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The technological steps of making pinned joints are different for the various types of pins used.
6.1. Joints Using Cylindrical Pins or Taper Pins
- Setting up and clamping
Clean the component parts and fit them together. Set them up and clamp them in a suitable device. While being held in the device, the component parts are to be mounted in the work-holding fixture of the boring machine.
- Drilling
Produce an undersize bore hole for cylindrical pins. The amount of undersize is removed by reaming. In general practice, the following amounts of undersize are employed for the respective nominal bore hole sizes in steel.:
|
N in mm |
U in mm |
|
up to 5 |
0.1 - 0.2 |
|
5 - 20 |
0.2 - 0.3 |
|
21 - 32 |
0.3 |
|
33 - 50 |
0.5 |
Allow a greater amount of undersize for bore holes in tough material and light metals.
N = nominal diameter
U = amount of undersize
· Use the following formula to calculate the drill diameter:
|
D = N - U |
D = drill diameter
Remember the following points for bore holes over 20 mm diameter:
|
|
1. Rough-drill using drills which satisfy the following formula: |
D = N - 2 mm |
| |
2. Countersink with a twist countersink. Use this formula: |
D = N - U |
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· Produce bore holes for taper pins to the nominal diameter of the taper pin: |
D = N |
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· Read the drill speed from the respective table or calculate it, using the following general formula: |
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· For producing large bore holes for taper pins, taper reamers of the appropriate size are used. The bore holes are produced stepwise. |
n = speed (min-1) |
Figure 22 Drilling steps
(1-2-3)
Stepped bore holes:
Calculate the diameter of the drill from the taper per unit length:
A taper per unit length of 1:50 means that the diameter is reduced by 1 mm for every 50 mm of length.
Example:
Produce a joint of two component parts having on overall thickness of 150 mm, use a taper pin of 20 mm diameter.
What steps will you drill?
|
Answer |
Diameter |
Depth |
|
1st bore hole |
Æ 20 mm |
150 mm through hole |
|
2nd bore hole |
Æ 21 mm |
100 mm |
|
3rd bore hole |
Æ 22 mm |
50 mm |
What holes will you drill for a cylindrical pin having a
diameter of 26
mm?
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How will you produce bore holes for taper
pins?
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- Countersinking
Using a 90° included angle countersink, countersink the bore hole on both ends 0.2 mm larger than the nominal diameter. This removes the burr from the hole.
|
DS = N+0.2 mm |
where
Ds = Countersunk diameter
- Reaming
Make the bore hole larger by reaming. Use a cylindrical or taper reamer that fits the type and size of the pin which is to be used.
When reaming a hole for a taper pin joint, test the fit of the pin before you drive it in.
With the force of your thumb, push the taper pin into the reamed hole. Clean the hole before you insert the pin. The upper edge of the pin should stick out above the edge of the hole by a length that depends on the nominal diameter of the pin. Where the size is that specified in the table below, apply two or three blows with a hammer to drive in the pin.
Testing the fit of taper pins having taper per unit length of 1: 50
|
Nominal diameter of the taper pin (mm) |
Size for testing the fit (mm) |
|
5 |
3 |
|
6 |
4 - 5 |
|
8 |
5 - 6 |
|
10 |
8 |
Remember:
The length of the taper pin you want to use must be 2 mm shorter than the thickness of all parts of the proposed joint.
Figure 23 Accurate fit
of a taper pin
Thus, the pin can be driven out with a drift from the opposite end. The drift will not slip and the one end of the pin cannot be mistaken for the other.
The upper edge of the pin is flush with the edge of the bore in the upper component part.
Where no taper pin of the required size is available, saw a longer pin to the dimension you need. Always saw off the thicker end of the pin. Do not change the nominal diameter of the pin. Produce a new head by filing.
What type of countersink will you use to deburr a bore
hole?
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What should be taken into consideration when reaming a taper pin
hole?
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What condition must be satisfied with respect to the length of a
taper
pin?
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How will you shorten the length of a taper
pin?
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- Cleaning the bore hole
Use compressed air or a brush to remove chips and any remaining fluid from the bore hole after reaming.
- Pinning
Apply a thin film of grease to the pin and drive it in by several blows with an aluminium hammer. Proceed from the end at which you applied the reamer.
Use a non-ferrous metal punch and a locksmith’s hammer to drive the pin in when access to its location is difficult.
- Checking
Check the pin for tight fit in the hole and that the upper edge of the pin is Gush with the surface of the component part of the joint.
How should a pin fit the
hole?
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What are the steps of producing a joint using a cylinder pin?
6.2. Joints Using Grooved Pins and Dowel Pins
- Setting up and clamping
Clean the component parts and fit them together. Set them up and clamp them in a suitable device.
While being held in the device, the component parts are to be mounted in the work-holding fixture of the drilling machine.
- Drilling
Produce a bore hole equal to the nominal diameter of the pin.
|
D = N |
- Countersinking
Use a 90-degree included angle countersink and countersink the bore hole at both ends or remove the burr with a triangular reamer.
|
Ds = N + 0.2 mm |
- Cleaning the bore hole
Use compressed air or a brush to remove chips and any remaining fluid from the bore hole.
- Pinning
Apply a thin film of grease to the pin and drive the pin in by several slight blows with a hammer. Proceed from the end at which you applied the drill.
- Checking
Check the pin for tight fit in the hole and that the upper edge of the pin head is flush with the surface of the component part of the joint.
What are the differences in the sequences of operations when
producing a joint by means of a grooved pin on one hand and a cylindrical or
taper pin on the other
hand?
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