Hello folks,
I am the sawyer for the company I work for, and generally run the saws, the bender and an assortment of punches. We've got a different fella who specializes in drilling, but he's gone this week, so I'm temporarily running the drills as well. Normally, I don't have any problem with this, but tonight I had to drill 2.5" x 2.5" x .25" square tubing instead of our standard solid stock, and I had nothing but problems- I'm hoping someone here will be able to give me some insight into the problem, or maybe just a link to a good drilling primer.
The material is held in a shop-built fixture that surrounds the tube on all four sides, and holds the material in place with a bolt on the side. We use infinately variable speed drills with pneumatic feeds, No.2 morse taper shanks, and a good coolant system. The material in question is 1018 mild steel (cold-rolled) and the problem I kept running into was that the drill did not want to finish the hole in the top side of the material- instead of drilling through, two small chips on either side of the hole would ride up the flutes and either twist the bit out of the chuck or jam the bit tightly enough to stop the quill (broke a couple of bits that way). The bits I was using were 17/32" HSS.
I monkeyed around with it a bit, and varied the drill speed between
250 rpm and 325 rpm, and tried feed rates between 1 and 6 inches per minute. It didn't sieze up every time, but the speed at which the drill press would operate properly for me (250 rpm with an approx. 2" per minute feed rate) seemed very slow compared to the speed at which we drill solid stock. The holes in the bottom of the tube went through just fine no matter where I set the speed and feed.Is this just a problem with drilling tubing, or is there something I am doing wrong here? Any thoughts would be appreciated. Like I said above, it's not my normal job, but it comes up from time to time, and I hate to be wasting bits for lack of a few moments of education.
Thanks for your advice!
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