looking to do a mailbox mod

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rickc1970

Fire Starter
Original poster
Apr 1, 2017
46
12
O have a question. I looking to do a mailbox mod. What is the best way to cut a perfect circle in the mailbox? 
 
Try drilling a pilot hole where you want the center of the hole to be. Use a ruler and measure out lines from the pilot hole in all directions that are exactly the same length as the radius of your exhaust pipe (that way your not trying to trace out your exhaust pipe on a round surface, which wont work too well). Then connect all the lines to form a circle; cut out the circle with a dremel cutter or aviation snips.
 
Then snip, about 3/4", the smooth end of the elbow to make even numbered tabs...  bend 1/2 of the tabs outward .....  leave the other 1/2 straight....   insert the pipe end into the hole you cut out...  insert up to the bent tabs...    reach into the MB and bend the straight tabs outward to make a good mechanical connection..  no air leaks...   no sealant needed...    Then I recommend 3/4" to 1" holes drilled in the MB door as shown....


 
Using a soft pencil I traced the outside of the duct I was going to insert. To make the cut I used a saber saw fitted with a very fine tooth blade. I put the sheet metal over a piece of wood that had a small hole in it and then rotated the work while holding the saber saw steady. I proceeded very slowly (it took 3-4 minutes to cut my 3" circle). In essence, I created an upside-down jigsaw. The result was very satisfactory.


One other "trick" was that when it came time to create the "in and out" tabs that hold the duct in place, I took a 3" expandable collar that you use to connect two pieces of duct, and fitted it temporarily over the end of the duct, at a distance from the end that was equal to the length of the tabs I wanted to create. I then cut the tabs with my tin snips. The purpose of the collar is to make it almost impossible to make any cut longer than another, since the collar is much thicker material than the duct. The tin snips cannot easily cut through the collar.  I got near-perfect tabs as a result.
 
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Here's how I've marked a lot of circles:

Take a piece of string, a pencil, and a nail.

Drill a hole in the center of where you want the hole.

Tie one end of the string to the Nail & the other end of the string to the pencil, near the point.

Now measure the distance of the radius from the nail hole & mark it.

Drop the nail in the hole, and roll the string up on the pencil until the point is on that radius mark you made.

Keeping the string tight, draw your circle, checking to make sure you end up on the radius mark you started with.

Naturally you have to keep the same side of the pencil pointed toward the nail at all times.

Bear
 
 
Here's how I've marked a lot of circles:

Take a piece of string, a pencil, and a nail.

Drill a hole in the center of where you want the hole.

Tie one end of the string to the Nail & the other end of the string to the pencil, near the point.

Now measure the distance of the radius from the nail hole & mark it.

Drop the nail in the hole, and roll the string up on the pencil until the point is on that radius mark you made.

Keeping the string tight, draw your circle, checking to make sure you end up on the radius mark you started with.

Naturally you have to keep the same side of the pencil pointed toward the nail at all times.

Bear
 
Here's how I've marked a lot of circles:

Take a piece of string, a pencil, and a nail.

Drill a hole in the center of where you want the hole.

Tie one end of the string to the Nail & the other end of the string to the pencil, near the point.

Now measure the distance of the radius from the nail hole & mark it.

Drop the nail in the hole, and roll the string up on the pencil until the point is on that radius mark you made.

Keeping the string tight, draw your circle, checking to make sure you end up on the radius mark you started with.

Naturally you have to keep the same side of the pencil pointed toward the nail at all times.

Bear
... and you have to make sure that the string doesn't wrap around the nail as you go around or you end up with a spiral instead of a circle!
 
 
... and you have to make sure that the string doesn't wrap around the nail as you go around or you end up with a spiral instead of a circle!
Didn't think I'd have to mention that.

You have to keep both feet on the ground (or Floor) too, or you might fall down.
biggrin.gif


Bear
 
The one I used most often when I had my Cabinet Shop was the Stick & two nails.

I used it one time when I bought a Woodstove & had it installed at our earlier house.

Two guys showed up without their Boss, and didn't know how to mark a circle to cut a hole through my Aluminum sided wall.

They needed, I think, a 10" diameter hole for the Thimble, to go through the wall (Plywood & siding).

So I took a paint stirring stick, put a nail through it at 1", and a nail in it at 6".

Then drilled a small hole at the center of where they wanted the hole.

Then I put the nail at the 1" spot in the center hole, and spun the stick around a few times, making a circular scratch with the nail at the 6" spot.

It was funny later, as they were leaving they asked if they could have that circle drawing thing.

LOL---Sure, you need it more than I do.

Bear
 
Thanks for the tips...I have to find my dremel at the old house and buy some cut off wheels for it. I saw a cheap metal mailbox at walmart I could get for about 10 bucks.
 
Cutoff wheels for the Dremel are absolutely amazing: I have cut off hardened steel that were part of a locking mechanism on a coin box at an arcade where I was helping the owner. I use them a lot.

However ...

I'm not sure it you are going to get a very smooth circle with that tool. I think someone else suggested it, so go ahead and try it, but I'd suggest seeing if you can find a piece of scrap that you can practice on. I already told you the tool I used to cut my 3" circle.

BTW, the cutoff wheels are brittle and will break if you apply even the slightest crosswise pressure (another reason I'm not sure how well it will work cutting a circle). Therefore, be prepared to go through quite a few, even in a simple job. Also, eye protection is mandatory, and face protection (a face shield) is a darned good idea. I'm pretty cavalier about safety warnings of all types, but when the disc suddenly snaps, the pieces fly off at a high rate of speed. They won't embed themselves in your flesh or anything like that, but you can get some pretty good scratches.
 
 
Cutoff wheels for the Dremel are absolutely amazing: I have cut off hardened steel that were part of a locking mechanism on a coin box at an arcade where I was helping the owner. I use them a lot.

However ...

I'm not sure it you are going to get a very smooth circle with that tool. I think someone else suggested it, so go ahead and try it, but I'd suggest seeing if you can find a piece of scrap that you can practice on. I already told you the tool I used to cut my 3" circle.

BTW, the cutoff wheels are brittle and will break if you apply even the slightest crosswise pressure (another reason I'm not sure how well it will work cutting a circle). Therefore, be prepared to go through quite a few, even in a simple job. Also, eye protection is mandatory, and face protection (a face shield) is a darned good idea. I'm pretty cavalier about safety warnings of all types, but when the disc suddenly snaps, the pieces fly off at a high rate of speed. They won't embed themselves in your flesh or anything like that, but you can get some pretty good scratches.
I agree about the Dremel cutoff wheels.

I would use my Bosch Saber Saw, but I guess not everybody has one.

That safety Shield & Goggles is a good idea!!!

Bear
 
ok...I went to Home Depot to get what i needed for the project. The only three inch duct pipe they had was the foil plastic type dryer vent. So I got the flex 4" metal duct tube with a 4" starter collar to go into the mail box..I'll attach a 4' elbow to that and then the flex pipe to the elbow. I bought a 4" to 3" reducer and a 3"elbow to go into the smoker. I know someone with a jigsaw I can borrow to cut the hole in the mailbox. I also bought some clamps for the duct work. I went to harbor freight and bought a cheap 10 dollar rotary tool like the dremel I can't find but it just scratched the mailbox. My wife's aunt has a jigsaw I can use so when I get that i will get started. I was thinking of putting the hole in the back of the mailbox towards the top. Any thoughts on that? I didn't want to do it on the curved top as it seems like it would be hard to get a good connection with the duct. 
 
ok got it done...haven't drilled the holes yet....I want to try it out first and drill only what I need. As you can see from the pics there are quite a few holes in it to begin with. I also didn't put the door handle on as it is plastic and I'm sure it wouldn't be a good idea. I can make something with wire i imagine. The elbow that goes in the smoker only goes in a little bit as there is a lip that keeps the chip feeder from going in too far. I don't want to permanently fix the duct work to the smoker. I also cut the hole in the mailbox too close to the top and couldn't bend those top tabs for the starter collar but I sealed the back with foil tape.I also might cut the flex duct as it seems a bit long.

 
ok got it done...haven't drilled the holes yet....I want to try it out first and drill only what I need. As you can see from the pics there are quite a few holes in it to begin with. I also didn't put the door handle on as it is plastic and I'm sure it wouldn't be a good idea. I can make something with wire i imagine. The elbow that goes in the smoker only goes in a little bit as there is a lip that keeps the chip feeder from going in too far. I don't want to permanently fix the duct work to the smoker. I also cut the hole in the mailbox too close to the top and couldn't bend those top tabs for the starter collar but I sealed the back with foil tape.I also might cut the flex duct as it seems a bit long.



Try it first without doing anything other than plugging all bottom holes except the second row (two holes) from the door. You can pull the amnps towards the door while it burns so the air source goes diagonally all around under the amnps. I turn the amnps around after 5 hours with more than one row of pellets are used so it always burns with the draft. I put the plastic piece to conver the side flag holes without the flag. Plenty of air comes in the bottom of the door at the hinge. Put the Amnps lit edge at the two holes with tbe amnps elevated. Mines on a rack. This pic show all holes plugged except the two I mentioned.

-Kurt
 
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