Drilling into metal questions??

[steve-u]

I am going to be doing a repair project in the near future that is going to require me to use my Delta 12 inch benchtop drill press for drilling into metal. I will need to drill holes probably about 3/16 in diameter and also to countersink the screw heads. The metal will probably be along the lines of angle iron with the metal no more than 1/4 inch thick. I have never drilled metal much before other than real thin stuff or sheet metal. Anyhow my question is for such metal drilling do I need to use some sort of lubricant or is then not needed?? If a lubricant is needed what is recommended? I will be using Milwaukee Cobalt drill bits for the hole but still need to buy a countersink that can be used in metal [any recommendations?]. Also is there a good way to tell what countersink size to get for a project?? I am thinking about testing the countersink on scrap wood to see how deep I need to go for the screws I use.

Thanks, Steve

[drillman88]

Be sure to mark your hole with a center punch to keep your bit from walking when you start your hole.If your bits are sharp you should be able to drill 3/16 with out needing to use a pilot bit, but if the metal is tough or your bit is on the dull side you may need to use a smaller bit to start the hole then move up.
A 60 degree HSS 1/2" diameter countersink should matchup to the tapered
machine screws if that is what you will be using.You can check with an angle gauge.wd-40 will work to lube the bit.you probably will not need to use on the 3/16 holes but it will be a good idea on the csinks.If they look like they are galling use more wd.

[LCHIEN]

I think flat head screws were standardized at 82 degrees, not 60.
Any size CS bit will work if you only want to make the FH screw flush.
I just use some 3-in-one household oil or such when drilling a few holes.
Sharp bits are obviously the way to go. I usually mark the hole with a punch then drill at least one smaller pilot hole and work my way up.

[shoottx]

Be sure and set the drill speed for metal not wood speeds

3/16 for steel shows 3000 rpm

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

[Uncle Cracker]

And... make sure your workpiece is well secured to the drilling table. When breaking through the backside of the piece, a drill bit will sometimes gouge. When it does so in a hard metal such as steel, it can grab the work and spin it, which can bust you up real good... (My neighbor's FIL had that happen, and it cost him half of his left index finger... )

[LCHIEN]

And... make sure your workpiece is well secured to the drilling table. When breaking through the backside of the piece, a drill bit will sometimes gouge. When it does so in a hard metal such as steel, it can grab the work and spin it, which can bust you up real good... (My neighbor's FIL had that happen, and it cost him half of his left index finger... )

that's true, it'll sure grab when it breaks thru the back. Can cause extremely painful and serious injury. Either clamp it to the table OR set the piece so that when it spins in the clockwise direction its already resting against the post. Or both. If its too short to rest against the column then you have to clamp it.

Good safety tip.

[master53yoda]

Be sure and set the drill speed for metal not wood speeds

3/16 for steel shows 3000 rpm

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

the 3000 looks way to fast I pulled my machinist book out and it says 1325 for 3/16 and 765 for a 3/8 counter sink.

I looked at a wood magazine speed chart and it shows 3000 for 3/16 and 1000 for 1/4" I think this is chart is just too gross in its measurements. also the speed for aluminum in the machinist book is 2580. In the main machinist calc section all the formulas are based on surface speed (feet per second )

http://its.fvtc.edu/MachShop1/drillpress/cutspeeds.htm This website has all the hard formula work for those interested. Bear in mind that these calcs all assume lubrication.

[iceman61]

the 3000 looks way to fast I pulled my machinist book out and it says 1325 for 3/16 and 765 for a 3/8 counter sink.

I looked at a wood magazine speed chart and it shows 3000 for 3/16 and 1000 for 1/4" I think this is chart is just too gross in its measurements. also the speed for aluminum in the machinist book is 2580. In the main machinist calc section all the formulas are based on surface speed (feet per second )

http://its.fvtc.edu/MachShop1/drillpress/cutspeeds.htm This website has all the hard formula work for those interested. Bear in mind that these calcs all assume lubrication.

I agree. 3000 is way too fast to drill metal. Also when you feel the bit start to break through the other side, back off the pressure. You need a thick cutting oil when drilling metal. What Loring described will work also. WD-40 is not thick enuff to protect your bit.

[Tom Slick]

according to my calc's for mild steel and a 3/16" drill bit should be about 2000 RPM

that's using RPM= (CSx4)/D
CS= cutting speed, 80 to 120 is safe for mild steel
D=diameter=.1875

100x4 = 400
400/.1875= 2133 RPM

80x4=320
320/.1875= 1706 RPM

[LinuxRandal]

The oils I tend to use are either straight 30 weight, or that 3 in 1 oil. More the first (larger bottle), as it keeps the bits cooler (stays sharper) and helps take the bits away from the hole.

At the ole garage, we used what was available (trans fluid, new motor oil as used was harder to watch chip flow, penetrating lube when drilling overhead).

[steve-u]

Thanks for all the replies - very helpful information! And yes I plan on using clamps to secure the piece I am working on and plan on first starting with smaller hole and working my way up. I do have both motor oil and 3 in 1 oil so it looks like I already have the needed lubricants.

Thanks, Steve