Wooden bicycle build

[BartRidesEternal]

You always want lots of edge distance on fasteners in wood. 7 to 8 bolt diameters for tension joints in most woods. 5 to 6 in the very hardest.

So normally a 5mm screw would want to be 25 to 40 mm in plus half the screw dia. to the center. Best to use other methods of anchorage against tension.

In structural work, connections with steel teeth keep things stable.

Thank you, I'll certainly keep that in mind.
Steel teeth could certainly be helpful, but I don't want to cut a percentage of the grain by those teeth, but that depends on the design and how they are used I believe.

This a favorite wood & copper (plated) bike.

View attachment 222671

Awesome! I have added that one to my inspiration list. Thanks!
Due to the tone of the copper, it makes the wood stand out a little less.
Do you know what wood type this is? Pine? Hickory? (Wild guess)

 

[BartRidesEternal]

I made a drawing and measured the "raw material" lengths, so I can lookout for wood.
This design drawing is not final, but close. The top tube part is a solid square at this point in the drawing, but I may change my tactics and use the leftover top tube and glue/clamp wood inside.

And made a list of common wood types and their mechanical properties. Its in Dutch, but happy to translate if you have questions.
Also taking the 'cut' or way that the wood is sawn into account.

Pine does not seem that bad.
Meranti (a hardwood collection with similar properties) is interesting too.

 

[Ulu]

This is the “edge distance” problem I mentioned.

It is very small here! This is asking for the wood to split about the screws.

 

[BartRidesEternal]

This is the “edge distance” problem I mentioned.

It is very small here! This is asking for the wood to split about the screws.
View attachment 222698

I see what you mean. Completely agree with you and I will keep that in mind when working on the 'physical' bicycle.

Thanks again for the heads up.

 

[BartRidesEternal]

I was thinking a lot about designs the past days. Had some time to think with my daughter sleeping in the carrier/wrap and walking for hours.

Decided to just go with the old plan (previous topic) and use some scraps and wood from my original idea.
Once I get a idea and feel of this bike build I can build a complete wooden bike next.

I always liked the strings or cables that were so notable on these world war one era planes and saw this picture on pinterest:

I have still the following sheets of wood lying on my attic:
Pine and hardwood strips, 4mm thick.

And made some plans for 'straight' lamination:

Headtube!

Headtube idea. Needs some stiffness checks and ideas. But it fits the lamination plans! Work in progress.

Final 'general' plan.
Some details need attention and sorry for the proportion/perspective distortion

I love this idea with the cables which will be tightened with nuts eventually.
And a wooden seat tube, or at least partially seems awesome.

Next: planning lamination, fabrication and assembly order. Once some pieces are fixed, you can't assemble it anymore, so needs a plan!

I will also do some research about the wood-to-frame connections: glue, screwing, riveting etcetera.

Thanks for reading!

 

[axeman88]

It doesn't appear to me that wires in the positions you show them, would have much effect on stiffening the structure. In a stick and wire structure, like the box kites that were early airplanes, wires are tension elements, and wood struts are compression elements. They should be placed in opposition to create a rigid structure.

If the lower wire you have running close to the frame tubes was instead held some distance below the crank, on a compression strut, that could take some of the wheel forces in tension. Like the support cable on this crane is supported on a strut high above the body.

I don't envision the central cables from head to rear wheel dropout plate being loaded in tension with the rider on the bike, and if they were, they could bend the head tube if placed as you show. My gut says that they will just hang there limp, but I'm no expert in bike design.

If you draw a simple sketch with the imposed loads, (upward at the head and rear wheel, in opposition to the downward rider weight at the seat post) you might better visualize what each element is being asked to do. I'd model the crank load as being the rider weight placed on the crank rather than the seat, as a starting point. Of course, in actuality, all static loads will be much higher dynamic loads, but you have to start somewhere.

After a simple load sketch, the next step in structural analysis might be free body diagrams of each of the four major corners. These are simplified sketches with constraints and imposed loads, like these examples:

Yours will be indeterminate structures, because they are over-constrained, and it's difficult to know how much of the load is taken by each of the elements, which are taking forces in bending as well as in tension, compression or shear. Indeterminate structures are analyzed by considering the relative values of the modulus of elasticity of the various elements. With some small deformation theorytically imposed, the resulting reaction forces of each component of the structure can be calculated to see how they contribute to carrying the total load.

In my opinion, the classic bicycle frame shape is at least somewhat married to the strong points of steel tubing. In other words, the design evolved because steel tubing was available.

Look at how different this bicycle designed from scratch to be built from plywood is from the standard metal frame:

Rather than use any "stick" elements, plywood is strongest at resisting the largely in-plane loads, when formed as a largely vertical sheet. Holes can be cut from the lower stressed sections. Lateral stiffness is obtained by using two sheet frame elements, arranged in a box some distance apart.

The following design is more along the lines of something familiar, but notice how the main frame is configured as a TEE section, and various elements are arranged with their largest dimensions either parallel to the main plane, or transverse to it, depending on how the designer wanted the stiffness and load capacity. They didn't try to make a wood fork though, that was too much of a challenge.

Your "box kite" idea can work, but I suggest thinking further outside the traditional safety bike frame design.

 

[Tallbikeman]

Another design you might want to study is the very successful Pedersen design bicycle. A Danish designer and built in England originally in or around 1900. One can still buy a Pedersen. You will see the wires and how Pedersen arranged them into a completely workable bicycle. No wood but his steel is mostly being used in compression on his design and wires are all tension elements. Wood could successfully substitute for the steel on most of the Pedersen design. There have been several successful wooden bicycle builders in the last 30 years or so. I don't know how many are working at this time but if you can find their websites or maybe u-tube videos showing production that might be helpful also. Good luck with your build.

 

[Ulu]

It would be interesting to see this developed into a real Bicycle.

This appears to have a big weak point right at the heart of it. By adding even more cables it can likely be stabilized. The other nasty spot is that head connection, as mentioned above.

Of course, like all barnstormer era aircraft it will have a huge amount of aerodynamic drag from all the wires.

 

[BartRidesEternal]

It doesn't appear to me that wires in the positions you show them, would have much effect on stiffening the structure. In a stick and wire structure, like the box kites that were early airplanes, wires are tension elements, and wood struts are compression elements. They should be placed in opposition to create a rigid structure.

If the lower wire you have running close to the frame tubes was instead held some distance below the crank, on a compression strut, that could take some of the wheel forces in tension. Like the support cable on this crane is supported on a strut high above the body.
View attachment 222912
I don't envision the central cables from head to rear wheel dropout plate being loaded in tension with the rider on the bike, and if they were, they could bend the head tube if placed as you show. My gut says that they will just hang there limp, but I'm no expert in bike design.

If you draw a simple sketch with the imposed loads, (upward at the head and rear wheel, in opposition to the downward rider weight at the seat post) you might better visualize what each element is being asked to do. I'd model the crank load as being the rider weight placed on the crank rather than the seat, as a starting point. Of course, in actuality, all static loads will be much higher dynamic loads, but you have to start somewhere.

After a simple load sketch, the next step in structural analysis might be free body diagrams of each of the four major corners. These are simplified sketches with constraints and imposed loads, like these examples:
View attachment 222913
Yours will be indeterminate structures, because they are over-constrained, and it's difficult to know how much of the load is taken by each of the elements, which are taking forces in bending as well as in tension, compression or shear. Indeterminate structures are analyzed by considering the relative values of the modulus of elasticity of the various elements. With some small deformation theorytically imposed, the resulting reaction forces of each component of the structure can be calculated to see how they contribute to carrying the total load.

In my opinion, the classic bicycle frame shape is at least somewhat married to the strong points of steel tubing. In other words, the design evolved because steel tubing was available.

Look at how different this bicycle designed from scratch to be built from plywood is from the standard metal frame:
View attachment 222914
Rather than use any "stick" elements, plywood is strongest at resisting the largely in-plane loads, when formed as a largely vertical sheet. Holes can be cut from the lower stressed sections. Lateral stiffness is obtained by using two sheet frame elements, arranged in a box some distance apart.

The following design is more along the lines of something familiar, but notice how the main frame is configured as a TEE section, and various elements are arranged with their largest dimensions either parallel to the main plane, or transverse to it, depending on how the designer wanted the stiffness and load capacity. They didn't try to make a wood fork though, that was too much of a challenge.
View attachment 222915

Your "box kite" idea can work, but I suggest thinking further outside the traditional safety bike frame design.

Axeman, I agree with you. The cables were not intended for a huge jump in stiffness or strength. I just enjoyed the aesthetics of it. The cables, anchored on steel eyelets, can mitigate a little of the pulling/tensile forces. But I won't trust on them because you don't exactly know what the result is with vibrations and flexing. I'll leave the cables for now, my enthusiasm got the better of me.


I already made static (not dynamic) "on the back of a beer mat" calculations on the frame to get a clue of the pulling and pushing forces in the tubing.
The chainstay and downtube will statically endure a pulling/tensile force. Which will be different when: Utilizing the front brake and when accelerating (chain pull from rear sprocket towards front chainring).
The seatstay and top tube will statically endure a pushing force and has to be check with the "euler buckling" method.
83,33% of the load is located on the rear shaft and 16,66% on the front shaft. Again, this is static, only sitting on the seat to get an idea.
This makes it a great wheelie machine I reckon
There will be a safety margin calculation.
Safety Margin Example

I will try and get my 'beer mat' calculations neatly on a paper, readable.

The current things I am looking at:
Tube diameter (I like to keep them small, but must be realistic regarding strength and stiffness) and the joining methods.
Joining wood-steel with screws is no issue, but like @Ulu mentioned, you need a certain distance from the edges.
Plus: With utilizing screws instead of a clamping method, you drill a hole and 'weaken' the stick. When you use composite/carbon fibres for example, you can change the matrix of fibre direction to compensate the area.
Glueing wood-metal could be a great alternative. But the fitting (or clamping force) must be just right. The method is also important: Roughness. Degreasing, sanding in the right direction and then degrease again. Processing temperature is a factor.

In the meantime I am wondering if this is still to be considered a 'scrap build'
Calculations are free fortunately, they require some time.

Another design you might want to study is the very successful Pedersen design bicycle. A Danish designer and built in England originally in or around 1900. One can still buy a Pedersen. You will see the wires and how Pedersen arranged them into a completely workable bicycle. No wood but his steel is mostly being used in compression on his design and wires are all tension elements. Wood could successfully substitute for the steel on most of the Pedersen design. There have been several successful wooden bicycle builders in the last 30 years or so. I don't know how many are working at this time but if you can find their websites or maybe u-tube videos showing production that might be helpful also. Good luck with your build.

I know the Pedersen bicycle, they are pretty awesome and great design! I have seen a wooden Pedersen on a picture a while ago! Thank you.

It would be interesting to see this developed into a real Bicycle.
View attachment 222919
This appears to have a big weak point right at the heart of it. By adding even more cables it can likely be stabilized. The other nasty spot is that head connection, as mentioned above.

Of course, like all barnstormer era aircraft it will have a huge amount of aerodynamic drag from all the wires.

Ulu, the circle is complete on Ratrodbikes, checkout:
THIS

Or look on the internet for: "Breezer Kite Bike".

And I agree on your notes. I think this picture is some sort of concept structure. A prototype if you like.
Torsional stiffness is also important since the cabling do not handle that entirely, that why the breezer kite bike has such a big center tube diameter.

Thanks guys, I'll add some 'quick n dirty' notes here soon:

Picture above: Static strength calculations. Just sitting straight on the seat, not hanging on the bars. But the most important is the fact that this gives a static idea of the forces. (Insufficient and not completed, so work in progress!). As you can see the forces are decomposed in vertical and horizontal directions. With four equations and four unknowns I can solve it in a matrix or use the torque equation. Or both and double-check myself. To be continued!


Pictures below: Scrappy notes about the connections.

 

[BartRidesEternal]

This is very interesting:

Structural analysis Sheldon Brown website

My main goal is to get an idea, what to keep in mind and then just 'learn by doing'. And have fun!

 

[BartRidesEternal]

I saw this nicely milled dropout today, but it features a crack! The illegal type.

This could happen if you overtighten the screws. More root causes could cause this.

 

[SwissGuy]

I saw this nicely milled dropout today, but it features a crack! The illegal type.
View attachment 223064
This could happen if you overtighten the screws. More root causes could cause this.

Placing the screws offset instead of in line would also help...
(passionate woodworm speaking here and following this thread with big interest!)

 

[curtisfox]

Cross grain inlay spline would help would help here from cracking..........Curt

 

[Ulu]

I saw this nicely milled dropout today, but it features a crack! The illegal type.
View attachment 223064
This could happen if you overtighten the screws. More root causes could cause this.

That’s what we call a knife plate connection.

That one has Lots of tension perpendicular to the grain. The state architect will reject you immediately for this practice.

In big structural work they combat this by using a flat washer with teeth on it, under the bolt heads.

This cuts your axial fibers but axial fiber strength is not the problem.

You’re never going to break a good stick in tension in the middle of the stick. It will Always fail at the connection.

It’s almost impossible to develop the strength of the strut at connections with bolts or rivets, unless you have a lot of them AND they have appropriate distances between them, and to the edges.

Overall, I think it’s a mistake not to socket the lumber in metal.

 

[Ulu]

To be clear. It may not be a styling mistake, but I feel it’s a structural mistake.

This is how it’s been done for over a hundred years now.

The steel rivets are tiny, yet much stronger than the wood. They go in two directions because each only works well in one. They are both very far from the end of the wood. 16 diameters on the end.

The state only requires 7 or 8 diameters in most cases of wood connections, be they to metal or to other wood. Any cross-grain tension is a bust. Normally it’s an instant rejection. Revise and resubmit.

But that’s for buildings that must last 100 years. Bike frames cracking can be much less deadly and expensive than failing buildings, so make appropriate value judgements.

 

[BartRidesEternal]

That’s what we call a knife plate connection.

That one has Lots of tension perpendicular to the grain. The state architect will reject you immediately for this practice.

In big structural work they combat this by using a flat washer with teeth on it, under the bolt heads.

This cuts your axial fibers but axial fiber strength is not the problem.

You’re never going to break a good stick in tension in the middle of the stick. It will Always fail at the connection.

It’s almost impossible to develop the strength of the strut at connections with bolts or rivets, unless you have a lot of them AND they have appropriate distances between them, and to the edges.

Overall, I think it’s a mistake not to socket the lumber in metal.

I know what you mean with this flat washer with teeth. It kind of grabs and holds the fibres. Pretty neat!

To be clear. It may not be a styling mistake, but I feel it’s a structural mistake.

This is how it’s been done for over a hundred years now.

View attachment 223086

The steel rivets are tiny, yet much stronger than the wood. They go in two directions because each only works well in one. They are both very far from the end of the wood. 16 diameters on the end.

The state only requires 7 or 8 diameters in most cases of wood connections, be they to metal or to other wood. Any cross-grain tension is a bust. Normally it’s an instant rejection. Revise and resubmit.

But that’s for buildings that must last 100 years. Bike frames cracking can be much less deadly and expensive than failing buildings, so make appropriate value judgements.

Wow those rules of thumb are pretty awesome.
Thats what I love most about old crafts and experience. You get rules of thumb and people passing that knowledge like no CAD tool ever can
Much appreciated!

A buddy of mine sent me the "ANC-18", building wooden aircraft. You can look into it online.

The builds direction is slightly changing:
I intend to keep and pursue the antique looks. And I will work with the frame I still have.

I found some laminated Russian birch from our old bed. I disassembled them (I have a lot) and decided to do some research.
Two pieces can easily hold me, it is incredibly strong.
I put one in water and rain all day and then back inside. It holds pretty well, no delamination. Just a few stains.

I think I can remove the paint on the backend and laminate these to build the frame and fork.
That means that the parts will have a slight curve, but that is okay.

They are 700mm in length, 50mm wide and 10mm thick each.
First thoughts:
4 pieces For the downtube.
2 pieces per side for the seat tube.
Maybe keep the steel chainstay.

Not sure if I'll mount it like this, just to get and idea.

First plan the options and connections and then lamination and cutting.

By the way I found this "Solid Ash" bicycle, this is what I would like to build in the future, gorgeous!

Thanks again for all the tips, learning and adjusting lot here!

 

[axeman88]

I think if I wanted to create a strong connection / terminal for wooden frame elements, I'd house them in tight fitting metal end pieces.

This would prevent splitting, spread the stress of the connections, and resist rotation.

 

[BartRidesEternal]

Exactly my thoughts. Thank you axeman88.

 

[BartRidesEternal]

Just a quick and dirty mockup to get an idea of the curves in the wood and the overall looks.
The top tube pieces are deliberately not clamped aligned since I thought it wood (see what I did there?) hit the seat tube.

The 4 stacks are 40mm high and 50mm wide. The tube O.D. is 35mm. I.D. is 32mm.

I am pretty happy with that look. I'll let that soak in my brain and come up with ideas soon.

 

[BartRidesEternal]

It appears that the coating on the wooden pieces are glued on strips rather than paint, since I tried some paint remover. Smelly stuff!
The grey strips came off, but the white glue layer is hard to remove. Hand sanding for an hour made me finish 4 pieces.

I'll have to check a local woodworking shop too since our milling/turning machine can't handle these long, large curved pieces. If the woodworking shop does not have the machine to turn a section to 'round 32mm' then I'll have to find another solution.
Well sanding and lamination first! I hate sanding.

All ready for a glue friendly paint stripper!

Result after sanding a piece.