100mm hole through 5mm acrylic sheet

[Ken from ontario]

You still need a circle cutter but this is how the center bit is modified:

 

[WobblyHand]

For a 100mm hole, using a circle cutter, does it matter about the drill? We're throwing away the center, so a minor crack shouldn't matter? I can see doing the mod for drilling holes in acrylic, but is it necessary for a circle cutter hole?

 

[Martin W]

For a 100mm hole, using a circle cutter, does it matter about the drill? We're throwing away the center, so a minor crack shouldn't matter? I can see doing the mod for drilling holes in acrylic, but is it necessary for a circle cutter hole?

No.

 

[WobblyHand]

No.

That's what I thought. Why alter a drill bit if you don't need to. The altering isn't hard, but you have to label the bit and segregate it from your normal bits.

 

[Ken from ontario]

For a 100mm hole, using a circle cutter, does it matter about the drill? We're throwing away the center, so a minor crack shouldn't matter? I can see doing the mod for drilling holes in acrylic, but is it necessary for a circle cutter hole?

most likely not , I have only one shop made hole cutter with a modified bit so I don't know for sure .

 

[RJSakowski]

I have four of that style of circle cutter, all purchased commercially. I replace the pilot drill with a dowel pin . It requires two operations but supports the cutter better. My largest has a 1/2" shank, a 3/8" fixed pilot pin and can cut an 8" circle. I custom grind the cutting bit with aggressive front and side rake and generous side and back clearance. In particular, the outer side clearance has to be ground to prevent rubbing on your cut edge. They work well and I used to cut dozens of 4" holes in .063 aluminum with very clean edges. Acrylic tends to melt easily, even with nery sharp tools. A cutting lubricant heelps to provide a clean cut. My mill has flood coolant which works great but a squeeze bottle of coolant should work well too.

 

[woodchucker]

For a 100mm hole, using a circle cutter, does it matter about the drill? We're throwing away the center, so a minor crack shouldn't matter? I can see doing the mod for drilling holes in acrylic, but is it necessary for a circle cutter hole?

Why yes, for 2 reasons.
1 you don't want the bit to pull the plastic up and speed the cut, it will cause the outside cutter to destroy the part. Imagine pulling up on the center, and now having the part tilted at even 5 degrees. (highly likely)

2 you don't want a crack to start before the outer bit cuts the hole all the way through. (less likely but a possibility).

 

[RaisedByWolves]

That's what I thought. Why alter a drill bit if you don't need to. The altering isn't hard, but you have to label the bit and segregate it from your normal bits.

Protip: Get a standard drill organizer and over time make yourself custom fishtail drills.


We make them like this, with the center just proud of the flutes which lets the center act as a piolet and the flutes cut through grabby materials (plastic, sheet metal, wood etc) without trouble. Make them and put them in an organizer and next time you need this you either have one on hand or have a reason to make another for your arsenal.

Bad paint rendering, but you get the idea.

 

[WobblyHand]

Protip: Get a standard drill organizer and over time make yourself custom fishtail drills.


We make them like this, with the center just proud of the flutes which lets the center act as a piolet and the flutes cut through grabby materials (plastic, sheet metal, wood etc) without trouble. Make them and put them in an organizer and next time you need this you either have one on hand or have a reason to make another for your arsenal.

Bad paint rendering, but you get the idea.
View attachment 458947

Maybe I got lucky (twice) on that sheet metal box I cut through. Thanks for the idea on modding the bits for plastic drilling. Haven't done much plastic drilling, so I just blunder my way through it. If I need to drill plastic, I will keep this in mind.

 

[RaisedByWolves]

Maybe I got lucky (twice) on that sheet metal box I cut through. Thanks for the idea on modding the bits for plastic drilling. Haven't done much plastic drilling, so I just blunder my way through it. If I need to drill plastic, I will keep this in mind.

Their good for much more than plastic.

I had to make and sharpen hundreds of these for drilling holes in copper tubing for one of our old AC coil manufacturing processes. Drilling the copper tube was a nightmare before we tried this as its thin, gummy and grabby. The tooling and parts were getting ruined with a very high rejection rate and it took way too long to even get a passable part.

We went to these and just gang drilled the manifold tubes after seeing how well this worked.

After posting earlier I remembered I did a writeup on this grind.

Hand sharpening fishtail drills. A brief primer.

I mentioned making these drills in THIS THREAD and was asked if I would be so kind as to write up a tutorial. Since I can find no reference of this type of grind on the internet I figured why not. I started sharpening this style of drill tip to cut into copper tubing in a factory environment...

www.hobby-machinist.com

Having these on hand is great and all you need is an old dull drill to get started.