Fly rod guide selection

[Paul Arden]

Hi Lasse,

Sorty I didn’t understand that you had measured it! What did you measure?

Cheers, Paul

[Merlin]

I made a comparison by calculation for the tip section of a 905 clamped at its base (2 inches clamp). Beyond that point there are 4 guides plus the tip top.

I have considered a snake type of guide and a single foot. The single foot is supposed to be made similar to the snake but twisted back to make a single foot (same mass then).

For the snake the length of feet is 16 mm and 8 mm for the single foot. I computed the extra stiffness for steel material. Finally the single foot, in such conditions, makes the 28 inch rod section stiffer by 1.7% by comparison to the snake. It should be possible to see the difference in deflection for this section (1.8 mm for 30 grams load), but I think the difference will go down for the whole rod. For sure, if I change the base for comparison, things would change (e.g. if I consider that the foot of the single foot guide is similar to one of the feet of the corresponding snake guide).

The difference in speed due to the stiffness of feet is less than 1% for this rod section. That is practically very difficult to measure. This is due to the fact that the mass of guides is kept the same for easiness of comparison.

Merlin

[Paul Arden]

Thanks Merlin. That’s not particularly significant. What would happen if you considered the entire length of the snake to be rigid and not just the feet?

I’ve realise that it should be quite easy to measure stiffness of the blank vs stiffness of the rod simply by CCSing each with the tip ring affixed.

Cheers, Paul

[Merlin]

This time I considered the snake to be equivalent to a 24mm foot, the single foot guide having a foot of 8mm long (plus the loop).
I carefully checked the position of guides and considered that for the single foot, the foot itself had 2/3 the weight of the guide (full weight taken equal to the snake version).

The single foot option is softer by 1% by comparison to the snake option (1 mm deflection difference for 30 grams load at tip). That means less than that for the full rod in percentage since the rod section stiffness will be less and less influenced by the guides.

If you make a CCS kind of test you will enter the non linearity domain of the rod and that should make the differences even smaller I guess.

Merlin

[Paul Arden]

Thanks Merlin! That surprises me. Next time we build a rod with Snakes I’ll still have it measured for stiffness before and after. I can’t think what else it can be! Now you’ve gotten me curious

Thanks!
Paul

[Merlin]

Hi Paul

I tried a more accurate approach with recoils single foot and snake guides (not the light versions). I confirm a 1% difference in between guides systems for the stiffness of a tip section of a 905, the snake version being the stiffer.

If I compare a blank tip to a section with guides, I find that guides increase the stiffness of the tip section by 2.5% to 3.5%. You should be able to find that if you measure a tip only. For a full rod it should be less.

Making a CCS type of test on the tip section shows a very small difference in mass at tip level in between the two guides systems: 1 grams among a total of 80 to get the 33% deflection.

Merlin

[gordonjudd]

Making a CCS type of test on the tip section shows a very small difference in mass at tip level in between the two guides systems:

Merlin,
How much different are the EI (stiffness) vs length curves for these cases?

I know my ODE model does not like step increases and decreases produced by the ferrule overlap in those curves to come up with a deflection vs tip load curve so I have to smooth those discontinuities to get the Matlab solver to work. I would think the added stiffness associated with the ferrule overlap would be much larger than the added stiffness from the relatively short guide feet.

Gordy

[Merlin]

Gordy

The corresponding curves are in your mailbox now.

Merlin

[Lasse Karlsson]

Hi Lasse,

Sorty I didn’t understand that you had measured it! What did you measure?

Cheers, Paul

I measured the same blank with different rings attached, CCS is not accurate enough to get a difference when I build the rod and do the CCS'ing... thats why I suggest you do the build and the measuring

Cheers
Lasse

[gordonjudd]

I measured the same blank with different rings attached,

Lasse,
How did you do those measurements? I don't think a single point CCS measurement would be very conclusive.

I think I will try do some deflection vs tip load tests on a rod with the guides on the inside of the rod bend and then do again with the rod turned 90 degrees so the guides are on the bending axis.

Doing frequency tests both ways might also show a measurable difference.

Gordy