12 Kapitel 3:Bohrmaschine

ZIEL

Nach Abschluss dieser Einheit sollten Sie in der Lage sein:

• Bohrmaschine identifizieren

• Verstehen Sie die Sicherheitsregeln.

• Beschreiben Sie die zu verwendenden Werkzeuge.

• Beschreiben Sie das Reiben eines Lochs.

• Beschreiben Sie das Bohren eines Lochs.

• Beschreiben Sie das Verfahren zur Stromzufuhr und zum Anbohren von Hand.

• Beschreiben Sie die Verfahren zum Abrichten der Scheibe.

Beschreibung

Bohrmaschinen oder Bohrmaschinen werden hauptsächlich verwendet, um ein zylindrisches Loch in ein Werkstück oder Teil zu bohren oder zu vergrößern. Die Hauptoperation, die an der Standbohrmaschine ausgeführt wird, ist das Bohren, aber andere mögliche Operationen umfassen:Reiben, Senken, Senkbohren und Gewindeschneiden.

Die Standbohrmaschine, die im Student Shop verwendet wird, ist eine weit verbreitete Maschine, die sowohl in Heim- als auch in Industriewerkstätten zu finden ist. Diese Art von Bohrmaschine besteht aus vier Hauptgruppen von Baugruppen:Kopf, Tisch, Säule und Basis.

Der Kopf enthält den Motor und den Mechanismus mit variabler Geschwindigkeit, der zum Antreiben der Spindel verwendet wird. Die Spindel ist in der Pinole untergebracht, die entweder durch manuellen oder automatischen Vorschub nach oben oder unten bewegt werden kann. Der Tisch ist auf der Säule montiert und dient zum Tragen des Werkstücks. Der Tisch kann je nach Bearbeitungsbedarf auf der Säule angehoben oder abgesenkt werden. Die Säule ist das Rückgrat der Bohrmaschine. An ihm werden Kopf und Fuß festgeklemmt und er dient als Führung für den Tisch. Die gusseiserne Basis ist das tragende Element der gesamten Struktur.

Sicherheit

1. Machen Sie sich mit der Position der Start- und Stoppschalter vertraut.2. Der Tisch der Bohrmaschine sollte von verschiedenen Werkzeugen und Materialien befreit werden.3. Stellen Sie sicher, dass alle Bohrer geschärft und die Spannfutter in einwandfreiem Zustand sind. Keine stumpfen Bohrer, angeschlagene Angeln oder Stecknüsse sollten verwendet werden.4. Versuchen Sie niemals, Reste von Hand vom Tisch zu entfernen. Verwenden Sie Bürsten oder andere geeignete Werkzeuge.5. Versuchen Sie niemals, Wartungsarbeiten an der Maschine durchzuführen, ohne dass das Netzkabel abgezogen ist.6. Führen Sie niemals einen Futterschlüssel in das Futter ein, bevor die Maschine ausgeschaltet und vollständig gestoppt wurde.7. Riemen und Riemenscheiben sollten jederzeit bewacht werden. Wenn etwas ausgefranst ist, melden Sie es sofort dem Ausbilder für Ersatz.8. Alle Werkstücke sollten vor Beginn der Bearbeitung mit einem Schraubstock oder einer Klemme gesichert werden.9. Wenn sich das Werkstück im Schraubstock oder in der Klemme bewegt:          • Versuchen Sie nicht, das Werkstück mit der Hand festzuhalten. • Versuchen Sie nicht, den Schraubstock oder die Klemme festzuziehen, während die Maschine             eingeschaltet ist. • Schalten Sie die Stromversorgung aus und warten Sie, bis die Maschine vollständig zum Stillstand gekommen ist             , bevor Sie den Schraubstock oder die Klemme wieder festziehen.10. Verwenden Sie die richtigen Geschwindigkeitseinstellungen und Bohrertypen für das zu bearbeitende Material.11. Beim Montieren eines Bohrers sollte dieser in voller Tiefe und zentriert im Bohrfutter sein.12. Beseitigen Sie die Möglichkeit, dass der Bohrer auf den Tisch trifft, indem Sie einen Abstandsblock verwenden und den Vorschubhub einstellen.13. Führen Sie den Bit immer langsam in das Werkstück ein. Wenn das zu bohrende Loch tief ist, ziehen Sie den Bohrer oft zurück, um Späne zu entfernen.14. Bevor Sie die Standbohrmaschine für längere Zeit verlassen, sollte der Strom abgeschaltet und die Maschine vollständig zum Stillstand gebracht werden.15. Wenn unsichere Bedingungen oder Bewegungen an der Bohrmaschine beobachtet werden, melden Sie dies sofort dem Ausbilder.16. Hinterlassen Sie die Bohrmaschine stets sauber und aufgeräumt.

Procedures

     Successful operation of the drill press requires the operator to be familiar with the machine and the desired operation. The following are some good observations to follow when drilling a hole:

1. Prior to drilling a hole, locate the hole by drawing two crossing lines. Use a center punch to make an indentation for the drill point to aid the drill in starting the hole.

2. Select the proper drill bit according to the size needed.

3. Select an appropriate size center drill.

4. Select a cutting fluid.

5. Properly secure the workpiece to the table.

6. Select the correct RPM for the drill bit. Take into account:size of bit, material, and depth of hole to be drilled.

7. Use an interrupted feed, called peck drilling, to break up the chips being produced.

8. Pilot holes should be used on holes larger than 3/8” dia. Holes are to be enlarged in no more than 1/4” increments.

9. Clean the drill press and surrounding area when finished.

*** Hard and fast rules are not always practical for every operation performed in a drill press, since many factors can influence the speed and feed at which a material can be worked. The above suggestions, combined with knowledge of the tool being used, will provide a reasonable guideline for the operator using a drill press.

Tooling

     Twist drills- A twist drill is a pointed cutting tool used for making cylindrical holes in the workpiece. It has helical flutes along its length for clearing chips from the holes. Twist drills are the most common used today, but there are many other styles with different purposes. A twist drill is composed of three major parts:a shank, body, and point. The shank is the part of the drill bit held in the spindle of the drill press. The drill press’ power is transferred through the shank. Shanks are either one of two styles, straight or tapered. Straight shank drills are held in a friction chuck. Slippage between the drill bit and the chuck is often a problem, especially for larger drills. When using drill bits larger than 1/2” dia., tapered shank drill bits are often used. These provide greater torque with less slippage than straight shank drill bits. The body, as described above, generally has two flutes to clear chips. These flutes are not cutting edges and should not be used for side cutting as an end mill. The point of the drill bit does all of the cutting action, which produces the cut chips. The point is ground on the end of the drill bit.

     Holes produced by twist drill bits are generally oversize by as much as up to 1% of the bit’s dia. The accuracy of the hole is dependent on the following factors:size of the bit, accuracy of the bit’s point, accuracy of the chuck, accuracy and rigidity of the spindle, rigidity of the press, and rigidity of the workpiece in its setup. All holes to be drilled should be started with a centerpunch, centerdrill, or both.

Twist Drill Formats

1. Number sizes:#80 (.0135”) to #1 (.228”)

2. Letter sizes:A (.234”) to Z (.413”)

3. Fractional sizes:1/64” (.0156”) upwards by 64ths/inch

Reaming a Hole

     A reamer is a precision cutting tool designed to finish a hole to a specific dia. Since drill bits produce slightly oversized holes, reamers are used where precision tolerances are required, .001”. Reamers have little if no cutting action on their ends, so a pilot hole is required as a preoperation to reaming. Some general guidelines for using reamers are:

• Drill a pilot hole that is a bit smaller

• When starting a hole, drill it a bit undersized.

• Drive the reamer at a slow, constant speed.

1. The cutting speed for reaming should be about 1/3 of the speed used for drilling operation of the same material.

2. Before reaming, leave about .010” of material on holes up to 1/2”, and about .020” of material on larger holes.

3. Never rotate a reamer in the reverse direction.

4. Use the proper cutting fluid for the material.

5. Remove the reamer from the hole occasionally while cutting to clear chips, which can cause galling on the surface of the precision hole.

6. Never stop the machine with the reamer in the hole.

7. Clean and return the reamer to its proper storage place.

     Countersinks – Countersinking is an operation in which a cone-shaped enlargement is cut at the top of a hole to form a recess below the surface. A conical cutting tool is used to produce this chamfer. When countersinking, the cutter must be properly aligned with the existing hole, and should be rotated about 1/3 the cutting speed of the drilling operation for the hole. Countersinking is useful in removing burrs from edges of holes, as well as providing a flush fit for flat-headed fasteners.

      Counterbores – Counterboring is the process of cylindrically enlarging a hole part way along its length. A counterbore cutter is similar to a drill bit in that it has a shank and fluted body, but instead of a point, it has a smaller diameter pilot portion. The pilot fits into a pre-drilled hole, and guides the counterbore. Therefore the counterbore must be aligned with the original hole, so the pilot will follow the hole properly. Counterbores are used to accommodate studs, bolts, or socket head capscrews where a flush surface application is required.

      Tapping – A tap is a tool used to cut internal threads in a cylindrical hole. A tap is fluted like a drill, but the flutes actually perform the cutting operation. The flutes extend the length of the threaded section and also serve to remove the chips being produced. The most common taps used are:

1.  The starting or tapered tap. This tap is used to start threads. At least the first six threads of this tap are tapered before the full diameter of the thread is reached.

2.  The plug tap. This is the general use tap, and is used to cut threads after the taper tap has been used and removed. Three to five of its first threads are tapered. This is the last tap used if the hole extends all the way through the workpiece.

     Cutting fluids should always be used when tapping holes. It is also recommended

to advance the tap one full turn and the reverse it 1/4 turn to break the chip being formed.

Always use a tap handle, not pliers or a crescent wrench to turn the tap. They can damage

the tap, and the unequal torque provided can cause a thread to be cut poorly.

Drilling a Hole

1. A center drill should be used to aid with the drilling.

2. A center drill has short flutes and a thick shaft. Therefore, it is very stiff and will not wander. Since a center drill doesn’t cut as easily as a drill bit, use cutting oil.

3. The hole is ready to be cut with a drill bit now.

4. It is recommended to use a smaller pilot hole before drilling the final one if the hole is large. This increases the accuracy of the hole and allow the bits to last longer.

5. If the hole is deeper than the diameter of the hole, use cutting liquid and back off occasionally.

6. The spindle speed should be reduced as drill size is increased.

7. When drilling a through hole, make sure the bit will not drill into the table after drilling through the work.

8. Set a depth stop on the quill to reach a desired depth of the hole.

Deburring a Hole

Often times the top edge of a hole will be clean, but the bottom edge will have some burrs. To remove the burrs, run a deburring tool in the hole around the edge with medium pressure. Repeat this process until the edges are no longer sharp.

Power Feed Tapping Procedure

1. Power feed tapping is similar to hand tapping. Instead of tapping by hand, however, use the drill press to tap the workpiece.

2. Before starting the machine, change the drill press to low gear.

3. Release the quill lock and move the quill to the lowest it can go. This ensures that there is sufficient space to tap to the desired depth.

4. Turn the spindle on FORWARD and set the spindle speed to 60 RPM.

5. Feed the tap down. When the tap grabs the stock, it will automatically feed itself into the hole.

6. When the desired depth has been reached, quickly flip the spindle direction switch from forward to reverse. This will reverse the direction of the tap and remove it from the hole. Reversing the direction in one fluid motion will prevent damage to the tapped hole and the tap.

7. Turn off the machine.

8. Clean the tapped hole, tap, and power feed machine before leaving.

Hand Feed Tapping Procedure

1. Ensure correct tap size for the drilled hole. If the size is off, the tap might break in the hole.

2. Place a center finder into the chuck and align the quill over the hole.

3. Fix a tapered guide to the chuck.

4. Position the tap and apply gentle pressure with the quill while turning the tap.

5. For every quarter turn of thread cut, it is wise to back the tap up slightly.

UNIT TEST

1. What is the chief operation performed on the drill press?

2. Please lists other possible operations performed on the drill press?

3. The drill press is composed of four major, Please lists them.

4. Please name three major parts of a twist drill.

5. All holes to be drilled should be started with What?

6. Name three types of twist drill formats.

7. What is the cutting speed for reaming ?

8. Before reaming, How much of material to leave on holes up to 1/2”, and on larger holes?

9. Explain the different between countersinks and counterbores.

10. Explain the Power Feed Tapping vs. Hand Feed Tapping.

Chapter Attribution Information

This chapter was derived from the following sources.

• Drill Press derived from Mechanical Engineering Tools by the Massachusetts Institute of Technology, CC:BY-NC-SA 4.0.
• Reaming derived from Reaming with a Reamer by CORE-Materials, CC:BY-NC-ND.