Im building a 2x72 grinder and it uses 1.5" solid steel bar for the arm. I have drilled one of two holes. The second hole just wont drill. At first I thought it was the cheapo Harbor Freight drill bit set (though they have acutally worked great) so I sharpened the couple bits. After sharpening...it still wont drill. Any ideas? Im using cobalt HSS bits. Did a 1/4" pilot, stuck on a 3/8" opening and need to open it up to 1/2".
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Need drilling help
- Thread starter 8mpg
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Are you using a drill press or hand drill? What kind of steel? When you re-sharpened the drill, did you put enough relief behind the cutting edge?
Assuming your drill is sharp, I would slow the speed down and increase feed pressure. You may have some work hardening and this should help you punch through it. There are all sorts of things you can try - end mills to cut through the hard stuff, carbide drills, etc.
If I had to guess, I would suspect your drill's geometry.
Assuming your drill is sharp, I would slow the speed down and increase feed pressure. You may have some work hardening and this should help you punch through it. There are all sorts of things you can try - end mills to cut through the hard stuff, carbide drills, etc.
If I had to guess, I would suspect your drill's geometry.
I have been using the mill to cut the steel. Its 1018 cold rolled I believe. I was worried about work hardening but am new to this so I wasnt sure. The drill has been sharpened in a drill doctor and looks good. I can add some clearance though by hand. I'll try an end mill.
What kind of RPM would you suggest? I have been doing about 800rpm on the mill.
What kind of RPM would you suggest? I have been doing about 800rpm on the mill.
RPM seems pretty close for a 1/2" bit. If you managed to harden it though, perhaps ~500 RPM and more pressure? Do you have a carbide end mill you can use to remove some of the material? That might work better on work hardened 1018. It could just be a thin skin you need to break through, think mill scale on hot rolled steel. You could also try another piece of similar material, perhaps a bit of scrap sheet, to verify your sharpened drill geometry.
Just a small point, a grinder arm doesn't need to be solid. Tube will be plenty strong, and it's a lot easier to drill.
Just a small point, a grinder arm doesn't need to be solid. Tube will be plenty strong, and it's a lot easier to drill.
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I have not seen 1018 to work harden, it does not have enough carbon content to harden appreciably, although, sometimes if you are running too fast, and the drill goes (very) dull, a bit of HSS can be wiped onto and bond with the CRS, usually running slow with plenty of feed pressure can bite through the hard layer, or as suggested a carbide end mill can do the job. In my opinion, cheapo drill bits are not worth owning. Another point is that when drilling pilot holes, they should not be bigger than the thickness of the web of the finish size drill, and stepping out such a small hole as 1/2" is not advisable, due to the tendency to wobble, and/or hog into the previously drilled hole, possibly breaking the drill or yourself and damaging the equipment.
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Sounds like you need to slow down the drill bit and use more pressure. 1018 will locally work harden when drilling, especially if you are using coolant as a cutting fluid, but normally a bit more pressure will break through the surface hardness. 1/4 inch is more than enough pilot hole for a 1/2 bit. The Harbor Freight cobalt bits are normally quite good, I have several sets.
Thanks guys for the advice. I was able to get through it with an end mill which is HSS. I'll slow down more when I drill. I have a slight problem as the mill uses a VFD and it seems like low RPM it loses some power.
The drill bits... I bought them because they were recommended here. They have done great until now which is probably my fault for going too fast. If I recall, when I started drilling, I was in the 1100rpm range because I wasnt paying attention. Once I noticed I slowed down. Good to learn about the pilot hole size and the web size on the larger bit. Makes sense and something I didnt know. Since I bought the bits, I'll continue to use them and sharpen them.
There are many many more tools I wish I had (reamers, lathe, better end mills, etc). Over time I'll slowly grow my collection. I just need to find some quality stuff that doesnt cost and arm and a leg.
Thanks again for the advice everyone!
The drill bits... I bought them because they were recommended here. They have done great until now which is probably my fault for going too fast. If I recall, when I started drilling, I was in the 1100rpm range because I wasnt paying attention. Once I noticed I slowed down. Good to learn about the pilot hole size and the web size on the larger bit. Makes sense and something I didnt know. Since I bought the bits, I'll continue to use them and sharpen them.
There are many many more tools I wish I had (reamers, lathe, better end mills, etc). Over time I'll slowly grow my collection. I just need to find some quality stuff that doesnt cost and arm and a leg.
Thanks again for the advice everyone!