Shower valve hole too small to allow replacement...how to enlarge?

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Plumber's granddaughter, Jul 16, 2014.

  1. Plumber's granddaughter

    Plumber's granddaughter New Member

    Messages:
    3
    I am in the midst of changing out our Kohler mixer pressure balance kit (regulator & cap Kohler kit #GP76851) but apparently the original pieces were put in place from behind. How do I safely enlarge the opening in the fiberglass surround to allow for replacement from the front? A hole saw cannot be used since the valve cap is in place. Would it make sense to drill a series of holes around a pencil outline or is there a better way?

    Here is photo...you can see the metal part is BEHIND the fiberglass. That lays on top of part of the valve unit so the hole needs to be very slightly bigger than the unit to slide out from the front as designed.

    The current hole is only 2-1/2" while the valve cap unit is 3". We need to get the hole bigger without damaging the fiberglass or getting too big...the faceplate measures 3-3/4" across.

    Thanks in advance!

    Attached Files:

  2. Reach4

    Reach4 Active Member

    Messages:
    2,233
    Location:
    IL
    Not a pro. My method would be way slow for a pro. Here is my idea.

    Get a 3-1/4 hole saw which uses a removable 1/4 inch pilot bit. A bigger pilot bit would not hurt, but 1/4 is the size I am familiar with.

    Get a suitable piece of wood such as a piece of 1/2 inch plywood maybe 6 by 12 inches. Size is arbitrary, so use what you have or what you think will be easy to hold.

    Determine the thread of the screw that goes into that handle. Get various length screws to match that thread. Flat head would be good, but not critical.

    Mark center lines into the wood horizontally and vertically. Extend the lines around the edge of the board. These side marks will be to position the board.

    Draw centerlines on your fiberglass centered on where you want the hole. Use a level If you cannot easily draw single lines through the center, you can draw equally-spaced lines (above and below) and (left and right) of the center. That could be easier if there is a protrusion that prevents you placing the edge of your level right in the middle.

    Use a center punch or drill a small hole in the middle of your board that will serve to make sure that pilot bit goes right in the middle of the board matching your lines exactly.

    Off to the side, cut the 3-1/4 inch hole with your hole saw into the plywood.

    Remove the pilot bit from the hole saw.
    Now how to avoid cutting too far? Put a long screw into the center of your brass piece. Select a screw length to let the screw head stop the hole saw. You can fine-tune by loosening the screw some. You may need to put a plug or 1/4 inch bolt where the pilot drill had been in the hole saw to make a better surface for your screw to stop against.

    Position the board against the fiberglass. You can use a helper, or you can use some strong tape. (Gorilla tape is strong, but harder to clean up). Be accurate.

    With the hole saw in your hand-held drill, drill through carefully, keeping the drill aligned well. The wood keeps your hole saw positioned accurately, but you have to keep your drill straight horizontal. The screw should keep you from breaking through suddenly. If you are almost through, but have some part of the circle not quite through, you may be able to break off the remainder.

    I have no familiarity with your valve. I am not saying I know that 3-1/4 would be enough. I am just trying to suggest how you might make the hole that you are asking how to make.
  3. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    With the valve in place, I would not use a hole saw.
    You can a router perhaps. Dremel makes one, and I have also used a tile router. Even a jig saw works sometimes.
    I have also just taken a drill with drill bit, and drilled a series of holes, breaking out between the holes with pliers. You only have to remove a little bit to get those holes large enough.

    With fiberglass, you even hole a hand saw option to work your way around. A drywall jab saw is a little rough, but sometimes works, or a hack saw blade hand held out of the frame.
  4. Plumber's granddaughter

    Plumber's granddaughter New Member

    Messages:
    3
    Thank you @Reach4 and @Terry Love for your quick replies. They are appreciated! I will do my best to get the hole enlarged and the valve replaced so that the dripping stops.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,626
    Location:
    Cave Creek, Arizona
    Use a RotoZip tool to make the hole larger.
  6. plumberjeff

    plumberjeff Mister Plumber

    Messages:
    21
    Location:
    Seattle WA
    I would use my cheap import imitation Fein Saw (multi-tool). Perfect for this. It's really easy to control depth of cut. Fein version is around $400, Harbor Freight has them for $20 or $40. I use the heck out of my $40 unit. And it's *great* for sheetrock.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,626
    Location:
    Cave Creek, Arizona
    For this job he does not have to control the depth of cut, but does have to control staying within the boundaries of the plate.
  8. Plumber's granddaughter

    Plumber's granddaughter New Member

    Messages:
    3
    Thanks to all of you for your suggestions. Drilling small holes around the opening then snapping them out with pliers did work. Afterwards I used a Dremel with a coarse band to smooth the edges and it worked wonders...I actually think it might have done the trick alone. The job is complete...no more drips!

    Attached Files:

    Terry likes this.
  9. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    I'm glad that drilling the holes and snapping with pliers worked. I used to work in a bicycle shop in my youth, and a few years of that were for a Boeing Engineer from England. We didn't have a power grinder in the shop, but used files a lot. I found that using a flat file turned out to be quicker and did a better job.
    When I broke into plumbing, the other plumbers would send out their self-feed bits for sharpening. They would come back almost with nothing left on them. I could take out a small hand file, and I could sharpen mine even better, and take almost nothing off. My bits lasted years and years, for the price of a small hand file. :)
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