Welding Tips and Tricks

I'm an Industrial mechanic at a plastics and fiberglass plant...lots of older machines and equipment. Well during one of my machine inspections today I found a badly cracked shaft...it's been repaired once. Not sure our miller 250 mig is the right welder for the repair? When I repaired it last fall I gouged the crack out and cleaned it up nice..this time it's way worse..cracked in 2 places almost all the way around..I think there were cracks on the inside I never seen? This pc of machinery makes man ways for water and septic tanks. Weighs about 1.5 tonnes.

Any idea what the material specification is?
Also can you post a pic zoomed out a bit so we can see the whole thing?


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Material is just reg. Carbon steel I believe. This winding machine is very old..I will get better pics tomorrow once I have it apart.

From my experience, I would give the crack a nice, deep bevel, and spray-transfer over it. I'm no old timer but that seems to be a solid way to fix most mild carbon steel cracks. Hope all goes well!

As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.



Just so you're not fighting an uphill battle against a base material that gets hard and brittle and crack-prone after welding on it.

Bye, Arno.

Even if it's mild steel it's very likely that that is a stress point that has caused the whole area around the crack to become work hardened and brittle. I would recommend a 250deg F pre heat and try to keep it above this temp even as you weld. Preheat at least 3-6 inches away from the weld as well. After you finish welding keep the temp up for at least 15 min before you let it cool.

Arno wrote:As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

Arno, what book is that chart from?

Here's some better pics...got part taken off today and cleaned and beveled the cracks..it worse then I though..
Thanks for the advice.

MarkL wrote:

Arno wrote:As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

Arno, what book is that chart from?

Mark, google "spark test chart" or "spark test pdf" you'll have many results

Whichever process you use, that crack is going to have to be bevelled out with root gap for full penetration weld with re-enforcement. The ends should be drilled to stop the crack.

It can be migged but you would need to be a solid mig welder to do it right with full fusion. Root pass downhill and fill/cap passes uphill.

Personally I think stick or tig would give a more reliable result.

I would lean towards stick or tig as well.

MarkL wrote:

Arno wrote:As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

Arno, what book is that chart from?

Very good question! It's a chart you see a lot online on blacksmith forums and such. The page does use kilograms and cubic metres. Perhaps a page from a US military training/reference book or Canadian/EU of origin. Don't find much other references though..

Bye, Arno.