How to Build a Bike Frame, Part 2

PB Forum :: Bikes, Parts, and Gear
How to Build a Bike Frame, Part 2
  • Previous Page
Author Message
flag draco
Posted: Aug 23, 2008 at 13:07 Quote
Original thread:
How to Build a Bike Frame, Part 1

Ok, so you should have your info ready about geometry.

Once you have the numbers you want, you can start with component consideration. This is important because certain parts have certain clearances that are needed, as well as giving you a range to work with for things like tire clearance, standover, etc.

I'm planning on using a 100mm RockShox Argyle for my fork. The first thing you should do, which helps a ton, is create a sketch of the fork itself, head on. Not 3d, just a sketch. Forks have offset- If you draw a straight line through the steerer tube, it will not go through the fork legs, or the dropouts. and if you draw a straight line through the legs, it wont hit the steerer or the dropouts!

This information can be found online, but I'm a big fan of just doing it the hard/easy way. hit up your local bike shop with a tape measure and find the fork.

Most forks have an offset of 40mm, which is the distance between the line through the steerer, and the dropouts. What this means in simple terms, is to draw a fork, you do it like this:

photo

2393914


So the total overall length is 501mm, because you need to include the lower headset cup.

Now someone will wonder about accomodating sag into the equation: Don't. See, bike companies don't, its all based off static measurements.

Ok, so we've got the fork length. Good.

Now, wheels and tires. I'll be running 26x2.3" tires. A quick search of google for 26x2.3" tire rollout lead me to a measurement of 208cm, or 2080mm.
This means if we take that length, and divide it by Pi (3.1415 is close enough), means the wheel diameter is 662mm. Therefore, radius is half that, at 331mm.

Now, the fun. Thats 13". Yes I know we are bouncing between standards, but it happens in this game. Actually, i suppose it doesnt, but I really am not concerned. Conversion from mm to inches is 25.4 per.

So your axle sits 13" from the ground at all times. This also means that the tip of your rear tire sits 13" from the axle, and thus, you must create clearances for it on the chainstays and seatstays. This also means that if you've selected a BB height based off the ground, you can factor the tires in too. If the bike you like the handling of had different tire sizes, calculate the difference between the two.

In this case I want my BB to be a touch above the axles. not a ton, just a touch. So I am going to say my BB height is 13.5". Thats a half inch boost above the axles. You may be above or below based on the geometry you selected.

We now can envision in our heads, or in a simple paper sketch, two identical tires sizes, and a bottom bracket shell floating in space, appropriately positioned.

If anyone wants to get into the fun, you can draw wheels and hubs too. We'll touch on that in a moment.

We're already done some of the hard calculations, now its time to change perspectives.

Onwards to sketching.
flag draco
Posted: Aug 23, 2008 at 13:48 Quote
Ok, drawing time. This gets fun, at least I think.

Drawings can be freehand, but its not as helpful as using some graph paper. We'll get tot drawing on the computer. You're going to need a CAD program, or its not worth doing on the computer. AutoCAD and SolidWorks are not only industry favorites, but they are student favorites too. Educational licences and versions can be obtained at college bookstores, and probably online too. I have not had to pay more than $50 for a book on how to use the program and the CD- call ahead and have it set aside.

We need to draw the Bottom bracket shell area. For a hardtail, you traditionally use a 68mm shell. We're going to do that too. A 68mm european bb shell is 68mm wide, and 1.5" in diameter. Again with the mixed units here, I know, but its the way it actually is for that one. Threads on a Euro shell are like 37mm left and right hand threads, but whatever. The outside of the shell we'll be using is exactly 1.5". More later on that.

I know my chainstay length, its going to be 16.5". All cycling measurements are center-to-center. So to draw out this BB area, I recommend using graph paper and getting a little scale going. Even if its rough- You just need to lay it out.

Draw a "T" that is 2.677" wide at the top, and 16.5" long. At the end of that long 16.5" line, you're going to have a line just like the other end of the "T"... but this one is 135mm or 5.314" wide. It should look like this:

photo

2393992


next up: you're going to need to add the tire. This is tough: The top of the tire is 13" from the axle center. Yet as you know, its not a square, so its not 2.3" wide at the top! I recommend measuring an existing wheel if you can. Or, look at pictures online and see if you can guess the shape. I do it all the time, its pretty easy. my general rule of thumb is that the tire is typically the wides from between 1/2" and 3/4" down from the tip of the tire. It's not truly a circle, the cross section. more like an upside down tear drop.

Anywho, sketch it in, and see how it looks. might as well add in some lines to represent spokes. We'll touch on that now:

assuming gears, its easy. Rear hub will be 135mm wide. If its a disc hub, The flat face that the disc bolts to is exactly 15mm from the inside of the dropout. Thus, the disc rotor can be sketched. This information used to be available off of maguras site, but I cant find it anymore. The page will also show hwo to draw disc brake moutns n stuff too... later for that one. All you need to know how is your rotor is a vertical line however long it is big around. for example im using a 160m rotor, so its 160mm long and centered on the axle, 15mm in from the disc side. Awesome!

Now, the cassette spacing is also a standard. And I can't rememeber what it is. its like 45mm in from the right dropout is where it stops.. but oh wait! we're got this series of tubes called the internet, I'll google it. Sheldon Brown FTW!! (RIP, i met him at interbike a couple years ago) 36.5mm for a 9spd cassette width. Since the built cassette sits extra darn close to the inside edge of the right dropout, I'm gonna not worry, and just draw it there.

Hub flanges typically have like a 5mm gap before they start, so, lets review.
In from the right dropout 36.5mm +5mm, in from the left dropout out 15mm +5mm so....

Voila:
photo

2394077


Combine drawings with the BB shell layout.

Now the fun part:
Ok, so if you've been drawing to scale or in a program, you should have a BB shell, and a rear hub sketch, with a tire someplace in the mix too. If it is all to scale, great! Now chainstays are up.

Not as simple as they seem- First, consider what size chainring you're going to run.
I myself, will be running a 34t chainring most likely. the smaller a chainring you run, the easier this gets. but, thats tough for your gearing choices. anywho.
What cranks too?

If you're running newer style outboard bearing cranks, this makes your drawing easier.
You can go to truvativs site and poke around, and actually find CAD drawings of the BB shells, the cranks, where the chainrings bolt, EVERYTHING.

I'll let you do that on your own- post it if you find it!

A little independence thrown in the mix: Use those numbers, even if you dont plan on running those cranks- its enough of a standard that most companies will fall into it.

Figure out where the cranks will fit on the BB, and where the chainring will fit on the cranks.
-beware- once you do that, your goal is to have a perfectly straight line from that chainring to the CENTER of the rear cogset! Thats good chainline. If you dont have it, see about moving the chainring to the other side of the crank arm.

Now. best bet is to draw those cranks with BOTH ARMS facing backwards. Why? because this way you can see if they will clear the chainstays you havent drawn yet.

Once you ahve the chainrings on the arms, and both arms towards the rear axle, and the tire drawn in, you can suddenly see what you're looking at for chainstay space.

When you get here, give me a screen shot, or ask some questions, or whatever you'd like. I'll sketch up some of this on a program so everyone can see as well.


Homework (haha):

Post a link to crank arm/BB specs.
Tell me how you figured out chainring size.
Ask me some questions, and:
vent out a little if you're starting to see what really goes into all this!

I'll be back tonight with drawings and more info. But for now I'm off to ride one of the bikes I built, by doing this same, exact process. Cheers!
flag kicksnlicks
Posted: Aug 23, 2008 at 21:22 Quote
Oops, Zak posted in wrong account.
flag roger-dodger
Posted: Aug 23, 2008 at 21:28 Quote
kicksnlicks wrote:
Alright, say I'd like to put a spanish or mid bottom bracket in the frame, I've searched google for a long time and can't say I've found anything past where to buy them. Would you happen to know them?

And, I've noticed certain frames use a yoke(I hope its the right name) and some just go straight tubing from BB to dropouts. A yoke would have to be machined right? They offer more tire clearance? Good idea to put in a frame if I could design one or am I in over my head even thinking about making one?
check out bmx sites.
heres one for can. 3ride.com
flag zwak
Posted: Aug 23, 2008 at 21:29 Quote
Alright, say I'd like to put a spanish or mid bottom bracket in the frame, I've searched google for a long time and can't say I've found anything past where to buy them. Would you happen to know them?

And, I've noticed certain frames use a yoke(I hope its the right name) and some just go straight tubing from BB to dropouts. A yoke would have to be machined right? They offer more tire clearance? Good idea to put in a frame if I could design one or am I in over my head even thinking about making one?
flag roger-dodger
Posted: Aug 23, 2008 at 21:30 Quote
roger-dodger wrote:
kicksnlicks wrote:
Alright, say I'd like to put a spanish or mid bottom bracket in the frame, I've searched google for a long time and can't say I've found anything past where to buy them. Would you happen to know them?

And, I've noticed certain frames use a yoke(I hope its the right name) and some just go straight tubing from BB to dropouts. A yoke would have to be machined right? They offer more tire clearance? Good idea to put in a frame if I could design one or am I in over my head even thinking about making one?
check out bmx sites.
heres one for can. 3ride.com
flag zwak
Posted: Aug 23, 2008 at 21:35 Quote
Edit, sorry friend is an idiot.

I checked 3ride, they didnt have any specifics on length or diameter.
flag laurie1
Mod
Posted: Aug 23, 2008 at 21:38 Quote
If this is what the finished product is going to be, I think I will look elsewhere for frame building advice. Razz
flag draco
Posted: Aug 24, 2008 at 0:55 Quote
laurie1 wrote:
If this is what the finished product is going to be, I think I will look elsewhere for frame building advice. Razz

pfft whatever, tandem version puts you right on the back of it.


MOre in the morning, including info on mid/spanish and where you can find it.

ps, I'm gonna use google... so I bet you can find it too.
flag draco
Posted: Aug 25, 2008 at 7:07 Quote
rancidfan05 wrote:
Alright, say I'd like to put a spanish or mid bottom bracket in the frame, I've searched google for a long time and can't say I've found anything past where to buy them. Would you happen to know them?

And, I've noticed certain frames use a yoke(I hope its the right name) and some just go straight tubing from BB to dropouts. A yoke would have to be machined right? They offer more tire clearance? Good idea to put in a frame if I could design one or am I in over my head even thinking about making one?

A yoke wouldn't have to be machined. I actually used a yoke for my first frames back in 2001. At the time, I saw no one else doing it. I just used a simple version of it. A little heavy, but not really, to be honest.

info on bb's from gsport

Mid-BB is just an american bottom bracket bearing set pressed into the frame, with no cups.
So its dimensions are the same as taking same, a profile crankset, popping the bearings out of the cups, and rolling with that.

the spanish is baaaaasically some wacky bearing that is close to the size of a eurobb... pressed into the shell, which is close to the size of a euro BB shell. but not exactly.

apparently there is a spanish bb-2 that fly is working on.

suddenly the very stable Mid-BB sounds great.
flag zwak
Posted: Aug 28, 2008 at 17:53 Quote
photo

2414252


Is this right?
For cranks I measured out my set of Truvativ Hussefelts, I'm pretty confident its decently accurate.

I'm going to run a 32T chainring and a bashguard. If I want to go smaller in the future I can right? Only problems with a bigger chainring?

Euro bb, 68mm shell with a Truvativ external BB

Its going to have 14.75" chainstays and its 24" specific.

I didn't get perfect chainline, though my BB comes with spacers, if I put spacers on the driveside it would push out my crank and make my chainline better. Thats possible?

I see how much work you need to put into building frames, I took a while to do this alone.

PS. I know I'm pretty late, but I really hope you continue with this tutorial.

EDIT:Good picture is up. Tire is a 2.3 K-rad and the rim height/width is the same as an atomlab pimp.
flag draco
Posted: Sep 3, 2008 at 8:50 Quote
nicely done! you're seeing whats involved now.

I'll do another feature tonight I suppose.

Until then, think about how on earth you're going to fit material around the tire without hitting the chainring and whatnot.

I'll be back with some help on that too.
flag ben24
Posted: Oct 27, 2008 at 17:09 Quote
go here:

http://sketchup.google.com/3dwarehouse/details?mid=d7fe5dcd80bf0803c19c634d198cfab3

it tells you perfectly how to build a sketchUP frame. Made by me
flag wrc21
Posted: Mar 20, 2009 at 9:27 Quote
Hey Draco, congrats for your work. Can you give me the standard measures of rear brake disc mounts? Thanks
  • Previous Page

 


Copyright © 2000 - 2024. Pinkbike.com. All rights reserved.
dv42 0.015925
Mobile Version of Website