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

Years ago I bought a little south bend lathe from a school district that had a similar problem. After disassembling the carriage I baked it for six hours at about 600° to burn out all the oil. After it cooled I ground out some nice big “V’s”, heated it up again and used a oxy-act torch and some brazing rods to do the repair. When I was done with the brazing I put it into a bucket of lime so it would cool real slow. I then had to bore out the bearing areas and bush them so everything ran true again. That was over thirty years ago and I’m still using that lathe with no problems.


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Thanks to everyone who has responded. Lots of useful information!

Many have said it makes sense to forget about repairing my mess and scrap the assembly for parts. That makes the most sense.

In my situation though, I think it may also make sense to go for a repair. I have the materials and the tools, so it's only my time. Plus I am now thinking that if the repair is successful, I will reinstall the unit in the lathe and try to sell the newer one - for which I have all the invoices ($550 new).

Thanks to those who have offered suggestions on the repair. I would appreciate any additional input on the how to do this. Here is what I plan to do:

These two photos show the front side of the casting wall and the back of the portion I plan to replace.
Weld Repairs.png DSC_0012.JPG
Plan:
  1. Get all measurements and develop a partial 3-D model
  2. Design and build all fixtures needed to ensure the casting goes back together in exact same dimensions and orientation
  3. Cut out the portion shown in lines above and grind arrowed cracks
  4. Machine a replacement piece, drill and bush the shaft hole with bronze then drill shaft hole slightly undersize
  5. Oxy-acetylene braze using bare bronze brazing rod and flux. Use techniques offered here and found online
  6. Set up the casting in the mill and bore/line bore to ensure everything fits
  7. Reassemble and thoroughly test
What do you think? Will this work, or am I being overly optimistic? (I feel pretty good about it, since you guys helped me resurrect my burned out 2x42 grinder without spending any money.)

Thanks again for your help, Bill
 
Plan:
  1. Get all measurements and develop a partial 3-D model Absolutly and include more in the 3d model than you think is needed.
  2. Design and build all fixtures needed to ensure the casting goes back together in exact same dimensions and orientation Perfect. Do a lot of checking, I think there may be more than it look like that is warped or bent.
  3. Cut out the portion shown in lines above and grind arrowed cracks I would enlarge your cut out area to completely replace that hole at the point so that you are not trying to deal with boring an interrupted cut. In addition to grinding the cracks drill stop hole just past the ends of the cracks and grind to the stop hole.
  4. Machine a replacement piece, drill and bush the shaft hole with bronze then drill shaft hole slightly undersize I don't think you need to bush the hole if you have replaced it completely.
  5. Oxy-acetylene braze using bare bronze brazing rod and flux. Use techniques offered here and found online Perfect just check again for any warpage or miss alignment.
  6. Set up the casting in the mill and bore/line bore to ensure everything fits Perfect.
  7. Reassemble and thoroughly test The moment of truth.
Good Luck and post lots of pics of your progress.
 
There are a number of ways to make good repairs on castings. First, I'd be shocked if that casting is grey iron. My money is on semi-steel. That helps. You have a few choices, unfortunately the best options require TIG (silicon bronze or nickel). Since you have a torch, you can use cast iron rod and a ton of flux to glue it back together. ->link<- You will need to pre-heat to 350 or so. Melting of base metal is not required, the cast iron filler will flow with flux. Then you'll have to use your shop kung-fu to clean up the casting. If nothing else, you will gain experience with a type of repair that many people consider voodoo magic.

Edit: Bill, I'll send you a pound or two of cast rod in the mail if you are interested in doing it this way.
 
Indeed, as the guys have mentioned, you can braze the semi-steel. It may go on easier that way because it melts at lower temperatures.
As @pontiac428 has indicated nickel also "wets" well.
I had to have a quick think about temperatures. I hazard a guess most folk meant °F.
 
When you go to braze the casting with the oxygen acetyltene you need to preheat it. And after your done try to cool the casting as slow as possible. I usually bury the casting in wood ash ,if it's too large for the heat treating oven. Slow cooling will help to prevent warping and cracking. Normally I would use stick arc with nickel rod it doesn't heat the casting as much there by preventing as much warping . Lacking an arc welder, brazing the casting is your best option. Let us know how it works out.
 
Bill,
attempting the repair sounds like a cool but complex undertaking. I'm guessing it will braze ok but there is a lot of work there. Have you considered either making the part from scratch or milling as much thickness off the flat face you can and laminating a steel plate over the top, machining all the bores and holes? I'm just thinking "aloud".
 
Flyinfool said:
Plan:
  1. Get all measurements and develop a partial 3-D model Absolutly and include more in the 3d model than you think is needed.
  2. Design and build all fixtures needed to ensure the casting goes back together in exact same dimensions and orientation Perfect. Do a lot of checking, I think there may be more than it look like that is warped or bent.
  3. Cut out the portion shown in lines above and grind arrowed cracks I would enlarge your cut out area to completely replace that hole at the point so that you are not trying to deal with boring an interrupted cut. In addition to grinding the cracks drill stop hole just past the ends of the cracks and grind to the stop hole.
  4. Machine a replacement piece, drill and bush the shaft hole with bronze then drill shaft hole slightly undersize I don't think you need to bush the hole if you have replaced it completely.
  5. Oxy-acetylene braze using bare bronze brazing rod and flux. Use techniques offered here and found online Perfect just check again for any warpage or miss alignment.
  6. Set up the casting in the mill and bore/line bore to ensure everything fits Perfect.
  7. Reassemble and thoroughly test The moment of truth.
Good Luck and post lots of pics of your progress.
Click to expand...
Thanks much, @Flyinfool. Appreciate the advice and support! I will post as I progress. Thanks!

pontiac428 said:
There are a number of ways to make good repairs on castings. First, I'd be shocked if that casting is grey iron. My money is on semi-steel. That helps. You have a few choices, unfortunately the best options require TIG (silicon bronze or nickel). Since you have a torch, you can use cast iron rod and a ton of flux to glue it back together. ->link<- You will need to pre-heat to 350 or so. Melting of base metal is not required, the cast iron filler will flow with flux. Then you'll have to use your shop kung-fu to clean up the casting. If nothing else, you will gain experience with a type of repair that many people consider voodoo magic.

Edit: Bill, I'll send you a pound or two of cast rod in the mail if you are interested in doing it this way.
Click to expand...
John: Thanks very much for the tip on ESAB's All State 3 Bare rod and for your kind offer to mail me a lb or two. I had a close look at their website - it's quite informative. The much lower melting temperature of the cast iron rod of 350F is certainly attractive. Should I be forced to use 1018 for the part I intend "graft in" will this rod be suitable? Also, any downside of using this rod over a brass rod? Thanks!
NC Rick said:
Bill,
attempting the repair sounds like a cool but complex undertaking. I'm guessing it will braze ok but there is a lot of work there. Have you considered either making the part from scratch or milling as much thickness off the flat face you can and laminating a steel plate over the top, machining all the bores and holes? I'm just thinking "aloud".
Click to expand...
NC Rick: Thanks. Appreciate your thoughts. Once I get into this, I am certain things will different that what I envision. I am planning to make a portion of the damaged casting from scratch and brazing that in. But I may end being forced into going further than that. Thanks!
 
bill70j said:
John: Thanks very much for the tip on ESAB's All State 3 Bare rod and for your kind offer to mail me a lb or two. I had a close look at their website - it's quite informative. The much lower melting temperature of the cast iron rod of 350F is certainly attractive. Should I be forced to use 1018 for the part I intend "graft in" will this rod be suitable? Also, any downside of using this rod over a brass rod? Thanks!
Click to expand...

I think grafting a plate to the casting is a decent plan. You'd want to use brass for that (nickel works very well for dissimilar metals with TIG). The 350F is for pre-heat, the cast iron rod melts at iron temps.
 
I’d braze that with oxy/acetylene and bronze rod. I’ve repaired a few cast iron castings. My Clausing master cylinder I just used nickel 99 and figured it would be a backup since I was able to find a housing mount on EBay. The “new” used eBay replacement is still in the cabinet since the repair is holding fine. It’s not a pretty repair but it’s been working perfectly for almost 8 months.
But with what you have there, you have a few shaft bores for the gears. So I’d do as Pops describes above. Bake it really good to get all the oil out. That thing will be like a sponge and oil will smoke out of it for over 30 minutes. I’d disassemble it and stick it on the bar-b-q for about an hour .
Then a preheat and braze. Then re-bore all of the shaft bores.FWIW, you probably have a few bent shifts too. Check them good.

also... make sure you cool it slowly after the braze. Bury it in sand or fiberglass. I have a big box of vermiculite I use for cool downs. But cooled slowly helps prevent cracks
 
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