LocostUSA.com

Hello,

It was brought to my attention that many people don't look through all the build logs, and that potentially some benefit could be had by locosters and fellow lo-costy people from me duplicating info on my seating project here. I'm building a custom tube frame MG midget, and am currently building some seats. I originally intended to build some Kirkeyesq seats, however the cost of the aluminum alone was more than the seats. Looking at other options I discovered that appropriate seats for our automobiles start at about $300 for the pair and go up from there. This was unacceptable to me so I am tackling building my own seats. I've looked at most of the attempts people have made and seen that most resources are dedicated to fiberglass/carbon fiber seats. The weight of these can't be beat, and done properly the comfort/look is second to none, however fiberglass wasn't for me. I don't like doing fiberglass projects and I would have to buy a bunch of new tools/supplies. So I reasoned the rest of the car is going to be steel tube frame with thin skin over the top. Why can't the seats?

So after that pre-amble (hope your still with me), I'm going to chronicle my either success or Failure of steel tube frame seats.

The plan-

I studied some dimensions from various race seats, and drew up a concept of the seat in CAD at work. This step was completely unnecessary as I really didn't take any dimensions from the drawing, and winged parts of it on the fly, however it did help me work out the overall plan. The inner portions of the seat are made of 1/2" square by .040 wall Mild steel tube. I used about 30 ft to build the seats. The tubing was 1.05/ft so I have about $35 into the square tubing. IN addition to that the contoured edges of the seat are made out of 2 10ft pieces of 1/2" EMT conduit at 1.47 ea.
WARNING! Precautions should be taken when welding galvanized metal. OSHA says you can, but the internet says you can't. The fumes are bad for you and should be avoided. Welding should occur in a well ventilated area, and I would clean the galvanized off as good as possible to reduce fumes. Apparently the toxicity that exists in Galvanized is not truly damaging, and if you weld to much galvanized you will get "weld fume fever". I just got done finish welding both seats and I fell fine though.
That out of the way, the bends are made with a 1/2" EMT conduit bender (available at menards/lowes etc. for ~$20). If you get lucky and have a cast iron one you probably can bend 3/4" thin wall (.040ish) ERW or DOM tube. The aluminum ones will break on iron tube, but are fine for conduit.



Here you can see the seat frame. As you can see I'm a glutton for punishment. Why experiment with 1 seat when you can double your risk with 2!



The seat dimensions are as follows:
Seat width-15.5" clearance along bottom (front edges of hip bolsters widen out ~.5" per side)
Bottom Plane is 8" long
front plane is at a 20 degree angle and is also 8" long
The back section is 20" long and is at a 20 degree from vertical angle.
The headrest is at a 15 degree angle to vertical and is an additional 15" long.
Total seat height is ~35".
Width at shoulder wings is 18.5", width at seat bolsters is 18".
Bolster depth is variable but starts at 7".


I put a 30 degree kick forward on the shoulder wings that you can see in this image. The wings themselves are 3" long.


Here is a picture of them in the car to give a sense of scale.

I will document the progress as I go along. Tonight I fully welded the frames. I can stand on the seats with them on the head rest and bolsters (upside down I guess) and they do not flex. Next step is to sheet them in aluminum.

The current weight is ~9lbs per frame. We'll see how heavy they get.

I appoligize that I don't have better construction documentation. IF there is enough interest and the seats are actually successful I will make a 3rd seat and document it's construction more/potentially create plans.

Thanks for looking and hope someone find this interesting and maybe even useful.

Daniel

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MG midget bodied Locostish car in progress

Nicely done. Reminds me of a seat I had in an old race car. It was out of a WW2 fighter and was pretty much the same construction, less the headrest area. The aluminum sheeting was very thin. Keep the updates coming.

Ron

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They say a journey of a thousand miles begins with a single step. By the time you finish the car it'll feel like you've done it on your knees.

nice job on the seats

Very nicely done. Do you plan to cover the aluminum with foam or upholstery?

WOW! Great work! Can't wait to see how they finish out.

Excellent job!
A brilliant idea to use your abilities and tools to make your own.
That is Locosting at its best I believe.

Looking forward to the rest of the seat construction....

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Attitude =
the Difference between
Ordeal and Adventure
James

Two thumbs up! I might try building some seats soon. Thanks for the pics/write-up!

Joe

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http://www.pbase.com/ninerjoe/lotus_19_build

I worked on the Aluminum skin some tonight. I actually had the camera with me so I will do a bit of Step by Step on how I fabricated the aluminum components. This will be long, and potentially boring for people who have done this kind of work before. I'm just trying to present what I did in hopes that it may help people that haven't done this type of activity yet. I picked up these techniques from various build logs I've seen and work I've done in the past.

I started by laying out what I wanted to cut on a fresh sheet of .040 aluminum sheet.
To make the marks on the sheet (this works for aluminum and Steel) I like to use a fresh razor blade. I don't mount it in a knife holder as I am careful with it and feel I have better control with it that way. You could use an awl, but they have to be sharpened where are razor blades are cheap enough that you can just throw them away (in a proper sharps container) when they dull.
(Ninja Edit: Per Carroll Smith via Sportscardesigner)
I mark the actual cut lines only bend lines should be markered/penciled not Scribed (from now on). For parts that tapper or have multiple bends I'm going to mark the center as well to ensure the taper or bends are symmetric. For cutting I simply used the Right and Left hand version of the Harbor Frieght offset shears (~$16 for the pair, If I bought again I would buy the USA made shears you can purchase at Menard's for about $16 each. The joints/pivots are much tighter and I'm sure they cut better). I have a full set of traditional (non-offset?) aviation snips (Yellow, Red, Green), and find the Offset shears to be easier to work with. They don't seem to cut arcs as easily, but because the handles stay above the workpiece they are much friendlier on your hands, and don't seem to bend the edges of the piece as much.


Here is the Back sheeting in the middle of construction. If you look close you can see the lines from the razor blade. Very sharp easy to see lines. This piece required 2 bends in close proximity to each other. I made the outer bend first, then the inner.

Now I'm going to show you how I made bends. I'm not saying it's the right way. Just how I did it. It seemed to work pretty good. The easy way is to buy a small sheet metal brake. I have one, but it's only 18" long, so it will only be of limited application.

To make the bends I used a long flat piece of bar stock, or a piece of angle iron (they are what I had around the shop). Requirements are really that it have a sharp edge, and be stiff. I'm going to experiment with some Oak I have laying around (hardwood has been used as form dies for aluminum for probably as long as aluminum existed, and probably used for copper before that). I'll clamp a piece of 1x1 .065 on top to stiffen the bend die (something every locoster should have). I suspect it will work really well, and be easier than buying a piece of angle iron just for bending.

I align the vertical portion of the bending die with the mark. I then clamped the ends, and clamped the middle. Now we are ready to bend!


To initiate the bend I used the rubber mallet and used light strokes. The hammer blows were directed as shown. Kinda up and in on the outer edge. Use light strokes and "sneak up" on the bend. As the part began to bend, I worked the hammer blows into the bottom of the flange. As I moved up and down the part I would move the Vice grip clamp back and forth allowing me to keep up with that part of the bend.


use light taps with the rubber mallet moving down the part. I only bent maybe 3-5 degrees per whack. Each length of this part (22") took maybe 10 whacks per 3-5 degrees. In this picture you can see that the far end of the part is bent more than the close end. As you bend you want the flange to become flat again. You can use a straight edge to check you progress.


As I approach 45 degrees of bend I get out the flat hammer and smack it right on the edge. It seems to tighten the bend radius up somewhat. Unfortunately if you screw it up, it will also dent the radius, so be careful with metal hammers on aluminum. Try to hit as "flat" as possible.


Sometimes I got carried away and caused some dents. It was easy enough to fix them by hammering with the flat hammer on my Vice beater pad thingy (that flat spot behind the jaws that is used to really mess up your thumb when you hit it with the hammer). For exterior panels, these dents would require some serious attention, but these are seats.. I'm going to stand on them. The vice pad thing does a good enough job.


Here the bends are done, dents corrected. All this piece needs is notching in the corners to clear welds, and the 70 degree flange on the bottom.

That concludes my aluminum bending web-inar. I hope it was helpful to someone out there.

My next post will show the progress on the seats I accomplished today.

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MG midget bodied Locostish car in progress

I completed the seat bottom and back on 1 seat today.

In all of the corners where seat tubes came together, I chose to notch the aluminum rather than grind down the welds. Believe me this is not because I want the pretty welds to shine through, it's just because I'm fairly sure the frame will be stronger this way.


This is the completed seat bottom. This is the first aluminum part I've ever made.


Here it is in place. You can see how I notched the edge where the tubes come in. I used a round file and a flat [Fatherless Child] to attempt to put a radius at all notch corners. Maybe it will help, maybe it wont. It looks nicer..
The vertical side sheet will slide in behind this flange and get riveted to the flange.


Here is the top of the seat back. Due to poor planing on my part the shoulder wing tubes do not come in at the edge of the vertical tubes. This makes a small disconnect that needs to be addressed. I relieved the end of the bend and will just distort the aluminum a little at the top to correct for this issue. I will highlight this a little more when I rivet the frames on. Please advert your eyes from the wonderful weld pile at the galvanized joints. I haven't even wire brushed them... Oh well.


Seat and back in position.


Seat and back in position from the back of the seat. Again on the back the flange on the edge will be used to rivet on the side bolsters. I really like the way the seats look from the back. I may add some holes and dimple dies to the flat areas. I'm not sure.


And finally here it is in the car. I like to end each day by putting the seat in the car and sitting in it if possible. It just makes me feel more accomplishment. I really liked the comfort of the seats. Even without a cover/padding it seemed quiet comfortable. I may drive it some with just raw aluminum for the seats. I'm not sure.

Anyway, Thanks for following along and I will keep updating as I make progress. Progress may slow as my wife is back from her trip tomorrow. But I will keep plugging along.

Thanks,

Daniel

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MG midget bodied Locostish car in progress

Very impressive. I'm sure your example will lead others to tackle building seats for the price of materials. Appropriately Locost for those who can find a little time easier than a lot of money.

... but regarding those lines you scribed for bends: Carroll Smith is rolling over in his grave.. it's been years since I last read his books and I still recall how adament he was on the subject. And on aluminum no less. As Gomer Pyle would say, "Shame, shame, shame."

Maybe those areas won't see much stress if the aluminum is fastened to the frame in enough places, but scribing lines (unless it's a cut line) is a bad practice: It's like pre-scoring where you want the part to break.
.

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http://www.SportsCarDesigner.com .... You want to design your own car... so go ahead. Sports Car Designer is the answer.

You bring up a valid point, one I hadn't really thought to much about. I wasn't to concerned because I'm so used to working with steel which is very forgiving of what you do to it. I also Only scribe on the COMPRESSIVE (inside) side of a bend.
You did make me think about what I've done enough to do a little investigation.

I cut quite a few different strips some 1/2 wide, some 1" wide. Each set of strips were scored lightly (like I am doing, just really scratching the surface), or Scored VERY heavily, Like curl of metal coming out of score line heavy. And some were not scored at all.
I then took the 1/2" strips and viced them ~1/4" away from the score line, grabbed them in vice grips and pulled.
I was able to pull all of the 1/2 strips appart.. They failed right where they were clamped in the vice, even the heavily scored ones.

I took the 1" strips and bent 1 of each of the score types with the score on both the inside and outside of the bend. Meaning I had score marks on 1 sample on the inside, 1 sample on the outside (Why you would attempt to mark the backside of a bend Is beyond me). I also again made 1 sample with no score lines.
During bending all parts bent fine. I was able to go past 90 degrees with no material failure, however the heavily scribed on the oustide of the bend sample was easier to bend and did begin to fail where the score was (which would be expected). As an additional activity I may bend all the way back to 180 (or to the point where the non-scored part can no longer bend without a failure at the bend line) to see if scoring effects the distance the material can be bent.
All of the samples were then clamped in the vice with the L of the 90 putting the face of the L ~1/4 away from the vice jaw (this simulates a line of rivets). I then grabbed the other L in the vice grips and pulled. On all samples with the exception of the Heavily scored outside bend the part bent at the vice jaw (1/4" away from the bend), and then failed as the inside of the bend came unbent due to the pulling action. The Outside bend part did the same thing, but did fail earlier than the other parts. Now my arm isn't an Instron machine, but the amount of force requied to fail all of the parts was very similar. The result of this testing leads me to believe that when Scored on the INSIDE of a bend your assembly will tend to become un-serviceable due to flange failure before it will fail due to inherent scribe weakness. More data and testing would have to be developed to find out if you built a structure that doesn't inhibit flange weakness if the scribed bends are somehow weaker than the un-scribed, but my intention is not to build a structure like that.

Obviously I was only doing destructive max force type testing. For fatigue life testing a lot more work would have to go into the test, with strain gauges to determine the real stress in the remaining material after the score thins the material thickness. However what I saw was that light scoring on the INSIDE of a bend seems to have very little effect on the strength of a part. I would never scribe the outside (Tension) side of a bend, what point would there be?
I'm confident that scribbing the parts is probably a no-no on a heavily stressed parts (say Airframes, sheet aluminum frames). However for the type of panels we do I'm fairly sure it would be ok.

However Just to be safe, I will stop recommending scribing of Bend lines. I stand by that it's the best way to mark CUT lines, however I will use a magic marker from now on to mark BEND lines. I'll change my how-to to indicate that bend lines should be marked not scribed.

Daniel

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MG midget bodied Locostish car in progress

Out-of-context flare for the melodramatic aside: I believe that realistically considering how well supported and minimally stressed the bends will be in this specific application, the scribe lines are of minimal concern.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

That's pretty much what I said:

I didn't say he should scrap it a start over.

(But) You needn't put it upon yourself to decide on a case by case basis where it's OK to cause stress risers when an easy alternative exists. Besides bends, the other place it's crucial not to mark with a scribe is a rivet line... your rivets may be in a nice perfect line, but that's where the fatigue cracks will prematurely appear. Probably grounds for dismissal if you're working on aircraft. A scribe line is a crack, and a "perfect" one at that, if it's a dead straight line. The thing about stress risers is they can decrease the number of cycles needed to break a part dramatically, like from 100,000 miles of flexing to 100 miles. A marker never caused a crack. Even where it's not a structural or safety issue, do you want to re-skin something after a couple years, or a couple months?

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http://www.SportsCarDesigner.com .... You want to design your own car... so go ahead. Sports Car Designer is the answer.

Then again since nobody here appears to have any directly related prior experience, there's only one way to find out exactly how much of an effect it will or won't have on the service life in this particular non-critical application.

If all else fails...He can just make sure that the experimental seat with the scribe lines goes on the passenger side.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

But then, you wouldn't want him getting high from the marker as he's driving, would you?

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Jest another locostusa lurker... for now