Roll bar hoop installed

 This weekend was very productive, I managed to end up with a really painful ankle after a piece of wood jumped out and bit me, and half a pinkie fingernail missing when a piece of metal that I was drilling decided to grab and spin... Anyway, on to the real purpose of the weekend.

The first job was to cut some mounting plate from 3mm plate, then drill the holes for the bolts. That was pretty simple, and meant I had a platform for the roll bar;

Supporting the hoop from above I could see roughly where it would sit, but I could also see that it wasn't even. Not overly surprising to be honest, I specifically asked for the material to be cut at a right angle. It's clear from the pictures above that there was too much of a gap, and it was quite clear that one leg was longer than the other. 

Once I'd figured out how to measure the tube, I was able to cut and profile the ends. Oh, cutting roll bar tube with a hacksaw is an exercise in futility! The angry grinder and cutting disc came to the rescue, although I was still giving myself about 20mm of grinding and profiling to do. 

Eventually I got it level and flat across the surfaces, so I mounted it back on to the car. At this point it occurred to be that I can gain myself a few centimetres in order to increase the angle between the hoop and the brace. I therefore moved the roll bar forward on the plate until it was inline with the bolts. A quick tack and weld up, and this is what I have now;

The tube still sits within the four bolt pattern, but it's closer to the chassis frame which hopefully is a good thing? I can do the same with the rear braces, move those backwards. Every couple of inches gets me another five degrees, so with this being one inch forward I'm halfway there. Obviously I'll never go racing in this (maybe a track day at most), but at least if I aim for what MSUK suggest then I can have a bit of peace of mind. 

One thing I did note that despite me getting everything really hot when welding, the bolts loosened off really easily. There was no misalignment or similar issues. I thought I had twisted something when I started tacking it up as the right hand side had deflected a few mm. but after bracing it, welding it up then letting it cool it all settled down into a good position. 

For the rear braces it's back to the frame;

This was a little easier, with the frame not yet on the car I was able to cut and drill the plates for the braces without having to contort myself across the back of the car. Once this is welded up and on the back of the car I can finish the roll bar. Oh, I did notice that the passenger side plate doesn't quite line up anymore due to the captive nut weld, I'll have to bear that in mind when I finish the welding (they're only tacked in place at the moment). 

However there is a sequence to follow now. I want to get to the back of the car, which does mean that turning the car round in the garage would be the best option. But the bodywork supports can also benefit from the car being the other way round. So next job is to tack on the side support that is visible, then spin the car, then do the other side support and the rear. That way I can have the roll bar done and the bodywork support ready to go at a similar time. I still need to understand how the braces go through the bodywork, especially with the saddle clamps that I'll be using.

Oh, on the subject of saddle clamps...  I can see how they would fit and I think they'll only need a small amount of trimming to get the angle. It's going to be how close I can get the braces to vertical that'll be the tricky issue. Too far along and the angle will be off, but too close to the bend and it'll be the bend itself that causes the saddle clamps to need adjustment. And I've just thought of something, I need to find the centre line of the roll bar. Logic would suggest that it's the centre line of the car, but even that isn't straightforward. I might get the centreline sorted tonight as a mini-project, I won't have enough time to get all the welding done and turn the car around. Tomorrow I'm in the office and Wednesday will be making planters for the front garden. 

Real roll bar

 After deciding how things were going to be set up, I placed the order. And here it is!

OK, yes it's just a bunch of tubes at the moment, but just by the weight of them I can tell they will do the job.

A big shoutout to Race Spec Cages, AKA Tube Bender on Ebay. I asked about the removable links between the hoop and the struts, and he suggested the clamps could work even though it was off centre. The clamps are lying on the hoop in the picture above. With a solution for removable links in hand I went ahead and ordered it. It cost me £140 all in, which is roughly what I expected for the three bars, the bent hoop and the brackets. 

A quick fit against the drain pipe version shows that it's slightly taller, which isn't a bad thing. I've got to finish the ends ready for the plate, and the struts are actually long enough to reach the taller hoop so I'm tempted to run it at the slight height increase. It doesn't affect the cross brace, as you can see in the photo I requested a bar long enough to fit anywhere in the hoop. 

Next step is to make the mounting plates ready to weld to the bottom of the hoops and struts. Then I'll level off the hoop and angle the ends correctly, then start lining everything up. It's a fair bit of work to be honest, but it's a nice 'isolated' block. I don't have to rely on anything else included in the test fit.

Of course, it'll all change when the bodywork goes back on as I'll need to thread it through, but that should be a minor challenge. 

Oh, and it all needs cleaning! It's all scaled up and oily, as you would expect out of an engineering shop. A quick degrease then ten minutes with an appropriate cleaning disc on the angry grinder will sort it. 

Tank platform and roll bar brace

 This weekend was another busy one, bringing out the rear of the diff cage to provide a good platform for the fuel tank and somewhere fort he rear braces to go. 

The first thing that had to change was the position of the roll bar support. I had originally planned it for right on the corner of the fuel tank like this;

But in real life that wasn't going to be possible. The platform for the roll bar would be sticking out into thin air and very difficult to support. Instead I went for bringing in the support to line up with the tank;

Using 1 inch steel in a U shape off the back of the diff cage means that both the fuel tank and the roll cage support get some pretty beefy metal. I reproduced the roll hoop base to make sure it's consistent, so it's a 110mm pad with 70mm bolt distances. The whole thing will be braced to the bottom of the diff cage, and I also cut some more 3mm plate to form a box. That might seem a bit 'excessive' but does that word have meaning when it comes to roll cage strength?

The only doubt now is that the angle of the bar is lower than MSUK yearbook requirements. It's sat at 25 degrees instead of the required 30. To get the 30 degrees I'd have to move it back 50mm. That might be possible if I can get the captive bolts in place inside the rear tube (which isn't a bad thing, I just need to cut open the tube in order to weld them in place).

[Maths reference, with a 734mm long bar, 20 degrees needs 251mm from base to base, 25 degrees is 310mm and 30 degrees is 367mm]. 

In fact, just thinking about that step... I could take the plates back off, weld the nuts to the bottom of the plate (the same as it's done for the normal suspension top), then just cut an appropriate hole in the bar. That would mean the nut is in place but the bar itself doesn't have a big gaping hole in it. Thankfully I've only tacked the plated in place at this stage, it won't take much to cut the tacks and start again. I just need to drill the holes first to make sure it lines back up when I'm done. That's this evenings job I think. 

For tube lengths, I've got each strut at 800, the cross bar at 1000, then whatever is needed for the hoop. 

In other news, I got the captive nuts welded in for the seat bases, and the matching holes drilled in the wood. It looks like the bolts screw through far enough to come up flush with the wood, so that should mean I won't feel the bolts through the seat. I'm still worried about the movement on the drivers seat though, it seems to bind very easily. Still, given that it won't be moving very often I am hoping it's ok as is. 

Final roll bar design

 Well, I think I finally have a good solution. As per my previous post, I will be able to go backwards for the support bars. With the fuel tank in place, I was able to measure where the corners ended up, and how I could brace them. This picture shows the angle of the first support in relation to the swirl pot;

Coming straight up from the bottom joint gives clearance up to the corner of the fuel tank. For the horizontal support I have plenty of options;

I'm tempted to come off the open tube as that needs sealing up anyway. With those two as the triangle to support the tank, I can then add a bar straight across for the tank to sit on.

That bar will then become the support for the roll bar;

So the fuel tank will be sitting between the roll bar supports, and the roll bar itself will be braced against the suspension brackets on the diff cage (which is probably the strongest part of the car at the moment!!).

to check the angle I took a picture of the side view;

That angle is 35 degrees, and considering MSUK yearbook says 30 degrees minimum I'm happy with that. 

So this weekend I'm going to weld up a platform for the tank. However, I've just realised the support structure for the rear of the chassis also needs to be included. I'll have to look at that and see if they can both be added at the same time. If not it's just an extra task a bit later on. 

Change of plan for the roll bar

 Once again locostbuilders to the rescue. I posted my pictures for the roll bar design and the feedback was, erm, not good. Some of the points were similar to what I was thinking, others I'd not really thought about.

MrWhippy was the most succinct in feedback;

1. Angle is far too steep. I wasn't sure about this, but it wasn't a good sign that 'the tube bender' only cuts roll bar fish mouths for up to 45 degrees. At what angle does a triangle no longer become a triangle? This MX5 roll bar is a perfect example;

Are those 'support bars' actually supporting? 

2. The brace is not mounted to a strong part of the chassis. This one I wasn't sure about, I think it was the picture angle. The brace comes down to the triangulation point of the chassis, as well as very close to the lateral support for the seats. That's five lengths of 25mm steel converging at one point. As long as I got the fixing right (welded 5mm plate for example) that would be more than enough. 

3. The brace is only supporting half the height of the hoop. Yep, very accurate. I'm introducing forces to the edge of a triangle rather than the corner. It needs to be brought all the way to the top. That would mean a tighter angle on the side bar though.

After a few back and forth discussions (thank you Russbost, Mr Whippy, adampage and adithorp) it is clear that whatever I do on the side I'll just be swapping one compromise for another. I wouldn't actually get the structure required to keep my head off the floor with the car upside down. 

adampage had an interesting idea though. Why not bring it down to the diff cage? Initially it was a no-go, that's where I have my fuel tank;

But as I looked at those photos I realised that I still need to build out a platform for the fuel tank. That strap is currently the only thing holding the tank on to about two inches of metal! Since I have to support the fuel tank already, why not simply build it out to either side to make platforms for rear braces. They could be triangulated to the diff cage (which is a substantial cube already) and I wouldn't lose any boot space because of it. 

The only thing I'd need to consider is getting the bars through the bodywork. I'd need to make sure that at least one end of the roll bar is as thin as it can get. There's a couple of options, both appear on this roll bar;

The first option is a sleeve with bolts through, the example can be seen top left and right and is a 'double bolt' arrangement. That would require finding some tube that fitted tightly inside the roll bar tube.

The second option is a double shear bracket with a bolt through, which is what is used on the diagonals in the image. I prefer that one to be honest. Demon Tweeks sell the OMP gudgeon pin and weldable roll bar connection, but I could also use steel plate. 

Hmm, looks like Race Spec Cages (AKA Ebat Tube Bender) have the sleeve option; https://www.ebay.co.uk/itm/331096168053. I'm not sure it would work though, to keep things tight the bar would not have any 'wiggle room' which would make it difficult to fit. 

Anyhow, first thing is back to the prototype stage to build out the platform and see if the rear stays would work around the fuel tank. 

Edit: A quick note on angles. Looking at the MSUK yearbook I can see that a minimum angle of 30 degrees is required. At least that gives me something to work to. It also gives some guidance on bracket types and there's a few options. I'm assuming if they're MSUK approved then they're good enough for me. Images K21 to K30 show the various brackets, starting on page 200 of the rule book. 

Seat belts

 When I was putting the seats in, my attention came back to the seat belts, in particular the buckles. The Mark 1 are on a large stalk and wouldn't be suitable. I bought some mark 2 buckles off Ebay, I had 'lost' them but managed to find them in my tool box.

Unfortunately while they are shorted than the mark 1, they're actually so short that they interfere with the seat! So they're not suitable. Back to the mark 1 buckles.

I did notice that the buckle was covered in a hard plastic with a metal support bar. I realised that if I remove the plastic and the bar it becomes a regular buckle. This picture shows what I'm working with;

The far right is the mark 2 belt, originally it looks like a good idea but turns out it's not. The far left is the original mark 1 with a plastic shell keeping it stiff. The centre is the one I'm going to use, it has a suitable length of webbing so that it doesn't interfere with the seat, but it also means that it's floppy enough to work as a seat belt. The buckle should sit roughly at the hip depending on where the seat is positioned. 

So that means at the end of the weekend I have;

1. Seats on working seat rails.

2. A roll bar ready to be measured and ordered.

3. Seat belts ready to be bolted in place (although the top seat mounting needs the roll bar). 

There's a few details to be finished up, then I can get the foam and cover on to the seats. 

Next big job, engine fit and propshaft measure.

Seat mounting rails

 Another job finished up this weekend was the chassis mounting rails. This was a pain because it wasn't until I tried to fit the drivers door that I realised they're not matching! The passenger seat went in ok, and it works;

I put the aluminium panels in just to make sure it all moved correctly without binding. It does go back far enough to touch the seat belt reel but it doesn't stop the mechanism from working. I could also put a stop on the rail if needed. 

The drivers side went in and I immediately realised there wasn't enough tension on the seat rail wire. Only one side would release. So I had to reposition the drivers side rail, but eventually I got them both fixed in place;

The seat bases need to be fixed in place, and the nuts need to be welded in place. Once I have the foam and covers on I'll only be able to get to one side, so I need to weld those nuts on. To bolt the seats to the car I have access top and bottom so don't need to weld them in place. 

This did present a problem though, there is very little clearance on either side. The seat belt locks won't fit...

Roll bar prototype finish

 Apart from an old geezer getting a posh hat, this weekend has been very busy. I'll split it into several posts because otherwise I might miss something.

First task was the roll bar. With the hoop bolted in place, I ran a second tube down the side of the car to get an idea of how to brace it. I wanted to minimise bends on this part to make sure the loads went into the chassis and not into the bends. 

I've attached the brace as high as I could before the bend starts on the hoop. It then comes down to halfway down the top bar, then parallel to the same bar all the way down to the floor pan. 

This picture shows the final result once it had been glued and taped up;

A couple of things to note. The bar bends upwards and inwards, but I actually managed to do both in one bend. That does mean I can just have it bent in one (and I know the angle now), but I can't get them to cut either end. I'll have to order them longer and cut them to suit. 

The other thing is the forces involved. With the plastic bar I can see how it would deform, and as expected it's the side bar bend. However what I can do is add another bracket so it's not just fixed to the bottom. 

So now I can get this ordered. It'll be four pieces. The roll bar hoop, two sides and the centre bar. I still need to prototype that length but it's not going to be difficult. I then need to figure out how to get the body over the top of it, I might do that before I have the real thing. 

Looks like I'll need about 5 metres of tube, and 4 bends. 44.45mm tube for 5 metres is £66, I don't know how much the bending is though. Hopefully because they're only small bends in a single line it won't be too difficult to produce. It would probably cost more to post than to bend!

But that's it for the roll bar mock up, the next time I'll be working on it will be to weld it up. 

(Edit) A couple of extra photos;

Bodywork brackets

 One of the things I've been working on is the bodywork brackets. The outriggers will stick out of the car around 4 inches or so, but I wanted to have them removable as well as load bearing.

I came up with this set up;

It consists of an outer sleeve that will be welded to the chassis, and an inner sleeve that will be welded to the rail. The left hand one is tack welded to the rail. When on the car, the rail will slot into the sleeve (centre), then an M8 bolt, washer and nut that will go through both (right). 

The 'cup' of the outer sleeve will provide support, with the length of the inner sleeve providing leverage. The bolt is in single shear which I wanted to avoid, but it does provide the clamping force needed to keep things tight. 

Roll bar prototype

 

The picture says it all really!! This was a fun task, making a prototype roll bar out of waste pipe. The CDS used for roll bars is either 44mm or 50mm for motorsport compliance. Not that I need compliance but it's nice to have a standard to work to. This waste pipe is 40mm, so basically 2mm out either side.

This is the main hoop with the correct bend radius. The distance between blue marks is the 140mm centre line radius that 'the tube bender' (AKA Race Spec Cages in Rugby) quotes on his ebay listing. 

This prototype has given me so much information. First is the expected height, I could see that from the top of the roll bar to the front of the car drew a line that was above my head height. Well, only slightly above my head height, I'll need to wear a helmet as well. The side angle is a decent look, it's not really clear on this picture but both sides are angled in a bit. 

The main thing it gives me is some guidance on how the side impact bars can come down and triangulate the roll bar. From the previous post I was aiming for this;

And I'm happy that it will work like that. I do need to get the body on though, I'm going to need to cut it for the roll bar but I may also need additional cuts for the side bars. I'm pretty much certain that I'll be removing the side pods inside the body though, I can't get them to match my chassis and I'd waste a lot of time trying to do so. I do need to figure out a shelf or something though, again from previous posts it's this look I'm after;

That reminds me, I do need to get some more photos from the kit car show for this particular layout. It also needs to be fixed to the body, so that'll be some angle brackets and more glue!

I'm digressing, this was a roll bar post. Next job, a bit more pipe and figure out how it can mount to the chassis without interfering with the body. 

Change of approach for the seats

 Along with a few other jobs (photos of my 'roll bar' to come next!), I've been looking at the seat mounting again. First job was to shrink the holes to M8. Using M14 bolts in the first place was just completely wrong, I'd decided on it based on the holes in the seat rails and not realised the Mazda screws are a 'top hat' design. Basically the head of the bolt is M14, the rest of it is much thinner. Anyway, some M8 penny washers welded in place seems to have done the trick. I won't change the frame, mainly because it's too awkward but also it's good to have a bit of tolerance.

So now it's on to the fixing. My first plan was to use self tappers into the wood. Now that was a really stupid idea!! Any impact at all would have left the seat torn from it's mountings, folded up like a deckchair! I need to fix it to the frame, either by welding directly or by mounting some plates on the frame and securing it to those. Thankfully the positioning of the rails is right up against the sides of the seat, so it wouldn't take much to weld some plate where the fixing holes go. 

It also means that I avoid a problem that I was seeing. The rail mountings have a slightly raised section where the locking mechanism is. Trying to mount that to the seats would have meant either channelling out a section of the wood or raising it up on yet more wood. I don't need to worry about either of those now as the plates will raise the seats slightly anyway.

And then it's on to the fixing. Now that I'm bolting metal to metal it becomes really simple, a captive nut (or bolt?) welded to the plate will provide the relevant anchor, a small recess in the wood will host the head. Actually, thinking about it I'll go for a captive bolt. Or can I... Hmm, I'd best check the clearance before I head out to the DIY store. Yep, it's a bank holiday so I'm going to a DIY store. Shelves to be put up and all that. 

(Later that day...)

Rather than start a brand new post I thought an extension to the existing one would be better. Back to seat belts. The rules are pretty straightforward and common sense, the main one is that the belt cannot be affected by the seat. They class it as a 'change of direction' and basically means that if the belt could apply force to the seat, the seat has to be able to take it.

The upper fixing also needs to be 450mm off the R reference point. That does mean I need to either lift the bracket, or simply work off the roll bar. I think a welded bracket on the cross bar is the easiest option there, it's how they do it in the book.

Time for an obligatory photo;

Yes, this is the passenger seat. I decided very early on that the seat belts would work better 'backwards'. That is the inertia reel and upper mounting would sit inboard rather than outboard, then the buckle sits on the outside.

This shows a few things. First, I need to remember to leave space for the inertia reel. I had forgotten this, but this doesn't cause an issue as I just need to remember to mount the seat on the runners so it can't go that far back. To be fair it doesn't take up that much space anyway, so I'm only losing maybe an inch of rearward travel. I've already figured out that having the seat that far back leaves me completely out of range of the pedals and the wheel!!

Second is the fixings. They need to be proper seat belt fixings that allow the belts to rotate. The standard belts do this by using a sleeve and a series of washers, I'll probably do the same. That'll be for both hip fixings and the shoulder fixings, the inertia reel needs to be fixed. And I mean fixed, these reels only work if they are vertical so they can't be allowed to move. 

Third is the buckle, I need to find out where I put the shorter buckles. I remember ordering them off Ebay, I remember receiving them, I remember having to strip one down to find out why it wasn't working. I just can't find them now!! I might go back through the blog and see where I last had them. 

Fourth is the sleeves. The inertia reel is currently clamped to the chassis rail, however I'll need to put a bolt through to secure it. This will mean drill, weld a sleeve, grind it flat, then bolts in place. Thinking about it only the inertia reel fixings need the sleeves for now, the two lap fixings are there by design and the shoulder fixing can't be done until I sort the roll bar.

So back to the seat fixings to the runners... there's still a few hours of today left so I'll get stuck in.

At least the colour will work nicely with the leatherette seat covers, but they do still need a good clean.

(Edit: It doesn't look like I posted anything about the seat buckles, they arrived September 2021 and the only thing more recent was the batch of ones from the last few weeks. Looks like I might have to find myself some new ones)