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What Material for DIY End Caps

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What Material for DIY End Caps

Postby Jure George » Wed Aug 28, 2013 12:39 am

Hello

I`ve been thinking of making some specialty End Caps. What material is recommended to use to make my own end caps then I can turn them on my lathe and put a O Ring groove in them and also install shaft and push rod seals in it that can be stuck in place to the material? Long winded question, Sorry.

I thought about Marine bondo from my local Canadian hardware supply. Sorry forgot that to mention, I`m in Canada and thanks to the U.S shipping rates now, it`s cheaper to buy locally, most of the time.

Please let me know what would be a good, water proof, shrink resistant OR do I compensate for the shrinkage rate and make a little larger to compensate for the expected shrinkage. I like the idea of mixing a paste and pouring it into a round mold and going from there BUT I also like the cone shape motor end end cap shape as well.

Thanks for the Help.

George
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Re: What Material for DIY End Caps

Postby Giovanni » Wed Aug 28, 2013 2:55 am

Grey PVC.
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Giovanni

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Re: What Material for DIY End Caps

Postby JWLaRue » Wed Aug 28, 2013 10:19 am

George,

Grey PVC will work fine. It's soft enough to easily turn on a lathe. It's inexpensive enough that mistakes aren't all that costly. Shrinkage isn't an issue. However, the weight of PVC is noticeably more than other materials...so you may want to take that into account.

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Re: What Material for DIY End Caps

Postby Sub culture » Wed Aug 28, 2013 3:00 pm

The density of pretty much all thermoplastics is very similar, it's what they're filled with that makes them heavier or lighter. Polycarbonate sheet can be quite dense, because they often fill it with glass to improve clarity and scuff resistance.

Don't know why everyone thinks they have to cast their own material for making end caps, I think it must be because the commercial units over in the U.S have cast endcaps, but they're made that way to enable simpler batch production. For one off's it's much easier and better to use pre-cast or extruded sheet stock, and machine them. Commercial modules in the UK e.g. OTW, Sheerline, A1 downunder all uses machined endcaps turned from acrylic.

As you have a lathe, this will be a cinch.

The lightest plastics tend to be the polyethylene type polymers. These actually float in water (just) and machine easily as the plastic is soft, but are difficult to bond to as they are naturally oily/waxy and they don't hold a tight tolerance very well.

The nicest plastic to machine is acetal/delrin. Is a very accurate plastic that doesn't tend to 'grow' as you machine it, but is also tricky to bond, and is quite expensive.

In a nutshell you can use any plastic to make your caps, just make sure they're reasonably thick to resist flexing, a minimum of 6mm (1/4") for up 2-3" tubes, and 8mm (3/8") or more for bigger cylinders.

Don't use bondo, it's probably the worst material you could use, having little to no tensile strength.
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Re: What Material for DIY End Caps

Postby JWLaRue » Wed Aug 28, 2013 4:06 pm

Sub culture wrote:The nicest plastic to machine is acetal/delrin. Is a very accurate plastic that doesn't tend to 'grow' as you machine it, but is also tricky to bond, and is quite expensive.

Agree...and it also absorbs water. (IIRC something like 0.25%) Not much, but depending on your machining tolerances it can be an issue. (It's caught me in the past)

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Re: What Material for DIY End Caps

Postby wlambing » Wed Aug 28, 2013 5:06 pm

Gents,

The bonding and growth issue in Delrin is due to the Teflon it contains. Good for ball valve seats in real subs, not so much fun for fancy stuff in little boats. If you are careful
in your machining, it does make excellent end caps!!

B^)
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Re: What Material for DIY End Caps

Postby Sub culture » Wed Aug 28, 2013 5:10 pm

JWLaRue wrote:Agree...and it also absorbs water. (IIRC something like 0.25%) Not much, but depending on your machining tolerances it can be an issue. (It's caught me in the past)

-Jeff


Not going to be an issue in this case. Most plastics are hydroscopic, including the resins we use for moulding and casting one of the least is polyethylene, possibly due to it's waxy surface.
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Re: What Material for DIY End Caps

Postby JWLaRue » Wed Aug 28, 2013 6:21 pm

I didn't say it was something that was a common problem, but that I've been caught by this in the past. I have not had similar issues with other materials.

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Re: What Material for DIY End Caps

Postby Jure George » Wed Aug 28, 2013 6:51 pm

Hi sub culture

I saw your brief post in an other section reg. end cap manufacturing. Would you be willing to give me a lesson on the making of one with the factors needed to fit properly an O ring as well?

I would really like to find a material that I can turn on my lathe and glue shaft, push rod seal housing to as well as servos, similarly like some WTC complete units being sold or near to it BUT for air bag systems.

Thanks for your help.

George
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Re: What Material for DIY End Caps

Postby Thor » Wed Aug 28, 2013 7:11 pm

George,

Go with PVC. It is readily available, easily machined, and quite easy to use adhesives on. My upcoming line of ballast systems uses machined PVC throughout the design.

Best,

Matt
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Re: What Material for DIY End Caps

Postby Jure George » Wed Aug 28, 2013 8:27 pm

Hi Matt

Thanks for the tip But I think I need a little clarification. When someone says PVC to me I think of house hold plumbing pipe, white, black or grey. What are you referring to and how do you machine it? a picture would be great as well as a source of it.

Thanks Matt.

George
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Re: What Material for DIY End Caps

Postby Thor » Wed Aug 28, 2013 8:36 pm

George,

You can purchase PVC in many shapes and forms; sheet, strip, tube, and rod. I purchase PVC solid rod in diameters ranging from 2" - 6" in diameter. I buy in 1' lengths and cut it down to lengths required for any particular part I am wanting to machine. I either CNC machine it, or use the manual mill or lathe to finish the part.

www.mcmaster.com


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Re: What Material for DIY End Caps

Postby Sub culture » Thu Aug 29, 2013 1:49 pm

Explaining how to make endcaps in written form is rather difficult to do in a concise and easy to understand format, because there are a few topics to address.

Providing you are competent with turning on a lathe i.e. you understand the basics of work holding, centreing tools etc. It then leaves a requirement to understand how to size o-rings, and dimension the grooves for them to sit in, getting sufficient o-ring squish to effect a decent seal. As such this really needs to be addressed visually. A small video is the best way, and it is something I've been meaning to do for a little while, as I think this the area that most sub modellers find intimidating.
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Re: What Material for DIY End Caps

Postby Jure George » Thu Aug 29, 2013 5:35 pm

Hi

If you do go ahead with the video, I would be very interested in the sizing of the O ring grove etc. Let me know if you go ahead with the video.

Thanks

George
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Re: What Material for DIY End Caps

Postby roedj » Thu Aug 29, 2013 5:39 pm

Sub culture wrote:Explaining how to make endcaps in written form is rather difficult to do in a concise and easy to understand format, because there are a few topics to address.

Providing you are competent with turning on a lathe i.e. you understand the basics of work holding, centreing tools etc. It then leaves a requirement to understand how to size o-rings, and dimension the grooves for them to sit in, getting sufficient o-ring squish to effect a decent seal. As such this really needs to be addressed visually. A small video is the best way, and it is something I've been meaning to do for a little while, as I think this the area that most sub modellers find intimidating.


Me too! I would love to see such a video. I have access to a friend who's a wizard with a lathe and both he and I want to try our hand at this.

Dan
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