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TS370 string, twist or no twist?

4488 Views 40 Replies 7 Participants Last post by  Farm Deer, 
Farm Deer
Received my 60X replacement string and cable set. My questions are:
  • Twist on the cables set the cam timing. How many twists do you use to start per inch of cable length?
  • Twist on the string affects total length. How many twists are standard per inch of string length?
I can call 60X but hoped to hear from someone on the forum.
Thanks!
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B
Here is what I would do:
Before swapping out the string and cables, record everything in case you wish to switch back or undo something:
1)check to see that the cams are in time and correct if necessary.
2)shoot the crossbow through a chronograph and record the arrow speed.
3)in the uncocked position, measure the axle to axle.
4)mark the cams where the cables cross when the crossbow is in the uncocked position.

a)Swap out the bow string and add 1/2 or full twists as required to match your original axle to axle measurement.
b)Swap out one cable and add 1/2 or full twists to bring the cam to the mark you made on it.
c)Swap out the other cable and add 1/2 or full twists to bring the cam to the mark you made on it.

With the crossbow in the uncocked position, block it level.
Put a level on the rail-stock and 90 degrees to the rail-stock.
Put a level on each cam, 90 degrees to the rail-stock.
If a cam tilts upward, add 1/2 or full twists to the upper "Y" section.
If the cam tilts downward, add 1/2 or full twists to the lower "Y" section.
At any time when either adding 1/2 or full twists to the single loop end of the cable and the "Y" section starts to wrap up, just remove a "Y" section and with out adding twists, bring it back around its partner to take out the wrap up.
Recheck your cam timing.

All these adjustments and close checking can be done while the riser is in the press. Just back the press off enough but still enough pressure so the bow does not fall out. Depending what bow press is being used the riser may not have to come off. The bow press I have, I am able to stand my bow vertical with the stock end up.

Once completed, then re shoot the same arrow-point combination through the chronograph to see if there were any speed changes.

Advancing cams to either match the advertised speed taking into consideration if an over weight arrow was used, adjust by adding equal 1/2 or full twists to the single loop end of the cable.
Advancing the cams to increase speed will lessen the axle to axle measurement.
Removing twists from the bowstring will gain axle to axle measurement but will back the cams off reducing speed.

Personally, I do not maintain the axle to axle measurement as that is just a guide line in the manual. My crossbows are upgraded and modified to shoot well over the manufactures advertised speed taking into consideration if an over weight arrow-point combination is used.

With the crossbow in the uncocked position, look from one cam to the other along the bow string. One is checking to see if the bow string humps up as it crosses the rail-stock. If it does this is where the shims are placed in the upper area where the riser meets the rail-stock. This illiminates the hump caused by extreme downward bow string pressure and greatly reduces serving wear in the arrow-latch area.

Wishing you all the best.
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Huntersthompson
bunnyrabbit said:
Here is what I would do:
Before swapping out the string and cables, record everything in case you wish to switch back or undo something:
1)check to see that the cams are in time and correct if necessary.
2)shoot the crossbow through a chronograph and record the arrow speed.
3)in the uncocked position, measure the axle to axle.
4)mark the cams where the cables cross when the crossbow is in the uncocked position.

a)Swap out the bow string and add 1/2 or full twists as required to match your original axle to axle measurement.
b)Swap out one cable and add 1/2 or full twists to bring the cam to the mark you made on it.
c)Swap out the other cable and add 1/2 or full twists to bring the cam to the mark you made on it.

With the crossbow in the uncocked position, block it level.
Put a level on the rail-stock and 90 degrees to the rail-stock.
Put a level on each cam, 90 degrees to the rail-stock.
If a cam tilts upward, add 1/2 or full twists to the upper "Y" section.
If the cam tilts downward, add 1/2 or full twists to the lower "Y" section.
At any time when either adding 1/2 or full twists to the single loop end of the cable and the "Y" section starts to wrap up, just remove a "Y" section and with out adding twists, bring it back around its partner to take out the wrap up.
Recheck your cam timing.

All these adjustments and close checking can be done while the riser is in the press. Just back the press off enough but still enough pressure so the bow does not fall out. Depending what bow press is being used the riser may not have to come off. The bow press I have, I am able to stand my bow vertical with the stock end up.

Once completed, then re shoot the same arrow-point combination through the chronograph to see if there were any speed changes.

Advancing cams to either match the advertised speed taking into consideration if an over weight arrow was used, adjust by adding equal 1/2 or full twists to the single loop end of the cable.
Advancing the cams to increase speed will lessen the axle to axle measurement.
Removing twists from the bowstring will gain axle to axle measurement but will back the cams off reducing speed.

Personally, I do not maintain the axle to axle measurement as that is just a guide line in the manual. My crossbows are upgraded and modified to shoot well over the manufactures advertised speed taking into consideration if an over weight arrow-point combination is used.

With the crossbow in the uncocked position, look from one cam to the other along the bow string. One is checking to see if the bow string humps up as it crosses the rail-stock. If it does this is where the shims are placed in the upper area where the riser meets the rail-stock. This illiminates the hump caused by extreme downward bow string pressure and greatly reduces serving wear in the arrow-latch area.

Wishing you all the best.
Click to expand...
Would it be safe to start with three twists on everything and work from there?
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Huntersthompson said:
Would it be safe to start with three twists on everything and work from there?
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I would just follow the procedure I wrote up. The reason I mention this is some companies that build bowstrings do not build them the proper length.
Another thing I will mention: add a drop of Gorilla Glue to each end of the center serving and to the cam serving of the bow string but at the end that faces the center serving as an added insurance to prevent serving separation.

Lube the cables well where they go through the "J" section as the only way lubrication can be brought in is when cocking or shooting the crossbow.

All the best.
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Farm Deer
Thanks BR. I have a friend with a CMM. I can record A to A and cam angles to center line of the rail and riser.
I don't have a chrono to check fps. My attempt to calibrate fps is to shoot at 20 then 60. If I'm low at 60 with the new string then I'll add a twist to reduce A to A. (I was dead on with prior string at 60).

I designed a slick portable bow press that fits a TS370 perfect. I can do it on the bow completely assembled under very controlled compression and release.

Wasn't sure all the specifics to measure but with your help, I do now!
Thanks
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tpcollins
Farm Deer said:
Received my 60X replacement string and cable set. My questions are:
  • Twist on the cables set the cam timing. How many twists do you use to start per inch of cable length?
  • Twist on the string affects total length. How many twists are standard per inch of string length?
I can call 60X but hoped to hear from someone on the forum.
Thanks!
Click to expand...
If you have new string and cables, they should have been “paper clipped” or the loops tied with a short tag holding them together at their specified length. If they didn’t do that I would find another string maker for the future.

However, since one cable usually has a longer route than the other one, twisting one or untwisting the other may be required to get the cams in sync.

I’ve seen vertical bow string making formulas that twist the string 75% of it’s length - but your string and cables should come already twisted. I don’t believe there’s a guide for twisting them after they’ve been built. Good luck.
.
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Huntersthompson
Farm Deer said:
Thanks BR. I have a friend with a CMM. I can record A to A and cam angles to center line of the rail and riser.
I don't have a chrono to check fps. My attempt to calibrate fps is to shoot at 20 then 60. If I'm low at 60 with the new string then I'll add a twist to reduce A to A. (I was dead on with prior string at 60).

I designed a slick portable bow press that fits a TS370 perfect. I can do it on the bow completely assembled under very controlled compression and release.

Wasn't sure all the specifics to measure but with your help, I do now!
Thanks
Click to expand...
Interested in picts of your press.
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TomOnTheRun
Yea, love to see BunnyRabbit's setup.
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TomOnTheRun
Bow press is my next investment into this sport.
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Fletcher
That's a good investment to make Tom. That way you can keep everything exactly the way it's supposed to be.
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samt
tpcollins said:
...I’ve seen vertical bow string making formulas that twist the string 75% of it’s length - but your string and cables should come already twisted. I don’t believe there’s a guide for twisting them after they’ve been built. Good luck.
.
Click to expand...
Actually the 0.75 number in the formula is used to determine the number of twists rate you plan to put in the string. Because every time you put a twist in the string it shortens it, the number of twists is then multiplied by a variable to find out how much longer to set the posts for layout.

I've read on different websites to use anywhere from 1 twist per half-inch to 1 twist per inch, both are extremes IMO but both would work. Most string builders I know of use either 2 twists per every 3 inches (0.67 twist rate) or 3 twists per every 4 inches (0.75 twist rate). The important thing is to have *some* twists in the string to help make the string stronger like a rope as opposed to a bunch of untwisted individual strands.

Here's an example: Suppose you were going to build a 46" string (cough, cough, Scorpyd). You'd multiply 46" times the twist rate you were going to use, ie 0.75 and get about 35 twists, rounded up. Those 35 twists would obviously shorten the 46" string, so to compensate for that you'd multiply 35 times a variable, such as 0.012 in this example, and it would give you to amount you'd need to add to the 46", 0.42" in this example. So now to begin your layout, you'd set the posts 46.42" apart. The variable number can be a little different for each builder based on their proceed and technique, so usually something like the 0.012 number would be a starting point until you figured yours out.

***
All this being said, TP is absolutely right about saying that your string should have come from the maker already twisted the right amount to achieve the specified length needed. The ends should have been connected together with something like a bread-twist, paper clip, bobby-pin, small ty-wrap, etc. When installing, care should have been taken to keep them from untwisting. If by some chance they became untwisted, they can be twisted back to spec using two 1/4" posts and a 100 lb scale in order to measure at the right tension.

Good Luck.
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tpcollins
samt said:
Actually the 0.75 number in the formula is used to determine the number of twists rate you plan to put in the string.



All this being said, TP is absolutely right about saying that your string should have come from the maker already twisted the right amount to achieve the specified length needed. The ends should have been connected together with something like a bread-twist, paper clip, bobby-pin, small ty-wrap, etc. When installing, care should have been taken to keep them from untwisting. If by some chance they became untwisted, they can be twisted back to spec using two 1/4" posts and a 100 lb scale in order to measure at the right tension.
Click to expand...
I thought the OP was initially asking how many twists are put in when building a string - my bad.

In a perfect world, I would think a new set of string and cables built to the crossbow manufactures specs should put the cams both close to being in time and in sync - albeit one cable probably has to be adjusted since they don’t travel the same distance from their anchor point to the cam peg.
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8
TomOnTheRun said:
Yea, love to see BunnyRabbit's setup.
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Here are some pictures of the Snyper Pro 5.1 bow press. The picture with the vertical bow in the shooting position, mine sets up at the opposite end of the crank wheel and does not require the hand winch. I use the wheel to draw the bow and with the remote trigger, the vertical bow can be shot with out me torquing or canting the bow. The frame can be rotated and also set vertical up.

The picture of the wood box shows some of what I received plus I enclosed a picture of all the accessories I did receive. Four pins can be installed for building a new bow string. These fit into the black flat plates. I have mine set up for doing reserving of the bow string as shown in the picture.

I can set my crossbow up vertical as shown and tune or swap out the bow string and or bowstring and cables without removing the riser. The bow press can close to 6 1/2" where with an adapter modification, the narrow axle to axle crossbows can be worked on. There are lots of tapped and threaded areas to reposition the accessories.

As seen, I have my press clamped to the saw table where I can roll the saw table to a different area or unclamp and remove the press.
Tool Playset Tool accessory
Bow and arrow Bow Vehicle Line Archery
Table saws Wood Table Machine Tool
Auto part Machine Tire Automotive wheel system Automotive tire
Vehicle Machine Trailer
Floor Flooring Wood Tool
Vehicle Machine Tool Tire Automotive wheel system
Floor Room Flooring Table Countertop

All the best.
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B
Referring to the 100 pound scale may be suitable for vertical bows but not crossbows. Crossbows as they increase in draw weight require a minimum of 300 pound tension when building the bowstring: 1)to prevent stretch which string builders that built for the vertical bows have to catch up on, 2)for safety factors.

Some of the newer, higher draw weight crossbows have up to 225 pound draw weight. Advance the cams for more speed or when the crossbow is shot, there is a lot of stress until the crossbow string etc. comes to rest.

Whether the bow string comes with clips or ties, this all changes when properly tuning a crossbow, whether to match the manufactures speed in feet per second or to increase speed, cam timing, cam leveling etc. Most of the crossbows, when first received whether from the manufacture or dealer are not properly tuned.

All the best.
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samt
bunnyrabbit said:
Referring to the 100 pound scale may be suitable for vertical bows but not crossbows. Crossbows as they increase in draw weight require a minimum of 300 pound tension when building the bowstring: 1)to prevent stretch which string builders that built for the vertical bows have to catch up on, 2)for safety factors.

Some of the newer, higher draw weight crossbows have up to 225 pound draw weight. Advance the cams for more speed or when the crossbow is shot, there is a lot of stress until the crossbow string etc. comes to rest.

Whether the bow string comes with clips or ties, this all changes when properly tuning a crossbow, whether to match the manufactures speed in feet per second or to increase speed, cam timing, cam leveling etc. Most of the crossbows, when first received whether from the manufacture or dealer are not properly tuned.

All the best.
Click to expand...
The 100 lbs is just for measuring per AMO Standard.

When serving strings, either vbow or xbow strings, higher tension is needed during the serving process. A lot of string makers use somewhere in the 300-350 lb range.

Sent from my SM-G975U using Tapatalk
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tpcollins
bunnyrabbit said:
Referring to the 100 pound scale may be suitable for vertical bows but not crossbows. Crossbows as they increase in draw weight require a minimum of 300 pound tension when building the bowstring: 1)to prevent stretch which string builders that built for the vertical bows have to catch up on, 2)for safety factors.
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Bunny you’re still confusing building a string versus checking the spec lenght.
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tpcollins said:
Bunny you’re still confusing building a string versus checking the spec lenght.
.
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Sorry, you are the one that is confused because you do not take time to properly read the posts I have submitted. I explained what tension the string has to be built under and why it does not require clips or ties as when properly tuning the bow 1/2 or full twists have to be added or removed.

Selecting different string builders, some may use a different bowstring strand, size, material, number of strands or tensile strength. Normally the string is put on a 1/4" peg and measured to the outside of the peg. I have strings come in where the builder measured out side of the loop which would make the string too short. I have bought string and cables off Ebay listed for whatever crossbow and they were too long. Adding twists to shorten them they would twist right up, making them useless. This is where in some of my posts, I mention buying directly from the manufacture and also by doing this, one gets the newest version, whether bow string and cables, targets etc.

The strings I have purchased for vertical bows came with clips as I have received them that way, but the vertical bow still has to be properly tuned, so 1/2 or full twists have to be added or removed. Try matching a new bowstring up with cables that have had a lot of use and some have stretched due to not enough tension when they were built.

As for crossbows, a manufacture does not build everything due to the high cost of equipment which may only be good for "X" number of years for a specific model due to new bows coming out. Many parts regardless whether for bows, vehicles etc are subcontracted out and this is where problems arise for the person doing the assembly. Add into the equation, imported products where there are different metric conversions, some which are close while others are not.
An example is where Barnett's cam bearings in the Ghost 410 were a failure due to over size axle holes. The assembly person was not paying attention and installed them any way. Ordering replacements, I received the same faulty style so I would not use them and went to one piece bushings which also re enforced the axle which is mild steel. Thousands of shots later and no problems.

All the best.
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tpcollins
bunnyrabbit said:
Sorry, you are the one that is confused because you do not take time to properly read the posts I have submitted. I explained what tension the string has to be built under
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And there it is again - confusing what tension the string is built under versus what tension is used to measure the string’s spec length. So all the string builders like ABB and Rogue an such are doing it wrong?
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tpcollins said:
And there it is again - confusing what tension the string is built under versus what tension is used to measure the string’s spec length. So all the string builders like ABB and Rogue an such are doing it wrong?
.
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I am not talking about tension used to measure specific length. I am talking about tension to properly build a crossbow string. If you spent a bit of time working on crossbows, you would learn something instead of trying to down one when obviously from your remarks you are not paying attention to what you are reading or have no experience when tuning crossbows.

All the best.
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tpcollins said:
And there it is again - confusing what tension the string is built under versus what tension is used to measure the string’s spec length. So all the string builders like ABB and Rogue an such are doing it wrong?
.
Click to expand...
In Post #15 "samt" explained that 100 pound is for for measuring AMO Standard (Archery Manufactures Organization).
This is for vertical bows and not crossbows.

As for ABB and Rogue, I have never had anything to do with them and if they are using the AMO, that is for vertical bows and not crossbows.

If you were to stop and think, vertical bows on the average might run 70 to 80 pounds and I had one that ran 91 pound from the 1970-1980 era where I picked it up at a garage sale. For these the 100 pound test would work. Why would you test a crossbow string at 100 pound when you are installing them on anywhere from 150 to 225 pound draw weight.

All the best.
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