Roskoe

I got my new Gibblet string installed yesterday and, after some tuning and adjusting, got the broadheads and field points hitting the same spot and generally grouping great. I did, however, notice that the draw weight seemed a little easier than before - with the limb bolts at the same setting. Today, one of my buddies came over and wanted to chronograph his Switchback. I also tried the Protec with the new strings, and expected a small increase in speed since I'm no longer running string leeches or a kisser button. To my surprise, same arrows were going 10 fps slower than before. I twisted the new string a little to get the ATA and brace height where it was before. Should I twist the cables as well?

badger109

The string must be a different length. Maybe there were speed nocks on the old string. I take it you didn't get new cables.

Have you ever timed the cams? There's a nice FAQ on AT. It should answer your cable twisting question.

http://www.archerytalk.com/vb/showthread.php?t=207391

nodog

Here's a guide I use. It used to come with pictures, don't know where they went.



>>posting the other information in the thread as well... Hope this helps...

[align=center]Hybrid Cam Sync & Timing
By Mike Javi.... Cooper[/align]


The timing system on the hybrid cams is somewhat different from other systems.

The cams need to be in synchronization and in draw stop timing; these are two entirely different issues but interconnected. It is possible to have the cams in sync, but not in time and visa versa.

The string is for all practical purposes, just along for the ride, the buss cable (yoke) controls the bow, and it is used to set the axle to axle (limb) preload and takes most of the weight of the limb deflection at full draw. The control cable (slave) ties the two cams together so that they rotate at the required speeds.

The reference marks or holes (depending on the cam) are there to provide a visual reference to cam synchronization not draw stop timing. I find that tiller is a more precise indicator of cam sync; if the limbs are bottomed out the tiller will reflect the position of the cams better than the reference holes (marks).

To adjust the cams, I back the string off until I’m sure it isn’t affecting the axle to axle (usually ten twists will do) then adjust the buss cable to bring the axle to axle measurement to a ¼” longer than the specifications for that particular cam/limb combination (see Hoyt tune charts). The control cable should be used to sync the rotation of the cams while doing this. If the cams are in sync at this point the reference holes will be equidistance from their respective cables and the tiller will be even (limbs bottomed out).

Now is the time to adjust the draw stop timing, using a draw board or similar device (you can draw the bow and have someone else look at the cams) when the bottom cam’s draw stop is just touching the buss cable, the control cable should lay flat in the groove of the top cam. If the cam is under rotated you can put a twist in the buss or untwist the control, I determine which I do by the draw weight and draw length of the bow. Shortening the buss cable will lengthen the draw and increase the draw weight. Shortening the control cable will decrease the draw length and decrease the draw weight.

At this point, I measure the draw length (using AMO standards); it should be long and the draw weight should be higher than spec for the bow. I will then twist the string to bring the draw length to spec; this should also bring the draw weight and axle to axle into spec.

I double check everything and tweak a half twist here or there to fine tune it.

Finally I use the hybrid cam creep tuning method to set the bow to my shooting style.

If you follow this method you will have a very solid wall and the bow will be practically vibration free.

A note: the regular cam & ½ should be tuned in the “D” draw length slot for best performance. You can then set the module to your required DL and tweak the DL using the string.<<[/align]

nodog

If your still slow, it's contact. Been there.

badger109

Here's the pic. Sorry, somehow some quality was lost. I had the picture saved in a word document.

Roskoe

Badger - I did get the whole setup - cables and a new string. That is a very interesting thread over on AT. My cams are obviously under-rotated. Fairly equal. I'm also pretty sure my DL got a little shorter -which I'm not sure is a bad thing at this point. Sounds like I could fix this by twisting the buss cable. But the bow is a quiet as a mouse and is shooting great groups. I might leave it alone for awhile. It shoots so good right now I'm not sure the 10 fps is worth it. Any issues with shooting a bow with under-rotated cams?

badger109

If/when you do tune, forget the timing marks. Use them as a reference, (get them close) but the tiller is what you need to get dead even (with limbs bottomed out) to get it synched. Get the cams synchronized and draw stop timed and perfect with correct draw length, axle to axle, and draw weight.

Edit: Didn't see the post.

If the cam is under/over rotated, the wall will be terrible. You should be able to get a solid wall.

Edit 2: My bow shoots great too. I actually just tuned it up now, and haven't shot it yet. Last year I just shot it how the shop set it up with new strings and cables; I didn't bother tuning.

Roskoe

OK - thanks. I currently have the tiller "tuned" to where the top limb is backed out about 5/8 of a turn and the bottom is maxed out. I'll crank the top one all the way in and see what the tiller looks like. With the previous string/cables, backing out the top limb gave me a real good nock travel. And that seems to have carried over into the new string/cables. But for the sake of setup, I'll put it back to even and see what we have. Advice and experience much appreciated.

badger109

you can pull on the cables and see what effect they have on the tiller, then adjust it while trying to get the timing right.

BTW control cable is the one that ties the cams togather, and buss cable is the yolk cable if you didn't know.


As far as I'm concerned, it doesn't have to be perfect. I got the tiller and timing set, and the a2a, DL, and DW were pretty close, which is good for me.

Roskoe

I kinda figured that out on my own, but thanks. This is likely going to be a good learning experience. When I got the new string/cables in, I thought that, since I already have a bow press, I would take a shot at installing them myself. Took some very careful measurements off the old string. But, apparently, I should have been paying more attention to the cables. Old setup was perfectly tuned. I was a little taken aback when the bow, after changing out the string/cables, shot about 8" higher than before. Broadheads shot low and left. But after spending most of the day yesterday tuning, I got them shooting the same. I think you are right about the back wall. I'm getting some interesting vertical dispersion - not bad - an inch or so. Thought it was just me. But with the shorter DL, probably getting into the back wall a little more than before. I'm heading out to the shop right now to do a little cable adjustment . . .