Best tool for cutting off a plastic-flange chunk from inside an enclosure?

[Martin F]

Hi all,

I have a project in which I intend to use a specific IP67 DT enclosure. The aim is to enable insertion of our existing electronics product within the enclosure.

The dimensions of the enclosure are almost perfect for our need. However, it comes with two 'plastic flanges' that block our device from entering sufficiently deep into the enclosure. We ideally want our device to be able to go e.g. 1 cm further in, but this requires that we can cut off the 1st cm in each side flange as indicated in the 3D step below.

I am unsure what method/tool would enable us to do this in the simplest manner, while enabling a fairly consistent chunk to be cut off (i.e. ideally we'd want to be able to calibrate the tool somehow so that we can avoid cutting off too much or too little of the plastic, as we want our device to enter the enclosure by approximately +/- a few mm in precision.

The enclosure opening is 3 x 10 cm, while the flanges are about 3-5 cm in. We'll need about 100-500 of these per year, so we're looking for a solution that makes sense at this scale (it can involve some manual labor).

[5U4GB]

Ask any woodworker :-).  What you'd need is a jig that the case slides onto the end of and that fits a Dremel with a cutting blade, you slide the enclosure onto the jig which positions the Dremel blade at the correct height and depth, press down to make the cut, repeat for the other side, and you're done, with perfect repeatability each time.

[xrunner]

A Dremel tool with a flex shaft attachment, the correct bit, and a person to do the job. Modding 100 to 500 a year is no problem at all.

Flex Shaft

[Ian.M]

The flanges appear to be attached to the side walls. The closer you need to cut to the side wall, the higher the risk of damage. Access is poor, so making two cuts, one parallel to the wall, and the other across is probably not viable, nor is there room to get a nibbler in there.  That leaves milling, grinding,  and hot knife cutting. 

Milling with a dremel or router style tool and a jig may be problematic as the feed rate is dependent on the skill of the operator.  Too coarse a feed is likely to result in excessive strain at the sidewall to  flange junction, possibly resulting in externally visible sidewall deformation or even cracking.  This is less of a problem for grinding operations, but the down-side is the need to clean-up fine, probably static charged plastic dust. 

Ideally you'd use a proper milling machine so the feed rate could be well controlled.

[langwadt]

fixture to hold it with the opening up, use milling cutter in miling machine or drill press with depth stop

[David Hess]

fixture to hold it with the opening up, use milling cutter in miling machine or drill press with depth stop

That is my suggestion as well.  A milling cutter in a milling machine or drill press will remove the flanges cleanly, safely, and consistently.

[Ian.M]

Milling is *not* a job for a drill press.  They usually have a Jacobs taper spindle and no drawbar, and a Jacobs taper can let go unexpectedly when subjected to a vibrating sideload with little or no end load, which at best will wreck the work and at worst result in a flying chuck bouncing round your workshop.  Also there is usually too much side slop in the quill for controllable side cutting.

Get a small mill or mill/drill, with a draw bar or threaded spindle so the cutter and collet or other holder is positively retained.  Also it will be designed for side loading, with a lot more lateral rigidity.  Chinese mini-mills are fairly affordable, and on one set up with a jig to hold the work and table and depth stops to define the limits of the cuts one could knock these out as required in a few minutes per part.

[langwadt]

Milling is *not* a job for a drill press.  They usually have a Jacobs taper spindle and no drawbar, and a Jacobs taper can let go unexpectedly when subjected to a vibrating sideload with little or no end load, which at best will wreck the work and at worst result in a flying chuck bouncing round your workshop.  Also there is usually too much side slop in the quill for controllable side cutting.

Get a small mill or mill/drill, with a draw bar or threaded spindle so the cutter and collet or other holder is positively retained.  Also it will be designed for side loading, with a lot more lateral rigidity.  Chinese mini-mills are fairly affordable, and on one set up with a jig to hold the work and table and depth stops to define the limits of the cuts one could knock these out as required in a few minutes per part.

sure, but I image a plunge cut not really milling, so less of a risk

[jpanhalt]

It is still an interrupted cut and will cause vibration.  Something with a draw bar is what I recommend too.  If you don't have that, then a drill press might work with caution.

Another solution is to cross cut the bottom with a saw, as others recommended, and use a chisel with thin slices.  That alternative is for one offs, not any sort of production.

[Ian.M]

People have and do mill with a drill press, and if the Jacobs taper is clean and well seated, usually get away with it for a while.   However, its a horrible idea to do so as a repeated operation, unless you are willing to reseat the taper before each cut!

[Smokey]

HA!  I'm using that exact same enclosure for a project. 
https://www.te.com/usa-en/product-EEC-325X4B.html
I'm not sure why they put those tabs in there, but I bet it has something to do with the injection molding process.

Here is one solution, which should be doable for 500pcs...   There are quite a few Chinese "second sources" for this enclosure.  I'm sure you could get one of those companies to make you some parts that just don't have that feature.

[coppercone2]

maybe a nail cutter/puller and a sideways nail puller if that exists lol

[jpanhalt]

There are "nibblers" that will do the job (attachment).   They cut on 3 sides, as opposed to a punch, and come in many sizes in both powered and hand operated versions.  Convenient for cutting inside curves in sheet metal.  They are slow and the edge finish may not look very professional without additional work.  I use mine for sheet aluminum.  With plastic, you run the risk of an unintended crack.

[5U4GB]

fixture to hold it with the opening up, use milling cutter in miling machine or drill press with depth stop

Doesn't that risk having the cutter grip the end of the long, thin shaft and snap it or otherwise rip it to pieces?  This is why I suggested cutting rather than milling it.

Having said that, you could possibly put a collar around the shaft to hold the section you're not milling away rigidly in place, but that makes the jig a lot more complicated.

[Kean]

I would set up a jig on a milling machine so that the plastic box can slide left and right while held firmly upright.  Have a slitting saw that lowers to a fixed height into the opening, and end stops at appropriate positions to control depth of cut to the left and right.  You slide the box each way in the jig to put a notch into the tabs, then remove it and snap away the upper part of the tabs.  If the tabs do not easily snap off, then maybe use a wood chisel to remove them.

[5U4GB]

In terms of non-mechanical removal methods, what about a strip of nichrome or similar wire held in a jig to set the correct depth?  Put it above the plastic flange, let it melt its way down through it, pull it out again.

[Kean]

In terms of non-mechanical removal methods, what about a strip of nichrome or similar wire held in a jig to set the correct depth?  Put it above the plastic flange, let it melt its way down through it, pull it out again.

That might work better than a slitting saw if the depth of cut is more than that of a slitting saw that can fit into the opening, but it could be difficult to cut right up against the inside wall.

[5U4GB]

I think the OP wanted to cut away only the first 1cm, thus my earlier comments about the problem of applying mechanical stress to a long thin flange while removing the tip.  Melting through it places minimal mechanical stress on the flange, although you'd want to experiment on scrap plastic first to figure out the correct amount of heat to apply.

[Smokey]

I would set up a jig on a milling machine so that the plastic box can slide left and right while held firmly upright.  Have a slitting saw that lowers to a fixed height into the opening, and end stops at appropriate positions to control depth of cut to the left and right.  You slide the box each way in the jig to put a notch into the tabs, then remove it and snap away the upper part of the tabs.  If the tabs do not easily snap off, then maybe use a wood chisel to remove them.

... and you want him to wood chisel 500 enclosures by hand?  This would add so much labor cost to an already expensive housing.  I hope his profit margin is HUGE....

I have one of these enclosures in my hand right now... The tab under question starts about 2.6inches from the top side opening. 

If you had to machine them, the housings already have mounting holes/surface on the flat bottom so bolt them to a fixture with the opening side up and go in with a long endmill and plunge out the tabs as desired.  Since it's plastic, you may be able to get away with this on a drill press if you had to.  If manually, do one side, flip the whole fixture and do the other side.

[Kean]

I would set up a jig on a milling machine so that the plastic box can slide left and right while held firmly upright.  Have a slitting saw that lowers to a fixed height into the opening, and end stops at appropriate positions to control depth of cut to the left and right.  You slide the box each way in the jig to put a notch into the tabs, then remove it and snap away the upper part of the tabs.  If the tabs do not easily snap off, then maybe use a wood chisel to remove them.

... and you want him to wood chisel 500 enclosures by hand?  This would add so much labor cost to an already expensive housing.  I hope his profit margin is HUGE....

To take off a thin plastic tab like that it only takes a couple of seconds each.  I've done it to remove the internal ribs on hundreds of plastic boxes myself.

Alternatives for the OP are to redesign the PCB to fit around those tabs, or pay lots to have a custom injection mold make without them.  A bit of additional manual labor may be cheaper than other options.

[5U4GB]

And right on schedule Big Clive posts a teardown of a dodgy tool you can use to melt through the plastic struts to sever them:

[coppercone2]

Don't fall into the trap of having to always go through the injection mold guys. It never makes sense to have to deal with them. $$$

hire a hand to do this labor (aka buy a small mill or other tools)

Nothing like being prevented from doing engineering because of some problem involving goop. That is a 5th avenue rush hour traffic jam

[DiodeDipShit]

Machining is the best and most accurate solution. It's has already been discussed. Martin only need just over 1/32 of an inch removed from 2 tabs. 
If Martin takes the lids off, he will save a about minute labor per box. He can expect the following prices:
100 boxes , 1/2 hour setup $50 (standard shop quote) 1 min run time each around $1.50. ~$200 total for 100 pieces. ~$2/ea.
500 boxes, the run time can be negotiated. $50 setup, ~$1.00 each,  ~$550 total  , ~$1.10 ea.

Crazy home version: Jury rig a wide flat tip high power soldering iron to a drill press. Set stop to minus 1cm.
Smoosh down one tab, slide sideways, handle up, smoosh second tab, slide sideways. Lots of plastic slag, but true to dimension.
Flick slag off is necessary.
Smelly melted plastic, Do this next to a door with good fan sucking outside.
Set up ~ 1-3 hours, runtime each ~30 sec ( minus cover removal)  I know its nuts, but it would work. Martin saves or after the stop gradually lowers because of drill press vibration,  he realizes he should have just gone down the the local machine shop. ..... The plot thickens....

[Martin F]

Thanks for all the inputs, appreciate the support!

[connectTek]

Long 90deg hot knife. Heat on gas flame
It would take 20 seconds per case.