Drilling 3D-printed plastic

Question

I need to do some post processing of my 3D-printed models that includes adding some holes. For each of PLA, ABS, PETG and other 3D-printing materials:

In what ways is drilling a hole in a model made from that material like or unlike drilling wood? Is it worth getting special "plastic drilling bits" that cost tons of money or can I use regular high speed drill bits? Do these plastics have grain that they will split on when drilled into, and if so, what are ways to avoid such splitting? Are higher speeds better, or lower speeds, or should I only use a finger-twirled bit holder?

Are some 3D-printing materials easier to drill than others?

What other methods also work for creating a hole in the different types of plastics?

Answer 1

Have to get this out of the way... Can you just print the hole into the part instead of drilling? That's usually best, when possible.

If you need to drill, you'll definitely want to print an undersized hole and then ream it out with the drill. This both provides alignment for the drill and adds extra plastic around the region you'll be weakening. If you don't know where the hole needs to go in advance, fill the model with a hex pattern of tiny holes in the general region of the future drilling. This is an easy way to strengthen the area with more plastic without making the entire part solid. (Using a slicer that allows localized print settings will also work.)

The hole should be aligned more or less vertical or "across the grain" (+/-45 degrees aligned with the Z axis) to ensure there are nice, strong hoops of plastic around the hole to keep it from splitting. Drilling into a printed part (particularly PLA) from the side / parallel to the XY plane is highly likely to split it. It may even be ok at first but crack later under load or due to creep.

Regular wood drill bits work ok, but you need to go slow and take nibbles, leaving the plastic time to cool so it doesn't melt and stick to the bit. (Coolant is an option.) Use a pilot hole, piloted bit, or step drill to remove less plastic per pass. A really sharp bit will perform dramatically better than a dull bit.

Put something hard and drillable like wood behind the plastic part to help avoid breakage and bit-jamming when you break through the opposite side.

Answer 2

I wouldn't recommend drilling a hole in a 3D printed part in a traditional sense like with wood. Instead, I would merely ream a 3D printed part.

I've done this quite a bit where I'll print my holes at a slightly smaller than nominal size and use a standard carbide drill to ream the hole.

Things to consider:

• Printing the holes smaller than nominal will ensure your hole is not printed larger than nominal
• Printing with a higher shell will ensure you can remove the material without exposing the infill

Note that drilling directly into (or thru) an infill area of the part could lead to cracking of the part later, depending on the hole's functionality. In general, a printed hole (even if reamed) will be significantly stronger than one drilled through an infill area.

Answer 3

In addition to the good answers already given, I'd like to add: Use a sharp drill bit, and don't go too fast. Dull drill bits and fast rotation are more likely to heat up the plastic (especially PLA) to a point where it gets soft again, and then you're usually in trouble because instead of a clean round cut, the material will start to bend and tear. And if you allow it to cool around the drill bit - well, I destroyed a thread tap this way...

Answer 4

Drilling is indeed possible, but as stated in previous answers you should preferably do this along the vertical from the print bed for maximum strength, and if possible use an undersized hole as a starting point/guide. Drilling horizontally may cause the layers to separate but if you clamp down in the z-direction you're much more likely to succeed. It's likely to start cracking if even a relatively small torque is applied (one layer with bad adhesion is enough to make it surprisingly weak). If you still need to apply torque from the horizontal consider reinforcing the structure in the z-direction or splitting your print and gluing/fusing the pieces together to get some strength in both directions. Two holes of decent strength (one along the vertical and one along the horizontal) can also be achieved by adding vertical holes and bolt the layers together. When drilling take care not to apply too much force and make sure the excess doesn't get stuck in the drill bit. Any drill bit should work but I find that wood ones have a slight higher tendency to make the bit jam.

Answer 5

The primary difference between drilling FDM printed plastic and wood is that the plastic part is not solid the entire way through, and that plastic will melt or burn at much lower temperatures than wood.

If you know before printing that you're going to want to drill the part or potentially need to, then you'll want to modify the design of the part such that there will be sufficient internal reinforcement and material in the location of the drill site. The way I've done this in the past is put a through hole through the the entire part and slightly undersize the hole. Then I also increase the number of shells on the part so that the threads will have some extra material to bite into.

If you know you're going to need a hole in the part but not sure where then I'd suggest using the highest level of infill possible on the print so that your part will be as close as possible to being solid plastic. Or if there are a few areas you think might need to be drilled you can build your own internal structure but that can take a lot of time.

If you didn't know your part was going to need to be drilled AND you printed with minimal infill then be very careful about drilling and only use minimal pressure to cut through the top layer to avoid crushing the part. Then once the part is drilled all the way through consider filling the part with an epoxy to reinforce the hole location (if necessary).

Best case scenario though is knowing where and how big you need the hole to be before print. Of course though specs change on the daily.

As for the heat generated from the drilling process I haven't had much trouble with dissipating it. My 'method' for drilling a printed part (technically reaming) is that after I align my hole with my drill press, I then tap the drill-bit cutting only a millimeter at a time, then retract, wait a few seconds then repeat until all the way through. A little time consuming but my reasoning is to minimize burning and overheating of the hole due to the cutting friction.

In all honesty I think my drilling approach is overkill. But, every time I've needed to do it has been due to an error in modelling. I didn't have the time to reprint and was under a time crunch. My post processing step therefore did not have the option to fail so I was extra careful. Whether it was overkill or not it definitely worked, and it's always better to be a little more cautious than late.

Answer 6

I realize this is an old post .. but playing around with drilling PLA myself .. 100 % infill .. and use dish soap for a lubricant .. it seemed to work really well .. I am a hobby machinist .. had a lathe and mill years back and used all the proper oils etc .. but in this case didnt want to expose the pla to oils and I did that once on a part I was trying to wet sand .. and it appeared as though the pla absorbed some of the oil .. Well that just gave me all kinds of thoughts and ideas as far as oil absorption goes .. lol Maybe need to experiment with how much a piece of PLA will absorb if its even measureable .. Anyways .. agree with all above .. and could give the dish soup a try in hopes that it will help lessen the amount of heat generated ..