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Loading ...Cutting and Finishing Fan Holes
syrillian
Cutting holes in acrylic can be approached in a number of ways. The first is with hole-saw bits, the second is with a rotary tool. A jigsaw could be used, but it is inherently difficult to cut a round hole with a flat-bladed tool. This becomes increasingly problematic as the diameter shrinks, or the blade becomes wider.
I use a rotary tool as it is what I have become accustomed to, and the radii are dynamic: I can cut holes from ¾” to 12” in diameter and any increment in-between. Also, the rotary tool takes up much less space and the cost is much lower than a set of quality hole-saw blades that are static insofar as the diameters that they can cut. This is not to bad-mouth hole-saws, had I the facilities and the funding I would most likely have taken that route.
When measuring the radius, ensure that the bit is on the inside of the measurement and that the center-point is bisected or the circle will not be to cut to the intended size. The radius for a 120mm can is 21/4″.
I drill the center-hole, and then use the pre-set circle-cutting guide to mark the bit-hole. This may seem somewhat low-brow…. and it is. Never-the-less I found this technique to be error-free 100% of the time when working without plans or drawings.
Here is a closer shot of an acrylic bit and a standard bit (acrylic on the bottom). As you can see acrylic bits have a more acute point. This bit design alleviates chipping that can occur upon inital entry, and yields a cleaner exit-wound. I have used standard wood bits with relative success, but if given the option then I would take the specialised bits - hands down.
When setting up to cut the hole it is a good idea to ensure that the rotary tool and the guide will be able to travel full circle without being impeded. If one is careful it is quite easy to stop the cut, re-clamp the work, and then continue on with the cut; but, I prefer to make the cut in one single rotation. The red dot in the image represents the location of the C-clamp. I eyeball the placement to ensure that the cut can be made in one single sweep, and not be obstructed by the clamps.
Here you can see that the clamps will not interfere with guide as it rotates through its arc.
One potential pit-fall to be aware of is that the guide will become “sloppy” toward the end of the cut, at about the point depicted below. The center point that has been the guide up to now has been rigid. As the circle is completed the center is no longer held in place.
This can be remedied by stopping and taping the circle that is being cut to the panel that it is being cut from. But, once again that means stopping and starting the cut multiple times; rather than do that I have chosen another method.
When the cut is almost done I shift the focus of my guiding hand from the center of the rotary tool guide to the end that is opposite from the tool itself. I start pulling the rotary tool in a decreasing radius manner.
This leaves a small barb in the panel, but it is easier to remove more material than it is to put it back should the bit jump and cut in to the portion of the panel that one is fabricating
Barb: Please take care if you use your finder to run the inner edge to check for smoothness. Acrylic can be razor sharp and will lay any flesh open at the slightest of provocations.
Since the inside of the cut will need to be sanded, I consider the barb to be “no big deal”, in reality it only takes about 3-5 seconds to remove it with the rotary tool sanding drum
Here you can see the rest of the rotary cut that was produced by the sideways bit. Not bad, but definitely needs some clean up.
To remove the barb I use the rotary tool at a medium setting and gently tap the barb to reduce it to the rest of the diameter. Then, I smooth the entire edge by running the sanding drum around the inner edge in a clockwise direction. To keep the circle balanced, the sanding should be uniform all the way around.
When I am sanding the inner edge, any flaws become apparent as I can feel them as I move the rotary tool. I continue to carefully sand down the edge until it is smooth, and the circle is perfectly round. This process will increase the diameter by about .5 mm - a negligible tolerance.
Enso… (or at least as close as this monkey can get):
Thus far I have profiled all edges, cut both 120mm fan holes, polished all edges, and have made the cut-out for the optical drive. Those processes will be in the next post.
Thanks for taking a look.
Nice guide, thanks (for this 1 and the previous ones) I did a mod about a week ago (ill write it up here soon) , using clear acrylic for lighting effects and it caused me no end of headaches. Should have read these first.
Greetings, gryphon.
I look forward to seeing the work that you have produced.
Yes. Acylic is not all that easy to work with in some situations as it is not a very unforgiving medium.
OUt of curiosity, what headaches did you run into?
Thanks for reading.
Another great guide as usual. When cutting holes for fans I normally use a Forstner bit. Thought these are relatively expensive, £18.00 from toolpost.co.uk they cut an excellent hole. It’s important to remember though that when cutting such a large hole in acrylic there will be a tremendous amount of heat generated and often the material being removed is hot and this can sometimes melt onto the tool. Remember to give the cutter a break every 10 seconds of cutting or the tool will soon become hardened and blunt. From experience hole saws are awful when it comes to cutting plastic as the cut is too aggressive, this is a sure fire way to snap an entire sheet.
Thank you for your comments, Matthew.
You bring to light one of the more salient points when cutting acrylic; the problem of melting, and the solution of pausing to let the heat disipate - thank you.
You mentioned Forstner bits. Ironically that particular bit will have a small section in my next post as I used one to drill the hole for the power switch.
Also, thank you for posting the potential hazards of hole-saw bits, “aggressive” is a very appropriate and accurate assesment imho.
Thanks again for your input, and I re-iterate to all readers that all comments and suggestions are welcome.
My mistake - i was using perspex, not acrylic. my problem was that the only sheet i had handy was very thin - 3mm. i wasnt sure how best to cut it. it was very reluctant to score, and i managed to crack the it a few times, despite using a flat, hardwood surface.
Obviously the dremel didnt work (with a cutting disk), melting rather than cutting. guess i should have realised that would happen before i even tried.
Lastly i tried a jigsaw with a metal cutting blade (the best one i had for the job) which didnt give a good cut at all.
I ended up scoring it and got a decent piece in the end… only to shatter it with a bit of clumsy drilling. At least i’ll know not to make the same mistakes next time.
As for the case - it seems to have stopped happening now that im back to school, wich is stupid because all i need to do is sort out some mesh for the window and drill a hole for the power button, wich involves digging up a 19mm drill bit from somewhere.
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