Windows

[Novice21]

Well, the nice man in the shop will have made us some new perspex windows for the boat by the weekend. They'll be the right shape, but he can't drill the holes apparently (for the bolts to go through).

Can anyone give me any advice on the pitfalls we're likely to encounter? I'd rather not have to get a second set of windows bevause I've cracked the first lot!

Also, we need to clean the old sealant off before we fit the new windows. Is it just a case of scraping it off, or is there more to it?

Many thanks for any help! /forums/images/graemlins/confused.gif

 

[samwise]

Need a bit more info really. How are the windows fitted? Are they in a frame? Is there a rubber gasket anywhere? How did you crack the first lot? Understand why he can't drill the holes because he doesn't know how they go on the boat. You should have given him a template. Drilling the holes in situ is a recipe for disaster. Re sealant, it depends where it is. If it is on the gelcoat you need to be careful. There are proprietory sealant cleaners but if your stuff is old, a scrape may be the only answer.

 

[FullCircle]

Hi C,
can come down and have a look for you on Sunday at the Yard?

 

[Talbot]

When I did this, I used the old window as a template for the hole. I used a slow speed on the drill and made sure that the window was on a backing sheet of wood. Dont remove the backing sheets from either side of the window until all the holes are completed and you are ready to fit.

You also need to make sure that the screw hole is sufficiently large for the screw to slide easily through it. There have been lots of winndows ruined by screw suffering thermal expansion in the summer, and the hole being too small - result cracked perspex.

 

[srp]

[ QUOTE ]
When I did this, I used the old window as a template for the hole. I used a slow speed on the drill and made sure that the window was on a backing sheet of wood. Dont remove the backing sheets from either side of the window until all the holes are completed and you are ready to fit.


[/ QUOTE ]
Agree with everything there apart from the speed. For machining acrylic you need a fast speed and a very light feed pressure. If you have a small grinder it also helps to grind the rake angle on the drill to 90 deg, so it has more of a scraping action.

 

[damo]

And what is the team's opinion on starting holes with a slightly dulled drill bit, to prevent tearing? It's a job I will be starting soon as well, with the added complication that several of the windows are curved /forums/images/graemlins/frown.gif

 

[SvenglishTommy]

Be really, really carfull. Perspex is a bitch to work with, and it is so easy to mess it up. I'm thinking about the same job, and got some to test on. Too fast and it melts, too slow and the bit catches and cracks the perspex. I found that using some lubrication with a slow, but determined, speed worked best.

 

[ningcompoop]

I've never drilled perspex but..... drilling holes gel coat grp i was amazed how much easier it was to get an accurate, clean hole using a manual/hand drill at a slow speed, as opposed to a battery drill. Would it be the same on perspex?

 

[philip_stevens]

What about one of those tile drill bits and a slow speed??

 

[ningcompoop]

Found this- working with acrylic
-backs up what has been said by several of the above forumites. What a jolly good place this forum is! /forums/images/graemlins/wink.gif

 

[Novice21]

That's great, thanks /forums/images/graemlins/smile.gif

I agree, what a great forum!

Fingers crossed...

 

[milfordman]

I agree with the previous posts. I fitted replacement acrylic windows in my boat 7 years ago and that involved drilling holes and countersinking. I used standard HSS drill bits and ground the edges to give zero rake, i.e. cutting edge perpendicular to the surface of work piece. The work piece was clamped to an 18mm plywood backing piece. I used an old Black and Decker electric hand drill mounted in a bench stand. the work piece and backing pad was clamped to the bench. The drill speed was probably about 1000 RPM the feed was kept as low as possible. The zero rake stops the inclination to dig in, and the slow feed rate helps to keep the temperature low which is important to stop the swarf from welding together. As previously mensioned the size of the hole should take into acount the high coefficent of expansion. The figure I was given was 1mm per meter per 10 deg C.