How to drill plastic
If like me you normally work with wood, brick, or metal materials to complete your DIY projects, working plastic or acrylic can be totally new and unknown and a bit daunting.
But working with new materials like acrylic, nylon, and other plastics or ‘non-ferrous’ materials doesn’t need to be scary.
I recently needed to create some new windows for my daughter’s wendy house and rather than use potentially expensive tempered glass, I chose to replace them with new plastic panels, they were cut to size already but I need to add some fixing holes, so I needed to know how do you drill plastic? Here’s how I did it.
To drill plastic and acrylic:
- Support the plastic on a flat surface that you can drill into
- Use clamps to hold the plastic down.
- Use masking tape and a pen to mark the centre of the hole
- Use a HSS drill which has been used before and therefore slightly dull
- Hold the drill perpendicular to the plastic
- Set the drill to a medium speed
- Let the drill sink through the material do not apply too much pressure
- Take care when breaking through, allow the drill to run into the support below
- Let the drill run whilst removing from the workpiece
Following these steps will make drilling holes into plastic really easy and help to prevent damage that can happen, like cracks, chipping or crazing, but let’s look at each step in detail to make sure.
Support the plastic
Plastic sheets are flexible and will bend if not properly supported which adds stress to the surface and this stress will cause the surface to crack when you try to drill a hole through the plastic sheet.
Using a stiff board underneath will reduce the amount of flex the sheet will have and the stress on the surface, an off cut of scrap wood or an old piece of plywood for larger sheets will not only support the plastic sheet but also allow you to drill into this as a sacrificial piece, which will will reduce chipping or break out when drilling through the other side.
Use Clamps to hold the plastic down
Along with supporting the plastic or acrylic sheet, clamping the workpiece down will stop it from moving around when you drill holes through
Make sure to spread the clamping force over as much of the workpiece as possible to reduce stress on the surface, and avoid camping the plastic sheet to firmly as this can cause cracking,
I used a piece of wooden batten on top of the plastic sheet then used several clamps to hold it in place, this means I didn’t have to force the clamps too tight which could have cracked the plastic.
It’s also a good idea to protect the plastic sheet with something to avoid scratches or dents. I used some old rubber strips that I had and placed them between the batten and the plastic.
You could use thin cardboard or something similar, just remember to avoid adding pressure in one spot and check for dirt on the surface before clamping, a good wipe with a cloth always helps.
Use masking tape and a pen to mark the centre of the hole
Most plastic or acrylic sheets will come with a protective film to prevent any marks or scratches during shipping or storage.
You can write on this but I avoid marking holes centres or cutting lines on the protective film, as it can be difficult to see and can rub off.
I used masking tape and a pen to mark the centre of the holes before I drilled through the plastic sheet, you need to avoid using a punch or scribe as this could crack the surface before you even drill the hole and the tape will help prevent chipping when you start to drill the hole.
It’s a good idea to use masking tape on both sides of the sheet to prevent chipping when drilling holes into plastic.
To drill plastic or acrylic you can use a normal HSS (High Speed Steel) drill with a drill angle of 118 degrees.
Use an HSS drill which has been used at least once before, this removes any burrs from sharpening a drill bit and helps the drill avoid biting into the plastic.
The drill bit needs to be sharp but not brand new. I found that brand new drill bits tend to bite into the surface and can cause chipping around the hole.
I ran a new drill bit through a wooden block a couple of times, just to take the edge off, the drill will still be sharp but this helps prevent any tearing or chipping.
Drilling holes in plastic creates heat and can melt through the material rather than drilling a clean hole, using a good drill helps reduce this heat.
Using the right speed and feed rate helps to avoid heat building up on the surface. Setting your drill to a medium speed and applying light pressure will allow the weight of the drill to push the drill bit into the material without adding too much stress.
The formula below is a good rule of thumb guide to setting the right speed for drilling plastic:
RPM (Revs per minute) = (3.82/Drill Diameter) x SFM (Surface feet per minute)
The SFM for plastics is:
100 – 300
For example, the speed required for drilling a 10mm hole through a plastic sheet will be:
(3.82/10) x 300 = 115 RPM
Most cordless drills work between 0-1900 rpm and setting the right rpm to drill through plastic needs a bit of finger adjustment on the trigger.
I used a medium trigger position to start and released the trigger slowly until I got to roughly the right speed, I found I had to adjust this position as I was drilling the holes.
To give you an idea, here’s a list of approximate speeds for the market-leading cordless drills:
- Hikoki 0-1400rpm
- Dewalt 0-1750rpm
- Makita 0-1300rpm
- Festool 0-1500rpm
- Milwaukee 0-1800rpm
- Bosch 0-1800rpm
- Erbauer 0-1450rpm
- Metabo 0-1800rpm
- Draper 0-1350rpm
- Einhell 0-1800rpm
- Worx 0-1600rpm
Hold the drill perpendicular to the plastic
When drilling the hole through the plastic keep the drill upright or at 90 degrees to the surface and try not to move around too much.
Holding the drill steady helps to keep the hole square through the plastic and will keep hole round and the right size.
Let the drill do the work, with the speed set and using a good drill bit the plastic should cut cleanly and the swarf should break off nicely especially when drilling holes in acrylic.
If not, try adjusting the speed of the drill, but be careful not to go too fast which will raise the surface temperature and the plastic will melt.
As the drill nears the bottom of the hole, reducing the pressure will help the drill cut through the other side and avoid chipping.
Allow the drill to cut into the support surface below the plastic, look for a change in swarf coming from the flutes of the drill bit.
When you have cut through the plastic keep the drill running and gently withdraw from the hole.
TIPs for drilling holes through plastic and related questions
Drilling near the edge of a plastic sheet
Like most materials drilling holes near an edge can be tricky, but with plastic this is more of an issue, as the stresses caused by drilling a hole through the plastic can easily crack the sheet.
A good rule of thumb to avoid cracking the plastic sheet is to keep the edge of the hole at least twice the material thickness from the edge of the plastic.
For example if you are drilling into a 10mm thick sheet, the edge of the hole should be 20mm for any edges of the sheet.
This means the hole centre will need to be marked at least 25mm from the edge of the sheet.
Drilling deep holes into plastic
Drilling deep holes requires a technique called ‘peck drilling’ to allow proper chip clearance and heat dissipation.
Simply put the drill is pushed into the material and released in a series of steps, rather than drilling all the way through in one go.
The drill bit should not travel more than 3 or 4 times the drill diameter before being withdrawn to remove swarf and reduce heat build up.
Keep checking the hole as you are drilling
It’s a good idea to keep looking at the areas around the hole as you drill to spot signs the drill is too fast, becoming dull or you are drilling too deep, all of which can lead to issues
Signs of poor drilling are cracks,crazing, melted surfaces, dimensional changes usually undersized holes.
Typically incorrectly sharpened or excess drilling pressure can induce stress and poor chip ejection which will create heat build up and cause these issues.
Use a pilot hole when drilling larger holes
If you want to drill larger holes into plastic it’s a good idea to use a pilot hole, any hole that is 1” (25mm) or larger should be piolet drilled to help keep the hole to size and avoid damaging the plastic.
For very large holes pilot drills can be stepped up several times to open up the hole.
A good rule of thumb for the pilot hole size is to select a size that cuts a hole just bigger than the chisel point of the drill to be used. This helps to reduce the stress on the material and drill bit and the power needed to drill through the plastic.
For drilling really large holes into plastic using a hole saw is best, check-out our post about cutting plastic for more detailed information.
Drilling holes in acrylic
Acrylic is available in two different forms, the first is cast acrylic and the second is extruded acrylic.
Cast acrylic can be drilled quite easily, as it has been manufactured with few stresses being created in the material.
Extruded acrylic is more difficult to drill holes into due to the manufacturing process which creates a lot of internal stress and it will quickly crack therefore when being drilled or machined and caution is required when attempting this.
Following the steps above should help to avoid any issues.
Always check the type of Acrylic you are using before you try to drill holes through it.