adding a fish plate or pin to throw-off lever (c&p 8 x 12) {updated}

If welds are breaking, I would ask around for someone who could braze it. I have had great success with several broken cast parts which were brazed by a local fabrication shop. If welding is all you can find, perhaps they should “sister on” a parallel bar of metal to strengthen the joint.

There’s little shear strength in a braze weld. I suggest the reason the previous welds have not been successful relates to the ‘burning’ of the parent metal by over-zealous application of direct heat in order to promote the brazing metal’s flow. That, and/or sloppy joint preparation. Proper cast welding of the break will now pose problems to a competent welder’s attempt to correctly effect repair. The addition of a fish plate or internal pin with which to strengthen the throw-off lever is sound advice; it’s astonishing how much pressure is exerted on that lever; and it’s all shear.

If you don’t know anyone to ask, call the oldest machine shop in town. They should be able to help.

thanks for the sound advice! I’ll call around

I found what seems like a good place…

I’m thinking adding a “fish plate” is probably a good idea. Now, of course I’ve left the lever at the shop & can’t visualize how thick of a plate could be added to the lever. I need to call the welding shop ASAP…

Could anyone near a C&P (or someone with a good memory) let me know how much ‘wiggle room’ there is?

Thanks!!

Before welding or adding a Fish-plate, I recommend that you re-visit the idea of brazing. After seeing several blanket “brazing is weak” comments on this forum, I pulled my ASME books off of the shelf and researched the matter. ( I am a Mechanical Engineer, by the way).

Actually, the Nay-sayers would have been right in their assumptions about welding vs brazing a few decades ago, but not today. The alloys have come a long, long way since the 1970’s.

The truth is that brazing is actually superior to welding, if done correctly. The brazing alloy is stronger in tensile strength and shear than cast irons of yesteryear, and the process does less damage to the surrounding base than welding does. In many, many tests, primarily by D.R. Totty of J.M. Metals and the ASME, the base metal breaks before the brazed joint.

Their tests are quite well documented, and accepted as our National Standard. If you doubt this, please reference ASME guidlelines for welding and brazing, and the related publication “Welding and Metal Fabrication rev 10/80”. I believe that they are available on the Internet.

I agree that poorly done brass and/or nickel based brazes are indeed inferior for cast iron….. but not all brazes. Alloy “Argo Braze 49 H” which is readily available, is a superior choice. It is a relatively low-temp alloy (700c) which is actually an advantage since it minimizes degraphitization, crystaline changes, and internal oxidation ofthe base metal… and it has superior wetting/adhesion properties.

“…the base metal breaks before the brazed joint (does).”
Precisely my point. Braze rod (largely a brass composite having selected additive metals) is a dissimilar metal to the cast iron. In the joining procedure, the cast must only be heated to the flow temperature of the brazing rod, not the melting point of the cast. In that doing, carbon ( plus other impurity) is brought to the cast surface which causes a physical barrier to be formed between the brass and cast. Additionaly, the difference of temperature causes a molecular repulsion as well. Yes, there have been great improvement in braze metals/fluxes in attempts to minimize such barrier. But no, it remains that the brazing technique is not superior to a true weld - simply because of the introduction of that aforementioned dissimilar metal. Welding produces a true melding of metal; brazing effects an ‘adhesive’ approach. Having the chunk of braze remain intact after the cast re-breaks is proof that a true join has not been achieved. And, not to put too fine a point here, one should remember that engineers designed the Tacoma Narrows bridge, the Challenger, and proved, conclusively, that bumblebees are unable to fly. Not all the answers are contained in the classroom textbooks.

Good points in our friendly debate Mr. Forme.

It is refreshing to discuss such matters with someone who understands the problems involved, even if we disagree on technical points. We could discuss this topic endlessly, especially about the finer points of adhesion, carbon outgassing and crystaline changes…. and probably not reach a definative agreement. (Even the various ASME members debate this matter, and they don’t always concur either.)

BUT I am sure that we both agree that the quality of the workmanship is the most important factor…. especially when we are talking about cast iron.

Now… on to the bumblebee thing….. it was not an Engineer who decried the Bumblebee, it was sir George Cayley, a scientist. As far as the Tacoma Narrows Bridge goes… oops, sorry.

WCP: Agreed. Workmanship is root of all successful endeavour. And great answer on ‘Galloping Gertie’! :o)