Window Interscrews

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SteveIOW

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I need to replace my cabin windows which are badly crazed and one has a crack. The aluminium frames are secured to outside of grp with stainless steel interscrews and have not been disturbed for 40 years. Unsurprisingly fixings are loathed to come apart. Am just able to turn the slot headed screws on the outside but instead of undoing it just turns the splines of the socket part within the grp cabin side and aluminium inner frame strips.The head of the socket section is plane and slightly domed with no obvious means of stopping it rotating once the splines have lost their grip on the grp and the inner aluminium strip.

My question is “How do I remove these interscews?”
 
SteveIOW said:
My question is “How do I remove these interscews?”
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It may be possible to drill off the chamfer inside at the dome end while someone holds a screwdriver in the outside slot. Drill just sufficiently so the inside portion can be punched outwards. Your new Inter screw should be slotted at both ends. To start you will need to centre punch the dome. It might also be easier if you start using a centre drill. these are stiffer than a normal drill and available from tool stores. Usually used on lathes.
 
When I did Jissel's windows, the cost of interscrews meant I used ordinary machine screws with Allen heads as I thought they'd be easier to remove in a few years than slots or pozi. On the inside, I used dome nuts.

I don't reckon they looked bad

Window.jpg
 
Not knowing what yacht you are talking about makes giving advice difficult.

If you have a Westerly, then the interscrews are not stainless steel but chromed brass. Stainless steel and aluminium causes the aluminium to corrode due to electrolsis, hence why brass was used. Westerly used a rare size of 3.5mm by 10mm long. Most should unscrew, but some will need to be replaced. I do have a small stock of this unusual size and should be able to help replace those that need replacing.
 
Concerto said:
Not knowing what yacht you are talking about makes giving advice difficult.

If you have a Westerly, then the interscrews are not stainless steel but chromed brass. Stainless steel and aluminium causes the aluminium to corrode due to electrolsis, hence why brass was used. Westerly used a rare size of 3.5mm by 10mm long. Most should unscrew, but some will need to be replaced. I do have a small stock of this unusual size and should be able to help replace those that need replacing.
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ITYWF later Westerlies used a more readily available size. 4mm ???
 
VicS said:
ITYWF later Westerlies used a more readily available size. 4mm ???
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The only inter screws sold by Trafalgar Marine (now closed) were the size I quoted and that is where I bought mine from. The owners of TM used to work at Westerly and were able to source parts from the original suppliers, but alas they have now retired.
 
I recently the same problem when I was relining forecabin.

I looked at which side would be best to 'drill' so to remove the 'head' and then push through the remains. Drilling the inner dome would have drill skidding of the dome ... drilling the screw head outside would have drill grabbing the slot. There is another possibility - a carbo wheel on a Dremel to create a screwdriver slot in the inner dome ...

What did I do ? I tried the Dremel making slot ... a few actually held OK with this and outer screw came out. Rest I used a cone shaped grinder in my drill to create a pit for actual drill to get started in ... some to the dome - some to the head depending on access.

Local hardware shop has stainless similar replacements .....
 
SteveIOW said:
The idea of drilling out 140 stainless steel screws fills me with dread!
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Just start with one window, ideally the smallest or maybe the one with worst leaks. As per Refueler I would try creating a slot with a Dremel. They do different thickness grinding / cutting discs but they can and do break easily. I like the idea of cone shaped grinder but there is still the problem of centring it to start with.
 
Boathook said:
Just start with one window, ideally the smallest or maybe the one with worst leaks. As per Refueler I would try creating a slot with a Dremel. They do different thickness grinding / cutting discs but they can and do break easily. I like the idea of cone shaped grinder but there is still the problem of centring it to start with.
Click to expand...

The cone is best used on the slotted head outside as it can more easily create the starter hole for a drill.
 
The replacement screws / inserts I used are metric ... the old 'marine' are not. Typical marine game !

So .... I spent time in local hardware shop with shop guy ... and solution was slightly larger inserts with ribbed tube section. The size was only a tiny bit more than the old. A small amount of filing to then have them a tight fit into the frame. That means that the insert is gripped and screw can be tightened with it turning.
The inserts were closed flat head instead of the dome .... but look nice.
All stainless of course ... screws and inserts.
 
Refueler said:
The cone is best used on the slotted head outside as it can more easily create the starter hole for a drill.
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When I've had to drill out rivets the whole lot starts to turn with the drill bit when nearly through. Normally succeed in the end but a pain.
Back to the OP; trying to start on the dome side at least leaves the slot for a screwdriver to stop the whole fitting turning. Either way it is an awkward job even with 2 people.
 
When we replaced the acrylic windows on our Jeanneau Tonic I used SS interscrews from I think Bristol Fastenings although a quick online search does not find them.

If doing it again I would probably use SS machine screws and lock nuts flush cutting the excess thread inside.

With the interscrews the thread length had to be quite accurate, as there was a curve to windows bending the acrylic and fitting relatively short screws was tricky. In the end I used some thin (3 or 4mm) threaded rod and nuts to pull the sheet in then replaced with the interscrews.

I have never had a problem drilling small holes in SS so far, maybe because I sharpen my own drill bits.
 
Just follow the advice given in #5 above by Bilgediver. Centre punch in the middle first. A lathe centre drill is ground very accurately so will not skid about in the centre dot & being short will not flex. (Drill bits will not start properly in slots)It must be held square to the item being drilled & one must not wave the drill about as if waving a flag at a procession. Hold it straight & firmly. ( Have you ever watched amateurs driving in a screw? :rolleyes: The handle of the screw driver does bigger rotations than a carousel at a fairground) Once the drill has made a start a larger dormer twist drill can be used to drill a deeper hole. Then the final drill to remove the dome completely.( please do not waste money on Lidl drill bits :eek: )
It all relies on the initial punch mark being central. To do this one can adjust the position by knocking the indent sideways a bit with the punch, if not spot on first time. Personally I would use an automatic centre punch, but that is because I have one. It gives a light tap & can be aligned properly.
 
In the end I used some thin (3 or 4mm) threaded rod and nuts to pull the sheet in then replaced with the interscrews.
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I forgot to mention I used similar ... idea was to align and hold window close in and correct position. It also helped to have 'interscrews / screws' easier to tighten.

I have to say - I resisted initai thoughts of centre-punch and decided on the Dremel approach. My boat is early 70's and I wanted to be as 'gentle' as possible
 
To get the drill to center on the domed head try making a small jig from a hard wood. Get a strip of hard wood about 25mm square and 150 mm long.
Measure the diameter of the dome head and use a drill of that size and drill a shallow blind hole in the wood deep enough so that that it will fit over the dome head. Then driil though the wood block using the point of the blind hole as the centre. Use a drill a fraction smaller than the interscrew diameter. Then place the jig over the dome head and drill through the jig and you should find that the head of the dome will come away quite easily. I have done this in other applications and I am sure it would work on interscrews.
David MH
 
davidmh said:
To get the drill to center on the domed head try making a small jig from a hard wood. Get a strip of hard wood about 25mm square and 150 mm long.
Measure the diameter of the dome head and use a drill of that size and drill a shallow blind hole in the wood deep enough so that that it will fit over the dome head. Then driil though the wood block using the point of the blind hole as the centre. Use a drill a fraction smaller than the interscrew diameter. Then place the jig over the dome head and drill through the jig and you should find that the head of the dome will come away quite easily. I have done this in other applications and I am sure it would work on interscrews.
David MH
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Drill jig is very good idea ...

Only thought in my mind ... is the number of screws holding these windows .. may mean that wood jig gets worn-out ?? I Know .. make another !
 
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