cutting hole in plastic firewall cover

Lawson Cox

Lawson Cox

Well-known member
I am about to install a heater, but I am going to have to cut a hole in the plastic fire wall cover. I have thought about a cut off wheel on my dremmel tool, however, that doesn't do much but melt the plastic and gum up the tool and it breaks the disc. Any suggestions. It is going to be a fairly large hole because I am installing a Southwind. All suggestions appreciated. Thanks in advance. Lawson
 
How about a hole saw bit or a wood spade bit. Ive cut holes in plastic tail lite lenses with a spade bit for blue dot tail lites. ken ct.
 
Not knowing what size hole you need if it was me I'd go to Home Depot and buy a hole saw for your drill. They come in popular sizes to probably 2".
 
Hole saw works very well. If possible remove the insulation behind the area you want to cut prior to drilling.
 
I have had my best luck with this operation by using a cone shaped stone bit, about an inch diameter, on an electric drill. Make a starter whole using a small drill bit and than use the cone stone to make the whole as large as you need. It makes a smooth, easy whole.
 
Harbor Freight has a cheap hole saw
set with up to 3 or 4 inches that will do an ok job on
Wood and thin plastic.
 
I would also suggest using a hole saw but use a drill motor that runs at low speed (~500 RPM or less). A 3/8" to 1/2" drill with a speed control switch would give you a good cutting speed that would not melt the plastic as you cut the hole.
 
I agree with the hole saw and the input given but I would run the hole saw in reverse as some times the teeth will grab and crack the plastic. Regards, Brian
 
I think Lawson needs a large square hole for the Southwind heater. There are small round saw blades that fit into a die grinder that will do the job. Be VERY careful these are dangerous.G.M.
 
G.M. said:
I think Lawson needs a large square hole for the Southwind heater. There are small round saw blades that fit into a die grinder that will do the job. Be VERY careful these are dangerous.G.M.
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Yes George, I will need a fairly large rectangular hole for the Southwind. I spent most of the night last night laying awake and running this thing through my head. I figured there must be a tool such as you describe. Or someone suggested a cone shaped stone bit, running on the slow side. Several good suggestions fellows. Hardest part is going to be getting the job done while the firewall cover is installed in the truck. I planned ahead and cut a hole in the insulation behind the cover before I put it in. Hopefully the hole is pretty close to where it should be. LOL
 
I have one of the Sonic Crafter tools and it makes very good plunge cuts in wood ,Sheetrock and most any other materials. I believe it would work well on the plastic insulator also.
 
One thing that can help is to spray the surface and cutting arera with WD-40 as you go. It helps to keep whatever blade you decide to use clean and cool so plastic doesn't build up on the cutter(this also works great when grinding aluminum).
 
Use a drill bit for each of the corners and a fine toothed blade in a mini hacksaw or keyhole saw, finish and square it up with a file.
 
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What about a box cutter drill 4 holes in the corners, Then a light cut with the box cutter ,each following cut it will follow the groove ,
 
Unlike many other rocket science projects, you have the advantage of being able to do some test cuts well inside the desired finish cut line.

I'll add another possible method to your list to think about: You might try a sheet metal nibbler. Full control and a clean cut edge. As with the other methods, be sure to remove the insulation from the backside first.
 
As stated maybe a mini hacksaw:D
 

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Johnson wax come in an 1 1/2" diameter cardboard tube that the blade is run in for lubrication of the saw blade when sawing aluminum. G.M.
 
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