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ZB-1, ZB-2: Scratch Build Cylinder design for limited Production by Zero Bubble.

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  • Hello all,

    I have yet to complete the internal arrangements for the ZB-1. I have turned back to working on the ZB-1/2. I really want to get this final end cap proto-typed, tested and certified by the end of the year. As a result I have spent a fair bit of time sanding and smoothing the end cap and the outer casing. However this was taken sideways by the decision that I took weeks ago to completely redo the shaft seal design.

    Having a 4 mm shaft meant that I had to take a length of 6 mm stainless rod and machine a section of it down to the required 4 mm for the seal and the oil lite bush and then onto the brass coupling. The shaft starting off at 6 mm for the bore of the delryn plastic gears that I was using. Then it dawned on me, "why don't I just use a 6 mm seal and 6 mm oil lites?' This would be so much easier..DUH!!!!!!

    This would mean next to no machining except a slight taking down of the shaft where it slips around the u cup seal. Why didn't I think of this earlier?

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    Old shaft, new shaft. Half the machining work, .more reliability and more surface area for a coupling to grip onto and just a more solid arrangement. Flat for brass outer coupling.
    Drilling a 2.3mm hole in stainless is a pain. I have decided to use this shaft in all the end caps even the ZB-2 with the direct drive. This will streamline production.

    The next step has been the redesign of the end "shaft support housing' at the very end. It did nothing. it was cosmetic and did nothing to hold the U cup seal in place and stop water coming in around the sides of the seal. So I took a long hard look at the designs that DM uses and decided to modify my own designs to press fit a 6mm U cup in place. What I found earlier in testing was that the old 4mm design was leaking as silicon was about the only thing holding the cup seal and place and stopping water from getting around the outside.


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    Seriously Crap set up.

    So I got cracking with a material that I like using on the lathe, Delryn, also known as Acetal. This stuff turns down beaut and was ideal for getting the precise internal dimensions for making a housing that would press fit the 6mm U-cup, with an outer dia of 10 mm nice and snug.

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    So i have completely redesigned the internal parts of the seal minus the outside housing which was big enough to fit the adjusted parts. Now the silicon doesnt do the work of keeping the seal in place, the press fit outer support does. To make it even more cunning the inner support has a lip that fits in and under the outer support to give a little more sealing to boot!.. Nice...


    More later.

    David H

    Comment


    • where do you get your gears

      Comment


      • Hi Rick,

        Did you not get my reply last week?

        Gears and Sprockets in the UK.

        https://www.gearsandsprockets.co.uk/

        Dave H

        Comment


        • The Acetal parts are what comes with the cylinder or will you cast them in resin?
          Jörg

          Comment


          • Hi Jorg,

            The gears will be the moulded acetal parts from the supplier. If I were to cast the part that would be IP Infringement. Also I think that if I were to cast gears the teeth would be brittle.

            Good to hear from you.

            Dave.

            Comment


            • No,i meant not the gears but the parts of the housing. Do you produce every piece on the lathe or am i looking at masters on the shaft in your last picture?

              Jörg

              Comment


              • Thank you I must have missed it somwhere

                Comment


                • Hi Jorg,

                  Yes they are the acetal masters. All the seal components will be cast out of Urethane, the only exceptions being oil lite bushes and rubber seals.

                  Dave.

                  Comment


                  • Hello all,


                    I have completed the acetal masters of the parts for the new 6mm seal assembly. All I had to do was to get the silicon out and create the molds. So pull out the particle board base and once again cut a profile for all the parts to sit in slightly recessed. The red shows the proposed air vents and the pouring channels for the urethane. Inside the acetyl parts will be play doh to create a seal around the parts and define the part line of the molds. The Balsa strip is standing in for the pouring channel.

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                    First Silicon mold half has been poured. Time to transfer the master parts into the half ready to mold however first I peel and clear away all the residual play doh and then I give it a good rub of lanolin as a release agent.

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                    Then pour the second half of the mold.

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                    In the meantime I have further run the ZB-1 underwater in the pool and run the motor for a lot of it. I have decided after about 5 hours worth of testing to take it apart and look at how the gears and parts have worn and fared. Looking mainly for wear points (mainly sheared or brittle teeth) , any corrosion, possible points of leakage and so on. I firstly undo the screws and then run a knife around the part line of the outer housing to pop it off. This prototype already had a 6mm seal installed. I decided to leave it, test it whilst at the same time creating identical parts as masters that you see here being used to create the molds.

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                    First I have a look at the 6mm seal that I made out of Acetyl masters. It looks really good. The oil lite bearings have held up beautifully.


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                    The mess is really just silicon. I could not find any moisture.

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                    There is a hint of green around the Oil lite bronze bushing. Seriously ,Bronze can't resist going green can it.. Only a hint. Most importantly the gears are not showing any signs of uneven wear or shearing. They are still engaging withe pinion gear. Overall, happy.

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                    These two cylinders are good so far. The ZB-1 I now consider tested and ready. The ZB-2 I'm still not convinced that I've got the direct shaft alignment caper down pat. I need to find a process that gives me a really centric shaft.


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                    Big difference between the 4 and 6 mm shafts.


                    Onward..

                    David H

                    Comment


                    • Nice surgery, David! Is there a brown spot on the motor pinion? Very interesting seeing the assembly after a fair time of duty!
                      Jörg

                      Comment


                      • Hi Jorg,

                        I suspect a tiny bit of rust at the end of the Motor shaft. Maybe a shot of WD-40 or some kind of rust resistant paint. Overall I was pretty happy with how the components have held up.

                        I have since re-assembled the stern cap of ZB-1 and am now working on the trays and building the Ballast system assembly and all the electronics. However my main focus has been recently on completing the ZB-1/2. I left it a couple of months ago whilst finishing off the fit out of the ZB-2, testing it and also testing the stern cap of the ZB-1. I finally wanted to get all three end caps pretty much done as I wanted seal testing to be completed by January if possible.

                        The ZB-1/2 is as mentioned before, a single motor twin shaft. This should reduce the cost, make synchronization of shaft speed pretty much exact and mean that there is only one possible leak point into the seal. It also from a production point of view, avoids the need for a direct shaft on motor friction. The stuff of night mares. I have found that the gear system on the ZB-1 to be reliable, I like it. Drilling a hole through the stainless shaft to lock the gear on has been a technique that i have finally mastered. Drill slowly.

                        The ZB-1/2 end cap hadn't seen much further development so I took it and continues sanding and smoothing down imperfections. I could certainly look at how the new 6mm shaft and seal would look as I had already created all the new casts for this

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                        Lots of layers of primer and some putty sanded back. Hard to get into some of these tight areas. I also filled up the center hole in the middle that was originally there to turn the initial end cap design.
                        Here are some of the delrin prototype masters of the new 6 mm shaft seal. The right shaft already has a 6 mm cup seal snugly pressed around it. I also ground back a flat on the ends of the 6 mm shafts. These look a lot better and more solid.


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                        So from here a lot of further sanding, smoothing and lots of assembly, re-assembly and fine adjustments to make sure that the teeth engage smoothly and all the components line up. It's a little hard when you can't see whats going on inside. I wish I had X-ray vision...


                        David H



                        Comment


                        • What if instead of accurately machining your end cap you oversized your shaft holes and have your bushing in a plate that you glue \ secure to the end cap. Your seal caps already look like they float to the correct position to align with the shafts as the sealant dries. You could probably get a machine shop to punch you out thousands of plates to great accuracy for the two shaft gears and bushing assemblies. You might even mount the motor on the plate.
                          Last edited by Scott T; 11-29-2020, 09:55 PM.

                          Comment


                          • Originally posted by Scott T View Post
                            What if instead of accurately machining your end cap you oversized your shaft holes and have your bushing in a plate that you glue \ secure to the end cap. Your seal caps already look like they float to the correct position to align with the shafts as the sealant dries. You could probably get a machine shop to punch you out thousands of plates to great accuracy for the two shaft gears and bushing assemblies. You might even mount the motor on the plate.
                            Damned good idea! That would eliminate the issue of resin's tendency to change state with no hard and fast rules as to shrinkage amount after the cure.

                            David
                            "... well, that takes care of Jorgenson's theory!"

                            Comment


                            • Hello all,

                              Thanks Scott, Dave.

                              At this point all I really had to do was clean up the parts and make sure they had acceptable surface finishes for the creation of the silicon molds. However there was two components that I haven't added as yet to the end cap and they are the two supports either side for the electronics tray. As is custom, these are made out of Renshape and simply sanded and cut to size. I decided to create two drill holes through these for a little extra support and make the thickness continue all the way inside and not taper off like I had with an earlier design.

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                              Here I have aligned them up so that the top surface is just a fraction of a mill above the edge of the motor can so that the acrylic/ Lexan or sheet metal electronics tray will not be bulged upwards be the motor getting in the way. I have also slightly tapered the outer edges to make them slope in. This means that if I have to shave the outer surface down a lot on the lathe to fit the lexan then a little bit less surface area getting in the way.

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                              After this I pushed filler in around the gaps between the end cap and the two supports. It can be tricky to get right into the lower corners where the supports but up against the inner surface of the end cap. This took a while and after done more coats of pray filler and they grey primer.

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                              A rough new coat of spray putty. Inconsistencies in the surface make it look like a dogs breakfast however I soon show it who's boss.

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                              I'll get around to molding next time.


                              David H


                              Comment


                              • The bigger shafts look promising, as does the new endcap.robust.i like that. Very unique streamlined design, like an old "Silberpfeil" racing car. Maybe you should add a serial number to every unit you build! At how many rpm are you running those twin shafts?

                                Jörg

                                Comment

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