Anyone ever mill a polymer lower using the 5D Jig

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  • StantonCree

    Watch your beer
    Jan 23, 2011
    23,932
    Just curious if anyone has tried it?

    50% of me says it should work like a champ, done in 20 mins. The other 50% of me is worried about melting plastic.
     

    trickg

    Guns 'n Drums
    MDS Supporter
    Jul 22, 2008
    14,584
    Glen Burnie
    Just curious if anyone has tried it?

    50% of me says it should work like a champ, done in 20 mins. The other 50% of me is worried about melting plastic.
    I've seen that happen at an 80% party one day, although they managed to get it done.

    I think you'd have to go really slow and use a very slow milling speed to prevent that.
     

    DutchV

    Ultimate Member
    Jul 8, 2012
    4,702
    I thought the big issue with polymer lowers is that they break at the receiver extension tower.
     

    StantonCree

    Watch your beer
    Jan 23, 2011
    23,932
    I thought the big issue with polymer lowers is that they break at the receiver extension tower.

    ive obviously read that as well but it seems a majority of them are reinforced there now a days.

    i'm not going to lie I kind of want to try this. I REALLY don't need or want another AR15 but I do want to see how well this works.
     

    twybyll

    Active Member
    Jan 20, 2021
    422
    MD
    Are you asking about the milling melting plastic, or the receiver melting due to use?

    If milling, then I believe a big part is using the right bit. I've heard single flutes bits work best on plastic.
     

    StantonCree

    Watch your beer
    Jan 23, 2011
    23,932
    Are you asking about the milling melting plastic, or the receiver melting due to use?

    If milling, then I believe a big part is using the right bit. I've heard single flutes bits work best on plastic.

    the receiver cast off melting, gumming stuff up is more of my concern.

    i was thinking of trying it using my milling bits that are sort of past their prime as far as metal is concerned
     

    StantonCree

    Watch your beer
    Jan 23, 2011
    23,932
    It should work just fine. You would have to go SLOW.

    i was hoping you would chime in! Thank you.



    Follow Up

    Anyone every utilize a friends uncles brothers dads (since I know no one has their own) polymer 80% and what issues. Do you have the reinforced tower?

    I saw the thread about cracking but honestly i couldn't tell chit from those pics.
     

    twybyll

    Active Member
    Jan 20, 2021
    422
    MD
    huh.......well that kinda throws my idea out the window. I gotta buy new bits anyway but I did not see that coming.

    Well, I've milled polycarbonate without the right bit before. It does gum up on the bit, but it's also really easy to remove, I just had to twist it off. Worth an experiment with a scrap.
     

    StantonCree

    Watch your beer
    Jan 23, 2011
    23,932
    Well, I've milled polycarbonate without the right bit before. It does gum up on the bit, but it's also really easy to remove, I just had to twist it off. Worth an experiment with a scrap.

    You and I are thinking the same. I'm in no rush for anything i was just under the impression I could utilize the dull bits with full on success. Seems that might not be the case.
     

    twybyll

    Active Member
    Jan 20, 2021
    422
    MD
    You and I are thinking the same. I'm in no rush for anything i was just under the impression I could utilize the dull bits with full on success. Seems that might not be the case.

    You can always save them for milling reloading trays out of wood :D
     
    I've done it with an end Mill chucked in a drill press using an XY vise. I've actually done it three times. All three times it needed a little cleanup with a small flat file but all three times it worked just fine. I used the drill press because it doesn't spin as fast therefore it doesn't generate as much friction where heat.

    I only use polymer lowers for dedicated rimfire though. I've built two using the cmmg conversion kits and I've built two using dedicated CMMG bolts with CMMG 22 long rifle uppers. I used an aluminum one for one of them
     

    Matlack

    Scribe
    Dec 15, 2008
    8,555
    Yes they can be milled. You have to use the lowest speed for your mill and your feed rate needs to be very low as well. I have done them using a manual mill and I went really slow and cut maybe 3/8 of depth at a time. I played with it a bit, if I didnt take enough material it would try to jump. I didnt feel comfortable doing full depth cuts, but it would probably be fine.
     
    Yes they can be milled. You have to use the lowest speed for your mill and your feed rate needs to be very low as well. I have done them using a manual mill and I went really slow and cut maybe 3/8 of depth at a time. I played with it a bit, if I didnt take enough material it would try to jump. I didnt feel comfortable doing full depth cuts, but it would probably be fine.

    A friend of mine has done his that way using a drill press. He simply set the depth of plunge to the depth needed and just plunged down through the plastic and then cleaned it all up. It didn't physically look as nice as my method but it function just fine
     

    Boxcab

    MSI EM
    MDS Supporter
    Feb 22, 2007
    7,862
    AA County
    What is the bit size for the 5D setup?

    I understand that they are hard to come by unless from 5D, so if you find a low flute count
    bit of the correct size, please share.




    .
     

    roosterfried

    Member
    Aug 3, 2020
    12
    i would agree with moving quickly with a router. i found chunks of melted together debris, but they were easy to pop out
     

    135sohc

    Ultimate Member
    Oct 27, 2013
    1,157
    huh.......well that kinda throws my idea out the window. I gotta buy new bits anyway but I did not see that coming.

    We do a fair amount of plastic on the CNC router at work (I do the programming part and some operation).

    A sharp cutter will shear the material off, a dull cutter will rub and melt.

    Edit: feed rate is also relative to how fast your spindle is turning, a hand router or cnc router is going to be spinning at 25k+ and you can really let it eat. A manual type mill is going to top out around 3k and most do not like to run that fast for any length of time so yes you need to feed slower if that is the case.
     

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