How to cut perfect holes in sheetmetal???, need vents on rear trunk lid.... Options

[Mueller]

body work is not my strong suit...so, I need some help or recommendations for adding holes with very clean edges....location is in the red (trunk lid)

I have an air-nibbler, but I think it would make a terrible cut for something like this

[Andyrew]

Air nibbler.. cutting wheel.. and something to clean it up a bit..

I've used the air nibbler with great success... Except when the sheet metal is double walled.. then you use the cutting wheel.. Then you use the cutting wheel or something like that (dont rember what its called) to finish it up...

PS.... Why the vents? Kinda gets rid of the "targa top holder" function of the rear trunk...


Oh ya, I just did the Dizzy hole for the v8 yesterday using this.. But I used a drill as well for starting..

[Jenny]

make a rough cut, then file to perfection? Of course, that's just my professional opinion. (IMG:style_emoticons/default/rolleyes.gif)

Jen

[balljoint]

Jigsaw with fine toothed metal blades.

[tdgray]

Alot of the MGA guys take thier hoods and have them louvered (sp). Professional shop can do this for small amount of $.

[lapuwali]

For a perfect hole that big in one pass: a huge shearing press that takes up most of a room. For a perfect hole with hand tools, something powered to cut the rough hole, a hand-nibbler to get nearly the exact dimensions, then a file to smooth the edges.

btw, if this is for the radiator in the trunk idea, I'd REALLY STRONGLY recommend you start with holes in the badge panel, and only put holes in the trunk lid when it's clear that's not enough. Some fascinating airflow studies done many years ago on racebikes by a brilliant gent named John Brittain showed that, with proper ducting, very small holes can be used to flow a LOT of air. He was doing this to provide radiator airflow with low drag (smaller inlet and outlet holes allowing the rest of the bodywork to be smaller). Drag really isn't a factor here, but if you can show that you can get adequate flow for a radiator without putting holes in the trunk lid, that would be very good to know. It certainly reduces the need for tidy bodywork.

[Demick]

Definitely a jig saw with fine toothed blades. Don't even try a nibbler or cutting wheel. Tape out the shape you want to cut and then cut away. You will be surprised how nice it will cut with a jig saw with sharp blades. Then use a file to clean it up.

Demick

[eeyore]

If a plasma cutter is not in your repertoire...

I've always preferred thin cut-off wheels on an angle grinders because the blade gives me guide of sorts. Use a hole saw at the corners. I prefer variable speed pneumatics grinders because they bog down when the workpiece binds, rather than jumping the cut and jittering across the surface you're trying to keep.

I'd scribe lines in the paint, and use a heavy masking tape as a cutting line, tape on part to be kept. AND, as usual, cover any glass or paint don't want permantently speckled.

I think I'd also get a very long file, and dress the egdes, if you need straight lines. I'd cut from the top, but when filing, I'd put the trunk upside down on a sawhorse, and use the edge of the sawhorse to 'back-up' the metal to keep if from bending, vibrating.


If for cooling, I like the louvers idea too, as well as the badge panel idea. The key is to have high pressure on one side, low pressure on the other, airflow is a result.

[andys]

IMO, regardless of edge quality, you'll end up with long unsupported edges of thin sheetmetal; not good. Rolling these edges would help tremendously, and yeild much needed rigidity (a folded edge would make it go flat, but you could hammer it back to shape, I suppose). It is not easy to accomplish this (to maintain straightness and trunk lid contour), but would result in a finished look, rather than an abrupt edge.

Andy

[TonyAKAVW]

Photolithography and acid etching should give nice results. Might take a while to go through all that metal though (IMG:style_emoticons/default/laugh.gif)

I agree with Jenny's suggestion of cutting first with a saw and then filing to perfection. I have an air body saw that I got from Harbor Freight that works amazingly well. With some practice you might even get a final cut with that. Otherwise, pull out some files and a dremel and go to town.

If you can't roll the edges, you could machine a frame out of an aluminum plate to support the edges, or steel so you can weld it. I'm just jealous that you have a milling machine, so I'm thinking of ways to use it vicariously (IMG:style_emoticons/default/sawzall-smiley.gif)

-Tony

[SpecialK]

Metal hole saw of the correct diameter for the radius you're looking for on the corners, nibbler for the sides leaving the line (I prefer a scribed type line as opposed to an ink line, It'll be obvious when you do your finish filing), and "draw" a file over the excess until the shiny scribe line disappears. Oh, and don't forget to wear good leather gloves, or you WILL get cut!

A fine carbide rotary file in a straight die grinder works great too for taking down the excess, but definitely finish by hand filing.

[Aaron Cox]

Alot of the MGA guys take thier hoods and have them louvered (sp). Professional shop can do this for small amount of $.

i agree...do it this way....

[tdgray]

Can't find a picture of an MGA but here is a picture from the other Whine and Cheese set. Big snobs that they are (IMG:style_emoticons/default/wink.gif)

[GWN7]

Louvers....unless your going to fill the holes with some screening material.....But louvers would look better....

[Mueller]

of course I'd cover the holes with screen or mesh...those punched in louvers are boring and totally take away from the lines of the car...they only belong on old hot rods, any other cars and they are goofy in my opinion (IMG:style_emoticons/default/smile.gif)

[SteveSr]

(IMG:style_emoticons/default/agree.gif) Mike,hole saw in the corners then jig saw/fine blade (IMG:style_emoticons/default/sawzall-smiley.gif) then draw file to smooth out any rough spots. Although (IMG:style_emoticons/default/agree.gif) with Andy....long unsupported edges....not good, but if you made a grill to fit in there that was stiff enough that would support the sheet metal. (IMG:style_emoticons/default/beer.gif)

SteveSr

[seanery]

louvres will keep the shape of the metal better. I bet your trunk lid will sag with two big holes. (IMG:style_emoticons/default/sad.gif)

[Trekkor]

Mike, a tool I used too punch holes through thick guage stainless sheet, works like this:

Drill pilot hole.
Special tool has die cutter that bolts through pilot hole.
Tool is fastened to both sides of the work.
As you tighten bolt it draws cutting blade through your metal into the receiving die part of the tool.
Only takes a minute or two to punch any size hole you want. Perfect hole every time.

I would inquire at an electric supply house for a K.O. punch ( knock out )
or a " slug buster ". (IMG:style_emoticons/default/smash.gif)

May be a rentable tool.

KT

[sgomes]

What size hole do you need? I can make 'em perfect in: .45, 9mm, .38, .270, .22, ...... (IMG:style_emoticons/default/cool.gif) (IMG:style_emoticons/default/ar15.gif)

[Trekkor]

I replied before seeing the picture of your design. (IMG:style_emoticons/default/headbang.gif)

Use the punch in the inside corners like above mentioned intead of hole saw.

Slow steady jig saw sounds good. Replace blades frequently.

Put blue tape over the metal, mark your cut lines, to avoid scratching metal with your saw.

KT