Fitting acrylic windows

[alahol2]

I will be replacing the bolted-on acrylic windows this winter. They are 1100mm x 215mm and currently 6mm, I believe.
I will be getting them cut and radiused but I intend to drill the holes myself.
Questions...
1) The windows are fixed with M4 pan head machine screws, the thread diameter is about 3.8mm what size holes should I be drilling? 4mm, 4.5mm?
2) I was planning to use Arboseal GZ mastic tape to bed the windows onto. The windows will need to flex round the curve of the cabin and I am wondering if they are liable to squeeze out too much of the mastic at the centre of the curve? Would I be better off with a single/double sided neoprene tape?
3) Should I put washers under the heads of the screws? There are currently no washers.
4) When bolting down, do I start at one end or in the middle to induce the curve?

 

[macd]

1. Drilling. A sharp, high-speed bit will cut too quickly and be inclined to grab. See this: http://www.bertram31.com/proj/tips/drill_acrylic.htm
It coincides exactly with my experience.
Perspex expands significantly in normal temperature ranges...something approaching 1%, so needs some freedom to move. I'd go for at least the more generous of your figures. Don't overtighten the fasteners, especially if countersunk. If countersunk, a small cone of butyl rubber under the head will make an effective seal.
2. Consider this stuff: http://affixit.co.uk/single-sided-fo...-2_204_205_208
3. No. Difficult to seal, apart from anything else.
4. The problem with starting at one end is you'll have the whole thing flapping about, maybe trying to bond itself to the wrong bit of coachroof. My preference would be to offer up the window carefully with a temporary, over-length fasteners towards each end to locate it. Then begin tightening proper from the centre and work outwards.

 

[vyv_cox]

I recently rebedded two of the four windows on my motorsailer, using the tape that Macd suggests. These are quite large windows on the wheelhouse, about 1000 x 600 mm. The tape method was excellent and has proved to be perfectly watertight. I had previously done one window using Arboseal but found the tape a lot easier and with no need for cleaning up afterwards.

 

[alahol2]

Thanks Mac & Vyv. I had found the page about drilling acrylic, I've got to find someone at the club who knows how to grind a drill bit.
The tape you suggest seems to be 15mm thick, is that right?

 

[vyv_cox]

The tape you suggest seems to be 15mm thick, is that right?

The tape I used was 25 mm wide, 6 mm thick. They recommend that it should be compressed to about 3 mm. It has adhesive on one side, probably best stuck to the boat so that the window can be removed if needed. I stuck mine on the perspex due to the poor condition of the window surrounds.

 

[alahol2]

Thanks Vyv, that sounds much more sensible. I think I'll have to do the same as you and stick the tape to the Perspex, it will be far easier to position it accurately.

 

[geem]

I replaced my windows recently. They are 10mm tinted perspex. The windows use Stainless Steel CSK screws and the windows fit into a recess in the coachroof so they are flush when installed. They were bedded on a mastic. The new ones are also bedded on a mastic. There is a curve to the front windows that means you cannot pull the bolts tight or you squeeze the mastic out. There was sufficient friction on the centre bolts that you can carefully tighted the bolts from the centre working your way to the ends without squeezing the mastic. once I had the windows flush with the coachroof I didnt tighten them any more. The next day when the mastic had cured, I tighten the screws down a little more being careful to hold the outside slot head with a screwdriver so only the nut moved on the inside. This ensure you dont break the seal made by the mastic around the screw thread and maintains the watertight fit.
We did leave room for the perspex to expand in the frame and the screw holes were over sized for the same reason. The windoes were masked off the next day to allow a bead of mastic to be fed into the expansion space between the perspex and grp to give a clean and tidy finish. They look great and are fully watertight.
I like the idea of the windows being glued in. The boat is designed for serious offshore sailing and this is how the windows were fitted from new. They will take green water over the deck without any concern for leaks.

 

[grafozz]

I did all my windows last spring after many years of putting it off !
I found that the water was getting in through the mastic seal AND through the fixing ss screws , so looked into not using screws again .
I found that Butyl tape was used in car windscreen fitting so thought it was worth a try,
the fitting was relatively easy , hardest part was finding a long enough dry spell .
the originals were removed and all edges totally cleaned of glue residue .
masking tape was placed around the cutouts and on the outer window edges to sop the mastic/ butyl tape from overspilling the contact areas .
Then one by one , the butyl tape was applied to the coachroof and the new perspex were pressed in and held overnight using bags of sand hung across the boat to keep the pressure on whilst the butyl tape bedded in .
then a bead of sealant was squeezed into the gap left between the window edge and coachroof cutout .
This way I did not fit any screws back , which of course means no holes !

windows look far better without screws too , most new boat windows are now fitted this way .
keep the protective covers on the acrylic on both sides until the job is completed

 

[geem]

I did all my windows last spring after many years of putting it off !
I found that the water was getting in through the mastic seal AND through the fixing ss screws , so looked into not using screws again .
I found that Butyl tape was used in car windscreen fitting so thought it was worth a try,
the fitting was relatively easy , hardest part was finding a long enough dry spell .
the originals were removed and all edges totally cleaned of glue residue .
masking tape was placed around the cutouts and on the outer window edges to sop the mastic/ butyl tape from overspilling the contact areas .
Then one by one , the butyl tape was applied to the coachroof and the new perspex were pressed in and held overnight using bags of sand hung across the boat to keep the pressure on whilst the butyl tape bedded in .
then a bead of sealant was squeezed into the gap left between the window edge and coachroof cutout .
This way I did not fit any screws back , which of course means no holes !

windows look far better without screws too , most new boat windows are now fitted this way .
keep the protective covers on the acrylic on both sides until the job is completed

Interestingly mine were not leaking from the screws. They were leaking where the mastic had come unstuck from the perspex in the corners. This had happened on 3 out of the 6 windows. I don't know what mastic had been used but it didn't adhere well to perspex. Leaking screws are quite easy to solve. You can simply pull out the offending screw and coat with mastic and refit.

 

[alahol2]

windows look far better without screws too , most new boat windows are now fitted this way .
keep the protective covers on the acrylic on both sides until the job is completed

As the windows are coming without holes, I do have this option. Can I ask what bedding/fixing tape you used please.
Has anyone had problems with windows fitted in this manner, ie just glued in, I'm a bit distrustful.

 

[grafozz]

butyl tape

I bought the Butyl tape here :
DL Glass
Norman Simpson
d l glass
mill street east
dewsbury
West Yorkshire
WF129AQ
United Kingdom

Phone:01924 465848
Fax:01924 458433
Email:dlglass@btclick.com

via E Bay ,and bought more than required and now finding many uses for it !

 

[alahol2]

Thanks Grafozz, I think that's the Arboseal GZ butyl tape that I was originally thinking of using. Still undecided but will probably get some for other purposes also.

 

[GHA]

1) The windows are fixed with M4 pan head machine screws, the thread diameter is about 3.8mm what size holes should I be drilling? 4mm, 4.5mm?

When I replaced some there was a surprisingly large difference in the expansion due to temp of the window and steel it's bolted to, think the holes came out about 1mm oversize. Worth working out.

 

[misterg]

I would use the Arboseal (or equivalent). It takes quite a bit of pressure to make it ooze out. Start tightening from the middle - you don't want to end up with a 'hump' in the window which you will get if you tighten the ends down first.

I didn't have to do any clean-up particularly, after doing two long windows with Arboseal - I laid the strip about 3mm in from the edge of the window and it flattened out to pretty much the right place. It's been ~12 months since I did the first one and no problems so far. I'm more confident about it remaining watertight than I would be for the foam.

I've used neoprene foam tape in the past, and found that it compressed over time (a couple of years) and the windows started leaking again until the screws were re-tightened (different boat).

Trying to do it with mastic from a cartridge (sikaflex, etc.) was a nightmare!

 

[alahol2]

OK, it's decided.
I will get a drill bit ground down to about a 60 deg angle for drilling the holes. I'll use a pillar drill and the old windows as a drilling template.
I will use the Arboseal GZ butyl tape as originally planned. I'll drill 5mm holes and there'll be a 'washer' of Arbo under each screw head. I'll try to get the window curved to the shape of the cabin side before I start tightening down from the centre.

Many thanks for all the ideas/advice.

 

[alahol2]

OK, it's decided.
I will get a drill bit ground down to about a 60 deg angle for drilling the holes. I'll use a pillar drill and the old windows as a drilling template.
I will use the Arboseal GZ butyl tape as originally planned. I'll drill 5mm holes and there'll be a 'washer' of Arbo under each screw head. I'll try to get the window curved to the shape of the cabin side before I start tightening down from the centre.

For completeness and in case the thread comes up on any searches...
The drill bit ground to 60 degree point angle didn't work, it broke out of the bottom of the acrylic in a shower of splinters even when feeding very gently. The best drill bit was a standard HSS bit with the actual cutting edges ground flat so that the bit scraped its way through the acrylic. It created very clean holes.
I have written up the whole replacement process, for the class association, here... http://www.troppo.co.uk/odds/Flying%20Fox%20Windows.pdf

I'll know in a couple of years if the chosen method was the right one.

Thanks again.

 

[grafozz]

Thanks Grafozz, I think that's the Arboseal GZ butyl tape that I was originally thinking of using. Still undecided but will probably get some for other purposes also.

I just built a timber studio and found another use for the extra butyl tape , fitting the glass windows , perfect seal .