Solder advice

[Burl]

Some of my brass parts came in this week. I couldn't resist putting one together, but the only small diameter solder I had was electronics grade.  Since these will be in an area of the model likely to be handled, I'm concerned with strength.



What would the experts recommend as appropriate solder/flux for this application?  I got a resistance soldering unit a few months ago (obviously, I need a little more practice).  Thanks in advance.

[darrylhuffman]

Solder with resin or rosin core is best.

Rosin core solder will not hurt your brass.

Acid core solder is used in industrial applications but the acid will "etch" your brass parts.

Of course, Jerry Kitts is the authority I would turn to so he will probably have more complete advice.

[finescalerr]

If Jerry doesn't answer, and he hasn't posted here for a LONG time (the no good scalawag!) I'll pass along what my friend and outstanding modeler, Richard Christ, taught me: Use a butane soldering torch (unless you prefer something else), Stay-Brite solder, and Tix Flux. I am a ham-handed clod when it comes to anything involving metal but, using those items, was able to solder up a 1:32 scale loco cab from sheets of brass and it actually turned out neat and clean, with no excess or messy joints.

Probably beginner's luck, so I carefully have avoided doing much soldering since then ....

Russ

[peterh]

Electronics grade is good: if it doesn't hurt electronics it won't hurt your model.all soft solders have similar strength.

I'm surprised your joints look so black: can you set the RSU to a lower temperature. If you clean the black off (with isopropyl alcohol or by scraping) is there a good join underneath?

I would have expected each joint to have spread a bit further. Did you clean both surfaces first with very fine wet and dry sandpaper (use dry) or by scraping.

Soft solder isn't all that strong. Even with a perfect join you'll be able to peel/rotate those cross bars off surprisingly easily.

[Burl]

Soldering has never been my strong suit.  The resistance unit is new to me (I am obviously inexperienced with it), so I will try your suggestions.

What would you recommend if I moved away from soft solder, towards something harder?

I have some I bought at a long since closed hardware store that was labeled as "silver bearing" solder, and it makes a very strong joint.  The diameter is something like 1/8" though, so its not appropriate for this application.  If I could find something like that in a small diameter, I think I'd do better. 

[NORCALLOGGER]

Burl,
Just in general your brass alloys have a melting point of 15-17 hundred degrees. Moving up to hard solders (silver solders) they will have a melting point range of about 600 to 800 degrees depending on which one you choose. 

The soft solders (50/50, 60/40 etc.) have melting ranges in the 350 -500 degree range.  ( there are specialty solders with lower temps, not part of this conversation)

The reason I mention this is because it is awfully easy to overheat the work piece to fluid stage, especially with the small profiles  and hard solders. 

I don't use a torch because , in my opinion, it is way to difficult to control the heat, especially on small profiles.

I have very little experience with resistance units but to me they were awkward in use, again just my opinion.

Successful soldering, like most things in life, is all in the preparation.

As has been mentioned the correct flux is of critical importance.

The correct solder for the application is also very important.

Cleaning and preparation of the surfaces vitally important.

Tinning one or both surfaces can make a major difference. 

If your not doing live steam I would think that a good 60/40 soft would be more than strong enough.

A good electric pencil iron kept shaped clean and tinned will transfer the heat to the work piece very rapidly and with soft solder you don't risk the work piece.

Just a few quick thoughts, there are a number of good tutorials on the net on soldering.
Like most things, it's easy once you know how.
Rick

[Lawton Maner]

     Practice on scrap until you feel comfortable.

     I prefer a fiberglass brush for cleaning joints like the one you are doing, just don't blow them clean use a paper towel and MEK to wipe up the dust.

     Rosin flux is available at electronics stores and is easily applied with a toothpick.   
   
     As for the plumbing solder its OK to use it just apply the flux to both sides of the joint as soon as you have cleaned them and use a razor blade to cut a tiny bit of the solder from the end of the roll.  Apply the solder to the far side of the joint from the heat as once it melts, the solder will flow toward the heat.  Applying solder this way allows you to use a smaller amount and frees up one hand for other uses.  With solder, the smallest amount to do the job is the best practice.

     There must be a gap (think 0.001") for the solder to flow into the joint so if you are clamping the joint together, use a center punch to raise a dimple on one side of the interior of the joint to assure penetration.

     With the plumbing solder application above, you can hold the parts together with a pointed tool such as the end of a modeler's knife.  More complex joints may require fixtures to hold things together to get an accurate assembly.

     Clean the finished piece with hot water and an old toothbrush.  For acid flux, use a brass brush and finish with a hot bicarbonate of soda rinse.

     I have found the best tools to clean excess solder off the finished assembly to be engravers tools as they are sharp and come in tiny sizes making it easier to remove the excess.

     To add to Burl's very good observations.  An electronic soldering iron with a needle tip and temperature controls might be all you need for this project.

     To teach yourself the power of the resistance unit in a place with VERY GOOD ventilation clamp a small piece of brass scrap between the tweezers and crank the heat all the way up.  The brass will vaporize.

     Finally, if you are a tool junkie and plan on doing a lot of soldering or metal working in the future: Rio Grande Jewelry Supply ( https://www.riogrande.com/ ) has more then you will ever dream about.  Usual denials of connection apply.

     

[peterh]

I think soft solder and the RSU will be fine for this. There's lots of advice for using an RSU on the internet. Generally, you should use a solder paste/cream so the solder can start out in the join (you don't need to artificially create a gap). And always use a separate liquid flux. Because the purpose of the flux is to clean the joint before the solder flows.

[Hydrostat]

I'ts quite easy to get to good results with this brazing paste: https://www.bengs-modellbau.de/werkzeug/loetzubehoer/silberlotpaste-zum-hartloeten (no additional fluids needed). I use a simple kitchen flambé torch for both soldering and brazing and with a little bit of exercise you won't melt down your castings. The washers with splints (0.2 mm diameter) shown here http://www.finescalerr.com/smf/index.php?topic=2355.msg52048#msg52048 are brazed the same way on a piece of chamotte stone for oven construction. According to your ladder there will be no problem to fix the parts with some needles for brazing.

Btw: I'm following your thread with big interest. Your approach and results are outstanding.

Cheers,
Volker

[Allan G]

This is  a real rookie comment. Reading many articles I have found that adding the solder to the iron (not the actual joint) works best for me and the right flux is critical. Comments? ....Allan

[Bill Gill]

The only soldering tip I know is if you use a soft graphite pencil to draw a line around the perimeter where you want to constrain the solder, the solder will not flow over the line.

[5thwheel]

For what it is worth.  Mainly I work in larger scale tin ware but I also worked in very small Ho brass stuff in the past.  Having a life time supply of 50-50 left over from stained glass business that is my main go to solder for the larger stuff.  For the Ho I like lower temp solders like Tiff or Stay Bright. Both are very low temp but very strong. The low temps use a liquid acid like flux but washes off easily. Rosin cores or rosin flux is messy and hard to clean up.  I use either a soldering iron or a mini butane torch.  I converted an electronics variable temp iron from an iron tip to a copper tip. I turned down a length of 3/8" copper bar to match the iron tip.  The copper holds the heat and solder best. Using hard solders requires a torch and that in turn anneals the brass taking the stiffness out of it. It is important to wash your work to remove any flux residue.  Even rosin will corrode in time.

[NORCALLOGGER]

That is interesting Bill.  I have never seen or heard of an iron soldering iron, only copper.
I agree with you completely about using liquid flux rather than pastes.
Rick


OK, I looked it up, apparently they are using a thin iron plating over copper on the tips of RS and electric pencil soldering tips/points/ends what ever.  Seems odd to me when the copper gives much faster/better heat transfer and is very easy to shape, clean and tin. 

I think the iron covering is used in machine controlled soldering situations where the temperatures can be constantly and completely controlled. 

Overheating is the biggest issue in maintaining a soldering tip.  Just a few degrees over for just a few minutes will pit and burn a tip.  The smaller the tip the faster it can happen. 

I built a little control box using a dimmer switch and a plug in, it gives much better control and saves the iron when I lay it down for a second then get sidetracked for several minutes clamping the next pieces together

[5thwheel]

The tip on this iron was solid iron or steel.  Like you I thought it might have been coated but not so. I turned the copper tip to 3/32dia. x 1 2/2" long and the tip filed to a pyramid  shape.  This gives me various ways to solder from flats to pointed tip. I found the soldering iron at an electronic supply store for $19+.  It is variable from off to high so I can turn it down and let it cost when jigging up. If you can keep a moist sponge handy you can wipe your tip before putting the iron down. Also if you can keep a small open container of water you can dip the hot tip down into it and blow away some of the crud from the tip. Also having wad of steel wool handy to rub the tipon will help keep it clean. This helps delay the pitting and eating away of the tip. Nice thing about the large size of the long tip is that it can be filed down many times as needed and can be reshaped as needed.

[Burl]

I appreciate all the input from everyone.

Volker: would you happen to know anywhere in the US I could buy that paste?