Hello

I have been asked to manufacture a roller that produces the top pastry circles ( with various designs ) for mince pies .
The roller Ø is 200 mm & 400mm long & the required circular tops are about 70mm so in total we will have 2 rows of 6 cavities around the roller . So as the roller rotates the pastry gets formed into circles.
My problem is after measuring an original roller with 70Ø circles on it something appeared strange to me & that is if you measure the circle across the roller is measures 70mm as you would expect but when measured around the roller in a straight line at the base of cavity it measured 80mm .
Now in my simplistic way of looking at things if you take a 70Ø paper circle and wrap it around a 200Ø roller it will measure 70mm across but actually less than 70mm in a straight line in the other direction as the ends start to get closer to each other.
I hope your following me on this so far ( not easy to explain ) so can someone shed some light or point out my stupidity as to why the cavities seem to be oval on the original roller .

thanks in advance

chris