Pro­fes­sor Ham­mer

Re­plac­ing Wood With Metal

Street Rodder - - CONTENTS - By Ron Covell

QI would like to thank you for a great col­umn and shar­ing your vast knowl­edge. I am a re­tired au­to­mo­tive en­gi­neer with many years of hands-on ex­pe­ri­ence, and I love build­ing hot rods. I am al­ways ea­ger to learn some­thing new and your writ­ing and DVDs have helped to im­prove my sheet­metal work­ing skills.

I am build­ing a “Dare to Be Dif­fer­ent” ’34 LaFayette four-door sedan, built by Nash. The body is a “Sea­man com­pos­ite hard­wood and steel body” in which most of the wood needs to be re­placed. What gauge steel tub­ing would you rec­om­mend to re­place the wood in the body? In the doors some of the wood is 3/4x1 inch, and there is no room for any­thing larger. Some odd sizes and shapes may re­quire fabri­ca­tion from sheet stock. Would you use the same gauge metal for that?

The sec­ond ques­tion I have deals with the rain gut­ter, which I would like to re­tain. The orig­i­nal con­struc­tion has a wood sup­port un­der the lower edge of the roof. The lower edge of the roof sheet­metal has a row of small slots punched through it. The gut­ter, which is formed steel, has a row of nails pro­trud­ing from the back side. The gut­ter ef­fec­tively “nails” the three pieces to­gether. When as­sem­bled orig­i­nally there was some type of seam sealer be­tween the gut­ter and the roof.

Since there will be no wood to nail the gut­ter to, I am try­ing to fig­ure out a good way to reat­tach it. I have thought about putting sealer be­hind the gut­ter and MIG weld­ing the nails to the top from the in­side. I am con­cerned about the sealer burn­ing dur­ing the weld­ing, al­low­ing rust to start there later. My sec­ond thought would be to solder the gut­ter to the roof af­ter the brac­ing is welded in­side. I am con­sid­er­ing us­ing a higher strength solder like a 70-30. I would ap­pre­ci­ate any sug­ges­tions you might have for at­tach­ing the gut­ter to the edge of the roof. Jack­Pat­ter­son ViatheIn­ter­net

A In many cases, 1/16-inch thick­ness tub­ing should be fine for re­plac­ing wooden struc­tures. If you have to build hol­low shapes from sheet stock this would be the min­i­mum thick­ness, al­though 14-gauge might be used in ar­eas where more strength would be ben­e­fi­cial. There are a few ar­eas where I would go thicker, such as the door­jamb ar­eas, where the door hinges and the latch striker plates go. You want th­ese to be very beefy, so I’d step up to a full 1/8-inch wall thick­ness in th­ese ar­eas, and any­where else where you want ultimate strength.

Re-at­tach­ing your rain gut­ter is a pretty chal­leng­ing prob­lem. I think your idea of sol­der­ing the driprail into place is prob­a­bly the best plan.

When do­ing sol­der­ing of this na­ture, you tin each part sep­a­rately, then align the parts, heat them gen­tly, and flow some more solder into the joint. If the body is in its nor­mal ori­en­ta­tion, grav­ity makes it dif­fi­cult to hold the gut­ter tightly against the body. It might be bet­ter to ro­tate the body on its side, so grav­ity will help hold the gut­ter against the body. There are ro­tis­series that are great for ro­tat­ing bod­ies, or in a pinch you could prob­a­bly roll the body gen­tly over on its side, us­ing an old mattress to cush­ion it.

Solder is des­ig­nated with the tin con­tent first and the lead con­tent sec­ond, so the 30-70 solder com­monly used on au­to­bod­ies is 30 per­cent tin and 70 per­cent lead. This lead-rich solder is de­signed to stay in a plas­tic state over a broad tem­per­a­ture range, to make it easy to pad­dle into shape, and it is not as strong as 50-50 solder. I’m con­fi­dent that 50-50 will be fine for your ap­pli­ca­tion. For ex­am­ple, mil­lions of ra­di­a­tors and gas tanks have been held to­gether with noth­ing more than 50-50 solder.

Steel tub­ing comes in a wide range of sizes and shapes, but for some odd-sized in­ner body struc­tures you may have to make your own by weld­ing to­gether strips of sheet steel.

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