1. Drilling Holes
Unit 42

2. Objectives Measure the size of inch and metric drills
Drill the correct size center holes in workpieces
Drill small and large holes to an accurate location

3. Drill Press Safety
Do not operate before understanding mechanism and how to stop
Always were approved safety glasses
Never attempt to hold work by hand
Keep your head back from revolving parts
As drill begins to break through work, ease up on drill pressure

4. Always remove burrs from drilled hole with file or deburring tool
Never leave chuck key in drill chuck
Never attempt to grab work that may have caught in drill
Stop machine first
Always keep floor around drill press clean and free of tools, chips, and oil

5. Drilling Hints Treat cutting tools with care
Always examine condition of drill point before use – do not use dull tools
Make sure drill point angle correct for type of material to be drilled
Set correct revolutions per minute for size of drill and workpiece material

6. Set up work so drill will not cut into machine as it breaks through workpiece
Work should always be clamped securely
End of workpiece farthest from hole should be placed on left-hand side of table so it will not swing toward operator
Always clean tapered drill shank, sleeve, and machine spindle before inserting drill
Use shortest drill length possible and/or hold it short in chuck

7. Good practice to start each hole with center drill
Provides guide for drill to follow
Thin workpieces should be clamped to hardwood block for drilling
Chips from each flute should be same shape; if blue during drilling, check drill point condition
Drill squeak usually indicates dull drill
When increased pressure must be applied during drilling, reason usually dull drill or chip caught in hole between drill and work

8. Measuring Size of a Drill
Good practice to always check drill for size before drilling
Check for size
Drill gage
Micrometer
Most accurate
Check measurement across margin of drill

9. Lathe Center Holes Use a combination drill and countersink
Commonly called center drill
Must be drilled to correct size and depth
Too shallow or deep, poor support for work
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10. Procedure for Drilling Lathe Center Holes
Select proper size of center drill to suit diameter of work
Fasten center drill in drill chuck, extend only about .500 in.
Place work in drill vise
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11. Set drill press at proper speed and start
Locate center-punch mark below center drill point
Carefully feed center drill into center-punch mark in work for about .060 in.
Raise center drill, apply drops cutting fluid
Frequently remove drill, apply fluid, remove chips and measure diameter of top
Continue drilling until top of hole proper size

12. Spotting Hole Location With a Center Drill
Chisel end on drill wider than center-punch mark on work
Spot center-punch mark with center drill
Small point on center drill will accurately follow center-punch mark and provide guide for larger drill
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13. Spotting Hole Location With a Center Drill
Mount small-size center drill in drill chuck
Mount work in vise
Do not clamp
Set drill speed to 1500 r/min
Bring point of center drill into center-punch mark and allow work to center itself with drill point
Continue drill until one-third of tapered section of center drill has entered work
Spot all holes to be drilled

14. Spotting Hole
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15. Drilling Work Held in a Vise
Spot hole location with center drill
Mount correct-size drill in drill chuck
Set drill press to proper speed for size of drill and type of material to be drilled
Fasten clamp or stop on left side of table
Mount work on parallels in drill vise and tighten it securely

16. Start drill press spindle and begin to drill
With vise against table stop, locate spotted hole under center of drill
Start drill press spindle and begin to drill
Holes up to 12 in. – hold vise against table
Holes over 12 in. – Clamp vise to table
Drill until full drill point into work
With drill revolving, deep drill point in work and tighten clamp holding vise
Raise drill occasionally and apply cutting fluid during drilling
Ease up on drilling pressure as drill starts to break through workpiece

17. Drilling to an Accurate Layout
Clean and coat surface with layout dye
Locate position of hole from two machined edges of workpiece and scribe lines
Lightly prick-punch where two lines intersect
Check accuracy of punch mark
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18. Scribe circle to indicate diameter of hole
Scribe test circle .060 in. smaller than hole
Punch four witness marks on circles up to .750 in. in diameter and eight witness marks on larger circles
Deepen center of hole location with center punch to provide larger indentation for drill to follow
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19. Center drill work to just beyond depth of drill point
Mount proper size drill in machine and drill hole to depth equal to one-half to two-thirds drill diameter
Examine drill indentation; should be concentric with inner proof circle
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20. Start drill in spotted and grooved hole
If spotting off center, cut shallow V-grooves with cape or diamond-point chisel on side toward which drill must be moved
Start drill in spotted and grooved hole
Drill will be drawn toward direction of grooves
Continue cutting grooves into spotted hole until drill point drawn to center
Continue to drill hole to desired depth
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21. Drilling Large Holes
Drills increase in size; thickness of web also increases to give drill strength
Thicker web, thicker point of drill
Thick web not follow center-punch mark easily
Two methods to overcome poor cutting action of thick web on large drills
Web is thinned
Lead, or pilot, hole is drilled

22. Using Pilot Hole with Large Holes
Drill pilot hole diameter which is slightly larger than thickness of web
Care must be taken to drill pilot hole on center
Pilot hole then followed with larger drill
Problems when pilot hole too large
Cause chattering
Drill hole out-of-round
Spoil top (mouth) of hole

23. Procedure for Drilling Large Holes with Pilot Hole
Check print and select proper drill
Measure thickness of web at point
Select pilot drill with diameter slightly larger than web thickness
Mount workpiece on table
Adjust height and position of table so drill chuck can be removed and larger drill placed in spindle after pilot hole drilled and lock table

24. Place center drill in drill chuck, set proper spindle speed, accurately drill center hole
Using proper-size pilot drill, drill pilot hole
Shut off machine, leaving pilot drill in hole
Clamp work securely to table
Raise drill spindle, remove drill and chuck
Clean taper shank of drill and spindle hole
Mount large drill in spindle
Set spindle speed, feed and drill hole to required depth

25. Drilling Round Work in V-Block
Select V-block to suit diameter of work
Mount work in V-block and rotate it until center-punch mark is in center of work
Check distance from both sides equal
Tighten U-clamp securely or hold work in vise
Spot hole location with center drill
Mount proper drill size and set speed
Dill hole (do not hit V-block or vise when drill breaks through work)