Common mistakes in deflex/reflex bows?

[willie]

heat shape the lams to the forms before gluup? I know the bamboo will be easy,

[Aussie Yeoman]

Here's one bow I'm working on in VirtualBow. It's a takedown with the riser omitted.

Brace: 150 mm
Draw: 711 mm

Handle-
length: 175 mm
setback: 0
Angle: -7.5

Profile: Spiral
Length: 750
R start: 3000
R end: 2500

Width-
0//40
12.5//39.9
50//39.9
75//31.4
100//10

Thickness-
0//12.05
100//5.75

The material is Ironbark. With a stiffness of 24.212 GPa, and a max working stress of 167 MPa.
 

[Aussie Yeoman]

And here's another I'm still tooling around with. This time a 1-piece.

Brace: 150 mm
Draw: 711 mm

Handle-
length: 0
setback: 0
Angle: -7

Profile: Spiral
Length: 838
R start: 4000
R end: 2250

Width-
0//30
2//30
4//30.7
6//31.8
8//34.4
10//37.6
12.5//39.8
50//36
75//28
100//10

Thickness-
0//25
2.5//25
5//24
7.5//17.2
10//12.5565
12.5//11.7125
15//11.556
100//6.68576

Same material as above

[Aussie Yeoman]

So, I've collated some commentary and for future reference the key things to keep in mind when making a D/R bow are:

• The laminations must be pretty accurate to begin with (difficult if using natural bamboo, but we must try what we can, eh?)
• Avoid having uneven reflex. Smooth curves at the start = smooth curves at the end. This would be a manifestation of the above point being gotten right, in addition to having a good form/caul.
• At brace, the limbs should be actually or close to pretty straight
• Avoid putting in too much reflex. Having the tips around even with, or just in front of, the back of the handle helps to avoid nasty problems during tillering
• Go slowly through tillering - this done to avoid putting too much bend somewhere in particular, which can happen very quickly with a bow like this. Consider using a scraper of some sort. The accuracy of the lams to begin with helps reduce the amount of bulk stock removal, making the scraper effective.
• Know exactly what it's meant to look like at full draw before you start. This done by sketching, modelling or emulating another bow. This helps prevent hinges or overshooting the limb's curvature.

Are those the main points or have I missed something vital?

[willie]

• Know exactly what it's meant to look like at full draw before you start. This done by sketching, modelling or emulating another bow. This helps prevent hinges or overshooting the limb's curvature.

Are those the main points or have I missed something vital?

with virtual bow you should be able to see what the bow should look like at any stage of the draw, eliminating the need to compare it to a different bow

[Bob Barnes]

How hard is it to download the Virtual Bow program and what do you use to open/use it?

[Aussie Yeoman]

https://www.virtualbow.org/

It's an independent program that you download and install. It's really easy to install and quite easy to use, with a fairly shallow and short learning curve.

[Bob Barnes]

https://www.virtualbow.org/

It's an independent program that you download and install. It's really easy to install and quite easy to use, with a fairly shallow and short learning curve.

I have win 11 and get a warning about it "not being commonly downloaded.  Be sure that you trust the link"   It did download something but the file is called "unconfirmed download" and it won't open...

[Badger]

 Several questions about the programs. Do they allow for some set at given stresses? Does increased set affect efficiency or FDC? If so, by how much? Are there any allowances made for working part of the limb length? Efficiency is lost in working limb length and increases as the working limb shortens, even though strain figures might go up.

[willie]

https://www.virtualbow.org/

It's an independent program that you download and install. It's really easy to install and quite easy to use, with a fairly shallow and short learning curve.

I have win 11 and get a warning about it "not being commonly downloaded.  Be sure that you trust the link"   It did download something but the file is called "unconfirmed download" and it won't open...

does  your file name end with  .crdownload?    if so try again

[willie]

Several questions about the programs. Do they allow for some set at given stresses? Does increased set affect efficiency or FDC? If so, by how much? Are there any allowances made for working part of the limb length? Efficiency is lost in working limb length and increases as the working limb shortens, even though strain figures might go up.

set is not taken into account with the program.   It is up to you to choose a MOE value for the materiel used,  and review your design to see that stresses remains below the level you feel set will occur at.

[Bob Barnes]

https://www.virtualbow.org/

It's an independent program that you download and install. It's really easy to install and quite easy to use, with a fairly shallow and short learning curve.

I have win 11 and get a warning about it "not being commonly downloaded.  Be sure that you trust the link"   It did download something but the file is called "unconfirmed download" and it won't open...

does  your file name end with  .crdownload?    if so try again

Yes... I have hit 'download 5 or 6 times and the file is the same every time.  "Unconfirmed(random number).crdownload"
Thank you for helping...

[Aussie Yeoman]

Nah, unfortunately it doesn't account for set. Alan Case's spreadhseet allows a bow to be 'pre-stressed' to account for set.

If One happens to have bend test data, then One can predict how much set the bow will take at a given stress level. That's what I've done with my D/R bows above, and anticipate they'll take between 3/4 and 1" set once shot in.

Several questions about the programs. Do they allow for some set at given stresses? Does increased set affect efficiency or FDC? If so, by how much? Are there any allowances made for working part of the limb length? Efficiency is lost in working limb length and increases as the working limb shortens, even though strain figures might go up.

[willie]

https://www.virtualbow.org/

It's an independent program that you download and install. It's really easy to install and quite easy to use, with a fairly shallow and short learning curve.

I have win 11 and get a warning about it "not being commonly downloaded.  Be sure that you trust the link"   It did download something but the file is called "unconfirmed download" and it won't open...

does  your file name end with  .crdownload?    if so try again

Yes... I have hit 'download 5 or 6 times and the file is the same every time.  "Unconfirmed(random number).crdownload"
Thank you for helping...

windows 11 may be too helpful for its own good
try checking these settings
https://www.supportyourtech.com/tech/how-to-allow-downloads-on-windows-11-a-step-by-step-guide/