Here's a quick primer and recommendations on drilling metals, the majority of the folks reading this are interested in the stainless steels of course : )
The following chart is a rough RPM recommendation for HSS (high speed steel) bits on the listed metals with the bit size along the top. If you have carbide/Ti/cobalt bits you can go faster, if you have carbon steel bits you'll have to cut your numbers in half. These are conservative numbers I've listed, start drilling with these speeds and you can go faster if conditions warrant.
The first column is a value called SFM, or surface feet per minute. This is a value commonly used in the machining world for the max tool speed per material, it is defined as the amount of linear feet the outside edge of the cutting tool travels in one minute. You can use that value to calculate RPM, here is the common approximation:
RPM = SFM x 4 / Diameter
Before we can start drilling we need to make a indentation in the metal to prevent the drill bit from wandering. A center punch is used and given a good whack at the drill spot to create a small dimple. Under some conditions punching may cause some local hardening but this should be minimal and IMHO worth the risk to prevent wandering.
The last step before drilling is lubrication. Drilling metals can produce high temperatures quickly which can damage your bits. Lubrication/drill fluid reduces friction, acts as a coolant to remove heat, and helps clear the cuttings. Ideally you should use a cutting fluid like TAP-Magic but many people use motor oil. WD40 is used by some but it is flammable. In a pinch vegetable oil can be used, just don't use water. To use: add a few drops before drilling, then periodically check and re-apply in similar quantities.
You're all set to go. But you will need to put significant pressure on the drill. If you don't the drill bit will just sit there, not biting into the base material, get hot with the friction, and ruin itself. And remember to keep to, or at least start with the speeds in the chart above.
Drilling large holes (7/8" in keggles for instance)
A very common and cost effective way to drill large holes in sheet metal is by using a step bit. First a smaller hole is made, then expanded to the desired size with the step bit. The step bit is pyramid like with multiple sizes and is used to gradually expand the hole with each step.
Trouble shooting
1) Drill produces a very high pitch squeal = Drill is running too fast
2) Drill Bit becomes very hot = Drill is running too fast
3) Drill bit dulls very quickly = Lubrication is required
4) Drill bit becomes very hot = Lubrication is required
5) Drill bit Wobbles = Damaged Drill bit, or ensure the Bit is correctly positioned in the chuck
6) Drill Bit skates across the metal surface = Centre punch is too small, or smaller pilot hole is needed
7) Drill Bit grabs as it breaks through = Too much Pressure, or drill is running too fast
A couple of last tips and notes:
1) Running a tool too slow will only decrease productivity. On the other hand, running a tool too fast (with regard to speed or feedrate) will either result in accelerated tool wear or outright failure. So always err on the side of running too slow.
2) High heat causes tools to lose their temper (heat treatment) resulting in a soft cutting edge. The soft edge quickly wears away and the tool becomes dull.
3) The deeper the hole, the greater the tendency is for chips to pack and clog the flutes of the drill. This increases the amount of heat generated and prevents the coolant from conducting heat away from the point. Excessive buildup of heat at the point will result in premature failure.
4) A countersink, large diameter bit, or step drill can be (carefully) used to remove burrs from drilled holes.
5) The harder the material, the slower the cutting/drilling speed.
6) Titanium bits are coated. Once the coating wears off they're done for. They cannot be re-sharpened as the grinding process will remove any remaining titanium.
7) Cobalt bits are a cobalt-steel alloy and can be sharpened. A few cobalt coated bit are on the market, these cannot be re-sharpened.
Good luck and please post any questions/corrections. There are a lot of knowledgeable folks in these forums who are here to help.
The following chart is a rough RPM recommendation for HSS (high speed steel) bits on the listed metals with the bit size along the top. If you have carbide/Ti/cobalt bits you can go faster, if you have carbon steel bits you'll have to cut your numbers in half. These are conservative numbers I've listed, start drilling with these speeds and you can go faster if conditions warrant.
The first column is a value called SFM, or surface feet per minute. This is a value commonly used in the machining world for the max tool speed per material, it is defined as the amount of linear feet the outside edge of the cutting tool travels in one minute. You can use that value to calculate RPM, here is the common approximation:
RPM = SFM x 4 / Diameter
Before we can start drilling we need to make a indentation in the metal to prevent the drill bit from wandering. A center punch is used and given a good whack at the drill spot to create a small dimple. Under some conditions punching may cause some local hardening but this should be minimal and IMHO worth the risk to prevent wandering.
The last step before drilling is lubrication. Drilling metals can produce high temperatures quickly which can damage your bits. Lubrication/drill fluid reduces friction, acts as a coolant to remove heat, and helps clear the cuttings. Ideally you should use a cutting fluid like TAP-Magic but many people use motor oil. WD40 is used by some but it is flammable. In a pinch vegetable oil can be used, just don't use water. To use: add a few drops before drilling, then periodically check and re-apply in similar quantities.
You're all set to go. But you will need to put significant pressure on the drill. If you don't the drill bit will just sit there, not biting into the base material, get hot with the friction, and ruin itself. And remember to keep to, or at least start with the speeds in the chart above.
Drilling large holes (7/8" in keggles for instance)
A very common and cost effective way to drill large holes in sheet metal is by using a step bit. First a smaller hole is made, then expanded to the desired size with the step bit. The step bit is pyramid like with multiple sizes and is used to gradually expand the hole with each step.
Trouble shooting
1) Drill produces a very high pitch squeal = Drill is running too fast
2) Drill Bit becomes very hot = Drill is running too fast
3) Drill bit dulls very quickly = Lubrication is required
4) Drill bit becomes very hot = Lubrication is required
5) Drill bit Wobbles = Damaged Drill bit, or ensure the Bit is correctly positioned in the chuck
6) Drill Bit skates across the metal surface = Centre punch is too small, or smaller pilot hole is needed
7) Drill Bit grabs as it breaks through = Too much Pressure, or drill is running too fast
A couple of last tips and notes:
1) Running a tool too slow will only decrease productivity. On the other hand, running a tool too fast (with regard to speed or feedrate) will either result in accelerated tool wear or outright failure. So always err on the side of running too slow.
2) High heat causes tools to lose their temper (heat treatment) resulting in a soft cutting edge. The soft edge quickly wears away and the tool becomes dull.
3) The deeper the hole, the greater the tendency is for chips to pack and clog the flutes of the drill. This increases the amount of heat generated and prevents the coolant from conducting heat away from the point. Excessive buildup of heat at the point will result in premature failure.
4) A countersink, large diameter bit, or step drill can be (carefully) used to remove burrs from drilled holes.
5) The harder the material, the slower the cutting/drilling speed.
6) Titanium bits are coated. Once the coating wears off they're done for. They cannot be re-sharpened as the grinding process will remove any remaining titanium.
7) Cobalt bits are a cobalt-steel alloy and can be sharpened. A few cobalt coated bit are on the market, these cannot be re-sharpened.
Good luck and please post any questions/corrections. There are a lot of knowledgeable folks in these forums who are here to help.
