Work-holding / clamping for silver-soldering

HI guys, raw beginner alert!

I'm about to start work on my very first metal project, a 'Hero's Engine' from the Stan Bray book.

I've no metal work experience at all, so am going to start with cutting and soldering the two stands which hold the drum... these are going to be a piece of 1/2" angle-brass for the base with a bit of 1/2 * 1/8 brass strip soldered vertically for the support... so it's a very simple operation, silver solder (as a learning exercise) the vertical strip to the angle.

I've read lots on soldering and watched many UTubes and (think) I understand the principals... one thing I'm (probably overthinking) is how to hold the two parts firmly together so I can heat them.

I assume that you shouldn't use big heavy clamps for this operation as they will either be damaged by the heat, or will draw heat from the parts, making the whole thing more complex and fraught.

The two parts are simply but-joined together, so won't hold on their own...

Any suggestions?

cheers. Jerry

Hi there. Welcome to the fun.

Often people put a screw or pin in the joint to hold it as it can easily move under even the blow from a gas torch. Florists wire is also a help.
You might designate some clamps and big crock clips as 'sacrifices' to get the paint burnt off and hold things. (keep them in a plastic sealed tub to slow down the rusting afterwards).
BIts of old gas fire mantle and thermalite block can be made as supports without sapping too much heat and reflect some back. Be sure the block is bone dry or it might explode from the steam.

Notes about silver soldering. It is best to heat up as quick as possible to avoid giving time for things to oxidise. The flux is mixed with water to get it into place as a paste but this evaporates obviously and the vigour of that can move it out of place. The actual powder then melts into a form of glass and as well as chemically cleaning it physically keeps the air off so make sure there is enough around the joint. Equally dirty metal won't solder so you can use this to your advantage by painting on tippex/snowpake where you don't want it to flow.

Not sure if I've told this story before. I read about an America physics professor decided to make a model of Hero's engine. It was so feeble he could only make it work by suspending it from two magnetised ball bearings to minimise the friction and he concluded Hero only theorised the engine, not made it. Within a week or two I read the story of a model engineer who made a working one out of scrap...

I suspect the difference was the nozzles./ I bet the former just used plain tubes in the hope of getting free steam flow, but to maximise the energy in the jet a fine nozzle to give the fastest jet possible is needed. Bear this in mind!

Neil

One of the interesting things about silver (or soft) soldering is that you don't want to clamp the parts together in close contact. There has to be a gap for the solder to penetrate into. The usual way to arrange this that I find works well is to lightly centre punch the contact surface over its area to raise small burrs which effectively space the parts apart. Then they can be clamped together in order not to move prior to heating.

On fabricated assemblies I always drill and pin with steel pins, the assembly is then is self supprting and needs no clamping at all.

Make allowances for after machining or filing and try to avoid pins where you may drill later. Pins need only to be 5 mm long and a semi loose fit.

Clive

I have used various approaches.

The ideal is when parts are self locating.

Next best if a light weight on top or some other simple arrangement can hold parts in the correct relationship.

For small things like specatacle frames and valve rods I use a pair of 'helping hands' - croc clips on universal joints on a frame fitted with a magnifying glass. Use with a cook's blowtorch, not a huge propane torch!

Another approach is wiring with soft iron wire. This can be easily filed off if it accidentally sticks. If you drill holes and thread wire through, the holes fill with silver solder and teh wire can be cut/filed flush.

Clamps can work, but it's tough on the clamp and heat can make them come loose.

Plaster (well dried) and even potatoes can be used to hold parts in position. Pushing a part into a spud is really useful for things like springs that your eally don't want to get hot other than at the ends.

One unusual way I have used to hold a really awkward shape was to make a shaped wooden plug to fit inside and then set four protruding legs in quick setting mortar! I had to let it dry overnight, but it worked very well. If I had used drawn angle instead of black rolled angle that didn't have any flat edges in sight I cold have used ordinary clamps.

Neil

word of caution - if you do nothing to hold it in place it will invariably move as the flux solidifies...and then again when it goes liquidus, and it can move a long way from where you set it!

Thanks very much for the suggestions guys, will let you know how I get on!

cheers. Jerry

Another word of warning when working with brass. The high temperatures involved in silver soldering will significantly soften the brass to the point where it might deform easily so watch your clamping forces. It will self harden again over the weeks but will be very soft after the initial solder. Also, it expands quite a bit on heating so again, try to make allowances when jigging it together.

Hi Jerry,

Remember when silver soldering

no joint = no capillary flow = no joint

Clamping effectively removes the joint gap.

As Chris suggests centre punching maintains a gap. If that is not practical place a piece of silver solder foil in the joint prior to clamping.

Neils' approach of using soft iron wire is also good. The wire deforms as the components expand so maintaining the gap.

keith

I use these things to hold small parts when soldering, I have no idea where I saw them or I would credit them,

just an odd lump of round with two legs and a probe, the weight of the lump holds things in place.

Roy

A Celcon block and a few nails/panel pins also works. Try not to place the joint directly on the block though as the flux glues the item to the block. I have used it many times and it works a treat, but as others have said sometimes it pays to locate parts with pins screws etc.

I use, and re-use, soft iron wire which is looped loosely around the assembly, with the amount of exerted pressure being easily adjusted by twisting the ends together with a pair of pliers. Have just bought some additional supplies from a very good small stand at the 2013 London Modelling exhibition in January. Hope this helps.

Trevor.

Dusty, re your "Celcon" reference-

I imagine you meant a cellular concrete or ceramic wool type block in your soldering post above. That, or firebrick would work well. However, "Celcon" is also a trade name for an acetal thermoplastic made by Hoechst Corp. I mention it in case the original poster or someone else goes to a material supply place and asks for a chunk of Celcon, and gets the acetal by mistake. Silver soldering on an acetal plastic block will not end well of course, the plastic will melt! A ceramic block or some firebrick will work fine at high temperatures.

JD

I use skamolex blocks. Disadvantage is they degrade when flux sticks to them, but they rapidly heat red hot and re-radiate heat into the work, with very little conduction through the material.

Neil

Yes Jeff, 'Celcon building blocks' also know as thermalite or used to be. Cheap as chips and when as Stub Mandrel say's they have degraded throw em away or use bits of them to help support the items being silver soldered.

Dusty,

Celcon and Thermalite are separate Trademarks of different companies. I have found that Thermalite branded lightweight concrete blocks are, for me, superior when used for a brazing hearth. It is just a matter of how they degrade with heat.

Have you tried this tip to stop flux bonding to "block" use piece if C Iron (I use piece 3x2x0.25 inches) on the block under the pieces to be soldered. This plate is covered with "Tipex" (Typing corretion fluid) which stops the flux and solder from bonding to the iron. The iron gives a even heat to the work pieces and stops degrade to the hearth.

Its been working for me on all my small soldering jobs (I learnt this from a silver smith quite a time ago)

Also the S smith always used soft iron wire to hold pieces together - also tipex in the wire if required.