100mm hole through 5mm acrylic sheet

[sacentre]

Can anyone suggest an efficient/better/easier method to cut a clean, accurate, 100mm hole through 5mm (or thicker) acrylic sheet on a SIEG SX2 mill? I don't own a boring head and as the workpiece is 185mm x 185mm, it's too large for a 7x12 mini-lathe otherwise it could be bored out in a 4-jaw chuck.

I've done this previously by drilling a circle of holes, knocking out the centre disk then finishing off the ID with a cutter in the mini-mill using a standard 8mm shank mini-lathe lathe tool. It's crude but works quite well as long as the cuts are small (not to mention the fact that the tool has to be adjusted manually). I'm just wondering what tips or tricks there might be for doing this (sans boring head).

TIA


Trevor

 

[Martin W]

Use a wood router with a pattern bit and template. Make a template from MDF by using a hole saw or jig saw. Sand template smooth and clamp to your work piece and router your circles. We did hundreds throughout the pandemic. Mind you we use a CNC. Before CNC we did it manually with a router
Martin

 

[sacentre]

Thanks for the reply, Martin. I'll give that some thought and reply more fully later.

 

[WobblyHand]

Perhaps a circle cutter? I made this.

I used it to cut two 100mm holes in a steel box.

You might have to play with the tool grind a little. This set up worked amazingly well on this sheet metal box. Make sure you have clearance before you turn on the mill! Clamp everything well, use a backer under the plastic and go really slow. Good luck.

 

[sacentre]

Hi, thanks for the suggestion. I hadn't thought of a circle cutter. Well done for having manufactured this one yourself. I might surf around to see if there are commercially available ones. I imagine I would still need to make a large hole first though. Essentially, it would be the functional equivalent of a boring head but a lot cheaper.

 

[woodchucker]

Hi, thanks for the suggestion. I hadn't thought of a circle cutter. Well done for having manufactured this one yourself. I might surf around to see if there are commercially available ones. I imagine I would still need to make a large hole first though. Essentially, it would be the functional equivalent of a boring head but a lot cheaper.

no, You want the existing bit to be used to center and hold the bit from wobbling, so just let that bit do the job. You may want to dull the drill bit a little by taking the cutting edge and running a hard stone parallel to the bit. This will prevent the bit from digging in, it makes the bit scrape the plastic.. Look up plastic drill bits and you'll see what I mean.

 

[Ischgl99]

I was going to suggest Home Depot or Lowes to find the cutter Wobblyhand posted, I think that is where I bought the one I have, but since you are in Singapore, that probably won’t work. If you have an equivalent type home improvement store, they may have it.

 

[sacentre]

Reply to woodchucker. Yes, of course, I was forgetting the centre pilot hole. I was still thinking of boring head type cutters. Thanks.

 

[WobblyHand]

Hi, thanks for the suggestion. I hadn't thought of a circle cutter. Well done for having manufactured this one yourself. I might surf around to see if there are commercially available ones. I imagine I would still need to make a large hole first though. Essentially, it would be the functional equivalent of a boring head but a lot cheaper.

Like @woodchucker said, you need the drill bit to keep things from wobbling. All you do is go straight in. No extra work required.

Making the circle cutter wasn't hard, some lathe work, a little mill work and I had the circle cutter. It was very satisfying to make and use.

 

[Nesse1]

forstner bit?