Making plastic servo parts (not injection modling)

Hi,
I am looking for a way to make parts of a servo case (body, servo horn) in a mold using some cold procedure (2k liquids, or something). Has
anyone done that? Can you tell me what plastics are out there?
The idea is to create a new and better servo horn. The original horns of most servos are made by injection molding nylon, but injection molding is extremely expensive for short euns. I am looking for some plastic that can be used in modl and is similar ly strong as Nylon when cured.
I also need another plastic to mold an alternative servo housing with different mounts. Any suggestions?
The goal is about 60 cases and horns.
Yhanks for any help or pointers
Matt
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Typically this sort of thing is done with a polyurethane casting resin in a rubber mould. I'm not sure that the result would be as strong as you need, but resin development is a hotbed of activity.
Injection moulding need not be out of the question. Simple aluminium moulds and hand operated (prototype) machines would probably be adequate for smallish parts with no requirement for rapid production. [see for example "The secrets of building a Plastic Injection Molding Machine" by Vincent Gingery.]
If strength is important I'd go down the route of CNC machining from solid plastic. You will have finished a batch of 60 units before you have even completed the moulds for casting or injection moulding. Additionally, you can modify the design without significant penalty. Finally, when you do want to make an injection mould, you already have the cnc program to make the mould !
have fun ! Dave
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Dave wrote:

Yes, I heard that they are going nuts with this right now. There goes injection molding... .

I thought about that and read some books, but it seems extremely time consuming. The prototyping machines seem relatively expensive. And since there is a CNC machine not too far...

... I'll probably go with this.

I'll do my best ;-)
Thanks!
Matt
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Does anyone by any chace know of what plastic exactly servo cases and servo horms are usually made? Browsing the catalog (or catalogoue ;-) of my local dealer brings up about 20 different basic plastics with many subtypes each. Maybe they will know if I sent them samples?
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    --IIRC horns are usually made of nylon; cases could be anything; maybe styrene? If you've got a pal with a CNC, unless you've got a problem with weight in the application, I'd have him make the horns out of aluminum. It's no more work than nylon; just gotta lubricate it better while machining..
--
"Steamboat Ed" Haas : My shop is open to
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steamer wrote:

But you probably want to use it with stainless steel control rod or clevis. Nylon / stainless steel is self lubricating. Aluminium on steel will wear out.
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Correct. I should have mentioned that.
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If you already have the originals then you just need to look up different types of hand mould-making practice (as opposed to machine moulding) to give you an insight into what`s required from a mould. Cheapest and quickest method would be to use some two-part silicone putty which you simply press around the original parts; this is then filled with low-viscosity polyester resin for the peices. Note that polyester resin on its own is extremely brittle but an additive (5%) can be mixed in with it called a plasticizer: the ratio of which will determine tensile strength, which can range from an indestructable rubber type object to a hard and glass-like one. Electronic circuitboards and sockets are made with this usually containing fine glass-fibre hairs (as well as colour paste, for any colour). You can also add wire reinforcement set inside the piece. ----------------------------------------------------------------------- Ashley Clarke -------------------------------------------------------

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How about something like Polymorph?
It's mouldable at 62C, so can be heated with hot water/hairdryer. Cools to be strong as nylon & can be drilled etc or re-used if desired.
Is available at www.maplin.co.uk & elsewhere (www.kelvin.com & probably eBay!).
More info at: http://www.mutr.co.uk/pdf_files/LIT0048.pdf
Dave.
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Dave wrote:

Awesome stuff! I will use that one day, no question! Not on this project though because 60 deg are easily reached in a servo.
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Matthias Melcher wrote:

I found this site, but have not used them.
http://www.protomold.com /
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Donald wrote:

Yes, thank you. It's too expensive for this project. However, the combination of rapid prototyping and injection molding seems to become a new industry. I am glad that they finally admit that an injection mold does not need to cost 20k and up.
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Try this site. They have how-to videos and a whole bunch of good stuff: http://www.freemansupply.com /

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Wayne Lundberg wrote:

This is one awesome link. I started to download all the knowledge just now... .
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On Sat, 13 Aug 2005 20:30:35 +0200, Matthias Melcher

As no one else has mentioned them, I'll suggest you look at ALUMILITE @ http://www.alumilite.com . Very useful line of molding and casting products. Some time back I took a gear with a 1/8 inch hub and drilled it out so that the outboard protrusion of a round servo horn would be centered in the gear, then glued the horn to the gear with CA and filled the remaining voids in the sides of the gear / servo horn with modeling clay and pored thin mold making compound (HSII /HSIII) around and over this "master". The results being a mold which I could use to cast servo spline hub gears which fit the splined output of the servo perfectly. If you wanted to reinforce the arms of a servo horn you might consider using strands of fiberglass or carbon fiber "roving" placed in the mold before the casting material is poured. If I were doing something like this, I might also consider using short sections of stainless steel tubing as a bushing to reinforce pushrod connection points.
ALUMILITE has some good info in the Applications, FAQ, and How To sections. Lots of helpful people in the Forums also.
No, I don't work for them, I just like the products.
M.L.
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Mike Lynch wrote:

Interesting stuff for sure. Thanks for the link!
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    --One thing to know about Alumilite: keep cross-sections from getting too thick, as the stuff gets HOT when it cures. Neat stuff; I used it quite a bit years ago..
--
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2 sources I have used who have real nice "how to" sections on creating a mold and then casting. Once you figure out the hardness of the plastic you are looking for you narrow down your products to cast.
http://www.polytek.com / http://www.smooth-on.com /
my local shops had nothing so I mail ordered direct to the above folks check out the trial purchase / intro packs to get your start.
The stuff is easy to work with. With the items I chose weight and time were critical so planning is important before you mix / pour.
regardless of where you buy, I recommend the how-to's that are on the sites.         
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Good links. Thank you! I was able to mill a few part out of a block of Delrin, but when I need more, I relly would like to pour them instead. So this was very helpful.
Matt         
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