Anyone up to “no good” with design ideas?

onetime

I agree about the risk. Maybe I'm wrong but my guess is that the gas is more than likely coming out without burning or grinding since the smell of it is present all the time as noted in the MDS sheet.

Physical Data

Melting Point 172-184 C (342-363F)

Solubility in Water Insoluble

Odor Slight formaldehyde

onetime

A couple of reasons for me as a potential homebuilder (potential because I haven't put together a real unit yet just playing with a bunch of ideas on paper):

1. Developing a deeper understanding of RBs as a whole and identifying what traits/characteristics are most important to me.

2. I see lots of room for improvement in the Rebreather world. More streamlined designs, opportunities for bail out RBs, more efficient scrubber designs, recovery from floods, etc, etc, etc.

Most home builders are not thinking about creating units for sale to others. While there are some who would love to follow the model of Gordon Smith and sell their designs the odds are greatly against them (as you point out). For me, even though I'm confident that some of my designs could be commercialized I doubt I would go through the expense or effort nor would I want to take on the liability.

If I had to lay money on where the significant innovation in the Rebreather market is going to come from I'd put it on the homebuilder (or modifyer) rather than the current manufacturers.

Just my .02.

--Paul

bgpartri

I would like to hear the basis for that judgement.

In my view, homebuilt rebreathers are safer than commercial rebreathers. As far as I am aware, there is only one homebuilt diver who has died. And that was on a Frog, which is arguably a commercial rebreather. We all know how frequently commercial rebreather divers die.

I have no way of knowing why they are safer, but I think homebuilt divers are safer because they have a deeper knowledge of the principles involved and are VERY mistrustfull of their work.

__________________
http://www.shearwaterresearch.com

Good judgment comes from experience. Experience comes from bad judgment.

AD_ward9

Certainly not from google. I can post picis of Grilamid if anyone is interested and I have posted lots of pictures of rebreather parts we have made from Delrin.

The issue was outgassing. ABS outgasses a great deal more than machined Delrin. A box of ABS mouldings smells strongly. We have used different grades of ABS over the years, but I do not recall any which did not have a smell.

I knew that last post would warm things up a bit. I am very cynical of guys in their bedroom trying to outrun the industry. When I see things made from plumbing bits, too many failures I have seen come streaming back into my mind.
Cheers,
Alex

bgpartri

While Gordon Smith did start in his garage, Gordon's garage contained 2 injection molding machines, 3 CNC mills, 2 edms, lathes, cutters, etc. and a team of toolmakers. This is before he started diving rebreathers.

While Gordon did start this as a hobby, at that point he had the resources of a commercial scale manufacturing facility to indulge his hobby, and a long career of materials experience.

I still hear people talk about Gordon as a "home builder."

__________________
http://www.shearwaterresearch.com

Good judgment comes from experience. Experience comes from bad judgment.

onetime

I look at a "homebuilder" as someone who starts off with limited experience or training in an area before tackling a project and/or without the explicit goal of making it a business. Ability and resources to accomplish the feat don't play a big part in the definition to me. If Gordon's goal from the outset was to take his business into the Rebreather market as a commercial venture then I wouldn't consider him to be a homebuilder. But if, as my understanding is (only garnered from heresay and some writings on the internet), he started off with the intention of just building a few for himself and friends then I think the term fits. But I certainly wouldn't mind having those resources to transform my ideas into reality!

bgpartri

Yes, that's right. And he shows the innovation of a homebuilder too.

__________________
http://www.shearwaterresearch.com

Good judgment comes from experience. Experience comes from bad judgment.

onetime

I agree completely! If I had to split my bet on where the innovation would come from within the "homebuilder" community I'd put most of it on Gordon since he's got more ability to go through the different iterations ideas need to be refined and get them just right.

AD_ward9

Your point 1 is an interesting one we could debate: I would suggest one would get more experience by training and using different rebreathers, than knock out one in a bedroom, but on the second point, who is kidding who here?
1. What home builder has the facilities to design a more efficient scrubber?
3D flow simulation tools, a processor farm to run them on? For testing the results, commercial companies designing scrubbers have access to big test facilities, heavily instrumented, calibrated gas on demand, running for months. Thousands of man hours.

2. Recovery from floods. Just buy a pump and use an ExtendAir scrubber so the scrubber does not turn into whitewash as soon as it sits in water. Are we really talking about a big home activity to improve a pump?

3. Lower profile. Come on, look at the things people are producing. Most have the profile of a barn, whereas some commercial rebreathers are very low profile.

In my post, I said that the modifying a rebreather I had no problem with: home build mods often come up with good ideas, but an entire rebreather home built seems to be waste of energy. Why not get a job with a rebreather company and improve it from the inside?

Cheers,
Alex

Duncan Price

I've used PVC pipe to make the scrubber of a couple of my homebuilds. i was quizzed about this once. PVC does tend to creep a bit so its difficult to get close tolerences on seals (had to use a face seal rather than barrel seal). When PVC burns it does give off nasties but you would have more pressing issues if your Rebreather was on fire. Plasticiser migration from PVC could be an issue but believe me is very minor compared to other stuff you are expose to everyday and whilst diving. The plasticiser loading in rigid PVC tubing (used for water transport) is small.

Nylon is not good because it absorbs water. Perspex (acrylic) stress cracks in water - especially sea water. Polycarbonate embrittles with time especially with exposure to solvent.

Although I work in a Polymer Technology and Materials Engineering Dept. don't necessarily believe what I say.