Some Bow or Bowstring Advice

[Even]

Hi all,

I'm looking for advice from some of the more experienced here, regarding an issue I have with a bow.   Its not a big deal, but its one that has been bothering me.

I own an 82# Zebra Grevy, built by Louis Armbruster.   Fantastic bow, and I absolutely love it: it shoots like a laser. 

It has ONE issue, and that is that it eats bowstrings.  I ran into a post a long while back, where someone said that their Grevy or Super Grevy did exactly the same thing.  Its a slow, methodical fraying at the front of the string groove, at the tip.  Its very slow, very predictable, but... inevitable.

I am looking for advice, and to see if anyone has had the same issue with a similar bow, and what they did to solve it (if they have). 

I THINK, that perhaps the string groove itself is at either slightly the wrong angle, or perhaps slightly too small in radius, but that is just a guess.   Mr. Armbruster made a LOT of bows, and knew his business, so I am loath to go farting around without a very clear idea what I can do to solve this. 

Any thoughts?   Its not affecting my enjoyment of the bow, and given its weight, I probably only put a couple hundred arrows downrange each year, so its a slow fray, and predictable, but its still annoying.

Has anyone seen this before?

[Roy from Pa]

Possibly the string groove has a sharp edge on it. Check that out and if so then lightly sand with about 400 grit sandpaper.
And 82 # is a lot of weight..

[Orion]

Yes. Check for a sharp edge in the string groove. Feel for it as much as look for it.  If everything is smooth, then the angle might be too great, and you might need to adjust the groove a bit. 

[Roy from Pa]

Dave could you post a picture of the tips and where the string frays?

[Terry Green]

Ah, agree with sharp edges and posting pictures.

[Mo_coon-catcher]

Agree with the above. No advice without seeing it. But I bet it could be easily remedied with a chainsaw file.

Kyle

[Even]

Thanks for the advice, guys.  I'll try and get some good pics up later this evening for you, when I have more time to fiddle with getting some good ones, at a good resolution.

[Orion]

Forgot to mention one other possibility.  Dirt in the string groove.  Not likely, unless you routinely lean your bow upside down against objects as you retrieve arrows, for example.  A rough string groove is the most likely culprit, as has already ben suggested, but grit in/on the string can have the same effect.     

[Even]

The groove looks and feels smooth, no dirt.  The current working theory is that the groove is a touch shallow, with too sharp a bottom edge, so as the bow flexes, it slowly frays the string.  Plausible?





The string always seems to slowly fray at this exact spot, and only on the top groove.



This is the bottom groove, which isn't as hard on the string.  To my eyes, its cut a fraction deeper.

I just wanted some more experienced eyes on this, as I've never cut or modified a string groove before, and I value this bow extremely highly.  With the poundage, and the fact that Mr. Armbruster's bows are hard to find these days, I didn't want to start sanding or filing without a very clear plan.

Thank you for your advice, guys... this is the best forum out there.   All thoughts are appreciated very much.

Sorry for the delay in posting the pics, I had to figure out how to do it again!  Been a while.

Regards,

Dave

[Alexander Traditional]

Hello Dave. You might have good luck posting this on the bowyers bench.

[Mo_coon-catcher]

To me it looks like the groove wasn’t cut quite deep enough for the string to clear the edge of the groove. So is just rubbing on it. I would take a fine file matching the size of the groove and deepen the groove just a little bit. Just enough that the edge of the groove isn’t contacting the string anymore.though it doesn’t look like there’s much room left before the overlay is cut through. So may be better to touch that lip with some fine sandpaper to smooth it over a little.

Kyle

[Roy from Pa]

I always cut my string nocks deep enough so the string loop seats down inside the nock top edge.
But 82 pounds is a lot of weight. Maybe have a bowyer glue on another thin overlay and have him round the edge a tad.

[kennym]

Maybe take a q tip and run thu there to see if it pulls a strand of cotton before you file on it.  Any sharper corner on that heavy bow could work on the string too, compare it to the bottom groove since it doesn't do it...

[Even]

A Q-tip is a great idea.  I'll do that when I get a chance.  To the eye it looks smooth, but that should show anything I can't see. 

Otherwise, I think Kyle is on the right track.  I'll just gently round the bottom edge of the groove if I don't see any snags with the Q-tip.  Maybe GENTLY take the groove in a bit deeper, if that doesn't work. 

Zebra bow ends are distinctive, and I do recall reading another post regarding eating strings quickly.  Perhaps its the nature of the overlay material he chose to use, that dictated the cut and depth of the groove, and he went a bit shallow.  Another possibility is that the original string was fewer strands, and the string it came with was aftermarket and thicker.  That might contribute to fraying if the string stands out from the groove too much.

Either way, I'll play some more when I get a chance.  Thanks, guys.

[Even]

Thanks for moving this thread here, Roy.  I should have thought of that in the first place.

No snags on the Q-tip at all, smooth as silk.  It has to be that bottom edge.

[Roy from Pa]

Welcome Dave.
That string sticking above the top edge is the problem for sure.

[Kirkll]

This is a good product to use for polishing up and even shaping tip notches. Or you can take regular emery cloth an rip it to 1/4” widths and twist it up. This will self center your finish sanding with a little shoe shine action.

I too believe a bit more depth would do the trick. You might find that fraying has more to do with it just rubbing it from the outside on things.

Btw…, when you get done sanding it. Seal it with a bit of clear fingernail polish or other sealer with a fine paint brush.

https://www.amazon.com/Mitchells-Abrasive-Emery-Tape-Grit/dp/B07H68HY55/ref=asc_df_B07H68HY55?mcid=8857365a03a2389ab9faad6f4adcbe99&tag=hyprod-20&linkCode=df0&hvadid=693071814232&hvpos=&hvnetw=g&hvrand=10850726631387280368&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9052493&hvtargid=pla-1601183624058&psc=1

[Even]

Great advice, thanks Kirk! 

It is definitely something to do with that string notch.  Given enough time, it will munch right through.  That string is new this summer, probably only forty arrows and a couple hundred pulls for strength work on it. 

[Roy from Pa]

Kirk, I love that rope sanding stuff. Does a great easy job on string nocks.

[Kirkll]

Kirk, I love that rope sanding stuff. Does a great easy job on string nocks.

It’s good stuff, but finding it large enough diameter to match a typical bow string size is tough to do. I’ve found buying different grits of emery cloth an ripping them into narrow strips and twisting them up gives me a much better job while shaping the overlays with heavier grit paper I like 120 grit after I use the chainsaw file to rough it out, then go to 180 or 220 to polish it.

The overlays on this particular bow are really thin, and only has two layers. The OP is going to have to be very careful not to sand through that white layer.  I much prefer doing a minimum of 3 pc overlays and have my string a bit deeper in the notch. 2 layers of phenolic and then the wood on top. Often times I use a thin piece of G-10 right against the glass , and white phenolic over it. Then my wood.


Another option here may be just using a continuous loop string rather than the thicker Flemish design. You can get a smaller diameter loop using serving that would give it a lower profile.    Just a thought…. Kirk

A few years ago I found some thin G-10 that had a lighter core color. It was black both sides with white in the center and only .050 thick.  This stuff made really cool looking overlays, but I can’t find it anymore ….  Check this tip out

https://photos.app.goo.gl/s3s9d7R8HyhEgAR19