Great Drill Bits for plastic

[Tundra Twin Track]

I got these Drill Bits at Auction and real impressed how they work in plastic,drilled 3-1/4” depth in one stroke no pecking,5/32 @ 850 rpm.

[nickel-city-fab]

Is that one of those parabolic flute deals? I've heard nothing but good about them. Kinda rich for my blood though.

[Paul Alciatore]

Is plastic a recommended use for parabolic flute bits? With their large rake angle I am surprised that they do not grab like crazy in soft materials like plastic. Your photo seems to show a blind hole being drilled or at least one so deep that the sides of the drill bit will provide a lot of friction when it breaks through. Have you tried these on through holes in thinner plastic? 1/8", 1/4"? How do they handle the break-through situation then?

I have a set of bits where I reduced the rake angle to zero. They are the ones that I reach for first when drilling softer materials like brass and plastic.

[BCRider]

No idea about the flute cross section but the lower helix angle would certainly clear chips better. Especially on fluffy plastic work. Nice score ! ! !

At the other end though the lower helix angle might make it have a more aggressive bite into the plastic. Does the cutting edge have a small neutral or negative top rake angle of any sort?

Adding such a small flat (shown on one of my modified drill bits used for plastics and brass) is my #1 favorite drill bit modification. I keep a separate drill index to hold the ones I've modified like this. It's already got all the more popular sizes and gets a new one each time I need it.

For anyone wondering this is a 29/64" size and the flat shown is roughly.025'ish from a quick check with a dial caliper. Smaller size drills tend to see me putting on a .015 to .02 flat.

[polaraligned]

Nice! They do look like parabolic flutes which are supposed to be good for deep holes. I have never used one though...

[garyhlucas]

Yes that is a parabolic flute drill. I used to use them drilling deep holes for aluminum air manifolds. Worked much better than standard twist drill

[Bented]

Is plastic a recommended use for parabolic flute bits? With their large rake angle I am surprised that they do not grab like crazy in soft materials like plastic. Your photo seems to show a blind hole being drilled or at least one so deep that the sides of the drill bit will provide a lot of friction when it breaks through. Have you tried these on through holes in thinner plastic? 1/8", 1/4"? How do they handle the break-through situation then?

I have a set of bits where I reduced the rake angle to zero. They are the ones that I reach for first when drilling softer materials like brass and plastic.

If the spindle feed is under control and the parts are well held no drill will ever take off on you, purposely dulling a $40.00 drill is counterproductive at best. This is the year 2021 not the year 1921 (-:

[Tundra Twin Track]

Is that one of those parabolic flute deals? I've heard nothing but good about them. Kinda rich for my blood though.

There were pretty cheap in Auction Goodies probably less than jobber length at hardware store.

Is plastic a recommended use for parabolic flute bits? With their large rake angle I am surprised that they do not grab like crazy in soft materials like plastic. Your photo seems to show a blind hole being drilled or at least one so deep that the sides of the drill bit will provide a lot of friction when it breaks through. Have you tried these on through holes in thinner plastic? 1/8", 1/4"? How do they handle the break-through situation then?

I have a set of bits where I reduced the rake angle to zero. They are the ones that I reach for first when drilling softer materials like brass and plastic.

I will try anything once and Drill Bits are one of those tools if price was very reasonable,I used a bunch of those Aircraft Drill Bits with 1/4” NF threads on shank on steel a year ago repairing Grain Dryer and there designed for Aluminum.They worked like a Champ.

Yes that is a parabolic flute drill. I used to use them drilling deep holes for aluminum air manifolds. Worked much better than standard twist drill

Thanks I was wondering if that was what there called.

[BCRider]

If the spindle feed is under control and the parts are well held no drill will ever take off on you, purposely dulling a $40.00 drill is counterproductive at best. This is the year 2021 not the year 1921 (-:

Tell that to the guy trying to use a hand drill on a piece of acrylic because he's fresh out of milling machines. A two minute mod to give the cutting edge the neutral or slightly negative top rake prevents the drill from spalling out the other side or diving in and wedging tight and cracking the plastic. Things that can also happen far too easily on a drill press too for that matter.

Hey Paul, I posted my reply thinking that no one had wondered the same thing. Looks like we were both thinking the same thing since our posts asking the same question are only a minute apart. Great minds and all that perhaps? ... If only I didn't take a couple of minutes to take that picture of the drill bit....

[Bented]

I fully understand the concept of a sharp drill corkscrewing into the work, have not had that happen in over 20 years or so,
Have also never ground a new drill dull (-:

Last week I turned 31 ft. of 304 stainless into chips using a single HSS .656" drill, this was a slow process at best.

[strokersix]

No idea about the flute cross section but the lower helix angle would certainly clear chips better. Especially on fluffy plastic work. Nice score ! ! !

At the other end though the lower helix angle might make it have a more aggressive bite into the plastic. Does the cutting edge have a small neutral or negative top rake angle of any sort?

Adding such a small flat (shown on one of my modified drill bits used for plastics and brass) is my #1 favorite drill bit modification. I keep a separate drill index to hold the ones I've modified like this. It's already got all the more popular sizes and gets a new one each time I need it.

For anyone wondering this is a 29/64" size and the flat shown is roughly.025'ish from a quick check with a dial caliper. Smaller size drills tend to see me putting on a .015 to .02 flat.

modifying rake angle in drill bits. This is an excellent method. I suggest naysayers are inexperienced.

[nickel-city-fab]

modifying rake angle in drill bits. This is an excellent method. I suggest naysayers are inexperienced.

No, it really does work I had to learn that one the hard way. Ever try drilling in copper without grabbing, you have to dull off the edges a bit with a stone.

[Tundra Twin Track]

Your photo seems to show a blind hole being drilled or at least one so deep that the sides of the drill bit will provide a lot of friction when it breaks through. .

Sorry Paul for not fully explaining pic,5/32” hole was drilled first then hole was countersunk with U drill bit,I usually do the finish cuts last.

[Paul Alciatore]

Changing the rake angle on a cutting tool does not mean it will be dull. There are many inserts that have a zero degree rake and even negative rake angles. They are still quite sharp.

I fully understand the concept of a sharp drill corkscrewing into the work, have not had that happen in over 20 years or so,
Have also never ground a new drill dull (-:

Last week I turned 31 ft. of 304 stainless into chips using a single HSS .656" drill, this was a slow process at best.

[Paul Alciatore]

Yes, your photo illustrates my/our point in an excellent manner. That is exactly what I did with my set of bits. I was too lazy to add a photo so your post is better then mine.

Yes, great minds...

Tell that to the guy trying to use a hand drill on a piece of acrylic because he's fresh out of milling machines. A two minute mod to give the cutting edge the neutral or slightly negative top rake prevents the drill from spalling out the other side or diving in and wedging tight and cracking the plastic. Things that can also happen far too easily on a drill press too for that matter.

Hey Paul, I posted my reply thinking that no one had wondered the same thing. Looks like we were both thinking the same thing since our posts asking the same question are only a minute apart. Great minds and all that perhaps? ... If only I didn't take a couple of minutes to take that picture of the drill bit....