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  1. #1
    Join Date
    Sep 2015
    Posts
    40

    Default Drilling acrylic without cracking the new windows.

    OK so what do I need to know so as to not foul up this job? Just about ready to order the replacement small windows.

    6 mm thick acrylic, and clearance holes for 5 mm screws. Hole centres will be 20 mm from edge.
    48 holes to drill.

    Is 20 mm far enough from the edge?
    Drill speed?
    Drill pressure?
    Anything special drill bit type?

    Thanks in advance

    Gordon
    Last edited by GeeW; 25-03-19 at 21:30. Reason: Spilling orrers

  2. #2
    Join Date
    Sep 2008
    Location
    Cambridge/Pin Mill
    Posts
    878

    Default Re: Drilling acrylic without cracking the new windows.

    I'm sure there will be lots of different views on this, but the important thing is to cut it and not melt it.

    I would use a slow speed, not too much pressure and a wood bit. But almost any sharp bit would do.
    ' The gods do not deduct from a man's allotted life span, his days spent sailing '

  3. #3
    Join Date
    Dec 2010
    Location
    South Oxfordshire, Gosport and Wellington New Zealand.
    Posts
    7,575

    Default Re: Drilling acrylic without cracking the new windows.

    Just done this job in Wellington, NZ.

    I ground the drill bit quite flat and without much lead on the cutting flutes.

    Always works, even when drillin double curvature motorbike racing screens which are very thin.

    I used .5mm clearance and bedded the new windows on butyl tape.

  4. #4
    Join Date
    Jan 2004
    Location
    Bricks & mortar: Italy. Boat: Aegean
    Posts
    10,414

    Default Re: Drilling acrylic without cracking the new windows.

    Quote Originally Posted by rotrax View Post
    Just done this job in Wellington, NZ.

    I ground the drill bit quite flat and without much lead on the cutting flutes.

    Always works, even when drillin double curvature motorbike racing screens which are very thin.

    I used .5mm clearance and bedded the new windows on butyl tape.
    +1 to all that**, plus lodesman's comment about overheating, which can cause stress cracking later. It's possible to buy bits designed for use on acrylic on eBay/Amazon.

    ** except that it's not strictly necessary to go to NZ to do it.
    All epigrams are false

  5. #5
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,052

    Default Re: Drilling acrylic without cracking the new windows.

    Quote Originally Posted by GeeW View Post
    OK so what do I need to know so as to not foul up this job? Just about ready to order the replacement small windows.

    6 mm thick acrylic, and clearance holes for 5 mm screws. Hole centres will be 20 mm from edge.
    48 holes to drill.

    Is 20 mm far enough from the edge?
    Drill speed?
    Drill pressure?
    Anything special drill bit type?

    Thanks in advance

    Gordon
    According to the little booklets I have from a couple of the drill bit manufacturers special drill bits ground to a more acute tip ( 60 instead of 118) and an increased lip clearance angle ( 20 instead of 10 to 12) should be used.

    The safe/ smart way is to get them drilled by the supplier. They will also polish the edges if required

  6. #6
    Join Date
    Nov 2011
    Location
    Nelson New Zealand
    Posts
    563

    Default Re: Drilling acrylic without cracking the new windows.

    I am contemplating replacing windows this off season so have a serious interest in this topic.
    My question is why drill holes at all? I have heard that Butyl tape alone is sufficient.
    Comments anyone?

    My boat is glassed over plywood construction.
    My plan was to remove the windows, fill the holes and sand back and epoxy undercoat and 2 pack polyurethane top coat the window frames. (I have been using the 2 pot system on other areas of the boat with complete sucess.)
    This means that if relying on butyl alone to bond the windows, it also means relying on the quality of paint bond to the subsurface.
    Is this a problem or should i do like OP and refasten with lots of screws?
    Aiming to live forever or die in the attempt!

  7. #7
    Join Date
    Dec 2010
    Location
    South Oxfordshire, Gosport and Wellington New Zealand.
    Posts
    7,575

    Default Re: Drilling acrylic without cracking the new windows.

    Quote Originally Posted by John the kiwi View Post
    I am contemplating replacing windows this off season so have a serious interest in this topic.
    My question is why drill holes at all? I have heard that Butyl tape alone is sufficient.
    Comments anyone?

    My boat is glassed over plywood construction.
    My plan was to remove the windows, fill the holes and sand back and epoxy undercoat and 2 pack polyurethane top coat the window frames. (I have been using the 2 pot system on other areas of the boat with complete sucess.)
    This means that if relying on butyl alone to bond the windows, it also means relying on the quality of paint bond to the subsurface.
    Is this a problem or should i do like OP and refasten with lots of screws?
    Not sure the Butyl tape would be enough if the windows were fixed externally.

    Our steel Hartley had 42 screws,84 washers and 42 dome nuts fixing each of the larger windows-there were 4 of them, and ditto 22 screws washers and nuts for the portlights, x6. They were fitted internally, leaving a lip open to the elements which, of course, corroded.

    I think a Sikaflex type product would be more suitable for screwless fixing. Butyl tape was used in our application for ease of use and cleaning up, as well as it sealing properties.

    I reused the portlights and their fastnings but filled and re-drilled the larger window apertures to take enlarged windows-+4inches-and half the fastners. This allowed the coroded apertures to be enlarged, removing much of the corrosion.

    The windows were fitted externally.
    Last edited by rotrax; 26-03-19 at 08:49.

  8. #8
    Join Date
    Jan 2004
    Location
    Bricks & mortar: Italy. Boat: Aegean
    Posts
    10,414

    Default Re: Drilling acrylic without cracking the new windows.

    Like rotrax, I'm a bit sceptical about using butyl tape and nothing else. I regard the tape as a sealant rather than a bonding medium and wouldn't trust it alone on a boat without fasteners or some sort of retaining trim.

    An alternative might be Arbomast BR, which is butyl-based but claimed to have some sealant properties. It's had excellent reports on here as a sealant. But I'd ask the manufacturer before going screw-less (and then not do so )
    http://www.arbo.co.uk/arbo-sealants/arbomast-br/
    All epigrams are false

  9. #9
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Richards Bay East Coast Africa
    Posts
    6,776

    Default Re: Drilling acrylic without cracking the new windows.

    To add to the above I always put some masking tape over where I wish to drill the hole to reduce the chipping around the hole and helps to stop the drill running away from the required position.

    Also hold the perspex down to stop it jumping up when the drill breaks through.
    Life is too short not to have a sea view
    Distantshaws tinyurl.com/yclt6l68

  10. #10
    Join Date
    Sep 2001
    Location
    Home - Sothampton, Boat - Gosport
    Posts
    9,693

    Default Re: Drilling acrylic without cracking the new windows.

    When I did my windows, I drilled them using a sharp wood bit, gentle pressure and slow speed.
    Steve
    Never believe anything until it has been officially denied.

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