Tacky

So it’s taken approximately 3 months but I’ve finally tacked together my first frame!

Here’s the process from start to finish:

Surface preparation

I roughen up the bamboo by using the edge of a Dremel sanding wheel. For the steel I sandpaper first with 80 grit, then follow the same sort of deal as with the bamboo. This will provide more surface area and texture for the epoxy to key into.

I then coat the steel parts in a thin layer of pure epoxy and set them aside to get tack-dry.

Tack glue

Starting with the chainstays, I fill the rear end with epoxy and then squish onto the threaded rod I’ve attached to the drop outs. I then position the bottom bracket and stick the other ends of them to that (forgetting to sand back the epoxy on the BB… oops!?). Next comes the seat-post and the down-tube. The glue’s pliant for about 30minutes so it’s pretty easy to move stuff around if you make a mistake.

I then go to the pub for dinner and a few beers with mates while these parts take hold.

Upon returning and checking that all is well I then attach the head-tube to the down-tube, along with the top-tube to the seat-tube. The angles of the head-tube won’t be exactly 72°, but it’ll be close enough I’d say. I really need a jig that holds the head-tube in place!

Finally it’s the attaching the seat-stays to the seat-tube. Proving harder than it should be I find out that they’re not exactly even in length. I make a few adjustments and compromises on the seat-post angle and set them anyway. If it’s wonky in the morning I can always cut thru the epoxy and try again. Fingers crossed I won’t have to!

Posted in Frame building | Leave a comment

Let’s set something straight.

Sharks with frickin’ lasers. That’s what I’m talking about. Ok, well minus the sharks. It’s more like jigs with frickin’ lasers. Close enough. Check out the hi-tech laser-level action below.

The mitres are all done, so now it’s a matter of setting my somewhat cumbersome frankenstein of a jig (can someone buy me a gift voucher for Maytec please?) into place for each pole. I’ve made a series of height adjustable stand-offs to hold up each piece as well as come conical shaped rubbers from some chair legs for the head tube placement. It’s all a bit too dependent on the table being level thou, making it quite painstaking to set.

With any luck I’ll have it all set tonight. Then it’s on to roughing everything up so epoxy will stick to it. Good times.

Posted in Frame building, jig building | Leave a comment

Mitre’s well show you

Here’s the results of today’s mitreing. Pretty happy with the results so far. Just have the top tube to go and then into the more finicky work of the rear triangle. The main thing I learned today is that getting both sides of the mitres straight and level (ie. so the BB sits at exactly perpendicular) is much more important than getting the curves right. Sure getting the curves right is a good thing too, but it’s ok if there’s small gaps as it will allow the epoxy to fill into the inside of the tubing and strengthen the join.

Posted in bamboo, Frame building | Leave a comment

Choosing the bamboo for your frame

This might seem obvious, but choosing the exact bits of bamboo you’ll use for your bike frame is one of the most important things to do in the frame building process. You need to know a lot of stuff before you can choose the right bits thou! Read on for a few pointers I’ve picked up along my bamboo selection journey.

So you’ve got your geometry right and you know what lengths of each bit of bamboo you need. So off to the shop/woods right? Wrong! You’ll need to know what diameters suit which bits of the frame and then work within a set of tolerances that you know won’t cause problems (or be willing to fix those problems in creative ways!).

The rear chain-stays are by far the hardest bits to work with, followed closely by the seat-stays, then seat-post. The top and down tubes are fairly open to how much trust you have in the strength of bamboo. You could go for skinny poles if you want a retro steel looking frame, or fat chunky one that might weigh a bit more, but are probably stronger, like on an aluminium or carbon frame.

The main problem areas (and questions to find answers to) are:

  1. Tyre clearance – what’s the widest tyre you want to put on your frame?
  2. Chainring clearance – how many chainrings? How many teeth?
  3. Crank-arm clearance – what’s the Q-Factor (width) of your cranks?
  4. Seat-post – what diameter and length will you need? Are you going to use a metal sleeve inserted into the bamboo for the seat-post to go in?
  5. Disc rotor clearance (if you’re using them) – how big are the rotors?

Only once you’ve got all those questions solved are you then ready to go in search of bamboo with the right diameter!

A rough diameter guide

The figures below are a rough guide to what you might need for a road or cyclocross frame. The figures in brackets are what I’ve used on my first frame.

Top tube: 26-36mm (35mm)

Down tube: 35-45mm (41-43mm tapered)

Seat tube: 40mm (the inner diameter needs to be more than the metal sleeve, which if you’re using a 27.2mm seat-post is around 30mm)

Seat stays: 20-25mm* (22mm)

Chain stays: 20-25mm* (25mm)

*Tyre and chainring clearances end up being very precise things, so try to find bits that will exactly match your spec.

What to look for in choosing your bamboo.

So you know what diameters you need. What else is important in your bamboo selection process?

Nodes

I still can’t find out decisively if nodes are strong or weak points in bamboo. Books tell me one thing, the internet tells me others. It’s confusing. If anybody has any definitive information on node strengths & weakness please let me know. What I think is right is that they add strength from crushing forces, but cause weakness from bending forces.

Wall thickness

Bamboo varies wildly in wall thickness from species to species, and due to its tapering nature will often be thick at one end and thin the other. Use the thick ends for areas of your frame you think will be under lots of force I guess. Where are those areas? All over the place!

Straightness

They don’t have to be dead straight, but my feelings tell me that any bends and kinks in bamboo will only make it weaker and more likely to fail when put into the triangle formations of a frame. A triangle with a bent side can easily be crushed!

Roundness

Bamboo is often not round! Lots of the pieces I’ve dealt with are quite oval shaped. This can be a good thing. Oval shapes provide more strength in certain directions. Use them on chain-stays and down tubes to your advantage.

Defects

Wood borers seem to love bamboo and often you’ll find pieces with trails left by these little critters. Most of the time they just eat the surface “skin” of the bamboo and don’t do much structural damage, but this surface is the strongest part or the culm, so if they’ve eaten away large chunks of it, or ring-barked it, be warned!

Cracks, scratches and splinters are also things to look out for. Remember this thing is going to be on a bike for a long time. Find the best bits you can!

Posted in bamboo, Frame building | 1 Comment

Mitre 10

Ever wonder where Mitre 10 got its name from? Neither have I. But mitres are what I’m working on this week.  I’ve printed off my mitre templates from the ever awesome BikeCad and wrapped them around the poles I intend to use for the frame. Here’s a pic:

Tomorrow I’ll use my trusty Dremel to cut, gouge, grind and sand those curves into things of beauty. Joy!

Posted in bamboo, Frame building | 2 Comments

What to do with cracked bamboo?

If you’ve read my previous post you’ll see I’ve cracked a few bits of bamboo.  Not wanting to throw them away I’ve made use of them by splitting them into two and then cutting them down further to form two less-than-semi-circle pieces that can then be glued together. I got the idea from Brendyn, another Melbourne bamboo bike maker, who’s done something like this in his latest build. Sweet stuff!

Below are some pics of what could be an oval shaped chain stay or seat stay. You can see in the first picture where the PVC tape I used to wrap it all up as the epoxy dried has left small amounts of epoxy behind. This would be sanded off later.

Next time I try this I’ll spend more time making sure the two pieces have bigger flat edges facing each other. Bigger area means more epoxy bonding area!

Posted in Frame building | 2 Comments