? number of spider legs = more stable.
- Thread starter theXman
- Start date
allmark
Participating member
Re: It\'s a mathematical point
Not necessarily. It all depends on the center of gravity and sling angle.
Not necessarily. It all depends on the center of gravity and sling angle.
now, while drawing this last one, i see where for a while, two legs could at some point, be holding all the weight.
Here, two legs on opposite sides of each other are longer:
Now, on a slow pick, it should sag to one side until one long leg got tight.
But even while in mid air, an operator's fast movement, wind, liquid shifting, etc. and the load could rock from one long leg to the other and while it did that, the weight is only on two legs.
Here, two legs on opposite sides of each other are longer:
Now, on a slow pick, it should sag to one side until one long leg got tight.
But even while in mid air, an operator's fast movement, wind, liquid shifting, etc. and the load could rock from one long leg to the other and while it did that, the weight is only on two legs.
Attachments
- Location
- NJ
Re: It\'s a mathematical point
[ QUOTE ]
I used only two straps for years, didn't know any better
[/ QUOTE ]
UUmmm what you tring to say! I'll put a 2 strap style vers fancy rigging anyday. KISS is the best way. (Keep it simple stupid)
[ QUOTE ]
I used only two straps for years, didn't know any better
[/ QUOTE ]
UUmmm what you tring to say! I'll put a 2 strap style vers fancy rigging anyday. KISS is the best way. (Keep it simple stupid)
Lumberjack
Branched out member
Re: It\'s a mathematical point
Regarding the rotation of the piece between the 2 looser legs: Assuming the taunt line isn't holding enough weight to keep the piece from flopping to the other sling, then it would teeter between the two.
If the loose sling wasn't there, and the piece rotated, it'd rotate until the formerly tight leg was tight on the other side of the 2 main legs. Much more rotation and shock loading.
In a 3 leg set up, all holding some amount of weight, lengthen a sling and you change the weight on all 3. This is because changing any 3 changes the COG, which thus effects loading. Sling angle matters, but the angles are still formed by the anchors position.
It's also rare for me to use more than 1 sling. Normally we have enough room under the head and in the environment that we can tip tie and lift. However there's times, especially at low boom angles, where we have to balance pieces (not enough head height), or the wood isn't strong enough for a single anchor. Other times we use 2 slings to share the load.
Don't see a 4 anchor pick offhand. But here's 1, 2, and 3 anchor picks.
1 anchor, choker set on the backside to tip the log towards the crane. 10klbs:
1 anchor set up to rotate the piece horizontal for loading on trailer. 4-500lbs.
2 anchors, each sling rated to 17.5klbs in a choker, 35klbs combined due to a small sling angle. The pick was 22klbs+ rigging. Can't see the top anchor, hey, it was 9:30 when the picture was taken.
2 anchors, tree fell into the building, set up to equalize so as the piece rotated upward, the slings could adjust.
3 anchors, 2 main and 1 to control rotation. You can see the 3rd anchor has slack. If you look closely you can see the 2 main anchor's chokers are opposing to help control the rotation. Want to say it was 4-5klbs, sitting atop a trailer still attached to the tree.
Regarding the rotation of the piece between the 2 looser legs: Assuming the taunt line isn't holding enough weight to keep the piece from flopping to the other sling, then it would teeter between the two.
If the loose sling wasn't there, and the piece rotated, it'd rotate until the formerly tight leg was tight on the other side of the 2 main legs. Much more rotation and shock loading.
In a 3 leg set up, all holding some amount of weight, lengthen a sling and you change the weight on all 3. This is because changing any 3 changes the COG, which thus effects loading. Sling angle matters, but the angles are still formed by the anchors position.
It's also rare for me to use more than 1 sling. Normally we have enough room under the head and in the environment that we can tip tie and lift. However there's times, especially at low boom angles, where we have to balance pieces (not enough head height), or the wood isn't strong enough for a single anchor. Other times we use 2 slings to share the load.
Don't see a 4 anchor pick offhand. But here's 1, 2, and 3 anchor picks.
1 anchor, choker set on the backside to tip the log towards the crane. 10klbs:
1 anchor set up to rotate the piece horizontal for loading on trailer. 4-500lbs.
2 anchors, each sling rated to 17.5klbs in a choker, 35klbs combined due to a small sling angle. The pick was 22klbs+ rigging. Can't see the top anchor, hey, it was 9:30 when the picture was taken.
2 anchors, tree fell into the building, set up to equalize so as the piece rotated upward, the slings could adjust.
3 anchors, 2 main and 1 to control rotation. You can see the 3rd anchor has slack. If you look closely you can see the 2 main anchor's chokers are opposing to help control the rotation. Want to say it was 4-5klbs, sitting atop a trailer still attached to the tree.
Re: It\'s a mathematical point
take a shoe box flip in over punch four holes in the top next to the corners take some throw line yarn attach to the shoe box then attach string to key chain notice that all the slings are a tiny bit different. notice the box deflect in a static level lift this happens every time you use a four leg bridle. in the shoe box example or in any rigging scenario at some point the rigging will take a load on just two of the slings. this as moray named it "the four legged stool problem" . by the way are you reading my post or just being argumentative, because this is a well documented fact. furthermore, i have seen the result of not heeding this fact. it is well documented too. read a rule for rigging, pre cast concrete manual for iron workers manual 11,rigging manual for ironworkers manual 3, the crosby master catalog 2005 states all bridles triple and quad have the same rated capacity. and you ask why its "the four legged stool problem". i have many times over and now with out a doubt proved my point. i have references with much more at stake than i do. so i will quit arguing. you can still take what i said or leave it. i am new to the trees, but ive been making my living as a rigger since i was 16 (i'm thirty one) and i am a journeyman ironworker with a bona-fide apprenticeship. i have traveled extensively doing and applying my trade. ive worked for barnhart crane and rigging as a foreman/rigger, ive worked for shurtleff and andrews as a forman/connector/phoneman/rigger building some of the nations largest coal burning powerhouse's. i've worked in nukes, on high rises, on casinos, on warehouse's, and grocery stores. all the rigging principle's are the same. now i get to climb trees and apply what i know and have a kick in the pants time. i have nothing to prove to you. only trying to drop a little knowledge and pick some up. loving the buzz you guy (and girls) rock. just my $.06
take a shoe box flip in over punch four holes in the top next to the corners take some throw line yarn attach to the shoe box then attach string to key chain notice that all the slings are a tiny bit different. notice the box deflect in a static level lift this happens every time you use a four leg bridle. in the shoe box example or in any rigging scenario at some point the rigging will take a load on just two of the slings. this as moray named it "the four legged stool problem" . by the way are you reading my post or just being argumentative, because this is a well documented fact. furthermore, i have seen the result of not heeding this fact. it is well documented too. read a rule for rigging, pre cast concrete manual for iron workers manual 11,rigging manual for ironworkers manual 3, the crosby master catalog 2005 states all bridles triple and quad have the same rated capacity. and you ask why its "the four legged stool problem". i have many times over and now with out a doubt proved my point. i have references with much more at stake than i do. so i will quit arguing. you can still take what i said or leave it. i am new to the trees, but ive been making my living as a rigger since i was 16 (i'm thirty one) and i am a journeyman ironworker with a bona-fide apprenticeship. i have traveled extensively doing and applying my trade. ive worked for barnhart crane and rigging as a foreman/rigger, ive worked for shurtleff and andrews as a forman/connector/phoneman/rigger building some of the nations largest coal burning powerhouse's. i've worked in nukes, on high rises, on casinos, on warehouse's, and grocery stores. all the rigging principle's are the same. now i get to climb trees and apply what i know and have a kick in the pants time. i have nothing to prove to you. only trying to drop a little knowledge and pick some up. loving the buzz you guy (and girls) rock. just my $.06
- Location
- NJ
Re: It\'s a mathematical point
UUUmmm Jeff not picking a fight just asking, wouldn't you make more money being a rigger than doing trees? I mean even a journeyman ironworker makes more than most climbers.?
UUUmmm Jeff not picking a fight just asking, wouldn't you make more money being a rigger than doing trees? I mean even a journeyman ironworker makes more than most climbers.?
allmark
Participating member
Re: It\'s a mathematical point
This explains cg
http://www.all-lifts.com/riggingconsider.htm
This explains diferent rigging. It mentions the 4 leg rigging as having very good control with majority of weight on 2 legs
http://www.all-lifts.com/hitches.htm
This explains cg
http://www.all-lifts.com/riggingconsider.htm
This explains diferent rigging. It mentions the 4 leg rigging as having very good control with majority of weight on 2 legs
http://www.all-lifts.com/hitches.htm
Re: It\'s a mathematical point
holley, i traveled to much i lost my family because of it. a young mans jaded dreams of glory. and i HATE getting burnt and the saftey has gone insane in the trade no climbing columns some jobs they won't let you walk the iron just coon in like a pumkin. plus climbing tree's is way way more fun. and i like pruning. it just seems artistic to me. it soothes the roaring beast within or something like that hahahahahahahaha.
holley, i traveled to much i lost my family because of it. a young mans jaded dreams of glory. and i HATE getting burnt and the saftey has gone insane in the trade no climbing columns some jobs they won't let you walk the iron just coon in like a pumkin. plus climbing tree's is way way more fun. and i like pruning. it just seems artistic to me. it soothes the roaring beast within or something like that hahahahahahahaha.
allmark
Participating member
- Location
- Gibsons BC
Re: It\'s a mathematical point
The more legs there are on a load, the less likely it is that each leg will bear an equal load.
You can tie 15 spider legs on a piece and there's still a fine possibility that only one leg will take the load if it's done wrong enough.
This is really mostly a moot point though for tree work though, it's not very often that a rig could be improved by a fourth leg.
The more legs there are on a load, the less likely it is that each leg will bear an equal load.
You can tie 15 spider legs on a piece and there's still a fine possibility that only one leg will take the load if it's done wrong enough.
This is really mostly a moot point though for tree work though, it's not very often that a rig could be improved by a fourth leg.
Lumberjack
Branched out member
Re: # of spider legs.
Wow this thread quickly went stupid.
Wow this thread quickly went stupid.
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