140mm Fan mounted on acrylic window - best way to cut hole?

[Napoleon]

Hello [H]oard-

I'm looking to add a side mounted fan to blow onto my motherboard in my Corsair 750D airflow case.

What's the best way to cut holes these days? I'd need a 140mm hole and then can drill the 4 holes to mount it.

Tools I have:
Power drill (no drill press)
Dremel (not sure which version, it's new)
Reciprocating saw with plastic blade

 

[NeedleArtist]

Option 1:
Use a 5-1/2" hole saw. Use reverse rotation to keep from shattering the hell out of it. When drilling screw holes, use an acrylic bit. Normal bits can easily grab and chip/shatter the material.

Option 2:
Buy a piece of polycarbonate (aka. Lexan) that matches the thickness of tbe existing window and cut it to size. Use the hole saw in normal (not reverse) rotation. then drilling holes, normal metal bits will work just fine. Polycarbonate is MUCH more machinable than acrylic. It won't crack or shatter when you're drilling or cutting.

No matter which material you use, make sure you cover both sides with marking tape. Makes for an easier to mark surface and provides a bit if grip for the drill bit or saw so that it won't "skip". Better yet, sandwich the material between two pieces of wood when you cut/drill.

 

[Napoleon]

I have a Dremel and the hole cutting attachment in this vid, what do you think?

 

[NeedleArtist]

To be honest, I haven't had much success using the device in the video clip, particularly on acrylic. I'd try it out on a scrap piece that's the same thickness and composition. If it turns out, great.

 

[Napoleon]

To be honest, I haven't had much success using the device in the video clip, particularly on acrylic. I'd try it out on a scrap piece that's the same thickness and composition. If it turns out, great.

Hmm, yes i think a test piece is a good idea. I have a router too but do not have anything good to use for a template

 

[Spotswood]

Hmm, yes i think a test piece is a good idea. I have a router too but do not have anything good to use for a template

I've used a toilet bowl flange as a guide for my router. Wonder the plumbing section of your local home improvement store, you'll find something you can use there.

 

[Napoleon]

Results of test one, 2.75" radius using deemed in two passes to cut. I wonder if a single pass will result in cleaner finish edge

Found out drilling 1/8 inch pilot hole then 11/64 larger bit to enlarge chips the fan mount holes, gonna do in in every pass next time.
End result isn't bad, I may reduce the radius slightly to 2.6 inches and try to get it centered better

 

[Susquehannock]

This my preferred method. Takes about 20 seconds. Imagine you could do similar with a drill.

Rotary file with drill tip. Edges cleaned up with half round files and sandpaper.

 

[Napoleon]

This my preferred method. Takes about 20 seconds. Imagine you could do similar with a drill.

Rotary file with drill tip. Edges cleaned up with half round files and sandpaper.

I cut another sample hole with my dremel, this time with one single pass. The edge was smoother but there was slight chipping, I may do method 1 ( 2 cuts) and clean up with file/sandpaper as you suggested.

I also tried drilling with my 11/64 bit instead of first 1/8 then 11/64 and found that when the bit started to bite it would bite really hard and slightly chip the hole (even cracking one of the holes). I may end up drilling 2 holes yet again; I'm not sure if I should slow down or speed up the bit. This is using a manual 2-speed dewault cordless drill; I also found if i purposefully went very slow and made sure the acrylic was held down on the work bench that the cut seemed to be better.

 

[Susquehannock]

Forgot to mention these are "double cut" style. Carves away with less digging action, so far less chipping.

 

[Guarana [BAWLS]]

I cut another sample hole with my dremel, this time with one single pass. The edge was smoother but there was slight chipping, I may do method 1 ( 2 cuts) and clean up with file/sandpaper as you suggested.

I also tried drilling with my 11/64 bit instead of first 1/8 then 11/64 and found that when the bit started to bite it would bite really hard and slightly chip the hole (even cracking one of the holes). I may end up drilling 2 holes yet again; I'm not sure if I should slow down or speed up the bit. This is using a manual 2-speed dewault cordless drill; I also found if i purposefully went very slow and made sure the acrylic was held down on the work bench that the cut seemed to be better.

take a scrap piece (you should have a few now) and try drilling with the bit running in reverse. It may work better.

 

[Napoleon]

Job's done, I think it came out well

 

[Susquehannock]

Looks good. A trick I like is to wave a small torch flame over the cut plastic edge. Makes it nice and clear.
Practice on a test piece first of course.