Matilda re design.

[Chris Knight]

As others have said, I see no point in a steel band. A decent twisted cord will provide far greater force on the blade than any such steel band ( one that is sufficiently light to use in such a saw). Just look at the Roman catapaults that used twisted hair or animal sinews to store energy.

It would be very easy to measure using a spring balance.

 

[swagman]

I like that design

are you building for selling??

Hi Mcluma. I am taking 1 step at a time. 1st off is to make sure this bow saw design will work.

Regards Swagman.

 

[swagman]

I've been wondering about the grip you are going to use. Having the steel band quite close to the handle means, I think, that you are expecting to use a single handed grip only. (If you were to use the two-handed grip, you would be wrapping your second hand around the steel, which would be uncomfortable.)
If you are planning single handed grip only, you might want to include a comfortable curve for an extended forefinger to rest on.

There's an interesting discussion on this point (and much more about design of similar saws) on the Tools for Working Wood site here:

http://www.toolsforworkingwood.com/...e=toolstore&nextpage=/extra/bowsawdesign.html

Hi AndyT. Will keep this in mind.

Regards Swagman.

 

[swagman]

It looks very nice - but my only concern would be the further away from the Fulcrum the less force from the top tension arrangement will be applied to the blade? It is acting as a lever.

As you say the "proof of the pudding is in the eating"?
Hope it works.

Rod

Hi Rod. On a traditional bow frame you would be spot on with you analysis of the fulcrum height to leverage. With this design though, the majority of tension is already being supplied by the outward expansion of the spring steel band. The top tensioners role is to draw in the top of the frame arms, even closer together, to maximize this outward expansion.

But, as you rightly say, ''the proof of the pudding is in the eating''.

Regards Swagman.

 

[swagman]

As others have said, I see no point in a steel band. A decent twisted cord will provide far greater force on the blade than any such steel band ( one that is sufficiently light to use in such a saw). Just look at the Roman catapaults that used twisted hair or animal sinews to store energy.

It would be very easy to measure using a spring balance.

Hi waterhead37. If you see no point in accepting a new bow saw design then I am still happy for you.It tells me that you have used a traditional bow saw design and it fulfills all your requirements. , I am trying to offer others a choice. The pro's and con's of either design will always be governed by the views of those that will try them.

Regards Swagman.

 

[Racers]

Hi, Swagman

How are you compressing the upper band? the only way I can see you doing and increasing the tension on the blade is to press it down towards the blade, any thing else will just cause the bow to comperes as it will pivot at the ends of the blade. But I don't think that will produce much force on the blade because it is held nearly 2/3rds up from the blade so thats point where the force is applyed.

Pete

 

[swagman]

Hi, Swagman

How are you compressing the upper band? the only way I can see you doing and increasing the tension on the blade is to press it down towards the blade, any thing else will just cause the bow to comperes as it will pivot at the ends of the blade. But I don't think that will produce much force on the blade because it is held nearly 2/3rds up from the blade so thats point where the force is applyed.

Pete

Hi Pete. A windlass will be used to draw the upper arms closer together. Outward spring pressure already generated within the upper band should compete against the inward compression applied by the windlass. This should in turn create a natural pivot point on which the lower arms can expand as the upper arms are pulled in.


Regards Swagman.

 

[woodbloke]

As others have said, I see no point in a steel band. A decent twisted cord will provide far greater force on the blade than any such steel band ( one that is sufficiently light to use in such a saw). Just look at the Roman catapaults that used twisted hair or animal sinews to store energy.

It would be very easy to measure using a spring balance.

My two euros, as ever.
Agreed...re-invention of the wheel as I said (I think) in a previous thread. The twisted cord design was perfected by the Romans or some ancient civilization thousands of years ago and hasn't been substantially improved upon.
The cord saw also breaks down quickly into a small, compact bundle that's easily transportable, which was probably important to journeymen in the Middle Ages. That feature is maybe of little importance today but still a useful design feature.
A nicely made piece though, but I fail to see where it's taking you...sorry - Rob

 

[Racers]

Hi, Swagman

So the solid crosspiece in an normal bow saw will be replaced by a springy piece of metal then will somehow resist the compressive force applied to it?

Its the first thing I dismmised when I was thinking how you would do it.


Pete

 

[swagman]

As others have said, I see no point in a steel band. A decent twisted cord will provide far greater force on the blade than any such steel band ( one that is sufficiently light to use in such a saw). Just look at the Roman catapaults that used twisted hair or animal sinews to store energy.

It would be very easy to measure using a spring balance.

My two euros, as ever.
Agreed...re-invention of the wheel as I said (I think) in a previous thread. The twisted cord design was perfected by the Romans or some ancient civilization thousands of years ago and hasn't been substantially improved upon.
The cord saw also breaks down quickly into a small, compact bundle that's easily transportable, which was probably important to journeymen in the Middle Ages. That feature is maybe of little importance today but still a useful design feature.
A nicely made piece though, but I fail to see where it's taking you...sorry - Rob

Hi Rob. This design also breaks down quickly. Take out the 2 spring bands; remove the blade and windlass, then pack it away for when you need it.

Regards Swagman.

 

[swagman]

Hi, Swagman

So the solid crosspiece in an normal bow saw will be replaced by a springy piece of metal then will somehow resist the compressive force applied to it?

Its the first thing I dismmised when I was thinking how you would do it.


Pete

Hi Pete. That's a fairly close description of what I will be doing.

Regards Swagman.

 

[swagman]

Hi, Swagman

How are you compressing the upper band? the only way I can see you doing and increasing the tension on the blade is to press it down towards the blade, any thing else will just cause the bow to comperes as it will pivot at the ends of the blade. But I don't think that will produce much force on the blade because it is held nearly 2/3rds up from the blade so thats point where the force is applyed.

Pete

Hi Pete. As an update to those following this projects completion. I have struck a minor problem with my original design. The concept of compressing the upper band to further tension the blade is still a sound proposition, but as I compress the upper band using the windlass, upward ballooning of the band is also happening. The solution is not a hard fix, as it just requires 2 holes drilled though the upper arms in line with the top of the band and a steel rod run through to stop this upward ballooning. I decided to use a length of 6mm all-thread, as it can also replace the windlass as a mechanism to draw the arms inward.

Regards Swagman.

 

[swagman]

Attached are images of the completed bow saw. From the blade to the top of the steel band curve is 9 inches. The blade tensioned up quite nicely with the 6mm allthread installed. I have a couple of small changes to make on the next bow saw design but that will have to wait till after new year.

Have a safe and enjoyable christmas /new year.

Regards Swagman.

 

[Harbo]

That was quick work - though it's probably not freezing "down there"?

What's the balance like - does the metal make it top heavy?
Like the shape - reminds me of a road bridge?

Happy Christmas to you too.

Rod

 

[swagman]

That was quick work - though it's probably not freezing "down there"?

What's the balance like - does the metal make it top heavy?
Like the shape - reminds me of a road bridge?

Happy Christmas to you too.

Rod

Hi Rod. The balance feel and of this bow saw was one aspect that really pleased me with this project. I rate this design better than the previous original bow saw in this regard. The visual appeal to this saw is another matter. I am not overly pleased with the look of the included all-thread. To me it lacks harmony with the natural flow and shape of the 2 frame arms. An important learning curb with this bow saw that can be included in the next design was an understanding that direct downward pressure to upper steel band could be a much more affective method of transferring tension to the lower cutting blade. With this in mind, I plan to get rid of the allthread, add a horizontal wooden spreader near the top of the frame arms, and use this to support a vertical jackbolt. This will be used to supply downward pressure onto the centre point of the steel band arch.

All the best to you and your family Rod, during this coming xmas period.


Regards Swagman.