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MORE Brazing help PLEASE!!!


...I'm a hobbyist machinist, I have just picked up a little knee mill that's probably about 70...

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Old 02-11-2008, 11:12 AM
11echo 11echo is offline
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Default MORE Brazing help PLEASE!!!

...I'm a hobbyist machinist, I have just picked up a little knee mill that's probably about 70 years old. I'm in the process now of cleaning it up, in this process I noticed that the cast iron pedestal is cracked in two places. Not real long cracks, one is about a 1 1/4" and the other is about 2 1/2". This is at the base that has cast in webs, so varying widths of cast iron. Which is kind of the problem, I'm finding it hard to get the area to braze hot enough to do the job! One problem with my brazing technique that I’m aware of is that I'm using my cutting torch to braze with! I find this is the only thing I have that can put enough heat into the cast iron to do the job! This pedestal is pretty thick in places! I have ground out the cracks with a carbide bit and a die grinder making a "U" groove, I use flux and a large diameter brazing rod, and I try to puddle the braze to get a solid area. BUT trying to do this with a cutting torch is abit trick, especially in tight areas. SO my questions ....what size tip should I be using? ...THX!
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Old 02-11-2008, 11:55 AM
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KeithW KeithW is offline
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Default Re: MORE Brazing help PLEASE!!!

I had a similar problem. What you need is a rosebud tip. They go through lots of gas but they shure do put out the heat! I found mine on ebay. One problem in using the cutting head is that the tip is cooled with the cutting oxygen. Using it just as a welding/brazing tip will overheat the head. Also, did you stop drill the end of the cracks? If not, the cracks may get bigger when you heat it, BTDT .

keithw
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Old 02-11-2008, 12:22 PM
11echo 11echo is offline
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Default Re: MORE Brazing help PLEASE!!!

I did stop the one small crack; the other goes clean thru to the edge, so nothing to stop. I do have a rosebud tip ...and I have used it before to heat things to bent steel, but how do you braze with a rosebud? My experience it throws out the heat in too large an area!??
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Old 02-11-2008, 01:56 PM
Rick McKay Rick McKay is offline
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Default Re: MORE Brazing help PLEASE!!!

When I have had to do brazing on heavy sections, I use the largest brazing tip I have in my collection, and have had a helper running a second torch with the rosebud preheating. That way I could concentrate on the brazing, not trying to jump ahead of myself to get the base metal hot enough to braze.


Have Fun, and good luck!
Rick
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Old 02-11-2008, 04:08 PM
Ron Weber Ron Weber is offline
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Default Re: MORE Brazing help PLEASE!!!

When you are fizing a crack, the first thing to do is find the end of the crack and drill a hole just past it in the way if the crack should grow. This will stop the crack from continuing while you braze it. I generally like to preheat large peices with a propane burner/grill/ etc and get them up on temerature. If it is really big then I build a firepit and set the item in it. Rosebuds are a great help but the metal needs to warmed up otherwise the rosebud will overheat the area and crystalize the iron, much like what happens to old manifolds. After I am done brazing the item, I slowly cool it down first by passing the flame over, then slower, then slower while i pull the flame farther from the item. Then I cover it up with Kitty liter (the cheap clay stuff) and let it slowly cool down. This reduces the internal stresses as well as reduces the amount of change in the molecular structure. Flux is very important with brazing cast iron; keep a hand wire brush handy to clean the area if it carburizes/oxidizes and keep plenty of flux on hand. I hope this helps!
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Old 02-11-2008, 04:37 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: MORE Brazing help PLEASE!!!

Your biggest problem is going to be stress fractures, as the metal cools. If possible, you might best try to have a welder do the repair, either with Ni I rod, or cast iron rod. If done right, area heating and stress is reduced with a weld, as there is less expansion and conteaction. If you must gas weld, or braze, in all probability, with the area you need to pre-heat, you will need 2 sources: a LARGE rosebud, to pre-heat the area, and keep it hot, and your actual brazing torch. If you use the cutting tip, you must use the biggest tip that you can get, and remember to use a carburizing flame (slightly rich on acetylene). Both a nuetral and an oxygen rich flame will cause oxidation and spot overheating. As posted by Ron, slow cooling is the key to avoid stress cracking.
Andrew
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Old 02-12-2008, 10:55 AM
11echo 11echo is offline
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Default Re: MORE Brazing help PLEASE!!!

I WISH I could use a NICAD rod on this! But this pedestal is way too large (4'-6"T & 18"Wx 24"L at base) ...So trying to control the cooling would be next to impossible for me! I have had "luck" with smaller cast iron parts (car manifold size) where I use a home made BBQ out of a 55gal barrel. But obviously that's not happening here. I do have a propane heater that I can pre-heat with, and then use it to try to bring the cooling down slower.
I do have some questions about using a carbonizing flame ...I know what your talking about but to what degree? ...How much of a feather off the tip of the blue flame?
And another question I have, is it better to try to braze this thing from the inside to the outside edge, OR the other way around??

...I would also like to THX everyone that has taken the time to respond to my question here! I find it VERY helpful!!! ...Mark
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Old 02-27-2008, 07:38 PM
VonDeemer VonDeemer is offline
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Default Re: MORE Brazing help PLEASE!!!

why not just drill ahole at each end of the crack , J B it paint it and call it a day?
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Old 02-27-2008, 08:08 PM
VonDeemer VonDeemer is offline
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Default Re: MORE Brazing help PLEASE!!!

Why not just drill a hole at each end of the crack to stop it,grind a vee the lenght of the crack,J B it,smooth it, paint it,polish it,kiss it good bye,for get about it,and have Guinness extra stout in cela(BRA)shin. Itill be just fine.
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Old 09-11-2013, 11:39 PM
Bob Phillips Bob Phillips is offline
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Default Re: MORE Brazing help PLEASE!!!

HAYeeee 11EHCO:
It seems like the crack/broken base is not affecting the "Machining" capabilities of the Mill... JB it and be done with it as someone has mentioned... Put a block under it and forget it... BUT, seems like you definitely not getting enough heat from your cutting head... The fella that suggested "the biggest brazing tip" and a rosebud for pre heat is right... The Lange Brothers, and me in the olden days when it was available, use a pure cast iron rod about 5/16" squarish... Use a rosebud to get the cast in almost a pouring state and apply the cast rod as one would apply brazing rod... I have some tricks using S/S Blue Max on cast iron....Bob Phillips
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Old 10-28-2013, 03:25 PM
sdowney717 sdowney717 is offline
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Default Re: MORE Brazing help PLEASE!!!

http://muggyweld.com/ssf6-silver-solder

How about the ssf6 silver brazing?
Wont need to be so hot.
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Old 10-28-2013, 04:13 PM
S Davey S Davey is offline
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Default Re: MORE Brazing help PLEASE!!!

I would v out the cracks pre-heat, stick weld it. Then post heat and let it cool slowly.

---------- Post added at 04:13 PM ---------- Previous post was at 04:11 PM ----------

Do you know if it is cast Steel or cast Iron?
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Old 12-07-2013, 01:58 AM
jererwin jererwin is offline
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Default Re: MORE Brazing help PLEASE!!!

it all depends on the thickness of the metal a number 3 works well up to about a half inch above that i go to a number 5 till about a inch thick cleaning with a carbide burr is perfect if your weld is out on a corner there is not much need to preheat a large area keep in mind the bonding temp for iron is 1200-1500f the iron will go dull for a min then shine bright like a mirror that is when you are at a good bond temp good luch hope is helps
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