Old timer at work trick for drilling in thin material is to put a shop rag between the bit and the material. This gets rid of the triangular hole that sometimes shows up. Not sure of the mechanics, but it works - maybe damps out chatter. For small holes the clamp between wood works great too.
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Basic sheet metal work
- Thread starter spike7638
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- Dec 27, 2014
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5/8 hole in sheet metal, sandwich the metal between to pieces of scrap wood/plywood. drill in one pass.
I'm going to be really naive here, but I've done that before... 
"Sandwich the metal between two pieces of ply/alu and then drill" is advice I've often heard/used, at least for non-precision things. But if I'm trying to drill nicely spaced holes in a piece, I tend to want to set it up on a milling machine, in a vise. At that point, I no longer have the piece itself to reference my hole placement, and ... I must just be missing something here. How on earth does one really do this in practice, and get the holes where you want them within a small tolerance (like, say, .06 inches, which is close enough for most of what I do)?
"Sandwich the metal between two pieces of ply/alu and then drill" is advice I've often heard/used, at least for non-precision things. But if I'm trying to drill nicely spaced holes in a piece, I tend to want to set it up on a milling machine, in a vise. At that point, I no longer have the piece itself to reference my hole placement, and ... I must just be missing something here. How on earth does one really do this in practice, and get the holes where you want them within a small tolerance (like, say, .06 inches, which is close enough for most of what I do)?
OK -- I'll try the "bit of cloth" trick if it turns out to be necessary.
But going back to the "clamp between pieces of aluminum" thing... when I'm drilling, do I use the light thin lubricant for aluminum (I'll be going through 1/2" of that) or the oily lubricant used for stainless?
Also: I'm hoping to make a disk-shaped part in this thin stainless, with a few holes drilled in the middle of it. About 3.25" diameter. I think I can manage the holes and slots in the middle, but making the piece "disk shaped" in the end is what's worrying me. If I were doing this in wood, I'd use something like a trammel cutter. Is there a similar tool I can use on thin stainless clamped between two sheets of 1/4 aluminum? I'm not using a CNC machine, so just milling it won't work. I could bandsaw it, with the two pieces clamped together, but it'd be tough to get a really nice circle. It doesn't have to be perfect, but my bandsaw skills are...limited, and it seems as if a milling machine is perfectly set up to help me do something circular like this.
But going back to the "clamp between pieces of aluminum" thing... when I'm drilling, do I use the light thin lubricant for aluminum (I'll be going through 1/2" of that) or the oily lubricant used for stainless?
Also: I'm hoping to make a disk-shaped part in this thin stainless, with a few holes drilled in the middle of it. About 3.25" diameter. I think I can manage the holes and slots in the middle, but making the piece "disk shaped" in the end is what's worrying me. If I were doing this in wood, I'd use something like a trammel cutter. Is there a similar tool I can use on thin stainless clamped between two sheets of 1/4 aluminum? I'm not using a CNC machine, so just milling it won't work. I could bandsaw it, with the two pieces clamped together, but it'd be tough to get a really nice circle. It doesn't have to be perfect, but my bandsaw skills are...limited, and it seems as if a milling machine is perfectly set up to help me do something circular like this.
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- Feb 2, 2013
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- 3,963
a trick to drill thin sheet metal is to clamp a sacrificial piece of thicker material on top of the intended boring victim.
then drill like you don't even care, the holes will come out just fine if you incrementally increase the drill bit size as you go.
as far as cutting 1" strips,
you can make a sacrificial fence from just about any substantial and straight piece of angle iron or flat iron bar.
simply clamp the sacrificial fence to the work and space the fence to 1" plus the thickness of the cut off blade.
use an angle grinder or die grinder to cut the strip free
clean up the edge after cutting with a sander or grinder and you are done.
i use this method all the time, as i don't have a sheer
then drill like you don't even care, the holes will come out just fine if you incrementally increase the drill bit size as you go.
as far as cutting 1" strips,
you can make a sacrificial fence from just about any substantial and straight piece of angle iron or flat iron bar.
simply clamp the sacrificial fence to the work and space the fence to 1" plus the thickness of the cut off blade.
use an angle grinder or die grinder to cut the strip free
clean up the edge after cutting with a sander or grinder and you are done.
i use this method all the time, as i don't have a sheer
Visit harbor freight and get s hole saw kit.
Make hole in plywood first (3 inch) next clam plywood over work an position on drill press and remove pilot bit as plywood is guide.
Drill press as slow as it can go and short light pecks.
If a mill with back gear then slow constant heavy pressure
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Circle on a mill, do the sandwich thing and use a hole saw. If you don't want the center pilot hole in the part, choke up on the pilot drill so it engages the sacrificial top, but doesn't hit the part. On a lathe, build the stack on an arbor, could be a bolt, and turn the outside down to size. Trammel cutters on a mill can work with a sharp pointed tool. Go slow, there's a lot swinging around and they look kind of scary. Boring head with a custom ground cutter would work similarly. This is better for hole making than circle making since holding the middle is harder than holding the outside.