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All About Pole Spears & Slings What is it about that traditional method of the early hunter/gatherers under the water? These devices are indeed interesting and effective.

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Old 07-15-2016, 04:09 AM   #1
Diving Gecko
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Help Needed, DIY Jap Style Polespear

Hey guys,
I am setting out to build my first polespear.

I live in China, have an affinity for carbon fiber and have a few guys who can help with the steel parts but the first question has to with the dimensions of the CF tubes.

Wall Thickness
I have read most, if not all, polespear posts here and it seems an outer diameter of about 15-16mm (app. 5/8'') is suitable when using carbon fiber. But what about the wall thickness?
I can buy CF tube with 1mm (0.04''), 1.5mm (0.06'') or 2mm (0.08'') wall thicknesses. I am leaning towards 1.5mm (0.06'') or 2mm (0.08''). Any advice here?
I wont hunt huge pelagics but think more of this spear as a fast one with nice range.

Length
I will make this a three-piece spear as I would like it to pack down and not be longer than a set of freedive fins. So, each section will be around 3.5 feet long. So, I will get total of 10.5 feet plus the pointy end which adds another 1-1.5 feet making the spear a total of 11.5-12 feet.
If I take out the middle part and mount shorted bands I will get a spear 3 feet shorter at 8-8.5''. My idea is that it would cover reef and blue water nicely this way?

Connectors
I know I will have to make a fiberglass barrier on the CF tube before bonding the stainless steel parts, but I am cool with that. I have thin glass and loads of epoxy resin.
I am considering bonding the parts on the inside instead of sleeving them over the outside. This is likely less strong in carbon fiber but maybe I will wrap a bit of unidirectional CF over the outside to help with potential splitting.

I know I am asking a lot, but can any of you possibly share a simple and foul-proof design of the connectors? In terms of thread size and such. Totally OK if you don't feel like it:-)
I'll probably have it machined in 316SS, maybe even - depending on whether I can get someone here to digitize my drawings - have it CNC lathed.
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Old 07-15-2016, 10:44 PM   #2
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Re: Help Needed, DIY Jap Style Polespear

A couple questions that I ask myself before I build any spear are "what (species) do I want to hunt?", "what kind of visibility would I be expecting when I hunt these fish?", "Do I want to take large big game fish or small fish?". Asking these kinds of questions will help you decide on materials and the way you'd like to build your spear.

A spear that I recently had the chance to feel was made with "T700 CF" and was very stiff, and was sold in lengths up to 8ft, but was designed to take Hawaiian reef fish, not big Ulua (giant trevally). The spear featured anodized aluminum joints.

That being said there is a japanese blog post by osakanatuki Kansai where he discusses his polespear used for all game in Okinawa. Osakanatuki blog jp
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Old 07-15-2016, 11:55 PM   #3
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Re: Help Needed, DIY Jap Style Polespear

All good questions, Ren.

Not 100% sure what I will be seeing in terms of species but most likely medium sized reef fish and small to medium pelagics.
I know, already there, there might be an issue as a free-swimming jack and a holed-up grouper will treat the spear differently. But I would think I would be shooting more at free-swimming fish.
They will often be a bit skittish in the waters I mostly go to, so that's why I am thinking fast and longer range.

I have CF tube for my pneumatic guns and they are only 1.25mm in wall thickness so I think that 1.5mm - 2mm will be strong enough for most fish.
But I am more worried about the front section. I see the Japanese spearos take both groupers and amberjacks on their long, skinny CF spears and I am beginning to think a lot of it has to do with how flexible the spear actually is. So, making the spear too stiff and not able to flex might actually be a bad thing.

I might have to look into a more flexible front end. We will see. I think I will just go ahead and order some tubes very soon;-)

The T700 spear you are referring to must be the Evolve one. I came across their site the other day. Looks cool. Red and black was always a great color combo seen in many other industries though Gatku may feel it's a bit close for comfort.

Last edited by Diving Gecko; 07-16-2016 at 12:21 AM.
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Old 07-16-2016, 02:41 AM   #4
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Re: Help Needed, DIY Jap Style Polespear

Quote:
Originally Posted by Diving Gecko View Post

I have CF tube for my pneumatic guns and they are only 1.25mm in wall thickness so I think that 1.5mm - 2mm will be strong enough for most fish.
The Outer Diameter of your pneumatic gun's CF is much larger than 5/8" ?

Determining wall thickness on that comparison might lead to bad assumptions.

Figure out what type of force / moment loading you want to be able to handle, and some basic calculations will put you in the right spot.

I had a mechanical engineer buy some tip parts the other day for his DIY build, he did a "gut feel" for what he needed for CF. The vendor sold connector too that were really low in cost.

Anyway, It broke and he's back to drawing board with a sharp pencil and big chief notebook now.

You have graphite rods out there too, some get them mixed up with CF.

Read the specification details, your design will be much better.
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Old 07-16-2016, 03:03 AM   #5
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Re: Help Needed, DIY Jap Style Polespear

Yes, I forgot to say that, of course, the pneumatic tubes are much larger in OD (40mm) so that makes them much stronger already.

On the topic of gut feel, I would think the vast majority, if not all, of polespear designs are based on that plus practical experimentation, no?
I mean, do you, Aaron or the Gatku boys run your designs through computers...?;-). And even if you did, how do you tell the computer where a particular rock will jam your spear and what about the force the grouper in the hole is putting on the spear?;-).
Seems like the only thing wrong with your customer's gut feel was that it was not based on much practical experience with polespears? Neither is mine which is why I tried looking into common dimensions and posted the question here:-)

I am not an engineer (sometimes, I wish I was) but honestly you don't get spec sheets with these Chinese tubes. Even if you did, you wouldn't be able to trust them. The manufacturers say they are the equivalent of T300, though. And they say it is 100% CF, but who knows. Who knows if they post-cured the tubes correctly, who knows if the resin content was correct, etc. Also, as I joked about above, we have little idea of the forces that any spear will encounter so again I wouldn't be able to do much math on it, even if I wanted to.

So, this will be a hands-on, trial and error kind of approach.
I have read about people using 1.15mm wall thickness, so if I go to 1.5mm or even 2mm I would feel OK.

Also, the Japanese spear I borrowed on a trip there used tapered golf club shafts for the front and back section and this is a very common design in Japan for both small and big fish.
I've spent a few hours reading about golf shafts and they are extremely light at about 50-80grams for about 40'', so they must have very thin walls. I suspect their thinking is that it is better to have the front flex than break.

I just tried to run some numbers on the density of a CF laminate and an average diameter of a tapered golf club shaft and according to this rude method, the shafts are between 0.8-1.2mm in wall thickness.
Btw, the shafts are about 0.355'' at the tip and 0.6'' at the handle/butt end.

Anyways, I will just have to "dive" into it. Order some tubes and see where it takes me. If it catches fish, great. If it breaks, I had an adventure making it.

I am thinking of running a "safety lanyard" of dyneema inside each tube tied to the metal connectors on each end of the tube. So, in case of a busted tube, I should still be able to recover the fish and front part of the spear.

Last edited by Diving Gecko; 07-16-2016 at 03:36 AM.
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Old 07-16-2016, 03:36 AM   #6
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Re: Help Needed, DIY Jap Style Polespear

Quote:
Originally Posted by Diving Gecko View Post

I am not an engineer and honestly you don't get specs sheets with these tubes. Even if you did, you wouldn't be able to trust them.

So, this will be a hands-on, trial and error kind of approach.
I have read about people using 1.15mm wall thickness, so if I go to 1.5mm or even 2mm I would feel OK.

I am thinking of running a "safety lanyard" of dyneema inside the tubes tied to the metal connectors. So, in case of a busted tubed, I might still recover the fish and front part of the spear.
Don't under estimate yourself, I have read some of your posts, you are more than capable... Granted I'm degreed engineer but I focus on electrons and software.

All you need is basic algebra, high school level beginner physics. Nothing fancy. U-tube has so much info on topic, you can watch a few and get tutored up in no time.

If a vendor doesn't provide basic specifications, you might not want to use it. One design trick is to assume it can only handle 1/2 of what it says. Figure out your weak spot and make sure that is beefed up.

Industrial engineering design has a lot to do with assuming and down scaling. Knowing what is important to focus on, is what separates the men from the boys. That typically comes with failures and having good mentors that had their failures.

If you want to minimize the stresses on your DIY pole, try a break-away Slip tip. After the shot, your pole can't get trashed, it's mathematically out of the equation.... lol
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Old 07-16-2016, 03:43 AM   #7
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Re: Help Needed, DIY Jap Style Polespear

Quote:
Originally Posted by Linghunt View Post
Don't under estimate yourself, I have read some of your posts, you are more than capable... Granted I'm degreed engineer but I focus on electrons and software.

All you need is basic algebra, high school level beginner physics. Nothing fancy. U-tube has so much info on topic, you can watch a few and get tutored up in no time.

If a vendor doesn't provide basic specifications, you might not want to use it. One design trick is to assume it can only handle 1/2 of what it says. Figure out your weak spot and make sure that is beefed up.

Industrial engineering design has a lot to do with assuming and down scaling. Knowing what is important to focus on, is what separates the men from the boys. That typically comes with failures and having good mentors that had their failures.

If you want to minimize the stresses on your DIY pole, try a break-away Slip tip. After the shot, your pole can't get trashed, it's mathematically out of the equation.... lol
Thanks so much, Linghunt,
All good thoughts and sorry for poking a bit at you in my previous post, it was all in good spirit. I am very full of respect for the work and craftmanship you bring to the world.

Settled, I will go for 2mm tubes, that is almost two times up from some others:-)

I might go for a golf club front section as an experiment. I will, likely, still make a regular front section as a backup.

I will def go for slip-tips. I was saving that for a later post, though. Even in Japan where they sometimes bang the spears into rock, they still use slip-tips.

It is a bit of a hassle having pointy things shipped into China. They are not too fond of that stuff, so I have to figure out if I risk ordering from overseas or try to design something myself and have it made here. But that's for a little later:-)

Thanks again!
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Old 07-16-2016, 04:43 AM   #8
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Re: Help Needed, DIY Jap Style Polespear

Quote:
Originally Posted by Diving Gecko View Post

On the topic of gut feel, I would think the vast majority, if not all, of polespear designs are based on that plus practical experimentation, no?
I mean, do you, Aaron or the Gatku boys run your designs through computers...?;-). And even if you did, how do you tell the computer where a particular rock will jam your spear and what about the force the grouper in the hole is putting on the spear?;-).
Seems like the only thing wrong with your customer's gut feel was that it was not based on much practical experience with polespears? Neither is mine which is why I tried looking into common dimensions and posted the question here:-)
Everyone does their designs in much different ways. Dustin (Gatku) Aaron and myself , come from different backgrounds that influence our designs and methods. You are missing many other players in the market as well.

This can be seen in the wide variety of products.

I don't run my designs through a computer, perhaps the others do , but I would guess not. FEA Software is spendy and not in my budget.

I have had access to it with an operator but it was for projects of high value.

Before that fancy software was available, what did engineers do?

Basic physics is the same, and one works from that. Paper, pencil and slide rule. Look at the designs in Ancient Rome and Greece. And the Great Wall in your Area.

As for Grouper location and loading, you got to keep it simple. you have to reduce the problem down to make it easier. If loading along the length was a concern, Do the problem with load at x position, then redo it as x+1. etc. You can look at those to get a gut feel of load per length.

A "Gut Feel" can be gained through numbers along with testing when it's cost effective.

I do have various force gauges that I use to help with that feel for material strengths and verifying my slide ruler is working correctly.
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Last edited by Linghunt; 07-16-2016 at 04:45 AM. Reason: typo
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Old 07-16-2016, 10:22 PM   #9
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Re: Help Needed, DIY Jap Style Polespear

Golf club (driver) tubes will work, as well as ski poles. My first polespear was made by epoxying 3-4 golf clubs together and then epoxying a 6mm adapter to the tip. Took many fish under 10lbs with it, but ended up snapping it when I overpowered it without twisting the handle.

It was 9ft before a 12" tip, and was my go to for reef diving in 20+ft visibility.


I'm working on a series at the moment of different pole spear builds. Hopefully this helps you:

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Old 11-02-2016, 08:32 AM   #10
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Re: Help Needed, DIY Jap Style Polespear

Hey guys,
Not much of an update, the polespear project is on the back burner. Too much work and traveling lately and also had to move apartments.

But I have the CF tubes and then, pretty much by coincidence, I found myself in a small mall in Bangkok with a hefty golf shop presence. And in one of the shops, I just happened to find some affordable 'naked' shafts, so to speak...

So, I am slowly getting there. Will probably start drawing the connectors next, but that will take a little while. But basically just wanted to say that the project is not dead, just resting a bit;-)
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Old 11-24-2016, 06:25 AM   #11
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Re: Help Needed, DIY Jap Style Polespear

So, I thought it would make more sense continuing here so this Jap styled spear and the thoughts behind it would be compiled in one place (I was beginning to hijack one of Ren's threads, so excuse me for a bit of C+P to get this thread up to speed).

My spear will be made up by three 5/8'' sections 4' long, then one tapered golf club shaft for the front section at 3' plus about 2' for the shaft and slip tip
So, in full regalia, I will be looking at a whopping 17' butt to tip! Yup, proper Jap style. It will, likely, only weigh in at about 2.2 pounds - so should fly fast.
This is actually the same length as a Japanese polespear I borrowed in Japan and the longest I have seen for sale there, too. I was actually going to make it three feet shorter, but then found the golf club shaft.

But with the sections I am using, and by switching bands, I can pretty easily take one of the straight sections out and make it a 13' spear still with the tapered front section, which would make it a tad more manoeuvrable and more in line with what I first envisioned.

If I will be more on the reef, perhaps it would make sense to not use the tapered, thinner golf club shaft at the front and instead go straight from the sturdier straight 4' sections (with an adapter) onto the shaft. With that setup, I can make it either a sturdier 10' or 14' spear. Mind you, it will never be a spear you'd want to shoot into caves or under ledges.
That said, I am considering running some dyneema between the metal couplers on each end of each section (well, at least the front one) so that if one of them snaps, I might still keep my fish and slip-tip.

I have seen some Japanese spearos going with single bands now and Aaron explained that it also helps with keeping the band parallel to the pole and thus reduce flex, so I will be trying that, too. I have some small ID Primeline in 13-14.5mm plus some Sigalsub small ID, too.
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Old 11-24-2016, 06:34 AM   #12
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Re: Help Needed, DIY Jap Style Polespear

Metal Couplers/Connectors
Originally I had intended to make the couplers internal but I was worried that it might easier split the tube. Then I noticed that all the Japanese spears I saw online had them external with the CF tube sliding into the coupler before being glued in placed. So, I was about to change my idea and follow the Japanese on this one.
But then yesterday, I saw Billfish Republic and I think some of Aarons spears, too have the couplers internal... So, now I might go back to the original idea.

My CF tube is 12x16mm, which gives it a 2mm wall thickness. That it pretty sturdy I would think. I think the unidirectional fiber is wound with 30% across the axis of the pole and 70% along it. Would you guys dare going with internal on that?
If I do, I might still wrap a little UD fiber across the tube where the coupler is inserted.

The golf shaft front section would likely still need to be external on account of the smaller wall thickness and tapered front.
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Old 11-24-2016, 05:35 PM   #13
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Re: Help Needed, DIY Jap Style Polespear

Draw a free body diagram and do some force and moment calculations.

Make some assumptions for an easier problem. (e.g. force distribution over a longer contact area)




I learned this stuff in high school. So math isn't that tough.

This will give you a feel for what to do, you are not looking to get numbers perfect within a moose hair.

This method can also be used to understand the rubber stretch and pole flexing to the side that is talked about in other thread.
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Old 11-25-2016, 04:29 PM   #14
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Re: Help Needed, DIY Jap Style Polespear

Most external connections are there due to the manufacture using smaller diameter tubing or solid rod. This is more common with 3/8" rod. With rod, it would be mandatory with the design. I would make the connectors internal to streamline the spear.
You'll like the 0.079" wall thickness.

I made a 12' custom spear a couple months back that went to Japan and it was 0.050" wall and it broke just when the end user went to draw it up. I really dont like this style spear and dont understand why they just go shorter and improve their hunting technique.

I'll find the connectors Ive machined and take some pics and post to give you an idea on how to design them strong.
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Old 11-25-2016, 09:02 PM   #15
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Re: Help Needed, DIY Jap Style Polespear

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Most external connections are there due to the manufacture using smaller diameter tubing or solid rod. This is more common with 3/8" rod. With rod, it would be mandatory with the design. I would make the connectors internal to streamline the spear.
You'll like the 0.079" wall thickness.

I made a 12' custom spear a couple months back that went to Japan and it was 0.050" wall and it broke just when the end user went to draw it up. I really dont like this style spear and dont understand why they just go shorter and improve their hunting technique.

I'll find the connectors Ive machined and take some pics and post to give you an idea on how to design them strong.
Hi Aaron,
Thanks so much! I'd love to see a few snaps. I do like the idea of internal a lot. If I find the time and can switch parts of my brain on that haven't been used for a few decades I would like to try to the math, too as John suggests. Just for a loose guideline though I will have to make some assumptions about laminate strength and such. I do think making sure the tolerances are tight and the plug length generous, so that the force is spread out are part of the solution.

I back tracked a bit myself in my head the last two days, went over my notes and originally I was looking for something in between a long Japanese spear and a "western" one. I can see even from my first post here, that I was aiming for about 12 feet.

The time I dived in Japan with the 5.5m polespear, even though the tail end was tapered, too (mine is not), there was a lot of drag when tracking the spear. Going shorter will help reduce that.

I do think I would appreciate a long "over hang" though as in Thailand and the Philippines where I most often spear, the fish are pretty skittish.
As a side note, I am hoping to go to Okinawa at some point, too - would be great to take my own Japanese-inspired polespear to Japan:-)

Last edited by Diving Gecko; 11-25-2016 at 09:55 PM.
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