So I'm a Mechanical Engineer, and I decided to just make my own body armor for below the doors, and later on maybe the cab corners, etc. My initial intent was to just make the body armor span the entire lower portion from wheel to wheel, which I still like, but over the weekend I was thinking that if I bought any aftermarket rear fender flares or any other products that were designed to fit with rocker guards that only went between the factory flares, they wouldn't work with mine, and so I thought I'd get the opinions of some people that have done this a lot longer than me to see what you guys like, prefer, feel is best. I also thought about maybe after I get all of the R&D done, I might just sell sets of these to who, like me, wanted some, but didn't want to spend the $300 to $400 that some places charge for them. Anyway, let me know what you guys think.
Thanks,
Doug
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A mechanical engineer? Awesome, I can explain some rules to you that are pertinent with the knowledge that you will fully understand them and then incorporate them into your design.
1- wheel well to wheel well only. Any other option leaves parts of the sheetmetal on the sides and underneath particularly vulnerable to damage that is very difficult to repair. Any flare will only have a small gap of 3/16" at the top of the rail to 0 right at the first attachment bolt for the flare above the rail. Hardly noticeable.
2- Sheet metal is thin and flimsy. Lots of small fasteners should be used to attach rail to tub. Rail should extend under to the torque box with a double bend to put the lower edge of the rail at the highest point or just at the lower edge of the tub. 2 rows of offset spacing not directly over each is best if you can handle the asymmetry. (I can't) 5/16" is the largest you should use and use nutserts to continue the pattern. Don't forget or overlook that the small 5mm screws that hold the flares on can easily distort the sheet metal simply by rubbing the plastic flare on a rock or tree. Think unitized structure like a riveted plane body or wing with lots of small fasteners.
3- Use backing plates to sandwich the sheet metal under the doors and inside the rear wheel wells. Use large "extra thick" fender washers inside the front fenders to pick up that area and spread the load.
4- Use nutserts to attach to the flat bottom section of the torque box. Keep the spread no longer than 8" if possible.
5- Avoid the use of hex socket flat head cap screws in countersunk holes. The driver size is very small for the thread shank diameter and presents torque problems when trying to achieve the proper clamp load. It is common to strip the hex when trying to remove due to the large amount of surface contact in the countersink zone. #4 Phillips has a larger driver size. Avoid the lower grade Stainless Steel which is softer. You don't need the super high strength stuff but the medium grade is fine.
6- Tube used as a step has issues. When used in the rocks, the tube collapses and typically bends. If you do intend to make a tube step, make it a separate item that bolts onto the face of the rail. Also consider using black iron gas pipe. Cheaper with a heavier wall thickness that stands up to the abuse far better but it needs special size bending dies.
7- Consider a backer on the tub that notches around the body mounts. Do not use any part of the body mount or brackets to attach the sliders. They have a job to do, let them do it and leave them alone.
8- This one is important- The total angle between the torque box surface and the outer face should be 1-2 degrees under a 90 degree angle. That way when you mount the rail, it requires that you use a jack to force it up into position and that adds some desired pre-load to slow down upward displacement when you slam down onto an obstacle.
9- Have the folks who do the bending step down about 5/8" from the top edge of the rail and put a slight bend inward of about .5-.3/4 degree. What that does is stiffen the upper edge and remove any warp that show up from relieved stresses when the material is cut or sheared. That puts the upper edge in full contact with the tub and makes it look like you know what you are doing when you design a product.
10- Be mindful of your clearances and don't give back hard won fractions of an inch. If you lay a straight from the outer edge of the torque box to the lower edge of the tub, that is about a 10 degree angle. If you do a bolt on step that attaches to the lower face, continue that same angle on the bottom of the step so you don't lower the clearance gains.
If I think of more, I'll add it later but that will get you started and by the time you get all that figured out, put into production, fasteners sourced, and the R&D done, you'll think some of the higher end rails out there are a bargain at 500 bucks a set.
