Replaced an old yellowed plastic crystal

[steve1811uk]

Hi, I wanted to share my replacement of an old yellowed crystal. Original crystal was yellowed and it was not possible to make it clear with abrasive and polywatch. In fact the polywatch seemed to dissolve the crystal making a sticky mess. I think the crystal was nitro cellulose and not acrylic.

Crystal dimensions were 13.3 x 13.3mm and I found one on eBay described as 14 x 14 and model S7. Upon receipt it was found to measure 14.5 x 14.5. After careful rubbing on 600 grit abrasive sheet I got it to size so it would just snap into place. I had to be very careful to keep the edges square. I finished the edges with some finer paper and polywatch aiming to produce a nice 45 degree bevel on the edge.

I finished off with some Minecol UV glue and had to illuminate with UV from the back side for nearly an hour to get it to set. Never had much luck with that glue as I have read that it should work in minutes.

Result is a big improvement. The watch has an FEF270 movement by the way, just waiting on a donor movement for some parts (stem and balance).

[steve1811uk]

On 6/22/2024 at 5:25 PM, steve1811uk said:

Hi, I wanted to share my replacement of an old yellowed crystal. Original crystal was yellowed and it was not possible to make it clear with abrasive and polywatch. In fact the polywatch seemed to dissolve the crystal making a sticky mess. I think the crystal was nitro cellulose and not acrylic.

Crystal dimensions were 13.3 x 13.3mm and I found one on eBay described as 14 x 14 and model S7. Upon receipt it was found to measure 14.5 x 14.5. After careful rubbing on 600 grit abrasive sheet I got it to size so it would just snap into place. I had to be very careful to keep the edges square. I finished the edges with some finer paper and polywatch aiming to produce a nice 45 degree bevel on the edge.

I finished off with some Minecol UV glue and had to illuminate with UV from the back side for nearly an hour to get it to set. Never had much luck with that glue as I have read that it should work in minutes.

Result is a big improvement. The watch has an FEF270 movement by the way, just waiting on a donor movement for some parts (stem and balance).

I think I know why the UV glue doesn't work too well when illuminated from the front. I did some reading up on acrylic and it has very good UV blocking properties below 400nm which I believe is the activation range for the Minecol glue.

[mikepilk]

Nice job. I usually replace acrylic crystals as they are so cheap - about £3 for round ones.

Cousins have a good range of shaped crystals - including 13.5mm x 13.5 mm square.

I recently switched to using UV glue. I illuminated it from both sides and it set nicely.

[Neverenoughwatches]

On 6/22/2024 at 5:25 PM, steve1811uk said:

Hi, I wanted to share my replacement of an old yellowed crystal. Original crystal was yellowed and it was not possible to make it clear with abrasive and polywatch. In fact the polywatch seemed to dissolve the crystal making a sticky mess. I think the crystal was nitro cellulose and not acrylic.

Crystal dimensions were 13.3 x 13.3mm and I found one on eBay described as 14 x 14 and model S7. Upon receipt it was found to measure 14.5 x 14.5. After careful rubbing on 600 grit abrasive sheet I got it to size so it would just snap into place. I had to be very careful to keep the edges square. I finished the edges with some finer paper and polywatch aiming to produce a nice 45 degree bevel on the edge.

I finished off with some Minecol UV glue and had to illuminate with UV from the back side for nearly an hour to get it to set. Never had much luck with that glue as I have read that it should work in minutes.

Result is a big improvement. The watch has an FEF270 movement by the way, just waiting on a donor movement for some parts (stem and balance).

Nice job Steve careful shaving down to size gives a good result, i prefer not to glue just a good tight locking in of the crystal as they are originally. But yes what a difference it makes.