Machining soft plastic tubing
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  1. #1
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    Default Machining soft plastic tubing

    My customer needs ends of soft plastic Tygon type tubing ends tapered and rounded. I tried inserting a steel rod and various methods but none seem to work. Surface must be smooth and easy to clean as they are used in food. Rough surface looks dirty.
    Another application I need soft Urethane type material 1-5/8" or 42mm ID X 2", 50mm OD. All I can find is 1-1/2" or 1-3/4" ID on ebay and McMaster Carr. Not much needed so I don't want to special order custom made.
    Any suggestions??

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    A sharp razor blade to shave it off at the angle? In a lathe with steel mandrel to hold shape. Kind of like a wood planer but the tube slowly spins against the blade.

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    Freeze it with a spray of liquid nitrogen, or try buffing it with a fine grinding wheel. If grinding be patient, too aggressive any you'll melt the tubing into the wheel.

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    I have heard of freezing rubber to machine it. But be careful, rubber expands when cooled . Maybe you could use one of those "Ice Lathes" I asked about years ago.
    Bill D.

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    Judicious application of heat will smooth it.

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    Compression mold the end. Simple mold of internal support mandrel, and two half to form the outside details. Heat the plastic with hot air or possibly a hot sand bed or hot oil bath, then press in mold

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    I have tried to machine 95 durometer urethane in the past and could not do it. Made the same parts in Teflon and it was a piece of cake.
    Recently we mounted our Vortex tube on the machine and could machine the urethane parts. Start the vortex tube and give it a minute(s) till the material freezes up, then press cycle start, take things slow so the gun can take away the heat as it progresses. Every thing said about sharp special tooling is still necessary.
    We tried cooling the bar (1/4 diameter) in a dry ice pack with alcohol but by the time you chucked the bar it was already warming up.
    Last edited by FredC; 08-06-2019 at 08:57 AM.

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    Wet grinding works remarkably well on soft urethanes.

    We do it with simple toolpost grinders.

    I have not used it on Tygon, but it is the first thing I would try.


    petersen

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