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Discussion Starter · #1 ·
So I want to build a custom frame, what I have in mind is pretty close to a Surly Karate Monkey. Single speed, 29er, room for a for a 100mm fork in the future, but rigid for now. The biggest change would be integrated rack, this will be a very urban commuter, but also for inter city trails that have some singletrack areas.

I am in welding school, so I have access to TIG welders, and I am pretty good at making AL stick together via TIG. I read up on AL and it seems to require some lengthy heat treatment, much more than I could do. Something else I saw when reading up was a debate on framefourms.org about precision tables to mount jigs on and check alignment on. This got me all thinking, how much precision do I need to make a bike that isn't crooked? The shop I'm in has drill presses so I can probably acquire the hole saws to do miters, if not there is always the old school way. What I worry about is how to hold the tube in the proper angle while being drilled, Can I take some scraps and some clamps and weld up a "jig" to hold things in place for mitering and later welding?

Should I go with steel because AL needs heat treatment?(I have welded some steel, but I am not nearly as proficient at welding steel tubes as I am at AL tubes)

Are basic measuring tools and some clamps enough to get a frame straight?

Should I just get a karate monkey frame and weld on permanent rack rails?
 

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Discussion Starter · #3 ·
I rode one around the parking lot, seemed to fit well, and it seemed to get good reviews on MTBR. You have any suggestions? I am not attached to one of those, just needed somewhere to start, never built a frame before. Main priority's are: handles like a mountain bike, 29" tires, single speed, disk brakes and an integrated rack.
 

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pvd said:
One of the worst bikes in production today. Why not start with a good design?
Why, because it's a 29er? Because it has a rigid fork? The only bad thing about the KM is the lack of offset in the fork, otherwise it is a durable, well made frame. People with short inseams may have trouble with standover. Otherwise I'm at a loss as to what could make it one of the worst bikes in production.
 

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pvd said:
pretty much any surly bike is complete junk. designed by drunks, built super heavy using gimmicks galore. The geometry is just the worst stinky cheese.
But what do you really think? :D
 

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pvd said:
pretty much any surly bike is complete junk. designed by drunks, built super heavy using gimmicks galore. The geometry is just the worst stinky cheese.
Wow, I've got disagree. I'm no frame builder, eventually maybe. But I've found Surly's build quality above par for the price point, and the geometry to be pretty damn good. I have not had any "G2" Fishers on a trail, but previous have not impressed. And I've been very happy with the Surlys I've had on a trail.

As for the super heavy claim, not really. Surly is in no way super light. but not much heavier than the steel Gary Fishers you praise earlier. I have no hard evidence but I've seen/heard of many more Fishers braking vs. Surlys. And yes there are more Fishers out there, but I'd bet the ratio of # sold to # broken is in Surly's favor. Hell, I'd say the ratio of Fishers broken at the seat tube / per frames sold is higher than total broken Surly at all / frames sold.

A little more on topic, possibly look at the Salsa Fargo frame geometry. A do all type bike with big wheels and thought given to loaded racks/panniers. No shame in copying the first frame.
 

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Well, I looked at both the fisher geo and surly and they don't seem too far off base, either one. the Fisher has too much trial IMHO.

I would say that part of building a custom bike, no all of it is the geometry. If you are just going to copy geometry honestly you are better off just buying the thing. It will most likely be better than your first attempts anyways.

A study of why you are choosing particular specs is critical to becoming good at framebuilding. One set of numbers may work perfectly for one person and not for another riding style, physique, skill level, terrain etc. Without knowing these things about you I cannot recommend any bicycle.

You will find that with the big wheel that many of your dimensions become constrained by the size. For instance, CS length just has to be what it has to be to create enough clearance for your tires. Since your frame will be a commuter I would not follow any of this geo at all. Build a great commuting bike that fits you well, has long stays for racks and bags front end geometry for a handling front loads and lots of braze-ons. Then build a 29nr for off road work. Like a SUV, bikes doing two jobs usually do not shine at either.

Dave Bohm
Bohemian Bicycles
http://www.bohemianbicycles.com
 

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Design & use

G-reg said:
Wow, I've got disagree. I'm no frame builder, eventually maybe. But I've found Surly's build quality above par for the price point, and the geometry to be pretty damn good. I have not had any "G2" Fishers on a trail, but previous have not impressed. And I've been very happy with the Surlys I've had on a trail.

As for the super heavy claim, not really. Surly is in no way super light. but not much heavier than the steel Gary Fishers you praise earlier. I have no hard evidence but I've seen/heard of many more Fishers braking vs. Surlys. And yes there are more Fishers out there, but I'd bet the ratio of # sold to # broken is in Surly's favor. Hell, I'd say the ratio of Fishers broken at the seat tube / per frames sold is higher than total broken Surly at all / frames sold.

A little more on topic, possibly look at the Salsa Fargo frame geometry. A do all type bike with big wheels and thought given to loaded racks/panniers. No shame in copying the first frame.
Well after listening to lots of Pugsley owners I have yet to hear anything other than how versatile and durable the bikes are. At 225 pounds with another 50 pounds of groceries/gear I have to look at strength first or I would spend all my time welding frames and replacing spokes...been there done that. I confess to missing the "built by drunks" comment...I am only interested in the lasting qualities of any bicycle or piece of equipment. (63 Dodge Dart owner)
 

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waunan said:
Well after listening to lots of Pugsley owners I have yet to hear anything other than how versatile and durable the bikes are. At 225 pounds with another 50 pounds of groceries/gear I have to look at strength first or I would spend all my time welding frames and replacing spokes...been there done that. I confess to missing the "built by drunks" comment...I am only interested in the lasting qualities of any bicycle or piece of equipment. (63 Dodge Dart owner)
Add me to one of those Pug owners, it's a large part of what ruffled my feathers. If you were to copy design/geometry for utility and versatility Surly is a good place to start.
 

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To the latter part of your question re: mitering, try Googling "tube notchers" to find what you're looking for (an adjustable fixture to hold the tube at an angle for notching with a hole saw). But the general consensus seems to be that these fixtures and drill presses aren't really up to the task of accurately mitering 4130, let alone the more exotic tempered steels (certainly my own extremely rinky-dink experiments using a drill press have not been too impressive). Most people who aren't mitering either by hand are using either a knee mill, a large mill-drill, or a lathe.

Mitering with a hacksaw and files is probably going to be a lot easier than rigging all that up, especially for just a single frame. By the time you miter and weld 20-30 practice joints, you'll be able to do it relatively accurately, if not yet quickly!
 

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Discussion Starter · #15 ·
Looking at the GF Superfly it is about 1 cm/degree different in most measurements than the Surly KM, with the exception of 2 degree slacker head angle and 45 mm more wheel base. Is that the difference you were speaking of or were you refering to the Surly's phisical construction?

My biggest concern is making a decent frame(not crooked), can this be acomplished by quarter-lining the tubes lengthwise and a level?
 
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