Drilling acrylic without cracking the new windows.

[BelleSerene]

The only thing I'd add is to just touch each end of the drilled hole with a countersink bit. Not to create a countersink but just to remove the 'sharp' edge of the hole.

That’s clever. Do you mean before drilling it?

 

[alahol2]

That’s clever. Do you mean before drilling it?

No, after drilling. I've always understood that sharp edges are 'stress concentrators' so removing the sharp edge will maybe help to prevent cracks from developing/propogating.

 

[PetiteFleur]

Also if you use butyl tape as a sealant, fit a stainless washer on each screw between the Perspex and boat - this prevents all the sealant squeezing out and provides a good flexible seal. Work from the centre of the window to the ends, particularly if the Perspex has a bend in it.

 

[KellysEye]

When I drilled hole in acrylic I covered the area of the hole with two layers of masking tape to protect it.

 

[Pirx]

I've always understood that sharp edges are 'stress concentrators' so removing the sharp edge will maybe help to prevent cracks from developing/propogating.

That's true: standard aviation practice when presented with a crack in a transparent canopy is to drill a small ( 2-3 mm ) hole right at the end of the crack to remove the sharp point at the end. I have never heard of anyone worrying about the edges of the drilled hole, but I don't see that it would do any harm to chamfer it. If one was really fussed then the inside of the hole could be polished !

If you want to polish the edges what I do is use three increasingly fine grades of emery paper finishing with approx 200 grit and then polish with car chrome polish: it's quite quick and easy. 'Autosol' polish works well but I'm sure there are others just as efficient.