Ask your WELDING questions here.

[Strong Bad]

In my not so humble opinion gas welding a cast aluminum part requiring structural integrity would be sketchy at best. I've seen gas welding done on a lot on aluminum race car bodies, never seen it attempted on a cast structural member. Wouldn't porosity be a major issue?

[Stan_R80/7]

Here is what I meant by a backing plate:


This was cut from 24 ga galvanized steel. The galvanizing needs to be etched off before heating, but that's the idea.
I also plan to remove that bit of rubber by the upper tang in the caliper pin hole.

Also, to reiterate, this lower tang has no load. It's the upper tang that takes a reaction force from the brake pad.

Edit: the notion is that this tang, cantilevered off the caliper support, takes the rotating force from the the disc as the brakes are applied. After looking at this bit of cast aluminum, I am not so sure that makes sense. The pad is steel but the aluminum is not gouged from the pad contact. Instead, I am thinking the pin on the back of the pad that fits into a hole in the piston transfers the pad force back into the caliper body. Otherwise, the aluminum would wear away as the steel pad rubs when the brakes are applied.

[tbarstow]

Originally Posted by Strong Bad

In my not so humble opinion gas welding a cast aluminum part requiring structural integrity would be sketchy at best. I've seen gas welding done on a lot on aluminum race car bodies, never seen it attempted on a cast structural member. Wouldn't porosity be a major issue?

Yes, along with messing with the heat treat condition of the part, depending upon the aluminum alloy.

[victor441]

Originally Posted by DADODIRT

I am not even going to pretend to be a welder. I'm just trying to bend something back into shape. The crash bar on my KTM 950 was bent on a get-off last year. I have removed the crash bar and would like to bend the lower mount so that the upper part of the bar is not touching the gas tank. I have a propane torch. Will this generate enough heat to bend the crash bar?
TIA

I'd at least get a MAP gas canister, burns hotter than propane, have successfully bent 1/2" tubing that way. If somehow that is not enough heat two torches might do the trick. BTW, recently bought a torch extension hose for $20 and it makes work much easier, you can hang the gas canister somewhere (it comes w/ a ring and hook) and the torch is waaay less awkward to handle w/o the canister attached

[David R]

Originally Posted by Stan_R80/7

Here is what I meant by a backing plate:


SNIP.

It looks like yer gonna cast aluminum to the fork leg. If welded properly you shouldn't need the backer at all.

both pieces beveled. Weld one side
Back grind the other side and weld. A full Penetration weld. Tig or spoolgun.

you should know what the fork is made of to know what filler to use

If I remember right, the pads are stopped in the caliper and the caliper has a nylon button that keeps the caliper from spinning. I will look, my bike is in the garage.

[David R]

Originally Posted by Strong Bad

In my not so humble opinion gas welding a cast aluminum part requiring structural integrity would be sketchy at best. I've seen gas welding done on a lot on aluminum race car bodies, never seen it attempted on a cast structural member. Wouldn't porosity be a major issue?

On cast aluminum, I usually weld it with a tig torch.

As part of the preparation, I make the first pass over the parts with the tig torch and no filler.
This will cook the junk out of the cast and float it to the top. It also adds some preheat. I then clean up again for the real weld.

I have seen a few make a first pass with filler and grind it all out because the junk in the cast.
They then start over and make a pass with filler for a weld that is cleaner.

Just a note, I only use wheels made for aluminum because most wheels made for metal are made of aluminum oxide. Exactly what I DON'T want in my welds.

[clintnz]

My old welding helmet is an ESAB bought by my dad back when auto helmets were pretty space age stuff, it's getting a bit flaky in the switching, I'll have a look at replacing the battery but am looking at getting a new one. What do I look for in the budget/med $ offerings? Adjustable shade & sensitivity obviously, big lens,anything else?

Cheers
Clint

[RidingDonkeys]

Originally Posted by clintnz

My old welding helmet is an ESAB bought by my dad back when auto helmets were pretty space age stuff, it's getting a bit flaky in the switching, I'll have a look at replacing the battery but am looking at getting a new one. What do I look for in the budget/med $ offerings? Adjustable shade & sensitivity obviously, big lens,anything else?e

Cheers
Clint

I ran into the same things a while ago. MrsDonkeys was unwilling to let me buy a Northern Tool special, and insist we take a trip to the welding shop for a proper helmet. It seems she values my eyes a little more than I do.

I don't really "weld". I am a hobbyist, and I do it for fun, and some necessity. I only pull the welder out of the garage a few times a month, so I struggled with spending a lot of money on a helmet. I ended up with the Miller Digital Performance Series. The comfort and larger viewing area have proved to be worth the extra money. I've noticed that I tend to play a little more now I've got something more comfortable on my head, and I get a little less frustrated with visibility issues. I think I walked out for around $200 all said and done. I've been happy with it, and would buy another in a heartbeat.

http://www.millerwelds.com/products/...s/performance/

[Stan_R80/7]

Also a hobbyist - this is the helmet I use most: http://www.northerntool.com/shop/too...6894_200416894

It came with a cover/bag and allows using diopter lenses. The 1.75x is nice and allows a good view. The second switch time and viewing area is what separates the expensive from not-so-expensive helmets all other features the same (i.e. you are paying for less eye strain and a better view). If I welded much or considered myself a welder, I would upgrade the helmet to a faster switch time. My helmet has a 1/25000 sec (40 microsecond) switch time and a Jackson pro helmet has a 0.15 microsecond time.

[David R]

I have a few harbor freight helmets with adjustable shade. Good units. They do not work for TIG, they flicker.
Small window, good price. Daily I use a miller elite.

David

[Pablo83]

Originally Posted by Stan_R80/7

Here is what I meant by a backing plate:


This was cut from 24 ga galvanized steel. The galvanizing needs to be etched off before heating, but that's the idea.
I also plan to remove that bit of rubber by the upper tang in the caliper pin hole.

Also, to reiterate, this lower tang has no load. It's the upper tang that takes a reaction force from the brake pad.

Edit: the notion is that this tang, cantilevered off the caliper support, takes the rotating force from the the disc as the brakes are applied. After looking at this bit of cast aluminum, I am not so sure that makes sense. The pad is steel but the aluminum is not gouged from the pad contact. Instead, I am thinking the pin on the back of the pad that fits into a hole in the piston transfers the pad force back into the caliper body. Otherwise, the aluminum would wear away as the steel pad rubs when the brakes are applied.

My $.02:
O-A and O-H alu welding is still used today, but only for non-structural projects and I've only heard of it being used on sheet alu.

O-H burns at a lower temp (closer to the melting point of alu) so it's easier to manage than O-A when working with alu.

You said you have experience brazing, why don't you braze the piece? You are likely to get much better penetration with less of a chance of warping the tube.

Also, why are there so many people hating on this man's project? If the brake fails he's always got the rear to fall back on (no pun intended ).

[dorkpunch]

Alright.... TIG welder question.

I'm to the point in my aluminum melting that I think I could do a lot better job if I had a foot control for my welder. Unfortunately, I see no way to adapt my welder to be able to hook up a foot pedal... So if I were to keep my eyes peeled for a used TIG welder, what would y'all recommend? It needs to be able to weld THIN aluminum, and be on the cheaper side for a TIG welder. Thinking of maybe selling my current set up (keep the tank, regulator, and maybe torch and leads?) and use some tax money to fund a nicer machine.

A quick perusal of KSL and Craigslist show a few used Millers- 180SD, 200 syncrowave, and a few other misc brands, all ranging from between $1,000 to $3,000 depending on what all comes with it.

Here is my current setup:

[David R]

Originally Posted by Pablo83

My $.02:
O-A and O-H alu welding is still used today, but only for non-structural projects and I've only heard of it being used on sheet alu.

O-H burns at a lower temp (closer to the melting point of alu) so it's easier to manage than O-A when working with alu.

You said you have experience brazing, why don't you braze the piece? You are likely to get much better penetration with less of a chance of warping the tube.

Also, why are there so many people hating on this man's project? If the brake fails he's always got the rear to fall back on (no pun intended ).

I am pretty sure you can't braze aluminum.

"If the brake fails" <~~~~~~~~~ Those words are not in my vocabulary.

David

[Benesesso]

Originally Posted by David R

I am pretty sure you can't braze aluminum.

"If the brake fails" <~~~~~~~~~ Those words are not in my vocabulary.

David

Easily done, but not for a structural part as per the OP's.

http://www.youtube.com/watch?v=RRWmpSE-hXk

[Stan_R80/7]

Originally Posted by Benesesso

Easily done, but not for a structural part as per the OP's.

http://www.youtube.com/watch?v=RRWmpSE-hXk

I originally thought the tangs were structural. Upon more evaluation, I realize the tangs stop the pads from spinning on the disc but do not take the load from stopping the disc. I am still considering the HTS/alumaweld/alumaloy aluminum-zinc path.

If both the upper and lower tang break, the pad will spin but still stay with the caliper and on the disc. There is also the original left side disc brake and the rear brake as mentioned. However, the hydraulics changes will affect the original brakes. So, there is some risk in this mod.