Silver Soldering

Silver soldered joints are quite strong and can be worked with a file, die grinder, or machine tools. This article is not a complete how-to tutorial on the subject of silver soldering, but does include good references. What is silver soldering, also known as silver brazing? Soldering is a process in which two or more base material parts (metal items) are joined together by melting and flowing a filler material into a very small gap between the parts. The parts need not be of the same metal alloy.

The filler material has a lower melting point than the base material(s). Soldering differs from welding in that the base material of the parts to be joined is not melted. Silver solder includes a significant amount of silver. This silver content makes it melt at a higher temperature, creates a much stronger joint (as compared to tin/lead solder), enables the molten filler material to "wick" and "wet" surfaces of many non-aluminum metals and alloys.

Wikipedia has good definitions of soldering, including applications thereof. Siver Solder vs. Welding Erosion and distortion. Welding erodes a portion of the base material (parts being joined). These eroded areas of mating parts melt together, with filler material added to the molten area to for a "bead." Good weld design often suggests that a V-grove be created by grinding down the mating edges of parts to be joined. This may not be a good option for very thin or small parts.

Very small parts can be successfully welded using TIG (Tungsten Inert Gas) process, but the smaller the parts, the more difficult the task becomes as the erosion area created by even the smallest arc may be nearly the same size as the size of the base part at the weld location. Less risk of damage to the base parts. Welding temperatures are hot enough to totally melt the base material. The welding process erodes away some of the base material which gets melted and combined with filler material.

This erosion, even when very quickly re-filled with the mixture of melted base metal and filler rod, changes original dimensions of the base material parts. Also, because of the increased temperatures used, distortion and other material properties changes are likely to be more extreme. As an example, it is nearly impossible to weld up to the edge of important features of existing parts (such a critical hole where a pin or shaft might ride) without erosion or distortion of the existing feature. Different materials.

TIG welding of stainless alloys is extremely sensitive to filler rod selection which must be matched to the alloy of the base material. The exact stainless alloy of many products including firearms is often NOT published as it may be a manufacturer’s trade secret. Experienced welders may be forced to learn by trial and error which filler alloys work best. For example, some gunsmiths report good results welding stainless steel Colt pistols with #304 filler rod.

In general, atop quality silver solder alloy has no sensitivity to the alloy of the base material. Silver solder works very well with different stainless steel alloys and can even be used to join dissimilar materials. Beware of "galvanic action" where dissimilar metals can create a corrosion process at the joint, especially if moisture is allowed to accumulate. Different material thicknesses. Silver soldering provides a relatively easy way to bond thin parts or sheet metal to thicker parts.

The key is to apply heat to the thicker part with more thermal mass while also carefully observing the thinner part. The thinner part may get hot enough just from being close to the thicker part. Strong enough. Good silver solder is strong. Some old-timers call it "hard solder" as compared to the "soft solder" (lead/tin solder) which, until recent years, was used for most copper plumbing.

As long as the silver solder joint has enough area so that the stresses are not localized there, the resulting strength of the joined assembly is usually more than adequate. Compare soldering two 10 penny common nails together end to end. Soldering would not work well for soldering the two pointed nail ends together. There would be no lap and just a very small joint with a concentration of solder only between the pointed tips.

However, soldering the flat ends of the heads together would work quite well because the solder joint is distributed over a much larger area. This is an example of a "surface mount" joint. Finally, there is a better chance for rework, if needed. All welders know the sinking feeling when a portion of the part being welded melts off and falls to the floor. With soldering, the highest temperatures seen by the

base material should never reach the melting point. A thin part may warp or distort from the heating, but the parts will still be there for another attempt, if needed. Joint Design There are many references available regarding joint design. In practice, for repairs and modifications of existing parts, you do not get many choices or options for joint design because the repaired or modified part must still fit and function within the confined spaces and interfaces of the original part.

This article will focus on examples of repair or modifications of existing parts where optimal joint design is not feasible. Leave a gap for the molten solder to flow between the mating parts. When rejoining a broken part, if simple remating of the broken pieces causes a perfect or near perfect fit, then it is very likely that there is not room for solder to flow everywhere between the two mating pieces. The mating pieces must not be firmly pressed totally together with zero clearance between.

One method to get nearly uniform separation between mating pieces is to use a small center punch to randomly create many dimple deformations in both mating surfaces. The exact separation is not critical and it will likely vary across the mating surfaces. Approximately 3 to 6 thousandths of an inch is recommended. Jigging (Holding Parts) You will need a method (jig) to firmly hold the parts in exact alignment with no movement.

Ideally, the holding setup should allow application of flame and filler rod all around the entire joint. Soldering one half and then the other half of a joint is possible as the joints can be made to flow together. If a change of position half way through the soldering is necessary, try to plan for a quick change with minimal heat being lost from the parts. Make your holding setup so that it is stable and can be recreated after "dry-fitting" and for rework, if necessary.

If you are using the services of an assistant to move the parts during soldering, practice dry runs with the assistant. Beware clamps which are too close to the joint or have too much thermal mass. For example vise jaws and and large Vise-Grip pliers may hold well, but due to their thermal mass they can conduct much of the heat energy away from the part to be soldered. Beware too much force applied to the parts by your holding jig as parts may warp or collapse when heated.

A good bead around the edge of the joint can add extra strength in some cases, especially when a break is on a thin portion of the original piece. When soldering, position the parts to join so that gravity can help create a nice "bead" (almost dripping) on the bottom side of the joint. As much as possible, just leave this dripping bead in place for additional strength. For tiny parts, surgical hemostats can be very handy, especially when tailored or modified.

Secure the hemostats in bigger clamps, vises, hold-downs, or custom jigging. Set up your soldering area indoors, if possible, to minimize drafts, and always in the shade. Direct sunlight or a strong arc lamp focused on the work may be helpful for arc or TIG welding but is a definite distraction for silver soldering or brazing. You need to be able to see as much as possible and learn the subtle variations in color of the filler material and base metal.

These color changes are your best indications of proper temperature. Jackson Products, Inc. recommends a #2 Shade (lightest available) for torch soldering. Finally, keep it clean. No dirt, grease, or oil. Some recommend mild acid treatments (mild sulphuric or citric). I prefer degreaser (Berryman B-12Chemtool) combined with mechanical methods, such as a wire brush and Scotch-Brite pads.

Beware any plating, bluing, or other surface treatment near the joint as these may cause contamination when the base parts are heated and can prevent wicking and wetting of solder at the joint area. Clean all surfaces near the joint and possible fillet area down to bare metal. Pre-fluxing (using a compatible, separate flux) of the joint area immediately before is a common practice.

Silver Solder Materials The subjects of alloy selection, flux selection, heat selection, torch fuel selection and associated techniques are deferred. With the use of cadmium metal no longer allowed in silver solder, the lower priced and hardware store silver solders will not work. Torch type and fuel selection offers many choices. The maximum adiabatic temperature available with most common fuels (with or without oxygen) is way above the melting point of the filler alloys.

In practice, flame temperature will be lower. The key is selecting a torch and tip which gives a fine enough tip for good control and delivers enough heat energy to quickly heat the base material. "Home-use" butane and MAPP gas torches do not have the necessary flame adjustment (different size tips) and heat controls needed. Go to a full service welding supply for torch selection and to buy the best filler alloy available. For only very fine work, consider a jeweler’s torch.

This article assumes you are using 1/16" dia. pre-fluxed filler rods, have an oxygen-acetylene torch on hand, a size 00 Victor tip (for small work-pieces) and a carburizing flame. Heating Think mostly pre-heating. Pre-heat the entire joint area of the base material, if at all possible. When parts to be joined are of different sizes, focus more heat on the larger part. Beware any portions of the base parts which are small and extend out by them-

The small button size can make this safety difficult to engage. The larger button size makes safety easier to operate. selves. Direct application of heat to these delicate "fingers" can cause them to melt off and fall away. Do not get in a rush and apply the filler material too quickly. Do not apply heat directly to the filler material as you might do when "filling" in material with TIG welding process. You are trying to get the base material to be just starting to turn color to a gentle, dull pink.

Bright cherry red is way too hot! Too hot will also cause solder "crystallization." The solder crystallizes when the silver separates from the other metals in the alloy and does not adhere to the parts. Usually you can reheat the joint and apply some flux to force the solder to realloy and adhere. Work quickly. If you have prefluxed the parts, be aware that once heated the flux will not last very long.

When the joint area of both base parts are pre-heated, touch the pre-fluxed filler rod to the joint near current application location of the flame to the joint. Let the hot base material cause the filler rod to melt. Melted filler material will tend to flow to the hottest point of the base material. Keeping the flame near the application of the filler rod will maintain a hot joint and prevent the thermal mass of the freshly applied filler rod from cooling the joint too much.

Observe the melting, running and wicking of the filler material along the joint boundary. Move the slightly separated filler rod and Pivot hole was not disturbed by soldering. flame combination quickly along the joint boundary and observe the melted filler rod running into the joint boundary. A small fillet at the joint boundary is a good thing, but easier to obtain for corner, step joints, or slip joints (like copper plumbing).

If necessary, you can quickly go back and revisit a portion of the joint—more heat first, then filler rod—while the assembly is still hot. Work fast with the heat and filler rod application and movement. The flux will not last very long. Heat applied for too long can give you a big oxidized mess.

Free References Download Additional references and resources for this article are available for free download. Visit americangunsmith.wordpress.com Clean Up Whether your results came out excellent, or if you need some rework, clean up is in order. If you did very well, most of the complete joint with fillet should be visible on the soldered assembly.

Some overflow and run-over of melted filler rod material onto the base metal parts away from the joint boundary might appear unsightly, but run-over spreading is not uncommon. There may be portions of the joint or base metal parts which are covered with baked flux, some of which may have turned to "glass." Careful picking, similar to removing slag from arc weld joints, may loosen the glass deposits. As I am often in a hurry, I often use a fine wire wheel aggressively.

Beware any remaining "glass" as finish treatments will not work there. Reworking A Total Separation Cleaning, preparation, and then resoldering of an existing joint is highly preferred over total separation. Depending upon the complexity of your parts, you may need to modify your jigging/holding fixture to allow the parts to be separated. If you can get the entire joint area of the assembly hot enough to melt all of the silver solder in the joint at the same time, the parts can be separated.

Beware the certainty of spattering and splashing of molten filler material. As soon as the parts are separated, with the solder still above melting temperature, immediately shake or tap the parts to remove filler material. After separation, expect filler rod remnants to be stuck to the parts. These can be removed. Heat the base material part until the solder melts and wipe very quickly with a well dampened cotton shop rag to remove the big pieces.

A very thin surface coating that remains on the base material piece will not cause any problem for the next soldering attempt provided it is cleaned. Finishing Careful examination of quality long guns and other firearms with varying finishes will often reveal a fine silver solder joint. If your joint has some spillage onto the base metal outside of the joint fillet, this overflow spot will show through the final finish.

Good cold bluing solution will turn most silver solder joints darker and make them less noticeable. Let’s look at a couple sample jobs. We’ll start with a modified S&W Model 41 thumb safety. Many firearms do not enjoy the prolific offerings of custom parts such as those available for 1911 pistols. The original thumb safety on the Model 41 is small, can be difficult to operate and hard on the shooter’s thumb.

The existing thumb safety lever is a precision but fairly thin part with the pivoting hole in very close proximity to the thumb button contact area. However, there is enough surface area to surface mount a much heavier and larger thumb safety switch button. Note the fine fillet joints on both top and bottom of the new switch button. This work was performed by Gary Bunker in 2004. The results have proven very satisfactory, user friendly and durable over several years and hundreds of rounds fired.

Next sample is a Remington 700 safety. Breakage of this part was due to an accidental blow which caught the end of the safety switch, and not due to Remington’s quality design. The break was horizontal, directly across the tapered hole in the vertical lever portion of the safety switch. For reasons of safety concerns, this part is not available separately. Only the entire trigger assembly is available and it must be delivered to an authorized Remington Service Facility for installation.

Silver solder was used successfully to join the broken pieces back together. Note the existing hole in the switch lever was preserved, the modest dressing near and above the solder joint area to remove extra run-over filler metal, and the small "gold" colored spot at the right end of the joint caused by "glass" residue totally removed. After careful safety function checks, this rifle was returned to service with no problems. Safety and Disclaimer Safety starts with common sense.

The reader is expected to have an in-depth working knowledge of shop practices, including soldering experience. All of the usual disclaimers apply. As we have no control over the execution of these processes, we can assume no liability. Your results may vary. AG