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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here! |
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09-18-2019, 07:58 AM | #16 |
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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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09-18-2019, 08:06 AM | #17 |
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Re: My Invert Roller
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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09-18-2019, 08:27 AM | #18 | |
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My Invert Roller
Quote:
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: Sent from my iPhone using Tapatalk Last edited by Diving Gecko; 09-18-2019 at 02:27 PM. |
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09-18-2019, 08:32 AM | #19 | |
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My Invert Roller
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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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09-18-2019, 01:29 PM | #20 | |
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Re: My Invert Roller
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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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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. Sent from my iPhone using Tapatalk |
09-18-2019, 02:27 PM | #22 | |
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Re: My Invert Roller
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09-19-2019, 10:51 AM | #23 |
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My Invert Roller
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. |
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. |
09-19-2019, 04:38 PM | #25 | |
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Re: My Invert Roller
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Last edited by popgun pete; 09-19-2019 at 07:32 PM. Reason: extra comment |
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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). Sent from my iPhone using Tapatalk |
09-20-2019, 12:01 AM | #27 | |
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Re: My Invert Roller
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09-20-2019, 01:46 AM | #28 | |
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Re: My Invert Roller
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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. Sent from my iPhone using Tapatalk |
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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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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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