forstner bit on plastics?

[LCHIEN]

I want to drill some 3/4" and 1-1/2" holes in 1/4" Lexan.

Suggestions? Forstner bit? or spade?
Techniques?

Edge of hole going to be 1/8" from outside edge of workpiece...going to break out or split???

[cabinetman]

If you have a very sharp Forstner, preferably with carbide tips, it will work. I wouldn't recommend a spade bit.

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[wardprobst]

I'd use a hole saw if you have one the sizes you need.
DP

[iceman61]

If you have a very sharp Forstner, preferably with carbide tips, it will work. I wouldn't recommend a spade bit.

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I'm with Cabinetman on this one. A Forstner bit is the best IMHO. This one is about feeds & speeds also. Just like with wood, slow down on the last bit to avoid blow out since you're so close to the edge.

I made some decorative signs for a commercial customer once. I used a spade bit and cut a very pretty triangular shaped hole.....by accident. The bit kept chattering and dancing around. Didn't realize what I had done until it was 3/8" deep.

[JR]

Forstner bits should do just fine, at slow speed. Once upon a time I had a job milling lexan for faceplates on aeronotic gauges. The problem to watch out for is the material melting. A slow speed drill is the answer.

[gsmittle]

Forstner bits should do just fine, at slow speed. Once upon a time I had a job milling lexan for faceplates on aeronotic gauges. The problem to watch out for is the material melting. A slow speed drill is the answer.

And back the bit out frequently so it can cool.

g.

[leehljp]

I used forstners on lexan several times when I was in Japan without a problem. Each time, it produced much better and smother edges than a hole saw. I used them on 9 mm (IIRC) thick lexan.

[eezlock]

forstner bit on plastics

I would use a forstner bit on the plastics also. Be sure to set drill at a low speed,and use some back up material (scrap wood) underneath the plastic for the time when the bits breaks thru, may help in preventing material shattering
or breaking off to the edge and ruining the piece.

[LCHIEN]

I imagine I'll do like I do when I want perfect forstner holes in wood....
Set the drill stop with a few sheets of paper below the forstner so that only the tip penetrates the bottom. Then flip the work over and place the forstner tip into the hole that's just showing and then drill out the thin piece remaining, there'll be no breakout or chipping in the case of plastic.

In Hanks case, 9mm = ~ 3/8". I'm only planning to do 1/4".

[herb fellows]

If you'll have trouble keeping the bit going slowly, you can also drill it in a shallow pan of water to keep things cool.
Fill the water to just go over the lexan by 1/32 to 1/16".
If you do go fast, you might need a raincoat, but it will keep things cool.

[LCHIEN]

as a side question, is plastic sold like like plywood for thickness? What they are selling as 1/4" lexan is more like .220 to .240" if you read the fine print.

[Stytooner]

I used to use both hole saws and Forstners.
Now just a router on cnc. Both of the first two types gave comparable cuts with the holesaw cutting cooler.

That is the thickness I generally get when I order 1/4". .220"

[LCHIEN]

I used to use both hole saws and Forstners.
Now just a router on cnc. Both of the first two types gave comparable cuts with the holesaw cutting cooler.

That is the thickness I generally get when I order 1/4". .220"

I suppose the holesaw just removing material around the circumference makes it run cooler as opposed to having to carve out the entire inside area.

But I don't have a quality holesaw in that size. Looks like Carbide tipped forstners.

[LCHIEN]

another question for smaller holes:
I've seen bits for drilling acrylic-plastics that have 60 to 90 degree points as opposed to the 118 degree on standard twist bits. Supposedly they are slower feeding, less prone to chip out or blow out the backside.

They're not cheap, a set of 7 or 8 costs around 50-60 bucks. individual bits run 5-12 bucks apiece.
http://www.amazon.com/Acrylic-Point-...pr_product_top
http://www.ebay.com/itm/Craftics-8-p...item22fd95b0b7

I've also heard that wood-style brad points work on plastics. Do they work as well as the specialty plastic bits?

[cabinetman]

another question for smaller holes:
I've seen bits for drilling acrylic-plastics that have 60 to 90 degree points as opposed to the 118 degree on standard twist bits. Supposedly they are slower feeding, less prone to chip out or blow out the backside.

They're not cheap, a set of 7 or 8 costs around 50-60 bucks. individual bits run 5-12 bucks apiece.
http://www.amazon.com/Acrylic-Point-...pr_product_top
http://www.ebay.com/itm/Craftics-8-p...item22fd95b0b7

I've also heard that wood-style brad points work on plastics. Do they work as well as the specialty plastic bits?

Yes they do. For through holes, backing up the hole with a substrate will in most cases prevent chip out/blow out on the back side. Pieces being drilled should be well stabilized from any movement.

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