ice]

Could you not diy anneal 6061 to halve the pricing? How touchy is it? Maybe with a torch.. or if it needs more time- Dig a pit, fill it full of wood, light it up, let it burn out, throw those bastards in there, cover it up with dirt..

 

[MitchJi]

Hi David,

I have been frustrated with my current frame. The quality just isn't there. For example, the bottom bracket is not even close to parallel to the jack shaft. I may ditch it all together and move toward a custom frame.

David.

Is that the brooklyn machine works racelink?

Is it really that bad?

What else is wrong with it?

I'm also interested in your reasons for choosing Aluminum instead of Cromoly.

 

[damcard]

Okay, the BMW isn't that bad. I think I may have gotten a prototype or something. This last weekend, I thought to use my cyclone with it while I waited for the rest of my parts to do the 3220. I only needed some wheels and I could bolt on my cyclone. Plus the jack shaft would allow me to pedal at the motors cadence, removing the need for the generator idea. While fitting the cyclone, I was frustrated to see the bottom bracket and jack-shaft were not parallel. The bearings appear to be bad on the jack shaft. I don't know if it was the force of the slightly off chain or if they got metal shavings in them from the washers he used for spacing the sprocket. When I pulled off the sprockets it was covered with metal dust or shavings and the bearings have a clicking sound and feel when I turn the jack-shaft. The rest of the frame appears to be okay, but being that the bottom bracket was misaligned and that I haven't assembled/ridden it I can't really tell if it is straight. I decided I can go ahead and cut it up.

As far as aluminum vs. steel, I am in favor of either. I am still planning on using this frame, but want to learn from it and build another when I am done because I can see it will not be what I wanted. I will probably use aluminum next time because I think it will be easier to make a cavity for the batteries and have been inspired by Paul's work. I think I will be able to machine out most of the parts with a router and templates. I doubt I would save weight by using aluminum because I will over "backyard" engineer it. I was just calling around to find out how much it would be to treat it after, hence the question.

I asked about annealing them myself, but the guy at the shop recommended against it, maybe so they get the money.

Again, I still plan to use my racelink but most likely with my cyclone or maybe my 8150. But who knows at this point because I have so many parts laying around. I am looking at separating the front triangle into two pieces and building a space frame with small cromoly square tubing. Then, blind riveting aluminum panels to each side to make my battery cavity. The idea being the panels would reinforce the tubing. I see them do it on kit car chassis. On one side panel, I am looking at using rivet nuts and screws so I can remove the panel to get to the batteries. I thought about using diamond plate for the panels but have some 6061 1/8 sheet already.

But, again I am curious if these prices are average. -David.

 

[MitchJi]

Hi David,

Okay, the BMW isn't that bad. I think I may have gotten a prototype or something. This last weekend, I thought to use my cyclone with it while I waited for the rest of my parts to do the 3220. I only needed some wheels and I could bolt on my cyclone. Plus the jack shaft would allow me to pedal at the motors cadence, removing the need for the generator idea.

Again, I still plan to use my racelink but most likely with my cyclone or maybe my 8150. But who knows at this point because I have so many parts laying around.

I am looking at separating the front triangle into two pieces and building a space frame with small cromoly square tubing. Then, blind riveting aluminum panels to each side to make my battery cavity. The idea being the panels would reinforce the tubing. I see them do it on kit car chassis.

-David.

Thanks for the information.

I think a frame with a jackshaft like the racelink is an excellent donor for connecting using both the crank and motor to drive the rear wheels. Even if you don't plan to pedal very often if you use dual FW's on the jackshaft the chain to the crank won't be backdriven by the motor so I don't see the problem. Should be easier and more efficient than a generator. In case you are interested I posted my thoughts on the dual FW/jackshaft configuration here:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=16535&start=45#p247977

Your battery cavity idea sounds good. Looking forward to seeing what you come up with.

 

[AussieJester]

Any particular reason to use Al instead of Cromoly? Good steel that's thin could be similar in weight and strength to Al, without having to go thru that kind of expense.

Think you will find its recommend cromoly be heat treated when you get to larger radius and thicker walled tube sizes also Amber. I saw Jeremy Harris post about it and he's a clever chap, he did mention rough sizes also i forget which thread it was now. He also speaks of DIY heat treatment with a torch IIRC? Of course the easier and cheaper way around heat treating for ali or steel is simply over build it, only so much force your can put on a frame adding gusstets will make it more than strong enough without adding too much additional weight to it.

KiM

 

[bigmoose]

Here is a little to get us going on annealing/heat treating 6061 Aluminum:

Annealing:
Annealing should be done at 775 F for 2 to 3 hours followed by controlled cooling at 50 f per hour down to 500 F, then air cool. (Controlled method)

Two home spun aluminum annealing techniques: (Temperature crayons are also useful)
1)Using your oxygen acetylene torch with no oxygen cover the aluminum to be annealed with the carbon soot. Now heat the part with a large soft propane air flame. When the soot just barely burns off you are at the right temperature.
2)Coat the part to be annealed with bar soap. Now heat the part with a large soft propane air flame. When the soap chars you are done.

Heat Treatment:
Solution heat treat at 990 F for adequate time to allow for thorough heating and then water quench. Precipitation hardening is done at 320 F for 18 hours and air cool, followed by 350 F for 8 hours and air cooling. (Solution heat treatment means heating and holding an alloy at a temperature at which one (or more) constituent enters into solid solution, then cooling the alloy rapidly to prevent the constituent from precipitating.)

 

[AussieJester]

1)Using your oxygen acetylene torch with no oxygen cover the aluminum to be annealed with the carbon soot. Now heat the part with a large soft propane air flame. When the soot just barely burns off you are at the right temperature.

This was the technique my father used and passed on to me to get the ali right temp before welding it worked amazingly well too!

KiM

 

[Papa]

Any particular reason to use Al instead of Cromoly? Good steel that's thin could be similar in weight and strength to Al, without having to go thru that kind of expense.

Think you will find its recommend cromoly be heat treated when you get to larger radius and thicker walled tube sizes

Most quality 4130 bicycle frames are NOT post treated - just no need. 4130 is 95kpsi-100kpsi tensile. Figure you'll lose 20% in the HAZ post-weld. That's 77,000-80,000 psi tensile. 6061T6 is 45,000 psi (notice that's tempered 'T6'), and will lose roughly 40% in the HAZ, resulting in a post weld tensile of roughly 27kpsi.

I build exclusively in 4130N, mostly .028" and .035" and rarely heat treat., and have experienced exactly zero frame failures in 20 years. If you're serious about building in aluminum, then go with 7005. It's ultimate tensile is, at least, 30 to 50% higher than 6061T6 and little need for post treatment. Nova typically carries it: http://www.cycle-frames.com/bicycle-frame-tubing/


damcard,

I have a lugged, Trek 930 MTB bare frame & fork (has True Temper OX Comp II, doubled butted (steel) tubes), PM if you're interested.

 

[MitchJi]

Hi David,

Okay, the BMW isn't that bad. I think I may have gotten a prototype or something. This last weekend, I thought to use my cyclone with it while I waited for the rest of my parts to do the 3220. I only needed some wheels and I could bolt on my cyclone. Plus the jack shaft would allow me to pedal at the motors cadence, removing the need for the generator idea. While fitting the cyclone, I was frustrated to see the bottom bracket and jack-shaft were not parallel. The bearings appear to be bad on the jack shaft. I don't know if it was the force of the slightly off chain or if they got metal shavings in them from the washers he used for spacing the sprocket. When I pulled off the sprockets it was covered with metal dust or shavings and the bearings have a clicking sound and feel when I turn the jack-shaft. The rest of the frame appears to be okay, but being that the bottom bracket was misaligned and that I haven't assembled/ridden it I can't really tell if it is straight. I decided I can go ahead and cut it up.

-David.

Have you contacted BMW about the problems?

Hopefully on a $2k frame they'd want to make sure you're happy.

 

[Jeremy Harris]

Most quality 4130 bicycle frames are NOT post treated - just no need. 4130 is 95kpsi-100kpsi tensile. Figure you'll lose 20% in the HAZ post-weld. That's 77,000-80,000 psi tensile. 6061T6 is 45,000 psi (notice that's tempered 'T6'), and will lose roughly 40% in the HAZ, resulting in a post weld tensile of roughly 27kpsi.

I build exclusively in 4130N, mostly .028" and .035" and rarely heat treat., and have experienced exactly zero frame failures in 20 years. If you're serious about building in aluminum, then go with 7005. It's ultimate tensile is, at least, 30 to 50% higher than 6061T6 and little need for post treatment. Nova typically carries it: http://www.cycle-frames.com/bicycle-frame-tubing/


damcard,

I have a lugged, Trek 930 MTB bare frame & fork (has True Temper OX Comp II, doubled butted (steel) tubes), PM if you're interested.

4130 most certainly does suffer from cracking in the HAZ if you weld it, don't do at least some basic stress-relief/normalisation and subject the joint to repeated stress changes whilst under high loads. The problem is worse with high local heat welding, done at a fast rate (MIG, for example) and less of a problem with slower weld techniques where the HAZ may be bigger (gas welding, for example). There is a great deal of info on this around, particularly in the area where I've used the stuff, airframes. I'd agree that the tensile strength is still OK, if reduced, it's the propensity for cracking in the HAZ under repeated flexure that is the problem I've seen many, many times and which has resulted in a mini-industry springing up doing steel tube airframe inspections.

Brazing neatly gets around the problem, because the tube doesn't get affected to the same degree, which is, I assume, why the majority of decent chrome moly bike frames are of brazed lug construction. I've never heard of a HAZ problem with brazed lug bike construction; I believe that frames built like this are more likely to suffer tube failure anywhere but the joints when over-stressed.

I'd agree that 7000 series aluminium alloys would be a slightly better bet that the general purpose 6000 series alloys, mainly because of their better crack resistance. To get full strength back you still need to heat treat 7005 post weld, although if you've over-designed the joint this may not be essential (I'm used to working in an aerospace environment, where we pare everything down to the bare minimum to save weight!).

Home-brew heat treatment for a heat-treatable alloy frame is probably achievable. The temperatures aren't that high, so a home made temporary oven could be cobbled together I would have thought. Fairly accurate heat control is needed, plus the means to quench the alloy at the end of the solution phase, but both these problems could be sorted with a bit of thought and effort.

Jeremy

 

[Papa]

4130 most certainly does suffer from cracking in the HAZ if you weld it, don't do at least some basic stress-relief/normalisation and subject the joint to repeated stress changes whilst under high loads.

I never implied that welded 4130 is oblivious to cracking - I said, "Most quality 4130 bicycle frames are NOT post treated". The 'cracking' problem usually only arises when the parent metal thickness is above .125" or the structure is poorly designed. Quality 4130 bike frames are substantially thinner, typically .035" and less. Even Lincoln Electric Company recognizes this issue:

http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

The only precautions I adhere to when welding thin wall 4130N with either TIG and O/A, is to avoid welding below 70 degrees ambient, and allow the joint to slowly air cool.

 

[Jeremy Harris]

OK, my misunderstanding.

My airframes are made from mainly 0.035 and 0.048 4130 tube though, and there are parts of them (like the engine mounting frame) that sure as hell WILL crack if not stress relieved. Equally, there are other parts (that aren't subjected to significant fatigue loads) that aren't heat treated and never crack. We're currently seeing a mini-epidemic of cracked welds on certified ultralight engine mounts here, brought about by the manufacturers (not me!) lack of post weld heat treatment.

Jeremy