Bowtech Limb Twist
02-19-2005, 04:08 PM
#1
Thread Starter
Join Date: Apr 2003
Posts: 25
Bowtech Limb Twist
Please, this is not meant to start a bashing thread about Bowtech. It is a simple, but serious (to me) question regarding the limb twist seen with the new binary cam system.
I will start by saying that I own a Defender that is fast, accurate, and pleasant to shoot. The only thing about the bow that bothers me is limb twist of the upper limb. Both cams are dead straight when the bow is at rest. At full draw, the upper limb twists so that a staight line drawn along the cam projects several inches inside the opposite limb tip. The bottom cam / limb remain perfectly straight.
I have dealt with this on other bows by twisting up one of the cable yokes. That is not possible with the new binary cam system. Probably because I am a bit of a pefectionist, I decided to take the bow back to the dealer to see if he thought I should send it back to Bowtech for replacement limbs.
They are more of a Walmart type sporting goods store and not what I would call a true archery shop. They were not aware of the problem, so we decided to look at their Bowtech inventory. We pulled back 2 Old Glorys, 2 Allegiances and 3 other Defenders to look at the cams. In every bow, the top cam pointed several inches inside the bottom cam / limb at full draw. His response was that they were all designed that way, so no need to send it back.
What are you guys seeing on your bows? Are all of them leaning/twisting like this or did my shop just get a bad batch? I will be the first to admit that I have not shot broadheads with my Defender to see how they group, but I do know that I have had problems in the past with other bows when I saw this much twist / lean. I do not want to give up on this bow because everything else about it is great.
Should I send it back for new limbs? Should I live with it?
I will start by saying that I own a Defender that is fast, accurate, and pleasant to shoot. The only thing about the bow that bothers me is limb twist of the upper limb. Both cams are dead straight when the bow is at rest. At full draw, the upper limb twists so that a staight line drawn along the cam projects several inches inside the opposite limb tip. The bottom cam / limb remain perfectly straight.
I have dealt with this on other bows by twisting up one of the cable yokes. That is not possible with the new binary cam system. Probably because I am a bit of a pefectionist, I decided to take the bow back to the dealer to see if he thought I should send it back to Bowtech for replacement limbs.
They are more of a Walmart type sporting goods store and not what I would call a true archery shop. They were not aware of the problem, so we decided to look at their Bowtech inventory. We pulled back 2 Old Glorys, 2 Allegiances and 3 other Defenders to look at the cams. In every bow, the top cam pointed several inches inside the bottom cam / limb at full draw. His response was that they were all designed that way, so no need to send it back.
What are you guys seeing on your bows? Are all of them leaning/twisting like this or did my shop just get a bad batch? I will be the first to admit that I have not shot broadheads with my Defender to see how they group, but I do know that I have had problems in the past with other bows when I saw this much twist / lean. I do not want to give up on this bow because everything else about it is great.
Should I send it back for new limbs? Should I live with it?
02-19-2005, 05:07 PM
#2
Join Date: Feb 2005
Posts: 53
RE: Bowtech Limb Twist
Its probably caused by the draw stop (on one side of the cam only) hitting the limb and them causing it to bend with the archers pull against it.
I haven't noticed it being a problem on my Allegiance as far as accuracy is concerned. This bow is the most accurate bow I've ever shot.
Insatiable
I haven't noticed it being a problem on my Allegiance as far as accuracy is concerned. This bow is the most accurate bow I've ever shot.
Insatiable
02-19-2005, 05:38 PM
#3
Giant Nontypical
Join Date: Feb 2003
Location: Dover, PA USA
Posts: 5,497
RE: Bowtech Limb Twist
courtesy of "Len in Maryland" :
Also question for you.......exactly how does one remove limb twist from the bottom limb of a single cam or Hybrid cam bow? exactly........you don't. And another reason you don't really hear anything about it , is the simple fact that nobody ever looks closely at the bottom limb at full draw. Your eye is at the top end of the bow so that is what you see and that is what you focus on...........
Grab a single or Hybrid style cammed bow and draw it upside down once.
I think it's great that some took the initiative; and, some of you were really on the right track.
When I first made comments about this new cam system, I said that it would take some time to really evaluate its positives and negatives. I still hold to that statement and will continue to analyze this product. A few have made a real issue about 'cam lean' that grew into a furor and quite a controversy in recent weeks. As with many issues on the forums, it was getting emotional and needed some context.
I had done some evaluation of its shooting characteristics/consistency and was impressed. I took one bow apart and did a tolerance check and was again impressed; especially with the axle fit to the limb and bearings. If anyone has the capability, I'd like to hear their input on these matters. After all, I've only been able to take a small sampling of the dozen units I have in stock. I plan to sample more later; but, I like to take samples from different 'lots'.
One thing we have to do is DEFINE cam lean as it is different from limb twist. Just like the definition of timing and synchronization can be confused, so can these terms. We also have to understand when things can be controlled, IF they must be controlled, and HOW they should be controlled. It is best to distinguish between these two for various reasons. First, identifying the causes becomes easier if you're analyzing both. Second, and in this case, it's more fair to the cam design. I'll explain later. *
Cam lean may be what you're seeing because the cam IS leaning; but, what is the cause. I refer to cam lean as a variance in the degree of straightness due to worn bushings and/or bent axles. Limb twist is where the limbs 'bend' due to various influences. In this case the influence would be the cable guard. There are other cases of limb twist which are permanent. This was the case in some older designs and some of the split limb designs that were manufactured inexpensively. In this case and in every case of bows using a cable guard, limb twist WILL be an issue.
During my Dealer Seminar at the ATA Show, I discussed the usage of lasers and how just one method shouldn't be totally trusted. This is apparent moreso now that this issue arose. If you laser or even straight-edge the cams, they will show minuscule lean in the static mode. In the dynamic mode, however, the lean becomes more noticeable. If I use one laser design, it just shows me cam lean. I have to use a second design that will tell me if the limb is twisting. If the two agree, it reads one way. If they do not agree, it reads another way.
I checked my entire stock of BowTech Binary and many other manufacturers, which is substantial. The amount of cam lean in the static condition was better than most. The dynamic condition for the binary system was average to better than average. Even the much more expensive limb designs were not significantly better.
Keep in mind that Gordon Glass builds about 80% of the limbs in the market. What we're really seeing, in not only in the design but the construction, is 'commonplace' with today's technology. And, it doesn't matter whether or not you have a split yoke system, there will still be limb torque/twist when using a cable guard. By adjusting a yoke, you're really just preloading the limb. It then becomes critical as to how much you're 'influencing' the end result. I've seen situations where the cam lean/limb twist was corrected by twisting yokes to the point where the cable(s) MISSED the stop(s). I've done a lot of dual cam bows for some tournament shooters. It's a tenuous job of obtaining that 'balance' of the system for optimal results. Can you get a better shooting bow? Yes, but it would take a top-notch shooter to see the difference. In most cases it would be a "feel good" situation.
What I have found is that the cam lean/limb twist in this design is really not as much as we've been subjected to for a decade - and we shot those well. I also have noticed nowhere near the cable wear as has been experienced with other designs. This might change, but I have my doubts.
*The reason I decided to report my findings at this time was not that cam lean wasn't there; but, that it was being misinterpreted and somewhat blown out of proportion. I must admit that I was negligent in doing the dynamic tests right away. The bows were shooting so well that we didn't see an immediate need. We have tuned these bows easily and shot FTs and FIXED BHs into the same holes at around 300 fps @ 25 yds. We haven't had the opportunity to do long-range tests because of the weather/facilities. If someone else could chime in on their long-range FIXED BH results, I would love to hear about it.
When I first made comments about this new cam system, I said that it would take some time to really evaluate its positives and negatives. I still hold to that statement and will continue to analyze this product. A few have made a real issue about 'cam lean' that grew into a furor and quite a controversy in recent weeks. As with many issues on the forums, it was getting emotional and needed some context.
I had done some evaluation of its shooting characteristics/consistency and was impressed. I took one bow apart and did a tolerance check and was again impressed; especially with the axle fit to the limb and bearings. If anyone has the capability, I'd like to hear their input on these matters. After all, I've only been able to take a small sampling of the dozen units I have in stock. I plan to sample more later; but, I like to take samples from different 'lots'.
One thing we have to do is DEFINE cam lean as it is different from limb twist. Just like the definition of timing and synchronization can be confused, so can these terms. We also have to understand when things can be controlled, IF they must be controlled, and HOW they should be controlled. It is best to distinguish between these two for various reasons. First, identifying the causes becomes easier if you're analyzing both. Second, and in this case, it's more fair to the cam design. I'll explain later. *
Cam lean may be what you're seeing because the cam IS leaning; but, what is the cause. I refer to cam lean as a variance in the degree of straightness due to worn bushings and/or bent axles. Limb twist is where the limbs 'bend' due to various influences. In this case the influence would be the cable guard. There are other cases of limb twist which are permanent. This was the case in some older designs and some of the split limb designs that were manufactured inexpensively. In this case and in every case of bows using a cable guard, limb twist WILL be an issue.
During my Dealer Seminar at the ATA Show, I discussed the usage of lasers and how just one method shouldn't be totally trusted. This is apparent moreso now that this issue arose. If you laser or even straight-edge the cams, they will show minuscule lean in the static mode. In the dynamic mode, however, the lean becomes more noticeable. If I use one laser design, it just shows me cam lean. I have to use a second design that will tell me if the limb is twisting. If the two agree, it reads one way. If they do not agree, it reads another way.
I checked my entire stock of BowTech Binary and many other manufacturers, which is substantial. The amount of cam lean in the static condition was better than most. The dynamic condition for the binary system was average to better than average. Even the much more expensive limb designs were not significantly better.
Keep in mind that Gordon Glass builds about 80% of the limbs in the market. What we're really seeing, in not only in the design but the construction, is 'commonplace' with today's technology. And, it doesn't matter whether or not you have a split yoke system, there will still be limb torque/twist when using a cable guard. By adjusting a yoke, you're really just preloading the limb. It then becomes critical as to how much you're 'influencing' the end result. I've seen situations where the cam lean/limb twist was corrected by twisting yokes to the point where the cable(s) MISSED the stop(s). I've done a lot of dual cam bows for some tournament shooters. It's a tenuous job of obtaining that 'balance' of the system for optimal results. Can you get a better shooting bow? Yes, but it would take a top-notch shooter to see the difference. In most cases it would be a "feel good" situation.
What I have found is that the cam lean/limb twist in this design is really not as much as we've been subjected to for a decade - and we shot those well. I also have noticed nowhere near the cable wear as has been experienced with other designs. This might change, but I have my doubts.
*The reason I decided to report my findings at this time was not that cam lean wasn't there; but, that it was being misinterpreted and somewhat blown out of proportion. I must admit that I was negligent in doing the dynamic tests right away. The bows were shooting so well that we didn't see an immediate need. We have tuned these bows easily and shot FTs and FIXED BHs into the same holes at around 300 fps @ 25 yds. We haven't had the opportunity to do long-range tests because of the weather/facilities. If someone else could chime in on their long-range FIXED BH results, I would love to hear about it.
Grab a single or Hybrid style cammed bow and draw it upside down once.
02-19-2005, 07:10 PM
#4
Thread Starter
Join Date: Apr 2003
Posts: 25
RE: Bowtech Limb Twist
I actually built a machine years ago similar to the Apple ultimate tune machine. I can draw the bow and check draw force curves, measure static nock travel, etc...
One thing that it allows me to do is look at the cams at different points in the draw cycle. My Bowtech Defender is not twisting because of the draw stop. And, I can assure you that the bottom limb has no twist or lean in it. All bows have some degree of twist or lean. I just have never owned one with as much as I am seeing on my Defender.
At the bowshop, we did just eyeball the other bows at full draw, so other factors could be coming into play.
One thing that it allows me to do is look at the cams at different points in the draw cycle. My Bowtech Defender is not twisting because of the draw stop. And, I can assure you that the bottom limb has no twist or lean in it. All bows have some degree of twist or lean. I just have never owned one with as much as I am seeing on my Defender.
At the bowshop, we did just eyeball the other bows at full draw, so other factors could be coming into play.
02-19-2005, 08:30 PM
#5
Join Date: Feb 2003
Location: Baltimore Maryland USA
Posts: 1,385
RE: Bowtech Limb Twist
I can't believe that archers buy short ATA bows and believe that there will be no geometric difference to a longer ATA bow. With the position and angle of the cable guard being somewhat fixed, and the angle of the cables being changed negatively, what do you expect?
This holds true for ANY short ATA bow; and, the longer the draw length, the worse it will get with any cable guard system. Again, this holds true with all designs using standard cable guards, flexible cable guards, or roller guards.[&o]
I guess a study will have to be made to determine how much things change considering DL at a given ATA and then varying the ATA from longest to shortest. It would take a lot of time, effort and tools. The manufacturers won't do it for you and I certainly wouldn't expect them to do it. It might show you too much and start more discussions like this. Don't look for me to do it. I've got a family to feed.
This holds true for ANY short ATA bow; and, the longer the draw length, the worse it will get with any cable guard system. Again, this holds true with all designs using standard cable guards, flexible cable guards, or roller guards.[&o]
I guess a study will have to be made to determine how much things change considering DL at a given ATA and then varying the ATA from longest to shortest. It would take a lot of time, effort and tools. The manufacturers won't do it for you and I certainly wouldn't expect them to do it. It might show you too much and start more discussions like this.
Don't look for me to do it. I've got a family to feed.
02-19-2005, 09:02 PM
#6
Thread Starter
Join Date: Apr 2003
Posts: 25
RE: Bowtech Limb Twist
Len,
Thanks for your reply. I lurk more than post and do appreciate your input.
I am sure that the short A-A would tend to augment limb twist. However, I did notice a similar degree of lean today in the shop with the 2 Old Glorys we looked at.
I have another brand bow that is only 33" A-A. It exhibits very minimal limb twist / cam lean. I would accept a little more twist dropping down to 31.5" A-A. But as I said in my first post, this is a very visible offset that does not require a laser or fancy tools to see.
I am not giving up on this bow because the other features are so good. While I do not put a lot of faith in paper tuning, I was able to tune this bow very easily (lots of recent storms here in CO, so it is easier to shoot in my basement).
The initial purpose of the post was to really find out if most of the binary cam Bowtechs are like this, or would it be worth while to send it back to Bowtech for new limbs.
Thanks for your reply. I lurk more than post and do appreciate your input.
I am sure that the short A-A would tend to augment limb twist. However, I did notice a similar degree of lean today in the shop with the 2 Old Glorys we looked at.
I have another brand bow that is only 33" A-A. It exhibits very minimal limb twist / cam lean. I would accept a little more twist dropping down to 31.5" A-A. But as I said in my first post, this is a very visible offset that does not require a laser or fancy tools to see.
I am not giving up on this bow because the other features are so good. While I do not put a lot of faith in paper tuning, I was able to tune this bow very easily (lots of recent storms here in CO, so it is easier to shoot in my basement).
The initial purpose of the post was to really find out if most of the binary cam Bowtechs are like this, or would it be worth while to send it back to Bowtech for new limbs.
02-19-2005, 09:11 PM
#7
Join Date: Feb 2003
Location: Howard PA USA
Posts: 2,221
RE: Bowtech Limb Twist
I personally think you answered your own question. You said the bow tuned very easily. Then what is the problem??? I say if the bow tunes with broadheads then it is good to go. I personally think Bowtech is fully aware of this in their bow design and has accounted for it. I own an Old Glory and I have been getting some of the best groups of my life with this bow. And I too was able to paper tune it very quickly. Just 2 minor adjustments and I had bullet holes. So what i'm saying is, if your getting good groups, it tunes right. and your broadheads and field points fly true, why raise a fuss?
02-19-2005, 09:41 PM
#8
Thread Starter
Join Date: Apr 2003
Posts: 25
RE: Bowtech Limb Twist
PA,
I apologize if this comes across as a fuss, that is not what I intended. You are probably right and I will know shortly after I put a few broadheads through her. I probably spend way to much time tinkering, tuning, and shooting my bows and I probably get more caught up in theory than reality.
I would rather there be no to minimal twist. But if this is how they are all designed, I will tune her the way she is and go from there.
I apologize if this comes across as a fuss, that is not what I intended. You are probably right and I will know shortly after I put a few broadheads through her. I probably spend way to much time tinkering, tuning, and shooting my bows and I probably get more caught up in theory than reality.
I would rather there be no to minimal twist. But if this is how they are all designed, I will tune her the way she is and go from there.
02-20-2005, 05:22 AM
#10
Join Date: Feb 2003
Location: Howard PA USA
Posts: 2,221
RE: Bowtech Limb Twist
No offense taken Radman. I can understand your thinking. In fact most of the regulars who come to the technical board can. We all love to tinker and want everything to be perfect and by the book, I'm even like that most times. But basically what i'm saying is sometimes there is something that just breaks all the rules and you have to throw out the book. And I for one think you have to throw out the book when it comes to these 05 Bowtech's and limb twist