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Old 21st October 2007, 16:46   #1 (permalink)
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How to machine plexiglass

How can I machine plexiglass?

I hava a bit of pipe that is 100mm thick that I need reduced to 97mm. So...

What speed should I run the lathe?

What tips and tricks do you know.

I have learned that I should heat it with a lighter to get it nice and shiny again after I have machined it.


Thank you...

Teoman
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Old 21st October 2007, 17:45   #2 (permalink)
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Re: How to machine plexiglass

Quote: (Originally Posted by teomannaskali) View Original Post
How can I machine plexiglass?

I hava a bit of pipe that is 100mm thick that I need reduced to 97mm. So...

What speed should I run the lathe?

What tips and tricks do you know.

I have learned that I should heat it with a lighter to get it nice and shiny again after I have machined it.


Thank you...

Teoman
In general:

Turn it pretty slow. Use SHARP High rake tools. Thermoplastics are good thermal insulators, so take your time, and let the work piece cool between cuts.

Your greatest challenge is work holding. You need to secure the work piece so there is no deflection.

For tubing the very best is a collet that full surrounds the tube.

If you have thin walled tube, and try to hold it with a three jaw chuck you are very likely to have trouble.

Sometimes a tight fitting "plug" on the inside will help.

Tobin
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Old 21st October 2007, 17:57   #3 (permalink)
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Re: How to machine plexiglass

I have a 4 jaw yoke.

I Think that a plug inside is the best idea. Or should I try to machine little bits to hold the pipe from the outside? Like another pipe that has been vertically cut in 2 (so that you see 2 "C" shapes when you stand the pipe upright like a coke can.)

Thank you for your post I was under the impression that higher speeds would have been better.

1. When you say slow how slow is that? 100rpm?
2. I using the machine shop at nigts, how do i differentiate between High rake tools an normal ones? Except the fact that they have to look sharp.

And one off topic question. I have a metal mesh that was originally intended to be cover/filter for speakers (not mine, that was wat the guy who sold it to me said). Could there be any dangers here? Some strange anodizing or something that can prove to be dangerous by offgassing. They do not have any paint on these.

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Old 21st October 2007, 18:12   #4 (permalink)
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Re: How to machine plexiglass

Quote: (Originally Posted by teomannaskali) View Original Post
I have a 4 jaw yoke.

I Think that a plug inside is the best idea. Or should I try to machine little bits to hold the pipe from the outside? Like another pipe that has been vertically cut in 2 (so that you see 2 "C" shapes when you stand the pipe upright like a coke can.)

Thank you for your post I was under the impression that higher speeds would have been better.

1. When you say slow how slow is that? 100rpm?
2. I using the machine shop at nigts, how do i differentiate between High rake tools an normal ones? Except the fact that they have to look sharp.

And one off topic question. I have a metal mesh that was originally intended to be cover/filter for speakers (not mine, that was wat the guy who sold it to me said). Could there be any dangers here? Some strange anodizing or something that can prove to be dangerous by offgassing. They do not have any paint on these.

Teoman
Teo,

RPM depends on diameter. Is your tube 100 mm outside diameter, or 100 mm wall thickness?

If you have a typical scrubber sized tube, ~150mm or larger you want to go slow, 100-200 rpm.

Keep the depth of cut as high as the set up will tolerate.

Also helps to "hone" or slightly "dull" the edge of the cutter, try to produce a small area of zero or negative rake right at the edge.

HSS tools are much easier to modify.

If you are producing a lot of chatter either your set up is not rigid or you need a smaller tip radius.

I'm sorry I can't better describe the cutting tool you need. I'd suggest talking to the "day shift" machinist, he can translate.

Tobin
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Old 21st October 2007, 18:24   #5 (permalink)
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Re: How to machine plexiglass

Thank you,

The pipe I have is 100mm OD with a wall thinckness of 5mm. So 200 rpm is ok?

Ill try oh see what kind of tools they have. I am not shure if they will be happy with me un sharpening their tools :)


Teoman

Do you have any advice on how to get it shiny again?

Teoman
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Old 21st October 2007, 19:12   #6 (permalink)
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Re: How to machine plexiglass

Quote: (Originally Posted by teomannaskali) View Original Post
Thank you,

The pipe I have is 100mm OD with a wall thinckness of 5mm. So 200 rpm is ok?

Ill try oh see what kind of tools they have. I am not shure if they will be happy with me un sharpening their tools :)


Teoman

Do you have any advice on how to get it shiny again?

Teoman
At 100 mm (~4 inches) you can most likely spin it up a bit, ~250-350 rpm, but keep in mind that many many factors control what RPM you can use.

The recommended cutting speeds of the material is only one factor. The rigidity of the work holding, the work piece and the cutting tool play a much bigger part.

In addition the "natural" frequency of the part is a major player.

Don't be afraid to INCREASE the RPM if you encounter chatter.

You can polish the part after cutting it. Sandpaper, finer sand paper, then jewelers rouge will yield a clear transparent finish.

Hope you have some additional material to practice with.

You'll know exactly how to do it with the tools you have just about the time you finish the project :D

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Old 28th October 2007, 14:50   #7 (permalink)
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Re: How to machine plexiglass

Another question.

I am also trying to make some displays. I will use plexiglass pipe again. Now, My ID has to be 25mm, what should the OD be? What thickness should I use? Is 3mm thick enough?

Thank you.

Teoman
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Old 28th October 2007, 15:07   #8 (permalink)
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Re: How to machine plexiglass

Quote: (Originally Posted by teomannaskali) View Original Post
I have learned that I should heat it with a lighter to get it nice and shiny again after I have machined it.

To polish you can finish off in lathe with 'Brasso' or similar metal polish paste
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Old 28th October 2007, 23:55   #9 (permalink)
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Re: How to machine plexiglass

Quote: (Originally Posted by teomannaskali) View Original Post
Another question.

I am also trying to make some displays. I will use plexiglass pipe again. Now, My ID has to be 25mm, what should the OD be? What thickness should I use? Is 3mm thick enough?

Thank you.

Teoman
That depends entirely on how deep you're planning on taking the displays. One other thought is how much is the curve of the tube going to distort the view through it. It could possibly make it a little bit difficult to read I would think.
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Old 29th October 2007, 04:56   #10 (permalink)
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Re: How to machine plexiglass

After you have gone threw 400 and 600 wet sanding you may want to use 1000 garnet (Speeds to polish greater than 350 rpm) use brasso like the other fellow suggested; I use a piece of soft leather a little damp for polishing finished off with polywax (soft cloth) Hint you must remove ALL machining marks or sanding marks from the previous machining or sanding procedure or you will not like it! Be very patient this will take some time.

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