OT- Preferred method for cutting conduit fitting holes in plastic enclosures ?

Milacron · Oct 20, 2016

ABS plastic, like this

McMaster-Carr

need to cut some 7/8" diameter holes and a few 1 3/8" (or 1 5/16") diameter. Would wood boring cutters be best ? Presume a typical Greenlee metal box knock out tool wouldn't work on plasitc without danger of cracking surrounding plastic ?

capital7 · Oct 20, 2016

I find that a sharp step drill works well in plastic.

FredC · Oct 20, 2016

If you already have a set of hole saws they would work about as well.

Scottl · Oct 20, 2016

There are step drills especially made for conduit fitting sizes and a sharp step drill with a little cutting wax on the edge is the cleanest and least stressful (to the box) way to make holes other than CNC milling.

Plenty of brands to pick from.

Google

Same for cutting wax.

Google

Zahnrad Kopf · Oct 20, 2016

Quality hole saws work the treat. Done it a fair amount.

EPAIII · Oct 20, 2016

I don't like the bit you have pictured. It appears to be a Forstner style bit that will cut the full radius. That could make it difficult. They are intended for wood and will clear out the plug. A hole saw would be better.

Actually, I have used all the methods that have been suggested below your initial post and they work. Even the chassis punches will work OK if the plastic is not brittle and most plastics used for such boxes are not that brittle. I have a great collection of chassis punches, but they are a slower process. For the smaller hole (7/8") my first choice would be a step drill. For the larger one, I would use a hole saw because step drills do not come that large. Both of these should be fast and easy. The step drill has the additional advantage of allowing you to clean up the edge by just kissing it with the next higher step. I do that all the time with them and it leaves a nice clean edge in the same operation with drilling. Great time saver.

Milacron said:
ABS plastic, like this

McMaster-Carr

need to cut some 7/8" diameter holes and a few 1 3/8" (or 1 5/16") diameter. Would wood boring cutters be best ? Presume a typical Greenlee metal box knock out tool wouldn't work on plasitc without danger of cracking surrounding plastic ?

adama · Oct 20, 2016

Good step drill, better ones work really well and truly last too!

jrmach · Oct 20, 2016

it's plastic,all ideas will work,,,,I would personally go hole saw,,,fwiw

Pathogen · Oct 20, 2016

Hole saws suck compared to step drills. I would use a spade bit before a hole saw. Step drills are the best for plastic, thin wall steel or aluminum, and fiberglass boxes.

Steve in SoCal · Oct 20, 2016

I do a lot of electrical work and hole saws work well on plastic. Forstner bits or even spade bits work but cutting a ring vs the entire plug, hole saw requires less force.

Steve

Camshawn · Oct 20, 2016

I use step bits for 7/8 and smaller, carbide tipped hole saws for larger sizes. Mostly it depends on how many holes and what bit is in the drill.one or two holes and a long walk to the hole saw, I will use the step bit. A lot of holes, hole saw every time.
Cam, drilling holes in electrical boxes for 35 years

JST · Oct 20, 2016

Hole saws work, AND I find that knockout punches work on typical "carlon" PVC boxes. You need to use hole saws of "conduit size", or the holes may be extra loose or too tight. That's where the knockouts work better if you have conduit sizes.

Use whatcha got.

The electrical boxes are made of a plastic that is not as brittle as you might expect. They do end to hang up the plastic slugs in the die, so if you have the slug-buster type they may work better. Other boxes may or may not work as well with punches, so hole saws tend to be a universal solution.

Don;t spin the saws too fast, or it will start to melt and weld-up the swarf from a hole saw.

adama · Oct 22, 2016

JST, try a good step drill, yeah its no good for larger sizes, but hole quality is amazing compared to a hole saw, generally the resulting hole is a near reamed level of finish.

sable · Oct 22, 2016

I have used a cone drill ,works fine ,I use it because it is what I have.

Milacron · Oct 22, 2016

I didn't see any step drills that go as large as 1 5/16" so I used a Fostner drill as shown but did so with box clamped in a milling machine. Worked fine that way but would have been nearly impossible with a hand drill. Could have interpolated the holes on CNC but only needed two that size, so not worth the programming time. The 7/8" holes will come later...probably do those on the mill as well since I don't have a 7/8 hole or step drill handy.

Chip Chester · Oct 22, 2016

Drilling plastic boxes with woodworking (center-guided) bits works better if you back the plastic with wood. Otherwise the center "wallows" out.

Chip

SteveBausch · Oct 22, 2016

I use paddle/spade bits. I might use a chainsaw file to enhance the cutting edges into "U"s, but they work well and don't wander as hole saws do.

wippin' boy · Oct 22, 2016

greenlee
spell check bastard

wippin' boy · Oct 22, 2016

http://www.ebay.com/itm/like/252260...7290-0%26rvr_id%3D1113087344045&ul_noapp=true

wippin' boy · Oct 22, 2016

Greenlee 925-11 Small Arbor with Pilot Drill for 7/8" to 1-1/8" | eBay

remember
you said the best not the cheapest

OT- Preferred method for cutting conduit fitting holes in plastic enclosures ?

Administrator

Cast Iron

Diamond

Diamond

Diamond

Diamond

Diamond

Titanium

Hot Rolled

Titanium

Plastic

Diamond

Diamond

Titanium

Administrator

Diamond

Stainless

Diamond

Diamond

Diamond

Similar threads