Finish: how much is too much?

[mmgrode]

Hey Gang,
   I've noticed that when I add more than about five or six coats of finish(poly or spar) on my bows it seems to slow arrow speed down a bit. I don't have a chrono, but that is what it looks like. I'm guessing it is adding mass weight to the limbs which will slow it down. I suppose much of it depends on the finish itself and the thickness with which it's applied. What do you guys think?  What has been your experiences with the effects of too much finish? Cheers, Matt

[mmgrode]

Anyone?

[Charlie Lamb]

Personally, I doubt it's the fault of the finish... unless it's like a quarter inch thick!

I could certainly be wrong, but unless you have shot the bow through a chrono before and after application of the finish, it would be very hard to tell for sure.

[gordonf]

I agree with Charlie, you'd have to put on a LOT of finish to noticably affect the bow's performance.

[droptine59]

No way. As Charlie stated, the finish woulr have to be an inch thick. The opoly does not have the tensil strength like in a lamination. It is all about moleculare compression. Clear coat is like putting a heavy weight condom on a bow. It wil bend but wil not addd rigidity to the bow. I hope you are sanding between coats.

[mmgrode]

Yes, definitely sanding between coats. "an inch thick" might be going a little far;) It would be interesting to see just how much mass that finish adds. It sure does look nice with several coats on though, that's for sure!
Now, the mass addition aside, the more coats you put on a bow the thicker it is. And considering that the most tension is on the surface of the back of the bow and the most compression on the surface of the belly where the finish is it is possible that this could effect it. I can guarantee that any dried finish is not as strong as wood, bamboo, or fiberglass in compression or tension. Therefore, it would be possible that it is hindering the performance, no? Opinions welcome! Cheers, Matt

[Dano]

"I can guarantee that any dried finish is not as strong as wood, bamboo, or fiberglass in compression or tension. Therefore, it would be possible that it is hindering the performance,"

How could finish hinder performance if it isn't stronger than the materials in the bow? Sorry but, Your statement is contradicting. One of the reasons a bow finish is chosen is that is flexiable, so I don't see that as a problem. The only thing that could hinder performance would be the mass, and as all above has said, it would take a lot of finish to do that.

[mmgrode]

Hey Dano,
    In being weaker than the materials in the bow in the exact place where the stress is greatest(surface of back and belly) and where resistance to that stress needs to be the greatest the finish would, in my estimation, be much weaker than wood, fiberglass, bamboo, etc. Therefore, the very inherint nature of the finish to be flexible is robbing the bow of cast. Look at the bows they are coming out with now with foam cores. It is the back and belly that makes the bow, not as much the core. With this reasoning, wouldn't it make sense that this flexible finish would be inhibiting the wood, bamboo, fiberglass, etc. from doing it's intended job(compress or tense) as it would be taking part of this load onto itself. The more finish put on, the higher percentage of the limb makeup would be of finish and therefore also more of the compression/tension forces. Hope that clarifies what I was going for. Again, discussion welcome! Cheers, Matt

[Matt E]

I agree with you to a certain extent but I would think it is an unmeasurable amount. The added weight of the finish and surface tension plays a minute part in performance. I also believe that the human element will play the greatest role in how a particular bow performs. The effects of the release alone can be measured . If you were to add up all of the human errors one would be amazed at the results. The finish wards off moisture which will kill a bows performance and in a major way.This you can definitely measure.

[wingnut]

Matt,

Dang son you got way to much time on your hands.  You need to be building bows and not worrying about the finish slowing it down.  The flexibility of the finish and the moisture barrier provided is the what's important.  

I don't think it is physically possible to build enough finish on a bow to get a measurable difference in speed.  I could be wrong but I sure won't loose sleep over it.

Now wrap your head around this one.  Is a high gloss finish faster then a matt finish because of air resistance?

LOL

Mike

[mmgrode]

This is what a physics with astrophysics final exam will do to you; get you analyzing things;)

Matt- I do realize that the effect on the performance would most likely be minimal, but I'd bet it's still there. I can also see that without that barrier to moisture, the bow would lose much of it's efficiency, so there's no getting around it. Yet, it would be interesting to test it out with a chrono to see how many coats really makes a difference in both arrow speed and efficiency.

Mike- If I could be building bows I would be, but I'm in Ireland!! Little too late to ship over the bandsaw and rasps;) LOL All I can do is think about it, and plan for the ones when I get back to the states. I got some ideas for the next one.  
Actually, you bring up a good point, Mike. High gloss might be superior to a matte finish in both compression and tension(as it's physically harder when dry). Now wind resistance.....LOL

I know I might be getting kind of picky with this stuff, but all the little stuff adds up. Performance is in the details. Perhaps this is part of what makes bowbuilding so interesting, we can always try new things and try to make them better(as long as there aren't wheels involved;)I'm enjoying the discussion! Cheers, Matt

[Matt E]

Mike, the matte finish should be faster.
I have read that a slick finish pulls a vacuum and the textured finish uses the microscopic pores by filling them up and acting as a lubricant. I am retired and have way to much time on my hands as well. It might be a Matt thing.  

[mmgrode]

It must be a Matt thing     I got to thinking again last night about this and wonder if the finish might have some effect on the set in a wooden bow. Taking into account the fact that set is caused by lack of resistance to compression on the belly, it could be possible that the more finish on the belly, the greater potential for set as it doesn't have adequate compression resistance. Set definitely would have an effect on the performance. What do you guys think?

Your friendly neighborhood fastidious fella;) Matt

[bow'narrow]

String up two identical bows - except one has a thick finish and one a thin finish.  Take a new tennis ball, cut a small hole in it.  Stick it on the upper limb.  Shoot the bow.  See how far the ball went.  Do the same with the other bow.  Now you can tell which finish was faster.  Or, just take either bow and go hunting.  Bow'narrow

[**DONOTDELETE**]

Hey Matt,

There is a forum called "Archery Talk" with a bunch of engineers very active in archery philosophy....mostly KE , velosity , Sping tension & elastic collusion in respect to arrow spine and performance is the hot subjects....but this one is unique enough to maybe get them going.....Have fun with it Bro.....

My take on it would be every coat you put on shortens your brace height, and therefore should increase your speed.....To answer your question..."How much is too much? ....when it starts cracking, or showing stess lines....ya got too much....Kirk

[Talondale]

It seems to me that unless the finish had the exact same properties of cast? (I think that's the right term) of the limbs then it would have to have a dampening effect on dynamics of the limbs.  I can't help but think of the analogy of having on a wetsuit.  When I have on a full length wetsuit I have resistance to movement and I can't swim as efficiently as I can without one but the suit has other benefits.  

Anyway the problem is whether it is a measureable difference or not. I doubt it would reach anywhere near 1% unless rediculous amounts of finish are applied.

[mmgrode]

Yes, the big question is whether the difference is measureable. I will definitely be doing some tests when I get back to the states in June.

Chuck- good analogy! Using the same analogy of a wetsuit, imagine putting on two wetsuits(twice as much finish). You would get twice as much protection from the water, yet it would be twice as hard to move. Again, there's no getting around using a finish, but there is a choice on how much is put on.

Kirk- your post got me thinking. The finish could still be under much stress without showing stress lines. Take a normal wooden bow limb for instance. That limb will still show set even when there aren't compression lines across the limb. Yet, when there are, you've definitely got problems as the limb has essentially given out in that spot. This would also screw up the tiller of the bow which definitely would effect the performance.  
     
This also brings up the issue of the amount of finish on a limb compared to the length of working limb, or more specifically, the amount of finish on the section of the limb that's doing the bending. If we take, for instance, a short recurve design and draw the bow there will be much more of both compression and tension in the working sections of the limb as compared to a straight limb longbow. Therefore, I would hypothesize that a longbow design could put up with a larger amount of finish in the working part of the limb before noticeable effects occur as compared with the recurve.

What do you fellas think?

Thanks for the posts guys. I'm enjoying the discussion!! Cheers, Matt

[**DONOTDELETE**]

Matt,

You are obviously an engineer with too much time on your hands, and a true love for philosophic meanderings, and musings of borderline BS....LOL! i couldn't help myself on that one....

Are you a published author Matt? Just curious...

As for seriously entertaining loss of performance with a build up of finishing products.....the mass is is the only thing that could effect it...like the wet suit theory....the additional mass  would have to be significant in a bow limb to even be able to detect any difference i believe....the common mistaken belief that putting a couple more coats of finish on a piece of furniture, or a hard wood floor will make the product more durable.....is a flat out untruth....the finish is only as hard as the wood you are finishing....unless you are using a fiberglass reinforcement cloth, the finish itself isn't going to be any tougher than the product you are finishing. Now if we are talking about serious epoxy based build up of an 1/8" t0 1/4" with a fiber base composition.....Well that is a different story......We are back to adding mass with its own structural integrity......Which comes first? The chicken or the egg??????

Kirk

[mmgrode]

"You are obviously an engineer with too much time on your hands, and a true love for philosophic meanderings, and musings of borderline BS....LOL! i couldn't help myself on that one...."

Now that's pretty funny right there! LOL Never been accused of being an engineer before!LOL But no, I am not an engineer, I do like philosophy, and I don't believe this is not worth exploring. I suppose, at the same time, Dr. Ashby's report probably seemed frivilous at times to some people(tanto tips vs. needle tip, 2 blade grizzlyvs. two blade Magnus, etc.), but look how much knowledge has been gained by his tests. Most guys probably just figure if the broadhead is sharp they will do the job the same, but that is not the case. The same might be the case with finish. Now, I am not on par with Dr. Ashby(not even close!), but I think we are often surprised at what is sometimes found, but we first need to ask the question.

I wouldn't so quickly dismiss the idea of the finish hindering/dampening the compression/tension forces in the bow. The very idea that the finish is not tougher than the bow material is the very principle by which I formulated my hypothesis. It is weaker in the same place that it needs to be the strongest. If two wetsuits are put on, it is not so much the mass that hinders the movement, but the dampening effect of the rubber. Now, the mass of the wetsuit may also add to this, but not nearly as much, in my opinion, as the lack of flexibility it causes.

I also have my doubts that there needs to be a massive amount of finish on the bow to noticeably effect it. When a bow is made, look at how small of an amount of material is taken off the belly to reduce weight and get tiller. The finish would, in essence, be comparable to adding on a super weak layer on the surface, therefore possibly effecting tiller, weight, and efficiency in the limb. I look forward to your comments and to testing this out! Cheers, Matt