Lotus Elan

Alex Black style window fixings - hole size

PostPost by: ericbushby » Sat Sep 11, 2021 8:23 am

Hi All,
I intend to make some window cable fixing bolts for a Club members S4. They will be based on the excellent design by Alex Black, possibly with minor variations. I do have dimensioned drawings of various versions of this fitting.
They will be fitted during this winter so I do not have the glass to hand.
Has someone got a window glass out and if so will you measure the thickness and more importantly the diameter of the hole in the glass.
Is this hole drilled in which case it should be accurate or is it moulded and the size might vary.
On my S3 the glass is 4.9mm thick. I assume for now that the S4 is the same.
Hope you can help.
Eric in Burnley
1967 S3SE DHC
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PostPost by: oldelanman » Sat Sep 11, 2021 10:53 am

Hi Eric,
Not sure how critical the glass thickness is to your design but my S4 glass is only 3.95 mm thick. Can't help with the hole size as my glass is not out but hopefully someone else will be along shortly.
Roger
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PostPost by: ericbushby » Sat Sep 11, 2021 11:29 am

Thanks Roger,
There you go, another weight saving. I did not expect that.
My glass appears to be original as it has the dot under the `N` in TOUGHENED which is the date code for 7 (1967) Thanks again.
Eric
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PostPost by: oldelanman » Sat Sep 11, 2021 12:18 pm

Hi Eric,
That's interesting, I didn't know you could date the glass. So I just checked mine and the etchings are different on the two windows and show different codes .... 1969 and 1971 ?? They both measure 3.95 mm thickness.
There is also a dot above the letters of "Triplex" .. any idea what that means ?

PXL_20210911_115249654.jpg and
PXL_20210911_115330469.jpg and
Roger
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PostPost by: RAJ2628 » Sat Sep 11, 2021 1:02 pm

My S4 Triplex glass measured 4.06mm. Given Eric's measurement of 3.95mm nearest imperial equivalent is 5/32"
Hole diameter is between 7mm and 7.5mm. Nearest Imperial equivalent is 9/32"
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PostPost by: ericbushby » Sat Sep 11, 2021 2:05 pm

Thankyou for that. It may be a breakthrough for me.
Previous designs have used a 6mm or a 1/4" bolt to make the fastenings. If a size of 7mm is possible then I can confidently make the diameter of the bolt where it goes through the glass thick enough and strong enough to make it from brass. As I cannot machine stainless steel, prototypes so far have been 1/4" dia. steel.
Can someone else confirm the hole diameter please.
Eric
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PostPost by: RAJ2628 » Sat Sep 11, 2021 2:29 pm

I wrapped one piece of electricians tape around the shank of a brand new 7mm diameter drill.
It produced a lovely sliding fit in both holes.
Measured diameter 7.2mm.
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PostPost by: ericbushby » Sat Sep 11, 2021 3:42 pm

That`s more like it, thankyou.
I didn`t like to be picky but I did need more accuracy, thanks
I can now allow a tolerance and turn a plain shank of maybe 6.8 mm. which will give me adequate strength in brass so that the internal grub screw cannot push the bolt head off at the cross drilled hole where the wire goes.
Prototype No 3 coming up. If this is a success I will post full details, but don`t hold your breath as I do not know when it will be tried out.
Eric
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PostPost by: Donels » Tue Sep 14, 2021 6:05 pm

The 'dot' under the toughened lettering tells you the year the glass was manufactured. No dot would be 1970 and a dot under the T would be 1971, under the O 1972, etc.
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PostPost by: ericbushby » Thu Jan 06, 2022 1:46 pm

DSCF0698.JPG and
I have now made a few prototype fixing screws for the window cable.
The body is brass with two brass and two fibre washers.
As my windows work quite well at the moment I cannot easily test these to see if it is all a good idea.
Has anybody in the UK got a window out or a door stripped down and is willing and able to test and evaluate these for me in order to spot any weaknesses or room for improvement. I will post them free to you.
I have no interest in the value of these fittings and do not intend to make any money from this venture.
Eric in Burnley
1967 S3SE DHC
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PostPost by: RAJ2628 » Thu Jan 06, 2022 4:24 pm

Eric
My windows are out and in pieces waiting to re-assemble.
If you want to practice on them you are most welcome.
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PostPost by: ericbushby » Thu Jan 06, 2022 4:48 pm

Hi RAJ2628.
Thanks for the offer. I will bear it in mind for now. All I need to fit them in the glass is the thickness and hole size which I have from one example.
I am hoping for someone to try these when fitting the window cables.
Factors such as total length, diameters, thread length, hole size, head clearance are all adjustable when making them. I am hoping for feedback and suggestions as any improvements are easy to make at this stage. It doesn`t take me long to make these screws, but I don`t want to make too much junk.
Thanks, I will come back to you.
Eric
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