Drilling Operations and Machines

Drilling Operations and Machines
Machining and CNC Technology

Overview A Fundamental Skill
Section 10 presents a family of operations where we spin a cutting tool then plunge it straight into the work to create a precise hole at a specified location. Machining exact diameters in the right location to a specified depth, is one of the most fundamental ways metal is shaped. The odds are that within any CNC program calling up three tools or more, at least one will perform some form of drilling to complete the work shape. Machining and CNC Technology

Machining and CNC Technology
Whether they are made on a standard drill press or a CNC machine like this, machinists must be able to setup efficient drilling operations. Here are the goals to get there: Machining and CNC Technology

Section 10 Goals Unit Basic Drilling Tools > Select the Right Drills For the Job > Measure, Name and Describe Bits > Select a Pilot Drill for a Reamer > Select Drill Shanks and Adapters Unit Setting Up Standard Drill Presses > Identify features on standard drill presses > Practice Safe Habits and Holding Methods > Use Vises, Plates, Fixtures and Clamps Unit Speeds and Feeds > Calculate RPM > Access Surface Speed Data Machining and CNC Technology

Goals Continued Unit Drilling & Secondary Operations > Perform layout-punch location to .030 in. repeatability. > Perform center finder location to .010 repeatability. > Choose tap drills for a specific tap > Cut threads using taps on the drill press > Counter bore and counter sink work. > Make setups for parallel and angle holes Unit Sharpening Drill Bits > Safely and correctly sharpen bits using a pedestal grinder > Recognize a dull or damaged drill needing re-grinding Machining and CNC Technology

Beyond the Basics There's more compelling reason to learn drilling. Today in CNC mill programs, drilling can be used for rough profile machining of extreme metals difficult to cut. CAM software can quickly create drill locations around the perimeter of the part, that rough machine away excess metal, even on complex shapes. Then with the excess drilled away, the work can be profile milled. Trade Tip The advantage is that a hard but brittle, carbide cutter will usually withstand a constant end push better than a sideways thrust into the metal. So, drilling is an efficient CNC option. Metal is removed faster and the drilling cutter lasts longer in many situations. Machining and CNC Technology

Unit 10-1 Basic Tools Drill bits and reamers are the first tools we’ll learn. Drill bits are also called twist drills for the way they are made – they are literally twisted to form the spiral grooves that carry chips up and out. Figure 10-4 Machining and CNC Technology

Four Drill Size Systems
Look on the Drill Size Chart text Page 321or Appendix I Pg 1041 You will notice drill bit sizes called out in four different ways. 1. Metric Sizes 2. Inch Fractional 3. Number Sizes 4. Letter Sizes Nothing needs to be said about metric sizes. By design, all metric tools are easy to understand. Inch fractions are also a simple issue, they graduate in 64ths of an inch, but not finer. It’s the next two we need to discuss. Have students turn to one or the other chart as questions are coming up Machining and CNC Technology

1/64th inch between fractional bits, doesn’t provide enough size differences for modern machining. Therefore manufacturers invented two more series that fit between the fractions. Machining and CNC Technology

Number Sized Drills #1 through #80
# in. diameter # in. standard set #80 Extra small in. Shop Talk So you see number drills can keep going smaller. If needed a # 81 can be manufactured Remember – Number drills go from for the largest down to inch in two different sets. Larger Numbers = Smaller Drills Machining and CNC Technology

Letter Series Drills Opposite from numbers, letter sizes get bigger with higher letters. Question From the Starrett chart in your book – what decimal size is an A drill? Answer in. diameter Not much different from a #1 Next Question – from the chart, how big is an R Drill? 0.393 in Just checking An R is really inch! Chart is on Page 321 and a larger version is Page 1041 Appendix I, easier to read. Machining and CNC Technology

Choosing the Right Bit For drilling holes the size on the drawing is the size to use. You will probably pre-drill the hole with a smaller size, but the final drill will be the specified diameter. But for reaming and tapping there’s some looking up to do. A specific drill size needs to be chosen from the drill chart. It will be smaller than the tap or reamer by an exact amount! For example, what size drilled hole is required to tap a 1/4 –20 thread? A number 7 drill at inch. Background for Question Coming Up Ask the class what is the next larger drill from a #7 then discuss if it could be used in a pinch if no #7 was available? Machining and CNC Technology

How Do You Know? Finding the required size is a straight forward issue that we’ll investigate more in the textbook. The real challenge is guaranteeing that the drill you’ve found is the size needed! Machining and CNC Technology

Drill Size Gages From the chart, you’ve seen there’s only a few thousandths between some sizes. So a gage such as this can only be considered a rough sorting tool. You couldn’t be certain the drill was a 13/64th or a #7! Just two thou apart! Machining and CNC Technology

Markings and Measuring
Drills are stamped with their size in either: millimeters, fractions, letters or numbers. If they can be read, they are correct. But due to daily chuck wear, they are often hard or impossible to read! So measuring the bit is the last word on drill size. Machining and CNC Technology

Drill Point Geometry Standard Point Longer Point Soft Material Flatter Point Hard Material Like all cutters, drill bits have the 3 tool bit angles, rake, clearance and lead. The lead angle is changed to create various point shapes. Beyond the standard point bit, there are several specialty bits you’ll need to understand. Some are used for both manual and CNC drilling while others are used mostly for one or the other. Spur Point Thin Material Step Point Special Shapes Spade Point Deep Holes Machining and CNC Technology

Reamers Follow Drills A reamer finishes a drilled hole to a more exact size, with better finish and form. (round and straight) Trade Tip Reamers are also stamped with their size but when re-sharpened, the diameter changes slightly. It should be remarked or put in a special undersize cutter drawer, but often isn’t. Always mic a reamer before use! Your instructor and the text will show you the technique for measuring both drills and reamers, using a micrometer. Machining and CNC Technology

Unit 10-2 Drill Presses Every shop, big or small, has one or more manually operated drill press. On those in your lab, you’ll be learning efficient setups and operations – much of that knowledge will transfer to lathes and mills where we also drill work. There are four types you might encounter in training or in industry. Machining and CNC Technology

Sensitive Presses Used for very small drills that break easily. These machines can achieve 20,000 revolutions per minute or more! Due to light construction the machinist has a good feel for the drilling action and can stop instantly if it isn’t drilling right – that’s something most CNCs can’t do! Usually drills no larger than 3/16 inch diameter are used on these micro-machines. Machining and CNC Technology

Floor Mounted Drill Press
Variable Speed Control The everyday “pickup truck” of drilling machines, very useful and found everywhere. Drills and reamers up to around ¾ inch are commonly used here . Bigger drills are possible but not recommended. Still fed by hand, these presses do not feature gear drives so the spindle cannot reverse. Note the table can raise or lower and swivel and pivot as well, on some floor presses Possible Table Adjustments Machining and CNC Technology

Gear Head (or Power) Presses
Power Feed System More powerful spindles, these machines usually handle tools up to one inch diameter or greater They feature: Reversing Spindles Power Down/Up Tool Feed They must be shifted to change RPM. These machines can be used to power tap threads in large batches Spindle Forward/Reverse Automatic Spindle Reverse Cams and Depth Control Machining and CNC Technology

Radial Arm Drill Presses
Usually the biggest machines, they have even more powerful spindles. Handling tools above 1.0 inch diameter. Not so great for small bits below ¼” They can pivot their head away from the table to allow crane loading of heavy work from overhead. Shop Talk The radial arm press is the only one where the drill head is moved in three axes of motion, over the stationary work, then locked in the right location. On all other presses, we move the workpiece under the spindle then clamp it in place before drilling. There are heavy industry, radial arm presses big enough that a car can be driven onto the table, they have more than one traveling drill head that moves on floor mounted rails! Machining and CNC Technology

Quill Feed These presses get their name from the way the drill head can be moved in a radius about the column. The rails can be elevated and the head moved out on the rail as well. Spindle Clutch Three Axes of Movement Machining and CNC Technology

Unit 10-3 Drill Press Speeds and Feeds
This your first vital lesson of many, shows how to hit the RPM sweet spot, The right RPM is not so low that the bit breaks or so high that it burns up or hardens the work! It’s a constant trade off between quality, speed and tool life – with safety overshadowing it all! Trade Tip There is an inverse relationship between RPM and drill size – or any spinning cutter. The smaller the drill, the higher the RPM. Bigger cutting tools receive smaller RPMs. Machining and CNC Technology

5 Ways to Determine RPM All machinists must have ability in each of the following. RPM Charts – dedicated to drill diameter in a given work material. See Appendix III – Page 1043 Question – From the textbook chart, what RPM is recommended when drilling aluminum with a 7/8 in. diameter drill. Trade Tip Some drill presses and other machines too, have RPM charts, similar to the appendix, engraved on metal plates, mounted on their front face. Answer = 1,143 RPM Machining and CNC Technology

All depend on knowing surface speed
Drill RPM Formulae There are three – the long and the short versions and one for metric tools. They return results within 5% of each other. The short version is designed to solve in your head, on-the-fly, in the shop. They all depend on knowing a magic number – the correct surface speed, also called the cutting speed All depend on knowing surface speed You might want to show the SS values you use in your lab. The ones in the chart are lowball for safety and easy remembering. Machining and CNC Technology

Surface Speed For Example The Appendix Chart IV - Page 1044, Recommended Cutting Speeds, was written with beginner safety and easily remembered numbers. It will produce conservative RPMs that will be increased with machining experience. Is a cutting velocity in feet per minute or in millimeters per minute Is found by experimentation, whereby tools are tested while cutting various materials, with the results compiled into charts. Different charts will offer slightly different rates due to the bias of the chart author. Question Using Appendix IV, what surface speed (SS) is recommended for machining carbon steel with a high speed drill bit? Answer 80 Feet Per Minute (F/M) Machining and CNC Technology

RPM by Insight 1,500 to 2,000 RPM Give or take a few? Machining and CNC Technology

No kidding, with time you’ll be able to look at the setup and do a fairly good job of estimating RPM! Experience will create the ability to look at a drill size & material combo and estimate a pretty close RPM! It’s a good thing, but never trust intuition for extreme situations with hard work material, very big or small cutters. Machining and CNC Technology

Speed and Feed Calculators
Provided by tool suppliers These handy speed and feed slide rules are entered with the SS and work material or material hardness, to return the correct RPM Shop Talk Using tool supplier’s data will yield maximized results compared to our appendices, since their bias is toward highest productivity. Machining and CNC Technology

CAM Built-in RPM CAM softwares, such as that on the student CD, Mastercam ®, feature the ability to auto-calculate RPM if given the same two parameters used in all formulae: Work Hardness – SS Tool Diameter Machining and CNC Technology

Drill Press Setups This is another area where skills learned here will extend all over the shop. Many drill table setup components are used elsewhere. One exception is the drill press vise, it’s only suitable for the down thrust of drilling – never for milling! Machining and CNC Technology

The Press Vise Note the shelf in the jaws to support downward thrust Also notice the quick release to allow for quick loading of work Quick release not strong enough for milling Support Shelf Machining and CNC Technology

Best Practice Setups Beyond solid setups that do not allow the work to spin or lift up if the drill grabs, the 2nd objective of a good setup is to protect the table! It’s considered really bad form to drill holes in your own machine! Turn to text pages 340 and 341 for a few good setup suggestions. 3 Precautions! 1. Never try to hold the work with your hands, drills do catch and spin the work. 2. Never leave the chuck wrench in the chuck! It becomes a missile when the spindle is turned on! 3. Loose items and long hair do catch on twist drills! I’ve seen it twice in my career! OK – this is a fake, there was only so much our staff was willing to do for good training demos! But still you get the point, tie it up or put it in a hat! You will undoubtedly have more safety rules to add – for drilling Machining and CNC Technology

Unit 10-4 Drilling Per Print
Similar to measuring processes, there are various ways to locate the work under the spindle on drill presses – each with finer repeatability. But none other than a drill jig, can locate holes with a repeatability better than inch, at best. Hole location tolerances finer than .015 inch are usually taken to a milling machine You may have a differing opinion from the 2nd paragraph – if so change the slide or add your estimate of center finder/wiggler accuracy. Machining and CNC Technology

2 Standard Location Methods
Small pilot starts drilling with less wandering compared to starting a drill bit alone. The first was discussed in Section 8 – laying out the location then center punching it. For best accuracy begin with a small pilot drill or a center drill at a fairly high RPM Machining and CNC Technology

Center Finder Method Delivering fairly good location repeatability, this clever little tool helps locate a spindle directly over a layout location using eyeball accuracy. Note, the center location is not punched for this method and the center finder does not touch the work surface – it’s an alignment tool only! Trade Tip A major part of the inaccuracy of any drill location method is in getting the bit to not wander as it bites into the workpiece. Pilot drilling helps. There’s a ton of Tips and Tricks for these tools – be sure to grab them as you go through Unit 4. Machining and CNC Technology

Secondary Drill Press Tools
Used on the press or elsewhere, there is a small family of other rotary tools well worth knowing. Countersinks, Counter bores / Spot Facing Tools Taps (dies not used on presses) Scan pages 352 to 358 to see the variety – some are also used on CNC lathes and mills. Enrich this slide by showing the various secondary tools you have in your lab Machining and CNC Technology

Back Spotfacing Tools for Inside Walls Core Drills Three kinds of countersinks Interchangeable Pilot, Spot Facers Machining and CNC Technology

Shop Talk Beyond the skill of sharpening drills, a major goal here is to be able to recognize when a drill is dull such that you do not use it in a setup or stop to replace it before serious problems occur if it’s already being used. On high profit CNC equipment, time lost from over-using a cutting tool, is never balanced against the minor savings of over-extending before exchanging bits. The point being – smart machinists keep their tools sharp! Unit 10-5 Drill Grinding Drill bits are re-sharpened in two different ways By Hand By Machine Depending on the level of production some shops consider smaller drills to be throw-away tools Hand Drill Grinding Note. Although the text discusses hand drill grinding, your curriculum may not teach it It’s pretty low tech these days! Some teach it, some don’t. Our planners and I felt it was a valid experience and good tool geometry lesson. I deliberately did not include pictures of hand grinding in this slide set – so you may need to discuss it with your group before dismissing if you do teach it. Machining and CNC Technology

Typical drill grinding machine in industry Machining and CNC Technology

Conclusion True, drill press work isn’t all that glamorous but Keep in mind the foundation skills learned there apply across the board And that CNC techniques use drilling both on mills and lathes. To write a program using drilling operations requires what you’ll learn on the good old drill press! Go forth and drill those holes in the right place, straight and deep! Machining and CNC Technology

Drilling Operations and Machines

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