Drill Press For Metal Work Versus Wood Work

According to Will :

Yep -- spindle speed. You need to run slower in steel than in wood, and even slower in stainless steel (depending on which stainless, some are more touchy than others.)

And -- you want the machine to be more rigid, as you will need to apply more force to keep the drill bit cutting -- pause with too little force and the bit stops cutting and work hardens the workpiece, making it *very* difficult to get the bit started cutting again -- even if you replace it with a new sharp one.

The actual speed, and actual force needed are a function of the diameter of the hole, which you have not yet specified.

Post the maximum diameter hole you will need to make, and which stainless steel, and we can calculate the highest spindle speed which you can use. The cheap import 5-speed ones typically won't go slow enough, except for the smaller holes (say 1/8" or smaller. The somewhat larger (still cheap) floor standing ones with 16 speeds (lots of pulley slots and two belts) will probably go slow enough, but with a large hole, they are not rigid enough, and once you start your hole, the needed force will cause the table to bend down a bit, making your hole not perpendicular to the surface of the workpiece.

Almost all of the import drill presses will not go slow enough to use the maximum size bit which the supplied chuck will hold for drilling through plain steel, let alone through stainless steel.

So -- the stainless steel alloy number (e.g. 304) will allow us to look up the proper SFM (Surface Feet per Minute) with HSS (High Speed Steel) bits.

Once we have that, knowing the largest hole diameter needed, we can calculate the maximum spindle speed for that diameter, and this will let you look up what the drill press you are considering will offer, and see if it is slow enough.

Smaller holes are typically no problem as long as you can handle the largest hole you need to drill.

Old US made drill presses are more likely to be satisfactory, even if they need a bit of work at first.

And I would suggest that you use split point high cobalt steel bits for the task, instead of the more common HSS bits.

Good Luck, DoN.

According to Will :

Add "high cobalt steel"

The carbides have the disadvantage of being very brittle, and can break if there is any side force while you're drilling.

High Cobalt Steel gives you a bit tougher steel than the standard HSS, without being as brittle as the carbide bits.

If you are drilling a *lot* of holes, perhaps the coated version of the cobalt steel would be better, and it might be worthwhile consulting one if the major manufacturers to find out what works best with the alloy you are drilling.

You also want coolant on the bit while you are drilling.

Which 300 series steel? 304 is a lot nastier to work with than

303.

All of the figures are in _Machinery's Handbook_, among other references. (And there are even nomogram slide rules for selecting the proper (maximum) drill speed. As has already been mentioned, too fast will burn up the bits rapidly, too slow only costs you time. If you are not drilling a lot of holes all of the time, it won't hurt to run too slow, and you'll gain a bit of bit life. Those maximum speeds are based on a tradeoff of cost of machinist's time vs cost of replacement drill bits.

And having the bits sharpened as "split point" will let you keep drilling with somewhat less force than a standard chisel-point drill bit will require -- which helps a cheaper machine do the job.

Proably for 1/4" holes, even one of the cheaper bench-top drill presses will do -- if the motor can handle it. (Often the import drill presses have shall we say "optimistically marked" horsepower ratings, and often burn out quickly with serious use -- after which you replace it with a *good* motor. :-)

Good Luck, DoN.

I'm pretty clear on the spindle speeds needed, thanks to all of the great information posted in this thread. Given that our holes would go between

1/4 and 1/2 inch, using 300 stainless, we seem to need about 300 to 800 rpm.

Given the requirement for using large pressing forces, and the need for rigidity, what manufacturers and models do you think might be good candidates? Honestly a very short model with a wide stable base would be preferred by me, just because it could be easily stored under a rack in a warehouse, or maybe floor mounted in the corner of a warehouse.

Someone here had picked up a 2/3 HP Craftsman 10 inch drill press, which is certainly short, and seems to be okay at 680 rpm for a 1/4 inch hole, but probably doesn't cut it for anything much larger than 1/4 inch diameters.

What advantages do those have?

According to Will :

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In the reverse order, of course -- that is the slower speed with the larger drill bit. :-)

To be honest -- I think that most import machines might be marginal, and it is hard to find *new* machines form US makers that are not really imports in disguise.

I would look for an older drill press of US manufacture. Go by the diameter of the column. A benchtop machine with a column of 3-1/2" diameter or greater should be plenty stiff. (Weight is rigidity.) And you'll want to bolt it to the bench top while using it, even if you unbolt it and store it later.

Obviously, look at the speeds available.

Hmm -- floor mounted would probably call for a 4" or greater column diameter. If you get one of the 16-speed imports with the round (and rotating) table, you may want to set up a 4x4 and a jack under the center of the table, to take out the flex which is present on the arm which reaches out to grip the center of the round table. This is actually what I happen to have -- bought years ago, when the imports were coming from Taiwan instead of China, and I find it to be too flexible at times. But I don't have the budget to look for something better, as it is hobby work for me.

Hmm ... how old a Craftsman? 10" drill press means only 5" from center of drill bit to the column -- that sounds like the current cheap imports which are selling on eBay for around $29.00 (but beware to check out the shipping, which can be a killer.) a craftsman from the early

1970s or before would probably be pretty nice -- as long as you got something capable of slower speeds.

Do you have any place nearby which sells used machine tools? That is where I would check.

The standard drill bit point is essentially two sort of curved planes which meet in the center making a blunt chisel tip which does not really cut, and has to be forced into the metal to get the edges of the tip to cut.

A "split point" drill bit has four planes, not two. The first two generate the main cutting edges and the relief angles, while the second two cut more steeply back on the back of the first planes, and are ground into the center of the bit, forming a second set of edges at right angles to the first which go right to the center. So it takes less force to drive the bit into the workpiece -- especially something which likes to work harden if your feed slows down.

But -- get an envelope of whatever the standard quantity is from someplace like MSC or a local industrial hardware store. (You probably won't find them in most regular hardware stores.) Typical package sizes will be something like ten or twelve for the 1/4" and smaller, and perhaps drop to five or six for the sizes up to 1/2". Obviously, buy just the sizes you need, and make sure to order more when you get down to one or two left. (MSC is pretty good about quick delivery. I get most things the next day if shipped from the Harrisburg PA warehouse. (I'm just a bit south of Washington DC.) The Atlanta warehouse takes an extra day, and I don't know what your shipping time would be.)

Anyway -- try the standard 1/4" bits and the split point ones in some scrap of your stainless steel and see how different the feel is.

Oh yes -- the other advice about having a good way to clamp down your workpiece is very good advice. If the bit grabs, it *will* spin the workpiece, and has been known to inflict serious cuts.

Good Luck, DoN.

I printed spreadsheet charts like this to hang behind my lathe and mill, showing the RPM for each belt position and the resulting cutting speed for common diameters.

If I want to drill a 12mm hole in hot-rolled, for example, I look in the 0.500" row for the highest pulley setting under 80-100 Feet per Minute.

Quick, simple, keeps oily fingers off the calculator.

On Nov 1, 9:20 pm, "Will"

Much info is already here on this subject, but as a piece of practical information: The most common configuration of cobalt HSS drill bit seems to be the 135-degree split point, which is what you should look for. The split point is indeed best for the application, and has tha added benefit of being able to self-center more accurately. These bits are available as well in screw machine length (shorter than jobber length), which makes them more rigid and less apt to wander.

According to Jim Wilkins :

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Yes -- though I have another way to accomplish that last goal. I keep the calculator in a Ziploc baggie, facing the back side, so there is no label in the way of reading the display or identifying the keytops.

Enjoy, DoN.

To add my comments to the many good ones that have appeared:-

If you can find a drill press with power down feed, you will find that it gives better results and drill life. Especially if you have to go to 1/2" or larger in 303.

Woodworking drills often seem to have table mountings that are lighter than is desirable. I have a woodworking drill (12", open slot, round table, 3" pillar) and a metalworking drill (12", closed T slot, square table, 2 1/2" pillar) and it's quite worrying how much the lighter table on the woodworking drill moves when you lean into a 1/2" or larger drill in steel. Having said that, the woodworking drill is where I can use it easily and the other drill doesn't get used very often :-)

If the motor struggles with the monthly metal jobs, don't forget that a pilot hole, about the diameter of the main drill's web, will make the main drill cut far more easily.

Mark Rand RTFM

Do you have any specific brands and models to recommend?