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fabrication advice needed

Posted: Mon Sep 21, 2009 3:51 am
by BrokenAeroVT
I would like to make a somewhat precise, circular hole about 1 to 1-1/4 inch in diameter through a cottle bottom. Not being an expert in fabrication and only possessing a drill, could someone recommend a specific type of bit and/or procedure to do this? I don't want to do any jig cutting and filing, other than to eliminate spurs.

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 8:41 am
by seudo_411
BrokenAeroVT wrote:I would like to make a somewhat precise, circular hole about 1 to 1-1/4 inch in diameter through a cottle bottom. Not being an expert in fabrication and only possessing a drill, could someone recommend a specific type of bit and/or procedure to do this? I don't want to do any jig cutting and filing, other than to eliminate spurs.
I would suggest buying the appropriate size hole saw, they're usually used to install down lighters, but they're available in various sizes, the other option is to buy (or construct) a compass cutter, which allows you to adjust the size of the hole made, these are semi precise methods, you would still have to finish off the cuts with some sand paper.

hope this helps,

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 2:39 pm
by BrokenAeroVT
seudo_411 wrote:
BrokenAeroVT wrote:I would like to make a somewhat precise, circular hole about 1 to 1-1/4 inch in diameter through a cottle bottom. Not being an expert in fabrication and only possessing a drill, could someone recommend a specific type of bit and/or procedure to do this? I don't want to do any jig cutting and filing, other than to eliminate spurs.
I would suggest buying the appropriate size hole saw, they're usually used to install down lighters, but they're available in various sizes, the other option is to buy (or construct) a compass cutter, which allows you to adjust the size of the hole made, these are semi precise methods, you would still have to finish off the cuts with some sand paper.

hope this helps,
Is there no such thing as a drill bit, sort of like a wood bore, that can handle soft aluminum?

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 3:13 pm
by Vibe
BrokenAeroVT wrote: Is there no such thing as a drill bit, sort of like a wood bore, that can handle soft aluminum?
It's not so much the bit handling the aluminum as it is the aluminum handling the bit. A bit that size, cutting at that radius, will twist a thin piece of soft aluminum into a pretzle as soon as it gets a good bite. The aluminum isn't really going to hurt the bit at all. A hole saw that distributes the cuts among many teeth will not develop a very large single cut on any one tooth - so the distortion of the aluminum piece will be kept to a minimum. Otherwise you can cut it by hand with a divider style cutter where you are more in control of how much force is applied and in what direction and are less likely to simply tear a random hunk out.

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 3:14 pm
by hoz
A Forstner bit might work, for a few holes...

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 3:20 pm
by Ridgerunner
What about using a Stepbit as the bottom of aluminum bottles is thicker material than the sides and less likely to distort. I have used a one inch stepbit with sucess and used the dremel tool to enlarge the hole further.

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 3:25 pm
by Vibe
An electrical connection "Knock out" set would probably work better. Harbor Freight has a set that would handle AL pretty well - there may well be a punch/die set in there that will do what you want. It's wrench/screw driven or there are hydraulic power units that will operate it. Manual is of course the less expensive route.

http://www.harborfreightusa.com/usa/ite ... emid=91201
Image

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 3:27 pm
by Ridgerunner
Here is a link to Skids ION stove process using a step bit.

http://www.whiteblaze.net/forum/vbg/sho ... toffdate=1

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 5:49 pm
by BrokenAeroVT
Vibe wrote:
BrokenAeroVT wrote: Is there no such thing as a drill bit, sort of like a wood bore, that can handle soft aluminum?
It's not so much the bit handling the aluminum as it is the aluminum handling the bit. A bit that size, cutting at that radius, will twist a thin piece of soft aluminum into a pretzle as soon as it gets a good bite. The aluminum isn't really going to hurt the bit at all. A hole saw that distributes the cuts among many teeth will not develop a very large single cut on any one tooth - so the distortion of the aluminum piece will be kept to a minimum. Otherwise you can cut it by hand with a divider style cutter where you are more in control of how much force is applied and in what direction and are less likely to simply tear a random hunk out.
Oh, I wasn't refering to a hole saw-- a cup with teeth and a center drill bit, but rather an auger type bit? I've used those to bore out holes in door frames for strike plates. I was hoping there was something similar to that for thick aluminum cottles, a flat wide bit with two teeth on the end and a center guide to keep the circle steady. I would drill a guide hole then twist the bit against the bottom of the cottle until a disc falls out.

Re: fabrication advice needed

Posted: Mon Sep 21, 2009 5:54 pm
by BrokenAeroVT
Ridgerunner wrote:Here is a link to Skids ION stove process using a step bit.

http://www.whiteblaze.net/forum/vbg/sho ... toffdate=1
The step bit only goes up to 1 inch diameter?