Mountain Bike Reviews Forum banner
1 - 20 of 58 Posts

·
Registered
Joined
·
27 Posts
Discussion Starter · #1 ·
Hello all,

I'm brand new to this forum and to frame building, so go easy on me.
Also, let me know if I'm posting this in the wrong place.

As stated in the title, I am hoping to build up a titanium framed dirt jumping bike. I am looking for any and all criticism and advice on this idea. I will also list below a number of questions that I will absolutely love to have you guys answer. Thanks.

I work at an aircraft tube bending facility and have access to quite a bit of scrap titanium. It will cost me nothing to acquire the main tubes, but I plan on Buying the BB, steer tube and other necessities from Paragon Machining. I don't know how to weld Titanium, but the welder at my shop agreed to do it for me. All and all, the frame shouldn't cost too much $ out of pocket.

Also, just for more information, I weigh about 130 and can make fairly smooth landings off jumps.

1 I can get free 3/2.5 class 1 type 1 CWSR 105 titanium tubing from my work. It is not butted. Is that an acceptable material? I know grade 9 ti is best, but will other grades work too?

2 What wall thickness is best for the respective frame tubes? The main one's at my work are .022" .025" .035" .044". I assume the thicker is the better, but at the same time I am trying to make this as light as possible.

3 What are the best ODs for the respective frame tubes?

Sorry for being such a newbie,

Thank you
 

·
Registered
Joined
·
549 Posts
The tubes can't be spec'd without knowing something about the design. If the frame is bigger or smaller it makes a huge difference in what tubes are needed. Besides I don't know much about dirt jumper frames but to get in the ballpark I would find an existing steel one and copy the tube sizes and just go twice as thick with the titanium.

You aren't going to get a super-optimized frame out of this project. You will have to overbuild, or else you are going to have failures, because the only way not to overbuild is to underbuild first and figure out where the failures are over time. Without a design to copy, you will have to overbuild. I'm not discouraging you because if I had access to Ti tubing I would probably try to build a frame too, just be happy with whatever you end up with as a unique project.
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #4 ·
You can compare to commercially available bike-sized tubing: Nova Cycles > TUBES TITANIUM > MAIN TUBES
Awesome! Yeah it looks like 0.035'' wall is fairly common. Do you guys think 0.035'' is fine or maybe a little heavier like 0.040" or 0.044". I realize that the thicker the stronger, but I'm trying to find the thinnest and lightest I can go without worrying about my frame snapping or bending on me.
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #9 ·

·
Registered
Joined
·
240 Posts
I think it sounds like an awesome project!
I was looking into it for a bmx frame, and I think stiffness will be a consideration vs a frame in chromoly of similar diameters/ thicknesses.
Mike Laird makes ti frames for jumping and BMX. He might be more helpful….
If it was mine, I’d start at 1.5x.035 TT, 1-3/4x .040 dt and at least .75 stays, preferably bigger like .875x.035. Then see if anyone on here freaks out about it being too weak.
I’d skip the whole forward geometry bullshit unless you want a dirt jumper that is light but handles like a semi truck.
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #16 ·
I think it sounds like an awesome project!
I was looking into it for a bmx frame, and I think stiffness will be a consideration vs a frame in chromoly of similar diameters/ thicknesses.
Mike Laird makes ti frames for jumping and BMX. He might be more helpful….
If it was mine, I'd start at 1.5x.035 TT, 1-3/4x .040 dt and at least .75 stays, preferably bigger like .875x.035. Then see if anyone on here freaks out about it being too weak.
I'd skip the whole forward geometry bullshit unless you want a dirt jumper that is light but handles like a semi truck.
Yeah, I was putting my money on the 0.035 wall thickness. I was thinking the seat stays could be 0.625 and chain stay 0.75. I was putting the top tube to be maybe 1.375 and down tube to be 1.5, both at .035 wall.

I wonder if it would be better to increase the seat and chain stays to 0.044 wall.

What do you guys think? I'm getting to the point of ordering parts and such so any advice would be appreciated.
 

·
Registered
Joined
·
3,779 Posts
What do you guys think? I'm getting to the point of ordering parts and such so any advice would be appreciated.
You haven't shown any design. There isn't much to comment on. Do you have a drawing, show. A fixture? Do you have finishing tools, prove. Doing that before ordering parts would make sense. Design review is good work.
 

·
Registered
Joined
·
27 Posts
Discussion Starter · #18 ·
You haven't shown any design. There isn't much to comment on. Do you have a drawing, show. A fixture? Do you have finishing tools, prove. Doing that before ordering parts would make sense. Design review is good work.
I do not have any paper drawings yet. Currently I have a picture of a Marin Alcatraz frame that I am using for a rough design. I just have some notes and numbers on it. Included is a picture of it.

I have a mental picture of what I want, but I just want to make sure I can acquire enough material before going further. Narrowing down my material dimensions to a simple exhaustive list will help speed up the process. That's mainly why I seek your guy's advice right now.

If you think I should go right into the drawing and design of the frame, then I can do that. I'll probably end up using CAD

Sorry for the length of this message, but for the sake of argument, let's assume I'm going to closely model Marin's Alcatraz for my frame size and geometry. Given that, do you think my proposed material spec's are adequate?

1938890
 

·
Registered
Joined
·
549 Posts
Copying an existing frame is a great idea, and very solid way to start. Copying a frame is the best way to prevent disaster and ensure your design is reasonable, and it is also the way to guarantee your end result doesn't need to exist, because you could have just used the frame you are copying, and saved a lot of time and money and had a more assured outcome.

I do hope you realize that you are going to have spent 3X more than you thought you would, just to have a copy of a frame you could have bought, and probably a slightly worse copy at that, and that's a pretty good outcome. And you are going to immediately want to build a second frame that fixes the errors or shortcomings of the first.

If you are down with all that then have fun, in all seriousness. It doesn't have to make sense if it makes you happy.
 
1 - 20 of 58 Posts
Top