Steel weighs 0.283 lbs per cubic inch, while aluminum weighs 0.100 pound per cubic inch. So the weight penalty for steel of the same size and thickness is significant. But steel is also stronger, so you can use thinner material. Of course the strength of each is related to the alloy, so if you compare high strength aluminum alloy vs mild steel, the weight savings using aluminum can be significant. Then again, if you compare a low strength aluminum to high strength steel, you will find they're usually very close for strength to weight. Designing parts like seat brackets involves lots of decisions and trade offs...since they're not generally very big, weight is not usually a big concern, but strength and ease of fabrication might be.
Wow. This is why I love the h.a.m.b. So much shared knowledge! After reading all the responses, i think i might use both steel and aluminum. I found a set of adjustable seat tracks in my stash. I think I'll use steel to adapt the seat to the tracks for the driver side. For the passenger side, I think we'll use aluminum to mount it solid with no adjustment.
^^^^ Please just be safe above all . I would like to know what exactly is your vehicle of choice and your specific plan(s) . A driver, racing like cross country off road where there are two people (driver/navigator) drag/ street racing etc. You say light weight seats , gives me an empty pit in my stomach. Are they aluminum, fiberglass or carbon ? How you mount them to spread force and particulars like bolt size and grade , washers and nut type also plays a big part in applied force , shear and your health.
I am reminded of a phrase that has always stuck in my head:"Take care of the ounces , the pounds will take care of themselves..
Well I didn't wanna get into the vehicle cause it's not real h.a.m.b.freindly. it's my kids car we built for bracket racing. The seats are the typical plastic Jaz racing buckets that summit sells. I got them with the vinyl covers for cheap. They weigh 10 pounds each. Obviously I wanna be safe but I don't wanna build 50 pound brackets. Ha. Like I said, the car's not h.a.m.b. friendly, but this is my go to place for knowledge. And MY cars are h.a.m.b. friendly
Given that its your son doing the racing, I would err on the side of being a little too heavy but strong. Having a seat mounting bracket thats "just strong enough" is not the best way. What I'm thinking is that if a seat bracket eventually fails during hard acceleration, it could cause loss of control. I think your decision to use an existing well engineered steel mount is a wise decision.
If the car has a roll bar or cage, the back rest also needs to be supported by the cross bar. This takes some of the load from the seat brackets themselves. You might be able to use extruded aluminum angle on the floor, and on the seat, and them bolt them together. It depends on the shape of the floor, and how high the seat sits off the floor. 1.5 or 2 inch angle, 1/8" thick, might work for this. If the seat sits too low, you can add a flat piece of 1/8" sheet between the two angles. If the floor is really uneven, then you might have to make front and rear brackets for the floor.
One thing I didn't see mentioned was the size of the person sitting on the seat. Seat brackets to hold a person weighing 150 lbs are a lot different then seat brackets holding a person weighing 300 lbs. A seat that can flex the brackets and move is bad news. I'd find a different place to save a few lbs other then seat brackets. Steel seat brackets in everything I build, and I usually bolt the belts to the seat brackets. If the seat is attached to the cage, that is better yet. Gene
It all depends on how the brackets are configured. How does it attach to the seat? How does it attach to the floor, if indeed it's the floor it attaches to? How many fixings, at what kind of centres? What kind of length and height? What kinds of beam conditions are involved? It's a bit the length of a piece of string. Aluminium alloys are prone to fatigue, so allow generous safety factors. For available extruding alloys, I shouldn't design to more than about 9000psi, though you'll see ultimate tensile strength of more than three times that quoted.
There are many educated knowledgeable men on here. Think/research about tech advice here or anywhere. When one starts quoting their degrees, always remember, associate degree- Ass, Bachelor of science degree- BS, the coveted "PHD"-piled higher deeper. This post is not meant as disrespect for education, lt's an attempt at humor from a Tradesman, small business owner that dealt with many highly educated "Train Drivers" engineers for many years, way too many Experts, these are just a few observations of mine. Sidenote, 3 of my 5 children are college grads, other 2 self employed, all successful, appear to be happy normal people in spite of me. LOL
I live near Kalamazoo MI, there are several supply houses here, in a pretty small market. ALRO Steel has a retail outlet where one can buy "drops" of all kinds of structural steel tubing, bar, angles, flat stock, sheet. Aluminum, stainless, brass, copper, you name it. Schupan Aluminum sells new, buys and sells scrap. I would think a quick Google search from whatever town you're in or near will point you towards a much better source of stock than a big box store. I have to say I LOVE going to ALRO, it's fun to think about all the stuff I could make!
IMS in Tucson has a pretty good selection. It's a 4 hour round trip for me....so I end up getting stuff in town at the big box store, or the welding supply store.
No doubt. I’m a mech eng, and wouldn’t even think about trying to tackle that from a first principals approach. Yes for static loading, but dynamic loading is whole other animal. Worked with Mercedes-Benz to determine cause of multiple floor cracks in our newly purchased armoured G-Wagons for the Canadian Army. Took them 2 months running two super computers to model what was causing the cracks. Of course, before you could even start, you needed to instrument a test vehicle to gather all the empirical data/forces required for the model.
Another way to deal with the analysis is to see what works, and what doesn't....reading the rules of various racing sanctioning bodies, pretty much does this, as the rules have been written with blood.
I had a chunk of the 2" L under my workbench stuff that I bought at ACE hardware. I cant tell you how strong it is but it polishes up real nice. and that is just 1500 grit, hasn't seen the buffer yet. I was surprised how easily it bent. In that 1st picture I had used the bandsaw to split the L in two in order to make that switch panel plate. The ragged end was from a plasma cut (turn the juice down when cutting aluminum) and I bent it over so I wouldn't snag myself on it. I thought it would break but it I guess not. So I guess what I am saying is, if you want to polish those seat brackets, it should work out just fine. I'm not a mechanical engineer, just a polish engineer (that's polish not Polish @DDDenny !)
Just build it, install it, check it at the end of each season, replace when necessary. We used to call that trial and error. The odds are the bracket will get loose and sloppy before it breaks, the concept is to replace it before it breaks. That is the traditional way. In the last 28 years, I've repaired a lot of automotive factory seat frames and seat brackets that didn't work like they were suppose to. Even with all the engineering the auto factories have available, sometimes stuff doesn't work like its suppose to. Gene
25 % of the seats I work on need welded. And I work on seats on a weekly basis. If you don`t look for cracks, you aren`t gonna find them. Some styles: every one you run across needs welded.
That was the reason I said in an earlier post that I wouldn't use aluminum seat brackets in any car or truck I build. I've seen way too many thin steel brackets and seat frames cracked or broken to even consider using aluminum. Gene
As I alluded to before you need to focus on what fasteners you use. I do not put much faith in those plastic seats and if God forbid he hits something hard or rolls it , a plastic seat is the would be the last thing I would want under my butt. Use the right bolts , nuts and washers. Any material can crack or tear around the mounting holes on the seat so don’t use a regular washer and call it good. You need washers that are going to spread the force and not pull through.
One other thought. If you are concerned with weight regarding seat brackets , remove the passenger side seat before going or at the track .
Sometimes car seats get broken because they are stressed beyond what they were designed for...........
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