Circle Cutter - any tricks to cut plastic ?

[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.

[Reefmagnet]

That gadget works fine for what you want to do. Test on scrap first, though.

[CharlzO]

Only other option would be to use your jigsaw to cut a slightly smaller hole, and then sand the hole opening back to the right size to smooth out the jaggedness. Does your gauge have enough bezel to compensate for anything less than perfect?

[model 10]

OMG don't use that thing, please! I was a wiz bang plastic window guy once, get a hole saw, a slow drill and double up the pilot hole area.

[wsmurdoch]

I have similar. #1. The cutter blades will flex in and out a little, so cut a bit undersize then file or sand to size. #2. The acrylic will soften and melt and perhaps expand and crack as it is cut. Spraying some WD-40 on the work will lubricate things reducing friction and heat and make cutting easier. #3. Back up the work with a piece of scrap wood and clamp it in place to help keep the pilot drill centered and to support the work. #4. Practice before you do it for real.

Bill

[Jammer]

The adjustable circle cutters work OK in a drill press. Not sure I would try one without.


A hole saw is the way to go. Over 50mm, get one that uses a pin mandrel -- they work much better. I have used them up to 6" (150mm) and they produce good results as long as the center is supported by the item being drilled or a suitable piece of scrap.

[JPA Cate]

Another tip: use kerosene to lubricate it while you cut. Worked for us, many times.

Ann

[Uncle Bob]

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.

These work quite well if used in a drill press with the material well supported, if you can't do this then I wouldn't use it with a hand drill. A half decent hole saw is the way to go, slow with a cutting lube if you're not too used to cutting plastics.

[sy_gilana]

Set your vernier caliper to the radius, use the internal measuring teeth and scratch the circle, both sides. Drill a 1mm hole for the center. After about 10 scribes per side, you can pop it out, then sand smooth and flame polish.

[Gin-N-Sonic]

Easy,

First no jigsaw, its going to make a mess.

There are a few ways, amongst which, I've done the following:

1- drill holes in the inside perimeter of your circle, cut across from hole to hole with an Olfa scoring knife. Drilled hole size will control the resolution of your overall finished product. This will involve a simple setup may lead to stress relief, take out some frustrations by drilling holes, lots of holes.

2- Get an acrylic scoring blade, add one articulate compass (with that wheel to adjust the width). Drill a small divot in the center of the hole, adjust compass, clamp on blade to the pencil side, zero in, go to town, round and round. This is the "I make my tools do too many things" version and may require some OCD.

3- If design and space allows, use a jewellers saw. I've done smaller acrylic with holes this way. If you have access to a scroll saw with a thin blade, this will be far easier. This way does give you control but your wrist may be out of action for about 2 hours once done.

If you haven't, practice fire polishing, it can lend to a great edge finish if done correctly, leading to a nice edge for your electronics to slide in and out of.

[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.

From the comments, it seems the cutter I ordered can be used successfully, but only if used in a drill press and work clamped very well (thanks for the detailed instructions, Bill). Won't receive the cutter for another week, so that option will be for future occasions.

You have to like the simplicity of this suggestion from SV Gilana:
"Set your vernier caliper to the radius, use the internal measuring teeth and scratch the circle, both sides. Drill a 1mm hole for the center. After about 10 scribes per side, you can pop it out, then sand smooth and flame polish. "

I feel like giving this a go, and hope I don't damage my caliper in the process. I think the crux is going to be the "popping out" moment. If your "scratch depth" is not even all around, the popping effort may deliver a craggy mess.

[GILow]

My vote is for the SV Gilana method too. I’ve done the same many times. You don’t want to be in a hurry but you can get a very good result. I scribe/cut with a very small and sharp chisel.

[coopec43]

Originally Posted by Ecos

OMG don't use that thing, please! I was a wiz bang plastic window guy once, get a hole saw, a slow drill and double up the pilot hole area.

I was about to say the same thing!

I got one of those hole cutters but in those days I didn't have a variable speed drill. I used it for about a second until it flew to bits. I heard one of the cutters hit the other side of the shed so I spent an hour or so looking for it but to no avail. Eventually I did find it about ten years later.

As others have said- cut a smaller hole with the jig saw and then file it to size. (I have small stones and burrs to put in the drill which would do the job quickly)

[njoynthewater]

How about this. Clamp the material between 2 pieces of 3/8" plywood. Make sure the plywood is bigger than the finished diameter of the plastic. Draw the circle on the top piece of wood. Use screws outside the circle to sandwich everything together. Bury the head of the screws. Cut out with jigsaw. As you get part way around with the jigsaw add a c clamp along the cut edge. Once cut out sand to the line if required.

[Checkswrecks]

Sandwiching tightly in plywood and using lubricant are always good ideas. A jig saw can work, especially with the wood sandwich but without the wood can break or melt (locally embrittle) the plastic fairly easily.

I find that a trim router works well.
https://www.harborfreight.com/14-in-...ter-62659.html