M758

Wow... I get a bar named after me!



Hmm... Well the good news with the bar is you took the load off of the support braces.

The BAD NEWS is that you cataleviered all the load from two based points to just one. Now all the belt load will go through the base plate in bending probably a worse situation.

Now... however you tie the front of the "joe bar" and either complete the hoop or tie it in to the main hoop and then to ground with a door bar system you are ok.


The only good thing is that my guess is that belts are the weak spot. With this or your old design the belts would fail before the bars would fail.

Worse case with this desing is a little flex may come in as bar acts like a spring.

Sorry... BTW... don't feel bad. I am a trained Mechanical Engineer and spent years designing and analyzing the structural components in Jet Engines.

gt3cup

John,
Let me rephrase... I think your welding is art unto itself , but have you ever done any motorsports related artwork? (in paint or watercolor mediums)
Mark

RedlineMan

Oh Ye of Little Faith...

...And quick surmize. Now, if you were to guess at what a good fabricator might do to strengthen such a structure, what would it be? If you are a good engineer, or guesser, you might say that he would create a triangle from the rear brace and the curved legs of the belt bar assembly. That, of course, is exactly what was planned from the start. When the half-round tube is welded to the rear brace, it becomes a triangulated assembly of considerable strength, more than enough to handle the job.

A bit obvious, no? Patience Joe... patience.

RedlineMan

My welding is adequate. Everything I do is a lot more than welding!

gt3cup

John,

That's the one I was talking about! Thought I recognized the name. Your artwork has been hanging in my office for ... close to 10 years?

It is still one of my favorites!

M758

Ok,
Lets see what else you come up with...

leif997

Nice work/welds.....You've never seen it done before because it'll never pass PCA club racing tech inspection....harness straps must wrap the bar and must be safety pinned......why go through the trouble of putting such a nice bar and then put all of your safety concerns into the shearing strength of a single eye bolt? Makes no sense at all. Back to the drawing board.....

RedlineMan

Indeed?

Here is the sum total of all text pertaining to harnesses from the 2006 PCA rule book.

13. Five or six point competition harnesses, properly mounted, are required as detailed in Appendix B. Harnesses cannot be mounted to seat or seat rail. Mounting must be to the chassis backed by large diameter washers or to the roll bar. No two harness straps can be attached to a single mounting bolt. No Y-type shoulder harnesses are allowed. The angle of the shoulder harness going back from the driver’s shoulders cannot be above nor exceed 40 degrees below the horizontal plane of the shoulders. The anti-submarine straps should be mounted such that they will not allow upward vertical movement of the lap belt due to “crushing” of the front seat cushion in any situation.

APPENDIX B - SEAT BELT SPECIFICATIONS
Harnesses must be SFI or FIA approved for competition, with 3" lap and shoulder webbing and 2" submarine strap webbing. Any FIA approved 5- or 6-point competition harness is allowed, specifically those with 2” lap webbing or 2” sections of the shoulder webbing designed to fit over the yoke of a head and neck restraint device. Strap material must be replaced every five years but straps should be inspected regularly and replaced sooner if needed.

Perhaps you have a different version of the rule book?

You've made some rather hasty assumptions here, Leif. Do you not know what happens when you ***ume? Ahh... if only Felix Unger could be here to explain it. He did it with such flair, don't you know.

Since there will obviously be two shoulder belts, there will also be two eye bolts. They are loaded in tension, not shear, by the way. They are also designed for this express purpose, although it is far more common to see them used for lap belts. I do not know the yield spec for them off hand, but as they are rather ubiquitous I must imagine it is rather lofty. As they are surely at least Grade 8 I would imagine it is somewhere well North of 3-4000lbs. Since the lap belt will see roughly twice the load as a shoulder strap, it would seem they were up to the task, no? The reality is that the belts will fail well before the eye bolt will.

Does your rule book say they are not legal?

FD Frank

John, I recommend you remove the cardboard from in front of the windshield before you drive...or at least secure it with more duct tape!
Keep well,
Frank

kurt M

Not to jump on a pile and I bet the setup you had to start with would have been fine overall but you could also just add a second brace on each side
1. Run a tube from the root of the main hoop to the center of the brace and weld cross bar to this. This is my choice. This will add to the overall system as well by triangulating the brace. Foward load will be taken up by the main hoop base in compression and the brace in tension. Both are easly up to the task. 2. Line a second brace, parallel to existing, but foward at the lower point and just below the upper point so it intersects where you want the harness bar to go. It will then add to the overall strength of the system.

Both. Add a short tube from the center of the cross tube down to the existing red painted cross tube and on to the tub to further spread load and prevent bending during an event.

I like simple is better whenever possible and it is hard to beat a strap around the bar and held by a 3 bar clip for simple.

Straps need to be wrapped OR pinned. The pins are for clip in ends. No clip on a wrapped end.

Ya gotta stop posting this stuff when there is no track driving to keep us busy!

RedlineMan

Yes, I could add all kinds of stuff. In full agreement with your subsequent statement about simplicity, I like it now. It is easy to add stuff. It's also easy to make a cage heavy... and ugly. I like where I'm at... mostly.

This one was on the short list of "possible" additions, if it does not muck up the workings of my floor, and if it don't look ugly! This might also be done with a tube from the belt bar to the diagonal that I have ready to weld in when other items are finished. I hate diagonals. They really make it hard to get back there once they are in!

Again, full agreement. I just wrapped mine around a clip instead of a tube. My setup has other advantages, too. 1) Free float to seek straight load paths (they are set narrower than the seat openings for my HANS). 2) Already fixed to prevent lateral slide on a tube (no messy padding, collars, or other visually distracting junk to hold them in place). 3) I can easily switch belts for other drivers (I'm quite a bit taller than my lady friend). 4) Since I do not have to leave room in my loop so that the belt can rotate on a tube, I can make my 3-bar install fully tight againt the clip. In other words, there is no slack to slip (3-bar slides WILL slide until all the slack is out of the loop!). 5) It just looks so incredibly sanitary!

I thought that was why I was posting? I'm not making you antsy, am I?

RedlineMan

OK;

Here's what I've got. I REALLY like the way it looks, but here is why I think it also works structurally.



Belt force will first be transmitted to the cage in line #1. In very simplistic terms, most would say this would also pull in on the rear brace as well. However, I can assure you that - having cut out more than one tube in my time - the by products of the welding process have this tube stretched VERY tight, putting it under quite a bit of tension. As such it will not bend nearly as easily as most people are likely thinking (as you stated, Kurt, it was likely fine in the first design). It will instead be pulling inward following lines #3 & #4. That will, of course, go no where.

However, before any of that can even take place, the triangle created by the half-round of the belt bar and the rear brace will send the force down following #2 where it terminates in the sill tube. Again, it's all going no where.

Nope, I don't think any of it is going ANYWHERE. Everyone's thoughts are welcome, of course... as long as it doesn't cause you to go into a bad case of track withdrawal!

More pics coming, probably this afternoon.

RedlineMan

Hey All;

Just a couple of new detail pics. A couple of years ago, I did a 930 cage where I boxed the side hoops of the cage into the area around the cowl and dash. It looked really tidy, and it stuck in my mind. To that end, I have been spending the last couple of days doing just that on my main hoop.



Here is how the main hoop intersects my signature sill tube that forms the foundation of my cages. I didn't want to bend the bottom of the hoop to meet the sill tube, so I plated the frame area and welded the tube to the plate as per normal.

You can also see the base of the main hoop diagonal brace coming in to intersect the sill tube. I did not necessarily want it to be set back away from the main hoop as it is here, but I also wanted to maintain full seat travel rearward, which tieing into the base of the hoop would have prevented. It is artfully gusseted into the sill tube in such a way as to tie it in more towards the main hoop where you would normally see them attach.



I then box it in with plate to tie it into the sill tube and inner side panel. I know that this boxing stands to potentially stiffen everything, but I am honestly doing it mostly for cosmetic reasons. It just looks so nice! This will also give a very solid beam structure from which to build a very stout door bar assembly. Door bars are only as strong as what they attach to, and this is FAR stronger than just a tube floating out in thin air!

As you might imagine, this detail stuff takes a LOT of time, but the end result is worth it!

More to come.

Cory M

The bolt shaft is in tension but the threads are in shear.

RedlineMan

Yes, that makes sense, Cory. I stand enlightened.

----------------------------------------------------------------------------------------
Now a question for the masses, particularly the injuneers! I am quite torn about x-bracing the rear of the cage. I know the perceived advantage; stiffness. I'm wondering if there is a truly worthwhile gain in this regard? Is it worth the weight? More importantly to me, is it worth fouling the rear view? Is it worth exceeding the point of visual purity?

Yes... I do think of such things. Performance is all well and good, but in the final analysis, there is a lot to be said for owning something that is esthetically pleasing... for the long term.

So, what say you?