Cutting holes in sheet metal

[seamlyne]

Two issues:

Issue 1: I really like the bit I put in my Dremel to cut holes in drywall: is there a similar tool for sheet metal, specifically the gauge used for home ductwork?

Issue 2: the ductwork has no place to put a filter. To change filters out, I have to remove the cover on the furnace and reach into a dark, dirty place. Naturally, it's such a p.i.t.a. that it doesn't get done as often as it should. In an effort to economize, I want to try my hand at creating a filter frame. I've found an idea location for it, just a foot away from the present location in the air return, accessible from three sides. Any references online?

Thanks!

- Wm in Kansas City

Measure with a micrometer
Mark with a crayon
Cut with an axe.

[LazyPup]

The simplest method of cutting the light guage sheet metal ducting is by means of a pair of aviation tin snips.

In the sheet metal trade aviation snips are referred to by the color of the handles:

RED- Straight & Left hand cuts
Green- Straight & Right hand cuts
Yellow- Universal- straight, right & left hand cuts.

While one might think the yellow universal type would be the most commonly used tool in practice most right handed sheet metal workers work almost exclusively with the REDS, occassionaly use the Greens and in most instances the Yellows tend to take up space in the tool box.

Step one is to layout your cut on the sheet metal. Typcially the layout is done with a machinist scribe or a fine point felt tip pen.

Once you have the complete cut laid out hold the point of a medium sized flat tip screwdriver against the metal in a waste area that will be cut out this the shaft of the screwdriver at about a 45deg angle to the surface of the sheet metal. Hit the shaft of the screwdriver with a hammer and it will tear a start hole in the sheet metal. You then insert the tip of the aircraft shears in the tear hole and begin hand cutting toward the right side of the desired opening. When you reach the right hand line turn a begin cutting up toward the top, across the top from right to left, down the left side, across the bottom and back up the right side until you finish the cut. As you can see you will be cutting in a counterclockwise direction around the perimeter of your desired opening. If you are right handed this keeps your line of cut within an easy line of sight and the REDS can make the sharp 90deg turns at the corners. Using the Greens would place the tool between you and the marked cut line which can make cutting awkward. (If you are left handed, use the greens and work in the opposite direction.)

In the trade we have a tool which is properly called a "HAND VISE" or "HAND SEAMER" but is commonly referred to as "Turning Tongs" It appears like a pair of pliers with wide flat jaws about 3" wide.

The desired opening would be cut about 1/4" inside of the desired line on all sides, then we use the turning tongs to roll the 1/4" excess inward and flatten it down to make a smooth edge around the cut, otherwise you opening will have very sharp edges.

[seamlyne]

Thanks! I didn't know about left- and right- oriented snips. Mine are (no surprises) yellow. I'll see about a set of greens (I'm left handed.)

Now, once the hole is cut, I'll need a holder for the filter. I'm thinking some angle-iron, the stuff with holes in it they sell at the local DIY store, bolted in around all four sides like so:



Assuming that the duct actually has four sides and the one I removed for the picture is the one with the hole for the filter in it.

Is there a better way? Any pitfalls, hints?

Measure with a micrometer
Mark with a crayon
Cut with an axe.

[Hube]

You have been given excellent advice from Lazy pup on how to go about cutting the hole etc.
But you may be creating an air restriction if you intend to cut in a filter into a main return duct or a return "drop leg". The size of duct INTO the unit is calculated on the cfm, and static presure, etc.
the unit entry inlet (blower compartment) is normally a lot larger in area than this entry duct.This entry will accomodate an oversized filter.
if you install this filter into the duct you can create an "air starved " situation.
if you are intent on doing it this way you should enlarge the duct somewhat to suit the filter size so it has the entire'free area of the filter.Your filter should be approx a minimum 20 % LARGER than your duct.

[seamlyne]

Well, like everything else in the house - and this has been an ongoing saga for years - it seems to defy all the excellent advice I've ever been offered.

quote:Originally posted by Hube
the unit entry inlet (blower compartment) is normally a lot larger in area than this entry duct.This entry will accomodate an oversized filter.

I don't believe that's the case. I'll need to measure, but I believe they're the same.

quote:Originally posted by Hube
if you install this filter into the duct you can create an "air starved " situation.
if you are intent on doing it this way you should enlarge the duct somewhat to suit the filter size so it has the entire free area of the filter.Your filter should be approx a minimum 20 % LARGER than your duct.

"Air starved." Can you say more about that?

The current spot for the filter accepts a 14" x 24" filter, and when I look at it from the duct side, I can see the frame of the filter all the way around. The way it is now, moving the filter to the duct instead of the side of the furnace won't change that situation any.

To anticipate a question: the furnace is too small for the house to begin with, and looks to have been kludged together from whatever my uncle could get his hands on back in '56. The whole house is that way. The hope is to have enough in the bank to replace the whole furnace/AC unit within the next two years - for now, it's spit and bailing wire.

I really appreciate all of you taking your time to discuss this with me.

Measure with a micrometer
Mark with a crayon
Cut with an axe.

[Hube]

ok, if you install this 14x24 filter and it is supported by a 1" angle on 2 sides means that you now only have a filter face area of 12x22.that is approx a 25% reduction in " free area" ,not to mention the great increase in esp (external static pressure)
The filter would be best where it was originally designed for, at the entry to the fan compartment.
If you re-install it in the trunk you will cause restriction because that air now is reduced somewhat and still has to make a full 90 degree turn before entering the fan compartment, thus less actual return air .
As you say, your furnace is already too small, but installing this filter as you want to do will only in a sense make it even become smaller.
But if you are h*ll bent on installing the filter in the trunk line, then you should cut out approx 12" and fab a couple of 14 x 24 to 20 x24 (on center) fittings with the filter(20 x 24) slot in the center of these 2- 6"long fittings.Or ,more practical, a ONE piece flared fitting approx 12" long overall
with the filter slot in the center. Now you will have a 'streamlined', non-restricted fitting for this filter.

[LazyPup]

I would definitely agree with HUBE. Sizing ductwork is a very critical process and even minor changes can cause dramatic end results.

Before you even begin installing a filter pack holder you may want to examine the interior of your air handler. Most air handlers already have a filter rack built in from the factory.

[LazyPup]

I would definitely agree with HUBE. Sizing ductwork is a very critical process and even minor changes can cause dramatic end results.

Before you even begin installing a filter pack holder you may want to examine the interior of your air handler. Most air handlers already have a filter rack built in from the factory.

[seamlyne]

quote:Originally posted by LazyPup

I would definitely agree with HUBE. Sizing ductwork is a very critical process and even minor changes can cause dramatic end results.

Before you even begin installing a filter pack holder you may want to examine the interior of your air handler. Most air handlers already have a filter rack built in from the factory.

So it does, though I have yet to find a filter that fits without some sort of help - my father's method was a scrap piece of wood wedged in to keep the bottom from flying out. It seems there is a top edge but no bottom edge. Welcome to my world.



Measure with a micrometer
Mark with a crayon
Cut with an axe.

[HayZee518]

I used to manufacture sheet metal parts when I worked at the power company. They had me making all types of transition fittings - 36" X 36" square to 24" round, turning elbows with turning vanes inside, custom made dampered shutter etc. If you have access to a press brake construction of a filter holder goes easy. If not then a hand seamer is a necessity or some means to bend long pieces into a ninety.

[Hube]

Yes, Hayzee, fabbing a return frame or transition fitting for this problem would be an easy piece of cake,(a 1 on a scale of 100)
I too was in metal fab almost 50 years, all types from 28 ga. down to 1/4" plate. Triangulation,and pattern layout,and Hvac were my specialties.
However, I would suggest that the seamlyne (op) should get the help of the the local tin knocker's fab shop.
No offense meant to the original poster)

[seamlyne]

quote:Originally posted by Hube

Yes, Hayzee, fabbing a return frame or transition fitting for this problem would be an easy piece of cake,(a 1 on a scale of 100)
I too was in metal fab almost 50 years, all types from 28 ga. down to 1/4" plate. Triangulation,and pattern layout,and Hvac were my specialties.
However, I would suggest that the seamlyne (op) should get the help of the the local tin knocker's fab shop.
No offense meant to the original poster)

None taken! With the information I have now, I would have to agree with your assessment anyway. I could probably manage making the return frame if I knew what I was aiming at, but time and learning curve are important points to consider: I have little of the former and wayyy to much of the latter. Considering that this was meant to be a convenience for me, there are other issues that came up over the weekend that will have to take precendence.

But those are for another category in this forum. Thanks again for all your time!

Measure with a micrometer
Mark with a crayon
Cut with an axe.