Post by wisconsinjoe on Sept 1, 2021 6:19:13 GMT -8
There are so many things that cause me anxiety in this hobby. One thing that bugs me is poorly bent J-rail. How to get a nice smooth curve? Here is my method.
First bit of advice is to have a helper, because it worked so much better when there were two of us working the final step of actual bending. The trick is to make a bending form and heat the aluminum.
20210830_163854 by Joe Mirenna, on Flickr
Since I had templates for the four corner bends, it was easy to cut those profiles from some scrap ¾ inch material, in this case some melamine particle board. That was screwed to a scrap piece of OSB. Because each bend led to a straight section, I was able to attach an additional stop to the bending form. That was made by routing out a shallow rabbit for the flat part of the aluminum to slide under and be securely captured.
20210830_163908 by Joe Mirenna, on Flickr
20210830_164013 by Joe Mirenna, on Flickr
From there the J-rail is marked with a sharpie to identify the position for the bend. Now the straight rail can be slid out from its position, supported at its free end, heated, and then slid back for the bend. The one cool trick (...learned from YouTube) is to mark up the aluminum with a black sharpie. The black marks will fade noticeably when the aluminum is properly heated. It is important to use MAPP gas rather than propane because it is hotter. For a bend about 24 inches long it should take only about 3 or 4 minutes of torching, moving the flame back and forth slowly (but not so slow that one end can significantly cool off). A longer bend takes more heat time because that aluminum quickly cools, causing you to move the flame faster along the metal.
20210830_164027 by Joe Mirenna, on Flickr
Once you think the metal is ready (the black marks will still be visible, but greatly faded), push it back to the position registration marks and bend to the form. Of course use heavy oven mitts because the metal is HOT. The first time I did this by myself the rail buckled from being so soft. I quickly used some screws to hold it down and in position. It was a little sloppy and needed some plier work to reform the buckled metal. It will clean up reasonably well with sandpaper and steel wool.
20210830_164945 by Joe Mirenna, on Flickr
20210830_164957 by Joe Mirenna, on Flickr
The process worked much better when my wife helped me. Together we bent slowly until the metal met the form at the first screw hole position. At that point I drove in a screw and we continued until all holes were screwed to the form base. BTW, I slipped a piece of ¼ inch scrap plywood under the clamped form to keep the screws from driving into my work bench.
I was pleased to see how nicely the J-rail bent smoothly. Once it gets removed from the form after just 15 minutes of cooling time, it still may need a bit of flattening, but the important bend will be nice.
20210830_165806 by Joe Mirenna, on Flickr
20210830_190716 by Joe Mirenna, on Flickr
Although the form is created from the template representing the outer edge of the camper profile (with the actual J-rail positioned INSIDE that edge), it is okay that the aluminum is bent on the outside. When unscrewed from the form, it will spring back a bit anyway. What is more important is accurately measuring and aligning the STRAIGHT sections between bends. I’ll make sure not to destroy those alignment marks completely when cleaning up the aluminum for assembly. That way I’ll be able to properly align the piece with the straight sections on the camper to follow the profile all around.
First bit of advice is to have a helper, because it worked so much better when there were two of us working the final step of actual bending. The trick is to make a bending form and heat the aluminum.
20210830_163854 by Joe Mirenna, on FlickrSince I had templates for the four corner bends, it was easy to cut those profiles from some scrap ¾ inch material, in this case some melamine particle board. That was screwed to a scrap piece of OSB. Because each bend led to a straight section, I was able to attach an additional stop to the bending form. That was made by routing out a shallow rabbit for the flat part of the aluminum to slide under and be securely captured.
20210830_163908 by Joe Mirenna, on Flickr20210830_164013 by Joe Mirenna, on Flickr From there the J-rail is marked with a sharpie to identify the position for the bend. Now the straight rail can be slid out from its position, supported at its free end, heated, and then slid back for the bend. The one cool trick (...learned from YouTube) is to mark up the aluminum with a black sharpie. The black marks will fade noticeably when the aluminum is properly heated. It is important to use MAPP gas rather than propane because it is hotter. For a bend about 24 inches long it should take only about 3 or 4 minutes of torching, moving the flame back and forth slowly (but not so slow that one end can significantly cool off). A longer bend takes more heat time because that aluminum quickly cools, causing you to move the flame faster along the metal.
20210830_164027 by Joe Mirenna, on Flickr Once you think the metal is ready (the black marks will still be visible, but greatly faded), push it back to the position registration marks and bend to the form. Of course use heavy oven mitts because the metal is HOT. The first time I did this by myself the rail buckled from being so soft. I quickly used some screws to hold it down and in position. It was a little sloppy and needed some plier work to reform the buckled metal. It will clean up reasonably well with sandpaper and steel wool.
20210830_164945 by Joe Mirenna, on Flickr20210830_164957 by Joe Mirenna, on FlickrThe process worked much better when my wife helped me. Together we bent slowly until the metal met the form at the first screw hole position. At that point I drove in a screw and we continued until all holes were screwed to the form base. BTW, I slipped a piece of ¼ inch scrap plywood under the clamped form to keep the screws from driving into my work bench.
I was pleased to see how nicely the J-rail bent smoothly. Once it gets removed from the form after just 15 minutes of cooling time, it still may need a bit of flattening, but the important bend will be nice.
20210830_165806 by Joe Mirenna, on Flickr 20210830_190716 by Joe Mirenna, on FlickrAlthough the form is created from the template representing the outer edge of the camper profile (with the actual J-rail positioned INSIDE that edge), it is okay that the aluminum is bent on the outside. When unscrewed from the form, it will spring back a bit anyway. What is more important is accurately measuring and aligning the STRAIGHT sections between bends. I’ll make sure not to destroy those alignment marks completely when cleaning up the aluminum for assembly. That way I’ll be able to properly align the piece with the straight sections on the camper to follow the profile all around.
