Drilling acrylic

[Neeves]

I need to drill some holes (3-5mm) in 5mm acrylic. At the back of my mind is the idea I need to use blunt drill bits - is this correct? If it is correct - what is meant by blunt. I have lots of blunt drill bits - which I would need to sharpen if I was drilling steel - are these sufficiently blunt or do I need to grind some blunt.

I have this idea sharp drill bits cause acrylic to crack.

All of this seems counter intuitive.

Jonathan

 

[jimmy_the_builder]

Last time I drilled an acrylic sheet I used a new lip and spur drill bit and it was perfect; no cracking.

 

[jasperthedog]

Hi Jonathon,
Any slightly dull/ blunt metal drill will be fine. It's just to stop the snatching you get with a new drill bit.
Nice and slow on minimum torque and you will feel if it bites to much.
Cheers
Richard

 

[Neeves]

Hi Jonathon,
Any slightly dull/ blunt metal drill will be fine. It's just to stop the snatching you get with a new drill bit.
Nice and slow on minimum torque and you will feel if it bites to much.
Cheers

Richard

Thanks Jimmy and Richard

That was quick!

I confess to being very ignorant and don't actually know what a lip and spur drill bit might be. I might even have some - and simply did not know that is what they were called.


Now I understand.

I will be using a bench drill so easy to keep the pressure off, its already set for slow and I have more than enough blunt drill bits!

I'm good to go

Jonathan

 

[rotrax]

I drilled about 80 5mm holes in 6mm Acrylic sheet this time last year using a main power drill, decent size, 12mm chuck, but with a pressure variable speed switch.

I ground, using my angle grinder held in a vice, the spiral drill bit very flat and with little slope. I did this by eye but I do have 50 years experience regrinding drill bits.

Every hole cut smoothly and I got no cracks.

The experience of drilling very thin double curvature motorcycle racing screens helped me do this. I used to crack almost every one until I learned the flat drill trick.

Whichever method you choose, Good Luck.

 

[DownWest]

I had to fit a/craft screens from time to time, so a mistake would have been VERY expensive. As Rotrax says flat angle drills with little back slope work. I did talk to the suppliers about it at the time, then ground a few drills. Like him, lots of experience in hand sharpening drills.
Possibly, the idea of blunt drills comes from them generating heat and half melting their way through, plus no sharp corners to 'grab'. Never tried it.

 

[rogerthebodger]

I need to drill some holes (3-5mm) in 5mm acrylic. At the back of my mind is the idea I need to use blunt drill bits - is this correct? If it is correct - what is meant by blunt. I have lots of blunt drill bits - which I would need to sharpen if I was drilling steel - are these sufficiently blunt or do I need to grind some blunt.

I have this idea sharp drill bits cause acrylic to crack.

All of this seems counter intuitive.

Jonathan

Jonathan

3 points

1) stick some masking tape over the place where you wish to drill. This will prevent chipping on the top service.
2) clamp the perspex onto a wood backing plate clamped down to a bench. Thi will prevent chipping the under service.
3) Dip the drill bit in water just before drilling. This will lubricate and cool the drilling.

 

[Pirx]

I happily drill 6mm holes in 5mm acrylic, about 2mm from the edge.

No special technique: ordinarty steel twist drills, possibly a bit blunt as not very new. Rattly old drill press on slow speed. Place a piece of wood behind the acrylic, start with a small drill and work up to finished size say 2mm - 4mm - 5mm - 5.5mm - 6mm or thereabouts. The dangerous bit is when the drill breaks out from the rear surface; that's when it can catch and create cracks or chips. Drilling in small increments largely solves this as any 'catch' is smaller, and the wood makes the drill's exit less abrupt.

If you'd like a small offcut to play with I can easily pop a piece in the post to you.

 

[Neeves]

Jonathan

3 points

1) stick some masking tape over the place where you wish to drill. This will prevent chipping on the top service.
2) clamp the perspex onto a wood backing plate clamped down to a bench. Thi will prevent chipping the under service.
3) Dip the drill bit in water just before drilling. This will lubricate and cool the drilling.

Roger,

I'm competent enough (well not really) to use the masking tape but would not have thought of clamping to a piece of wood (though I might have used to wood to 'drill into') and would certainly not have dipped the drill bit in water.

Thanks.

Jonathan

 

[rogerthebodger]

Roger,

I'm competent enough (well not really) to use the masking tape but would not have thought of clamping to a piece of wood (though I might have used to wood to 'drill into') and would certainly not have dipped the drill bit in water.

Thanks.

Jonathan

Clamping down stops the perspex jumping up the drill at break through and chipping the underside.

I found this due to bitter experience.

 

[RichardS]

I had to drill around 40 5mm holes in thin acrylic a couple of years ago. I left the backing paper in place and drilled through that with the first 5mm bit I had to hand.

I had no issues with any of the drilling .... although I did have some failures with the sheet cutting.

Richard

 

[Neeves]

I happily drill 6mm holes in 5mm acrylic, about 2mm from the edge.

No special technique: ordinarty steel twist drills, possibly a bit blunt as not very new. Rattly old drill press on slow speed. Place a piece of wood behind the acrylic, start with a small drill and work up to finished size say 2mm - 4mm - 5mm - 5.5mm - 6mm or thereabouts. The dangerous bit is when the drill breaks out from the rear surface; that's when it can catch and create cracks or chips. Drilling in small increments largely solves this as any 'catch' is smaller, and the wood makes the drill's exit less abrupt.

If you'd like a small offcut to play with I can easily pop a piece in the post to you.

Thanks for the offer of a small piece on which to practice - but I'm in the nether reaches of the world 'The Lucky Country' and more importantly I have some scraps of acrylic.

Jonathan

 

[Neeves]

I had to drill around 40 5mm holes in thin acrylic a couple of years ago. I left the backing paper in place and drilled through that with the first 5mm bit I had to hand.

I had no issues with any of the drilling .... although I did have some failures with the sheet cutting.

Richard

Just out of interest (and for future reference) how, or with what.did you cut the sheet (mine is already cut)

Jonathan

 

[[176172]]

I use a wood bit with a centre point.
First drill a small pilot hole the same size as the centre point, go slow and you will have nice clean holes.
Alternatively, if you know how the grind a drill, do so with a negative rake the same as used for drilling brass, this prevents the drill 'grabbing' and doing damage when breaking through.

 

[RichardS]

Just out of interest (and for future reference) how, or with what.did you cut the sheet (mine is already cut)

Jonathan

I cut it with a very sharp Stanley knife. I got through several blades and had to cut through the same line several times until a clean cut was made. Mind you, it was only 3 or 4 mm sheet.

Richard

 

[ltcom]

I need to drill some holes (3-5mm) in 5mm acrylic. At the back of my mind is the idea I need to use blunt drill bits - is this correct? If it is correct - what is meant by blunt. I have lots of blunt drill bits - which I would need to sharpen if I was drilling steel - are these sufficiently blunt or do I need to grind some blunt. And do have backing wood under acrylic whilst drilling.

I have this idea sharp drill bits cause acrylic to crack.

All of this seems counter intuitive.

Jonathan

In my past job I always used acrylic drill bits.
Some links here because I can't remember the exact bit I purchased
https://www.google.com/search?q=acr...OLer1fAP-fiVoAU56:0.5.5.5.5.5.5.5.5.5.5.5.5.5
And do have backing wood under acrylic.helps a lot. I learned the hard way with normal drill bits.

I cut sheet with a band saw or jigsaw of correct blade. Teeth just right not to melt and not to cause cracks. Speed of blade through acrylic is a skill learnt to avoid melt too.

 

[rogerthebodger]

Just out of interest (and for future reference) how, or with what.did you cut the sheet (mine is already cut)

Jonathan

I cut perspex with my wood circular saw with a fine tooth blade.

I have just made done washboards with 15 mm thick perspex with 5 mm edging to fit the 20mm wide companway slots.

Next I will be replacing the polycarbonate windows that had gon cloudy through UV with 10mm perspex with 10mm edging to make up the 20mm wide window frame.

 

[PetiteFleur]

I've often drilled and cut acrylic, no special bits, just used slow speed and gentle pressure with a backing piece of wood. Using either a pillar drill or cordless drill. For cutting I've used a jigsaw, slow speed, with a metal cutting blade.

 

[Keith 66]

Blunt drills are not the answer to drilling anything. In school we drill a lot of acrylic & the real answer is to alter the cutting edge of the drill to negative rake so that it scrapes the acrylic away cleanly with no breakout or digging in.
All you need to do is take a small diamond file or dremel & file or grind the leading cutting edge of the drill so there is a small flat on the cutting lip. Clean sharp holes with no breakout!

 

[Neeves]

We had an acrylic washboard on our X-99, when we needed to modify the original board for Cat 2 (with cat 1 safety gear). It made the interior so much brighter.

Obviously for cutting thicker acrylic, noting Richard's technique for thin sheet, one obviously needs a jigsaw with variable speed.

I'll be spending some time honing the tips of drills - and practicing.

Jonathan