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PostPosted: November 30, 2018, 8:41 pm 
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Location: Carlsbad, California, USA
I looking for a low cost way of duplicating the curves found at the rear of a Caterham chassis. Here are the ones I'm talking about shown on a bare chassis.
Attachment:
Caterham Curve 1 -Small.jpg


Here's a view with finished body panels in place.
Attachment:
Caterham Roadsport Boot 2.jpg


Here is a typical upper, rear hoop on a Locost. In this case it's my as yet un-built one, modeled from the Haynes Roadster. The hoop is flat in side view. The fender guards are usually traced out in plate material separately.
Attachment:
Haynes Upper Hoop.jpg


As I see it, there are two classes of curves here. One is a simple radius bend at the rear corners of the boot, and the other is a gradual, more sculptured, side curves, which give the sensuous shape to the boot best illustrated by the body panel photo above.

I need to make these from tools I can afford, which basically means something I make myself. It seems silly to buy machines costing hundreds of dollars just to make these few parts. I'm looking for ideas, or solutions, from folks who have done curves like this in the past. My parts will be built from 3/4" (19 mm) mild steel tube of 16 gauge. I would like the radius curve to be around 3-1/2" radius. I'll do the gentle curves by eye on a pattern I lay out on the garage floor, I think.

It would be nice to do the rear hoop in one piece, but I'm willing to do it in 3 parts and weld them together if necessary.

I'm thinking I'll need something similar to this (but home made) for the radius curves.
Attachment:
Radius Bender.jpg


For the gentle curve, I'm expecting I'll need to do a low cost version of the classis, 3-wheeled bender like this one, only home made.
Attachment:
3-Wheel Tube Roller.jpg


How have you done curves like this on a budget?


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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: November 30, 2018, 11:29 pm 
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How have you done curves like this on a budget?[/quote]

The tube roller will do indeed both shallow curves and 90 deg. The difficult parts to make are the rollers. You will need three for each tube size. One cheap way to go about this would be to do all your bending in the same tube size, buy the rollers (only) and fabricate your own machine. Not all that complicated but time consuming. Harbour Freight or Easwood will sell you the rollers . :cheers:


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PostPosted: December 1, 2018, 8:23 am 
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I'd use 12 ga instead of 16 ga or 3/4 std schedule pipe. Much easier to bend thicker wall material without kinking the 90 deg bends. The rear hoop is largely unsupported crumple so a little more wall is not a bad idea.

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PostPosted: December 1, 2018, 9:48 am 
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Location: 4AGE in S.E. Michigan
I was able to make the rear top boot radius tube from an old steel lawn chair. It work out perfect for the boot. It was 2 pieces with a sleeved center section at the mid point weld. The fender radius was made using a plywood form and some heat. The form was a crispy critter when finished but you only need two loops. That large a radius, will bend easily, just heating the inboard surface.
I would suggest that when you weld on the top boot loop, to add a slight downward sloop 1 to 1 1/2", which will make it look better and prevent any rain water from flowing into the cockpit area during braking. "Don't ask how we know".
DaveW


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PostPosted: December 1, 2018, 1:30 pm 
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Joined: January 14, 2006, 1:06 pm
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Location: Vista (north of San Diego CA)
I did mine on the cheap - The old "fill with sand, plug the ends, bend" method. I made a jig out of a wood round with a steel strap wrapped around it and sandwiched it between a big post and a piece of 3/8" steel. The pictures give an idea how it was done. I'm not sure this would work if you were using 16ga steel tube. The EMT is soft stuff and bends easily. Welding is a bit tougher than the 16ga. though.

John H.


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PostPosted: December 1, 2018, 4:17 pm 
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Location: Delaware
We did the gentle curves on my chassis with a 3 wheel roller from HF. The roller was originally purchased to make garden low tunnels out of conduit.


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PostPosted: December 1, 2018, 6:07 pm 
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This bender is on my (constantly expanding) list of tools to make


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PostPosted: December 1, 2018, 9:35 pm 
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A conduit bender worked for me.


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PostPosted: December 2, 2018, 12:51 pm 
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Thanks everyone for the great responses. I'll include a response to each one here, so I don't create a blizzard of entries.

@phil
I'm going to look into the rollers, Phil. I've never used a machine like that. I didn't know you could do 90 degree bends with them. For right now, I only need to do 3/4” tube, but I've found that 1/2” tube has many uses too, and it would be nice to have that capability too.

@MV8
I have several 10' lengths of 3/4” by 16 gauge. So, I'm just going to consume the material I have on hand. Thanks for the input, however.

@davew
When you used the plywood form for the gentle shape, what did you use to force the heated tubing down onto the form, and what held it in place to cool once it was down?

It's interesting that you mention just heating the inside surface. What is the reason for doing it that way versus heating the whole tube? I would think doing one side would tend to make it kink when bent. Not so?

@Locost_John
Hey, John, long time no see. Now that you have a new barn, have you had any itch to do another Locost? I was just looking at your clamshell fender method a few day ago and wondering if I'd want to take that on. I like the notion of doing ones that fits just right for my build and track, but I'm also trying to cut down on my task list, so I can get this car on the road.

As I mentioned above, I've got the 3/4” x 16 gauge on hand. I know people have worked 3/4” x 16 gauge with the sand method before. It certainly is a low cost method. I'd like something more mechanical because I like the control and repeatability of a machine/mechanical process.

@hfmaxi
Thanks for that input. That reinforces the idea that it may be a good solution now that I know you can do 90 degree bends too.

@Sean in CT
That bender in the photos is an interesting personal story for me, Sean.

I first saw it in a metalshaping book. The fellow in the photo does a lot of Cobra bodies, among other things. He's in business, so I wrote to him and offered him $100 if he supply me with more info and let me build one for my personal, non-commercial use.

He was very friendly, and thanked me for not just ripping him off and said he'd do it. However, when I followed up some weeks later, he said he entered into an agreement to commercialize it, and it would appear in the near future. He has a metal shaping school and a relationship with Baileigh. I assume that's who he now has the commercialization relationship with.

It's probably the most appealing tool I've seen yet: super-simple; intuitive; easy to build and store. I've seen some of the shapes he's made with it. It's quite versatile despite its simplicity.

@nick47
Thanks for the input, Nick. I did look at those. The smallest radius I've found for a 3/4” tube is about 4-1/4”. I felt that was too big for what I wanted to accomplish. I'm hoping to keep the radius to around 3-1/2”.

Thanks all for your responses.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: December 2, 2018, 5:45 pm 
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Lonnie - i found those pics on the net a while back. I think it is scanned from a book. Also saw some pics of a giant version of the same used in ship building. Looks not only simple, but very versatile. I think his name is Mark - i have seen youtube videos of him building cobra parts with Balleigh tools (as you mentioned)


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PostPosted: December 4, 2018, 5:16 pm 
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Location: Vista (north of San Diego CA)
Lonnie - It has been a while, but I get on in stealth mode occasionally and check your progress. ;-)
I have a boat now that is taking up too much time on land and too little on the water. I've had the engine out 3 or 4 times in the last five years either replacing it or getting it out of the way for a new fuel tank. I happen to be home today waiting for delivery of my nearly new and just repaired (warranty service) outdrive. Like the Locost, I do it all myself.

I had the rear axle out of the car to replace the ring & pinion a couple of years ago. Turned out the 6-3/4" Ford was different for the late 60's Falcon and the early 70's Pinto. I lost interest at that point and just got the axle back in this past weekend. Should be on the road again soon.

John


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PostPosted: December 4, 2018, 11:38 pm 
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[quote="Lonnie-S"]Thanks everyone for the great responses. I'll include a response to each one here, so I don't create a blizzard of entries.

@phil
I'm going to look into the rollers, Phil. I've never used a machine like that. I didn't know you could do 90 degree bends with them. For right now, I only need to do 3/4” tube, but I've found that 1/2” tube has many uses too, and it would be nice to have that capability too.

A foot note to my comment:

The 3 wheel roller will bend tubes to 90 degrees but the radius will be larger than with the single die handle types.


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PostPosted: December 5, 2018, 9:33 am 
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@davew
When you used the plywood form for the gentle shape, what did you use to force the heated tubing down onto the form, and what held it in place to cool once it was down?

It's interesting that you mention just heating the inside surface. What is the reason for doing it that way versus heating the whole tube? I would think doing one side would tend to make it kink when bent. Not so?

The form had a cut out to allow a C clamp to be used at one end for holding the tubing down. I had 5 or 6 small sections of wood attached along each side to prevent the tubing from slip off the form.
I heated the inside of the tube, because compressing the wall is more difficult then stretching the out board side. In reality there probably was not more than 200* difference in the heating temp, between the inboard and outboard surfaces.
I did have a few small kinks on the inboard side, [at the start of the curve when it was the hottest] but those are covered up sheet metal or interior trim.
To bend the tube, I just had a couple extra feet of tubing, as leverage, and a gloved hands to bend it around the form. I did not have to worry about cool down time. I Could only get about 2/3 around the form and then have to reheat, to get the last 1/3, to finish the bend. If you apply to much heat the out board surface of the tubing will flatten out.
DaveW


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PostPosted: December 5, 2018, 1:12 pm 
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@Locost_Johnh
We'll have to get together sometime in the near future, John. There's actually much more done on my build than shows at this time, but once I get it off the build table, and the engine/transmission goes back in, it will look pretty much like a car. Maybe then?

@phil
Thanks for that additional info Phil. I really like the idea of a 3-roller setup because it is more general in terms of the curves you can produce. I can see using the die/radius type bender in several future projects, so that is nice too. Just by accident, I discovered a much cheaper die/radius bender from an online article. It's only $139 and does 3/8" through 1". The fellow writing the article claims to get excellent result from it. I'm tempted, but I think I want to do the 3-roller type too - just build my own. That way, I'd have extensive capabilities from tight radius to gentle curves.

@davew
OK, I get the picture, Dave. That sounds pretty do-able. I have a propane-fueled, hand torch that should do the heating job pretty well. Thanks for the additional info.

Cheers all,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: December 5, 2018, 10:59 pm 
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Location: ontario
Lonnie-S wrote:
@Locost_Johnh
We'll have to get together sometime in the near future, John. There's actually much more done on my build than shows at this time, but once I get it off the build table, and the engine/transmission goes back in, it will look pretty much like a car. Maybe then?

@phil
Thanks for that additional info Phil. I really like the idea of a 3-roller setup because it is more general in terms of the curves you can produce. I can see using the die/radius type bender in several future projects, so that is nice too. Just by accident, I discovered a much cheaper die/radius bender from an online article. It's only $139 and does 3/8" through 1". The fellow writing the article claims to get excellent result from it. I'm tempted, but I think I want to do the 3-roller type too - just build my own. That way, I'd have extensive capabilities from tight radius to gentle curves.

@davew
OK, I get the picture, Dave. That sounds pretty do-able. I have a propane-fueled, hand torch that should do the heating job pretty well. Thanks for the additional info.

Cheers all,


One last point, if you are serious about the 3 roller tube bender you may want to build something like this (2 wheel drive):

https://www.princessauto.com/en/detail/ ... -p8536708e


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