Hankl

Once the tubing is cut, you'll need to prep it even further, to assure that your weld joint meets the standards for correct construction of the structure.
Some would be very quick to take the tubing from the notcher and just weld it to the appropriate tube and be done with it. Here's where the details help your
cage survive that impact that none of us wants.

In this picture we have the first example of the tubing that was inserted 1/2 way into the tubing notcher. As you progress up the outside of the horizontal
tube, the wall of the vertical tube gets thinner. If you were to weld the two tubes together, where would you run the weld bead? If you follow the edge of
the vertical tube, where it was cut, you are welding .005 to .010 wall tubing to .120 wall tubing, guess how long that joint will survive a impact!



Here is what we consider a correctly prepared tube for our construction. You have full exposure of the thickness of the vertical tubing, to weld to the
horizontal tube. The weld will be stronger, and help insure full penetration of the weld bead to both tubes.



Here is a look at what the two tubes look like side by side.



OK, how do you do that?

A belt sander is my weapon of choice for sanding down the tube to get it prepped for final fitting. Basically, you use a arcing motion to sand the tubing to the desired profile.
It takes a bit of time doing the first one, but checking your progress and getting the hang of it will provide excellent results.

NOTE!! In this picture I'm not running the sander because I'm shooting the picture with the other hand.
The tubing gets HOT during this operation, wear thick gloves!! This is a two handed operation!!





The time need to sand the tubes to the correct profile is also impacted by how you cut your tubing, again, which tube would you rather sand down to profile,
the one on the left, or the one on the right, again, time and tooling saved.



All of the vertical main tubes cut and prepped.

Now that the manual part of the tube preparation is mostly taken care of, we'll move on to bending the long tubes. Again, we are using the specified tubing required by SCCA/NASA, 1 1/2" .120 wall, DOM tubing.
The use of a Tubing Bender vs. a Pipe Bender is significant, but often confused. You only want to bend "Tubing" with a Tube Bender, not a pipe bender. What I use is a Pro Tools 105 Tubing Bender, this unit has provided
me with very good service, relatively easy to operate, with very repeatable results. The dies for this unit are 1 1/2" with a 4 1/2" radius. According to the SCCA/NASA rule book, the bend radius of the tubing, must be 3
times the diameter of the tubing, this is how we end up with the 4 1/2" radius on the bend. Often times, a 6" radius is also used in Race Car cage construction, but the minimum radius was selected for several reasons.
There are several other manufactures such as JD Squared, Medford Tools, Trick Tools, etc. All of these use the same basic method of bending the tubing, and they look eerily similar in construction, so picking one to buy
is rather more dependent on what options your choice offers, and the price point.






The degree indicator on the 105 is extremely helpful in bending successive tubes to the same angle of bend, suggested if you want to purchase a bender for several projects.





One thing that I found very important, was to mark the position of the tubing in the bender. This also helps in the final bending done to the top bar of the SIB, more on that later.
Here you can see where I mark the tubing at the end of the die, and use that as the marker for the beginning of the bend. It's also useful if the tube is not bent enough, and you
happened to have pulled it out of the bender, the mark will take you right back to the correct spot.

Thanks for taking the time to post this info. It's really helpful. By any chance would you be willing to talk about weld shrinkage, how it affects your measurements and what you do to counteract it, if anything?

Jim,

Give me a call, 831-588-4308, any time during the day.

Hank

The design of the SIB

In reading the rule books, we had to comply with some very straight forward requirements.

SCCA GCR Section 9.4.D

SIDE PROTECTION

Two side tubes connecting the front and main hoops across both door openings are mandatory. Tubes that are welded to any
part of the same mounting plate are considered to be connected to one another (see 9.4.E.3 below).NASCAR-style side protection or one bar bisecting another
to form an “X” is permitted. Door side tubes may extend into the front door. In Improved Touring, Showroom Stock, Spec Miata, and Touring the door window glass, window
operating mechanism, inner door trim panel, armrest, map pockets, and inside door latch/lock operat- ing mechanism may be removed and the inner door structural panel
may be modified, but not removed only if the door bars extend into the door cavity. The stock side impact beam and the outside door latch/lock op- erating mechanism shall
not be removed or modified unless specifically authorized in the category rules.


NASA

15.6.12 Door Bars / Side Impact Protection

At least two (2) door bars on the driver side and one (1) door bar on the passenger side
are required in all vehicles. Note- an “X” design counts as two bars.
Unless superseded by class rules, modifications to any non-chassis structure (such as door panels, inner door sheet metal, windows, door internals, etc.) may be made to accommodate any
allowed door bar configuration. However, removal of material and / or modifications is limited to 1) the least amount to accommodate the door bar(s), and 2) can serve no other function.
Holes in the door jam (B-pillar) may be permitted to accommodate door bars; however the structure should not be “notched” so as to weaken it.


Along with these requirements, the Coupe owners also had some Suggestions/Requirements. We would need to obtain as much room as possible with the SIB configuration.
Safety was to be the controlling factor in the direction that would be acceptable. We would need to make sure that Hand/Arm clearance existed in the final configuration, as that could be a factor
with the different heights of drivers in these Coupes. I had a distinct advantage in designing the SIB's, and that advantage was Anthony Vanni, for those of you who don't compete here on the west coat, Anthony is a par-excellence fabricator and a NASA Scrutineer. With His help I was able to bring the final design to fruition. I would bring a initial design and Anthony and I would work out the pluses and minus of the product and then look for ways to make it better. In the end, I think you will all agree that we have a easy to produce SIB that meets all of the NASA/SCCA requirements. Thanks Anthony!!

All of the above finally put us on the path to a NASCAR type of bar configuration. The "X" bars would be very hard to mount without them taking up room in the seating area. The rear of the "X"
would be a bit of a problem to attach to the rear bulkhead without bending the tubing more than necessary. Foot clearance would also be impacted, as the front bar would slat down from the front
bulkhead towards the center of the door opening, and thereby limit how you could swing your foot in the doorway. Anyone that has gotten into one of these knows what I'm talking about.

As we moved towards the NASCAR bar configuration, another request was that we would move the upper bar outwards, to allow the driver more room to "Slide Down Into the Cockpit" I feel that
with what we came up with, meets all of the requirements for the rules, and Driver/Owners. We also had to make sure that what we came up with would be applicable to any of the suspension
configurations available in the Coupe chassis, 3 Link, 4 Link, and IRS.

Tom Coons Coupe, Passenger side all tacked in ready for final welding.





I was presented with some very different problems that needed solving with the SIB. The Coupe does not have straight up and down Bulkheads front or rear.
The front bulkhead splay outwards from the bottom up, as does the rear one, but they are not in the same general location front to back. If the rear bulkhead was any
further towards the outside of the chassis it would hit the rear tire, so there would be some creative thinking needed.


In the two pictures below, you can start to see what I had to do to make things work. As the front bulkhead goes up and out, the bottom SIB tube would have to move outwards
to contact the bulkhead in or near the outside edge of the bulkhead. To do this I added small 2"x2" .120 wall square tubing, 3/4" of an inch deep. This is the same tubing as the outer
main frame rail that they are welded to are made of. This basically let me run a straight tube from the front to the bend point going to the rear bulkhead. Only one bend in this bar
for simplicity sake. The bend point and angle of the rear bend would be controlled by two things, clearance to the rear tire, and clearance to the rear of the drives seat. I stayed
away from the tire as much as possible, and tried to gain as much seat clearance as I could, but you can't have it both ways with these Coupes, it's one or the other, I chose Tire clearance....





This is a better shot of the lower bar with the bottom extensions in place, this is Karens Coupe.



The next thing to address was the position and design of the top SIB bar, taking in mind that we would need to move the bar as much as possible outwards in comparison to the lower bar.
I installed the drivers door frame to see what we could make work, fortunately the problem answered itself. All that needed to be done, was to miss the door frame, and that would allow
the top bar to extend into the door cavity, it would be just a matter of cutting reliefs in the door fiberglass for the SIB tubes.

The back end of the top bar would be bent at the same angle of the lower bar, but I had one other thing to contend with at the front of the bar.
The door frame needed some clearance, and the top bar needed to turn inwards to meet the front bulkhead.





A simple 30 Degree bend took care of both problems.





Now that I had the top bar at the height that it would need to be at, I just had to find the length that the verticals from the lower tube would need to be, to keep
the top bar in position, no biggie, since my jigs and magnets held everything in place while I took measurements. I'll post more pictures of the jigs used.

Very cool, Hank. I like that little trick for marking where the tube sits in the bender's die. I fabbed up one of your tubing measuring tools last evening and cut the 6 lower verticals. I cut them at 4" from the bottom of the notch to the other end. It looks like your lower verticals are about 4." Thanks for posting this.

Jake,

The bottom ones are 4.5" & the top ones are 4.25", you could always make up the difference on the top ones. If you need a top bar jig, just let me know, I have some tubes that were bent at the wrong length, and they'd be perfect for making a jig from, just let me know. I'll make it up and send it to you.

Hank

Since Jake brought it up, I might as well should you the jig and how it works.

From this picture you can see that the length or distance between the two bend points can be changed at will, and there are set screws (10-32) to hold the adjustment in place.

The front angle is 30 degrees as indicated on my Pro 105, the rear angle is 55 Degrees indicated. This is indicated in the relaxed position, there is usually a degree of spring
back that you will need to account for. That entails bending past the 30 or 55 degree mark. Experience with your particular bender will dictate how much is needed.



The rear portion of the bar that meets the rear bulkhead can also be changed in length, and the tube can also be rotated to change the angle cut orientation.



The indexing point cut into the jig, assures a precise measurement every time. The measurement that I constantly see, at least on my Coupe is 19 7/8" bent point to bend point, either side.



The index point you see above, is the same as the index mark I place on the tubing based on the die mark, as seen below.

The jig to hold the top bar in place consist of a 2' to 2 1/2 foot long piece of 2x2" square tubing, two pieces of tubing(with the ends cut with a 1 1/2" hole saw), cut so the bottom of the tube cut out is 9 1/2" from the bottom.
Unless you have multiple hands available, some good welding magnets are a must, 4 at least, but 6 would make things easier. A small Torpedo Level, with one side having a
magnetic base, one large carpenters level(To check the chassis level front to back & side to side), some magic markers, a steel ruler, two "C" clamps, and some scrap that will hold the
2x2 level to the frame.

If this was where you were obtaining the bend point to bend point measurement, you'd be done for now. After bending the tubing to met the Jig dimensions, we'd be back here again, this time to
place the next set of vertical tubes. The next set of verticals are a 4.25" inner cut radius to inner cut radius, and I'll have some tricks for cutting them a little later towards the end.




The reason you'll need extra hands, is that you'll have to pull the top tube away from the jig to insert the row of verticals, those pesky little tubes can get away from you in a hurry!




Once you have the verticals installed, you'll need to jockey the jig a little in and out, or back and forth to get the ends where you want them. As you move the bar, the extra
set of hands keeps pressure on the bar from falling away, while you adjust.



You shouldn't need to adjust the front part of the jig, but moving the rear part of the jig is OK. This whole exercise is just to place the verticals in position to do the final
cutting on the top bar, front and rear. The length of the bar, bend point to bend point is now fixed, as you've already bent the tubing, and rough cut the piece based on the jig,
leaving a couple of extra inches of tubing on each end.

Here, Rick is Tacking the top vertical tubes in place. Once done, they will now hold the top tube in place for final fitting.





You will have extra length at both ends of the tube, the verticals will hold the tube in position as you push it in from the rear.
It will contact the large 3x4 tube, and you can mark where the angles are, remember that the top of the cut will be shorter than the bottom,
as the bulkhead slants away from top to bottom. There is also a slight angle side to side, as the tube is coming in from the side at an angle.
Definitely a lot to keep track of, but making good marks, cutting a 1/4" away from where it should be final, and then sneaking up on it with
a grinder is the safest was to go. As you grind away, you're also checking the level of the tube, it's a sign of a good fabricator to keep the details in check.

CAUTION! if you cut too much, it's a new TUBE!!

As you get closer, the length of the front end will stop you from moving any farther forward. When that happens, you
measure the distance from the front side of the rear tube to the front edge of the 3x4, and that is what you should trim, minus a 1/8".
The reason for the 1/8" is that there will be a slight angle at the front also, so chamfering the front for welding will eat that up.


A few things to take note of here, just in front of the torpedo level is what is left of the door striker mount. You'll need to cut out most of the
structure before starting the SIB measurement & install. You'll be cutting out the horizontal long bar that the body sits on first, cut it as long as you
can, this piece will then be welded back on the car, with one point being the tunnel horizontal, and the other end to the top of the door striker mount.
(you have to weld this back in before you cut the other ones out, or you'll have problems).
You'll also cut out the bar running reward and downward to the aft end of the 4" chassis tube, and the tube that goes downwards to the frame rail,
leave the one at the top going the side to side bulkhead alone.




You can see that Rick left about 2" of 1"x1" tubing on the striker mount, on the passengers side, you'll need to only leave about an inch. Way back when
these Coupes were first made, back in the Old days of Russ Thompson, we found out that the door frame mounts were not symmetrical side to side. The passengers
door mounts are any where from 3/4" to 1" lower than the drivers side. I had totally forgotten about this till we were working on Karens Coupe and Rick thought he
had done some thing wrong in measuring his cuts. So cut more on the passenger side than you do on the drivers side. I will have a fix for the door frame in the next week or two,
no major thing, just a little cutting and welding....


It will be worth it!!