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I want to cut a piece of plastic peg. The peg will be visible (it is on my laptop stand), so want it to have a smooth finish. I could just use a saw, but the finish will not be good. How should I go about it? I am not sure if a file will be enough to get a proper finish.

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Saw blades with more teeth produce a finer cut - you might be able to use a saw if you have the correct blade –  Steven Sep 24 '12 at 12:40

6 Answers 6

up vote 7 down vote accepted

I would recommend cutting the peg(s) using a fine toothed saw like this one: enter image description here

These saws cut very smooth and are made by Xacto. Should be available from most serious hardware stores and craft centers.

One Source:

http://www.sears.com/shc/s/p_10153_12605_SPM6183582501P?sid=IDx20110310x00001i&srccode=cii_184425893&cpncode=30-71592542-2

Many types of plastics can be sanded with very fine sand paper. You want to look for a product known as "wet or dry" sand paper with a grit number up to 1500 or more. If the cutting operation leaves some saw kerf marks on the stub of the peg you may need to start with a courser paper and then work your way up to the highest numbered grit to get the polish you desire. The Silicon Carbide type wet-dry sandpaper should be available at good hardware stores. Sometimes you can also find this at auto parts stores.

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Just a quick note (as I use these from time to time) these saw blades are not bi-directional. You only get a cut on the pull. –  Edwin Buck Sep 25 '12 at 12:27

As a follow-up to the advice about using very fine saws and super fine sandpaper, jewelers rouge is often used to do a final polish on plastic to get to a clear finish.

jewelers rouge

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A good choice if you don't want to deal with heat assisted cutting. –  Edwin Buck Sep 24 '12 at 14:27

To smooth up the XActo saw cut (a truly excellent tool), you can often flame-polish most thermoplastics, provided you do so carefully. Flame-polished is smoother & shinier than sanded.

Here's the general process:

First, to determine whether this is a thermoplastic or a thermosetting plastic, expose one waste (past the projected cut) edge to high temperature (candle flame, cigarette lighter, etc). If it's thermoplastic, it'll melt. Good sign.

To flame-polish a rod of this material after sawing, carefully expose it to the flame from - say - a stovetop burner. Heat very gently, retract often. The plastic at the cut line will "heal" itself, flowing into the scratches made by the saw and finishing up with a high-gloss surface if done well.

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Sure. First, to determine whether this is a thermoplastic or a thermosetting plastic, expose one waste (past the projected cut) edge to high temperature (candle flame, cigarette lighter, etc). If it's thermoplastic, it'll melt. Good sign. To flame-polish a rod of this material after sawing, carefully expose it to the flame from - say - a stovetop burner. Heat very gently, retract often. The plastic at the cut line will "heal" itself, flowing into the scratches made by the saw and finishing up with a high-gloss surface if done well. –  TDHofstetter Aug 14 at 20:40
    
Excellent description. I took the liberty of adding your comment to the answer and upvoting. –  Doresoom Aug 15 at 2:15

Depending on the type of plastic, and the thickness / dimensions of the cut, a hot knife or a heated wire knife might be what you are looking for.

There are many ways to go about rigging a hot knife, the simplest being to attach an xacto knife blade to a soldering iron. Larger jobs might require a purpose built tool, or at least a much better setup.

Another option is to get the cleanest cut you can, and experiment with a heat gun to soften the cut area. Again, even heating without burning is key, and some plastics are easier to work with than others.

Keep safety in mind, plastic burns giving off very nasty fumes. Most people die on airplanes due to plastic fumes far before any in-plane fires reach them. While you (hopefully) won't scorch your plastic, even heating it should be done with ample ventilation (preferably outdoors).

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If you are working with acrylic you should check these technical bulletins for information about how to work with arcylic.

I have successfully used a tablesaw to get a good straight cut then used a variable speed bench jointer to smooth the edge. I was working with 1/4" and 1/8" thick acrylic and resulting parts were all rectangular and more than 1" in each dimension.

If you don't have a jointer you might be able to use a bench mounted router to get a smooth edge but I haven't tried it myself.

I tried other methods for cutting the acrylic but only the table saw could gave me consistently straight cuts. (I tried a band saw, jig saw and the score and snap method)

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I used an electric saw and my plastic rings did not crack in half.

enter image description here

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Using a band saw will not result in a smooth finish. –  Doresoom Aug 14 at 19:19

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