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General Category => Tips, Tricks, Techniques & Tools => Topic started by: Burl on December 23, 2017, 02:49:01 PM

Title: Solder advice
Post by: Burl on December 23, 2017, 02:49:01 PM
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.

Title: Re: Solder advice
Post by: darrylhuffman on December 23, 2017, 05:02:35 PM
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.

Title: Re: Solder advice
Post by: finescalerr on December 23, 2017, 11:03:26 PM
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 ....


Title: Re: Solder advice
Post by: peterh on December 24, 2017, 02:38:27 PM
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.

Title: Re: Solder advice
Post by: Burl on December 25, 2017, 02:46:41 PM
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. 

Title: Re: Solder advice
Post by: NORCALLOGGER on December 25, 2017, 09:14:24 PM
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.

Title: Re: Solder advice
Post by: Lawton Maner on December 26, 2017, 08:05:00 AM
     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.


Title: Re: Solder advice
Post by: peterh on December 26, 2017, 12:13:25 PM
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.

Title: Re: Solder advice
Post by: Hydrostat on December 27, 2017, 01:48:04 AM
I'ts quite easy to get to good results with this brazing paste: https://www.bengs-modellbau.de/werkzeug/loetzubehoer/silberlotpaste-zum-hartloeten (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 (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.


Title: Re: Solder advice
Post by: Allan G on December 27, 2017, 10:41:40 AM
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

Title: Re: Solder advice
Post by: Bill Gill on December 27, 2017, 11:16:57 AM
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.

Title: Re: Solder advice
Post by: 5thwheel on December 27, 2017, 12:45:33 PM
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.

Title: Re: Solder advice
Post by: NORCALLOGGER on December 27, 2017, 04:27:02 PM
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.

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 :-[

Title: Re: Solder advice
Post by: 5thwheel on December 27, 2017, 08:55:53 PM
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.

Title: Re: Solder advice
Post by: Burl on December 28, 2017, 09:33:34 AM
I appreciate all the input from everyone.

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

Title: Re: Solder advice
Post by: 5thwheel on December 28, 2017, 04:37:32 PM
I have bought it from Rio Grande riogrande.com    It lasts a very long time.  melting point about 400 degrees. Very high tense strength.  Quite expensive now. Bill Hudson
They also have other types of solder paste in syringes for higher temp.


Title: Re: Solder advice
Post by: Hydrostat on December 29, 2017, 02:38:20 AM

Mr. Bengs ships to the US. English websizte: https://www.bengs-modellbau.de/en/tools/soldering-and-brazing/98/soldering-paste (https://www.bengs-modellbau.de/en/tools/soldering-and-brazing/98/soldering-paste)


Title: Re: Solder advice
Post by: Hydrostat on December 29, 2017, 02:39:34 AM
Sorry, links directs to the homepage. Please choose your language at top of it and browse the site ...

Title: Re: Solder advice
Post by: Lawton Maner on December 31, 2017, 10:04:01 AM
     The iron plating on soldering tips is to control the erosion which occurs when using plain copper tips.  Copper readily dissolves into molten solder and will pit making it difficult to keep the tip clean.  The iron plating retards this and makes the tips last much longer. 
     For solder to work, everything must be clean.  For electronic solder, a simple moist pad will work.  And there needs to be a microscopic gap between the parts for the solder to wick into the joint.
     To all a Happy New Year.

Title: Re: Solder advice
Post by: greenie on February 03, 2018, 07:24:33 AM
Apologies for a late answer to this posting.

If you want to use a soft solder for the job, then possibly this will help you out.

Go buy a roll of rosin cored solder, here's the kicker though, make sure the thickness of the solder is as fine as you can get hold of, the stuff I use is 60 Tin/40 Lead and the thickness is 0.56mm, or about 0.025" of an inch thick.

If you use this real fine stuff, you just cut a bit about 2 or 3mm long, place it under/wrap it around the bit your soldering to, then heat it all around the solder with a "bong lighter" or some other form of 'flame thrower'. By doing it this way you will NOT get any big blobs of bird shit solder on your job at all. Just check out how big 2 mm is and turn it into a blob and you'll soon get the idea of why using this very small amount is the way to go.

By using a fine flamethrower, it will just heat up the area you want the solder to run and join together, looking at the photo you have supplied, you are using sewing pins as locators. That's a good idea and if you wrap a small 2 mm piece of solder around the shank of the pin and when it's pushed into the hole in the frame, the solder is now exactly where you want it to be. So by using the fine flamethrower you just melting the EXACT amount of solder directly where you want it, easy peasy, eh.

If you want to use an iron with the solder added to the hot tip, then just look out for them birds, they gunna leave ugly great deposits of bird $hit, all over your nice clean job.

A soldering iron can be used for the heat in a particular spot, BUT, with NO HOT WET solder on the tip AT ALL, if you DO get any solder on the hot tip, then out with a file and file the copper tip clean of any solder, then right back at it with a clean dry tip.

Try this method out and you'll be pleasantly surprised with the good clean results you'll get without those ugly blobs of bird$hit.

Title: Re: Solder advice
Post by: Lawton Maner on February 03, 2018, 09:17:50 PM
     NEVER FILE A TIP USED FOR SOFT SOLDER.  If you do so you will remove the iron plating on the tip and the copper center will erode as the copper dissolves into the solder.  First use a damp sponge to remove as much solder as possible and then wipe it 2 or 3 times with a damp cloth to clean it as best you can.  Remember that solder flows toward the heat so heat the part on the opposite side from where the parts come together.  The copper wool which comes with some soldering stations also works well.
     60/40 electronic solder comes in very small cross sections and for many applications the amount can be TINY.  These bits can be held in place with a dab of rosin applied with the tip of a toothpick and yes, a pocket lighter can be used, but there are some very inexpensive pencil soldering torches out there that one might trip over in the $1.99 bin in strange places such as drug stores or even Dollar stores.  Always shop with yours eyes wide open.