Cutting through foam board/mountboard

[Mary Lever]

Hi
I need to trim half a centimetre off the top and a mere quarter of a centimetre off the sides of a foam board backed window mount which doesn't come apart. It measures just under .75mm. I've been told I should be able to do it with a Stanley knife with a fresh blade but am very nervous of trying it. I think my Ultimate Gold mount cutter would not make a clean cut either. Any suggestions? Many thanks.

[David McCormack]

Hi Mary,

Could you not get some scrap foamboard and mountboard of the same thickness and glue them together and then try cutting that on your ultimat gold or with knife & ruler?

If that works out then you can cut your window mount with confidence?

Try cutting in several passes and a little deeper each time rather than one single cut

[Mary Lever]

Thanks for that advice David . I've just taken a really close look and realise that it is in fact just very thick mountboard and not foam board - almost .75mm thick of mountboard - that's going to be even tougher to trim isn't it?

[easypopsgcf]

Why nervous? Is it going in a frame? Do you have a decent L/T square? Straight edge? Do you have a decent desk/workbench to cut it on?
As already said, sharp Stanley blade, lightly at first to create a score, somewhere for the blade to run, then progressively harder. The mountborad is the only real work though as foamboard is a doddle to cut(with a sharp blade)

Edit: just spotted your response, no change just a few more passes with the knife.....sometimes you just have to do it

[David McCormack]

...almost .75mm thick of mountboard...

Just checking.... are you saying .75mm ie less than 1mm or do you mean 7.5mm?

7.5mm is rather thick so yes, new blade and several passes and should be OK even if removing a very small amount.

[prospero]

The trick is not to try and slice the whole thickness at once. Do a light score just to establish the blade track and then successive cuts with a bit more pressure.

A good non-slip straightedge helps.

[Mary Lever]

Thank you so much everyone for your advice. Yes, it was 0.75mm and, as you suggested, I used my Stanley knife and scored it, followed by successive cuts rather than trying to cut it all at once and it did make a clean cut. For some reason, I feared it was going to be a ragged cut and bits of mountboard subsequently rub off and get onto the glass. Great relief to have it all done. Manay thanks.

[Mary Lever]

Apologies......just read through my post yesterday and of course I meant 7.5mm not 0.75. Sorry .