How to cut a rectangular hole, smaller than 1", in sheet aluminum?

[johnyradio]

Originally Posted by Gadgeteer

I suggest you consider the set of 3 (1", 3/4", 1/2") wood chisels from HF, Item No. 69544 for $4.79. You can grind off the sides of the appropriate chisel with a bench grinder (or, secure the chisel in a vise, and size it with a hand grinder) to give you the sizes you need. Grinding the 3/4 will give you 2/3", and grinding the 1/2 will give you 1/3". And, you will still have the 1" chisel for future projects!

brilliant!

thx

[johnyradio]

Originally Posted by cutter

Johny, I've carried a set of Marples Blue Chip chisels in my work for probably 20 years.

I can find a set of Irwin Marples for about $25 on ebay, but these sets are about half the price (after shipping):
http://www.harborfreight.com/3-piece...set-69544.html
http://www.harborfreight.com/4-piece...set-42429.html

Contrary to Gadget's advice, I suggest you use only the 1/4" for your purpose because it will give you better control, at least starting out.

i likely will, until i get around to going to the workshop to grind 'em.

I did a little fast & nasty demo for you using the front of an old project box.

awesome!

Also notice the marks left in the sacrificial masonite that I used to back the cutting.
You're going to need something dense enough to support your work but not so hard as to ruin the chisel.

ok, someone else recommended the end of a log.

I used a maple tinner's mallet to flatten the puckered edges

ok! tho i'm concerned that flattening puckered edges might leave wrinkles, esp with youths doing it.

smoothing it with a small, fine tooth file. you will need ...a file or two or three.

can you link me to examples of the right types of file? what angle do you hold it at? straight perpendicular, or angled?

they don't usually come from the factory with a decent edge.

wow, seriously? ok!

thx!

[johnyradio]

[QUOTE=Gadgeteer;578889]

Originally Posted by johnyradio

Can you change the placement of the plug (inside the box?), so that the supplied wire just goes through a round, grommeted hole in the pie plate?

actually, this is maybe something i should consider, since getting a perfect square hole is so challenging, and getting a perfect round hole is easy.

What wires are fed through the plug?

these are wires going from the main circuitry to the front panel controls. Power switch, LED's, microcontroller switches, audio-input, radio switches. My plan is to use VGA type multi-conductor cable for all the wires. Theoretically, i could forego making it detachable (which would make upgrading the boxes a bit more involved).

[johnyradio]

Here a cut i made with a spiral coping blade, purchased here, 0.040" diameter, $6 incl ship:
http://durafix.com/blades/copingsaw/index.html

It's all misshapen, But, i cut it just holding the tool and the piece in the air. it cut very fast, and is a pretty clean cut too. No flares or bends as i might get with a chisel. No burrs either (the junk you see is my blade going off course).

I'm convinced i could do acceptable cuts with a table power scroll saw with a similar spiral blade. A finer spiral blade than this one (if i can find one) might not need any filing. I think the control one has with a fixed table saw would enable a very good cut.

Question is, how can i achieve a good shape with the coping handsaw? Clamp down the piece, i guess. But still need a reliable way to guide the blade. Maybe a NEGATIVE guide, instead of a positive one?

[Gadgeteer]

johny,

I like what you were able to achieve with the spiral blade. Now, all you need is a steel template, cut to the size of the rectangular opening. You can then simply clamp the template to the plate, and run the spiral blade around the inside of the template to produce a perfect cut in the aluminum. (I think this will be the way to get the quality look you are after, and with due deference to cutter, will out-perform Miss Marple's favorite chisel.)

If you will provide me with a mailing address for you, via a private message, I will be happy to send a template.

[johnyradio]

Originally Posted by Gadgeteer

I like what you were able to achieve with the spiral blade. Now, all you need is a steel template, cut to the size of the rectangular opening.

cool! now how do i make the template? :/

thx!

[Gadgeteer]

Originally Posted by johnyradio

cool! now how do i make the template? :/

thx!

Perhaps you posted before I added the last line to my previous post?

I poked around in my garage and found a rectangle hole in tin in the size you need.

Or, anyone with a cnc plasma, laser, water cutter can make one.

[johnyradio]

Originally Posted by Gadgeteer

I poked around in my garage and found a rectangle hole in tin in the size you need.

ha! i appreciate that, but i think it's best if we fabricate our own, as we will need several. However, i can get access to a more pro machine shop just to make the templates.

[Gadgeteer]

Originally Posted by johnyradio

ha! i appreciate that, but i think it's best if we fabricate our own, as we will need several. However, i can get access to a more pro machine shop just to make the templates. What would be the correct machine to cut this in steel? Any kind of steel? I'm guessing water, plasma, or laser cutter?

I'm betting the machine shop will be able to tell you which method is best for your needs. Any piece of tin around 1/16" should suffice.

A simple template could be made by crisscrossing four pieces of the tin to make the open rectangle, and spot welding them together. It would take a sheet metal fabricator about a minute to put it together.

Be sure to take one of the plugs with you when you visit the shop, so it can be used as a guide.

[johnyradio]

correction about the above test, it was with this blade, .040" diameter $6 incl shipping:
http://durafix.com/blades/copingsaw/index.html

so now awaiting these blades, nearly half that diameter, at 0.028"! which i expect will give even cleaner results than above, at 5 blades for $12 incl shipping!:
http://bestwayproductscompany.com/products.html

Feeling very optimistic, since the coping saw is maybe the least-expensive method. The 360 deg makes it easier to hit those curves and corners. I can get the saw and spiral blade for about $8 incl shipping. Good for any size/shape hole. I think it will take a few tries to get the technique down (even with a template), but i feel it's something one could quickly get good at with a little practice. i think it may give me more consistent, cleaner results than chisels, so will hold off for a minute on the chisels. but thanks for that, Cutter!

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Still awaiting these two shipments:

nibbler/shear (flat blade, doesn't punch little half-moons):
http://r.ebay.com/Pd8EA1

jeweler's blades, 89 TPI (not 360 deg blades):
http://r.ebay.com/9FpArk

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For templates, i'm thinking i could buy one of these pre-punched plates (and chop them down if they contain more than one hole):
http://www.l-com.com/patch-panel-ser...-cutouts-black
http://www.l-com.com/patch-panel-ser...b15-hd26-holes
http://www.blackbox.com/Store/Detail...-1-Punch/WP080
http://www.globalspec.com/industrial...15_patch_panel
http://www.blackbox.com/Store/Detail...nel-DB25/JP221
http://www.ebay.com/itm/Stainless-St...item3f1c42f1af
http://www.ebay.com/itm/White-Single...item20cf81e30f

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Another possible approach: get pre-cut DB15 plates, then cut a ROUND hole in my end-cap that's big enough to encircle the entire punch-hole, and affix the pre-cut plate to my end-cap. However, this method seems less sturdy then attaching the DB15 directly to the endcap itself.