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I have a question about the cg bi-metal hole saws. I am using a drill press to cut an 1 1/4" hole into 3/16" mild steel. What is the recommended speed for using the hole saw on this thickness metal?
Hi Mud Bug. I Work in stainless, and do a lot of cutting with hole saws. The same tips will apply to mild steel, it's just easier & faster. Metal thickness is in principle irrelevant. It just takes you more time to get through, 4mm takes 2x as long as 2mm.
It's much better to use a big drill press that can go real slow. Feel your way with the pressure. Up to a point, the more pressure the better you cut. past this point, you cut slower. Look at the swarf! If you're getting nice long curly swarf, (in stainless! In mild, it may vary according to the composition of the steel), Then you're doing right. As written further up, use lots of oil or cutting paste, stop often, & oil.
Make sure the work piece is clamped really well, Look at the cutting all the time, make sure you're cutting & not "wearing" through.
Ive seen hole saws ruined after cutting just one hole, IN WOOD! You can cut several hundrede holes with the same saw, even in stainless. Heat is the enemy.
What is the slowest speed your drill press will run at? Drilling mild steel with a 1-1/4" hole saw the correct speed is about 250 RPM and you'll want to use a good cutting oil or tool coolant. Are you using a good bi-metal hole saw? In addition be ready for some serious torque. Be sure everything is clamped down to the drill press table if you can do so. If not put a pad (rag may work) on the piece being drilled and use the column to brace against.
Try to get some cutting oil rather than engine oil. Even just water is better than nothing for cooling, but you'll have to dry it up fast. Don't flood anything, just a little fine mist does well for water or a water based coolant. If you have a Home Depot or Lowes near you, look for Cutting Oil like used for pipe threading. It's in the plumbing department near plumbing tools if they have it. In a worst case, just use some non-detergent automotive oil. It's better than nothing and get ready for some smoke.
One last thing: Please have a small ABC dry chemical fire extinguisher handy just in case you catch the oil on fire.
Run your drill press nice and slow. Use good pressure to keep the hole saw cutting but don't force it.
Hint: Place a thin sheet of plywood or hardboard on the drill press table so you don't cut into it with the hole saw when it passes though the steel.
Thanks again...I've been using motor oil...but I think I'll try some cutting oil. I just bought my drill press from Harbor Freight. It's pretty nice for the money. Probably not for a production environment, but pretty good for a home shop. I'm building alot of "stuff" for my Jeep, bumpers, skid plates, tire carrier, roll cage...stuff like that. This particular hole is for the spindle to slide into for the swing out tire carrier in my bumper. I'm drilling a test hole first in a piece of scrap. It's my form of stress relief!