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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here!

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Old 09-18-2019, 07:58 AM   #16
popgun pete
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Re: My Invert Roller

Well these ones look to be roller bearing shackles because you can see one of the balls in the open side bearing race. You don't want any sand getting in them.
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Old 09-18-2019, 08:06 AM   #17
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Re: My Invert Roller

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Originally Posted by Diving Gecko View Post

No disrespect to Neven at all, as he is one of the most amazing builders, but in case he is dropping by on this thread, I am just wondering how come the pulleys don't go all the way to the front in the loaded position?
Top deck travel is double the shackle travel, so the space required on the gun determines where you put that length. The closer to the butt the lower rear anchor hooks are the better, hence the band battery does not have to travel right to the muzzle.
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Old 09-18-2019, 08:27 AM   #18
Diving Gecko
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My Invert Roller

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Originally Posted by popgun pete View Post
Well these ones look to be roller bearing shackles because you can see one of the balls in the open side bearing race. You don't want any sand getting in them.


They are indeed SS roller bearings. But quite open, so perhaps any sand getting in can get out, too. Even though dinghies are raced on the surface of the ocean and not the bottom it's not unheard of to have conditions where we get some sand on our gear. So, perhaps Harken has tested it.
Either way, a lot of guns have been using the 16mm series for a while now - Roisub alone probably have 100s or maybe even a few 1000s (?) of them out in the wild. But admittedly, they may not do much sandy or surf entrance/exits in the Med where I guess most of these guns are being used.
The Ronstan blocks Musubi are using now have roller bearings, too. Any yachting block pretty much does.

Here's a promo pic with a cut away to show the bearings:



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Last edited by Diving Gecko; 09-18-2019 at 02:27 PM.
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Old 09-18-2019, 08:32 AM   #19
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My Invert Roller

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Originally Posted by popgun pete View Post
Top deck travel is double the shackle travel, so the space required on the gun determines where you put that length. The closer to the butt the lower rear anchor hooks are the better, hence the band battery does not have to travel right to the muzzle.
Still a bit confused. Yes, the travel on the bottom will always be half of the distance from roller to rear shark fin. So, if that top distance is 120cm, the pulley will only ever move 60cm.
So, I guess as long as there is still enough room left to stretch the bands at what ever max ratio you are comfortable with, it’s all fine.
Eg. 60cm of pulley travel with a band stretch ratio of a lowly x3 means the bands are only 20cm long. So, you just need enough space on the bottom for the 60cm travel + 20cm of band length + tackle. Not yet sure how prestretch factors into it.
Higher stretch ratio means less overall space is needed as the bands are shorter?

Last edited by Diving Gecko; 09-18-2019 at 10:31 AM.
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Old 09-18-2019, 01:29 PM   #20
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Re: My Invert Roller

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Hey Musubi,
Sorry, I was mistaken - if you wanna try the Harken option with a pin, you don't want the Micro series, you want the even smaller '16mm' series.
(I used to race sailboats and just looking at Neven's pics I always thought it was a Micro block, but nope).

This is the smallest Harken with a pin:
https://www.harken.com/productdetail...4395&taxid=410
The specs say it weighs in at 11g.
If I am not mistaken, you now have the RF25019 block, which Ronstan says weighs in at 9g, so a 2g difference. Probably nothing to sweat over.

I downloaded tech drawings for both and dropped them into a CAD program to give you a bit of a size comparison. The measurement is in mm:




I hope Neven doesn't mind I share a few of his pic of how sleek it can be done with these blocks (If one was to make his own block you could eek out a few mms more, haha). I think the reason, he and others use a spacer bar is to have no friction between the bands. But for your use, leave out the plate and just imagine your dyneema loops going around the pin:

Thanks Diving Gecko for taking the time to upload the images (pulley's and Neven's guns) and place in CAD. Seems like the pulley with the pin is the smart way to do this, since I know first hand how much of a pain it is to disassemble everything.

I noticed the Harken 16 mm MWL is 250 lbs. What's your thoughts on approaching this rating? Right now, I'm estimating 300lbs going to 2 pulleys, so 150 lbs per pulley. If I sought to shorten things, maximize use of the pulley's movement, and increase band size to 16 mm, I could see possibly coming close or exceeding the MWL. I'm not too familiar with the limitations of pulleys, but it seems like the MWL still rests below the Breaking Load by some factor.

For my current setup, I really like the Harken 16 mm and I do plan to pick them up. I'd like to use them with my current 14 mm, but try and shorten the connections and maximize the pulley's movement along the barrel. I shouldn't exceed the MWL.
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Old 09-18-2019, 02:16 PM   #21
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My Invert Roller

Honestly, I don’t have a roller at all;-). I’ve just been sucking up bits and bobs of info over the years as they are very intriguing to me and I think I’ll build one some day. So, no real world advice from me, just passing on stuff.
But if you look at some of Neven’s guns, they often have five-six bands. I think I’ve even seen seven or eight and his guns have been out in the wild for years by now - so, I’d say the 16mm blocks are likely fine:-)

Also, I think you can probably go over MWL on most well engineered things for a long time before running into issues and Harken is an old, well-renowned brand and if I had to speculate I’d say they’d rather understate these values than the opposite.


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Old 09-18-2019, 02:27 PM   #22
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Re: My Invert Roller

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Originally Posted by Diving Gecko View Post
Still a bit confused. Yes, the travel on the bottom will always be half of the distance from roller to rear shark fin. So, if that top distance is 120cm, the pulley will only ever move 60cm.
So, I guess as long as there is still enough room left to stretch the bands at what ever max ratio you are comfortable with, it’s all fine.
Eg. 60cm of pulley travel with a band stretch ratio of a lowly x3 means the bands are only 20cm long. So, you just need enough space on the bottom for the 60cm travel + 20cm of band length + tackle. Not yet sure how prestretch factors into it.
Higher stretch ratio means less overall space is needed as the bands are shorter?
The inverted cable rollerguns follow this "rule" regardless of stretch. Here the other band set and sub-pulley or shackle pulley are on the other side of the gun. To use every inch of the gun you could go to these lengths, but good luck with loading it unless you cut back on the band stretch.
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Old 09-19-2019, 10:51 AM   #23
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I spent some hours on a flight today to think this over and I think I might have figured it out. To roller guys, this is probably basic stuff. And as always, I could be wrong...
It has to do with prestretch. Of course, Pete is right on the basic premise that the pulleys will only ever move 50% of what the wishbone does. And in most designs if there is little to no prestretch there should be plenty of room for the pulleys, bands and connections and still have space left over. In that scenario, the pulleys probably don't have to go all the way to the front rollers in the loaded position.

But what if the maximum attainable amount of prestretch is a good thing? Perhaps it is, as the power graph should drop less at the end of a shot and hence, the total power should be more, right?

Oh, I just noticed Pete's second diagram now. I guess that one is about prestretch and though I think I have seen one gun where the band went back around the handle, then no, I don't think that makes sense in the whole usability vs. power balance. But I do think it could make sense to eek out as much space as you can from the muzzle to the trigger guard to be able to raise the prestretch as much as possible and still have easy loading. (When I talk about prestretch here, I assume end stretch ratio of the bands should be the same with or without prestretch).

Last edited by Diving Gecko; 09-26-2019 at 12:58 PM.
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Old 09-19-2019, 02:38 PM   #24
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Re: My Invert Roller

I already consider my setup fairly powerful and I know it can be even more so if I prestretched the bands (without going around the handle), or if I went up in band size. I ordered the harken pulleys and that should be a big help in not only disassembling the gun, but fine tuning it. Right now when I prestretch the bands I use locking type pliers (with a barrier wrapped around the pliers teeth) to give me the line slack I need to untie stuff. It kinda sucks doing it this way.

My 110 invert roller is primarily used for reef hunting, but I've always considered it a partial bluewater. I have a couple barrels sitting around and would like to build like an 85 cm invert for holes and general maneuverability. Sometimes its such a pain to swing a 110 down below and then the fish get spooked sometimes.
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Old 09-19-2019, 04:38 PM   #25
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Re: My Invert Roller

Quote:
Originally Posted by Diving Gecko View Post
I spent some hours on a flight today to think this over and I think I might have figured it out. To roller guys, this is probably basic stuff. And as always, I could be wrong...
It has to do with prestretch. Without prestretch, Pete is right. The pulleys will only ever move 50% of what the wishbone does and in most designs if there is little to no prestretch there should be plenty of room to add bands and still have space left over - in that scenario, the pulleys probably don't have to go all the way to the front rollers in the loaded position.

But what if the maximum attainable amount of prestretch is a good thing? Perhaps it is as the power graph should drop less at the end of a shot and hence, the total power should be more, no? In that case, I think you would want as much space as possible for the bands, no?

Oh, I just noticed Pete's second diagram now. I guess that one is about prestretch and though I think I have seen one gun where the band went back around the handle, then no, I don't think that makes sense in the whole usability vs. power balance. But I do think it could make sense to eek out as much space as you can from the muzzle to the trigger guard to be able to raise the prestretch as much as possible and still have easy loading. (When I talk about prestretch here, I assume end stretch ratio of the bands should be the same with or without prestretch).
Blue lines on those diagrams are pre-stretch, the pre-stretch push the bands up the force triangle as the force gets used from the top end first naturally. Leave pre-stretch in your speargun bands with the gun stored and the bands will crack from oxygen attack which preferentially damages stretched rubber. The diagrams are schematics, the guns could be longer or shorter. The wrap around the rear was an idea before Alemanni ran his bands through rear windows in the stock using another roller set. Incidentally the horizontal rear pulley (or pulleys) evens up side to side band pull as the bands are continuous around the gun body.

Last edited by popgun pete; 09-19-2019 at 07:32 PM. Reason: extra comment
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Old 09-19-2019, 11:08 PM   #26
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Re: My Invert Roller

Yeah. I didn’t see the second drawing before but I got it all now and finally started thinking in force graphs, too;-).
So, yes, the more space you can make from the rear of the pulley to the rear anchor point the more prestretch for a given final stretch ratio you can run - giving you a bigger force graph area.

I noticed another thing going over Neven’s pics. It looks like he has gone for shorter kicker bands - in shorter travel - over the years. They used to be starting at the muzzle but not anylonger. Perhaps they don’t move fast enough after the initial kick to even add to the tots force or why else don’t run them full length? Carbonia does (but I speculate Neven must have tested this and have a reason).


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Old 09-20-2019, 12:01 AM   #27
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Re: My Invert Roller

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Originally Posted by Diving Gecko View Post
Yeah. I didn’t see the second drawing before but I got it all now and finally started thinking in force graphs, too;-).
So, yes, the more space you can make from the rear of the pulley to the rear anchor point the more prestretch for a given final stretch ratio you can run - giving you a bigger force graph area.

I noticed another thing going over Neven’s pics. It looks like he has gone for shorter kicker bands - in shorter travel - over the years. They used to be starting at the muzzle but not anylonger. Perhaps they don’t move fast enough after the initial kick to even add to the tots force or why else don’t run them full length? Carbonia does (but I speculate Neven must have tested this and have a reason).


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I think post #4 covers it, the band only has to jerk the system into motion, so no need to pull any futher from up the front of the gun. The Alemanni top band is anchored some distance back from the muzzle (band group 5 on the diagram).
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Old 09-20-2019, 01:46 AM   #28
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Re: My Invert Roller

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I think post #4 covers it, the band only has to jerk the system into motion, so no need to pull any futher from up the front of the gun. The Alemanni top band is anchored some distance back from the muzzle (band group 5 on the diagram).


Yes, I saw that. I get the stiction argument (surprising as it as with dyneema and ball bearings). But since you have the hassle of having to load that band no matter what - why not use it all? Maybe its speed is not fast enough to keep up once the bottom battery gets going. Or maybe it’s short to keep the platform from much recoil even with a classic band.


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Old 09-20-2019, 02:11 AM   #29
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Re: My Invert Roller

In the photo it is pulled onto a mid-tab that seems to have the shooting line attached to it. Just did a quick check on how far it would flop forwards after the shot.
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Old 09-25-2019, 06:11 PM   #30
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Re: My Invert Roller

The pulleys came in last week and managed to grab a couple photos of them today next to the Ronstan pulleys.

Definitely the Harken's are smaller all around.





I've also been researching knots, particularly tying from the band end to the pulley only (Harken pulley with pin). What I've decided to go with is an improved Buntline Hitch called the EStar Hitch. Both knots can be found on this page. https://www.animatedknots.com/buntline-hitch-knot
The EStar modified the Buntline specifically for dyneema, which is what I'll be using.

Otherwise, looks like the Harken will be much more streamlined running through the water.

I'm waiting on my SS line guide for the muzzle end to come in before I start disassembling everything.
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