Tool time.

[He Who Shall Not Be Named]

Thanks David and everyone,

I have another series of questions that I hope you don’t mind answering, even though some aspects we’ve been over. I suppose I just need a little further clarity.

Leaks in drive shafts.

David, do you guarantee that your shafts don’t leak? Or is this a hot potato? I can vouch I have one of your older SD’s and it don’t leak. But are you that confident in the product?

My latest design hasn’t leaked until today, So I was really disappointed and I am assembling the first ZB2 for a customer and am currently checking the shaft seals and Uh oh, a leak.

Now you know my seal design is similar to yours, I use an Oil lite Bush with an outer housing and a U cup seal lightly glued to the top of the outer housing and the shaft is pushed through. My biggest unknown is how much grip should the lip of the cup seal push around the shaft. Obviously when you push the shaft through the lip it should flex outwards and wrap around as you push the shaft up. I am still trying to work out the fine balance between how tight this should be.

I am guessing that if it’s tighter then the motors just pull more amps? But also if you run the motor for longer periods out of water then the lip rubbing against the shaft will cause wear?. Do you not run the shaft out of the water for any length of time?

I am am convinced that there is something really subtle and tiny that I have missed, maybe it’s just getting the tightness of the lip on the shaft just right? Maybe my lip seal isn’t tight enough?

I have some pics here of my set up if it helps, I have looked at all your photos of the shaft arrangement that many times. I hope my line of enquiry make sense.

Thanks for your time,

david H.

I would say that 90% of the shaft seals I assemble and test are leak free -- this testing of course is part of the MSD/SD test and certification process each WTC gets here before sending it off to the customer (these days, The Nautilus Drydocks).

Leaking shaft seal assemblies are either repaired or replaced. The major cause of a shaft leak is a crack or scratch of the seal inner bore where the cup-seals outer edge makes contact; that portion of the rubber that makes the watertight seal between seal and inside bore of the shaft seal body. My seal bodies today are machined pieces of polyurethane sprue. A cracked or scratched inside bore would permit water to flow around the outer rubber seal lip, through the crack, letting water into the motor bulkhead.

I see that you are adhering the rubber cup-seal outer lip with adhesive. Stop doing that! Use silicon oil (not silicon grease!) to lubricate the outer and inner seal lips during assembly.



Typically the manufacturer supplies the cup-seal with an inner lip diameter slightly smaller than the stated diameter of shaft it is supposed to seal against. In our sizes that's a few thousandth's of an inch smaller. They don't have to be tight.



Are you using proper cup seals or the spring tensioned seals used by the piston crowd?

David

[Davidh]

Hi David,

Thanks very much. I am using Cup seals, not the spring ones. Not simmering. I suppose it would make sense that the outer edge of the cup seal not pressing up,adequately against the inner dia of the housing would be where the leak is occurring. It’s a larger circumference.

I will give silicon oil a go.

David H.

[He Who Shall Not Be Named]

Hi David,

Thanks very much. I am using Cup seals, not the spring ones. Not simmering. I suppose it would make sense that the outer edge of the cup seal not pressing up,adequately against the inner dia of the housing would be where the leak is occurring. It’s a larger circumference.

I will give silicon oil a go.

David H.

There you go: reduce the bore diameter of the seal body, use

[Davidh]

Hello David,

I hope you and Ellie have a good Christmas.

I have a request of you. A couple of months ago I was looking through some photos of your work (today’s work) and you were testing motors. (Brushed) you had a pic of an ammeter attached to a circuit with a speed controller. I assume that you were seeing how many amps were being pulled by a given motor on a circuit. Could you possibly upload any more pics of this set up?. I am testing endcap assemblies with motor at the moment and have an amp meter. I Am just not sure how to set it up.

I have been running tests on my ZB-1/2 single motor twin drive and have found that the motor gets warm, but one of the leads gets really hot really quick.doing something wrong somewhere. I don’t know if there is too much friction on the shaft?

any suggestions...?

Thanks,

David H

[He Who Shall Not Be Named]

Hello David,

I hope you and Ellie have a good Christmas.

I have a request of you. A couple of months ago I was looking through some photos of your work (today’s work) and you were testing motors. (Brushed) you had a pic of an ammeter attached to a circuit with a speed controller. I assume that you were seeing how many amps were being pulled by a given motor on a circuit. Could you possibly upload any more pics of this set up?. I am testing endcap assemblies with motor at the moment and have an amp meter. I Am just not sure how to set it up.

I have been running tests on my ZB-1/2 single motor twin drive and have found that the motor gets warm, but one of the leads gets really hot really quick.doing something wrong somewhere. I don’t know if there is too much friction on the shaft?

any suggestions...?

Thanks,

David H

New type brushed motor are examined to determine no-load and stalled current draw for a specific voltage. My torque meter are my pinkies and wrist. I'll tear into a new motor type to get ACTUAL dope as to number of poles to the armature, winding turns per pole, gauge of the windings wire, and if spark suppression is provided.

You always wire the Ampere meter is series with the device whose current load you are measuring. I only bother with these numbers because they drive the type BEC and fuses I will select to control and protect the motor.

Increase the cross-section (wire gauge) of the power cable if it gets warm -- heat generated is inversely proportional to the conductors cross-section. The power cables must be able to handle the load of a stalled motor getting full power from the ESC.

Hint: fuse the motor, not the battery! That boat ain't coming back up if hotel services go dark.

Here's how to wire the Ampere meter and some other shots showing how I hook things up as well as how I test things:

















































David

[Davidh]

Hello David,

I hope that you are enjoying your retirement. Well deserved..

I have a question for you when you have the time...

As you may remember I developed a twin shaft single cylinder end cap for my ZB range of cylinder last year. The gearbox for this unit featured three oil lite bushes to support the shaft. My main question that I am asking about is whether I can reduce the number of bushes used. I am simply after your opinion.
This is what the ZB -1/2 looks like.



I have a drawing that shows the design as is and one that shows the proposed new idea. I intend on taking out the middle flanged oil lite bush, labeled number 2. I would replace it with a washer and so this would leave just the flanged bush at the back behind the spur gear at the back of the end cap and the on flanged one inside the seal unit siliconned to the front of the gearbox housing.



The reason for me doing this is to reduce the complexity of the unit, reduce friction but mainly to reduce the preciseness of shaft alignment as possibly being an issue.
If I can make the design less reliant on having the shafts absolutely perfectly perpendicular to the face of the endcap then alignment with the shaft seal housing will be less critical. Sure I want the shafts to be parallel with each other but I want to build less ‘critical’ points into the system. It also means that if the outer gearbox housing doesn’t actually precisely aligned with its base it won’t chafethe shaft against the side of any cast parts.

I hope this this makes sense?

what do you think?

David H

[He Who Shall Not Be Named]

Hello David,

I hope that you are enjoying your retirement. Well deserved..

I have a question for you when you have the time...

As you may remember I developed a twin shaft single cylinder end cap for my ZB range of cylinder last year. The gearbox for this unit featured three oil lite bushes to support the shaft. My main question that I am asking about is whether I can reduce the number of bushes used. I am simply after your opinion.
This is what the ZB -1/2 looks like.



I have a drawing that shows the design as is and one that shows the proposed new idea. I intend on taking out the middle flanged oil lite bush, labeled number 2. I would replace it with a washer and so this would leave just the flanged bush at the back behind the spur gear at the back of the end cap and the on flanged one inside the seal unit siliconned to the front of the gearbox housing.



The reason for me doing this is to reduce the complexity of the unit, reduce friction but mainly to reduce the preciseness of shaft alignment as possibly being an issue.
If I can make the design less reliant on having the shafts absolutely perfectly perpendicular to the face of the endcap then alignment with the shaft seal housing will be less critical. Sure I want the shafts to be parallel with each other but I want to build less ‘critical’ points into the system. It also means that if the outer gearbox housing doesn’t actually precisely aligned with its base it won’t chafethe shaft against the side of any cast parts.

I hope this this makes sense?

what do you think?

David H

So far retirement has been a let-down. Things will work out in time, though. Transitional ****.

Anyway...

Keep that #2 bearing.

It not only takes the astern loads, but works with the #1 bearing to provide thrust loads and lateral alignment of the shaft. Keep the original design.

Make the *******s pay for it -- if you have to play it cheap to get product out the door then you are selling to the wrong idiots.

The number #3 bearing is near useless, but does serve to keep the cup-seal centered onto the shaft -- vital if you're using a flexible adhesive to adhere the seal body to the gear foundation.

David

[Scott T]

How about using flanged bearing two to align cup seal section? See arrow.

[Davidh]

Thanks David and Scott.

Got me thinking...

Dave

[He Who Shall Not Be Named]

How about using flanged bearing two to align cup seal section? See arrow.

I like that -- using a portion of the after Oilite to align the seal body to center the shaft. (you got the cup-seal on backwards, duh!).

[JHapprich]

Shorten the seal housing and put the cup seal just in front of the forward seal to eliminate vibration

[Davidh]

Hello all,

David, this ones for you..

I have been looking very closely at your section in today's work on the creation of the molds for the fin of the Blueback. I have decided to create molds in just the same way for the main conning tower section of my upcoming U-23 class. I just have a couple of questions for you regarding this procedure and how i should apply it to what I am doing.



I intend on inverting the main conning tower section that I wish to mold. It is a through piece with the deck of the conning tower molded as a separate piece I will have a thin boundary inside the main cavity in the middle to create a barrier between the top and bottom halves of the mold. I don't intend on splitting the molds down the side. So there will be a base and an insert. Here is a pic of the part i am going to mold and base beneath.



I though I would include these sketches as they may help explain what i am trying to. My main question is with regards to wall thickness. How thick should I make the wall around the side and also the end of the mold. Do you cast the part inside the original wooden box scaffold that you made or is your rubber mold thick enough. ( You have split the mold down the side, could you still use rubber bands and blocks? I am not quite sure. Is the base shown above a bit too thick?


I am holding the part upside down as it would be suspended in the mold.



In this drawing I propose to use a Bubble ring/ catcher along the top rim of the upside down conning tower piece. I will have air vents coming off this curved to encourage the air bubbles to move their way upwards. Is this realistic or do you think, unnecessary?


What are your thoughts?

I have another question if you don't mind.

I am also planning on molding some fine and very thin parts. I am molding the framework and canvas covers for the deck structure that is found on early U-boats. These pieces wrap around with a curve and feature a fine brass frame on the inside glued to a styrene sheet of 0.5mm thickness on the other side that simulates the fabric covering. My concern is that producing the usual two side mold with the pieces lying on the part plane there may be some pressure from the blocks of wood rubber banded to the sides that they may press the sides of the silicon just enough to close the gap between the molds where the thin styrene / fabric is being simulated. This could lead to urethane resin not completely getting to these thin sections and leaving holes in the "fabric' that is simulated by the styrene. Have you found problems with really thin planes being molded?



I have closed the gap between the frame work and the styrene so no silicon will get in. I have also down the bottom placed a piece of styrene where the gap is between the
fabric and the lower base curve.

I hope all this makes sense.

Thanks David,

Dave H

[He Who Shall Not Be Named]

As to the proposed sail tool: Good sound design. Go with it.

As to the thickness of the rubber between flask wall and pattern side surfaces. Rule-of-thumb is 1.5 times the minimum width. Assuming your sail is 1" thick, then the inside of the flask would measure 4". For the length, figure 1" in front, and 1" in back. Say your sail is 8" long, then the length of the flask, on the inside, would be 10". And allow 1" of rubber over the top and bottom of the sail master.

Us displacing blocks to minimize the amount of rubber needed, like this:



And use the flask as your strong-back during resin casting:



As to the very thin sectioned canvas shield: When you make the pour first subject the tool (and the resin within) to a hard vacuum to force out all the air that inevitably got trapped in the narrow tool cavities. Then quickly pressurize the work to at least one-atmosphere and let it stay there till the resin cures hard. Provide 'frothing' extensions to your sprue and vent network so you don't make a god-awful mess when pulling the vacuum.

David

[Davidh]

Thankyou David.

[Davidh]

Hello David and all,

Thanks for the advice on the last questions regarding molds for the sail/ conning tower. I have created the molds for this and the parts have turned out well. My next question is regarding the main hull which I am almost at the stage of creating all the molds for. I intend on doing a seven part mold. Yes, seven. The reason is that the hull unlike my usual Soviet boats ain’t simple.

The stern and the bow sections have some really intricate undercuts and design features that mean I need molds that will need to be removed at various angles. It will also be a hybrid mold, the stern and bow section will be silicon glove/ hard shell and the middle will be a glass hard shell mould spilt down the axis to make the box keel easier to deal with. I have some drawings of what I intend to do and would like your feedback if possible. I would be able to mold the bow and stern sections individually or bolt them onto the middle section and layup in one go. Will there be expansions and contraction problems with the two different types of molds combined?
Are there any other issues that your experience tells you I need to be aware of?

Anyway, if you could look at the drawings and tell me what you think..