making a rollbar safe and removable
01-01-2018, 05:20 PM
#1
Junior Member
Thread Starter
Join Date: Nov 2017
Posts: 112
Total Cats: 7
making a rollbar safe and removable
particularly this one
https://flic.kr/p/233Gjnkhttps://flic.kr/p/233Gjnk by https://www.flickr.com/photos/150940429@N02/, on Flickr
https://flic.kr/p/EV33QShttps://flic.kr/p/EV33QS by https://www.flickr.com/photos/150940429@N02/, on Flickr
spec miata main hoop segment, 2000 miata if you needed to know.
this is a $2018 challenge car, but im building in maximum safety that I can within budget and ability. its a thing i have....anyway, i learned about the absolute pain in the dick of a fully welded, NASCAR door bar equipped cage with the AMC IMSA clone we built last year. that car was never destined for anything but competition, so i dealt with it. made everything 100 times more difficult after it went in though. always in the way.
my NB daily has a hard dog ace in it. a bolt in. that is still in the way for a lot of various service procedures.
the challenge car will have essentially a radically overcomplicated hard dog sport. with extra tubes. as you can see in the picture (yes, no rear downtubes yet, as i haven't made them. they will go as far rearward as i feel comfortable with going and still being able to have some sort of top. im hoping to land them after the rear strut mounts.)
anyway, this thing needs main hoop feet made first and foremost. the hard dog sport has roughly 6 inch wide plates under the main hoop that go way down the rear bulkhead to clear a boxed section for the body, and bolt in there. they use some sort of backer plate on the other side. same way with the rear downtubes. plates under the body that are cut to clear the body.
i have no qualms about cutting things in this car. or welding. but i want to be able to remove the bar for service fairly easily. my thought was to make a 1/8 steel plate that goes into the hole where the seatbelt reel used to live and down the body about 10 inches. that would make it roughly a 12x6 solid plate. weld a few grade 8 1/2 nuts to this plate, and weld the plate to the body. make a corresponding plate welded to the main hoop feet with holes in it to put bolts through. 6 1/2 inch bolts per side minimum. in addition, weld a tab to the hoop that bolts to the seatbelt tower where the factory seatbelt guide mounted. i would also weld the seatbelt towers completely after cutting my clearance notches and such in to make them as strong as possible.
rear downtube feet would be done the same as space allows
but i question if this is the right approach. all the bolt in bars have the factory floor sandwiched, with a bigger plate on the interior side, and a smaller on the underside, and then use a nylock nut and bolt through. im uncertain if this is a safety reason, or an install reason, or both. may even have a touch of manufacturing reasoning.
welded in cages just have the 1/8 plate welded to the floor with the bars welded directly to it.
what are the thoughts of you guys? is this a good approach? would it pass tech for SCCA autocross, NHRA 11.99 and quicker tech, and possible HPDE in the future?
too long didn't read: can i weld a 1/8 plate to the floor with captured nuts, make a similar plate welded to the roll bar, and bolt the thing in and pass tech/not die?
https://flic.kr/p/233Gjnkhttps://flic.kr/p/233Gjnk by https://www.flickr.com/photos/150940429@N02/, on Flickr
https://flic.kr/p/EV33QShttps://flic.kr/p/EV33QS by https://www.flickr.com/photos/150940429@N02/, on Flickr
spec miata main hoop segment, 2000 miata if you needed to know.
this is a $2018 challenge car, but im building in maximum safety that I can within budget and ability. its a thing i have....anyway, i learned about the absolute pain in the dick of a fully welded, NASCAR door bar equipped cage with the AMC IMSA clone we built last year. that car was never destined for anything but competition, so i dealt with it. made everything 100 times more difficult after it went in though. always in the way.
my NB daily has a hard dog ace in it. a bolt in. that is still in the way for a lot of various service procedures.
the challenge car will have essentially a radically overcomplicated hard dog sport. with extra tubes. as you can see in the picture (yes, no rear downtubes yet, as i haven't made them. they will go as far rearward as i feel comfortable with going and still being able to have some sort of top. im hoping to land them after the rear strut mounts.)
anyway, this thing needs main hoop feet made first and foremost. the hard dog sport has roughly 6 inch wide plates under the main hoop that go way down the rear bulkhead to clear a boxed section for the body, and bolt in there. they use some sort of backer plate on the other side. same way with the rear downtubes. plates under the body that are cut to clear the body.
i have no qualms about cutting things in this car. or welding. but i want to be able to remove the bar for service fairly easily. my thought was to make a 1/8 steel plate that goes into the hole where the seatbelt reel used to live and down the body about 10 inches. that would make it roughly a 12x6 solid plate. weld a few grade 8 1/2 nuts to this plate, and weld the plate to the body. make a corresponding plate welded to the main hoop feet with holes in it to put bolts through. 6 1/2 inch bolts per side minimum. in addition, weld a tab to the hoop that bolts to the seatbelt tower where the factory seatbelt guide mounted. i would also weld the seatbelt towers completely after cutting my clearance notches and such in to make them as strong as possible.
rear downtube feet would be done the same as space allows
but i question if this is the right approach. all the bolt in bars have the factory floor sandwiched, with a bigger plate on the interior side, and a smaller on the underside, and then use a nylock nut and bolt through. im uncertain if this is a safety reason, or an install reason, or both. may even have a touch of manufacturing reasoning.
welded in cages just have the 1/8 plate welded to the floor with the bars welded directly to it.
what are the thoughts of you guys? is this a good approach? would it pass tech for SCCA autocross, NHRA 11.99 and quicker tech, and possible HPDE in the future?
too long didn't read: can i weld a 1/8 plate to the floor with captured nuts, make a similar plate welded to the roll bar, and bolt the thing in and pass tech/not die?
Reply
0
0
01-02-2018, 06:53 PM
#2
Senior Member
Join Date: Oct 2011
Location: Northridge, CA
Posts: 842
Total Cats: 412
This does not answer your question regarding the bar being removable, but honestly the answer should be that this roll bar shouldn't be welded at all since there's almost no chance of slipping this past tech since the design is not legal.
There are right ways and wrong ways to design roll over structures, this is definitely the wrong way.
Your diagonal needs to be a continuous piece with no bends, at a bare minimum.
There are right ways and wrong ways to design roll over structures, this is definitely the wrong way.
Your diagonal needs to be a continuous piece with no bends, at a bare minimum.
Reply
0
0
01-18-2018, 05:17 PM
#3
Newb
Join Date: Jul 2017
Posts: 22
Total Cats: 2
Yeah, the way you're describing to do this is no bueno. The reason for a sandwich plate on bolt-in bars is to better distribute the stresses that will be seen, with captive nuts the way you're saying, in the event of a rollover the structural integrity of your main hoop basically comes down to 100% the welds on those captive nuts - and if those shear, your roll bar is going to come loose, and you're then going to have a MUCH more interesting situation at hand.
I'm also a bit curious about what appears to be a bend in the middle of the top of your main hoop...I'm not sure whether or not that will fly. Which specific series are you prepping this for, and what does that particular rule book say?
I'm also a bit curious about what appears to be a bend in the middle of the top of your main hoop...I'm not sure whether or not that will fly. Which specific series are you prepping this for, and what does that particular rule book say?
Reply
0
0
01-18-2018, 05:27 PM
#4
Newb
Join Date: Jul 2017
Posts: 22
Total Cats: 2
OK, so looking more into this it looks like the $2018 Challenge falls under SCCA Solo rules.
"F. REMOVABLE ROLL BARS Removable roll bars and braces must be very carefully designed and constructed to be at least as strong as a permanent installation. If one tube fits inside another tube to facilitate removal, the removable portion must bottom on the permanent mounting, and at least two bolts must be used to secure each such joint. The telescope section must be at least eight inches in length."
Also, more in section 9.4 here: https://www.scca.com/downloads/39621-gcr-january-2018
While it may sacrifice some convenience, if it were me I'd rather sacrifice convenience vs safety.
"F. REMOVABLE ROLL BARS Removable roll bars and braces must be very carefully designed and constructed to be at least as strong as a permanent installation. If one tube fits inside another tube to facilitate removal, the removable portion must bottom on the permanent mounting, and at least two bolts must be used to secure each such joint. The telescope section must be at least eight inches in length."
Also, more in section 9.4 here: https://www.scca.com/downloads/39621-gcr-january-2018
While it may sacrifice some convenience, if it were me I'd rather sacrifice convenience vs safety.
Reply
0
0
Thread
Thread Starter
Forum
Replies
Last Post
mgeoffriau
Miata parts for sale/trade
0
02-05-2010 09:20 AM
mgeoffriau
Miata parts for sale/trade
7
12-04-2009 04:44 PM
