Repairing cracks in cast iron

Thanks Trevor - I have sent you a PM.
BobH

As far as I know where the cast iron needs to retain it's strength on machine tools and etc the stitching method has always been the best. Generally it's going to be best when something has been "broken" some how. I'd guess this thread is more concerned with stress in a casting causing the cracks. Add heat, welding etc and more of that can occur.

I have a model engineer made rotary table. I needed to dismantle it to do a bit of additional machining due to it distorting over time. There was a strap across 2 parts of the casting. Shortly after removing that the casting cracked. It doesn't cause any problems but both aspects are down to who ever produced the castings allowing them to cool to quickly. This reminded me of when I started getting interested in model engineering. Many wise older people said don't make your tooling from castings for exactly this reason. Fabricate instead. They were implying that there will always be some movement over time. Given that "important" castings are generally left lying around for varying periods of time they are very likely to be correct.

John

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Just an update on the village cross.
In the end I decided to use MIG with Stainless Steel wire / Argon gas.
To support the joint, I mounted a piece of box section in the vice to support the weld area. To make sure the two halves were correctly supported, I put two big dollops of plaster of paris onto the box section, put some cling film on top of the plaster and then placed the broken cross on top of that , adjusting the cross to get the two broken sections aligned correctly. (Nb: I left the joint area free from support as the plaster would more than likely cause problems)
I then cut a "V" preparation at the cracked joint , removed the cling film and clamped the two halves onto their plaster supports.
Heated the general area with a propane torch then wire brushed the area whilst still hot. Then used the MIG starting in the centre and then the two outside fragile legs. It took about 3 runs of 0.8mm wire to fill the joint. Again after welding, I cooled the area gently using a diminishing propane flame and finally left in the hot sun. Some gentle tapping of the joint with a small hammer annoyed the neighbours for 10 minutes! I didn't dress the weld very much - didn't see the need to.
Just need to paint it and put it back onto its stone plinth.

Plaster support sitting on the box section

Finished joint.
BobH

Nicely done, Bob

... Hope you don't get a repeat performance from "the lads".

MichaelG.

The repairs look great! well done.

Michael G's post echoes a thought I had - maybe a replica cross could be cast in resin and painted, then the original stored safely in the church and the resin replica model placed outdoors in the path of the rampaging barbarians.

A silicone mould could be made from the original cross then copies cast in resin in the silicone mould. With a silicone mould there is extremely low risk of damage to the original cross and minimal cleanup compared to making a plaster mould. If a polyurethane or epoxy resin rated for outdoor use were used for the cross castings it would likely last many years and it would be resistant to damage.

Just a thought.JD

Our village has a cross at each road that leads into it. There are about 5 crosses in various states of repair. I don't think there is any real historic value in them, its just a nice to have and nice for us English to do something that preserves the heritage of this small French village. Our headcount is about 160, but only about 60 of us live here all year, the others are holiday homes.
BobH

I would try to repair the crack by a "cold" method, I think that preheating the cylinder to a high temperature could cause some distortion of the cylinder bore resulting in further expense i.e. boring and sleeving or boring and new piston .If the crack can be reached or seen from the inside of the water jacket then a thorough clean and a good dollop of plastic padding will seal the crack, I successfully repaired a Ruston Hornsby Cylinder head in this manner