Silver Soldering threaded joint technique.

**thehomeengineer** · Jun 16, 2024, 02:11 PM

Hi All

This is a technique I use to silver solder two components held together with a thread.

I am currently making the pistons for my 3” Foden Steam Wagon. These could have been machined from solid bar but would have been very wasteful. So opted for a two piece fabrication, silver soldered together. The fabricated pistons and rods are left oversized so they can be machined to dimensions after silver soldering, to make sure everything ends up true and concentric.

The two pieces were threaded M8 for added strength and then soldered. To ensure the solder on a joint like this can flow freely through the joint and around the threads, I like to plane a groove along the thread to aid good penetration through the joint. The threads are also not tightened as the solder relies on a gap for the capillary action for the solder to flow.

The photos will help show the process.

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HSS chamfering tool turned on its side so the grove can be planned/broached.

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Tool in place ready to cut grove.

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Cut grove along thread.

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Piston and rods ready for soldering.

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High pressure piston blank.

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Fluxed joint ready for heat and soldering.

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Pickle bath to remove flux.

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Solder flowed all the way through the joint.

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Both HP and LP fabrications ready for finish machining.

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Finished turned low pressure piston. The solder has flowed in and around thread and the groove is also filled by the solder making for a strong joint.

Thank you for viewing and hope you find this helpful.

The Home Engineer.

**thehomeengineer** · Jun 19, 2024, 02:31 AM

Hi All

I have added a couple more photos to show the piston rod side of the joint on both the HP and LP pistons to show the thin ring of silver solder in joint.

Silver Soldering threaded joint technique.-silver-solder-ring.jpg

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Still a little bit more machining to complete the pistons and rods. Piston ring grooves and a taper on the rod with slot for locking key to connect to crosshead.