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  • Mechanical joints using solder?

    Got a question about using solder for mechanical joints. What kinds of solder are acceptable, and what type of fit is used for each?

    The details:

    The threads were shot on the tail stock screw for my lathe. So I ordered some 1/2-10(L) precision acme screw from McMaster. Once it came in, I worked out the correct length for full travel and ejecting the taper and cut to length. Next I parted off the old one threaded rod and drilled/bored the bearing shaft portion. Opps, made a mistake and bored it too large, oh well, no big deal, there will just be a bit of the thread root left rather than a smooth shaft. Should give more room for the solder to flow in to the bottom. Turned the 3/4" long male part of the joint in the screw to a light press fit in the bore and I'll freeze/heat for mating. Should be about 0.0005 interference fit.

    Now, will common 50/50 lead/tin solder hold this? Or should I bite the bullet and go buy some silver solder tomorrow at the welding supply? I've used the stuff before, but no idea the formulation. I know silver solder has gotten stupid expensive, what alloy is the best balance of cost/strength/ease of use for these type of mechanical joint projects? AFAIK, MAPP gas should be fine for a heat source, and I would like to use that for convenience with small parts, but I have O/A and some small welding/brazing tips if needed.
    Russ
    Master Floor Sweeper

  • #2
    Silver solder

    Dont realy know But i would at least Silver Solder it
    Every Mans Work Is A Portrait of Him Self
    http://sites.google.com/site/machinistsite/TWO-BUDDIES
    http://s178.photobucket.com/user/lan...?sort=3&page=1

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    • #3
      But then, what alloy? From what I see, it ranges from around $80+ for 10 oz of "bulk" sticks down to somewhat reasonable $20+ for a 16 oz bag of sticks (though those only mention copper and the like for applications, not steel, seems for plumbing?).
      Russ
      Master Floor Sweeper

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      • #4
        Dog,
        I'm having a little trouble picturing exactly what you're doing. It seems you want to attach the new screw to the old stub and the bottom line is you have a press fit screw to bore you dont want to spin.

        Why don't you cut a keyway and key it or pin it, or cross drill and setscrew. I think there are lots of solutions but you need enough clearance for capillary action of the solder to flow throughout the joint for strength. Otherwise you just have a solder plug that will not withstand rotational torque.

        50/50 might be OK to plug a radiator, but I think I would go a little stronger in a mechanical application.
        Last edited by LarryinLV; 09-16-2006, 12:24 AM.

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        • #5
          BadDog,

          You want to "Silver Solder" or "Hard Solder" it with 45% Silver Brazing wire, not Silver Solder as used in electronics. Hard Soldering is actually a form of brazing and involves solder that has a melting point above 450 C (800 F).

          Any welding supply store will carry it. It's expensive, but an ounce of wire will last you a long time.

          Edit: I just checked in my shop, and I use J.W. Harris Safety-Silv 56 (56% Silver Brazing Wire)

          http://www.jwharris.com/jwprod/hisilverbrazealloys/#56

          High-Silver Brazing Alloys

          SAFETY-SILVآ® 56 - This high silver (56%) content alloy makes first quality brazes.It is free-flowing with unequaled capillary attraction and deep penetration. Ductility is high, corrosion resistance suitable for all but strong chemical applications. Offers highest elongation of silver brazing alloys. Suitable for use in the food processing industry. The silver color is an excellent match for stainless steel and silverware applications. NSF Certified to NSF C2.

          Robert
          Last edited by lazlo; 09-16-2006, 12:26 AM.
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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          • #6
            I am by know means an expert, but here are my thoughts...

            I picked up some silver solder off ebay last year (Vulcan's workshop?/No affiliation) it's either 50% or 60% silver--don't have it right in front of me now. Anyway this stuff is killer for joining bandsaw blades and I would think it would have plenty of tensile strenth for your application. As far as the expense part goes, I have also had great results with the flux-coated brazing rods you can get at the big box/tractor supply-type stores. A package of 4 or 5 is only 2-$3. I believe they actually produce a stronger weld than silver solder, but they also require a bit more heat. Not good for bandsaw blades but probably okay for what your doing(?)

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            • #7
              With the kind of interference fit you're describing, I doubt you'll have any luck wicking the solder into the joint. Yes, the groove created by the thread root will help with this, but you'll also want to have a vent hole so that gasses can escape as the solder flows in. I would opt to use silver braze rather than tin/lead solder, as the flux has a better chance to clean away oxides to allow proper wetting by the solder. Another thing to consider is that silver solder needs a gap to flow into, so if there's an interference fit between parts, it won't want to flow in there. That safety silv 56 might be better for this than other alloys, but I don't know. Do you want to experiment? Possibly mess with the heat treatment-?

              I would be most inclined to pin it, as Larry suggested, and forget the solder. You have alignment already because of the close fit- a roll pin can be pressed in and will not allow any rotational slop- then can be pressed out when or if another repair is ever needed.
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #8
                Larry:
                I have nothing that will make a keyway inside a 3/8" hole with reasonable effort. And my first idea was a roll pin, which should work well with the light press, but that comes up right in the bearing area. No big deal I guess, but I figured to avoid it using the solder. I've seen it used for other stuff like this, and it seems a good thing to know/have, hence this question. And you mirror my thoughts on the 50/50.

                Lazlo:
                That's exactly what I needed, but not what I hoped to hear. That's expensive stuff...

                SideGrinder:
                I also thought of brazing, but brazing rod doesn't flow well from my experience. That also leads into my question about clearances for the various options. I'll have to check into the ebay sources...

                Darryl:
                The interference fit was a first thought and at least gives me options. As I indicated, I have no idea what the proper fit is for (hard) solder or brazing rods in this application, and I can always turn it down further. Not really to enthusiastic on experimenting here, and yeah, 800*F is getting into annealing range for my B7 threaded rod.

                So yeah, maybe I will just put a 1/16" roll pin in there. Shouldn't really affect the bearing surface and with the interference fit, it should be more than adequate... And with the pressure off, I can look into the ebay and on-line sources to save a few bucks on hard solder/silver brazing rods for future projects.

                Thanks all...
                Russ
                Master Floor Sweeper

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                • #9
                  Yow, make that 1200*F for the SafetySilv 56...
                  Russ
                  Master Floor Sweeper

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                  • #10
                    Not sure if I understand what you're trying to do,but it sounds to me like if you make the part a sliding fit some Loctite would work.

                    Allan

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                    • #11
                      I did think of the Loctite too. In fact, I was considering my "bearing and sleeve retainer" green Loctite (whatever the number). And of course, there are all the new adhesives that have high claims. Then I got off on the solder option, but maybe I should sniff around on the Loctite site later for more info...
                      Russ
                      Master Floor Sweeper

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                      • #12
                        The crossfeed screw in my Clausing was worn out. I spliced in a new piece of precision acme rod with silver solder. I believe it was 45%.

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                        • #13
                          I have nothing that will make a keyway inside a 3/8" hole with reasonable effort.
                          It depends on what you consider reasonable. Make a plug to fit the hole and drill and tap about 10-24. Put plug in hole. Drill 1/8" axial hole so that hole cuts half of the plug and half of the ID of the bore. Use 10-24 screw to extract plug. Toss plug.

                          Bore a hole in a piece of steel to fit end of lead screw shaft that fits in hole. Put lead screw shaft in hole. Drill the same size hole in the same manner so that a half round keyway results in the shaft.

                          Assemble with a 1/8" pin in the new round keyway. Some loctite wouldn't hurt either.
                          Last edited by Evan; 09-16-2006, 02:19 AM.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            Any solder will require some clearance to work, usually 2-3 thousandths. In a low stress application like yours, lead or low temp silver bearing solders will probably work as well as anything. You will need to remachine the parts to allow the solder to flow into the joint.

                            Since you have a light press fit, Loc Tite will work as well. There is a press fit enhancer available, or the sleeve & bearing will probably work.

                            Make sure both surfaces are clean and free of grease & oil, use acetone, brake cleaner or Loc Tite promer to clean. Coat both surfaces and install with a twisting motion if possible.

                            With something like this, I always try the simplest fix first. There is nothing to loose, and you may be happily surprised. If the loctite fails, then remachine and use solder or silver braze.
                            Jim H.

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                            • #15
                              Originally posted by BadDog
                              Lazlo:
                              That's exactly what I needed, but not what I hoped to hear. That's expensive stuff...
                              It's not that bad -- $15/ounce. An ounce will last a long time.

                              I've bought from these people before -- they're great:

                              http://www.cycledesign.org/brazingandsilvertoc.htm

                              I think the roll pin would work well also -- the point of this exercise is for the screw thread splice to resist the torque from the keyed end driven by the tailstock handwheel.
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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