Buying a tubing bender - which dies to purchase?

[RidgeRunner]

     Bought a used manual Pro Tool with 1" and 1 3/4" dies then ordered the Hydraulic ram and related parts from Pro Tool, good folks to do business with.  Ran the ram with the hand pump from my porta power set, slow but got the job done on some cage bends using 1 3/4 DOM mild steel. 

      Started with using grease then read about using plastic bags so tried that and liked it better, less mess.

                    Ed

[Richard 2]

I have a Hydralic JD Bender w/air over hydralic pump with 1 5/8"-6"radius-180 deg. Die. It makes a perfect bend (no egging). I had one of the guides chip, I called them and they sent me a new one no questions asked.
Richard

[Saltfever]

Please consider that when you bend any tube you stretch the outside wall significantly. That means the wall becomes thinner. If you use .120 wall, the wall thickness will be too thin to be legal on the outside of all the bends. So far this condition has been passed by tech. The rule book hasn’t changed on tubing sizes for quite a while but that doesn’t mean the issue hasn’t been discussed frequently. Key inspection people would recommend using .135 wall even though it is not required at this time. As mentioned in another post; the rule book is a minimum.

[Dr Goggles]

  spend the little extra mon-e and get the 32 that will do the 180 deg I went with 1.75 dies because 1.75 ew is stronger than 1.625 dom and is cheaper to purchase

Int-e-resting Sparky.......... that is a VERY useful point for new builders.

[SteveM]

Good stuff here....  From a technical standpoint, has it been confirmed that 1-3/4 EW tubing is stronger in practice than 1-5/8" DOM?  If so, I would tend to lean towards using the 1-3/4" tubing.  I have not yet purchased a bender.

I have also read others talking about the thinning of bends on the outside of tubes, and how they would be under-spec with respect to wall thickness.  I have the rulebook in front of me now, and it's certainly not definitive, which is not a surprise.  To me, it looks like the rulebook has been written by racers for racers, with a lot of very practical and easy to understand material.  A lot of the material in the rulebook can be readily interpreted by someone with some fabrication or racing experience. However, the rulebook lacks the kind of technical detail that you might expect to see in something like a Military or commercial specification for manufacturing or purchasing of specific items.

The wall thickness rule is one of those areas, as is the portion about how to attach the roll cage to the chassis of a unibody vehicle, both of which I will be doing very soon. 

The language on tubing is "Minimum requirements for the roll cage structure and the roll cage structure braces are 1-5/8 in. O.D. round steel tubing with a minimum .120 in. nominal wall thickness......" .   Certainly, using 1-5/8" x 0.120" walled tubing to make the cage would meet this rule, as the use of the terms "nominal wall thickness" is significantly different than saying something like "tubing must be greater than 0.120" thick at all locations on the roll cage structure".  I realize that these differences may seem pedantic to some, but a clear understanding of what is written in the rulebook can be a "make it or break it" difference when it comes to being allowed to race or not.   Maybe it's my engineering background, but it would be nice to have a little more detail in some areas of the rulebook.

The other area of immediate interest to me is how to attach the roll cage structure to the unibody vehicle.  The rulebook seems to address cages which are bolted in, using a sandwich of 1/4" plates above and below the floor.  However, there are no guidelines which specifically deal with welding a cage into the structure of a unibody car.  I can find plenty of racers who say they have used 1/8" sheet to reinforce the areas where the roll cage attaches to the unibody, and they have been allowed to race.  I'd be interested in hearing from anyone with respect to this item (attaching a roll cage to a unibody vehicle by welding, as opposed to bolting).

Thanks again,

Steve.

[SPARKY]

Steve, good point on proving my statment,  I have just spent 3 hrs trying to find the chart that I had seen by an online supplier---I can not find it this morning--- so I will just say that I am more comfortable with 1.75 ew than I am with 1.625 dom.  I can find 1.75 more easily  than I can 1.625.
All so I may add my new lakester has 2' dom in the front hoop that has a 180 with reverse bends set fairly far forward to try to give me more forearm protection. 

This is THE MAJOR trade off in lakesters---the ability to get in and out and protect your hands.

Follow up re post: 
The way I have done this is to have my cage fairly deep and the front hoop slope back like they wanted which moves the lower attachment point even farther foward, the upper hoop strikes my fore arm about mid way between my elbow and wrist. My upper rail is fairly high because it slopes down toward the nose/frt axle attachment point.

[Tman]

Steve, good point on proving my statment,  I have just spent 3 hrs trying to find the chart that I had seen by an online supplier---I can not find it this morning--- so I will just say that I am more comfortable with 1.75 ew than I am with 1.625 dom.  I can find 1.75 more easily  than I can 1.625.
All so I may add my new lakester has 2' dom in the front hoop that has a 180 with reverse bends set fairly far forward to try to give me more forearm protection. 

This is THE MAJOR trade off in lakesters---the ability to get in and out and protect your hands.

Just spent a few minutes last night talking to Nathan about the same hand protection issue. Glad to see others addressing it.


Steve, locally I can find 1 5/8" .144 wall, plenty of meat left after the bends.

[SteveM]

There are a lot of options available to me for tubing, but I haven't priced them all out.

In ERW, the first items I see are:

1-5/8 x 0.120 - I don't think that's a good choice

1-5/8 x 0.134 - What do people feel about this material?

1-3/4 x 0.120 - Definitely stronger than 1-5/8, but still has the wall thickness issue

1-3/4 x 0.134 - Right now, I'm leaning this direction, but appreciate all feedback


In DOM, the available sizes are:

1-5/8 x 0.120" - wall thickness issue

1-5/8 x 0.134 - seems like a safe choice, but is it better than 1-3/4 x 0.134" ERW, at a considerably higher price?

1-3/4 x 0.125" - is the extra 0.005" of wall section a factor over 0.120" wall material?

1-3/4 x 0.134" - very good material, but almost twice the price of ERW tubing.

[Saltfever]

Steve, thanks for starting this thread. That is a good list and I would like to add to your knowledge base to hopefully filter through some of the conventional misinformation. YMMV. First I apologize for not being able to back-up the following with technical references. A recent move has buried all my engineering, design, and technical manuals and I ain’t taking the time now to bring them all together.  

ERW has greater precision and consistent wall thickness than any other type. It is rolled from flat stock and we all know how precise the sheet metal rolling process is. The ERW joint is strong. In the few accidents I have seen at Bonneville I have never seen a failure or splitting of the ERW.  (Glenn, if you are reading this I would appreciate your thoughts on this. You have seen it all.) However, due to many variables like poor weld technique, skill, filler rod alloy choice, lack of knowledge, and ego, there have been many weld joint failures that have nothing to do with ERW. The ERW process is a well engineered, controlled, and inspected manufacturing process. I have never seen a failure. There are far more variables in producing a welded joint than the manufacturing of ERW material.

DOM is slightly stronger than ERW in tensile strength due to work-hardening during the mandrel draw. I don’t remember any changes to ductility though. Slight strength increase has rarely been a reason for selecting DOM over ERW due to the increased cost. Contrary to popular belief, wall thickness varies greater than in ERW. Yes that is true. DOM starts out as ERW but during the draw the protruding inside seam is fused into the existing wall. The action of the mandrel, during the drawing, produces inconsistencies in wall thickness greater than ERW. DOM cost is in the region of 2x more than ERW. DOM is usually chosen when a design considers the lack of the inside seam as important enough to justify the increased cost. Telescoping tubing, hydraulic rams, and the like justify the cost of DOM.

I have some rule book concerns as well but due to length I'll do it in another post here.

[Saltfever]

I don't think you mentioned the class you are running but you can't believe the amount of cars that add ballast. Typically, less than 1,000 lbs due to the cost of lead  but one driver told me they added 3,000lbs to the car! Don't know how true that was  . . . you know how racers are

So if you are going to add ballast anyway, putting weight into your cage can never be bad. Unless it affects the CG location to your determent! 

[Saltfever]

Edit . . . The rulebook seems to address cages which are bolted in, using a sandwich of 1/4" plates above and below the floor. . . I can find plenty of racers who say they have used 1/8" sheet to reinforce the areas where the roll cage attaches to the unibody, and they have been allowed to race.  I'd be interested in hearing from anyone with respect to this item (attaching a roll cage to a unibody vehicle by welding, as opposed to bolting).

No backup plate is needed if base plate is welded.

Steve, this is an old but excellent thread that I think might greatly help in your information gathering. I wouldn’t post to it because some people resent bumping a thread that has died. However, I would like to point out a couple of posts. Look at my picture in post #8 and read Rex’s post #11. The unibody floor in my picture is 0.037” thick because I know that car. My concern is using such a thick plate would impart a shearing action to the substrate. An important aspect of impact attenuation is compressibility or structural yield. That buys you time and allows the G-force to be distributed over more area and more time. I would think, on such a thin floor, you would want the base plate to yield and distort rather than apply a shearing perimeter load on such thin material. However, I don’t have access to FEA so I can’t show a model to SCTA. I have talked to both Lee and Steve about the thickness issue.

http://www.landracing.com/forum/index.php/topic,8446.msg132829.html#msg132829

So as not to be thread jacking, I will start a new thread on my base-plate concern.

[Seldom Seen Slim]

Here's a word from the head handlebar holder of the site and the Forum:

If you want to resurrect an old thread for any half-way decent reason (and the present case seems to qualify) -- you go right ahead and do it, okay?  It's fine by me.

[SteveM]

I really appreciate the honest sharing of information on this site.  Not that it matters tremendously, but I am a Metallurgical Engineer by profession, and I agree with your assertion about the strength and wall thickness consistency of ERW tubing.  The rolling process for flat stock results in VERY consistent thickness of material, which is then rolled and welded into tubes.

From what I have seen specified, the ERW tends to be lower carbon (1008 or 1010), whereas the DOM tubing that I've seen specs for is generally 1018 or 1020 steel.  The additional carbon content of the DOM material will account for some of the increased strength (at the cost of slightly decreased ductility).

I did a search on "roll cage" on this site earlier today, and came across that thread you showed about the 1/4" plate welded to the flat piece of thin sheet metal.

Right now, my plan is to weld some 1/8" sheet to the inner rocker panel, which will extend up to the door sill.  At the front, nearest to the driver's feet, there will also be the top of a piece of 2-1/2" x 3/16" walled square tubing, which will be the replacement for the stock subframe rail.   I want the front roll cage base plate mount to span this gap between the top of the square tube and the inner rocker panel.  This piece of plate/sheet will probably be either 1/8" or 3/16" thickness, and will be about 8" x 6" in area. (Does it need to be 1/4" thick, as described in the rulebook for bolt-in applications?)

I'll be interested to read the thread about your base-plate concern.

I intend to run in H/DT for starters, then possibly in G/DT and F/DT.

Steve.

[Saltfever]

Yes. The top plate, for either a bolted or welded installation, is identical ¼” thickness. A bolt-in installation requires an additional ¼” thick plate to be bolted underneath. Spanning a gap is unique and may be problematic without FEA or engineering calcs to back-up the design! You should talk to Lee Kennedy and/or Steve Davies for approval before proceeding.

Here is their contact information.
http://www.scta-bni.org/contact.html

[SteveM]

The terms "spanning a gap" is probably misleading and technically incorrect.  There will be 1/8" thick sheet already in this position, where the 1/4" sheet will be welded.  There won't be an actual gap, (i.e. nothing underneath the 1/4" plate). That description was only intended to indicate that there is about a 6" distance between the subframe rail and the inner rocker location.

The total thickness will be 3/8" at that location, 1/8" of which will be floorboard, and then the 1/4" base plate for the cage.  The base plate will be larger than the required 22 inch perimeter size.



Steve.