[How-To] Help Please. How would you repair this Cracked Cast Iron Lathe Apron (Off a Smithy Granite). Braze or Weld?

[G-ManBart]

Thanks a lot for your response. Much appreciated!

To answer your question, no I don't have any experience with this brazing approach to repair.

My photos don't show well, but most of the cracks extend through the wall and into the bosses inside the casting. I had first thought about drilling the ends then grinding those cracks, but it seemed like an impossible task, given the difficulty of access. Thus the grafting approach.

As far as testing the feasibility of the repair: Yes I plan to do so. I have this worn out drill press head that's roughly the same size as this casting, so will be using it for a test.

That seems like a good substitute and should give you a good some practice and an idea if it will work.

In messing around with welding old cast stuff I've found you just never know, and trying unconventional things sometimes works when you least expect it. A while back I was trying to repair the box nut on an old post vise....I bored out the old threads, turned down some new Acme thread to a press fit and was trying to weld the lip where the two met. I simply couldn't get it to work using my TIG...tried every filler rod I have (lots) and kept getting crazy porosity. That old nut could have been made of anything, and had years of contamination. In frustration I fired up the MIG and immediately got a perfect bead with normal ER70S6 wire....no idea why, but it worked! One time I bought a stick electrode that the manufacturer said worked best on DCEP for cast iron but I wasn't getting great results. I switched to DCEN and suddenly got nice beads. I called the manufacturer to ask if it was a misprint, or I ran into a unique situation. Their tech guy laughed and said on old, cast, mystery metal anything can happen and it didn't surprise him a bit. Short version....don't hesitate to try every combination you have, but since you have a MIG, there is one thing I just thought of.

They do make silicon bronze wire for MIG that might be worth trying....very similar to brazing with a torch, but possibly easier to control since you can adjust the voltage and wire feed precisely. It works best with 100% argon, but it can be used with more typical MIG blends like 75/25 on thicker pieces like your parts (adding CO2 makes it run hotter). I haven't tried it yet, but the next time I order wire from a place that carries it I think I'm going to get a spool just for fun...seems like it could be handy to have around.

 

[fixit]

Personally I'd scrap it, especially since you have a working replacement.

I have no welding experience but have seen others turn out good repairs with TIG brazing. The temperatures are low enough to not melt the iron and reduce the stresses of welding. Perhaps not as strong as the original material, but plenty strong nontheless.

Another option is Lock-N-Stitch cast iron repair system. Very time consuming but a proper way to repair damaged castings.

Metal Stitching & Thread Repair Inserts. - Turlock , CA - LOCK-N-STITCH, Inc

LOCK-N-STITCH Inc. provides cast iron repair services such as metal stitching, emergency thread repair, fusion welding, & machining services for industries in power generation, gas compression, shipping, and pumps.

www.locknstitch.com

was to be my suggestion we did this many times on BIG OLD compressors This is another similar design BOTH work well https://www.metalockengineering.com/en/typical-repairs/metal-stitching/

 

[Tim9]

I wouldn’t try the way you’re planning either. Although it looks good on paper, heat and cast iron does weird stuff when heated and then cooled. Never predictable in my opinion. And that’s why I agreed with Pops recommendation of brazing. No matter what you do, I recommend waiting to drill /bore your shaft holes. That’s because if you drill those first and then weld, it’s going to move on you. Personally, I find bronze old school brazing the absolute best repair for cast iron. It’s a tried and true proven repair which has been done for over 75 years. And it’s damned strong. Go to the welding web website and read up on some cast iron threads. Tig works well. And if you have a good Tig welder and are up on your game, Tig silicone bronze is probably the best. But, oxy/acetylene works too. And it’s strong. But when you start mixing steel with cast then everything changes because of the different expansions of the metals. That’s just my take. I know that brazing would fix that housing.

 

[bill70j]

I wouldn’t try the way you’re planning either. Although it looks good on paper, heat and cast iron does weird stuff when heated and then cooled. Never predictable in my opinion. And that’s why I agreed with Pops recommendation of brazing. No matter what you do, I recommend waiting to drill /bore your shaft holes. That’s because if you drill those first and then weld, it’s going to move on you. Personally, I find bronze old school brazing the absolute best repair for cast iron. It’s a tried and true proven repair which has been done for over 75 years. And it’s damned strong. Go to the welding web website and read up on some cast iron threads. Tig works well. And if you have a good Tig welder and are up on your game, Tig silicone bronze is probably the best. But, oxy/acetylene works too. And it’s strong. But when you start mixing steel with cast then everything changes because of the different expansions of the metals. That’s just my take. I know that brazing would fix that housing.

Thank you for your input, @Tim9

I think we are in agreement that bronze brazing is a good way to repair this cast iron casting.

We also agree on waiting to drill/bore the holes as the last operation. In the case of the three shaft holes, they will be drilled and line bored from the thee existing holes in the back wall of the casting after the replacement part is brazed to the casting and final machining is complete.

And lastly, I think we both have concerns about brazing dissimilar metals for various reasons. That is why I am doing a test repair before carving up the casting for the real repair. I am going to bronze braze a patch of 1018CRS into a worn out drill head casting that is very similar in size and shape to casting I am seeking to repair -- just to see exactly what happens.

Here is the drill head casting on the mill ready to clean up the hole cut out with a metal cutoff wheel


And here is the casting and CRS patch ready to be brazed together. The patch is 30 thousands proud
to allow for final machining

 

[brino]

I am very much looking forward to this!

Thanks for sharing the test results.

-brino

 

[Flyinfool]

Before you braze it, chamfer the inside of the casting also. It will be a lot easier before brazing than to get in there with a die grinder later. You want to braze from both sides to be sure of full penetration so that there is not a crack built in to propagate.

 

[Tim9]

Agree on going heavy with bronze A/O brazing. Cook it on the bar-bq. Cast iron is like a sponge. And you must get that oil out if you want to get a good braze.
The hardest part is the pre-heat and cool down.I find.... Once your bronze starts flowing... it’s nothing to continue brazing the housing. So do both sides. Do it all in one shot. You can always mill and grind out the access.

 

[bill70j]

Thanks for everyone's input. Made some progress on this project. Completed two test brazing joints - one has problems. Appreciate any and all additional comments.

1/8" bare bronze rods, flux, and Harris Model 16 torch handle with 03 tip. 3psi acetylene and 5psi oxygen


First joint: Cast Iron - to Cast Iron. Material is scrap from a cast iron grinder table. Process: (1) Bevel edges of both pieces, front and back, (2) Wire brush, (3) Clamp to fire brick, (4) Heat and tin, (5) Braze front, air cool, (6) Braze back. Joint looks good. One void -- looks to be due to a lack of filler bronze. (Click to enlarge.) Comments?


Second joint: 1018 CRS patch to Cast Iron drill press head casting. Process: (1) Bevel front edges of both parts, (2) Fixture patch in place, (3) Preheat assembly to 400 deg F with a rose bud, (4) Heat and tin, (5) Braze front, (6 ) Wrap in welding blanket and let cool slowly
Numerous voids in the joint. I did not braze the back of this joint due to space limitations, and I did not heat soak the casting prior to brazing, since it was relatively free of grease and oils. (Click to enlarge.) Note: For the "real" repair, I will heat soak the assembly prior to brazing." Comments?


Made some progress on the apron casting repair. MIG welded the replacement part with multiple passes. Process introduced about 10 thousandths of twist. Milled faces of bosses back to flat and planar. Will mill plate flat once brazed in.



Designed and built a fixturing jig for brazing in the replacement part. Will use a c-clamp to provide clamping force between back face of fixture plate and front of replacement part. Part will be adjusted in place using nuts on the three long bolts


,

 

[Tim9]

Personally, I wouldn’t worry about the voids. You can seal those with JB weld. Too much risk of screwing the pup if you try to go back and fill them with bronze. They are fairly small voids. If they were a lot bigger, then I’d give it a go a second time.
You lost me when you said you went back with MIG ?

 

[bill70j]

Personally, I wouldn’t worry about the voids. You can seal those with JB weld. Too much risk of screwing the pup if you try to go back and fill them with bronze. They are fairly small voids. If they were a lot bigger, then I’d give it a go a second time.
You lost me when you said you went back with MIG ?

Thanks !for your comments

The bronze joints I showed are only test joints for the "real" repair. So I was showing those voids only to see if anyone has ideas on ways to improve the results. Those parts are merely scrap.

The "real" repair is brazing a replacement part to a cast iron lathe apron housing. That replacement part consists of three parts: (1) a 3/8" CRS plate, and two 3/4" thick CRS blocks that serve as internal bosses for the replacement part. Those blocks were welded to the plate with multiple pass MIG welds, then the part is machined to get it ready for brazing to the casting.