HELP! Windows delivered with holes too small

najsmith

najsmith

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Just recieved my order of 8mm perspex windows cut & drilled to my templates... only I'd spesifically asked for 6mm holes to be cut so I could use M% bolts and cater for expansion/lateral movement in the summer.

Guess what - they look lovely apart from the 4.25mm holes...

What do I do? I wanted to fit them this w/e -- the only slot I have a full w/e free for another month.

HOw do I drill larger holes using the 4.25mm as guides, when I want to be sure they line up with the holes already in the GRP topsides.

Plan is to now drill though and use inter-screws to pull the new windows against 3mm neoprene sheeting to provide a snug and watertight seal.

How can I rememdy my drill hole prob? What drill bits do you use for acrylic?

Arghhhh!
 
The holes should be slightly countersunk each side to prevent a stress riser (right angle).
If this has not been done then do it and use this as a drill guide, use a sherp drill slowley and with no pressure and just ream out the .75mm .
 
Re: HELP! Windows delivered with holes too small

Normal high speed steel bit (HSS) use a slow cutting speed would best be done using a pillar drill to ensure that you can centralise the bit to the existing holes, that assumes they have got the centres right and just driiled too small. Better still bite the bullet take them back and refit in a month after the "professionals" have rectified their error.

Good Luck
 
Very carefully. You need idealy a bench drill so they can be held flat and square but more importantly you need to take the edje off the drill bit ie make the rake angle negative. If you use a sharp new drill bit they will snatch and split.
Same technic as drilling a number plate. Personally if i had paid someone to make them and they were not correct i would reject them and plan another date to fit.
 
Ordinary high speed steel metalwork drill bits are OK for acrylic. If the small holes are in the right place, then they will still be correct when opened out, because the larger drill will centre in the pilot holes. Use a fairly low speed and just enough pressure to keep the drill cutting. Do not use a blunt drill as the pressure needed could cause a piece of the plastic to break out when you near break through. Best method of all is to back the acrylic with a piece of plywood so that it is fully supported, and drill though the acrylic in to the ply, using a bench drill.

One final thought. I do not like the idea of bolting acrylic down to soft 3mm neoprene sheet which will compress and cause local distortion and possible cracking of the acrylic.

EDIT: Davido is right, ideally the drill should have slight negative rake put on to the edges with an oilstone to stop it "grabbing" just as you should do for drilling brass. This does not mean that it should be blunt, just a tiny sharp edged flat stoned on to the cutting edge, not the edge rounded off.
 
Put your power tools away! Just open them out by hand using an ordinary hand brace. Make sure your drill bit is nice and sharp and you will wonder what all the fuss is about!
Using a power tool by hand the drill will have a tendancy to grab. It's fine when drilling a new hole but opening out is safer by hand.
 
Thanks All.

Contacted the firm in question. Were very apologetic and are coming down to meet me at the boat tomorrow to drill out the holes for me.

At least this way, if anything goes wrong, in the words of Shaggy.... "It wasn't me!".

Heres to a rian free weekend and succesful installation of 4 new windows.

I plan to celebrate heavily if they are water tight!
 
Glad they are going to come down and sort out the problem /forums/images/graemlins/laugh.gif

Whenever I have problems with my Windows, I always like to blame Bill Gates and his Cronies!! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
 
Use a hand held taper reamer like this (3rd one down):
http://www.axminster.co.uk/product-Halls-Countersinks-Reamers-and-Deburrers-22276.htm
An ordinary twist drill is ok but not ideal in this case as the existing hole will encourage the 6mm bit to snatch. Normally when machining acrylic you should use a HIGH speed and a LOW feed rate, cooling if necessary with water or compressed air.
If it was me in your circumstances, I'd take them back. If you crack one of them trying to do it yourself you'll have no come-back.
 
Good news!

Windows were drilled out as prommised.

New windows fitted against neoprene gasket with M5 & interscrews.

Tightened up quite a bit but know I should allow for expansion. Worried Rain will enter the holes from the outside if bolts not down tights, but also aware danger of cracking.

Thinking about putting marine silicone sealant in holes with bolts for belt and braces -- concerned this will put yucky silicone stuff on the windows themselves.

How tight is tight enough?
 
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