Source for Custom Polyurethane bushing?
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  1. #1
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    Default Source for Custom Polyurethane bushing?

    Any of you guys have a company you have used for custom Polyurethane molding?
    I have a very simple bushing I need made in a quantity of about 400pc.

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    Scant info, but for 400off, it might be cheaper to get em machined

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    Material will be too soft for machining or I would do it myself. Actually looking into doing a mold and poring them myself but sometimes you are better off paying an expert in their own nich.

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    Global Urethane in Tulsa, Oklahoma might be able to help.

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    Quote Originally Posted by edge22 View Post
    Material will be too soft for machining or I would do it myself. Actually looking into doing a mold and poring them myself but sometimes you are better off paying an expert in their own nich.
    Thanks edge - it was just a thought as some PU's are hard enough to machine.

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    I'd go to google maps and search for "rubber molding near me". I get 5 rubber molding shops within a 25 mile radius of me that all do anything from prototypes to large runs. We've used a couple of them for custom vacuum cups over the years.

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    Check with Engergy Suspension and Prothane. They may have something off the shelf.

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    Quote Originally Posted by edge22 View Post
    Any of you guys have a company you have used for custom Polyurethane molding?
    I have a very simple bushing I need made in a quantity of about 400pc.

    I've used Meridian Laboratory with great success. I tried casing myself, and found that its just better to pay people that do this day in and day out. I've used them for prototypes and production runs. Super responsive, and quality parts.

    Contact Us | Meridian Lab | Brushless Slip Rings & Polyurethane Molding

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    Precision Urethane, Hempstead TX

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    If you have the time don't let it intimidate you to do it yourself. I make some rubber mounting pads with a nut cast into them. I don't pull vacuum on these, but I vibrate the edge of the mold with a DA for a few seconds after pouring. They come out better than I need.
    20201228_120835.jpg
    20201228_120912.jpg

    I probably spent a full day making my mold (spread out over a week or two), but once I had the mold I can cast 20 parts in about 10min. Then just come back around to it once they are cured enough to de-mold, and cast 20 more. Obviously you could cast as many as you want to make a mold for at one time.

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    I do short run polyurethane casting. Used to send it out, but hard to find a company that does short runs.

    PM me with more details, hardness, anticipated loads, color, with a print. We do our tooling in house as well.

    Chuck
    Burbank, CA

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    I thought I would add to this since edge22 pm'd me with some questions.

    I have had good experience with polytek products, though there are others out there. The color is achieved through adding pigment, and you want to have precise measuring if you need exact consistency from batch to batch. (polytek can supply you with everything you need for the material and mold release)

    I did cast a number of single parts perfecting my mold, and the only problems I ever had was over pigment trying to achieve a bright enough white color. The rubber never cured fully on those attempts.

    This picture also shows just how easy the mold making process was for a simple part like this. If you are going to be working with small quantities at a time do yourself a favor and get a box of catheter tip syringes for measuring out materials. (much easier to not make a mess when working with resins)
    20201228_163356.jpg
    20201228_163501.jpg

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    I needed a special 10-3/4” lip seal and decided to prototype it in polyurethane. I turned a mold in HDPE and poured the first one. We made about 5 versions, not because of casting problems, except for occasional bubbles there weren’t any. It worked so well they are still making the seal this way for $3 worth of material.

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    Default Need to make some small bushings

    The best high end Victor (JVC) tonearms have a rubber bushing that have deteriorated over the years. These tonearms were probably last produced in the mid 80's. This bushing isolates and dampens vibrations that travel up the tonearm and go between the tonearm and counterweight stub. The major diameter is 12mm. I have never cast polyurethane but I think this would be a perfect candidate for that.
    The bushing has a flange at both ends, one is about 4mm thick and the other I haven't measured but I suspect is only 1 to 1.5mm thick. There is also a brass shoulder screw that passes through the part. Maybe 4 or 5mm in diameter on the shoulder. The thin flange on the rubber part is trapped by the square head on the shoulder screw in between the 4 cut out notches in the aluminum collar as shown in the picture.
    victor-ua-tonearm-bushing-2.jpgvictor-ua-tonearm-bushing.jpgvictor-ua-tonearm-bushing-2.jpgvictor-ua-tonearm-bushing.jpg
    I don't know the durometer of the rubber but suspect it was a normal rubber compound, maybe Shore A70. I would like to mold new ones out of Polyurethane but have never done this before.
    I'm thinking a simple mold machined from a block of aluminum with a couterbore at both ends for the flanges. A bottom plate with a reamed hole to insert a snug fitting pin for the bore of the bushing that is pined and screwed to the block.
    I assume that I will need to pour the liquid into the top of the mold slightly over filling it as air will be trapped inside and than put the mold in a small vacuum chamber and pump it down to pull out the air. After the poly has set up I would pull the pin and using a razor blade trim off any excess poly that is spilled over the top.
    I would make the mold with 5 cavities all in a row.
    Do I need a release agent on the metal mold parts or will the polyurethane parts release on their own?
    Do I need to calculate shrinkage on parts there small?
    Am I missing something?
    Also, how best to mix and handle the small quantities that I will be using and where can I purchase this in smaller quantities?
    I have seen small vacuum chambers on Ebay that are reasonable.
    I will probably make a small run of these. It's a semi popular tonearm and they all have or will have issues like this.
    Thank you for any advice that you can give me.

    Mr Bridgeport

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    Mr. Bridgeport,

    I would direct you to Smooth-on.com

    Urethane Rubber from Smooth-On, Inc.

    They have trial size packaged kits that are great for starting out.
    Something like the PMC 770 would work, degassing probably not necessary.

    Download the TDS to get a feel for the process and follow it to the letter. My only advise is to get a good gram scale to weigh the components rather than doing by volume.

    Chuck
    Burbank, CA

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    Saw this on Ebay, 50 bucks shipped. Has anyone used something cheap like this before? I'm mainly worried about getting a good seal on the lid. Uses a silicone gasket at the top of the 3 quart pot. Still looking for other answers, first time I will be doing something like this. Chuck, that link to Smooth On is good, I'll be using PMC-770 compound.

    Mr Bridgeport
    Attached Thumbnails Attached Thumbnails 3-quart-vacuum-chamber.jpg   3-quart-vacuum-chamber-2.jpg  

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    Quote Originally Posted by Mr Bridgeport View Post
    Saw this on Ebay, 50 bucks shipped. Has anyone used something cheap like this before? I'm mainly worried about getting a good seal on the lid. Uses a silicone gasket at the top of the 3 quart pot. Still looking for other answers, first time I will be doing something like this. Chuck, that link to Smooth On is good, I'll be using PMC-770 compound.

    Mr Bridgeport
    I've used a probably more expensive but not very different version of that. It's basically a big stock pot with an elastomer coated lid. The one we have has a clear lid that I suspect is just a 3/4" thick piece of polycarb/acrylic with a big rubber band around the outside to serve as the seal. The benefit of the clear lid is you can see when pulling the vacuum is about to make something bubble over, and also when the air bubbles have all risen out/popped. I've also used a few that were glass domes where you had to put a dab of silicone vacuum grease around the flange before use. Both work well, but the clear lid version was easier to use as I didn't need to mess with the grease.
    While I'm guessing it won't matter for a lower vacuum application like this, the biggest failure point I've seen is improperly sealed fittings. I would pull a vacuum and then let it sit overnight. If it bleeds down, just pull all the fittings, re-dope them with pipe dope, reassemble, and your issue will probably be gone.

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    What about an old pressure cooker from the thrift store? About that size.

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    Thanks jccaclimber, just ordered it. gbent, your idea isn't a bad one but I like the idea of watching whats going on and by the time I buy a vacuum gage, 2 ball valves and so on...Well, you get the idea.

    Mr Bridgeport


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