Cutting holes in the firewall

My 37 Chevy p/u is going to get a heater so I will have to cut holes in the firewall,is there any way I can cut the holes without damaging the paint on both sides.

 

Small starter hole and a step drill. Then maybe a hole punch used for electrical work. Greenly punch.

 

They also make HUGE step drills. Maybe ask any machinist friends?

 

What size holes?

 

Vintage Air sells these. I'm sure they come in other configurations. Look at these and I'm sure with just a little imagination, you could come up with something similar. probably cheaper, too. Let the plate hide any damaged paint.

When drilling holes, in a painted surface, cover the area with masking tape. Draw your holes. Cut them out and remove the tape. That's an easy way that's been done for years.

 

A sharp step drill will do the best job. A KO punch will leave an edge, and if the spot you're making the hole isn't dead flat, the punch will flatten it, probably loosening the paint.

 

A KO punch is designed to cut thicker-gage metal; generally 16-12 gage. If you have a nice new one, it will cut thinner stuff cleanly, but one that's seen some use won't do as well.

I've used these a few times myself... Still have a hand set up to 2" conduit size....

 

5/8 or slightly larger.

 

A Rotobroach would also get the job done in a very clean matter. Any good fastener place would carry a kit (which aren't cheap) but after using them you won't know how you lived without them.

 

A good, sharp Greenlee Knockout has saved my *** a few times on painted surfaces where a hole needed to be made afterwards. May be redundant but I still put tape around the area I was cutting before drilling or punching the hole.

 

Thanks for the info and this is what is going in.

 

Maybe I have just been lucky but I have had good luck with a step drill with high quality masking tape on each side.

 

I am more concerned about damaging the paint on the engine side,if something happens on the inside its no big deal as I can hide it with a firewall pad.

 

Masking tape both sides a good 1/8" pilot hole and a sharp aerial hole cutter or hole saw. They did make another male / female cutter that tightened up with a centre bolt through larger pilot hole. Clean precise cut with no burns to edges.

 

I'd rather clean up the minor sharp edge from a KO punch hole than the huge burrs of a step drill! Plus there's no heat around the hole when using a KO punch set, vs. how hot the metal/paint gets with even a sharp step drill.
My KO punch set starts with a 1/2" conduit punch that takes a 3/8" hole, and once the 7/8" punch is done, the larger sizes all go through that hole. My set is probably 75 yrs. old since it was used by my dad before me, and still doesn't pull metal when punching holes.

 

Cut as clean a hole as you can then pop in a rubber grommet, it will be neat and should cover any paint chip.

 

Can you cut the inlet/outlet tubes, add elbows and re route the hoses through the floorboards?

 

5/8 or slightly larger? Step bit. The KO punches need a hole about that size as is just to bolt the punch in.

 

Yeah, the smallest 'standard' size KO punch will be 7/8". Greenlee does make other sizes as 'specials', but the prices will make you choke....

 

tape it up good, punch the center and hole saw would be my method. then touch up the edge with a bit of paint, if you have the color of the firewall use that, otherwise flat black looks OK. just brush it on the bare area of the cut

 

I used a broach for the very same purpose. So much better than even a new hole saw or a step drill. Quite often there's no room to use a hole punch.

 

I am going to look into that,it looks like someone extended the tubes and no hub on the ends to keep the hose from slipping off so I might have to do something to it.

 

http://www.ebay.com/bhp/greenlee-radio-punch

used ch***is punches are cheep and nice to have when you need them

good luck

 

"I'd rather clean up the minor sharp edge from a KO punch hole than the huge burrs of a step drill"

I don't have any high dollar step drills and none of mine leave burrs.

 

It looks like I can not modify the tubes so I will have to cut two holes for them and drill two 1/4 inch holes to mount the heater,I am going to look into a ch***is punch.

 

Try to get the size hole figured out before you start cutting. If you are using grommets you may be able to use the 7/8" Greenlee KO deal. If you go with a step drill or a hole saw, keep the speed as low as you can to minimize burnt paint.

 

No, Greenlee and others sell a small 7/8" punch that uses a 3/8" bolt, so you can start small and work up from there. I've got one in my kit, and use it often.

 

Even high quality step bits leave small burrs. Not hard to clean up with a file or razor knife, but more work than a clean cut KO punch hole. I can pop a grommet right in a punched hole with no clean up.

 

I would think a hole punch would put a lot of pressure on the surround hole and
would try a Step drill in a variable speed (very slow) drill and keep the heat down.
Make a pattern first and cover the area with masking tape.
HF step drills are cheap and work fine. I have used them for up to 1 inch holes in
1/4 plate - if you go slow and use a lubricant. A small round file will suffice for cleanup.

Try whatever solution you choose first on some painted s**** metal.

 

I have the Blair spot weld cutter kit...or rotabroach.
It works so well that I went looking for their holesaw kit.
Same technology. .kit comes with standard sizes up to 2 inch...if I remember correctly. .
Tha absolute best tools for cutting holes. ..low speed..no burning paint..
As posted earlier. .mask thoroughly and presto..
Clean..precise hole..
Dave

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