Tunneling

As usual, no matter how realistic you believe your goals to be, progress typically occurs at somewhere between 1/2 and 1/3 of the anticipated rate.

Since my last post I've been making progress, but nothing terribly interesting to take and share photos of...Not that most of my photo updates thus far have been overly 'exciting' either.  I spent some time finish welding the second two chassis rails.  Then some more time mocking up the chassis rails while debating between 17.5" wide seats with a 8" wide tunnel, 17.25" wide seats with a 7.5" wide tunnel, or 17" wide seats with a 7" wide tunnel.  And finally this weekend, making the transverse tunnel tubes and prepping the two tunnel rails to be mated together.

To ease any potential issues with the differential pinion being offset to the passenger side, in addition to focusing on my personal seat width, I decided to keep moving forward with the originally planned 17" wide seats and 8" wide tunnel.  As with every other decision, this has both advantages and disadvantages vs the alternatives...But all minor relative to each other, as well as in the big scheme of things.

Everything is now prepped so that next weekend I will be almost certainly be going "3D" with at least a tacked up tunnel.  I hope to get even further, but I'll direct you back to my first statement in this post.  The last decision to make before doing so, is how I want to install the transverse tubes that will make up the bottom of the rear firewall.  Options "A" and "B" are shown below...But I'm also considering secret option "C" with some type of hybrid between the two shown by using additional portions of tubing or gusseting.  Obviously this is one of the more 'detail oriented' decisions that will make little difference either way, but it does give me a little something to ponder until next weekend.

Chassis Multiplication

So that's what happens when you leave two sections of chassis alone in the garage together!...

Sharpies

Mental note: Industrial Sharpie is almost as tough as mill scale. Acetone barely fades it. Stick with Original Sharpie for marking welds on Steel.

Chassis Tube Templates

With the mill-scale scourge defeated, I'm almost ready to actually be productive again.  I have but one mental block to break through before welding up the remaining two sections of cut chassis tubes.  The amount of time it took to produce the second identical set of, now welded together, tubes was a mere fraction of the amount of time it took to produce this first set that I'm now finally preparing to weld together.

As my skills grow through the process of building this chassis, so too will the quality of my workmanship.  I am confident that my fabrication of this chassis will be more than adequate for safely cruising around town or hitting the local autox.  But I do also want to take this car to the race track, and I'm not yet sure of my confidence level in this same fabrication when traveling at speeds well into triple digit speeds...But I need to find a way to keep moving forward if I ever want to get this car on the road.

I also know that as much as I'd like to make it look like I can design everything perfectly on the first try as I go along, I know that I will have to make changes to previously 'completed' work, as well as there will be things I wish I had done a bit (or a lot) differently when seen in hindsight.

So to assuage my fears and bring me the inner peace I need to proceed, I am making templates of every tube.  These will allow me to build a second chassis with relatively minimal effort, if at any point in the future I see fit to do so.

It's actually a quick and easy process, the hardest part of which was finding a suitably sized and priced material.  I happened across 5/8 vinyl J-channel for cheap at my local hardware store.

Using a utility knife, score down the full length of the inside corner on the shorter side.  Fold the short side "open" to lay flat with the base, which will cause the vinyl to fracture along the scored line.  Then peel the short side off leaving a vinyl L-channel.

Orient the tube into the L-channel as necessary, use a sharpie to mark the tube end profiles, and cut with a tin snip to match.  Lay it back over the tube to verify the angles and lengths are correct.

And before you know it, you've got a whole family of templates.

Note that some are simply numbered, while others have "A" and/or "B" associated with the number.  As usual, there is a method to the madness. Due to my band saw only being able to make angles in one direction up to a 45 degree angle, numerous tubes needed templates that either oriented a specific way or needed one template for each side.  It takes a bit of thought to get them all sorted out the right way, but apparently is nothing that the average idiot who thinks he can actually build a car from scratch in his own garage couldn’t figure out on the third or fourth try.

Today's Brain Teaser

Spot the differences:

Mill Scale Sucks

So far I have gotten two batches of steel tube.  The first was ASTM A500 and the second was ASTM A513.  Each was all they had in stock for 1x1x0.065 tube at the time.  So what's the difference, besides about 13 whatchamadingers?  In terms of mechanical properties, not enough for me to worry about.  They're both pretty standard hot rolled, seam welded steel tube.  However, at least as stocked by my steel supplier, the A500 was protected by a light mill scale...Where as the A513 was cleaned and protected by an oily residue.  Then which is better?  During initial handling, neither is great.  The A500 leaves black grime on everything it touches, and the A513 leaves oily residue on anything it touches.  However, the oily residue cleans off easily with a quick wipe down of Acetone.  The same cannot be said of the mill scale.

One of the popular ways to rid yourself of the Mill Scale plague, is by using a diluted acid solution, which can cause all manner of hazardous material problems that I have absolutely no interest in dealing with.  To mechanically remove it though simply takes time...Much more than anybody wants to spend doing it.  Some people simply do a half-assed cleaning of the tube, while only doing a whole-assed cleaning where the welds will be.  The idea is that the mill scale is well adhered to the tube, and there are paints that at least adhere well enough to the mill scale for it to not be a problem...But if you couldn't tell from my previous tube prep on the A513, I'll be doing it the complete and total assed way.

As seen in the picture below, at the top is the original flat black mill scale wiped of the initial loose grime.  Below that is the 'half-assed' cleanup.  This is a few lighter passes with a wire wheel, and has basically polished the mill scale to kind of a satin black.  The bottom shows the fully cleaned up steel, after numerous heavier passes with the wire wheel.  Off to the right, you can see the pile of tubes in the semi-finished state, and the one tube on the left that is fully-finished.

So if your steel supplier tries to sell you on tube with mill scale...In the immortal words of Bing Crosby, "don't think, don't pause, don't hesitate for a moment, just spit in his eye."

Weld Sequencing

As with anything else, the more welding I do, the better my welds are becoming.  It also means I'm figuring out those little tricks that create significant improvement in various specific welding scenarios that you don't even think about until after throwing yourself into those scenarios.  By the time I'm done with the chassis, I might actually make a half way decent welder!  Of course in the mean time, this means I get to look back on all of the welds up to the point of each new revelation and try to force myself not to simply start over.  It may however mean that the earlier sections of chassis will be getting a little additional gusseting...Just in case.

On the other hand, my overall results have been good with keeping weld distortion to a minimum so far.  After tacking the section all together, I pull it out of the 'jig' so that I can flip and rotate it around into whatever position will allow me to reach any given joint the most easily.  My technique starts off with welding all of the fillet welds on the inside corners for the main boxed segments first, alternating corners around the chassis.  Then doing the same with the outside corners.  After that is the fillet welds on all of the diagonals.  And last comes all of the the butt welds on either side.  Really the primary source of what distortion I have seen appears to be coming from any minor variances in tube fitment.  Wedge a tube in too tight, and when welded it bows the tubes on either side out.  Leave a little gap, and the weld will pull it closed.  None of this shows up well in pictures though.

However, I do have a picture illustrating one other method I'm using.  I find the hardest to reach weld for every tube joint, and figure out what position both of us (the chassis and myself) need to be in to most easily weld it.  This includes determining which direction the weld will go.  I then mark that next to the joint.  Every other joint around that tube intersection is then welded moving the same direction, such that the coldest part of the weld at the beginning overlaps the hottest part at the end of a previous weld.  Alternatively the hottest part of the weld at the end overlaps the coldest part at the beginning a previous weld.