I was wondering if any of you all could provide a direction with this subject. I notice that many lowracer recumbent bikes are quite simple in their design. Many are simply a single frame tube bent into the desired shape with a welded rear fork, welded head tube, and bottom bracket boom added for completion. Here is a picture of one example so that you know what I am talking about.
http://www.twbents.com.tw/HTM/gallop.htm
Could anybody suggest what the prcess should be and the equipment one would use to create such a frame. The first thing that I am concerned with is the equipment to bent the tubing. Particularly there are some products on ebay that I was wondering if they would do the job. Here is the link to one of the tube benders to which I am refering.
What happened? I thought I had put this thread in frame builders?
RecumbentTriker
09-26-07, 08:45 AM
I've researched a similar bender to the one you're referring to - they have the manual posted online in PDF format - and it states it's not for thin-walled steel or exhaust tubing, so I wonder if if it might not be too powerful. I'm considering one, but it seems a bit of a gamble.
Find out how large that particular one you posted will go. It's about a third of the price of the one I researched.
danielmramos
09-26-07, 10:49 AM
Maybe it is the same machine. It does say on the ebay site that it retails for over $200. I will look around to see if I find anything. What is the url to the one you are looking at?
danielmramos
09-26-07, 11:31 AM
I've researched a similar bender to the one you're referring to - they have the manual posted online in PDF format - and it states it's not for thin-walled steel or exhaust tubing, so I wonder if if it might not be too powerful. I'm considering one, but it seems a bit of a gamble.
Find out how large that particular one you posted will go. It's about a third of the price of the one I researched.
I found the three models that are linked to the above linked URL. The models are from Northern Tool and Equipment. All three models are of similar design. Below I will list the description for the three different models.
12 ton hydraulic model:
General Specs
Bends virtually all types of pipe except conduit!
6 cast iron shoes for 1/2in.-2in. diameter pipe
Top rollers adjust for degree of bend
24in.L x 21 1/2in.H x 6 1/4in.D
Makes 90 degree bends
1 year limited warranty
16 ton hydraulic model:
Description
More powerful! Bends pipe in 8 diameters: 1/2 inch, 3/4 inch, 1 inch, 1 1/4 inch, 1 1/2 inch, 2 inch, 2 1/2 inch and 3 inch. Bending bars can be adjusted to distances of 11 1/2 inch, 15 1/4 inch, 21 1/4 inch, 23 1/4 inch and 27 inch. Includes hydraulic bottle jack and 8 bending forms.
General Specs
Radius Per Die Size:
1/2in. = 2.75in.
3/4in. = 3.34in.
1in. = 5.31in.
1 1/4in. = 5.31in.
1 1/2in. = 6.29in.
2in. = 7.87in.
2 1/2in. = 10.03in.
3in. = 12.20in.
Note: Will not bend conduit or exhaust.
16 ton air/hydraulic model:
Description
The Northern Industrial 16-ton pipe bender is designed to bend water pipe, rigid conduit, heavy-gauge galvanized pipe used in commercial applications, and other similar types of pipe. Can also bend thin-walled pipe or conduit if pipe is filled with sand and capped on both ends.
General Specs
16-ton limit
Dies include 1/2in., 3/4in., 1in., 1 1/2in., 2in., 2 1/2in. and 3in. diameters
Bends up to 90°
Ok, now that we can read what the manufacturer states about the different models I find it odd that the 16 ton air/hydraulic version states that it will bend thin walled pipe and conduit when it is sand filled and capped, while the hydraulic only model states that it will not do conduit and exhaust. If you look at the model I believe that they are exactly the same for the exception of the power unit. I believe that the 12 ton unit is also of the same design except for the strength of the power unit. I bet all of these units have no problem with thin walled stock if it is filled with sand and capped. I did not find any manuals online for these models. Were these the models you were refering to? The 12 ton model is listed at $94.99, the 16 ton hydraulic model at $199.99, and finally the 16 ton air/hydraulic model for $229.99. They seem to all be good deals. The question is will they work well for bicyle frames like the one I posted the URL to in my first post? It may be that it takes more inate skill to use these and get exactly the same bend every time you use them; although, I can't say without reading the manuals.
There's a link to the PDF file from the manufacturer.
Material thickness plays an important part, also. These will bend up to a Schedule40 thickness. I found a chart on the 'net that gives thicknesses for each diameter, but I don't have it now. Take that into account before you buy.
danielmramos
09-26-07, 12:38 PM
So what are the other types of benders out there and how are they different from this one that they can easily handle the thinner stuff? I am just having a difficult time understanding the differences in the ways these machines bend tubes.
RecumbentTriker
09-26-07, 01:38 PM
I don't know - I'm just kind of learning, myself. I'm thinking I just might take the tube somewhere and have it bent by a professional. But I have time to think on it - I'm not in a hurry. I've watched people use a mandrel bender on exhaust pipes before, but those are expensive.
If you use this one, it might help to fille the tube with sand before bending it - to keep the tube from pinching. I may just have to get one and experiment - a friend is a mechaninc and there's plenty of scrap exhaust tube laying around.
velonomad
09-26-07, 07:04 PM
look for a race car, custom car shop or custom motorcycle shop, most will have a quality tube bender (not a NT or HF Chinese copy) that can make a smooth bends in chromoly tubing down to .9mm wall thickness .
Draw your bends out full size on poster board or butcher paper. bring $40 and a 12 pack of good beer. If they do it for free give them the beer, If they want money it will probably be $40 for a couple of simple bends.
Greg Fox
09-26-07, 07:08 PM
Typically to make a frame like you are describing out of relatively large diameter, thin walled tubing e.g. 0.035" x 2" (0.9 x 50 mm) you need to mandrel bend this type tubing to avoid kinking it. This site (one of many) has a good overview of the equipment needed to do this. http://www.omnibend.com/scripts/omni_guide.asp
If you just want to do one frame you would be better off finding a tube bending shop to do the job, but it fairly expensive. With slightly thicker mild steel tubing, 0.049" or 0.054", some muffler shops will bend it for you. Bentech bike plans call for this approach http://www.bentechbikes.com/ Tom Porter on the WISIL recumbent site cuts the tubing at the desired angles and brazes a gusset across the cuts for strength as shown in Frame build 2005/2006 here http://www.wisil.recumbents.com/wisil/porter/porterplans1.htm
danielmramos
09-26-07, 08:12 PM
Hey, I was just thinking, wouldn't it be easier to bend aluminum tubing instead of using cromoly or steel? It just seems like it would be easier to work with as long as you are going to be working with a frame that doesn't require many welds.
RecumbentTriker
09-27-07, 07:42 AM
Hey, I was just thinking, wouldn't it be easier to bend aluminum tubing instead of using cromoly or steel?
I'm not sure - I think it has to do with the stiffness of the material (and again, I'm new to this) but if two tubes have the same stiffness, it would take the same amount of pressure, wouldn't it?
danielmramos
09-27-07, 11:27 AM
look for a race car, custom car shop or custom motorcycle shop, most will have a quality tube bender (not a NT or HF Chinese copy) that can make a smooth bends in chromoly tubing down to .9mm wall thickness .
Draw your bends out full size on poster board or butcher paper. bring $40 and a 12 pack of good beer. If they do it for free give them the beer, If they want money it will probably be $40 for a couple of simple bends.
You make it sound so easy. I guess I will try your method and see if it works before buying the tube bender. If worse comes to worse I can just drink the 12 pack and forget about the frame. ;-)
RecumbentTriker
09-27-07, 12:47 PM
I can just drink the 12 pack
After you attempt to bend the the frame, please *grin*.
velonomad
09-28-07, 05:23 AM
You make it sound so easy. I guess I will try your method and see if it works before buying the tube bender. If worse comes to worse I can just drink the 12 pack and forget about the frame. ;-)
I don't know about it being so easy, most racecar/ custom fabricators aren't in the yellow pages, nor are all of them going to be willing to do it anyway. If you have race car fabricators or custom car shops around you can usually find someone willing to make a couple of bends for you.
BTW Like Greg Fox mentioned above it has to be a mandrel bender.
danielmramos
09-28-07, 06:40 AM
So all this stuff about sand filling is bogus then?
RecumbentTriker
09-28-07, 07:30 AM
Filling a tube with sand is not bogus. It's a bit 'old school'. Professionals who have the proper equipment don't do it. It was just a thought if you were going to experiment with bending on equipment that might be too powerful for the tube. It might help, it might not. M best friend has been a professional mechanic for over forty years, and it's a technique he's used. He doesn't do tube bending on a regular basis, so he's not invested in the equipment.