what kind/size/thickness of tubing is best for a mini bike frame?

#1
Hello, i am building a minibike for my shop class from scratch, and i was wondering what kind of tubing would be best for the frame. I am leaning towards 1 inch square tubing with a 1/8th inch thickness. Does this sound like an adequate tubing for a frame? I am aiming for looks similar to a Rupp minibike, with rear suspension using shocks from a old Honda xl185. It is being powered by a Princess Auto Honda gx200 clone with a centrifugal clutch. I plan to get the frame mocked up on Christmas break and after the break i will have 15 88 minute classes to completely finish it, which i think is reasonable.

Thanks in advance for your input.:thumbsup:
 
#3
Hello Detroitdiesl : Take a look in the OldMiniBikes photo section and look up the Houndog it is a good mini bike built with square tubing and possibly the only one that was factory built using square tubing. You project sound ambitious but that is the kind of challenge worthwhile doing. Good luck. Steve :smile:
 
#5
Detroit, The standard tubing for the majority of minibikes is 7/8"dia. x .083" wall thickness. The type you want is 1018 DOM mild steel. The DOM means that it has been drawn over a mandrel which makes it perfectly round, with a uniform wall thickness throughout, and removes any internal seams. Let me offer you the following advice even though you didn't ask. Anyone can weld square tubing. That's why most beginners choose it. As long as you're in a shop class with an instructor and access to all kinds of equipment; do this. Learn to weld round tubing and learn to do it using the TIG process. It will give you a skill that you will use the rest of your life, And I guarantee you that someday you're going to say: Damn that Ogy was smart; I'm glad I listened to him. Or, damn that Ogy was smart; I should have listened to him. Good luck on your project. Post pics. Ogy
 
#6
Hound Dog Picture

"Hound Dog 400". They were made in San Dimas, Calif. back in the late 1960's (I think). Same town that Bill and Ted's "excellent adventure" took place.
 
#7
I don't see houndog listed in the photo section, Where di I look?

LK
Puttputt I hope I spelled that right? Put a nice photo up. I thought I had some scaned but I don't. I have a few differant photos of them, two styles. You could try google, it was the Dave Grattan Co. that built the bikes.
The Nov. '69 MBG has a cool artical, they used them to run around the set of Daniel Boone. But theres photos with Fess Parker riding and Darby Hinton cruising around.
 
#8
Detroit, The standard tubing for the majority of minibikes is 7/8"dia. x .083" wall thickness. The type you want is 1018 DOM mild steel. The DOM means that it has been drawn over a mandrel which makes it perfectly round, with a uniform wall thickness throughout, and removes any internal seams. Let me offer you the following advice even though you didn't ask. Anyone can weld square tubing. That's why most beginners choose it. As long as you're in a shop class with an instructor and access to all kinds of equipment; do this. Learn to weld round tubing and learn to do it using the TIG process. It will give you a skill that you will use the rest of your life, And I guarantee you that someday you're going to say: Damn that Ogy was smart; I'm glad I listened to him. Or, damn that Ogy was smart; I should have listened to him. Good luck on your project. Post pics. Ogy
Well, our shop is very limited in metal working tools, and does not have a pipe bender, or a tig welder. it only has the basic mig/arc welders, a plasma as well as the basic power tools, (as well as my shop instructor is completely useless when it comes to anything metal) which is why i am leaning towards square tubing, but i might have to look at some round pipe.
 
#9
Well, our shop is very limited in metal working tools, and does not have a pipe bender, or a tig welder. it only has the basic mig/arc welders, a plasma as well as the basic power tools, (as well as my shop instructor is completely useless when it comes to anything metal) which is why i am leaning towards square tubing, but i might have to look at some round pipe.
You say your school shop is set up mostly for woodworking and your instructor is metallurgicaly challenged? Well have I got a minibike project for you. Just scale it down to 1/2 size and you'll be in business. Ogy
 
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#10
Thanks for the suggestion :1orglaugh:. My instructor may not be the smartest metal worker around, but i myself do have experience working with metal, and am doing this entire project by myself with no actual input from my instructor, and am going to build it with steel.
 
#11
No bender?

Here's some options...

Someone else's square tube frame...

Someone else's round tube frame done without bends...

My chain frame...no bender needed...

My chopper frame...bicycle top tube and twisted 1/2" square rod...no bender needed...

My speedster frame...1" square tubing and 1/2" steel rod...no bender needed...
 
#12
Or...

$69 Harbor Freight bender...

Round tube bends welded to twisted 1" square tubes...

Or a simple frame made entirely from 1/2" square rod...



Build your bike from whatever materials and equipment you want...it's your bike...it can be whatever you want it to be.
 
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#14
Maybe you could have your parents get you this for Christmas. :xmas-smiley-016: I got it off ebay it sold under the Hines name, It bends up to 1 inch round tubing, some of the other kits do not have a 1 inch round die so check first. I bent up some 7/8 DOM steel in .083 wall thickness with no problems for a frame I made. I MIG welded my frame and have had no problems with any of the welds.
 
#15
No bender?

Here's some options...

Someone else's square tube frame...

Someone else's round tube frame done without bends...

My chain frame...no bender needed...

My chopper frame...bicycle top tube and twisted 1/2" square rod...no bender needed...

My speedster frame...1" square tubing and 1/2" steel rod...no bender needed...
yellowhand you build some crazy stuff those frames are too cool im gonna have to have you make me one
 
#17
Will the HF bender do a tight bend like on a mini bike frame? A lot of them are over 90 degrees, I guess you could cut & weld to get more radius but it would be nice to do it in one piece if possible.

LK
 
#18
Will the HF bender do a tight bend like on a mini bike frame? A lot of them are over 90 degrees, I guess you could cut & weld to get more radius but it would be nice to do it in one piece if possible.

LK
No,I does not do very nice bends in DOM tubing, My buddy has that bender and it for bending Pipe and does not go beyond 90 degrees with out kinking the pipe. Pipe is measure in ID. Like the gas piping in your house is sold in schedule 40 thickness, in commercial building it is schedule 80 thickness. also there galvanized water pipeing out there in the same sizing. There is also rigid electrical conduit in that pipe size that looks like galvanized water piping but has different threads on the pipe, that is what the H.F. bender will bend OK.
 
#19
Well i bought the tubing today. I went with 1/8 inch thick 1 inch square tubing. I will just cut the angles and weld the pieces together rather than bending anything. I also have purchased a magnetic angle finder to keep everything symmetrical. I will start a thread in the project section for my progress from here on in.

One more question though. What is the average length of a larger sized mini bike frame from front to back?
 
#20
here are some bikes i made from square tubing

made from 1x1 1/4" 1/16 thick square tubing, got alot of abuse and held up very well, no bends.




this is the bike i posted here like 50 time already, made from 1.5x1.5" 1/16" wall square tubing, no bends. the swing arm is made from 1x1" 1/8" square tubing.




this is the bike i made along time ago, everything is made from 1/8" thick 1x1" square tubing, no bending. this frame held up pretty well too. nothing broke after offroading, except the crappy wheels i used.

 
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