There was a recent thread mentioning the length of inserts effect on stiffness.
I'm finding the length of the insert is a very big variable in tuning and understand why some shooters get frustrated trying to tune carbons. Just going to a different insert to change spine may throw you way off.
Each length of insert has it's own stiffness properties so that other from end weight recipes using different length inserts are not interchangeable.
It's a very big difference.
An example of this - Using the Three Rivers Trad .300 shaft with a 100 grain brass insert and a 250 grain point shoots stiffer than the same shaft with a 50 grain brass (shorter) insert.
You can spend hours playing with weight/insert combinations. And a lot of hot melt glue!
Tedd

A lot will depend on the centershot of the bow you are tuning.I had bought some used carbons that were an inch longer then my draw.They were showing stiff,so I though to add more weight upfront to weaken the spine.Well they were showing stiffer the more weight I added.They were in effect bouncing off the riser instead of flexing around it.Like yours they shot better with a lighter weight point but still alittle stiff.Carbons recover much quicker then other arrows.They were giving me a false reading.I did tune the same spine to that bow but started out with a full length arrow and they ended up about 2" longer.

Hey Gents

Just want to know how do you tell if it's a false reading (bouncing of shelf) what can I do to test this? I think I've experienced the same with my previous set of arrows.

Thank you in advance

I agree Ted, having weight behind the point in the shaft will be stiffer than having the same weight all on the point in front of the shaft.

I run three different weight inserts behind the points on my Easton Axis shafts, 50, 70 and 100 grains.  When I correspondingly match the difference with point weight, I get no difference in impact. For that matter, I can shoot them all with the same weight head and get very little difference in impact. Nothing that fletching won't clear up.

Sometimes we make this harder than it should be.  Sure there are tiny differences depending on where the weight is located, but they're just not enough to worry about.  A half inch, maybe even quarter inch, difference in draw, a clean release vs a pluck, etc., will produce more impact variation than whether 50 grains of weight is moved a half inch farther forward or backward in/on the shaft.

100 grain inserts are longer and is acting as an internal footing

same goes for footings.

actually i use a footing a little longer than the longest insert you'll use, this way you can use shorter inserts and not change the length of the flexible portion of the shafts. this means you can use any length insert that's shorter than the footing and not have the issue tedd talks about. so long of course that the total weight upfront doesn't change.

example- i shoot 350gr upfront. my footing extends a little past where a 100gr inserts ends. i use a 250gr point with the 100gr inserts.
i can use the same footing with 50gr inserts and a 300gr points and not change the spine of the shaft because i haven't changed the flexible portion of it.

also, i recently had a problem with tuning for my heavier limbs. i want to shoot 400gr up front with it. i had trimmed to stiffen until i reached my minimum arrow length but they were still a little weak. i increased the length of the footing and this worked a treat. it stiffened the shaft enough to have them tuned.

Good thinking clint!
I also have a new set of limbs I'm working with.

Scitty, say your shafts are showing stiff and you add point weight and they act stiffer ie. opposite of what you expect, good sign its a false reading. Rule of thumb verify with point weight changes before cutting.

I usually shoot full length shafts and do not see spine changes using different inserts as long as total weight is same.

Looks like a few more are seeing the light and catching on to the benefits of footings and high FOC.

This thread makes me wonder if I solved my issues by just changing point weights? I used the brass inserts at first but got cheap and just bought different weight points. I did increase my footing to 2 in so maybe that has effect as well. I shoot my carbons off a raised rest on my recurves. Have pretty much gone back to alum for my longbows.

I really shot s bunch of scenarios yesterday. Just testing weights. It was fun. I tried my regular hunting arrows when I was finished. They are Arrow Dynamics Traditional tapered.  In there end I'm still a tapered carbon fan. Quality tapered carbons are a struggle to purchase. But they do make shooting more fun. They just work with almost anything on the front. like center seeking missiles! I wish there was a tapered shaft the quality of the 3 rivers parallel shafts.
Tedd

QuoteOriginally posted by katman:
Scitty, say your shafts are showing stiff and you add point weight and they act stiffer ie. opposite of what you expect, good sign its a false reading. Rule of thumb verify with point weight changes before cutting.

I usually shoot full length shafts and do not see spine changes using different inserts as long as total weight is same.

Thanks Katman, it's exactly what happened with my heavy hunter shafts, traded them before I had this helpful insight