How to Measure Window Thickness?

[SteveIOW]

I need to replace a cracked Perspex window. I would like to purchase the new Perspex before I remove the old so that I am not held up during the boat's short time ashore. The problem is knowing what thickness to purchase as it's difficult to measure the thickness of the old whilst it's still in its frame. The 4 sided frame( inside & out) is secured with interscrews. Non-removable mahogany lining hides the interscrews within the cabin. If I could fully remove one of the interscrew I could measure the distance between the outside of the outer frame to the inside of the inner frame. Then I could sumtract the thickness of outer frame, the thichness of the inner frame and the thicknesses of the window sealant inside and out. The resultant value should be the thickess of the Perspex but there's a good chance of getting it wrong. What I think I want is some Cheap form of thickness gauge (ultrasonic)?) that I can simply hold against one face of the Perspex and it displays the thickness. I do own an elcometer but this is deigned for measuring paint thicknesses and windows are well outside its range.

Any suggestions?

 

[[70521]]

Cut a bit out of the window and measure.

Gaffer tape the hole.

 

[pvb]

Cut a bit out of the window and measure.

Gaffer tape the hole.

True Practical Boat Owner stuff!

 

[Deleted member 478]

Deleted.

 

[Don107]

You could drill a small hole in the perspex and this would let you measure the thickness

Regards Don

 

[Daydream believer]

Drill a 2mm diameter hole. Put a bolt( small brass one best)of known length through the hole & measure the length that protrudes. That enables you to calculate the thickness of the material. Then coat the bolt in mastic. Place it in the hole with a nut on & tighten it to prevent leaks until the new windows are available. Cut the end off with some cutters when finished so it does not stick out too much ( that is why you want a 2mm bolt). Put the hole in a position that is not obtrusive.
If you do not have any bolts try some discarded electrical fittings. They normally have something suitable that you can use

 

[Refueler]

You could drill a small hole in the perspex and this would let you measure the thickness

Regards Don

That's what I was going to say ! Beat me to it ...

All I would add is glue a pad on the other side so you don't need another person to stop the end of measuring rod at level to the surface ...

 

[dutyhog]

Beam a laser at the glass at an angle. Measure the distance between the two reflections and do the geometry.

Gordon

 

[RupertW]

Simple trig to avoid a destructive measurement.

Sellotape a clear ruler either side with mm scale and measure the parallax at 3mm, 5mm and 7mm away from a point approximately opposite to triangulate and if you can’t immediately see how to work out the thickness then draw out the right angled diagram with thickness and distance from approximate opposite as the adjacent and opposite.

 

[smithy]

Why muck about and risk making mistakes? Drill the hole, measure it with with the depth gauge part of the digi calipers. You are going to repace the perspex anyway.

 

[dutyhog]

Why muck about and risk making mistakes? Drill the hole, measure it with with the depth gauge part of the digi calipers. You are going to repace the perspex anyway.

Because in practice you may not really get round to the job before the sailing season.

 

[Daverw]

Drill a hole then blank off with nut and bolt with rubber sealing washer, would last until when ever you changed it

 

[Daydream believer]

Drill a hole then blank off with nut and bolt with rubber sealing washer, would last until when ever you changed it

Try & keep up-- see post #6

 

[Refueler]

Try & keep up-- see post #6

And post #7 .....

Gluing a pad behind does two things .... 1. Depth gauge gives you proper measurement without need of another person behind ... 2. seals the hole till item is replaced.

 

[Daydream believer]

And post #7 .....

Gluing a pad behind does two things .... 1. Depth gauge gives you proper measurement without need of another person behind ... 2. seals the hole till item is replaced.

But the pad might fall of if the glue fails & a bolt will not.
So let's ask the OP what system he is going to adopt once he has collated all the ideas & perhaps he can post a virtual glass of wine to the winner.
Assuming he has not lost the will to live & given up on the idea

 

[SteveIOW]

Because in practice you may not really get round to the job before the sailing season.

Thank you Dutyhog, you've hit the nail exactly on the head. Whist the boat is ashore I must first concentrate on underwater jobs such as cutlass bearing, hull anode, A/F & boot topping, rudder repair............ If these, and others which can only be done when boat is out of the water, go well then I will do the window replacement. If not then I will have to live with cracked window for another year. Would rather not drill then blank hole in existing window - it could initiate another crack.
Thank you for other suggestions - I certainly didn't anticipate using lasers!

 

[maggietwo]

if you need new ones why not just take the broken window out and replace with the same

 

[Daydream believer]

Would rather not drill then blank hole in existing window - it could initiate another crack.

Drilling a small hole at the end of a crack ( assuming it is not already cracked for the full width of the panel) could sometimes prevent the crack from getting longer.

 

[Refueler]

Correct - its common practice to drill hole at end of a crack to stop crack spreading further.

 

[Ian_Rob]

Glass Thickness Gauge

Perhaps?