LocostUSA.com

Learning how to build Lotus Seven replicas...together!
It is currently November 15, 2019, 6:31 am

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: August 22, 2013, 1:53 am 
Offline

Joined: June 11, 2013, 10:54 pm
Posts: 18
From what I've read silicon bronze is:

Easier for thin gauge mild steel tubes (like 16 gauge and thinner) as you're not supposed to melt the steel, only the rod. Thus less likely to melt the tubes and also reduces heat distortion.

Its fillet allows to fill not-so-perfect fitting joint gaps a little bit.

Its fatigue resistance allows to withstand cracking better.

By being not as brittle as other weld types and actually stronger than the parent metal it allows moderately stressed joints to survive better. (For a not perfectly designed custom frame design).

Time proven. Decades of trouble free welds so low volume sporty automakers like Caterham and Ar-i-el At-om continue to use it.

Hi power electric power are not required at all.

Finally, cost. If you already have acetylene/oxygen tanks and torch then the initial investment is minimal.
You only need to buy the rods although they might be somewhat expensive. Are Eutectic-Castolin the better ones?
BTW Do you also need a special torch for silicon bronze? High or low pressure?

Please provide me some downsides and advice.
Thanks guys.


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 2:34 am 
Offline
User avatar

Joined: November 7, 2008, 4:48 am
Posts: 1097
Location: snow city - it's wet!
I am definitely not an expert in this area, and have no experience with the process you are discussing, but I did do some research on the process, as my thinking seemed to be similar to yours when I first researching this locost madness.

About the only point of difference with your research I came up with was that very good quality tube fitment seemed be more critical to good joint strength with silicon bronze welding, making MIG/TIG more forgiving of imperfections and small gaps in the tube cutting and fitting process. Given the fact I've never had to build a cut & fit structure like a chassis before, my thinking was that I would be very likely to have a large number of small imperfections in tube fitment. That moved my decision process back in the direction of MIG.

I am always looking to learn, and hopefully we can hear from people who have hands on experience with the process.

_________________
.. in the world


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 9:39 am 
Offline
User avatar

Joined: October 19, 2010, 11:57 am
Posts: 490
Location: Waterloo, WI
At last something that I'm somewhat qualified to respond to! :D 20+ years ago I was working for a custom (bicycle) frame builder and I still work in that industry today. In addition to engineering, I also wore another hat (goggles, really) and pitched in doing production welding at times. We primarily did fillet brazing (what you're describing). In short, most of your points are true in my opinion. I don't agree that the filler is stronger than the parent material but it certainly is more forgiving and easier to use in certain regards. Fillet brazing is more accomodating to less than perfect fit joints simply because it allows you to fill gaps and basically hide things better. Whether this makes for a better joint, probably not; you still want as tight a fit as possible. And there's no question that, generally speaking, the joint will be much more fatique resistance than a MIG or TIG weld.

Now for the problems. To do a halfway decent job, you really need to be able to move whatever you're welding into a position that gravity will help you make a proper fillet (hence, fillet brazing!) You can weld "uphill" to a degree but it's not optimal. TIG (or, I presume, MIG) is much easier as you can keep welding further past the "easy" zone. Put it this way, imagine you're joining a simple set of round tubes. You have a 1" round tube with a cope/mitre/fishmouth so that it joins a 1 1/8" round tube forming a "T" shape. Looking at the tubes tacked together there on the welding table with the 1" tube pointing towards me, with a TIG welder I could pretty much start all the way on the right, come across the top (the easy zone) and back down to the halfway point on the left. Then I'd flip the part over and do the same. Done! And I only had to reposition the workpiece once. With fillet brazing, I would have to reposition the part several times in order to keep the material flowing nicely. When I did this in production (on tandems no less) we had a nifty gimble mounted clamp that allowed us to quickly move the workpiece into ANY position. It required probably hundreds of small movements to get the part fully welded. Now imagine doing that on a car frame. I might do it on some small parts like a control arm, but only if I didn't have a TIG welder available. :P

The next problem is the SOP of the Locost crowd to use square tubing. Welding size on size is always a little problematic with fillet brazing as you invariably end up with a lump of sorts where you are welding across a "flat" section. Imagine our T shaped sample again but this time made from two 1" square tubes. That nice flat section right on top is going to lump up with weld material no matter what method you use. Given good penetration, with a TIG/MIG weld you could safely smooth it out to a degree, I would be more hesitant with a fillet weld.

Finally, tacking parts together is sooooooo much easier with TIG/MIG. ZAP and you're done. With a torch it just takes longer. Again, multiply that by every tube and joint in the structure.

Don't get me wrong, I LOVE a nicely fillet brazed structure (like a bicycle frame) and it certainly has a relatively low cost of entry. But it would not be my preferred method.

Hope this helps! :cheers:

_________________
-Keith


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 11:48 am 
Offline
User avatar

Joined: July 4, 2006, 5:40 pm
Posts: 1978
Location: Novato, CA
I'm a big fan of brazing too, and did a lot of it when I was younger, but I only really trusted it for lap joints. For butt or tee joints I have to defer to Acer's fillet brazing expertise. I think if I was going to braze a Locost frame I'd use a lot of gussets.


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 1:09 pm 
Offline

Joined: October 19, 2009, 9:36 pm
Posts: 2139
Location: meadview arizona
first let me say that in 1970 i built my first race car chassis and it was braised.

the longer i have been aware of what goes on in the welding process, the more i now understand.

braising can be described as gluing the two parts together and the process is, heat the joint until the molecular structure opens but does not become fluid, this happens to be the melting point of the sic bronze rod, like they designed it that way, the rod is applied, binding the surfaces together by being absorbed into the metal surface structure.

the joint should be as good a fit as posible, as the filler material is nothing like as strong as the parent metals being joined, what you are looking for is an amount of filler in each surface and very little in between, in a right angle joint the fillet is just a by product of this and like welding, it is not the stuff on the surface that does the real job but what is actually in the joint, although some "gusseting" effect is a benifit.

unlike welding, these joints are somewhat flexible but only as far as the joint fitment, if the joint was made tight and a perfect fit there would be less flex in the joint than if it were a poor fit.

the process is heat sensative in that you can over heat the joint especially if there is a gap that you have to fill, the flame temp is constant and you should use a carborizing flame to maintain this, using the light blue cone to lick over the joint to prevent oxegen from bubbleing in the braise thus making weak "pockets", this is also a problem if the tubes to be joined are a close structure where the air trapped in the tubes will expand and blow out the braise, this can be rectified by drilling the tube with a 1/16" hole to vent the tube and left open when finished or fillied with a pop rivet.

over heating due to a bad fit joint is common and will fatigue the tube at the joint and may crack the tube, if you have a complex joint, then this should be done in stages, allowing the tube to cool and "normalize" to prevent this overheating.

it is important that the tubes are very clean to remove any type of contamination included in the joint and the correct flux is used, this must be removed after the joint has cooled and not before as it shields the braise from the air and prevents oxidization, if the flux is hard to remove it can be desolved with water, again after the tube has completely cooled as the steel in the tubes will now rust quickly due to the heat that was applied.

braising is a thing that must be well practiced, unlike mig it really is not forgiving, with mig you just point and squirt, it should be considered more like tig in it's need for good preparation of the joint with regard to fitment and cleanliness.

the current chassis from Caterham are nickle bronze braised which is a harder filler than sic bronze but the rods are more expensive.

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 1:26 pm 
Offline
User avatar

Joined: October 19, 2012, 9:25 pm
Posts: 2863
Location: Summerville, SC
Good description John

When I went to welding school, oxy-acetylene brazing was the second technique taught (after soldering)

A good braze joint is like a good solder joint; strength comes from surface area in contact, so lap joints rock, fillet and butt joints are best for welding.

Good surface prep is important. Cleanliness is next to Godliness (it's also next to impossible, but that's another story)

Tight fitting joints are ideal because the braze fills the joint due to capillary action. Look at a bicycle tube frame and the tube to neck on most is a slip joint, one tube inside another. Slip joints are just round lap joints.

The small fillet on lap joints isn't structural BUT it does help tremendously in preventing fatigue cracks. Poorly filled fillets create sharp angle stress risers in the joint.

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 1:59 pm 
Offline
User avatar

Joined: November 12, 2008, 6:29 am
Posts: 3540
Bigtime, Acerguys post is spot on.

Braze welding that you are refering too that uses bronze as a glue, which stupiding sounds like Brazing which is melting metals together, like the other old guys around here I did as a young bloke, had to actually for my apprenticeship.

Unless you want to do some arty or traditional skillz work, stay away and use your time to learn TIG and/or MIG.

john hennessy wrote:
first let me say that in 1970 i built my first race car chassis and it was braised.



What basting sauce did you use? :mrgreen:


Top
 Profile  
Reply with quote  
PostPosted: August 22, 2013, 7:34 pm 
Offline

Joined: June 11, 2013, 10:54 pm
Posts: 18
Wow
Thank you so very much guys for your replies.


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 5:42 pm 
Offline

Joined: December 20, 2011, 10:19 pm
Posts: 198
A potential downside for brazing is that the price for acetylene has gone up significantly in the last couple of years (since 1 of the 3 plants in the US blew up in March of 2011).

It might actually be cheaper to use MIG or TIG than to pay for the fuel gas. Something to at least investigate before committing one way or other.

YMMV....

JustDreamin


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 8:54 pm 
Offline

Joined: October 19, 2009, 9:36 pm
Posts: 2139
Location: meadview arizona
Cheap, interesting comment, comes from actually furnace braising, they still do torque converters that way, assemble the parts with the joints fluxed usually with killed spirits and a strip of braising metal, the whole assembly is then put in a furnace/oven and heated til the braising metal melts and runs into the joint.

it is possible to braise with a tig set, but i've never tried it so i can't comment.

anyway, i marinade in lemon juice over night and rub with garlic salt and brown sugar, place in the oven at 200 degrees for 2 hours covered with foil then remove the foil and continue to cook for another hour at 350degrees, slip some potatoes in when you remove the foil.

not satisfied with my speed secrets, now i'm giving everything away!

i draw the line at giving away my secrets on how to satisfy women though, actually it's just my charm and witt and pickup lines like "whats a girl like you doing in a nice place like this?" works every time!

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 9:07 pm 
Offline
User avatar

Joined: July 27, 2013, 3:16 pm
Posts: 336
Location: Cedar City UT
john hennessy wrote:
... not satisfied with my speed secrets, now i'm giving everything away!


:lol:

imho MIG welding is still the best thing for a beginner
however, i would never use flux to start with :ack: ...
spending the extra $$ for shielding gas lets you actually see what your puddle is doing

... and dont forget to move your wire/arc in tiny little ovals :wink:

_________________
- Stephan - Image


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 9:29 pm 
Offline

Joined: October 19, 2009, 9:36 pm
Posts: 2139
Location: meadview arizona
having never used a mig set with flux cored wire before, i tried it, man i could not see anything for the smoke, mind you, if you don't have shielding gas you could use a fan to blow the smoke away.

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 9:39 pm 
Offline
User avatar

Joined: October 19, 2012, 9:25 pm
Posts: 2863
Location: Summerville, SC
flux cored MIG isn't too difficult if you've ever done any stick welding. IT takes a little practice to learn where your puddle is going and how the penetration is based on the surface of the flux puddle.

You have to deal with similar issues with brazing.

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


Top
 Profile  
Reply with quote  
PostPosted: August 28, 2013, 11:25 pm 
Offline
User avatar

Joined: October 23, 2010, 2:40 am
Posts: 1116
Here's a couple of variations on the Silicon Bronze brazing question that some of you may be able to answer.

I'm TIG welding my chassis, but some of the really tight angles on some of the joints will be hard to weld properly. Does it make sense for both joint sealing and strength reasons, to braze the portion of the seam that I can't reach any other way?

I have a case where two 1" square tubes are being sistered and stitch welded together (TIG.) Rather than using an adhesive seam sealer to prevent moisture from living between the tubes, does it make sense to braze the parts of the seam that aren't stitched to seal the joint?

Like John, I've heard that a TIG torch (at low heat) can be used for doing silicon bronze brazing. Any thoughts/experience on this technique?

_________________
Cheers, Tom

My Car9 build: viewtopic.php?f=35&t=14613
"It's the construction of the car-the sheer lunacy and joy of making diverse parts come together and work as one-that counts."

Ultima Spyder, Northstar 4.0, Porsche G50/52


Top
 Profile  
Reply with quote  
PostPosted: August 29, 2013, 8:07 am 
Offline
User avatar

Joined: October 19, 2012, 9:25 pm
Posts: 2863
Location: Summerville, SC
yes, maybe, and yes

1. You're better off welding if you can, but a braze fillet will perform better than a crappy weld.
2. You should clean and flux the joint really well. A nice little fillet will be water tight. I still used GM seam sealer cause it's fast, cheap, and works great.
3. Use argon gas for shielding, keep the current low ~ 50-80 amps, I like to have high frequency on continuous to help maintain the arc with a wider than normal gap at low current. The feel is A LOT like welding aluminum

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 18 posts ]  Go to page 1, 2  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
POWERED_BY