Circle Cutter - any tricks to cut plastic ?

[model 10]

Originally Posted by belizesailor

If you are dropping an instrument in the hole then the finish of the hole may not matter much as the trim ring of the instrument will typically cover the edges of the hole. Is this the case?

No, any surface imperfection could lead to a crack. It has little to do with aesthetics.

[Djarraluda]

Thin acrylic is very brittle. Uneven loading will simply split it, which is why your ordered tool is inappropriate here. If pushed, I have used a smaller hole saw and then a flap wheel sander on a stemmed to sand to size. Watch out with acrylic that you work steadily, if it gets hot it will distort, so keep moving the sanding wheel.
Roger

[Marqus]

Some feedback on my circle cutting endeavours:

(1) Firstly, I changed the plastic I am using from 2mm to 3.1mm thick (1/8 inch). So it makes the job tougher.

(2) The vernier caliper method did not work for me (using the sharp prongs meant for inside measurements). Main problem I experienced is that when you press harder on the swinging prong, it sort of unloads the central prong which starts to 'walk' and spoils your circle. Even when you drill a tiny hole in the middle.

(3) Given the number of responders cautioning about flying blades and parts with the contraption pictured in post no1 of the thread, I've decided not to go for that one any more. I realise some folks state that with appropriate care and technique it can work, but I'll explore other options first.

(4) I have since come across another manual cutter (see photo below) used by plasterboard trades, but plasterboard being quite a bit softer than many plastics makes me wonder if that one will work effectively (experience, anyone ?).

(5) Since I'm keen to get this done and am not at home where my router and serious tools are, today I made up a metal hand cutter myself to try out.
I include a photo of it below. However, after operating this cutter for what 'feels' like a couple of hours, carving out a circle on top and bottom surfaces, I am not yet through. Bit disappointing I have to say. Though I imagine if I keep at it it must go through, eventually.

Beginning to think that, for future hole cutting, a type of "mini" or "micro" jig saw may be worth considering if they are obtainable.

[roland stockham]

The problem with cutting plastic is the head generated so work slowly either with lube or flooding with water. Also for cutting thin sheet try placing a peace of plywood each side with a couple of screws to lock it in place to get a neater cut.

[Ken Pole]

Drill press definitely the preferred option; I have a single-blade circle cutter which does a clean job. Was advised by my plastics supplier to dial down the press' speed because high speed tends to melt the plastic. That said, why not have your plastics supplier cut the hole? Likely won't cost more than buying the tool. Best wishes.

[skenn_ie]

Clamp the stuff between two pieces of plywood, then use a hole-saw very gently in a drill press. You can get hole saws specifically for plastic, they have zero rake on the teeth, but not widely available.

[Robert Jansen]

If you can find it (it shouldn't be that difficult), I would recommend using abrasion resistant lexan over acrylic.


If you don't want the (unsightly) indentation at the origin, consider making a template out of another material, clamping the two together, and using the template as a cutting guide. Then you have a radius without the center point.

[seabreez]

Originally Posted by Marqus

Hi all,

I need to cut an 86mm circle in thin acrylic sheet (2mm thick) to fit an instrument. Preferably a neat, tight fit.

Ordered this, but will take a while to get here; cheap, so not sure it's any good either.

I worked in plastic and if you use the tool in the picture you will have a hole in the center of your piece, (the guide drill bit). The best way is to masking tape both sides, mark out what you want to keep, then cut as close as you can to the line then sand or file the remainder up to the line, then use a utility knife to scape away the excess and round and smoothen up the edge.

[hikersailor]

I used a similar device to cut a 6" hole in 1/2" thick acrylic with no problem going slow with a battery powered handdrill on a vertical window surface.

[Buzzman]

Originally Posted by coastalexplorer

Since I am a retired Engineers Pattern Maker. And thus very professional at this sort of thing. I cut all circular holes with a router Trammell that I made during a machine shop training course in 1978.

How ever for just one specific hole you should attached a price of scrap plastic or wood panel product to the base of a router.. with a center hole at the correct radius. Drill a corresponding hole in the center of the desired location. And router it out.

Holes produced by this method are round to within .010 thousands. And with applied skill in the set up potentially absolutely accurate as to diameter requiring no clean up.

^^^^^^
+1. What he said. Use a trimming router.

These were known back in my day as 'laminate trimmers' and we used them for trimming back the overhang on hand laid melamine and laminex sheets when making laboratory benches etc. The trimming was done with a ball-bearing-fitted special cutter, but the above method, utilising a carefully measured/made guide attached to the bottom of the trimmer base, is the correct method for an inside circle such as the OP requires.

The 'trimmer' is like a miniature router, about 1/4 the size of a normal shop router. Weighs about 1lb. But has some serious torque, so usually has 'torque twist' when first starting (they usually don't have 'slow start' like modern shop routers do) so beware the 'kick'.

I'd probably use a 3mm straight cutter and set it for 1mm depth (to be sure it's all correctly set up, then re-set for another couple of mm (or right through if thin plastic).

8mm or thicker sheet might require several passes of a cuppla millimetres. You don't want to try cutting too much and have it heat up and melt.

Melamine, and Laminex especially, 'burn' when overheated and discolour. Ask me how I know this.....

[Uncle Bob]

Originally Posted by seabreez

I worked in plastic and if you use the tool in the picture you will have a hole in the center of your piece, (the guide drill bit). The best way is to masking tape both sides, mark out what you want to keep, then cut as close as you can to the line then sand or file the remainder up to the line, then use a utility knife to scape away the excess and round and smoothen up the edge.

He is wanting to mount an instrument into a clear plastic sheet 2 mm thick, the cutout will be a throw away so the hole in the middle is of no consequence.
I had a plastics vendor/manufacturer cut a hole in an acrylic hatch for me to install a ventilator, Thirty seconds with a battery drill and holesaw. No damage or drama.