Circle Cutter - any tricks to cut plastic ?

[a64pilot]

That thing will work fine, I call them blood letting devices, so be careful.
Mine was single armed, never seen one with two cutters.
You need a drill press and go slow, cut slightly undersized and sand to fit.
It’s best to practice on scrap.
I cut out all the instrument holes in my airplanes instrument panel with one. Aluminum of course. Only a little blood, no serious injuries.
Do not use a drill, you will get it slightly canted and the cutter will jam suddenly if you try.

[JimsCAL]

I've had good luck with a Dremel and a circle gauge attachment.

[TrentePieds]

I have one of those circle cutters too. And I second what A64 sez! Even in a drill press those things are dangerous. If your hand slips into the wrong place, or if you let your attention waver, you WILL be going to hospital!

86mm = 3 3/8". A 3 3/8" hole saw is available at all good hardware stores. But it really requires a drill press to power it because of the torque required. A good drill motor WILL do it, but it is dangerous because the torque required to drive the saw is great enuff to wrench the drill motor out of your hand if you are the least bit inattentive. It is also extremely difficult to maintain perpendicularity so the saw will cut evenly all around. The drill press is most certainly preferred!

TP

[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.

An alternative I used in some awkward locations is to use the same method to make a router template in scraps of panel and hot glue that in the desired location then use a guide on the router base.

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.

[Jammer]

Originally Posted by Marqus

Thanks for every reply, gents. Always learn a lot on CF.

If I was to use a hole saw, I will use a lube (like kerosene, thanks for suggestion) but not entirely sure how practical it's going to be to hand sand the opening from 76mm dia (my closest hole saw) to 86mm.

Suppose with a lot of care and attention one could keep the hole round for a tight fit, but it would be less of a task if I had an 85mm saw to start with.

When hand sanding, wrap the sandpaper around a dowel. Use the largest size dowel that will fit. You can get much better results than sanding completely freehand.


You can also use a piece of half round or quarter round stock, for sanding, with good results. Sometimes I use a half-round file wrapped in sandpaper.


Another trick that is out there is to get a roll of emery cloth and wrap it around the hole saw to make a sort of a drum sander. I haven't done it but it seems like it would work.

[neflier]

That circle cutter works well. I've made several hundred cuts in aluminum with mine. With that said, this tool is considered the most dangerous tool in my shop. Treat it with respect and you will not have a problem. Mine only has one cutting blade, so I assume the adjustment of both blades will be critical. As others have said, you need a drill press, set to the lowest speed. Mine is set at 250 RPM. The work needs to be securely clamped in several locations to the drill press. Do not clamp in only one spot. Before starting, I place my left hand in my back pocket, turn the drill press on and slowly feed the cutter. Once contact is made, think in terms of applying pressure to let the cutter do the work. If the cutter binds, and will not lift up, then turn the drill press off with your right hand. In other words, never let a body part get anywhere near that cutter.

[Boatwright]

Whoever designed the circle cutter pictured can be found at the left hand of the Devil.

Mark the hole with a sharp compass point. Get a sharp jigsaw blade made for cutting plastic. Cut at slow saw speed so you don't melt the plastic. File and sand to fit.

Hole saws and trimmer routers also work well - but expensive for one hole.

[blubaju]

Plexiglass (German Acrylic) asks for plenty of water, less for lubricating, but for COOLING. Acryl melts easily. Water helps you avoiding the fire brigade ;-) We have done all our catamaran windows that way and no problems. you have 2mm material thickness only, with no holesaw available I'd go for the next size available or just drill a series of small holes ands and sand to size usind sandpaper over the largest dowel, it is thin and easy. Circle cutters on thin materials tend to catch, I would not use them on 2mm Acrylic freehand, but other might be more sklilled

[Cheechako]

That cutter will work. It's better than the old one I have that only has a blade on one side! At least the one you ordered has two blades to help balance out the tool. Just take it slow. and yes water, you don't want it melting, just cutting.

[gonesail]

a hole saw would work much better. the size may not be exact but it will be close.

[Cadence]

That looks like a knock off of a fly cutter, Cut very slowly. If you can do it on a drill press so much the better.

[model 10]

Lot of danger here. I've cracked very expensive plastic windows. It causes you to abandon tools that could cause things to go wrong. That flycutter for example, total POS wrong tool for plastic windows. Free hand Jig saw, almost the same thing. Even a drill bit needs to be sharpened differently. A regular bit catches as it cuts thru the back side. Really easy to get a crack if you drill a bunch of holes.

After you get a pilot hole, switch to a Unibit and a glass of water to keep it cool. Hole saws are a safe way to go. For a bigger hole, use a die grinder with a carbide bit for AL so it won't clog. All edges should be chamfered and polished almost clear. Any screw hole thru a plastic window needs to be oversize so that expansion and contraction never lets the screw touch the plastic, you will get a crack.

[Q Xopa]

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.

I have a set of hole saws but nothing at 86mm. My abilities with jig saw will leave a very rough edge. No router avail at my current location.

Web browse found this cutting device (see below) which I ordered, but will probably take a week to arrive.

In the mean time, I'd like to get on with my install, so any suggestions of DIY methods/tricks to cut this 86mm hole nice and clean ?

Thanks
Marqus

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

When Im cutting holes in plastic, go slow, dont go right through, then go from the other side.
I actually just turn it by hand for the last bit. You dont actually want the cutter too sharp that it will bite and catch and crack the edges. Its more of a slow wear through process.

[dennismenace111]

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.

I have a set of hole saws but nothing at 86mm. My abilities with jig saw will leave a very rough edge. No router avail at my current location.

Web browse found this cutting device (see below) which I ordered, but will probably take a week to arrive.

In the mean time, I'd like to get on with my install, so any suggestions of DIY methods/tricks to cut this 86mm hole nice and clean ?

Thanks
Marqus

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

This will require the use of a drill press to do it properly... doubtful you can do it successfully with a hand held drill.

[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?