# tacks cracking



## AGCB97 (Mar 9, 2017)

I'm building a buggy and want to put the brake disks on the trany output CV joint similar to a garden tractor. I machined the CV bell and made a 1/4" disk. I can get it very concentric but am now having trouble with the tacks cracking.
I'm wondering and planning to try heating the entire assembly before the final weld.

Will this help I stop the cracking? I'm not sure ( better said surely don't) I understand the expansion and contraction forces and what causes the cracking. It usually cracks a few minutes after the weld is done.
I'm using TIG w/ ER70-s2
Might I be better off using silicon bronze?
This will be low a speed (<20 MPH) vehical


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## brino (Mar 9, 2017)

My first reaction is that it's due to very different rates of thermal expansion/contraction of the two pieces. Of course round parts also tend to expand and shrink in diameter too. Pre- and post- heat should help with this.

I'd also apply some of the rules for welding cast-iron
-preheat
-weld with a forgiving rod (high nickel)  _OR_ braze (silicon bronze, aluminum bronze)
-peening after welding (an air powered needle de-scaler)
-slow cool

Jody at weldingtipsandtricks.com had a segment on silicon-bronze and aluminum-bronze.....I'll see if I can find a link.

-brino

EDIT: here are some useful links:
http://www.weldingtipsandtricks.com/tig-brazing-vs-welding.html
http://www.weldingtipsandtricks.com/tig-welding-brazing.html


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## dennys502 (Mar 9, 2017)

Can you machine a side so that you can drill and tap to bolt it on? I agree with brino on the welding aspect.


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## tertiaryjim (Mar 9, 2017)

Different metals? 
Unless you can get the bad tacks fused down to the base metal, they may cause cracks to propagate
through the new weld. Grind em out as much as reasonable. At least thats what I have experienced.


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## AGCB97 (Mar 10, 2017)

I'll try preheat and silicon bronze


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## brino (Mar 10, 2017)

AGCB97 said:


> I'll try preheat and silicon bronze



Please let us know how it goes.

Some idea's for slow cooling are to throw it in a woodstove/fireplace or even on the charcoal grill and just let it burn down and out overnight.

-brino


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## f350ca (Mar 10, 2017)

I'm guessing the CV joint is hard for wear reasons so probably has a high carbon content. The carbon may be precipitating into the weld and the crack is forming as it cools. Preheat may help take the stress out of the weld but expect you'll soften the CV joint. As Denny said is there any way you could bolt it on.
Greg


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## AGCB97 (Mar 10, 2017)

OK, I heated it to about 300 F (per IR thermometer) and used silicon bronze. Just tacked in 3 places. Slow cooled it in a super insulated container (old double boiler full of fiberglass).Removed it still warm after 5 hours and NO CRACKS!.

Now I will have to figure out how to keep it from lifting on one side and getting out of concentric. I don't know if it can be clamped down enough to get 2 tacks done without it pulling to one side. I do have a shoulder on the bell that the disk sits against. I'm going to remachine that shoulder for a better edge and indicate it to the bell edge (again) which is perfectly true.  Might even try gas brazing it. I used to be pretty good at that 47 years ago!

Any suggestions?

P.S. Sorry for all the typos in the 1st post. Guess I was in a hurry!

P.P.S. This is going to be a 1/2 ATV/1/2 tractor, center articulated using an old 4WD Subaru engine/trany. It's entirely scratch built of my own design. Eventual plan is to have 4 tracks on it.

Thanks
Aaron


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## Holescreek (Mar 10, 2017)

I'd TIG it with brazing rod. No cracks, instant satisfaction.  I did it by accident the first time then googled it and found out that it was a thing.


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## dennys502 (Mar 10, 2017)

AGCB97 said:


> OK, I heated it to about 300 F (per IR thermometer) and used silicon bronze. Just tacked in 3 places. Slow cooled it in a super insulated container (old double boiler full of fiberglass).Removed it still warm after 5 hours and NO CRACKS!.
> 
> Now I will have to figure out how to keep it from lifting on one side and getting out of concentric. I don't know if it can be clamped down enough to get 2 tacks done without it pulling to one side. I do have a shoulder on the bell that the disk sits against. I'm going to remachine that shoulder for a better edge and indicate it to the bell edge (again) which is perfectly true.  Might even try gas brazing it. I used to be pretty good at that 47 years ago!
> 
> ...




That sounds like it will be awesome - you should start a project post with pics as you go along.

Denny


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## Ironken (Mar 10, 2017)

Also, don't forget to fill the crater when you terminate your weld and make sure you have good fusion and fill when you begin your weld.


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## brino (Mar 10, 2017)

AGCB97 said:


> P.P.S. This is going to be a 1/2 ATV/1/2 tractor, center articulated using an old 4WD Subaru engine/trany. It's entirely scratch built of my own design. Eventual plan is to have 4 tracks on it.



Aaron, that would make a great thread. I'd appreciate being brought along for that ride.
-brino


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