Need an 8mm Drill Bit or Hole Saw Safe for Styrene Sheets

[tehachapifan]

Regular drill bits tend to snag and tear edges. Any recommendations for an 8mm bit or hole saw that will work on hobby grade styrene sheets?

[peteski]

Sounds like a punch/die set could make a nice clean hole (assuming the sheet is thin enough).

[tehachapifan]

This is for somewhat thicker styrene sheets. 2-3mm or so.

[nkalanaga]

How many holes do you need?  A smaller drill bit and a reamer might be easier than finding a special bit.

For just a few holes I'd drill them undersize and carefully ream them with a hobby knife.  Don't try to cut the plastic, use a #11 or similar tapered blade and turn the knife in the hole.  Measure frequently until the hole is the right size.

[Jim Starbuck]

A couple thoughts I had were a brad point bit which is designed to make clean holes in wood or a step drill that looks like a cone and make progressively larger holes.
If possible back up the work piece with a sacrificial wood block so the bit continues to drill true past the styrene and  turn the bit at a slow speed.

[Lemosteam]

I suggest you try a set of brad point drill bits.  The bit has a center point, and the outside edge of the drill has a sharp knife-like cutter tip that engages the material before the main cutter flute does.

I am not aware of Metric Brad points.

5/16" (7.9375mm) is just shy of 8mm by 0.0625mm (0.00246") and may be close enough for your needs.



Here is a link to an 8mm reamer if the hole must be as close to 8mm as possible: https://drillsandcutters.com/8-0mm-hss-straight-shank-chucking-reamer/

[thomasjmdavis]

I suggest you try a set of brad point drill bits.  The bit has a center point, and the outside edge of the drill has a sharp knife-like cutter tip that engages the material before the main cutter flute does.

I am not aware of Metric Brad points.

Metric brad point drill bits are definitely available.  A quick net search will bring up a number of vendors and manufacturers.  And as with any bits, at a wide range of prices (my quick survey yielded prices between $15 and $250 for a set of 10 or so), depending on brand, quality, and nowadays... country of origin.  If a nearby home center sells European style cabinet hinges and hardware (like metric shelf pins), it is just possible they will have some sizes of metric brad point bits.

[peteski]

an 8mm punch/die set could punch a hole in a 3mm plastic but I also think that for that thickness a brad-point wood bit should work well.  You just have to go easy (not too much pressure). Just make sure that the bit you purchase has the pointy protruding outer edge surfaces.  I was recently looking for an Irwin brand spade brad-point bit, but the current ones no longer have that feature on them.  I found another brand that had the raised edge surfaces but that brand has a threaded center point and that also causes an undesired results.  The twist bit type brad-point bits John showed are likely your best bet.

[tehachapifan]

Thanks for all the replies, guys! Drilling smaller hole(s) and then using a hobby knife to make it bigger was the original plan, but I have several holes to do. Still, not enough to warrant purchasing a hobby drill press, which I would need for precision drilling. I was looking at brad point bits last night but, while I did find 8mm ones, the descriptions didn't mention drilling through styrene.

[thomasjmdavis]

Just for the sake of demonstration...
Thickest styrene I have handy is .040 (1 mm more or less).  Used my 40 year old Greenlee 3/8" brad point drill bit- very good quality bit, but it has drilled thousands of holes over those 4 decades, and hasn't been sharpened recently.
Styrene was laid on a piece of scrap pine, and drilled through into the wood- so the rim of the hole was supported.
Note that there is a small raised 'lip' (similar to what one gets when you score a straight line)  but otherwise the hole is very clean.  The lip can be removed with a scraper, file, or razor blade/xacto.

[tehachapifan]

That hole would work fine! Thanks for posting those pics!

[robert3985]

The best results in Styrene are going to be with a Forstner drill bit. 

I did a quick search and couldn't find an 8mm Forstner bit, but I found several 5/16" bits, the most precise one from Freud. 

I have a couple of sets of Forstner bits for my woodworking mostly, both in inches and metric, and they drill extremely precise holes in wood, acrylic sheet and, I am sure, in Styrene.

Just run it at a medium slow speed as to not melt the Styrene and drill slowly also.

Another possibility would be to use a 5/16" four flute end mill.  You'd need to be able to clamp your Styrene sheet down firmly, drill a pilot hole, then mill your 5/16" hole using a drill press.  I wouldn't use a hand drill for this tool.

Cheerio!
Bob Gilmore

[Lemosteam]

The best results in Styrene are going to be with a Forstner drill bit. 

I did a quick search and couldn't find an 8mm Forstner bit, but I found several 5/16" bits, the most precise one from Freud. 

I have a couple of sets of Forstner bits for my woodworking mostly, both in inches and metric, and they drill extremely precise holes in wood, acrylic sheet and, I am sure, in Styrene.

Just run it at a medium slow speed as to not melt the Styrene and drill slowly also.

Another possibility would be to use a 5/16" four flute end mill.  You'd need to be able to clamp your Styrene sheet down firmly, drill a pilot hole, then mill your 5/16" hole using a drill press.  I wouldn't use a hand drill for this tool.

Cheerio!
Bob Gilmore

As a woodworker, I thought of a forstner bit also, but the horizontal cutting edge worries me in that the two edges will shave simultaneously, and put more amount of torque on the plastic, whereas the brad point edges will cut first and direct the plastic to the inner cutting edges of the flutes more gradually.

I have both and will try both later.

[peteski]

As a woodworker, I thought of a forstner bit also, but the horizontal cutting edge worries me in that the two edges will shave simultaneously, and put more amount of torque on the plastic, whereas the brad point edges will cut first and direct the plastic to the inner cutting edges of the flutes more gradually.

I have both and will try both later.

I agree with you John, at least in theory, but I guess if someone proves us wrong, I'll be ok with that too.
Tom also showed that the brad-point bit does the job.

[Maletrain]

When I have to drill plexiglass, I use brad point bits.  They don't grab when they go through.  Grabbing cracks plexiglass.

I prefer the old style with the actual knife-like cutter ears on the outer diameter.  But the newer ones that just have a more perpendicular blade at the outer end work OK for me, too.  A guy who owned a plastic working shop that I used for sailboat parts showed me how he modifies bits to prevent grab, and it is mainly by making the cutting edge work mostly perpendicular to the surface being cut.

And, you do need to cut slowly enough to not melt whatever it is you are cutting.  I always do a practice hole first to make sure I have everything working as I expect.