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  1. #1
    Join Date
    Jun 2017
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    369

    HDPE question

    I'm hoping this is the right location to post this question.

    I recently built my CNC Router Parts 4896 Pro and I made my dust shoe that is on their website.

    Universal CNC Dust Shoe | CNCRouterParts

    The top piece of material started out as a 1" piece of HDPE and after being machined it is about 3/8" thick. After I finished mine looks great except for the fact that the top section bows up so the bottom piece wont snap into place.

    My question is can I use some heat to straighten / flatten the HDPE or do I need to start over?

    Thanks
    Gary

  2. #2
    Join Date
    May 2005
    Posts
    1662

    Re: HDPE question

    I bend 1/4" HDPE with a heat gun all the time.
    3/8 " just needs more heat or patience ?? Test on scrap.

    EDIT/ OOPS. Went into the shop to check and the HDPE I've bent is 1/8". My mill enclosure among other things.
    The problem with this stuff as it gets thicker is the outside can be heated to melting without warming the core.
    More of my rubbish advice unfortunately.
    Anyone who says "It only goes together one way" has no imagination.

  3. #3
    Join Date
    Dec 2003
    Posts
    1206

    Re: HDPE question

    I have had UHMW polyethylene curl up when removing a large proportion of the thickness,Delrin too.It seems likely to me that the material is rolled to thickness while still a bit pliable,at the factory,and the stresses induced are balanced until you remove some material and unbalance the forces.It comes as a real shock when you have held the stock flat with a vacuum hold down and then it curls up when the vacuum is switched off.The only solution I found was to rough machine to a slightly oversize shape and then a much lighter finishing cut.

  4. #4
    Join Date
    Jun 2017
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    369

    Re: HDPE question

    Cyclestart - thank you, I still think I'm going to try to heat it because if it works I'm good if not I'll need to start over anyhow so it's worth a shot, right?

    Routalot - I'm not real familiar with plastics, how close is UHMW to HDPE? I would think that CNCRP Would design in a way to negate the bow if it happens often. What would be a better material to use so this doesn't happen? If I'm going to have to remake it anyhow I'd like it to be see through if possible.

    Thank you
    Gary

  5. #5
    Join Date
    Dec 2013
    Posts
    5717

    Re: HDPE question

    UHMW and HDPE are both polyethylene. The UHMW has a higher density, but other than that no substantial difference for most applications. If I wanted a ''see through'' something for an application requiring strength and resilience, polycarbonate (Lexan, Tuffak) would be my choice.

    Warping is common when machining some plastics (and some metals), but if you take off about the same amount of material from each side you can minimize this. In your case, heating the material and trying to straighten it might work, or it may get worse. Just depends on the stresses in the material.
    Jim Dawson
    Sandy, Oregon, USA

  6. #6
    Join Date
    May 2005
    Posts
    1662

    Re: HDPE question

    Quote Originally Posted by Jim Dawson View Post
    If I wanted a ''see through'' something for an application requiring strength and resilience, polycarbonate (Lexan, Tuffak) would be my choice..
    I bought a clear cast acrylic dust shoe from kentcnc. There are 3 LED lights on the bottom of the router. The ability to watch the cutter while the brush is in contact with the table is something I'll never do without. The shoe wouldn't be hard to replicate if you have a good source for brushes.

    The HDPE used used by Cnc Router Parts may have less internal stress. It's also possible your tool/speeds/feeds introduced additional stresses. I was tempted to suggest stress relief in an oven at low temperature but there might be toxic fumes ? If the canary dies it's time to evacuate.
    Anyone who says "It only goes together one way" has no imagination.

  7. #7
    Join Date
    Mar 2015
    Posts
    409

    Re: HDPE question

    he HDPE used used by Cnc Router Parts may have less internal stress. It's also possible your tool/speeds/feeds introduced additional stresses. I was tempted to suggest stress relief in an oven at low temperature but there might be toxic fumes ? If the canary dies it's time to evacuate.
    If you want to stress relieve HDPE, PP or LDPE, boil it in water in a large tub for one hour, put the lid on and let it cool down by itself, the slower the better!

  8. #8
    Join Date
    Jun 2017
    Posts
    369

    Re: HDPE question

    Hfjbuis - I'll try the boiling water prior to starting over. Would it be best to remove the metal nuts & bolts to keep it from heating that area more than the other areas?

    Cyclestart - I'll check into that dust shoe. I have a good source for brushes. I purchased mine at mastercarr. Where does the power for the LED's come from?

    Jim - thanks for the reply I'd need to get a piece 2" thick to remove the same from both sides. Plus I'm learning one sided cnc I'm not ready to attempt 2 sided yet.

    Thanks
    Gary

  9. #9
    Join Date
    Dec 2013
    Posts
    5717

    Re: HDPE question

    Quote Originally Posted by Gary-Wiant View Post
    .............

    Jim - thanks for the reply I'd need to get a piece 2" thick to remove the same from both sides. Plus I'm learning one sided cnc I'm not ready to attempt 2 sided yet.

    Thanks
    Gary
    Not sure why you would need a piece 2'' thick. Let's look at the math here. Let's say you start out with a piece 1 inch thick (1.000) but you need to make it 0.375 thick, so 1.000 - 0.375 = 0.625, therefore you would take half of the difference off of each side or 0.625 / 2 = 0.312 So if you were to take 0.312 off of each side then you would have removed the same amount from each side, and the final part thickness would be the target of 0.375 thick (ok, yes I know the math works out to 0.376, but trying to keep things simple here).

    2 sided is simple if the part is symmetrical, just flip it over. If not symmetrical, then you need to do a mirror part in CAD, as far as I know all CAD programs will do this.
    Jim Dawson
    Sandy, Oregon, USA

  10. #10
    Join Date
    May 2005
    Posts
    1662

    Re: HDPE question

    Quote Originally Posted by Gary-Wiant View Post
    Cyclestart - I'll check into that dust shoe. I have a good source for brushes. I purchased mine at mastercarr. Where does the power for the LED's come from?
    My router happens to have them built-in. There's also angel eyes or halo rings available that run on 12V so use a wall wart or tap into a power supply.
    Anyone who says "It only goes together one way" has no imagination.

  11. #11
    Join Date
    Jun 2017
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    369

    Re: HDPE question

    Jim - I'd need a 2" piece because I start with a 1" piece & in the end part of the finished piece is 1" so if I need to take even amounts from both sides I'd need a 2" piece.

    Cyclestart - ok thank you

  12. #12
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    Dec 2013
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    5717

    Re: HDPE question

    Quote Originally Posted by Gary-Wiant View Post
    Jim - I'd need a 2" piece because I start with a 1" piece & in the end part of the finished piece is 1" so if I need to take even amounts from both sides I'd need a 2" piece.

    Cyclestart - ok thank you
    The top piece of material started out as a 1" piece of HDPE and after being machined it is about 3/8" thick.
    OK, I guess I am confused, according to your first post, the part finished at 3/8''
    Jim Dawson
    Sandy, Oregon, USA

  13. #13
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    Jun 2017
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    369

    Re: HDPE question

    Did you look at the dust shoe I shared the link to?

  14. #14
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    Dec 2013
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    5717

    Re: HDPE question

    Quote Originally Posted by Gary-Wiant View Post
    Did you look at the dust shoe I shared the link to?

    No, but I just looked at it. I see the problem. That being the case, about the only solution is to try to stress relieve it, maybe before machining. I have had some UHMW and HDPE try to turn into a pretzel when machining.
    Jim Dawson
    Sandy, Oregon, USA

  15. #15
    Join Date
    Mar 2015
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    409

    Re: HDPE question

    Hfjbuis - I'll try the boiling water prior to starting over. Would it be best to remove the metal nuts & bolts to keep it from heating that area more than the other areas?
    Just make sure everything is submerged in water, then is will be ok.

  16. #16
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    Jun 2017
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    369

    Re: HDPE question

    I'm planning on boiling the top section of the dust shoe today but even if it does work I'm considering making the top piece out of clear acrylic and attaching an led to is so I can see what the router is doing. My question is. Once I route out the 1" piece of acrylic like I did the HDPE the acrylic will be milky white & not see through. If i flame polish the routed area will it actually be clear enough to see through? I looked at the Kentcnc dust shoes and I'd have done that if I hadn't already spent the money to make my own & I see that his are not routed and he uses a black plastic piece that mounts to the dust collection hose and his spindle pushes into the top section then righted with a screw, so his isn't routed near as much as the CNCRP dust collector. How can I go about doing this?

    Also does anyone have a link to a 90mm led that is AC powered? I've found plenty of a DC powered but the adapters power wire isnt near long enough to reach my control panel & I don't know if the small adaptors would be able to have that much wiring added without causing power issues.

    Thank you
    Gary

  17. #17
    Join Date
    Mar 2003
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    35538

    Re: HDPE question

    You'll probably need to do some sanding before flame polishing. The finer the grit used, the clearer it will be.
    Gerry

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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  18. #18
    Join Date
    Mar 2015
    Posts
    409

    Re: HDPE question

    the acrylic will be milky white & not see through
    You can get the acrylic absolutely clear by sanding and polishing using a soft cloth and copper polish liquid. You can do it using a dremel or power drill.

    I've found plenty of a DC powered but the adapters power wire isn't near long enough to reach my control panel & I don't know if the small adapters would be able to have that much wiring added without causing power issues.
    You don't see any difference even if the power lines are very long. Just give it a try.

  19. #19
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    Dec 2003
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    1206

    Re: HDPE question

    Wouldn't it be a whole lot easier to use a piece of 1/4" clear acrylic and then attach a boundary piece to it?

  20. #20
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    Jun 2017
    Posts
    369

    Re: HDPE question

    Gerry - thank you

    Routalot - thank you I know it wouldn't matter with AC power but I wasn't sure about DC since the inverter is right at the outlet.

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