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Preliminary sketch of my frame design

2.7K views 38 replies 15 participants last post by  Tygen1  
#1 ·
I am in the planning stages of my frame. I want to build a frame for my Z50R. It will most likely use an xr80 monoshock swingarm and it will be a wrap around kind of frame so the engine isn't a stress point. It will be a single top tube not twin spar like the primmy frames. Then it will come out like a Y to fit around the swingarm mounts and the motor mounts.I don't know what forks I plan to use, or what wheel size. It won't really resemble a Z50R except for plastics/tank/ and motor. I know the head tube is low and would require really short forks so I will move that up when I re-draw it. I am only 15 years old but that shouldn't stop me. The BBR guys built their XR75 frame when the middle brother was 12 years old. So don't doubt me. I have all the tools but a welder and if I don't get that for Christmas, I'll buy my own. Anyway, does anyone have any opinions on how to improve this design?



Image
 
#7 ·
It looks pretty nice. But here are some factors.



1.Getting around the motor to connect to the head tube. That design would make the frame a +3, 4, or 5. To make it shorter go around the cylinder?



2.Putting z50 plastics would be hard. Cause the really short seat. You would be better of putting 70 plastics.



3.I wouldnt connect to the head tube. I would bend it more torwards the backbone.



4.Get a pegmount or just a brace to weld to the frame. Cradle.



But still you have a really good concept. Also a good swingarm to use would be a +5 bbr or a +4 1/2 rcm swingarm. Use 12/14
 
#8 ·
That's ambitous to try your own frame. If you have never welded, then you will learn alot trying to make a frame :) The heat from welding will do crazy things to your frame, you might not end up with a straight frame. That's not important though, because you will never learn if you let things like straight frames worry you :D

If it were me, I'd try to use thin wall chromoly tube and gas weld it to help minimize distortion and stress related cracks. That may be to advanced though if you've never welded. But it would make the strongest and lightest frame with the simplest equipment.

You might want to make jig first to make sure your head angle is correct. You can use and existing frame to set the head angle, then just pull back the swing arm mount until you got the length you need.

I like to use as many existing parts as possible. Maybe get a head tube and swing arm mount from a broken frame. You could e-bay a decent chinese swinger and shock, and maybe a subframe to. The less parts you need to fabricate the better. I'd recomend a 50 based swinger over another bikes swinger because the offset will be the same and you won't have to deal with those complications.

Make your top motor mount removable also. I could go on and on, but I won't. I don't think you've realized how much work you have ahead of you. So make sure you have three times the money and time budgeted in to your estimate :)
 
#9 ·
crf150r said:
Getting around the motor to connect to the head tube. That design would make the frame a +3, 4, or 5. To make it shorter go around the cylinder?


Can you explain that a little better? I'm not sure I understand.



Tygen1 said:
I like to use as many existing parts as possible. Maybe get a head tube and swing arm mount from a broken frame.


I know what you mean. There is no way I could fab a headtube. I'd buy a Z frame and probably a choppered CRF50 frame to make this.



Tygen1 said:
Make your top motor mount removable also.


What does that do? Make it easier to put the engine in the wrap around frame? I'm not sure how I'd do that. Would it be easier to make the smaller tubes in front of and under the engine removable? Then it might not be as strong. I know I have a lot of planning to do. I probably won't even start the actual work for a year. I'm still planning. I have wanted to make a custom frame ever since I knew aftermarket frames were available. But this actual putting forth of effort to plan it only started today in math class.
 
#10 ·
For the head angle, I took the angles of four bikes and averaged them. I don't know what that accomplished, but it gives be a number to shoot for. And I think I would like to use a CRF70 fork and front wheel. That would give me a 14 front. Then I could get a CRF50 wheel laced to a 12 inch rim.



XR75-60.5°

Z50R-63.75°

CRF70-63.75°

CRF450R-61.25°



That averages to 62.3125°. I don't know if I can get an angle that accurate. But it gives me something to shoot for. Not just make it the same as that, but actual measuring stuff. The angle I had drawn is 69°. So I know what to do in the next drawing.
 
#18 ·
Make sure you get a MIG welder that comes with a gas regulator and switch. You MUST run a 75% CO2/Argon mix to weld frame tubing without having brittle welds. You can learn to weld with the cheap flux cored wire on old scrap metal before setting up the gas bottle and good wire. The good news is you don't need a high powered welder. If fact you are better off looking for a welder with the lowest current setting available (25A@ the lowest setting).

I have found a good source of tubing for doing a mock up frame. EMT electrical conduit can be found as scrap at alot of places or bought cheap at Home Depot. EMT is electro plated with Zinc and has to be wire brushed with a bench grinder to weld properly and then it's cheap crappy tubing, but it welds nice. Buy real tubing before you actually ride anything in the dirt.

I have the Lincoln Pro-MIG 140 which has been replaced by the Lincoln SP135 plus and I like it.



Only do this project if you love metal. It's still cheaper in the long run to buy a Pitster or a G2.
 
#19 ·
Good welds don't come easy. Start with a stick on the thinnest stock and practice, practice, practice..... A weld ' pulls' the adjacent metals to one. I've done some welding but I don't do it that frequently. (If you don't use it you lose it). If my life depended on the weld I'd get a friend to assist or do it for me. A frame is a pretty crucial part of going faster than 25 mph. I'm not trying to discourage you but would advise you to find someone with experience to teach you to weld correctly. GO FOR IT!
 
#21 ·
I thought you had some more gun time. Ya try welding other stuff for a while. Cause the frame is your life support. It takes some practice to get good welds. Make a jig for the frame so you can practice welding. Also when you get a welder rear the manual! It showa you how to do it. So read that a couple times.





BTW later on your going to want a plasma cutter and a drill prees. Even a lathe. Those are really good machines to make your on parts.
 
#22 ·
Welding come on guys. As long as you get good penetration it will hold. You also can build a whole frame with flux core wire also. Shielding gas wire just make a prettier less splatter welds. If you want the best welds buy a tig set up and master that art.
 
#23 ·
i argue that he onbly need spenitration and flux core to make a frame safe. in high school we statred building gokats with a stick welder, then flux core, then mig, and now tig, i have broke a lot of welds too.



Auto cad does rock, i do cabinet work. Im sarting to do 3d modeling too, but im stuck with autocad 2002, so i dont have the new 3d fetures
 
#25 ·
nikbrewer said:
i argue that he onbly need spenitration and flux core to make a frame safe. in high school we statred building gokats with a stick welder, then flux core, then mig, and now tig, i have broke a lot of welds too.



Auto cad does rock, i do cabinet work. Im sarting to do 3d modeling too, but im stuck with autocad 2002, so i dont have the new 3d fetures


The flux core welding i am speaking is mig and yes it will hold. But really that is my opinion i have only been welding for twenty years.