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

[Davidh]

Hello David,

Thanks for getting back so quick. I have pretty much created parts very similar to yours and as you have seen, put them through testing for fit and water tight integrity. They have passed. I will be using this design. However I could really do with you input about my previous post about orientation of parts from molding. The emphasis being on how to mold these parts as accurately as possible, which I am confident I should be able to do.

thanks,

David H

[He Who Shall Not Be Named]

Hello David,

Thanks for getting back so quick. I have pretty much created parts very similar to yours and as you have seen, put them through testing for fit and water tight integrity. They have passed. I will be using this design. However I could really do with you input about my previous post about orientation of parts from molding. The emphasis being on how to mold these parts as accurately as possible, which I am confident I should be able to do.

thanks,

David H

The best practice with cast parts with a bore to them is to orient the tools (molds) flange faces -- the parting plane -- parallel to the axis of the parts bore. Like the tool on the left, not the tool on the right. Examples of best practices pictures below, my friend.

[Davidh]

Thankyou David.

Gold as usual.

David H

[Davidh]

Hello David,

just one thing,

could you post some photos showing this detail in a little more depth?



and





This is what I am really interested in. I will soon be posting the write up on the push rod glands. I have already molded and made some just like yours.
These pics here show parts that are very similar to the ones I want to mold.

Once again,

Thank you for the info and advice...

David H

[He Who Shall Not Be Named]

Hello David,

just one thing,

could you post some photos showing this detail in a little more depth?



and





This is what I am really interested in. I will soon be posting the write up on the push rod glands. I have already molded and made some just like yours.
These pics here show parts that are very similar to the ones I want to mold.

Once again,

Thank you for the info and advice...

David H

BEHOLD!!!!















David

[Davidh]

Thank you David,

What I was getting at was to have a closer look at the silicon mold that created those outer supports. However thank you for the added pics.

Time to create the molds for the push rod glands.
For many years I have been using a push rod gland simply made up of a small off take barb combined with a small piece of nitro tube and an O-ring. For some time I have been looking at Daves, push rod seal design and though that it was beautifully simple. I thought that I could produce something like that. I had tossed up the idea of producing a design similar to what I had been using however thought I would give the embedded O ring gland a try.

Weeks ago I machined up a series of brass pieces that would serve as the outer housing for the gland. I machines a flange on the out side to differentiate a bit from David's and as a stopped for the outer end. I then took a piece of 2.39mm brass rod and ordered some small o rings from a Beaut little supplier in the US called "O-rings and more". Swift delivery. I could have used a smaller diameter push rod, but this in the one I have been using for years.It is a good dia.





Eventually I reduced the flange width on each of these. As you can see the O ring looks pretty bit compared to the diameter of the brass gland. This caused concern, however I pushed ahead anyway confident that the pour of urethane would close any gaps.

I took a block of MDF and once again started creating the structure for creating the silicon molds. This involves taking the parts and arranging the layout for them. In this mold I also would produce the two parts for the electrical cable conduit through the end cap. The development of this could be another write up.. one day... I have pretty much taken Davids advice, that you should really angle your pieces to the horizontal so that all the bubbles will rise to the top.






The Acetl white pieces are the electrical pass through's for the wires in and out of the Cylinder. KISS. These brass tubes are hollow and allow the wires to be passed through, glued in and silicon'd.





The balsa strips are the runners that run to the top of the mold. The wire strips are the air vents. Around the runners I will press down Play-doh to make funnels and seal around the flat planes of the parts in their place.












Above: The first half of the mold has cured. I have unscrewed the side off that butts up against the play-doh funnels. I will then pull the rubber mold off the base. You have to make sure that the silicon has clearly cured. If the outer layer of silicon has set but it is still liquid immediately underneath and it tears as you pull. That's not great.



Once this has come off I can start turning around the mold for the second half.



The darker lines are where the paper clip wire for the air vents have been removed. I have filled them with extra lanolin so that the silicon from the top mold does not fill them.
I am careful to remove all the lanolin off around the register bumps.



Here is the finished mold. The inserts of brass come out. All they do is create the hole and hold the O ring in place to be embedded.





Close up and pour the mold. I will go into this next time..


David H

[Davidh]

I am always saddened when I hear that one of the 24 have left us..

I only just heard, because it didn’t even make the news once again, Alfred M Worden, Command module pilot of Apollo 15 has left us.
The first CMP of a Lunar ‘J mission’ and the record holder of being the most isolated human in History has gone.

This photo shows Worden in the middle with David Scott on left and Jim Irwin LMP on the right.


We only have Commander Dave Scott left from 15.

These guys have always been heroes of mine. The United States should be proud of them. I was only 1 month old when the last mission landed. I wish I could have seen them

Regards,

David H

[Davidh]

Hello all,

Bunkering down for this Covid-19 business. Doing all my classes from next week on-wards via Zoom. But this does give me less commute time which could potentially mean more workshop time, Yay!

So I placed the brass insert rods into the mold and then some brass tube into the Electrical connectors that I have made. Slip O rings over the solid brass inserts to embed into the Polyurethane. Then close up the mold and then strap two pieces of plywood to either side and rubber bands, then mix up and pour some urethane. Place the mold into the pressure pot and sit at 2 ATM for about 1 hour just to get really stiff and fully cured.



After that, de-mold the parts. These have just come out of the mold and need a little sanding. You can clearly see the rough part line running down the axis of the top gland part and down the electrical connection off to the right. I then pulled out the brass rods from the Glands and checked for friction. The 'O' rings being very well embedded. There is a little friction they should certainly seal. Getting some fine 800 grit and giving the rod a fine smooth sanding just to reduce the friction. Mind you the servo's that I use should have plenty of torque and overcome the stiffness that is there.

So i cleaned up two of the glands and pressed them into the two top holes of the stern end cap on the test piece that I have spent a fortnight testing with the shaft housings. I used some silicon to glue and seal around the gland as it was pressed into the end cap. Tight fit. As long as these cast parts don't leak and don't create too much friction then i will not have wasted too much silicon!



This pic shows the push rod gland in place and not leaking. It was a little hard to push and pull on the brass shaft. So I decided to bend up these small lengths so that I could push and pull underwater to check for sealing.



So far so good...



I then took the electrical connectors and ran two wires through. I then ran some silicon around the outside of the plug and placed it through the hole in the front test end cap. Had to mark out and drill that first. Then pushed some more silicon into the brass tubes and some heat shrink.


Heat shrink over silicon, over wires...



The plug in the middle of the Renshape test piece is where the original hole was for securing to the lathe. I then filled this in with a small piece of Renshape. Then I will fill over and sand.



This allows me to run cables from the inside out to a battery to really run the motors underwater easily. Looking really good, no leaks...



These are the first cast pieces for the design. They don't leak. I am very happy with this. All i need to do now is just check that the brass rods that pass through the gland don't create too much friction when I put these into limited production. The embedded 'O' ring Idea is brilliant. Next will be the creation of the molds for the stern motor shaft supports and housing. Then once again the testing of the first production pieces just like here.


Keep isolated and keep safe everyone...

Reduce your cabin fever by talking to me....

David H

[He Who Shall Not Be Named]

Here's my trick to open up the bore of the pushrod seal body so you reduce the friction between it and the pushrod: Ream out the bore with a drill bit that is about .002" larger in diameter than the pushrod you are using. First coat the bitt with bee's wax then open up the seal body bore with it. The wax will let the cutting edges of the bits flukes push the rubber seal out of the way rather than cutting the O-ring, but the bit will still cut into the resin portions of the seal body's bore. Further: lubricate your pushrod with silicon grease, AKA 'distributor grease' available at car supply stores. These two steps will greatly reduce the friction between seal and pushrod.

David

[Davidh]

Hi David,

Nice, will do. Got that shaft extension write-up? I’ll understand if you’ve been too busy.

Dave.

[Davidh]

Hello all,

The push rod gland /seal and the electrical plug are the first two pieces that I have made molds of and have cast the first production pieces. I decided to turn to producing the molds for the shaft supports, these are the round parts that support each shaft as it comes out of the rear twin end cap.



So that means the Seal inner support, outer ring and the shaft support ring. This last piece is really cosmetic and simply keeps all the silicon looking neat. Molding these parts made me stop and pause as i thought about how i should orient the individual parts relative to the parting plane. Should i have the parts perpendicular or parallel. I asked HWSNBN and he responded about them being parallel with the part plane. I have largely taken this advice however with the Outer ring I did decide to mold it in a vertical position with the resin coming down from on high. The inner support and the shaft support housing will me molded parallel to the plane.

The prototype master parts of the seal inner supports are brass. They have a fairly large diameter bore in the middle which would mean that I would need to fabricate the biggest insert that i had ever made. I decided to machine up some pieces of Delrin / Acetyl to make the inserts. (really nice stuff to machine actually) These turned into a really tight fit. They needed to be precise as the oilite bearings should have a nice fit inside them.





Once they were done I could start fabricating my usual mold board arrangement. This mold would feature 4 pieces, the two seal inner supports and the two as mentioned shaft support housings.
I take a piece of MDF and mark out where the parts are going to sit. Them I start drilling shallow holes around the profile are and then continue with a Dremel.



I hold these pieces in with Play-doh. The black lines are the air vents, reservoir space and the channels for resin. The white areas will be replaced with registering points made by shallow drilling.



Finally I use paper clip wire to create the air vents. Bend them to shape and super glue them to the base along the lines. The channels are made from Balsa strip glued down and the funnel , reservoirs are created with play-doh once again.



Screw four sides on and seal along the edges if needed and ready to pour. I use a pen to mark out the ideal height of where the silicon should come up to . You want a reasonable level of thickness but too much and you have probably wasted it as it will reach optimum support after a certain number of mm above the work. Its been a trial and error kinda thing..




Mix up and pour the silicon. Leave for a couple of hours as it sets and work on other things. Then come back and unscrew the sides off.


The silicon picks up every little detail. The wire air vents are sometimes buried inside the silicon. This is because the wires may have been sitting slightly off the flat surface of the mold board. I will either leave the wire in there for the next half or I will fill these vents full of lanolin so that the other half layer doesn't see the vents fill with silicon. I rub lanolin all over the molded half, strip the original wooden base of any left over wire, balsa or play-doh and lay this flat. I then replace the balsa channels in to the half channel that they molded, ready for the next half and fill in the cavity formed by the play-doh that will become the other half of the reservoir. Sometime i'll use a knife just to open up some of the channels.



Then box it up.



Repeat the process. Pull apart and have two halves that you can pour resin down. As you can see a fair amount is used up in the channel and the reservoir. This is just one of those things that you need to accept as the reservoir is there to provide extra material in that brief window of opportunity when the unit is under pressure but not going 'plastic' yet and requires a little extra as air bubbles collapse. You have to work quickly. The air vents get a filling too!



Happy with how these parts turned out. The delrin inserts of the inner support have done a great job. After taking them out and cutting of the fettling, these supports took the Oilite bearing beautifully!

Next time the outer ring..

David H

[Davidh]

Hello all,

Powering ahead with design and producing the first masters for this cylinder design. As I am now teaching all my classes from home via zoom I have no commute time my Garage to work after school. As a result I have been able to move along further than I expected at this point. As you can see I am very much at the stage of tooling up the masters with silicon molds into the final urethane parts. I have been happy with the level of precision that these silicon molds afford when producing parts that have to be dimension-ally accurate. This has been shown with the pieces that came out of the seal inner support parts. They hold the Oilite bushes perfectly.

Now I am creating the molds for the outer ring. This is a larger part and reminds me a bit of the pumpjet propulsor shroud I mastered a couple of years ago with the Project 955 Borei. I have decided to mold this outer ring in a similar way with the axis of the part perpendicular to the mold plane. So in other words, the ring will be sticking up.



These outer rings have been mastered in Renshape. Once again I got a MDF board to mount the pieces on. The process that I used for this mold is in essence similar to how I do all my parallel molds but the variation will happen further down the line. The containment vessel will be a 100mm dia piece of PVC pipe I 'borrowed' from the school maintenance guys. They would have chucked it anyway. I mark out the outer limit of the mould and drill holes for the registration points. I then drilled out two circles as I would mount the outer ring in. I did'n't want the mold plane to line up with the bottom edge of the part. The part line can run around the tapered out side of the part.

I placed a raised rectangular block on the mold plane in order to help orient the two mold faces as they join.



The inner part line will be near the top of the parts. If it were down at the level of the board, then you would have a major problem with the tapering of the part making it really hard to extract the part. This would be because you would need to compress a lot of silicon on order to get the narrowing end out. So I filled the inner area with Play-Doh to create a part line closer to the top of the unit. I then sealed around the base where the outer ring sits lower then the base.



Get some silicon and run it around the base of the pvc pipe and stick it on the circle perimeter. I actually made this series of molds at the same time as the one for the other smaller parts. Then pour the Silicon and wait....



The PVC pipe pretty easily lifts off around the hardened silicon and then pull it off the MDF base and hey presto, you have one half.



Having two levels of parting line makes removal of the masters easy, just as it would the cast part when the molds are used. I then rub lanolin onto the silicon as a release agent. At this point I had to make a modification to the masters. I would need to make some additions to the top rim of the parts as seen here (which are actually the bottom of the outer rim that buts up against the end cap and is silicon-ed.) I would need to add a pouring channel and funnel, along with a "Bubble-ring" or bublle catcher. Previous experience had shown me that air can easily get trapped up the top of the casting and that extra space would be needed to avoid this. My bubble ring involves taking a piece of cardboard and cutting a curve profile that allows extra material to fill above the upper level of the cavity and air bubbles deflect up come curved upward channels and out. (That's the theory anyway).


It is hard to see but the balsa blocks are a attempt at making a a funnel above the channel. One master has the bubble ring in place. This is simply glued in place
with superglue. At this point i need to make sure that the pour height of the Silicon does not exceed the height of the pour channel, funnel and the air vents arising from the bubble ring.





Rub the whole ensemble with lanolin to act as the release agent. Wipe any excess lanolin off between the register points and determine the amount of Silicon needed.
I find that using rice, poured into the mold and then poured into the cup for mixing the Silicon does are really good job. I then have to spend a couple of minutes flicking out the last bits of rice stuck down lightly by the lanolin.



The tops of the Balsa funnels can be seen. You can just make out the tops of the air vents. Leave for a couple of hours and pull apart...



The two parts of the mold. You can just make out the groove rim caused by the bubble ring in the far half around the base of the recess. Light spray of stoners mold release agent, fire up the air compressor and get the pot ready. I have a new supplier of Polyurethane resin. The one in Sydney is good but charges double the cost in freight considering it has to travel 150kms approx. This new company in Melbourne charges less and it travels about 1,050 kms.



Mix up the resin, pour and put into pot. Come back in an hour....



Pull these parts off, cut off the excess flashing from the Bubble rings, give a sand down and see how the fit is this the seal inner support and the Oilite bushing..



So far so good...



All parts fit. The Oilite as mentioned goes in snug to the Inner shaft seal and that then goes in a firm fit to the outer ring. I have had to work my way around the inner top rim of the outer ring to make a nice seat for the U-cup but otherwise a really nice seat. This is looking good.

Any comments, suggestions ideas would be appreciated..


David H

[Davidh]

Hello all, quiet of late.

So I now have all the small components of the stern end cap cast with corresponding molds. Now it was the time to finally get around to molding the end caps. Apart from Hull top molds, these will be the largest silicon molds that I have produced and for some time had been a little apprehensive about how to go about it and that the molds would turn out well enough to produce acceptable parts. I have been more confident about it lately after all the silicon molds that I produced for the stern shaft parts proved to produce parts with the right amount of precision. All the cast parts fit where they should with just the right fit, so I have been really happy about that.

For several months I have been working up the detail on the end caps both front and back end. Lots of sanding, filling and sanding, then the odd resin coat then sanding down to give a beautifully smooth finish. The biggest challenge I have found has been getting the inside of the cap as smooth as the outside, with rims, bulges for screws and holes getting in the way. The finish is acceptable and the motors will but up nicely against the inside surface. You aren't really going to pay much attention to this surface when its up and running.



I have spent a fair amount of time looking at How HWSNBN does his end cap molds. By the number of pics online you would have through he's done hundreds, How many have you done David?
In a lot of ways the set up for these should be easier than how I usually do molds like this. I wont be adding air vents and won't use Play-doh to form channels and funnels. The set up should be rather quick.

Like how I molded the outer rings, I decided that I didn't want the part line to be in line with the face of the end cap. So I got two pieces of plywood from the scrap bin at school in the one day I was in and drew a circle around it the same diameter as the end cap . I then cut that circle out and filed it down so that the end cap would fit through it.



I then glued this piece onto another piece of ply the same size. I then took the 90 mm segment of PVC pipe from the earlier molds and drew another ring around the outside. This area would then be drilled shallow to create the register points. Once again to be able to orient the mold, I placed an inverse rectangular block to stand out form the rest and give a point of orientation. I needed to create breaks in the holes so that the silicon going into the holes wouldn't go all the way through. So I pressed Play-doh into the holes to create a shallow impression where needed..



Wiping this sideways to create a level flush surface and then mounting the outer face of the end cap onto the recess. I then took out the excess from the other side so there would be a half-half arrangement when it came to the two sides of the holes.



I then pressed play-doh around the sides. (I had no idea when i was growing up in the suburbs of Canberra all those years ago how useful this stuff would be.) Then wiped it around and made it flush.
I had to stick down tape to cover the holes otherwise I would spend all this time digging the Play-doh out of the holes. The light grey is a spray putty over the grey primer. Usually not the way around that you do it however the finish after sanding is ridiculously smooth.



This photo shows in further detail the pressing down of the play-doh to make the silicon mold for each hole meet halfway.



Once i am happy with this and all the excess play-doh has been wiped away, I took the 90mm pipe and ran some formed in gasket silicon around the rim. I tried running it around the outer edge as
much as possible so that when the pipe was pushed down it wouldn't so much squish into the inside. I then had to run a long stick to wipe up any siliocn that had.




Let this dry. It doesn't take too long, then pour in the rice to get the quantity right. Once that was determined and pesky little pits of rice summarily picked out of the mold, I then mixed up the required amount of silicon and pigment and went for the pour. There must be about 10 mm worth of silicon above the rim. This mold is going to be solid. Fingers crossed it would get all the detail.




Yep its a solid mold and to my great relief, the detail is really good. In this photo I still need to trim off the flashing around the side and wipe off the races of Play-doh.
The detail of the holes is good. The grooves inside the side walls also came out really well.



This is a solid chunk of Silicon. It's a bit disturbing. I really like the smell of this stuff. I then had to put the part back into the mold. I rubbed it with a thin coat of lanolin but not before rubbing the whole mold in the same stuff to act as a release agent for the next phase of mold making.




Slide the 90 mm PVC pipe over the mold and pour the next half.



An even more solid mold. This thing is thicker than the Reich fuhrer bunker..



Pull these part and then pull the part out..



as you can see I have also cut the funnel in one side. I have made mine without a deliberate 'reservoir' of sorts. I am confident that the resin that I sue which remains liquid for a little longer then the last stuff I have been using will pour really well and this wider funnel with provide the extra material for bubble collapse.



A fair bit of Polyurethane goes into each end cap. This is a bit chunk of urethane so I thought I would give the mold longer then normal in the pressure cooker. I left it for about an hour and then came back. Pulled the lid and the funnel had hardened.


Hey presto, The part came out and was hard and rigid. The surfaces were flat and there were no bubbles and loss of detail especially around the grooves where I though there may be. Really nice detail even the branding came out good. Wink, wink..

Happy with the result.


Until next time.
As mentioned, any ideas or comments welcome. David, something about shaft extensions?....

[He Who Shall Not Be Named]

Well done. David!

[Davidh]

Hello all,

I have now poured a couple of stern end caps out of the mold and all of them have been totally consistent. The first thing to do is cut off the pouring sprue that sticks out. The pouring aperture is obviously a good size. All the air comes out and the molds are bubble free.

A couple of weeks ago I made a wooden lathe fixture to fit the end cap on it in order to be able to shave and machine it down to size. This fixture is designed to take the front and the stern end caps even through the fixing bolts are in different locations for each. The fixture holes for the stern cap being the motor shaft holes and the holes for the front are for the electrical conduits. In the front end cap they are close to the sides and so the wingnuts wouldn't really work. So I decided to cut a flat piece of Acrylic, some tube, and a couple of washers slide down a washer slide over the tube and another washer then the wingnut over the top took it above the level of the outer rim.









The fastener is bolted through the slots in the face plate. The material between the end cap and the wooden fixture block is sponge. This absorbs some of the pressure from the screws being tightened
down securely and helps to not mark the end cap. Then you spend however long just getting the end cap aligned and centered. This can take ages. It is one of those things I don't think you can ever get perfect but you can get it within reason and limits. After about 30 minutes I pretty much had the End cap where I wanted it with almost no perceptible deviation. The noise of the cutting tool was almost totally constant.

Turn on the lathe and start making passes. Polyurethane shaves very finely and leaves a smooth surface. I had to get my calipers out and take regular measurements as I did not want to take this down to far and have to re-cast another piece. I also grabbed the Lexan and pushed it up against the piece for checking. I did this a few times without the 'o' rings just to see how the flanges would go with the fit.



Once the inner flange had been machined I them needed to re machine the "O" ring grooves. I marked them out with pencil from the original grooves that were there and then used the
parting off tool with a tiny amount of sideways movement to create some width. In the meantime checking the fit with the tube and slipping on "O" rings to get a =n idea about the fit. I want these
to be pretty tight.



When I was happy with the amount of material take on off the sides I got a piece of 400 grit and gave a light sanding to get it smooth. There were a couple of very small pockets of air bubble but nothing bit or near the corner of an "O" ring groove that may cause problems.








At this point could take off the end cap and see how the end cap looked from all angles. The end cap is a really tight fit. All that has to be done now is to get a file into the holes and
get them smooth and round. Then start assembling the twin motor mount pieces and screw in the two motors.



First to go in were the two pushrod seals. These are still a little tight and will need Davids suggestions put to them to loosen them up a little, but,, they don't leak. Then after this take the 2.6mm screws and bold the motor from the outside in against the inner surface of the endcap.




The next work is just the installing of the motor mounts, Straight forward.

David H