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Motorized Bicycle Welding, Fabrication and Painting - The Chop Shop Custom fabrication and projects, tanks, frames and more.

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  #1  
Old 04-08-2010, 09:45 AM
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BarelyAWake BarelyAWake is offline
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Default DIY tank... even if you can't weld

This is a basic tutorial on how to cut, form & fit the panels for a tank, even if you can't weld - bringing in the finished pieces to your local welding shop will not only get you that in-frame tank ya always wanted, but you'll save a buncha cash in the process;


Buried in the Rustoration Build Off was a request and the resultant rant, I thought I'd dig it outa there for ya. It's a lil weird as there was a buncha other stuff mixed in at the time... but it still may help those unfamiliar with basic sheet metal work. Please feel free to post any questions or comments, tips, suggestions and advice - even where to get tanks ifn ya know a guy.


Gettin' a fuel tank is often a stumbling point preventing some from considering a build they'd like - while you can pay to have one made it's often cost-prohibitive. Most folks without welding equipment wouldn't consider a DIY tank as a possibility, or really know why it costs so much...

It's the time & labor involved in making and fitting the panels that costs the big bucks, even for the most experienced makin' a new shape for the first time as it jus' eats up the hours. With a lil practice & patience you can make those panels and fit them yourself - bring the finished pieces in to a skilled local welder to zot them can save you tons of yer hard-earned pennies, not to mention the braggin' rights in being able to say "I made this FTW!" it also allows you to choose the material you'd like the tank made outa - steel, aluminum, stainless, even copper... although that'd need to be soldered together ofc. A sheet of mild steel is cheap enough, there's no fancy tools beyond a jigsaw, dremel & a coupla files. It's so worth an experiment, the potential outweighs the cost - even if you end up jus' scraping it you've learned a bunch, keep at it and you'll have a unique bike worthy of yer efforts and a valuable skill learned.

Still... somethin' like fabin' a sheet metal tank is both much harder and far easier than you would think... if that sounds strange - just get some thick construction paper (think cereal box, corrugated cardboard won't work well) and make a simple box with some tape holdin' it together. While initially it's easy - any misalignment, dent, crinkle, or gap (particularly in the corners) will skew the whole thing. While the welder can make up for a poor fit somewhat by filling the gaps it'll show up like a sore thumb. Also, the longer you need spend "filling" with molten metal - the more heat is generated and so distortion is inevitable.

So it's all about how well you can get the pieces to fit in the first place - if ya get that down, the welding part is easy for anyone that knows their stuff. Flats and angles are somewhat easier than curves, but the shape is up to you and yer build. With that in mind, it's best to get far more materials than what you'd think would be necessary. Although I'm just cuttin' two side panels at the moment - I got enough sheet steel to make five. Cutting out three to start with I choose the best of the two for the tank - the third I save for experimentation and the rest of the steel I save for when I mess up (notice "when" not "if" lol). It's best to not commit to any one panel till yer done - often it's far easier to just cut out another than to try to "fix" something that went horribly wrong... or even jus' a lil screwy.

I decided to do as much of the tank as possible at home, bringing it in only to be welded to speed up the process a bit and while there's far better tools for it at work, I've simply more time at home to make sure the various panels fit as well as I can manage.

I must say though - getting a 2' x 2' sheet of 20 gauge mild steel home on a motorized bicycle is... interesting lol

The tank will be about 24"L x 5"W x 3"T with the only real challenge being finding some vented fill cap and base that's about 1 3/4" wide... I'd really like a brass cap but we'll see what I can find. There will be a "fuel sight gauge" made from brass elbows and a hunk of clear fuel line, and ofc copper fuel lines... tho that's not really part of the tank lol

The poor, filthy Schwinn bein' a workhorse;


and the initial measurements bein' figured out fer the tank; (click to view larger, same goes for all lil pics)


In the pic it looks as if the tracing is off, it isn't - it's just the angle of the pic. There's a 1/4" gap all around the tank to allow for the fasteners BTW

Last edited by BarelyAWake; 05-31-2010 at 02:30 AM.
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Old 04-08-2010, 09:46 AM
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Default Re: DIY tank... even if you can't weld

While some may make a mock-up of the tank first usin' the above method (construction paper/cardstock) then use those cut outs as templates, there will always be some variance between the model and the real-life tank - mostly due to the difference in thickness between the cardboard and the sheet metal, particularly in the corners. With that in mind I'll be using the metal side plates to fit the top and bottom, mostly because of the curvature of this tank. If you've not made something like this before - then you'll defo wanna make a "cardboard" tank first and use that for templates.

So - the first step is obviously to make a trace template like I did in a previous post, then simply tape the template to the steel and outline it usin' a Sharpie. If you put the bits o'tape only where there's a straight line - they're easy 'nuff to put in afterward with a ruler. Be very careful when making the marks tho as they'll be your only guide while yer cutting. Also don't ever use the panel you just cut to trace the next, always use the template - while you would think that would result in a near perfect copy of the first cut panel, in fact you'll just be amplifying the errors in the first one and adding more;



Ya prolly noticed I'm using a simple jigsaw with a "bi-metal" blade, essentially the same as a hacksaw blade. Inexpensive and easy to use - know that no tool (other than an industrial stamp machine) is going to be terribly accurate at this stage, so you'll want to cut on the outside of the line, never coming within 1/16" of your "final" edge. This will be your "buffer zone" of error and blade wander - something jigsaws are famed for. You'll also want to keep your cutting area as close to the table as possible - the vibration of the tool gets amplified by the sheet to the point where the blade will "springboard" out of the cut, best case scenario it's just annoying - far more likely what will happen is you'll dent/distort the panel and will hafta start over. While you could try and flatten it back out - it will never be the same so yer better off making another.



If you make the long cuts first then trim off the ends, you wont get that twisted off end that happens with a long cut... well, you will - but it wont be anywhere near where you care about so it doesn't matter heh, or you could be clever and put a squeezeit clamp on the tailing end to support the cutoff. Here's the panels all cut out - while I always stayed outside the line (actually I cut half the line off... but I've done stuff like this before) you can see the slight wavering and inaccuracies inherent in the tool... and me actually lol, so the next stage is to clamp the two best together and grind down to the inside of the line - this way they'll be smooth and almost perfectly flush with each other, as close to symmetrical as I'm gonna get;



That "X" denotes the one I didn't like as much and will serve as a backup/test piece. Again, it's best to not get too attached to any one bit as it's simple enough to make another that's better. That lil rule of thumb will save much frustration and will result in a far better end product than fussin' over some lil screw-up. They first attempt at something is always the sloppiest so why worry? Heck - I may well make a second entire tank if I don't like the first, if I get a better idea - or if I just don't like the welds, recognizing yer own limitations is a valuable skill - that way ya can always work around 'em FTW
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Old 04-08-2010, 09:49 AM
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Default Re: DIY tank... even if you can't weld

Clamping the two side panels together using popsicle sticks to pad the C-clamps and making sure to not crank 'em down too tight (metal distortion);


I started bringing down the steel till the two pieces were flush and to the indicator line. I started with a Dremel of course, but this leaves a wavering finish with low and high spots no matter how careful you might be, but if ya always make long, sweeping passes it'll reduce the amount of "dig-out" and result in smoother lines. For the outside curve and flats - I used a large, flat file much like you would a planer. Slow and somewhat tedious, it's really the best method for getting a nice, smooth, regular surface - particularly on an outside curve. Inside curves are the same deal - ya just need a 1/2 round file (bigger = better) and remember - long passes result in less irregularities and "even out" high and low spots.


The two panels now about as identical as humanly possible and this is where I call it quits for now. Although it's tempting to round the corners to what it's "supposed" to be - it's far, far better to make the top and bottom panels and bend those first, then grind the rounds on the sides to fit. While I know what shape/angle I want the bends to be - no amount of planning can account for the real world and I'm sure the rounded bends wont be quite exactly as I thought they would be. I'd rather wait to grind and test fit then guess and hafta try and put metal back lol Also... the math gets tricky with mutable bends & curves... and math was never my strong suit heh


Most of this back & forth, test fitting & shaving a bit more off is simply due it being a curved tank and the fact it's a "one-off" - the first attempt at a product you've not made before. Should you ever wish to make another - it'd be far easier as you'd already know what shapes you'd need and if'n yer clever - you'd have used the original bits to make "finished" templates before ya weld them together. Even tho I don't think it likely I'll ever run into another, identical Rollfast that needs a real fuel tank - I'll be makin' 1/8" thick, epoxy-coated plywood trace templates for each piece... *shrug* Ya never know - I might dent this one and want another, maybe - just maybe someone else will have a Rollfast and those bdanged templates are where all the effort is...

I've done three test layouts for the top and bottom panels, the first two proving yet again that there's a huge difference between "planning" and the real world lol

My first idea was to have a somewhat angular tank, sorta coffin shaped if viewed from above. It's quite important for the tank to have a fairly abrupt taper in the front as the rear forks for the springer will hit it when I turn the handlebars all the way to one side or the other. Too wide and I'll limit the steering - too narrow and I'll not only have a dang strange lookin' tank, it wont hold much and I'd be forced into havin' a pinhole for a fuel fill. While some cap will be smaller than normal - I really don't want to be forced into using a funnel to fill the blasted thing.

So while the angular tank looked great in my brain, when I got around to draftin' out the shapes it jus' didn't work. Sure - I got it to all "fit together" (sketched out anyway) but it jus' looked stupid as heck. The sides will be rounded front and rear (they're only angled in the pics 'cause I've not ground the rounds yet) and the clash of rounds and angles combined with the gently swooping frame was too much to bear. Additionally, the taper in the front needed to be so abrupt to give me the flat sides where I wanted 'em... well... trust me - it looked really bad lol

No materials wasted tho, as I didn't cut anything and it's funny how easily Sharpie wipes off with a lil acetone FTW. My second attempt was similar to the first just with the bends/angles in slightly different places, but with the same disastrous results - they offended mine eyes. More acetone and back to the drawing board.

I really don't know why I had my heart set on angles... they don't make the math any easier and the Rollfast is all curves so I shoulda known better *shrug* For whatever reason that's what I had envisioned from the moment I thought about makin' a tank and bein' a stubborn fool I ignored alla my past experience and tried to make it work anyway. Sure - I could make it work, I've even finally figured out where the bends need to be - but on my third attempt I jus' grabbed a batten (jus' a thin strip of scrap plywood to plot curves, ply so the grain doesn't effect anything) and did a test curve... lo and behold, a classic curve pleasing to the eye with alla various widths in all the right places o_O BTW, battens are also handy for figurin' out what the length of a curve is if flattened out - bend the batten to the curve - mark, flatten and measure. Ya can use a bit o'string... but it tends to get all squirrely on ya.

K - so I'm going to have a curved tank then heh, it's sometimes a lot better to listen to what the materials have to say than my silly brain;



This is actually just my test piece - I'll be cutting out just the top half of the drawing, the bottom isn't to scale and is just there to help me envision the shape. Once the top half is cut, I'll use it as a trace template and flip it over to get as close to a symmetrical, mirrored shape as possible. While battens are great for plotting nice curves - you'll never get quite the same shape twice so it's best to not rely on 'em too much. The 1" band going down the middle is the top tube of the frame, the straight lines comin' off the ends are for the wrap-arounds front and rear. As they'll need to be some mysterious hourglass shape from the sides tapering in - I'm gonna wait till the rest is cut and I can bend them into place and trace. Yeah, I could use the ol' math... but we've already discussed the insidious shortcomings of my brain;



While it's all ready for the jigsaw... it's also about 5:30am here and despite all my threats of audio revenge - I'm still jus' not bastid 'nuff to make screamin' sheet metal death noises and wake the entire house.

Ah well heh
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Old 04-08-2010, 09:49 AM
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BarelyAWake BarelyAWake is offline
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Default Re: DIY tank... even if you can't weld

While you can easily bend 20ga mild steel with your bare hands, there's no way to control the amount, location, or uniformity that way. To make matters more interesting should you overbend or do it wrong - the metal has a "memory" of sorts and it's dang hard to get it back to perfectly flat. While it's ofc fine to do long, gradual curves by hand, for sharp, uniform bends with a predictable shape it's best to make yerself a DIY sheet metal brake (or buy a lil one, they're cheap... but I'm even cheaper lol: sheet metal brake - Google Product Search).

As this is just a lil project and somewhat narrow bends, just two chunks of angle steel works great. I've welded flatstock to these with C-clamp heads for heaver gauge bends, a vice would be the next level - for something like this tank it's not really needful tho. For sharp bends I use the other piece of angle steel (the sharp bend coulda been "sharper" in the pic but was just an example), for rounded bends I find some pipe or something of the correct diameter to use instead (in this case a plunger handle) The square block is jus' to prop it up for the pics - you'll need room for the metal to bend up to a 90 degree angle, depending on what you're doing;



A warning however - while the sharp bends with the two chunks of angle steel will always be right on the line, with one angle and a round it seems to always place the bend on the tailing end. In any case the bend itself takes up room so you should always make lines and do a few trial bends on a scrap chunk to see where/how much you need to offset your marks.

Under bending is fine as you can just do it more (spacing out the next bend can also give you a larger radius than you have pipe for... but that's tricky), but over bending can spell doom. Do NOT just try to free-hand it back, the metal will develop a waver right next to the bend your trying to flatten - it's best to clamp it in two pieces of flat stock (at least twice as thick as what you're working) and squish it flat with a C clamp or two. If it's close - put those next to the bend (on the side you don't wanna mess up, or both) then give it a couple, gentle presses to "urge" it back.
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Old 04-08-2010, 09:50 AM
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Default Re: DIY tank... even if you can't weld

Here I've the top and sides of the tank cut and filed to fit - saving the rounded corners till after I make the bends in the top panel;



First bend went slick and smooth and the corner of the side panel just needed a touch of the Dremel to round it to fit - very reassuring as despite the "know-it-all" tone of these posts it's been quite a while since I've done anything like a tank lol;



Now that I know for sure that my madness will work out - the rest of the bends are quick and easy (small gaps are only because I'm using tape to hold it together... and the pesky stuff stretches heh);



Now I just need to make the bottom panel which has the same 1/2 round in the back but only a single bend in the front so it should be simpler. The bending stage is a bit tricky as if it's off by even a little it screws everything up - particularly if the angle from side to side is even just a little wrong as that'll "twist" the whole project... so again, test bends, good marks as guides, rounding the corners after the bends are made, spare panels to test/replace, and ofc - patience... the one commodity that I'm actually a lil short on sometimes heh
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Old 04-08-2010, 09:51 AM
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Default Re: DIY tank... even if you can't weld

It's a lil thing but I thought I'd share it with some fellow geek... erm... *cough* "enthusiasts" that may appreciate it heh

I've been hunting after this lil widget for a while now, I'd seen them before on other, larger machines and I thought that a glass bowl style fuel filter would defo add to the "vintage" appearance of my Rollfast build. While it's true the the screen mesh is slightly more porous than a good inline filter, I suspect with these engines that doesn't matter very much and the quality built in fuel petcock makes up for that anyway. I could I suppose take the screen out and put in another filter inline - but I'm trying to avoid the "look" if you know what I mean and it'd be awkward as I'm going for flared copper tubing for fuel line. Water is actually more a concern of mine anyway and the bowl traps that (and sediment) quite well.

I asked around a bit and all I got for my troubles was the ol' crazy eye... as per usual lol so I hunted the dead engine piles we have where I work. After a buncha digging (reeking of varnished gas) I found an old smashed Kohler with one stuck to it and once I actually had one to show - it was a simple matter of tracking down the part number and gettin' a new one from Napa (part# 7-02350). As it turns out it's a commonly available part just no longer in common usage, it's mostly seen on older Briggs & Stratton engines.





Other minor advantages is ofc it's cleanable/rebuildable, and I may well be able to mix my fuel/oil in the tank at the gas station without fear of clogging by closing the shutoff and shaking the bike. Once I reopen the petcock any excess oil trapped in the fitting will just end up in the bowl, flushed out by the passing fuel as the engine runs (the theory anyway)
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Old 04-08-2010, 09:51 AM
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Default Re: DIY tank... even if you can't weld

Whoohoo! The shaping of the tank panels is pretty much done, I need to take about 1/8-1/16" off the sides of the bottom panel to conform to the taper of the sides in just the back (and only 'bout 2" needs that touch up) - but that will be a heck of a lot simpler when it's all tack welded together and I can just grind it flush. As you can see in the pics, the tape isn't all that happy 'bout holdin' all the parts of the tank together at the same time lol

As you can see I also managed to dig up the lil brass elbows for the fuel sight gauge, they're exactly what I was hoping to find - with only an 1/8" OD on the chunk of line, it's sits flush with the tank side and the heads of the elbow fittings so it only protrudes from the tank 1/8".



I still need to cut the holes for the various hardware bits and have the backings welded (and trim/clean the hardware too ofc), but although I'm sure I (or anyone trying this) can do it with just a drill and/or Dremel I think it's also going to wait till I bring the panels in to work so I can use the hydraulic punch for nice, clean, slightly beveled holes.




So, I've got all the backings made and holes cut except the mounts, I forgot those at work so I dunno the hole spacing. That'll only take a minute to take care of tho...

So now I set all the panels on a shelf and wait for my buddy to get some time *crosses fingers*

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Old 04-08-2010, 09:52 AM
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Default Re: DIY tank... even if you can't weld

Here's a shot I've noticed ya don't see too much with the DIY tanks, the inside - particularly the mounts... there was much discussion and debate regarding those mounts, the backing plates and their size my idea - their thickness his, neither of us thought it a good idea to just weld nuts/studs to the tank itself as the stock tanks have, for obvious reasons. (click to view larger);



You'll note the perhaps overly thick backing plates for the mounts, the thickness just to help make the welding easier - they're also not welded completely around their edges. While this would ofc be desirable, it's not particularly needful as I won't be relying on them to seal - they'll have studs sealed on the outside w/a nut... the thought being for strength and having lots of material should I ever need to retap them. All the internal fasteners, fill cap, and backing plates were MIG welded to help "build up" the material. The tank will be lined ofc.

I do feel the need to mention that this fastener method was experimental, the tried & tru technique is welding acorn nuts on the inside. Provided they're welded completely around, they won't leak. Weld the acorn nut to a large washer first, then welding that to the tank helps prevent the stud from bending/distorting the tank.

Before the bottom was tacked in place - the tank got a ride home again for one final test fit. Much as I tried, there was never a chance to get it all in one piece, accurately - with nothing but mere tape. To say I was happy to note a near perfect fit and uniform frame spacing would be an understatement heh



Back to work again, the bottom panel tacked in on a lunch break - it now sits on a shelf gettin' dusty as Murphy has his way with us...

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Old 04-08-2010, 09:53 AM
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Default Re: DIY tank... even if you can't weld



The tank welding done, it wasn't quite flawless - but far, far better than I feared. A "small" detail overlooked when setting alla this up is my poor buddy's lack of a foot control on his TIG machine... essentially just a stick welder with a TIG gun instead of a clamp - he's got no amperage control and the machine's lowest setting 'bout twice as much as needed for this lil project. With that in mind - I've nothin' but respect for my friend as he managed to not incinerate alla my work lol

Upside? While the welds may not be the most cosmetic in the world - they're freakin' strong and with the over-penetration developing a consistent bead on the inside, it's "gusseted" so to speak. So... a lotta grindin' and a lil filler... and a bunch more sanding and I've my fuel tank FTW ...and no, it's not gonna stay flat black heh - there's more sanding and painting to be done ofc... which is all that managed to prevent me from stickin' my nifty fuel filter and sight gauge on it for the pics.

The temptation was there tho lol, bad enough I hung the chainguard just for the pic - let alone the tangled nightmare of cables o.O

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Old 04-08-2010, 09:56 AM
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Default Re: DIY tank... even if you can't weld

...and "finished" with copper mounts & paint;


Last edited by BarelyAWake; 04-02-2011 at 01:48 AM.
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