So my Duncan butterfly (plastic version) is somehow cutting my poly string through the axel even though I understand that you have to use cotton string for wooden yo-yos but does that also apply to the butterfly ?? Although I think the butterfly has a metal axel I’m not really sure though ?? And any mods or tips would be appreciated thanks 
When you look at the axle/gap does the axle look rusted? Do you see any little plastic pieces sticking out at all? And on average how long does it take for the string to break?
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I’ve had the metal axle in a butterfly or imperial get damaged over time (in one case, probably due to decades long storage with a used string wrapped around it. The first thing, as Garrett says, is to visually inspect and see if there are any obvious defects or sharp points (although it’s easy to have a spot that can cut string but isn’t visible to the naked eye). It might be something easy to fix or it might be pretty much impossible. You should also look at the string that is getting damaged to see where the damage is occurring, as this should give you an idea of where, specifically, to look.
While they aren’t intended to be taken apart, and doing so does some damage to the plastic where it meets the axle, it is possible to attempt to carefully pull it apart and remove the axle. At that point you can either try to fix the issue (axle or starburst or other) and either reassemble it or get a 1/2 inch dowel and cut your own wooden axle replacement to glue in there, just be careful to get close to the same gap width. If it’s too wide it won’t respond well.
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I find the butterfly performs much more consistently with a wooden axle. I used a 1/4” dowel.
It performed ok with metal axle and poly, but I had to adjust my play style to be a little harder throwing all around to get a reliable response.
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I do have one more question for y’all sry 
Do all fixed axel yo-yos need the string tension to be really tight or can you play with it normally. Cause I always have to tighten my string tension in order for the yo-yo to come back up reliably. Does anyone else have this issue as well or is it just me ??
On the butterfly with poly I usually double loop to make it snappier.
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Thanks for the tip !! I’ll try it out later 
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Ehhh, it’s more like a 1/4 inch or 3/16 inch axle.
Adjust it as needed. As one guy above said he double loops the string. In most cases I just adjust as needed.
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I guess the better recommendation would be to measure the axle and find a dowel that matches. The two that I have taken apart were both old and they both had 1/2 inch axles.
Wow. I have some really old ones (10 and 20 years old) and they were all 1/4 or 3/16 inches.
I’ve had older and none were that large.
In the mid 90’s people regularly posted about replacing the steel axle with 1/4 inch wood. So are we talking about the same thing?
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I guess “really old” is relative. These were from the 1980s or earlier.
The Necro strikes again!! I think I’ll be giving this a try. 
An unfortunate necro. I’ve changed my opinion!
Maybe I won’t try it then…
I did it on an American made butterfly that actually plays quite badly without the mod. The new Target butterflies are all high quality with awesome and consistent responses.
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