Aligning HDPE plastic with pins - Woodworking Talk - Woodworkers Forum
 
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post #1 of 8 Old 01-23-2013, 01:15 PM Thread Starter
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Aligning HDPE plastic with pins

First post. Hope this isn't too simple. I am trying to align two pieces of 1/2" HDPE plastic so that they can be separated and attached 1) quickly and 2) over and over and 3) cheaply. I figure, drill a hole, stick a pin through it. Done. Then I start to worry: will the pin wear the hole bigger and bigger? (Tolerances are in the realm of thousanths of an inch, and I am going to market this to the general public.) I figure maybe I should use some kind of sleeve/pin combination. After hours in hardware stores and the internet, I've come to the conclusion that such a sleeve doesn't exist. So... three questions: Is HDPE strong enough that I don't have to worry about the hole wearing bigger? 2) Does a sleeve/pin combo exist? 3) Is there a different (cheap and simple) way to solve this problem? Thanks.
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post #2 of 8 Old 01-23-2013, 01:36 PM
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Limited information. A picture or sketch would be very useful.

The more we understand, the better we can provide guidance.

HDPE is soft. If an item is being attached and removed many times, there will be wear. The softer the item, the more it may wear.

If your tolerances are 000's of an inch. This feels to be to contradict anything being attached many times and with holes and pins for attachment.

What is the HDPE being attached to? Metal, wood, etc. If metal which metal. If steel, iron or a magnetic material, you could consider rare earth magnets.

We need more information from you to be able to provide more guidance.
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post #3 of 8 Old 01-23-2013, 02:17 PM Thread Starter
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Wow. That was quick. Thanks

I don't know how to get a picture or drawing onto my computer, but that will be my project for today. The problem is my tolerances, I know. If they weren't so slight, this would be easy.
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post #4 of 8 Old 01-23-2013, 06:55 PM
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Sleeves do exist. Something similar to what's used for mold (as in injection) alignment pins and sleeves.

Check out Misumiusa.com they sell this type of hardware. If your looking at McMaster Carr look for drill bushing. These have tight tolerances good wear characteristics.

Also might want to look at CarrLane.com

If you are aligning two parts with pins you will need to use two pins. In order to not over-constrain the parts and cause binding upon assembly; the part that receives the pins should have one hole and one slot. With the slot being oriented colinear with the pin hole. Hope that makes sense.

You might also consider looking at kinematic mounts which are extremely repeatable and do not over-constrain the assembly.
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post #5 of 8 Old 01-23-2013, 07:51 PM Thread Starter
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Good news, bad news

SLAC engineer... thanks. You pointed me in exactly the right direction. And if I was making one of these for myself, that's where I would go. Unfortunately, I want to produce hundreds or thousands of these (and each unit would require four) and bushings, ejector pins, etc, price them right out of the market. Funny... I am trying to design a product that is 1) easy to use, 2) easy to build, and 3) inexpensive. If I could get by on any two of those three, no sweat. Getting all 3 has, thus far, eluded me. (Meat Loaf (Two Out of Three Ain't Bad) was wrong.) (Joke for my generation only.)
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post #6 of 8 Old 01-23-2013, 08:25 PM
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1/2" High density polyethylene is some pretty tough material. Unless what your making has a tremendous amount of stress applied to it you can probably get by using screw post. screwpost.com is a good place to find them.
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post #7 of 8 Old 01-24-2013, 01:04 PM Thread Starter
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Aligning HDPE

Dan... thanks. I think under normal circumstances, the HDPE WOULD be tough enough. But a combination of lots of in's and out's and too small tolerances worries me. Again... if this was for me, I do it and worry about it later, (if I even needed to). But I would like to sell these and don't want 100% returns in a year. Those screw posts look good, though, and give me another idea. Do they have them without threads? Here is where I'm at now: Chop an aluminum rod into 1/2" pieces and slide them into the HDPE. After aligning, drill a 1/8" hole through the aluminum and align with 1/8" stainless rod. Excuse the ignorant question, but is aluminum less likely to wear out than HDPE?
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post #8 of 8 Old 01-25-2013, 03:39 PM
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It's hard to suggest something without seeing what you are doing and how it is used. A couple other places that might have something you can use is FFR (Fasteners For Retail) or Outwater.
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