Drilling a 1-1/8" hole in plastic with a Dremel

Question

Forgive me for being a complete beginner to this; I have a Dremel 3000 with the standard complement of attachments, and it's been useful to sand some items and brush up others.

I have a piece of plastic in which I need to cut a 1-1/8" hole, preferably as accurately as possible.

Can I do this with the Dremel, perhaps by buying another bit for it? I'm in the UK, if that helps with sourcing.

In my research, I've been told that standard drill bits will probably not survive the higher RPMs of the Dremel. A suggestion has been to crudely cut a hole to size, and smooth it with the Dremel afterward.

Is there a better way than the above, or am I somewhat stuck without buying a drill?

Re: "I've been told that standard drill bits will probably not survive the higher RPMs of the Dremel": it's more likely that the Dremel's motor will not survive if used with a hole saw. When high-speed electric motors slow down, they draw a lot more power, which can fry them. Similar question in this regard https://diy.stackexchange.com/questions/29342/do-i-need-a-corded-drill-to-mix-thinset — Fizz, Jul 12 '17 at 16:54
Just curious, how were you gonna fit a standard size bit into a dremel? Their chucks only accept up to 1/8'' if I remember correctly. — Sidney, Jul 14 '17 at 14:28
@Sidney Was likely hoping there'd be a Dremel-sized attachment or converter, I expect. Hope springs eternal in us newbies, apparently ;-) — Dan, Jul 14 '17 at 18:05
@Dan TBF I was hoping you knew of something I didn't. There are a lot of (not terrible, or at least not terribly terrible) reasons I'd like to be able to put a regular size drill attachment in a dremel. — Sidney, Jul 14 '17 at 18:07

score 3 · Accepted Answer · answered Jul 12 '17 at 16:34

While this can be done with a Dremel (I've done it), you'll get a much better result picking up a paddle bit or hole saw and a hand drill. If the exactness of 1.125" is not particularly required, you can go with the dremel, but if you need exactly that hole size (say, you're trying to minimize possible air leaks in something) I'd say you need a drill.

Edit: I just realized you're using a dremel on plastic -- This will lead to bits of high static plastic everywhere. In addition to that, whatever you cut will not have clean cuts, there will be melted plastic all the way around the edge. I won't say this isn't an irreparable situation, but getting a drill probably is your best bet.

Aside from that, almost any home based project will be 100x easier with a drill. It's one of the few tools even the least DIY people should have around the house.

I'd not thought about the higher-RPM consequences when Dremeling plastic! Drill and hole saws it is. A minor investment, let's call it. — Dan, Jul 14 '17 at 14:04

score 2 · Answer 2 · answered Jul 12 '17 at 17:42

If your requirements mean no additional purchases, about the best results may come from careful marking of your workpiece, a clear and accurate circle. Consider even to glue paper or use masking tape to have a good marking surface.

With a drill bit chucked in the tool, create a hole near to one edge, but not engaging the marked line. Create a number of these holes around the edge of the circle. If one hole is too close to another, no worries, but keep it clear of the drawn circle.

Once you've created this ring of holes, use a burr bit to break the edges, allowing the center section to drop out. If you have a burr bit with a long cutting portion (not just a ball or cone or other small shape), use that for faster removal and better control.

Keep the speed low, keep the tool square to the work.

You may find you have sufficient control to remove the outer edge of the "toothy" ring using the burr bit. If not, switch to the sandpaper drum.

Again, keep the speed slow and the tool square. Too much speed and/or too much pressure will melt the plastic.

If you have a piece of scrap on which to practice, you can get a better feel for the tool before you plunge in for the final attack.

I'll second the suggestion that a good quality cordless drill is a must-have for a DIYer. Shoot for lithium based batteries (part of the advertising kit) and the highest voltage you can afford. That's off-topic, however, so feel free to ignore this last opinion.

A great suggestion and well explained, thanks. I ended up jumping for a variable speed drill and a cheap hole saw set, as all answers seemed to suggest that'd be the best option-long term. It's not going to be the best quality, but it's fine for the occasional project. — Dan, Jul 14 '17 at 14:03

score 1 · Answer 3 · answered Jul 12 '17 at 19:45

You're right, the Dremel is too fast. Use any of the tools actually made for punching that hole. One is a 1-1/8" hole saw, made for wood. These need a normal (slower) drill such as a drill-driver. Someone should make a 20:1 gear reduction for Dremels! LOL!

src: wikimedia

Another is a bevel drill, which lets you pick any of many sizes, again requiring a larger size, slower drill.

src: wikimedia

Another is a punch, where you drill a pilot hole and then use a bolt to pull the punch halves together. These are widely used by electricians for conduit; the standard sizes they use are 13/16, 1-1/16 and 1-5/16, if that's helpful.

src

Drilling a 1-1/8" hole in plastic with a Dremel

3 Answers3