TrailManor Owner's Forum - View Single Post - Shell Latch Mod / Entry Door Alignment / Slideout

10-29-2002, 05:16 PM

DenTed,

I am listening up, or rather, reading your interesting commentary. I believe that I understand your description of the TM Factory's fix for the problem of the latching bracket's screws pulling out: they install a steel strap that is placed underneath the existing upper bracket (that holds the latch pin) and secure both strap and bracket with 4 sheet metal screws. The strap must have 2 short pins that fit into the existing slots of the bracket so that the bracket will be fixed in place.

If this is correct, then it is almost like the fix that I used last year on the driver's side of my upper shell when that bracket pulled out. The strap that I fabricated, however, was a short one and only extended to one side of the bracket. It depended on using one existing screw (that was still holding) and a new one in the end of the strap. The strap also contained a short, welded pin that fitted in the other slot so that the bracket was fixed in place.

It's my opinion, however, that the Factory's modification still has its inherent weakness. That is, the screws, whether sheet metal or machine screws, are driven into a wall that is only 1/16" thick. The 1" square tube that makes up the bottom edges of both upper and lower shells has a wall thickness of 1/16". Conventional machine thread teaching tells us that there must be at least 3 machined threads in a part into which the screw is threaded. In a 10-32 screw the pitch of the threads is 0.03125". In a 1/4"-28 screw the pitch is 0.03571". In lay terms the "pitch" of a screw is the distance the screw advances for every single revolution. It is also the dimension between two adjacent ridges of the threaded portion of the screw. If a 10-32 screw were used to fasten the bracket to the 1/16" (0.0625&quot

thick aluminum wall, the hole into which the screw was inserted would contain only 2 threads. This might be sufficiently strong for a lightly stressed application. The latching brackets, as we all know, have to exert a considerable amount of force to hold a shell down. This resistive force must increase when the trailers are bouncing up and down on the roads while being towed; because the brackets must resist the momentum of the shells caused by this up and down motion. Sheet metal screws are coarse threaded. They were never intended for high strength applications such as holding latching brackets in place. They were, as their name implies, intended to hold sheet metal parts together. I believe that the Factory's modification eventually may fail in some of the trailers in which it's used.

Visualizing the Factory's mod as best as I can, I am still convinced that I can do a stronger modification by the method that I've planned. That method consists of replacing about 36" of the existing tubing (mine is also cracked at one screw hole) with a 36" length of 1" square aluminum tube with a 1/8" thick wall. At the part where I intend to drill and tap the screw holes for the bracket, I will slide a short length of 3/4" square aluminum bar into the tube. I will then weld the square bar to the tube using rosette welds. This will result in the bracket's screws essentially being threaded into a solid, 1" square bar. I will also reinsert the screws driven into the tube from the inside (fastening the tube to the inner sheet). I will also fasten the tube to the outer aluminum sheet with solid, Q-type pop rivets and machine screws (at the location where the tube contains the square bar). For those who are technically minded, I will use alloy 6063 square tubing and alloy 6061 square bar. These are both easily joined by TIG welding - first abrading off the anodizing if they are finished in this way. I've located a source for both materials, will order them soon and will do the repair in the coming month. Hey, I can't keep my TM mothballed too long. Winter will soon pass and it will be Spring again!

I couldn't visualize exactly what you did to take the flexing out of your slideout's floor. My slideout's floor also flexes and it annoys me a little every time I step on that part of the trailer.  ??? ???

I'll let you all know how my bracket's modification works out after I complete it. Theoretically, it should work out, but, sometimes snags do occur - such as aluminum misbehaving when it's welded.

10-29-2002, 05:16 PM	#2
Larry_Loo Guest Posts: n/a	Re: Shell Latch Mod / Entry Door Alignment / Slide DenTed, I am listening up, or rather, reading your interesting commentary. I believe that I understand your description of the TM Factory's fix for the problem of the latching bracket's screws pulling out: they install a steel strap that is placed underneath the existing upper bracket (that holds the latch pin) and secure both strap and bracket with 4 sheet metal screws. The strap must have 2 short pins that fit into the existing slots of the bracket so that the bracket will be fixed in place. If this is correct, then it is almost like the fix that I used last year on the driver's side of my upper shell when that bracket pulled out. The strap that I fabricated, however, was a short one and only extended to one side of the bracket. It depended on using one existing screw (that was still holding) and a new one in the end of the strap. The strap also contained a short, welded pin that fitted in the other slot so that the bracket was fixed in place. It's my opinion, however, that the Factory's modification still has its inherent weakness. That is, the screws, whether sheet metal or machine screws, are driven into a wall that is only 1/16" thick. The 1" square tube that makes up the bottom edges of both upper and lower shells has a wall thickness of 1/16". Conventional machine thread teaching tells us that there must be at least 3 machined threads in a part into which the screw is threaded. In a 10-32 screw the pitch of the threads is 0.03125". In a 1/4"-28 screw the pitch is 0.03571". In lay terms the "pitch" of a screw is the distance the screw advances for every single revolution. It is also the dimension between two adjacent ridges of the threaded portion of the screw. If a 10-32 screw were used to fasten the bracket to the 1/16" (0.0625&quot thick aluminum wall, the hole into which the screw was inserted would contain only 2 threads. This might be sufficiently strong for a lightly stressed application. The latching brackets, as we all know, have to exert a considerable amount of force to hold a shell down. This resistive force must increase when the trailers are bouncing up and down on the roads while being towed; because the brackets must resist the momentum of the shells caused by this up and down motion. Sheet metal screws are coarse threaded. They were never intended for high strength applications such as holding latching brackets in place. They were, as their name implies, intended to hold sheet metal parts together. I believe that the Factory's modification eventually may fail in some of the trailers in which it's used. Visualizing the Factory's mod as best as I can, I am still convinced that I can do a stronger modification by the method that I've planned. That method consists of replacing about 36" of the existing tubing (mine is also cracked at one screw hole) with a 36" length of 1" square aluminum tube with a 1/8" thick wall. At the part where I intend to drill and tap the screw holes for the bracket, I will slide a short length of 3/4" square aluminum bar into the tube. I will then weld the square bar to the tube using rosette welds. This will result in the bracket's screws essentially being threaded into a solid, 1" square bar. I will also reinsert the screws driven into the tube from the inside (fastening the tube to the inner sheet). I will also fasten the tube to the outer aluminum sheet with solid, Q-type pop rivets and machine screws (at the location where the tube contains the square bar). For those who are technically minded, I will use alloy 6063 square tubing and alloy 6061 square bar. These are both easily joined by TIG welding - first abrading off the anodizing if they are finished in this way. I've located a source for both materials, will order them soon and will do the repair in the coming month. Hey, I can't keep my TM mothballed too long. Winter will soon pass and it will be Spring again! I couldn't visualize exactly what you did to take the flexing out of your slideout's floor. My slideout's floor also flexes and it annoys me a little every time I step on that part of the trailer.  ??? ??? I'll let you all know how my bracket's modification works out after I complete it. Theoretically, it should work out, but, sometimes snags do occur - such as aluminum misbehaving when it's welded.