Casting Deep Hole Repair, Weld or Braze?

[Spindle]

I need to fill, drill and tap the chewed up hole to the right of the center hole in this cast iron piece. The hole has a 1/4" diameter and is 1" deep.

What would be the best way to fill this? I've found oxy-acetyline cast iron rod and flux but haven't ever used it.


http://i648.photobucket.com/albums/uu201/ironrelic/rmign03.jpg

http://i648.photobucket.com/albums/uu201/ironrelic/rmign01.jpg

[Langanobob]

It looks like the part gets painted when you're finished? Not the approach for a purist but the simplest fix might be to just fill it with epoxy. Also looks like it might have been threaded at one time? You could re-thread it and screw in a stud, grind it smooth and fill any remaining flaws with epoxy, again assuming it gets painted.

[Spindle]

langanobob-

It had been painted but won't be when reinstalled. This is an ignitor for a hit and miss engine. The cylindrical part goes into the engine cylinder. The spring loaded trip finger shown in this picture gets pushed away by an actuator, then snaps back to the pin. More heat/cooling and impact cycles than I'd want to subject epoxy to.

http://i648.photobucket.com/albums/uu201/ironrelic/aaign2.jpg

[TGTool]

I'll describe what I would do, but to put that in perspective for your judgement, I don't have a great deal of welding experience so I may shy away from a good solution just from inexperience.

I would drill through about .040 larger than the thread OD. Then I'd make a steel (or cast iron) slug to go in the hole that's .003 to .005 smaller than the hole. The drill could run oversize, it won't matter since you're fitting the plug.

Then I'd get out my silver braze compound with the good fluidity characteristic, flux things up, put the plug in the hole, and braze it with a torch. The braze will wick into the joint nicely and you can verify that on the opposite side.

Then you can redrill and tap the hole for the pin.

If space it tight you probably wouldn't need to drill it any oversize since the braze will fill in any spaces around the plug even if the drill wanders. And when you drill and tap it will still work even if the tapped holes runs out. If you could really see the partial threads, partial braze and partial plug it would seem like a mess, but the mess would be solid enough and cohesive enough to secure the pin.

[Spindle]

TG-

Originally I wanted to drill and tap the existing hole and thread a plug in, but the wall of the hole is so close to the outside wall of the cylindrical portion there isn't enough material for the thread major diameter.

I do like the unthreaded cast iron plug plan, I can turn one on the lathe to fit the hole.

Is the silver brazing the flat copper coated type?

Would there be flux involved?

Is preheat and slow cooling neccessary for a solid shape like this?

Rex

[Don Young]

I would consider a helicoil or similar insert. There is a solid insert like a helicoil, with matching inside and outside threads so it can be very thin. Or use a helicoil tap to clean up the threads and then make a new pin with oversize threads.

Depending on the condition of the hole, it may be possible to just make a new pin with slightly oversize threads. You could also make a special slightly oversize tap if necessary. I prefer not to use heat on valuable old cast iron parts if possible, although lots of people have good results with it.

[TGTool]

Rex,

I'm basing this my experience on a job where I'd turned the OD too small for my threads. Sort of the inside out problem compared to yours. I made a sleeve and used my brazing rods to sweat it into the crack between the two parts. It didn't work worth a ****. The braze only adhered at the top and the sleeve was pulled right off after it was put in operation.

What I got then was Rador Safety Silv 45 by Harris with a fluidity rating of 6.5. (I didn't know there was such a rating for brazing) This is the Harris site with various materials http://www.harrisproductsgroup.com/consumables/alloys.asp?id=30

I found this at the Airgas store while I was doing some other stuff. In any case, for the remake of the first failure, this had good capillary action to get the stuff all the way through the joint. I took what they had hanging on the wall there which happens to be 3/32" rod but I'm sure if you needed a particular form you could get it. Somewhere I do have some flat strip which is useful if you're just making a sandwich of your pieces with the braze material in the middle.

My original rod will probably be more helpful in cases where I'm trying to build up an area that's chipped or V-ed out.

Yes, it does require flux and I'm just using a general purpose paste brazing flux.

I don't think you need to take the same precautions against cracking that you would if you were welding, both because you're working at lower temperatures and because the filler has more ductility.

You might want to solicit Glen (PTSideshow) who has a lot more experience with this than I do.

Jan

[Arcane]

I need to fill, drill and tap the chewed up hole to the right of the center hole in this cast iron piece.



Originally I wanted to drill and tap the existing hole and thread a plug in, but the wall of the hole is so close to the outside wall of the cylindrical portion there isn't enough material for the thread major diameter.

It looks like Don Young's suggestion is the best one given the constraints you are dealing with. I certainly second it! :)

[Langanobob]

Give me an "F" for reading comprehension. I managed to miss the part about having to redrill and tap it and I thought it was just a cosmetic repair. My apologies.

I think TGTool has a good point about possible problems getting good wicking or capillary action between a plug and the existing iron. Any air gaps are probably going to end up being air gaps in the new threads.

I think if it were mine, I'd clean the heck out of that hole until it was as clean as I could get it. Then I'd carefully preheat it and completely braze the hole full with nothing but brazing material. I'd leave it a little high on the surface as I'm thinking it will shrink slightly as it cools and want to form a slight concave crater. If it's clean and you get good flux action it should eliminate any issues with poor capillary action. The brass can then be drilled and tapped. The brass threads won't be as strong as the original cast iron threads but I think they will still be strong enough.

[Bob Ford]

You might try a 7 mm X 1.25 tap to clean up the threads. Then make a stud for the new threads. ENCO has them. http://www.use-enco.com/CGI/INPDFF?PMPAGE=89&PMITEM=311-4211

Bob

[boslab]

Tig, extend the electrode, heavyish gas, fill it up, redrill, retap.
theres a book Die repair that outlines tig as a repair
http://www.eng4ever.org/handbook_of_mold_tool_die_repair_welding.html
mark