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dvo
04-16-2010, 12:09 AM
Is there an adjustable tool for the mill to cut large(4+") circles in sheet metal similar to the adjustable one used on drill presses for wood?

dp
04-16-2010, 12:22 AM
See the trepanning tool on this page:

http://www.enuii.org/risley/training_school/tool_time.htm

TriHonu
04-16-2010, 01:08 AM
I have a couple of Snappy Hole Cutters (http://www.standexadp.com/pdf/mh.pdf). They don't need a mill, just a portable drill.

I've seen inexpensive copies of this design at the local home center along with replacement bits.

Mike Burdick
04-16-2010, 02:00 AM
See the trepanning tool on this page:

http://www.enuii.org/risley/training_school/tool_time.htm

Beware... that tool will grab the tin and make a nice hole in you! :eek:

dp
04-16-2010, 02:05 AM
I was just about to complain that the Snappy tool would not leave appendages on the floor nor put out your eye nor even leave you wishing for a tourniquet and opposing thumbs to apply it.

Where's the fun? :)

darryl
04-16-2010, 05:32 AM
Don't know if there's a too like this, but it comes to mind that you could shear a hole with the right circular cutter mounted on an arm in the mill, and an appropriate female die mounted to the table. The spindle would turn, and you'd slowly lower the spindle as the cutting disc is forcing a disc out of the sheet material.

Your Old Dog
04-16-2010, 09:57 AM
See the trepanning tool on this page:

http://www.enuii.org/risley/training_school/tool_time.htm

He ask the question "Question, has anyone out there ever used on of these at home in a hand drill? "

I can answer that for him. Not more then once! :D

Spin Doctor
04-16-2010, 10:05 AM
Sounds like a job for a nibbler

metalmagpie
04-16-2010, 10:08 AM
My local import tool store (called "Tool Town" in the Seattle area, several locations) carries a reasonable selection of the cheap hardware line sold under the name "General". General makes a much better spring-loaded center punch than do Starrett, by the way .. I own both and only use the Starrett when I can't find the General. General makes two sizes of these "hole cutters" and I own one. I used it with a hand drill to cut a hole in thick plastic, and it worked great.

It is easy to cut holes in sheet metal with a plasma cutter with circle attachment, and to work off of a center punch mark. The edge will be a little rough, though.

metalmagpie

Rustybolt
04-16-2010, 10:19 AM
When cutting holes with a hole saw in sheet metal, I like to backup the sheetmetal with a piece of wood. trepanning isn't reccomended for thin material.

paulsv
04-16-2010, 11:09 AM
I'm speaking from memory here, but I believe that in the book "Machine Shop Trade Secrets" Author James Harvey suggests using a fly cutter.

JoeCB
04-16-2010, 12:05 PM
Fly cutters on sheet metal !!! "fly" would be the operative word.
I have used the lathe. Sandwich the sheet metal between wood or masonite and clamp with the live center using a steel disc pad. Cut with a properly relieved tool bit. To help hold the stock if it wants to slip, use a strip of the thin double backed tape.
Joe B

Black_Moons
04-16-2010, 12:28 PM
An idea:

Negative rake on your trepanning tool for sheet metal, with a backup of wood.

Idea being that negative rake should greatly reduce tendency to get stuck as it breaks through.

While it make seem like you'd need a LOT of force to run a negative rake cutter, my experiance just hand shaving mild steel with a negative rake HSS bit attached to a handle shows that even with light pressure, metal will be shaved off.

Tony Ennis
04-16-2010, 12:44 PM
Depending on the accuracy needed, skillsaw and a piece of plywood.

1. Attach plywood that center of circle.
2. Attach skillsaw on plywood at appropriate distance from center.
3. Steal underwear
4. ???
5. Profit!

dp
04-16-2010, 01:08 PM
When cutting holes with a hole saw in sheet metal, I like to backup the sheetmetal with a piece of wood. trepanning isn't reccomended for thin material.

I wonder if a small cutting wheel, like a glass cutter, would bring some degree of safety to the job. It would do a cut similar to a tubing cutter.

rockrat
04-16-2010, 01:22 PM
I have something like the snappy tool. The only thing that I dont like about it is that the center point looses support within the last 10 of the cut. I will make a support for mine if I need a more accurate circle.

Otherwise a Lenox circle cutter is the way to go.

rock~

RKW
04-16-2010, 02:13 PM
Why do I need to steal someone's underwear as part of this procedure? ;-)


Depending on the accuracy needed, skillsaw and a piece of plywood.

1. Attach plywood that center of circle.
2. Attach skillsaw on plywood at appropriate distance from center.
3. Steal underwear
4. ???
5. Profit!

hojpoj
04-16-2010, 03:04 PM
Why do I need to steal someone's underwear as part of this procedure? ;-)

It's a reference to a television show that I'm sure few here would actually watch.

The Artful Bodger
04-16-2010, 05:03 PM
Please pay more attention to post #3 by TriHonu and get a "snappy hole cutter".

If you think it is dangerous it may be best to just stay in bed all day.

dewat
04-16-2010, 07:04 PM
This is how I cut some aluminum 2.250" flanges using a parting tool, the proper amount of relief is needed.

http://img688.imageshack.us/img688/7774/mill006.jpg (http://img688.imageshack.us/i/mill006.jpg/)