Correcting drawlength

[jcason]

Been a rough season including having to change out limbs, cams, string and rest. Now im.trying to fine tune my Firecat TR2 back to factory specs. Here's what I have now. ATA 32 3/8. BH 6 7/8. Gap between cable post and cable is 3/16 on both cams.

My problem is that my drawlength is measuring long. Using an arrow marked in 1/4 inch intervals the dl is measuring 26 1/2 to the most forward point on the backside of the grip. Adding 1.75 according to standard measuring technique makes the actual dl 28.25. This with the modules set on the 3rd hole or 27 inch dl.

Also my draw weight is measuring 65 lbs with limb bolts tightened all the way.

If I twist the string to reduce dl will this also increase ata and unwrap the cables or will it also shorten ata more and increase poundage? Basically how can I decrease the dl and keep the other measurements close or closer to specs and recover the lost poundage?

Naturally I lost speed in the process.

[SonnyThomas]

http://www.martinarchery.com/mtechfo...ead.php?t=8279

[jcason]

Thanks Sonny. Very helpful. A couple of follow ups. First, is true draw length measured as distance to the most forward part of the grip + 1.75 or is is truly measured to the front of the arrow shelf? If I measure to the front of the shelf, it is 27.5, only half inch long. By the first method it is 28.25 or 1.25 inches long.

Second, if I twist the string and untwist the cables, won't this advance the cams and increase the measurement between the cable post and the cable? In reading all the tuning threads, it seems that keeping this gap at a minimum is ideal for the Cat cams.

Thanks again!

[copterdoc]

You measure DL from the throat of the grip, to the bottom of the nock at full draw, and add 1.75" to that.

The throat of the grip, is the part that the web of your hand, between your thumb and forefinger, is pressed against when you grip the bow.

It's the same part of the grip that you measure brace height from.

[copterdoc]

...If I twist the string to reduce dl will this also increase ata and unwrap the cables or will it also shorten ata more and increase poundage? Basically how can I decrease the dl and keep the other measurements close or closer to specs and recover the lost poundage?

Naturally I lost speed in the process.

If you shorten your string and your cables the same amount, your cams will not change their timing. It will only do three things to the bow.

(1.) It will reduce ATA by the exact amount you shortened the string and cables. If you shorten the string 1/2", and each cable 1/2", your ATA will shorten 1/2".

(2.) It will increase your brace height. How much, depends on your bow's limb angle. If it's a parallel limb bow, like your Firecat, it won't increase very much. If it's a C4 Elite, it will increase a whole bunch.

(3.) It will increase your draw weight, but not very much.

It will not change your draw length a bit! It will take away from your power stroke, because your brace height was increased.

If you change the ratio between the string and cables, then you change your cam timing. Shortening the string and/or lengthening the cables, advances the cams.

Advancing the cams does two things.

(1.) It decreases draw length.
(2.) It decreases draw weight.

Doing the opposite, and lengthening the string and/or shortening the cables, has the opposite effect. It increases both DL and DW.

[jcason]

OK, I understand that. My question is specific to the Cat 2 cam. If I twist my string up and untwist my cables to get the drawlength back to spec, the ATA and BH should all stay the same. The cams will also advance. With other tuning posts stating that the Cat 2 cams like to be wrapped as much as possible to get optimum speed, should I expect that the drawlength will be longer than spec, or can I get the drawlength to spec and get the cam wrapped to the point that the gap measurement between cable post and cable is roughly 1/8" at the same time?

In thinking it through, it seems that I may not be able to get both.

[SonnyThomas]

jcason, as copterdoc said draw length is to the deepest part of the grip and add 1 3/4".

The procedure I set forth does not change timing or sync of cams. Done properly you are equalizing them, syncing if you will. I'm going to rattle and stuff will be sort of out of place.

I've read of this space thing that initially came with tuning Firecats. Well I've tried some of these "super tune" tricks for bows and all are not what they seem. I would point out the one for the Pearson Z7 cam system. Here, the procedure was to give more "whip" to the cam and gain a bunch of speed. Yep, sure did, but also increased bow poundage. I hammered this all the way back to the factory. When this procedure was followed and all of the bow's specs checked ata was shortened and brace height increased, but mainly the bow draw weight went up dramatically. The Pearson Speed Procedure has gone away.

When Martin includes the great tuning procedure in their manual I'll believe. Okay, Martin isn't stupid. The Martin crew has been far more innovative than most think. The Onza 3 bridged riser. Some think Martin took this from Hoyt. No they did not. Martin had the bridged riser years before Hoyt. The drop rest of today. Martin had this way back before most in here were born. I can go on and on, but if want to see some real old "new" ideas try the Archery History website. Oh, the roller guide on today's bows, wanna guess how old that idea is? And I believe the TRG is a step in the right direction.

My post reflected of keeping ata the same. This retains brace height and draw weight and only advances the cams to shorten the draw. *Regardless the claims of having two buss cables on the half breed cams you actually have a true buss cable, control cable and bow string. The buss cable always comes off the bottom cam and is the work horse. Why? Because you need to start somewhere and where is the positive stop? On the bottom cam. The control cable comes off the top cam and used to time/sync the cams. Basically, the bow string is just along for the ride. *Exception would possibly come with those bows having two positive stops, like the Pearson R2B2 cam system. The R2B2 first came out with only the bottom positive stop.

If you will go to AT, Bow tuning forum, and read the Hoyt Draw Stop Sticky at the top by javi. Within you will read of adjusting the draw length. This is done before finalizing the bow. Hence, rotating the cams, but also keeping timing/reference points equal. Pull out your Martin manual as you will see basically the same draw stop procedure used all over again. The only difference is Martin has the lower mod and the top mod and the draw stop set after the procedure. Also, nuts&bolts has a tuning manual you can down load. Twisting the string to correct draw length is in there. I questioned nuts&bolts when I first read of twisting the bow string. He had no other option than to agree with me. I believe I still have the PM reply.

The only thing I can add is each person is different. Of recently, two years or so, javi's procedure has been improved with having the top cam hit a tad quicker than the bottom stop. Size of hands and how hard you pull into the wall can effect timing on a Hoyt or a Martin. Why? Because Hoyt does not have positive stops and Martin has only the bottom positive stop and the top is like Hoyt's, the flat groove of the mod. I personally spoke with Javi for perhaps a hour. He was beyond his time and a exceptional archery coach. I'm disheartened that he had a stroke and has not returned.

Though I haven't tried it, advancing the top cam just a tad over the bottom cam and then setting the bottom positive draw stop by normal means could induce even a harder wall. But then Martin's wall is hard enough for me.

My opinion, bow tuning is not rocket science. It's using common sense. And Martin's manual is probably the best I've ever read.

[copterdoc]

The CAT cam is not a hybrid, like the Hoyt Cam & 1/2.

The CAT cam, is a slaved Binary. It is impossible to place more load on one cable than the other, like you can with dual cams.

The reverse cable track in a slaved Binary system, forces the cables to pull each other in opposite directions. They are always under equal load.

If you pull up hard enough, on the loop on a dual, or hybrid cam system, the split yoke cable takes all the load, and the other cable goes slack.

If you do that with the CAT cam, the string above the loop goes slack, but both cables stay tight, and both cams still rotate as normal.

[SonnyThomas]

Lost me copterdoc. The advent of any of the half breed cams was to off set the faults of the true double cam. Thus, virtually all allow the cams to rotate or give good nock travel if set within given parameters. This has been the main sales pitch from the get go.

The upper called cam of a Hoyt Cam & 1/2 is more a oval wheel than cam.
Hoyt's timing marks are not true timing marks and are noted in their manual as reference points.

Improperly adjust cables on any of these newer double cam system and you will get what I call a "double clutch" feel. As such, whatever cam hits it's draw stop first and then feel the other cam hit it's draw stop. Some call this a mushy feeling.

Martin's dual cam positive draw stop system is no different. And then most don't understand about proper letoff procedure of the Martins. Cam and draw stop set as per the manual and in theory or actuality you have 80% letoff. Change the draw length and you have to adjust the draw stop to maintain the 80% letoff.

Now, adjust the draw stop so you have, say 65% letoff. You have effectively stopped the bottom cam before the top cam rotates to it's draw stop. Pull harder and the top cam will rotate to it's draw stop and thus give the "double clutch" feel or mushy feeling.

[copterdoc]

...Pull harder and the top cam will rotate to it's draw stop and thus give the "double clutch" feel or mushy feeling.

Not with a CAT cam!

A hybrid will do that, but a Binary won't.


There is no reverse track on the top cam, of a hybrid system. The split yoke cable that attaches to the top cam's axle, is the one that takes the lions share of the limb load.

If you were to fix the riser to a hard mount draw board, and only pull the bottom cam with the string, this is how each cam system would respond.

(1.) Dual cam. The bottom cam would rotate, reeling in the cable attached to the top axle. This would compress the limbs the full amount. However, the top cam wouldn't rotate at all. It's cable would go completely slack. At that point, you could sever the cable attached to the top cam, and nothing would happen.

(2.) Single cam. The bottom cam would rotate, reeling in the cable attached to the top axle. This would compress the limbs the full amount. The string above the nock point would go slack, and fall off the idler wheel. At this point, you could sever the string, above the nock point, and nothing would happen.

(3.) Hybrid cam. The bottom cam would rotate, reeling in the cable attached to the top axle. This would compress the limbs the full amount. The string above the nock point, and the control cable attaching the top cam, to the bottom cam, would go slack. At this point, you could sever both the string above the nock point, and the control cable, and nothing would happen.

(4.) Slaved Binary cam. The bottom cam would rotate, reeling in cable. However, it's cable isn't attached to an axle, it's attached to a reverse track on the top cam. The reverse track, forces the bottom cam to "wait" for cable to be fed out, before it can rotate. This happens simultaneously, so both cams turn together. At this point, if you were to sever either cable, the bow would blow up.

This drawing illustrates a slaved Binary cam system operating with string tension applied only to the top cam. It works the same way, if it was only applied to the bottom cam.