How to cut a precice square hole

[ilovemygt35r]

hi
im looking for advice/guidance hoping someone could tell me how to cut a precise hole 35mm by 100mm approx in a plastic box the electrical junction box type box that bolts onto a wall, the plastic is 3mm thick approx.

the hole is for an LCD display to poke through flush was thinking maby of using an oscillating type cutting tool maby?
thank you

 

[tigler]

Depends what you mean by precise, if it truly has to be precise with clean edges then water jet or laser is the only way. Any hand technique as a one off will be impossible to make ultra precise. By hand, I would cut the hole almost to size then file out to the final size.

 

[CRB]

Normally yes, a router with a jig to ensure position and size, but I assume you do not have access to such kit.

Someone with a mill could do it, as long as it is supported properly.

There is no reason why you cannot do it by chain drilling, hacksaw blade and careful filing.

Good practise too.

 

[rtbcomp]

I'd cut & file or could you get a bezel to fit the display? That way you could hide any rough edges.

 

[ilovemygt35r]

no no bezel for this lcd i may have quite a few to do in the future id really like to do it in house really, and dont mind paying for the right equipment though.

the last resort is to farm it out, but the price of the unit is very low not really sure there is the money to do that

 

[wheresmejumper]

they are very soft(if im thinking of the right one).you could do it with 2 chisels.one good tap would go through and give a clean cut.35mm shouldnt be hard to find,and i know carpenters use one 100mm for door hinges


edit:i misread q

 

[gavuk]

no no bezel for this lcd i may have quite a few to do in the future id really like to do it in house really, and dont mind paying for the right equipment though.

the last resort is to farm it out, but the price of the unit is very low not really sure there is the money to do that

As CRB,if doing multiples,buy a router and make a jig to hold the box...

 

[MattF]

Coping/fret saw, or a hot wire cutter would be my preference, if you're liable to be doing plenty of them. If just the odd one or two, the chain drilling and filing, as suggested above would be the method I'd go with. Some plastic housings are devils for working with, (the plastic will literally shatter or peel if cut badly), so the above methods should cover all types for a modest outlay. If you can cut the aperture cleanly, I find scraping the edges with a sharp knife blade gives a good final finish. Leaves it looking smooth rather than the duller finish given by a file.

 

[awemawson]

Q-Max do make square and rectangular hole cutters as well as the more common round ones - pricey though

 

[Polished]

My preference would be to make or buy 100mm x 35 mm steel box , sharpen edges to form cutter and use hydraulic bench press to cut out- fast, accurate, etc. Usual safety warnings apply

 

[MattF]

My preference would be to make or buy 100mm x 35 mm steel box , sharpen edges to form cutter and use hydraulic bench press to cut out- fast, accurate, etc.

That sounds a good method. Could even be done with a flypress, or an arbor press at a push, if there's one to hand.

 

[GeorgiePorgie]

My preference would be to make or buy 100mm x 35 mm steel box , sharpen edges to form cutter and use hydraulic bench press to cut out- fast, accurate, etc.

Could shatter the plastic depending if the plastic is of the brittle variety?

 

[slim_boy_fat]

Dremel?

 

[ilovemygt35r]

great suggestions, really like the steel box one, i think the plastic would shatter maby,
think im going down the router option then file corners
thanks for the help

 

[rtbcomp]

Could you heat the steel box up and cut slowly through the plastic?

 

[tigler]

There could also be a problem with a router, the plastic may melt due to friction from the high cutting speed ?

 

[MattF]

Another possible approach, if you try the pressed cutter option, is to drill a pilot hole in one corner and have the sectional blade slanted down towards that corner, so that the blade is gradually pressing in outwards from that corner. It all depends on the plastic type though. Warming the plastic itself before working it, if it is the fragile type, may help too.

 

[Tiggy_dorset]

Could a scroll saw be an option?

 

[madkayaker]

Q max would be my first choose

 

[CRB]

There could also be a problem with a router, the plastic may melt due to friction from the high cutting speed ?

Adjusting the speed, just like all cutting, will give the desired finish. Roughing out first and skimming the last1-1.5mm out would be the cleanest way. Also means there is less chance of big cuts snatching and cracking the box.

There should be some material identification on the box, moulded into the inner face usually.