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View Full Version : Cutting Holes in Plastic Enclosure - How to do it quickly?



Fasttrack
02-16-2015, 02:34 PM
So I have to cut out holes for some 9V battery trays in the side of a plastic box. I need two 9V battery trays per box and I have about 100 boxes to do. The box is pretty rectangular and made from a thin ABS plastic. I'm thinking about coming up with some kind of jig and using something like a rotozip or dremel to plunge in and trace out the pattern. What I really need is a very small router bit with a guide bearing that can plunge cut and then use a jig/template.

What do you guys think? Any ideas?

Battery tray, Page 9 BX0023:
http://www.hammondmfg.com/pdf/1591D.pdf

Box:
http://www.hammondmfg.com/pdf/1591D.pdf

Carm
02-16-2015, 02:52 PM
"Any ideas?"

What fer hole size? Most sparkys I know swear by uni-bits.
I like drill bushings, if the pattern is all the same, easy work, and you can use a plunge router without interpolating. For your run quantity lathe cut bushings would be fine, with a little care. Or make 'em bigger and use a collar.
Upshear might eliminate burrs. Think about support inside the box or clamp your pattern plate if the tool has any thrust. ABS cracks pretty easily.

Fasttrack
02-16-2015, 03:01 PM
The holes are rectangular, roughly 1" by 1.34" with two screw holes on either side. It doesn't have to be super neat because the battery tray has a flange that will cover the cutout. See the posted data sheet, page 9.


Heat is an interesting idea but not sure how I feel about the smell. I was hoping to come up with something that could be done at a workbench in a lab instead of in a shop with ventilation.

RichR
02-16-2015, 03:10 PM
What I really need is a very small router bit with a guide bearing that can plunge cut and then use a jig/template.
Or if you make the template thick enough maybe you could use part of the body of the Rotozip as a guide.

Carm
02-16-2015, 04:26 PM
"What I really need is a very small router bit with a guide bearing that can plunge cut and then use a jig/template."

Dead simple, find a ball bearing with an I.D. that fit's your shank, what 1/4". Loctite below the collet grip. I have a can of quarter and half inch bearings for this, bought surplus.
Or turn a bit of UHMW or brass to do the same thing.
If your pattern is steel, you don't need the bearing, just a deft touch. But I was thinking a reasonable grade of ply, like Baltic birch.

davidh
02-16-2015, 04:45 PM
make a steel band mounted on a block of wood like a cookie cutter. heat it with your propane torch, set the plastic on a backing board and press the hot cookie cutter thru it. . . a little stink and its done. . . quietly too. . .

Yow Ling
02-16-2015, 04:53 PM
does your mill have stops on it ? I assume you are cutting rectangles
just set the stops to confine the work envelope of the machine, then make a jig to hold the part and cut the biggest rectangle possible within the stops

Carm
02-16-2015, 05:03 PM
I don't work for OSHA and I'm not a safety Nazi, but if you're gonna melt plastics read up and form your own opinion about toxicity.
Ya got yer health, ya got everything.

MotorradMike
02-16-2015, 05:04 PM
I'd make 2 jigs.

1/ Outside 'template jig' for hole drilling - drill x6 (4 battery tray mounting holes and 2 for rotozip start points.)

2/ An internal wood block with suitable sized/positioned wells cut into it.
- Clamp block in box.
- Start rotozip in hole and go around the 'wells'. Go the right way, the other way will be too exciting. Make sure rotozip follower tip touches wood but not cutting edges.

Maybe have a vacuum cleaner set up to collect chips as you go.

Paul Alciatore
02-16-2015, 05:40 PM
I have made many electronic enclosures and control panels. When I want a square or rectangular hole, I usually use chassis punches.

https://images.search.yahoo.com/yhs/search;_ylt=A0LEVvY1buJUInAAxE0nnIlQ;_ylu=X3oDMTB0 N25ndmVnBHNlYwNzYwRjb2xvA2JmMQR2dGlkA1lIUzAwNF8x?_ adv_prop=image&fr=yhs-mozilla-001&va=chassis+punch&hspart=mozilla&hsimp=yhs-001

In this case, I would use a 1" square punch twice to get the 1.34" width. Drill two (1/2") holes, 0.34 inch apart. Punch one side. Keep the slug from the first punch in place and punch the second side. Done.

For plastic, you can use a reversible electric drill to power the operation. Fast punch and fast release of the slug. With the punch part on the inside and the die part on the outside you can punch right up to an adjacent wall. And there is little or no cleanup.

I have a larger collection of chassis punches for things like this, but they can be purchased from a number of sources like McMaster and WW Grainger and electronic supply houses like Mouser, Newark, and Digi-Key. For punching plastic, you do not need the ball bearing models, just a bit of lube on the bearing surfaces of the punch.

lwalker
02-16-2015, 07:21 PM
Seriously? If I had 100 to do I'd call Hammond and ask how much they charge you to do it, or check if Polycase has an equivalent enclosure. I know Polycase's prices for enclosure modification are well below any reasonable value of my time.

If that was not an option, I like the template option but there would have to be a way to keep the tool perfectly vertical. I know from experience I'm not good enough to hold the dremel perfectly correct without a good guide, so I just use my mill. It's slower, but I've never had to do more than about a dozen at once.

I've tried punches, but you still have the problem of keeping the punch aligned properly as you screw it in if it only has one guide hole.

rdfeil
02-16-2015, 08:02 PM
Seriously? If I had 100 to do I'd call Hammond and ask how much they charge you to do it, or check if Polycase has an equivalent enclosure. I know Polycase's prices for enclosure modification are well below any reasonable value of my time.

I would check this out as both of your parts are from Hammond, they might be very reasonable as they have a lot of fast CNC equipment.

R

Fasttrack
02-16-2015, 08:11 PM
Seriously? If I had 100 to do I'd call Hammond and ask how much they charge you to do it, or check if Polycase has an equivalent enclosure. I know Polycase's prices for enclosure modification are well below any reasonable value of my time.

If that was not an option, I like the template option but there would have to be a way to keep the tool perfectly vertical. I know from experience I'm not good enough to hold the dremel perfectly correct without a good guide, so I just use my mill. It's slower, but I've never had to do more than about a dozen at once.

I've tried punches, but you still have the problem of keeping the punch aligned properly as you screw it in if it only has one guide hole.

That's interesting - I thought about this and discounted it, assuming the cost to have them tool up for a run of only 100 would be too high. I will contact Hammond and see what they say.

lwalker
02-16-2015, 11:23 PM
I took a quick look at Polycase's calculator. For the enclosure I most commonly buy from them, it would be a one-time setup fee of $100 + $1.04 per enclosure to machine a single feature @ qty 100. Their prices went up a bit since I last did this, but still much cheaper and faster than I could do it by hand.

Happy to plug Polycase. Been doing business off and on with them for almost 20 years.

darryl
02-17-2015, 02:17 AM
Personally, I'd use a router bit with a guide bearing up on the shank, and use a real router also. A trim router would be perfect for this. The guide hole jig would have a 'nest' made on it to hold the boxes in the right position. I would set the box down, position the jig over it and hold with one hand, then plunge cut and guide the router around the guide hole with the other hand.

vincemulhollon
02-17-2015, 08:17 AM
I've tried punches, but you still have the problem of keeping the punch aligned properly as you screw it in if it only has one guide hole.

You can make two jigs, one hole drilling jug and one lining up the overlapping punch jig. There will be some filing, however little, and depending on labor cost vs parts cost you might end up rough punching it and installing a bezel thing. The corners of a square punch will also follow a hole, if you can afford very small diameter holes in all 4 corners.

Its a pity about the numbers. If it was 10 you'd just do it by hand. If it was 100000 you'd order a custom punch.

Georgineer
02-17-2015, 10:22 AM
ABS is vile stuff to work with. It melts easily and the swarf will ball up round your cutter. If you move too slow and don't get the heat away from the cut, the swarf and the workpiece melt down into a sort of sticky pudding which traps the cutter and sets like rock as soon as it's cold. If it gets hot enough to burn (for example in laser cutting) the smoke contains cyanide fumes, and the workpiece stinks for days. I just turned down a request to machine 900 ABS panels and suggested they get them cut by waterjetting.

George

Rosco-P
02-17-2015, 10:30 AM
If it's a repeat job, get a quote from Greenlee for a custom chassis punch.

Paul Alciatore
02-17-2015, 02:57 PM
Greenlee punches are made for steel. This is plastic so you can make your own. Bolt four pieces of prehardened steel together for the die. Make it a few thousandths large for clearance. Mill the punch from same prehardened steel. Observe the shape of the Greenlee punches and be sure to imitate them. Points on the corners and a generous angle along the edge so it is only cutting at one point at a time. This reduces the pressure by a LARGE factor over a flat punch. For plastic I would probably imitate their slug buster style of punch with the cutting starting at two diagonally opposite corners and proceeding to the other two corners.

Get a 3/8" keyed screw and the nut from Greenlee and incorporate it. They do sell the individual parts. Their screws are incredibly strong. Or just use a couple of pins for alignment.

You could probably make it to work on a press for greater speed.




If it's a repeat job, get a quote from Greenlee for a custom chassis punch.

Weekend_Scientist
02-17-2015, 03:10 PM
A small CO2 laser will do a reasonable job of cutting ABS. I've done it a few times. Find someone with a laser and you can knock those out in no time.

kendall
02-17-2015, 05:03 PM
I did similar not too long ago, had to place 40 opening for electrical outlets in 1x6 oak trim.
If you have a router or rotozip, measure outer edge of the base to the cutting flute on the bit, build a flat tray out of plywood, using that dimension to provide the correct hole size. if hole is 1x2 inches, and edge of router is 2 inches to cutter flute, the 'tray' will be 5 inches by 8. build another tray on the opposite side to hold the box you need to cut in position. Make it slightly large so the rounded corners don't get in the way, or file the corners if you need a tight fit.
Tip router, turn it on and rotate it into the cut, then use the edges of the tray guide the router base. No need for guide bits or bearings.

Hmm, double posting is back, or is it just at my end?

kendall
02-17-2015, 05:04 PM
I did similar not too long ago, had to place 40 opening for electrical outlets in 1x6 oak trim.
If you have a router or rotozip, measure outer edge of the base to the cutting flute on the bit, build a flat tray out of plywood, using that dimension to provide the correct hole size. if hole is 1x2 inches, and edge of router is 2 inches to cutter flute, the 'tray' will be 5 inches by 8. build another tray on the opposite side to hold the box you need to cut in position. Make it slightly large so the rounded corners don't get in the way, or file the corners if you need a tight fit.
Tip router, turn it on and rotate it into the cut, then use the edges of the tray guide the router base. No need for guide bits or bearings.

Black_Moons
02-17-2015, 05:06 PM
ABS is vile stuff to work with. It melts easily and the swarf will ball up round your cutter. If you move too slow and don't get the heat away from the cut, the swarf and the workpiece melt down into a sort of sticky pudding which traps the cutter and sets like rock as soon as it's cold. If it gets hot enough to burn (for example in laser cutting) the smoke contains cyanide fumes, and the workpiece stinks for days. I just turned down a request to machine 900 ABS panels and suggested they get them cut by waterjetting.

George

Last time I had to cut something like ABS, I used a diamond burr in a dremel. Can't tell if it abraded, melted or cut half the time, but it sure made a slot in the plastic quick. And thousands of strings, everywhere. looked like spiderman attacked. Molten plastic would stick to the diamond burr and get slung off forming long strings. Don't recall getting burned or any plastic stuck to me, but take care to stay outta that plane of slung plastic.

Basically, it was like the most wrong way to cut plastic except it worked like a hot damn and it didn't seem to give a damn about being coated in molten plastic. It raised a burr but the burr came off easily enough.

When I was done, the remaining plastic that hardened on the diamond burr came off easily, as diamond burrs are a closed grain structure (No holes for stuff to stick in, and not much sticks to diamond)

And worst came to worst, I think the diamond burrs where like $10 for a 10 or 20 pack at princess auto, so throwing one out after the job was totally an option.