Clamping open-topped box for milling an end

Just a WAG here, but how about using a shaped wooden block for a backer? I've done similar things for routing thin wood and the like. You might even want to use a trim router and a template. We used to use routers for cutting aluminum/foam/wood stringer/panel sandwiches for putting windows in motor homes, so routing even aluminum panels with wood-working tools is possible. Hot melt glue is a perennial favorite for temporary fixturing in the woodworking world, might be that would help, too.

Stan

"Bill Schwab" wrote

Bill, FWIW, a rectangular hole with work with D-Sub connectors. It's not quite as pleasingly "perfect" as a trapezoid, but the holes still have enough material to grab, if you back up the studs with small washers.

LLoyd

Clamp it in the vise with the opening toward you and maybe some cardboard between the box and the jaws. If you are worried about clamping pressure put a block of wood in the box so you are clamping only the bottom and a parallel or such behind it if it has molded feet. Mill it with a 1/8" bit at the highest speed. I'd mill it square and file the longer side. The mounting holes can be milled out from the opening or drilled separately.

Size the hole for the male connector regardless of which one goes on the box.

jw

Hey Bill,

Yep, pretty tough to work on a plastic thingy at some distance above the chuck jaws, if I read you right. I think I would forget the vise altogether.

1. I'd start with a decent size hunk of scrap 3/4" plywood, maybe about 6" wide by 8" long or so (width to suit Step 4.) 2. Screw a block of 2 X 2 X the-inside-width-of-the-box, on the face of the ply crossways at one end.
2. Bore out a couple of 1" holes just below the 2X2 to allow 3" C-clamps a reach in and so the C-clamp can sit on the "bottom" of the

2X2 (in Step 5.)

1. Allowing for the C-clamps, fasten the ply (more C-clamps??) to an angle bracket on the mill table, with the 2X2 up and away from the angle plate and parallel to the mill table.
2. Clamp the end of the box to be cut onto the 2X2 with C-clamps.

If you do a bit of fiddle with the sizes beforehand, you can probably also clamp the "bottom" of the box onto the 2X2 also.

Take care.

Brian Lawson, Bothwell, Ontario.

I machine cases like that all the time on my mill. Get an angle plate tall enough that the whole case can fit on the upright part of the plate, mount the plate on the table and clamp the box to the plate.

or similar suppliers sell angle plates pretty cheap if you don't mind the cheap and probably radioactive chinese cast iron. If you have to do a lot of these boxes, drill holes through the plate that line up with the holes for the case cover, and instead of clamping the case screw it to the plate from the backside.

I just use a 3/8" endmill to make a slot for d-sub connectors, as follows.

Drill the screw holes for the D-sub connector first. Then use a 3/8" endmill, centered on the screw holes, and mill a slot up to about 0.050" of the holes.

Low cost import d-sub "Greenlee" style punches are also available if you shop around a little.

Good luck-

Paul T.

If the connector has a metal shell, and the box is plastic, just buy an extra connector, heat it up with a torch, and push it thru the plastic while the connector is still hot.

Lloyd,

Thanks for mentioning it!

Bill

Jim,

It does have small feet that would cause problems, so the parallel sounds like a good idea. Is the opening facing me for visibility or is there more to it?

Just out of curiosity, what is the reason for doing that?

Thanks!!

Bill

If you were near Milwaukee I'd let you borrow mine. Your address implies that you're not...then again, my address implies I'm in Germany, so...

You'll never be unhappy with a Greenlee punch. It only hurts when you pay for it, but like any other good tool, it's a pleasure to have and use. That said, if you're only making a few, ...

Because if you make the opening to just fit the female connector, the male won't seat all the way. And yes, I did make that mistake once....

Paul,

Can we go back to the radioactive part? =:0 Do I need to borrow a counter and go over my mill? I read some interesting cautions about buying machine tools, but this was not on the list.

Nice! I don't have to do many right now, but I will keep that one in mind.

Does the remaining material serve an important purpose? As Lloyd pointed out, the holes sometimes communicate with the opening.

No offense to the company, I hadn't noticed that low-cost and Greenlee went together :) I will take another look, because it would be an efficient way to make these holes.

Thanks!

Bill

I'd be inclined to clamp it directly to the table and use some blocks of scrap and machinist jacks inside the case to support the top solidly. That general idea seemed to work well for some rectangular openings I milled in a

12" Hoffman box a while back.

Here's a picture:

The metal box was just barely rigid enough that the internal support was not needed, though there was a bit of chatter during the cut.

I'd probably also try milling a rectangular opening and then file the angled corners - shouldn't take long with plastic.

Mike

According to Mike Henry :

Yes -- D-shaped Greenlee chassis punches are only nice if you have them. Also -- some plastics might shatter on an attempt to punch them with such a tool.

Since this is plastic, I think that what I would do is to take some sacrificial lumber -- perhaps a chunk of 4x4 cut to near length, and put it inside the box to fully support the surface which you are cutting. Then put some straps of metal or more (thinner -- say perhaps

1/2" thick) wood on top, and apply the hold-down clamps to that surface.

Then mill through the top wood, the plastic, and a little way into the support wood, and you should have the plastic fairly well supported and unlikely to crack. If the position of the hole is not too critical, draw it out on the top piece of wood, and mill to that line.

Good Luck, DoN.

Is this for just a few D-connector slots in a plastic box? Many suggestions here are way too time consuming, I could file the slot in less time than one requires to locate the T-nuts and clamps for the milling job. I'd use a 1/8 round saw file, these have very coarse grit teeth and are bendable rather than brittle like ordinary files.

OK, you have plenty of time? Find a CNC mill and write a program to mill the slot :-)

Klaus

sounds like a good idea. Is the opening facing me for visibility or is

there more to it?

Visibility and convenience. I've tried the methods other posters suggested and use the angle block and plywood for larger boxes but for the small one you have a 2X4 spacer in the box should be enough. You need to see that the wood doesn't touch the lower corner of the box when you tighten the vise, and it's easier to add a C-clamp or 2 for extra stiffness near the cut when you can see the upper edge of the wooden block.

I generally saw/nibble/plasma a large opening in the chassis and make a separate bolt-on control panel out of 0.062 aluminum. Flat panels are MUCH easier to fabricate. Make sure the wired panel will pass through the hole.

jw

Bill,

Don't you just hate it when people post an answer to the question you didn't ask? Here's another one.

I've had good luck in the past (for short runs) by using woodworking techniques.

1. Router template method. Make a template out of wood that is the size of your box plus connector hole in each dimension. So, if the box side is 3" wide, and the connector is one inch, make it 4" wide. Box side 2" high, connector 3/8" high, make template 2

3/8". Offset template as required for positioning. (If you want to get fancy, you can put in a taper.) Cutting carefully with a jigsaw is fine for the template. (Of course, check my math -- haven't had enough coffee yet...)

Then chuck a 1/8" end mill in a Dremel tool collet with tool mounted in their little drill press, plunge in, lock down, and, by hand, move the box around the borders of the template. Be sure to keep control of vertical/horizontal alignment. (Don't use a chuck for this, stay with the collets.)

This is too much work for one. It's appropriate for 10-100. It's inappropriate for thousands.

1. Guide method.

Similar to above, but I use a metal stamping recovered from a junked PC. It has D9, D25, and a couple other shapes already on it. Place where required, and mark your mounting holes only. Drill 'em out, then mount the steel pattern (oh, yeah, you have to find one. But it's not hard to come up with one...) up to your mounting holes, raising it off the surface by about 1/4" by using nylon spacers. Then, take your Dremel and end mill, (freehand or with drill press) plunge it in and trace around the guide. Make sure the cutting edge of the endmill stays in the plastic, and that the shaft only of the endmill contacts the metal guide. Trace around the guide in the appropriate direction (this will be immediately obvious) 'til you're done. It's sort of like cutting out outlet holes in drywall. And about as messy.

Reasonable effort for a one-off. Acceptable for 10, but too picky for 100.

1. Re-design the whole thing....

Last time I did this in quantity, we used a Panduit box with free-floating ends. The front was an IR red translucent thing, but the back had a bunch of connectors and labels on it. We ended up going to a plastic badge engraver, and having them label everything, and cut out the D9 and D25 holes by just "engraving too deep" and popping out the waste. The badge material was fine for the back panel.

There. Three answers to the question you didn't ask. My work is done here.

Best o' luck

"Chip" in Columbus

Easy. Just find or make a piece of wood that fits inside the box. Clamp the fact to be milled to the piece of wood with at least two clamps. I use small Kant-twist clamps for this. Grab the wood in the mill vise. You'll mill thru the plastic into the wood a little.

For trapezoidal D-sub holes, don't try to mill the trapezoid. Just mill straight ends, then run the mill far enough to make the wider corners, using an endmil of radius similar to the radii of the corners. You can then easily file away the remaining plastic to make the trapezoid.

Jim,

Got it - thanks.

That's an interesting idea, especially for a future D-shell problem that will hopefully surface. There I would be making several units with multiple ports. As that design evolves, I will have a better idea of how many different types of holes will be required, and that will help me decide whether punches make financial and political sense.

With your .062 panels, could I reasonably expect to drill and bolt several of them to mill at one time? What I have in mind is to drill holes and bolt to maintain alignment, and then clamp the stack over plywood or something, probably moving clamps around (add one then remove another to make way for the endmill/bit) as work progresses.

Then I guess there is a question about whether the alignment holes can/should be the mounting holes. Confused by what I mean? That makes two of us :) With the understanding that I am trying to maintain precision largely for practice, I am not sure I would be able to drill the holes add the bolts w/o losing the setup [*]. If a first set of alignment holes are drilled in margin to be removed later, then I could stack, drill, bolt, clamp, and then mill a clean edge, drill mounting holes, and mill the ports/slots. Clamps come off, more bolts in the mounting holes, remove the bolts in the scrap, clamp, dial the clean edge to re-align and then clean up the other three edges. If the panels are small enough, they might be squared up in the vice using the clean edge as a starting point.

[*] it might be possible with enough relief in/under the plywood support, which could have corners removed or something to make room for fingers or a wrench to hold a nut underneath the stack.

Am I making this too complicated? Better ideas are welcome.

Bill

Hello Bill; I have a part time gig as the machinist/metalworker for an electronics lab, so I'm constantly cutting odd connector holes in plastic boxes, both hard plastics (grey FRP, like Hoffman enclosures) and soft plastics (Pelican cases). Personally, I wouldn't waste your time setting it up on a mill. It's hardly worth the trouble trying to get the box mounted stable and level. I usually just do a hand layout of the connector pattern with a scriber, right on the box. Use an electric drill to make a few small holes to take most of the material out of the hole, then clean it up with a couple of small files. With a little care on the layout, it'll be neat and sufficiently accurate.

If you're going to do multiple connector holes of something common like a D-sub, use your mill to machine up a pattern out of 1/8" aluminum. With that, you can quickly and consistently center punch the screw hole locations and scribe the opening outline. I have a bunch of patterns for the connectors that we most commonly use.

I hope this helps!

Bruce Johnson