Generation 5 homebuild off to a good start

S. Marc · 25th September 2007, 02:47

This is the 5th generation of homebuild Kiss style rebreather I am in the process of finishing. Some final machining steps and tig welding left, but it is starting to take shape.

Based roughly on Meg dimensions, but using PVC as the can (there are two, one is 14 inches long and the second is 16 inches long with an ID of just under 6"), and T6061 as the head. It will hold a min of 6 lbs in the axial scrubber, and 7 to 8 in the radial - the radial is just a rendering on paper right know but will be roughly similar in design to the one Skipbreather made for the meg with a couple of changes in the sorb bed tensioning mechanism and materials. If the axial bed is too long and exhibits high WOB I will part a couple of inches off the length of the scrubber can.

I did the machining on the PVC, and the rough machining on the aluminum head, but after ruining about $700 in 6061 trying to machine the o-ring grooves on 3 heads - they start out at 7" solid rod and are 3 inches tall before machining (it is a piece of cake to machine oring grooves in delrin or pvc, but I can't for the life of me machine oring grooves in aluminium without galling), I had a machine shop do the final steps. I still have to enlarge the inhale port on the head as the diameter was machined a little to small by me. Very nervous about messing up a 4th head

I still have to bore out the PVC base a few inches for a water trap.

Unit will use a 3rd generation Kiss valve, and the Buddy inspiration over the shoulder counterlungs that have been gathering dust in my basement for the last year or so, together with Narked @ 90's awesome 02 remote add which will work in conjunction with the Kiss valve.

I have some new Nielsen clamps for the head of the can, and the base will be bonded in with the appropriate PVC glue.

Plans are to use a type 3 hard coat anodizing on the head, and truck bed liner on the can to protect the fragile pvc base.

Still have to Tig the inhale and exhale tubes on the head, and I am not sure if I will machine threads first so it can accept Buddy inspiration connectors as that is the DSV and hoses I am going to use on this new beast.

The next step is to machine a sensor plate to hold the sensors and a spring to exert some downforce on the scrubber bed. Exhale tube is machined as are top and bottom plates for the axial scrubber bed - just can't locate them right now as a result of a move and too many unpacked boxes.

I also have to spend a few minutes drilling and tapping the head for cable gland threads for the Mark Munro PPO2 board I will use. If the rig works well I will likely go with a shearwater or subsea systems setup.

My plan is for the entire loop and can to come in under 22 LBS once complete - may be wishful thinking and I may take a 1/8 inch or so off the OD of the entire lenght of the can and head to reduce weight if it comes in too heavy.

Any suggestions for improvements, modifications and / or constructive criticism is welcome, especially before the final machinng and welding is done

.

Pics follow -sorry for poor quality I am a terrible photographer:

S. Marc · 25th September 2007, 06:11

Bnscherm · 28th September 2007, 22:36

That lid is a thing of beauty! Keep up the good work, I can't wait to see more.

Just out of curiosity why did you decide to use aluminum for the top, but PVC for the bottom? In comparison to the PVC the aluminum seems like way over-kill, especially when considering the cost and time on the machine.

I'm sure it will work great, and it looks awesome.

How many Nielsson latches do you plan to use? I'm currently only using two on my 6" scrubber, and have had some frustration with minor positive pressure leaks. Just can't figure out a good way to mount three or four...

S. Marc · 28th September 2007, 23:31

Hi Bnscherm,

I am using an aluminum lid as on previous versions with PVC, I was forced to machine inhale and exhale tubes that had thicker walls for strength, and as a result, when bonding to and through the scrubber lid I could never get the center tube centered. This made removing the scrubber lid quite difficult during initial testing, and on a few occasions I had to remove both hoses, block one of the tubes coming off the scrubber lid, and blow hard to get the lid to pop. Not very professional looking and would be quite embarrasing in public as I like to think I am a pretty good hobby machinist - which I really am not

I tried machining thinner walled PVC tubes, but after a few experiences when both boring the center or machining the OD of the tubes, of having to duck as the tubes flew out of the chuck I gave up. I tried doing it in both orders (boring first and turning the OD first) but no matter what I did I found that the tool put too much pressure on the PVC causing it to flex in the chuck and fly out. Pretty scary stuff as I usually turn PVC at around 1000 rpm. I am very impatient when turning PVC as it makes one hell of a mess. Aluminum is much less messy to machine.

By using aluminum I managed to machine thinner walled tubes and as they are going to be tig welded on, the center tube is dead center, which I hope will make removing the lid easier.

I only plan on using two latches for the lid for now (180 degrees apart) and I hope there are no problems with positive or negative tests. I have heard that some Meg divers have removed the two lid latches behind the divers back and are not experiencing any problems.

The aluminum lid has two orings that seal to the inside of the cannister wall, and two internal orings in the exhale central tube. As the lid penetrates approximately an inch (I don't have the exact measurements with me right now) into the cannister, I hope there are no issues.

I will post some pics of one of the prototype PVC lids tonight if I can locate the digicam. That one was never put into use and does not have latches or threads for O2 fittings and PPO2 cable glands. It was just too much of a pain to remove.

More pics will follow as the unit progresses.
Marc

S. Marc · 29th September 2007, 00:50

Pics of PVC lid

teomannaskali · 1st October 2007, 12:57

Where exactly are the pictures?

S. Marc · 1st October 2007, 19:24

Don't know what happened to the pics.

Here they are again

kiwi_diver · 1st October 2007, 21:24

Hi, when you hollow out the base for the water trap, have you considered making it a curve or V shape, and tapping a bung hole at the lowest point? Then you can drain it without dissassembly. I don't know if any other scrubbers have this feature but it's a suggestion.

Cheers, Ray.

S. Marc · 2nd October 2007, 05:39

Hi Ray,

The drain idea is intersting but I have no plans for a drain in the bottom of the scrubber. I hate o-rings and extra possible failure points and I think the drain would just end up being a likely point of failure with more orings needed, and one extra tool that would have to be carried in the save a dive kit. If the unit is as light as I hope it will be emptying the can will not be much of an effort. The whole rig has been designed so all I will need to service it is a scuba tool.

My distrust of oring seals is the reason why I am going to weld the exhale and inhale tubes to the lid. I considered cutting threads and using oring seals, but any time I machine a part that needs an oring I use two - paranoid I guess- and my machining ability does not leave enough room on this diameter head to use two orings for the tubes. A real machinist could do it but it is beyond my abilities.

The base of the can will just be milled out so there is a water trap about 1 1/2 to 2" deep. I considered milling the base out in two sections with a dividing partition, to keep any water in one part of the base, but decided against it as I would lose 1/2 of the water traps capacity (depending on my position in the water).

Marc

DanFountain · 2nd October 2007, 14:37

Quote: (Originally Posted by kiwi_diver)

Hi, when you hollow out the base for the water trap, have you considered making it a curve or V shape, and tapping a bung hole at the lowest point? Then you can drain it without dissassembly. I don't know if any other scrubbers have this feature but it's a suggestion.

Cheers, Ray.

(Hijack)
This is what I did with my "KISS Tribute" homebuilt - the canister has about an inch or so of space below the scrubber bed to collect any fugitive water, with the OPV positioned at the lowest point (during normal swimming). (Old picture of an early iteration of this project...)

Also has a manual dump - it's from a BCD and a little stiff - the overpressure is not adjustable. A drysuit OPV might be more appropriate.

Dan

25th September 2007, 02:47	#1 (permalink)
S. Marc Custom Title Allowed! Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Dec 2005 Posts: 199	Generation 5 homebuild off to a good start This is the 5th generation of homebuild Kiss style rebreather I am in the process of finishing. Some final machining steps and tig welding left, but it is starting to take shape. Based roughly on Meg dimensions, but using PVC as the can (there are two, one is 14 inches long and the second is 16 inches long with an ID of just under 6"), and T6061 as the head. It will hold a min of 6 lbs in the axial scrubber, and 7 to 8 in the radial - the radial is just a rendering on paper right know but will be roughly similar in design to the one Skipbreather made for the meg with a couple of changes in the sorb bed tensioning mechanism and materials. If the axial bed is too long and exhibits high WOB I will part a couple of inches off the length of the scrubber can. I did the machining on the PVC, and the rough machining on the aluminum head, but after ruining about $700 in 6061 trying to machine the o-ring grooves on 3 heads - they start out at 7" solid rod and are 3 inches tall before machining (it is a piece of cake to machine oring grooves in delrin or pvc, but I can't for the life of me machine oring grooves in aluminium without galling), I had a machine shop do the final steps. I still have to enlarge the inhale port on the head as the diameter was machined a little to small by me. Very nervous about messing up a 4th head I still have to bore out the PVC base a few inches for a water trap. Unit will use a 3rd generation Kiss valve, and the Buddy inspiration over the shoulder counterlungs that have been gathering dust in my basement for the last year or so, together with Narked @ 90's awesome 02 remote add which will work in conjunction with the Kiss valve. I have some new Nielsen clamps for the head of the can, and the base will be bonded in with the appropriate PVC glue. Plans are to use a type 3 hard coat anodizing on the head, and truck bed liner on the can to protect the fragile pvc base. Still have to Tig the inhale and exhale tubes on the head, and I am not sure if I will machine threads first so it can accept Buddy inspiration connectors as that is the DSV and hoses I am going to use on this new beast. The next step is to machine a sensor plate to hold the sensors and a spring to exert some downforce on the scrubber bed. Exhale tube is machined as are top and bottom plates for the axial scrubber bed - just can't locate them right now as a result of a move and too many unpacked boxes. I also have to spend a few minutes drilling and tapping the head for cable gland threads for the Mark Munro PPO2 board I will use. If the rig works well I will likely go with a shearwater or subsea systems setup. My plan is for the entire loop and can to come in under 22 LBS once complete - may be wishful thinking and I may take a 1/8 inch or so off the OD of the entire lenght of the can and head to reduce weight if it comes in too heavy. Any suggestions for improvements, modifications and / or constructive criticism is welcome, especially before the final machinng and welding is done . Pics follow -sorry for poor quality I am a terrible photographer: Last edited by S. Marc : 1st October 2007 at 01:29.
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25th September 2007, 06:11	#2 (permalink)
S. Marc Custom Title Allowed! Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Dec 2005 Posts: 199	Re: Generation 5 homebuild off to a good start Test __________________ My MK15.x is really a BMR 500 and is as Koputai says a "Bastard immitation of a proper rebreather"!!
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28th September 2007, 22:36	#3 (permalink)
Bnscherm New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Not Bought Yet Join Date: Nov 2006 Location: Michigan, USA Posts: 29	Re: Generation 5 homebuild off to a good start That lid is a thing of beauty! Keep up the good work, I can't wait to see more. Just out of curiosity why did you decide to use aluminum for the top, but PVC for the bottom? In comparison to the PVC the aluminum seems like way over-kill, especially when considering the cost and time on the machine. I'm sure it will work great, and it looks awesome. How many Nielsson latches do you plan to use? I'm currently only using two on my 6" scrubber, and have had some frustration with minor positive pressure leaks. Just can't figure out a good way to mount three or four...
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28th September 2007, 23:31	#4 (permalink)
S. Marc Custom Title Allowed! Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Dec 2005 Posts: 199	Re: Generation 5 homebuild off to a good start Hi Bnscherm, I am using an aluminum lid as on previous versions with PVC, I was forced to machine inhale and exhale tubes that had thicker walls for strength, and as a result, when bonding to and through the scrubber lid I could never get the center tube centered. This made removing the scrubber lid quite difficult during initial testing, and on a few occasions I had to remove both hoses, block one of the tubes coming off the scrubber lid, and blow hard to get the lid to pop. Not very professional looking and would be quite embarrasing in public as I like to think I am a pretty good hobby machinist - which I really am not I tried machining thinner walled PVC tubes, but after a few experiences when both boring the center or machining the OD of the tubes, of having to duck as the tubes flew out of the chuck I gave up. I tried doing it in both orders (boring first and turning the OD first) but no matter what I did I found that the tool put too much pressure on the PVC causing it to flex in the chuck and fly out. Pretty scary stuff as I usually turn PVC at around 1000 rpm. I am very impatient when turning PVC as it makes one hell of a mess. Aluminum is much less messy to machine. By using aluminum I managed to machine thinner walled tubes and as they are going to be tig welded on, the center tube is dead center, which I hope will make removing the lid easier. I only plan on using two latches for the lid for now (180 degrees apart) and I hope there are no problems with positive or negative tests. I have heard that some Meg divers have removed the two lid latches behind the divers back and are not experiencing any problems. The aluminum lid has two orings that seal to the inside of the cannister wall, and two internal orings in the exhale central tube. As the lid penetrates approximately an inch (I don't have the exact measurements with me right now) into the cannister, I hope there are no issues. I will post some pics of one of the prototype PVC lids tonight if I can locate the digicam. That one was never put into use and does not have latches or threads for O2 fittings and PPO2 cable glands. It was just too much of a pain to remove. More pics will follow as the unit progresses. Marc __________________ My MK15.x is really a BMR 500 and is as Koputai says a "Bastard immitation of a proper rebreather"!!
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29th September 2007, 00:50	#5 (permalink)
S. Marc Custom Title Allowed! Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Dec 2005 Posts: 199	Re: Generation 5 homebuild off to a good start Pics of PVC lid __________________ My MK15.x is really a BMR 500 and is as Koputai says a "Bastard immitation of a proper rebreather"!! Last edited by S. Marc : 1st October 2007 at 01:29.
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1st October 2007, 12:57	#6 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 384	Re: Generation 5 homebuild off to a good start Where exactly are the pictures?
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1st October 2007, 21:24	#8 (permalink)
kiwi_diver Alias - Ray Mansell Current Rebreather/s: Other SCR Other Rebreather/s: Other SCR Join Date: Aug 2007 Location: Auckland, New Zealand Posts: 157	Re: Generation 5 homebuild off to a good start Hi, when you hollow out the base for the water trap, have you considered making it a curve or V shape, and tapping a bung hole at the lowest point? Then you can drain it without dissassembly. I don't know if any other scrubbers have this feature but it's a suggestion. Cheers, Ray. __________________ Ray. == Latitude 36 South, where the deeper you dive, the warmer it gets! ==
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2nd October 2007, 05:39	#9 (permalink)
S. Marc Custom Title Allowed! Current Rebreather/s: MK 15.X Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Dec 2005 Posts: 199	Re: Generation 5 homebuild off to a good start Hi Ray, The drain idea is intersting but I have no plans for a drain in the bottom of the scrubber. I hate o-rings and extra possible failure points and I think the drain would just end up being a likely point of failure with more orings needed, and one extra tool that would have to be carried in the save a dive kit. If the unit is as light as I hope it will be emptying the can will not be much of an effort. The whole rig has been designed so all I will need to service it is a scuba tool. My distrust of oring seals is the reason why I am going to weld the exhale and inhale tubes to the lid. I considered cutting threads and using oring seals, but any time I machine a part that needs an oring I use two - paranoid I guess- and my machining ability does not leave enough room on this diameter head to use two orings for the tubes. A real machinist could do it but it is beyond my abilities. The base of the can will just be milled out so there is a water trap about 1 1/2 to 2" deep. I considered milling the base out in two sections with a dividing partition, to keep any water in one part of the base, but decided against it as I would lose 1/2 of the water traps capacity (depending on my position in the water). Marc __________________ My MK15.x is really a BMR 500 and is as Koputai says a "Bastard immitation of a proper rebreather"!!
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2nd October 2007, 14:37	#10 (permalink)
DanFountain Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Dec 2005 Location: Lake Superior Posts: 102	Re: Generation 5 homebuild off to a good start Quote: (Originally Posted by kiwi_diver) Hi, when you hollow out the base for the water trap, have you considered making it a curve or V shape, and tapping a bung hole at the lowest point? Then you can drain it without dissassembly. I don't know if any other scrubbers have this feature but it's a suggestion. Cheers, Ray. (Hijack) This is what I did with my "KISS Tribute" homebuilt - the canister has about an inch or so of space below the scrubber bed to collect any fugitive water, with the OPV positioned at the lowest point (during normal swimming). (Old picture of an early iteration of this project...) Also has a manual dump - it's from a BCD and a little stiff - the overpressure is not adjustable. A drysuit OPV might be more appropriate. Dan __________________ Try not. Do - or do not. There is no try. -Yoda
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