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buoyance arms review


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#61 cor

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Posted 28 February 2007 - 08:28 AM

I went to a local paint store and talked to the owner about this issue. He recommended just trying a cheap acrylic polyurethane paint. I paid a few bucks for a 29 oz can that he whipped up for me in a darkish blue. I did only 1 dive with it so far, but the paint looks untouched. I went to 140 feet to see if the paint would crack as the floats compressed, but nothing happened. The guy told me this paint stretches well. I'll do some more testing, but this paint seems to work just fine, especially if I do 2 or 3 layers of it.

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#62 james

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Posted 28 February 2007 - 08:43 AM

I got mine at West Marine which is now Boat US

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#63 drsteve

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Posted 05 March 2007 - 10:03 PM

Here are my buoyancy arms. I followed the lead a friend and others on these forums. They consist of capped PVC tubing cable tied to my ULCS arms. It isn't pretty but it is cheap, effective, and doesn't change buoyancy at depth. Total cost was < $20.

Unfortunately since the PVC is soft, the paint chips off pretty easily. I probably should have left them white, but it appealed to my vanity though to have it beautiful if only for a little while.

It is almost neutral in the water. I still need to do a little more fine tuning to get the balance perfect. It is much more manageable this way than before I added the floats. The arms are 12" and 8". I put double floats on the 8" arms. I also have 5" arms, but I have pretty much discontinued using them.

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#64 NWDiver

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Posted 10 March 2007 - 11:19 AM

Somebody may have asked this but I will be "The Jerk" and try to go cheap...

Can you just buy the floats and jam them over existing TLC or ULCS arms?

#65 Kory Nakatsu

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Posted 10 March 2007 - 12:15 PM

Somebody may have asked this but I will be "The Jerk" and try to go cheap...

Can you just buy the floats and jam them over existing TLC or ULCS arms?



Thrify question but the STiX arms have removeable ball ends to allow the slotted floats to slip on to the arms with a snug fit, and are much smaller in diameter than TLC/ULCS arms.

By the time you bored out the floats enough to get them on to the TLC arms, over the the ball ends, you would have lost a majority of the float volume (buoyancy) and, they would be extemely loose on the arms.

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#66 malodiver

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Posted 10 March 2007 - 09:44 PM

Cor,
Just back from the Voyager trip. 1300 miles !!!! Got some great shots. I used John's arms on my Sea Cam D2X system and I dont need physical therapy on return from the two week trip. They worked fantastic. I needed two long arms on each side for the 9 inch wide angle port. Perfect neutral bouancy. WOW what a new experiance.
As I was afraid of, the short arms were not enough to float the Macro port. John rigged up a floatation collar for the Macro port that I trialed for use with the arms. It worked great. Perfect ballance. The two together provided neutral bouancy. He will probably have that available for those that need more than the arms for Macro. I cant believe how much easier it was to focus the 105 on those Pigmy Seahorses, when I wasnt trying to hold up that heavy camera.
Jack

#67 Kory Nakatsu

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Posted 11 March 2007 - 06:40 PM

Cor,
Just back from the Voyager trip. 1300 miles !!!! Got some great shots. I used John's arms on my Sea Cam D2X system and I dont need physical therapy on return from the two week trip. They worked fantastic. I needed two long arms on each side for the 9 inch wide angle port. Perfect neutral bouancy. WOW what a new experiance.
As I was afraid of, the short arms were not enough to float the Macro port. John rigged up a floatation collar for the Macro port that I trialed for use with the arms. It worked great. Perfect ballance. The two together provided neutral bouancy. He will probably have that available for those that need more than the arms for Macro. I cant believe how much easier it was to focus the 105 on those Pigmy Seahorses, when I wasnt trying to hold up that heavy camera.
Jack



Jack,

Thanks for the great report. Just a few questions - What arm length(s) and floats did you use for both WA and macro?

I am thinking of adding a StiX arm and float to my focus light to compensate for the macro port but don't know if it will be enough. Thank you.

Kory
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#68 bobf

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Posted 12 March 2007 - 07:54 AM

I would begin any buoyancy compensation project by first deciding on the goal. IOW, do you want your rig to be positive, neutral, or slightly negative underwater.

I would next determine how negative the rig is underwater before any modifications. This could be approximated with the aid of a hand held "fish" scale (spring or digital style). Attach a fishing line from the hook of the scale to the camera rig. Immerse only the rig into water (keep scale out of the water) and hold it as motionless as possible (if the camera is "bobbing" up and down, so is the answer :) ). If fresh water is used, keep in mind that salt water will make the rig more buoyant (3%?).

An alternative (preferred?) method for finding the underwater weight of an object is to determine its actual displacement (volume) (*see below*) .

If the weight of the water that is displaced weighs more than the dry weight of the rig itself, then the rig will be positively buoyant ( why boats float).

Once you have determined the rig's underwater weight, then determine the buoyancy of the material you choose to add to your rig. If you are purchasing a brand new strobe arm system, StiX offers a guide to the buoyancy of each component they offer.

If you wish not to purchase a new arm system and are adding to strobe arms already owned, then buoyancy of the chosen material can be determined in the following manner:

choose a known size of buoyant material (volume in cubic inches)
weigh the known volume dry

Salt water weighs 0.037 pounds per cubic inch. Multiply the volume of the buoyant material (in cubic inches) by the weight of water (in cubic inches) it will displace. Subtract the dry weight of the material from that subtotal and the result will be how much lift is created.

For best results, choose materials that will not compress when exposed to recreational dive depths. As materials compress, they lose volume and subsequently the ability to displace water.

Example of a material that does not compress at recreational dive depths:

A 4' by 8' sheet of 1/2" Core Cell A weighs 5 lbs per cubic foot (12x12x12= 1728 cu in.)
Core Cell A weighs @ 0.0028 pounds per cubic inch

Since water weighs 0.037 pounds per cubic inch and Core Cell A weighs @ 0.003 pounds per cubic inch, then 0.034 pounds of lift can be created with every cubic inch of Core Cell A added to the underwater rig.

Lets assume you wish to add 1 pound (16 ounces) of buoyancy to your rig using Core Cell A. Divide the target of 1 pound by the benefit lift of 1/2" thick Core Cell at 0.034 pounds per cubic inch. According to the math, @ 29.4 cubic inches of Core Cell A would increase buoyancy by 1 pound.

If you had a single 12" long strobe arm, you'd probably only wish for 10" of linear material placed on it so that free movement was not impeded upon by the strobe arm clamps found at either end of the arm. If you were to cut and install 4 pieces of Core Cell A measuring 10" by 1.25" by 0.5 inches around the arm (encapsulate the arm), 25 cubic inches would be added to each strobe arm. 25 cubic inches of Core Cell A would yield a net benefit of (25 times .034) 0.850 pounds or 13.6 ounces, about 2.5 ounces shy of the target.

If you had a pair of 8" long strobe arms:

a 6" by 1.25" by 1/2" section of Core Cell A would yield 3.75 cubic inches of displacement per section
4 sections per strobe arm would yield 15 cu in per strobe arm
15 cu in realizes a lift benefit of (15 times .034) 0.51 pounds or 8.1 ounces per arm
therefore two 8" long arms with the above modification would yield a benefit of @ 1 pound of lift. If your dual strobe arm system consisted of 4 x 8" arms including the above modification, then 2 pounds of lift could be created.

Paint and fastening system used to attach material to strobe arm (glue, cable ties, plastic nuts and bolts, wire, o-rings, etc) should be chosen carefully as they will affect the end result.

* To determine Volume:

Choose a container of known size. A common household pot for boiling large quantities of water would be sufficient as long as the sides of the pot were straight and not angled outward. For example, my wife has a straight sided pot that measured (diameter) 13" across. Its radius therefore is 6.5". In order to determine the displacement of my rig, I filled the pot with 7" of water. I next placed a ruler along the interior side of the pot, vertically into the water. As mentioned, the water depth read 7". I then placed each component of my rig separately into the water and noted the increase in height of the water on the ruler.

Say once the component was immersed, the height of water as noted on the ruler increased one inch, from 7" depth to 8" depth .

To determine volume of a cylinder, the following formula is used:

V=L*Pi*r²

The increase in height of the water inside the pot will now be noted now as the Length of the cylinder

Volume equals Length times Pi (3.14) times the radius of the pot squared
V=1 (height increase of water) times 3.14 times 6.5²
V=1*3.14*42.25
V=132 cubic inches

The object that I placed into the pot of water that increased the level of water by 1" therefore displaces 132 cubic inches of water.

Edited by bobf, 12 March 2007 - 08:47 AM.

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#69 H2Oplanet

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Posted 12 March 2007 - 10:24 AM

Two Questions:

(1) Can someone explain how best to make a buoyancy collar for a flat port when shooting macro? i shoot macro with the 100mm Canon as well as the 180mm Canon. Just purchased the Stix system and I like the idea of using the collar in conjuction with the buoyancy arms for macro which would allow me to limit arm lengths and reduce bending moments.

(2) You guys got me concerned about Sharks now since there are many species here in North Carolina plus I'm joining JASA/Wetpixel for the Bahama shoots in July. I can use techniques in this thread to cover the white floats with black but shouldn't I really be more conerned with my large, shinny SeaCam housing and the two large SeaCam 250 strobes??

Please advise...

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#70 seagrant

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Posted 12 March 2007 - 11:09 AM

If you had a pair of 8" long strobe arms:
a 6" by 1.25" by 1/2" section of Core Cell A would yield 3.75 cubic inches of displacement per section
4 sections per strobe arm would yield 15 cu in per strobe arm
15 cu in realizes a lift benefit of (15 times .034) 0.51 pounds or 8.1 ounces per arm
therefore two 8" long arms with the above modification would yield a benefit of @ 1 pound of lift. If your dual strobe arm system consisted of 4 x 8" arms including the above modification, then 2 pounds of lift could be created.

Paint and fastening system used to attach material to strobe arm (glue, cable ties, plastic nuts and bolts, wire, o-rings, etc) should be chosen carefully as they will affect the end result.


Bobf you are a wonder with the math!! :) I do admire that ability you have!

As you know I tried the corecell on the 8" ULCS arms and it did not displace the weight that was calculated. I'm sure it works out on the "drawing board" but in real water situations......, well obviously in my real-water situations I got 1.6 oz of buoyancy per section for the 8" ULCS arms. Ryan spent a lot of time and effort making the core cell floats and I felt terrible for all his caring and efforts that they didn't displace the nearly 4oz that he thought they would. They only displaced slightly more than the existing ULCS buoyancy 8" arms. Of course the corecell material could be stacked but it proved very unwieldy for me personally (but that was just for me). I did have another WetPixel member help me with some of the tests. We were very careful and only used one or two zip ties so as not to add weight to the tests.

I do feel a corecell buoyancy collar in addition to some sort of float on the arms would be beneficial. Problem is some ports have focus knobs that can make that difficult I'm told. Still I'm hoping to get a buoyancy collar made for me at some point (it has been promised...... :P ....)

As you probably know I've used two of the Patima BCs, one on each inside 8" arm and find them very easy to live with. Every buoyancy solution has some drawbacks but the drawbacks for me personally with the Patima BCs were less than stacking the arms with so much foam (6 sections per arm wasn't even enough), and I didn't want longer arms because of the difficulty of handling them for me.

Of course not everyone would feel as comfortable with the Patima BCs and adjusting their air volume once in a while but I do, I, along with a number of others who shoot a lot, find it quite easy (and actually sort of fun to fiddle with, like a lift-bag or something like that). And I don't have to adjust it that much, sometimes not at all.

Hopefully I can use those BCs on the arms in conjunction with a corecell collar for the Subal 105vr port which is quite heavy. And I might even try a couple of the new ULCS buoyancy arms in addition when they are released. Granted I do need the rig a little lighter than most divers.

Upshot is I'm really glad John is distributing these Stix arms and floats, etc. I'm glad ULCS is making new and more buoyant buoyancy arms. I'm glad you are doing the math to find a corecell solution and I'm happy Ryan Canon cares so much to help people get their rigs less negative. I'm also happy Patima made a simple BC float to attach to the housing or arms. All these things and others are steps in the right direction. Of course it would be a lot easier for all if the housings just had a bit more air space designed in at manufacturing time to result in less negative housings, etc. But that is a wish and what we are dealing with is what is here and now.

Again, thanks for the math and all the suggestions!

Take Care, Carol ^_^

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#71 bobf

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Posted 12 March 2007 - 12:30 PM

Bobf you are a wonder with the math!! :P........I got 1.6 oz of buoyancy per section for the 8" ULCS arms...........


Carol,

Thank you for the kind words.

When you first contacted me it was in the middle of my busy season..............I wish I could have been more helpful at the time...........

I do not fully understand yet what size Core Cell (HxWxL) is meant when you refer to "section" in your post. When you state you realized 1.6 ounces per "section" for the 8" strobe arm, can you please define "section". Is that for each single piece of Core Cell A (if so, what HxWxL)) or for a set of four pieces as described in my post:

a 6" by 1.25" by 1/2" section of Core Cell A would yield 3.75 cubic inches of displacement per section
4 sections per strobe arm would yield 15 cu in per strobe arm
15 cu in realizes a lift benefit of (15 times .034) 0.51 pounds or 8.1 ounces per arm


If I quickly do the math, a 6" by 1.25" by 1/2" piece of Core Cell A will displace 3.75 cubic inches of water.
3.75 time 0.034 (weight of water minus weight of core cell per cubic inch) equals 0.1275 or about 2 ounces of lift per 6 by 1.25 by 1/2. I arrive at this conclusion based upon acknowledged fact (Archimedes Principle).

I do agree however that what takes place on the blackboard and what takes place in real life does not always jive......... :)

And I strongly agree with you that all of this discussion is extremely important...........especially including the fact that strobe arm manufacturers are addressing the issue with renewed vigor.

One important note to consider with whatever direction anyone is to take, whether starting from scratch with a brand new strobe arm system or modifying an existing system. Length matters!!!!!! The longer the arm, the more surface available to add "streamlined" buoyancy.

btw, I should also mention as a clarification. There are several types of Core Cell, each with their own performance specifications and subsequently letter "suffix". The particular type I refer to in my post is called "Core Cell A". There is also a "Core Cell S", "Core Cell T", Core Cell P", etc............
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#72 cor

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Posted 12 March 2007 - 12:58 PM

btw, I should also mention as a clarification. There are several types of Core Cell, each with their own performance specifications and subsequently letter "suffix". The particular type I refer to in my post is called "Core Cell A". There is also a "Core Cell S", "Core Cell T", Core Cell P", etc............

Also, within the different types there are different densities. Core Cell S has several densities, and if you get the wrong one (very dense, usable for deep sea rovers) you will get very bad buoyancy properties as opposed to less dense versions of core cell S or even A.

When I spoke to a boat maker in Amsterdam he told me that the dense versions are the most commonly sold ones because they're used in boats. He had a hard time getting me the lightest version (usable upto 300 meters I think).

But, eventually I ended up buying the stix arms, as this thread shows :)

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#73 bobf

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Posted 12 March 2007 - 01:46 PM

Also, within the different types there are different densities. Core Cell S has several densities, and if you get the wrong one (very dense, usable for deep sea rovers) you will get very bad buoyancy properties as opposed to less dense versions of core cell S or even A.

When I spoke to a boat maker in Amsterdam he told me that the dense versions are the most commonly sold ones because they're used in boats. He had a hard time getting me the lightest version (usable upto 300 meters I think).

But, eventually I ended up buying the stix arms, as this thread shows :)

Cor


For more information on Core Cell options, visit:

http://www3.gurit.co...ts_corecell.php

If you download the Core Cell S .pdf file, you'll notice as Cor has mentioned, that it is available in three variations, ranging in average density from 9.3 lbs per cubic foot to 19.7 pounds per cubic foot. As previously stated, the Core Cell A that I've experimented with has an average density of 5 pounds per cubic foot. My first samples of Core Cell A were from the remnants of a 51' sailing vessel being constructed near my home port. More specifically, off cuts from the sailing vessel's structural bulkheads. This is tough stuff!
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#74 cor

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Posted 12 March 2007 - 05:35 PM

For more information on Core Cell options, visit:

http://www3.gurit.co...ts_corecell.php

If you download the Core Cell S .pdf file, you'll notice as Cor has mentioned, that it is available in three variations, ranging in average density from 9.3 lbs per cubic foot to 19.7 pounds per cubic foot. As previously stated, the Core Cell A that I've experimented with has an average density of 5 pounds per cubic foot. My first samples of Core Cell A were from the remnants of a 51' sailing vessel being constructed near my home port. More specifically, off cuts from the sailing vessel's structural bulkheads. This is tough stuff!

Did you ever try out what the max depth is for core cell A300? The main issue right now with the floats from the stix arms is that the max depth is around 110-130 feet. After that the floats start compressing. The biggest benefit is its weight, next to nothing. Id like to try some core cell A300, which is probably a bit better than what the stix arms use. I can probably cut floats out of A300 myself.

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#75 bobf

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Posted 12 March 2007 - 07:28 PM

Did you ever try out what the max depth is for core cell A300?

Cor


No.

But if you wouldn't mind allowing "math" to get wet for us again...............

According to the Corecell A spec sheet, A300 compression strength is rated at 65 psi.

Next, calculate pressure (psi) at your target depth of 130 feet..........

Air pressure at the surface = 14.7 lbs
descend the first 33 feet and add 14.7 lbs
descend another 33 feet and add 14.7
descend another 33 feet and add 14.7
descend another 33 feet and add 14.7

total depth equals 132 feet = 73.5 lbs psi

To determine specifically how deep you can go in salt water to reach 65 pounds absolute psi, first subtract 14.7 to compensate for pressure at the surface (1ATM):

65 psi - 14.7 psi = 50.3 pounds per square inch

We know a single square inch column of salt water 33 feet deep weighs 14.7 pounds. Every foot of salt water therefore weighs .445 pounds (14.7/33=.445). To find how much water is needed then to exert 50.3 pounds of pressure per square inch, divide 50.3 by .445. Answer= 113 feet.

At 113 fsw, 14.7 psi will be exerted by the air in the atmosphere and another 50.3 pounds per square inch will be exerted by the salt water equaling a total psi of 65..........the tested limit of Corecell A300. After that point, according to the spec sheet, A300 should begin to compress...........just as the StiX buoyancy foam reportedly does.

Corecell A500 has a compression strength rated at 135 psi. Using the same formula as above, first subtract 14.7 to acknowledge the first ATM, yielding 120.3 psi. Divide 120.3 by .445 equals 270.33. Corecell A500 should be fine until a salt water depth of @ 270 feet is reached.............according to how I read the specs.......and do the math.......... :)

Id like to try some core cell A300, which is probably a bit better than what the stix arms use. I can probably cut floats out of A300 myself.


As far as the ability to cut floats from A300, I can state through experience that 1/2" Corecell A500 cuts relatively easy with a standard utility (matt) knife (2-3 passes). Corecell A500 can also be shaped easily with sand paper, rasps, belt sander, etc.......I would therefore "assume" you would have no trouble.

I have also cut 3/4" thick Corecell A500 and 1" thick Corecell (unknown letter suffix because it was another "leftover" piece) with a standard utility (matt) knife.

hth,
b
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#76 cor

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Posted 13 March 2007 - 05:06 AM

No.

But if you wouldn't mind allowing "math" to get wet for us again...............

lots of math

I dont mind math at all :) Looks good. I'll try some A500. The S1800 I tried at some point needed power tools to be cut :P It's hard as rock.

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#77 Kory Nakatsu

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Posted 14 March 2007 - 12:10 AM

I just received my second order of StiX arms/floats. I had installed my original arms/floats on the housing with strobes just to test the arm articulation with the floats. It has been sitting for 3 weeks until tonight when I broke it all down to measure different configurations. I found that the ball ends on 3 of the 4 original arms had stress cracks.

_KRN4192.jpg _KRN4190.jpg

From the appearance and consistency of these cracks, it leads me to believe they were caused by the tension of the set screw and not the clamps. When I originally installed the balls ends, I intentionally did not overtighten and used lock-tite instead to prevent them from coming loose.

In comparing the cracked ball ends from my initial order to the ones I just received, there is a clear difference between the two so I'm wondering if this has been an issue with others. Given the cost of these things, this is somewhat concerning but glad that it was discovered before anything hit the water.

I am sending a note to John at 4th Generation with these pictures in hopes that he is already aware of the issue. Has anyone else seen this?

Edited by Kory Nakatsu, 14 March 2007 - 12:12 AM.

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#78 cor

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Posted 14 March 2007 - 04:25 AM

I just received my second order of StiX arms/floats. I had installed my original arms/floats on the housing with strobes just to test the arm articulation with the floats. It has been sitting for 3 weeks until tonight when I broke it all down to measure different configurations. I found that the ball ends on 3 of the 4 original arms had stress cracks.

How long did you have the first set? I have had similar stress cracks on older ball ends. Supposedly the newer ball ends are made of a different material, and ive not had any problems yet. It almost looks like you have the newer material though, so that would be very worrisome.

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#79 Kory Nakatsu

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Posted 14 March 2007 - 09:28 AM

Cor,

The ones that cracked were ordered the day you started this post so I would assume they are older. The ones I just received are noticeably different and have a very slight seam in the center of the ball. Here is the initial response from John - he is going to do some testing with the Loctite 277 I used.

This is the first occurrence of the cracking shown in the pictures. I will need to take a look at them to make a determination about the cause of the failure. My first thought is that the loctite may have caused the problem. Most plastics have their Achilles (often some kind of aromatic hydrocarbon) heel and you may have discovered one. I have not found loosening to be a problem but if you feel it is, a better solution would be screws with a nylon “patch”. Can you tell me what kind of loctite you used. I am doing some tests and want to emulate the conditions. -- John


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#80 cor

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Posted 14 March 2007 - 06:35 PM

Cor,

The ones that cracked were ordered the day you started this post so I would assume they are older. The ones I just received are noticeably different and have a very slight seam in the center of the ball. Here is the initial response from John - he is going to do some testing with the Loctite 277 I used.

Ive been emailing with John today and he told me earlier that he suspected some interaction with the Loctite. It seems that that has been confirmed now. Loctite 277 (and probably other loctite as well) is not recommended for use with thermoplastics, which is what the ball ends are made of. It can cause stress cracking, which is exactly what you see there. John probably emailed you the PDF with the loctite specs, but if not, you can find it here.. Check page 2 under General Information.

So the conclusion is..avoid Loctite with these arms ..

Cor
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