RG402 Cable Bender
INSTRUCTION
RG402 Semi Rigid Cable Bender
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C.J. Humphris manufactures a professional hand operated cable bender specifically designed for RG402 semi rigid coaxial cable. It can be used with either copper or aluminium jacketed RG402.
The bender is capable of forming complex, fully formed bends without any distortion of the critical internal dimensions of the cable. Bend angles ranging from 0 to 180° are possible.
Bend radius is fixed and all bends are formed around the minimum bend radius recommended for RG402. The minimum bend radius for most coax cable is Ø x 2.5. The diameter of RG402 is 3.6mm; therefore the minimum bend radius is 9mm. This tool is designed to bend through a radius of 9.5mm, or an inside bend radius of 9.5 – 1.8 = 7.7mm, which leaves a slight margin, guaranteeing that the minimum bend radius is never exceeded.
The tool is capable for pushing or pulling the cable into the desired shape. This capability was designed in to maximize the possibility of forming the most complex shapes.
In use, the body of the tool can be held by hand or secured in a bench mounted vice by means of the lower platform section.
All components are constructed from brass and aluminium with stainless steel screws.
Figure 1
INSTRUCTIONS FOR USE
It is difficult to describe exactly how to use this tool. To most professional technical persons with an understanding of the requirements of the cable to be manufactured, the operation is self-evident.
A photo showing examples of bend capability is shown on the last page of this document.
However, I will outline instructions for an example below:
Assume that you need to make a U shaped RG402 cable assembly with SMA (M) connectors on both ends to connect between 2 mating SMA (F) connectors mounted in the same plane but 50mm apart.
1. Using a steel rule, measure the distance between the two connectors (in this case they are 50mm apart).
2. Calculate the distance that the two bend points need to be apart by the following formula. (Distance between bend points = distance between connectors – the diameter of RG402), in this example 50 - 3.6 = 46.4mm. This is a “rule of thumb” and gives answers correct to within 0.5mm when using this tool with RG402. For a more accurate calculation, we have written a spreadsheet calculator program see: http://www.rfshop.com.au/Portals/22/doc/cable%20bend.xls
(Right click and Save Target as:)
3. Round this result to the nearest 0.5mm (in this case 46.5mm). This is because the nearest resolution you are going to achieve using a steel rule will be 0.5mm.
4. Estimate or measure the distance that you need the parallel sections of the U shape to be. (Remember that the minimum that this distance can be is 19mm) (Shorter distances are possible but they need to be “cut back” after the bend is formed on a minimum of 19mm).
5. Add 2 times the distance estimated or measured in Step 4 to the result obtained in Step 3. (In this case 19 x 2 + 46.5 = 84.5mm)
6. Using a junior hacksaw cut a straight length of RG402 to 84.5mm.
7. Deburr both ends using a small fine flat file.
8. Using a steel rule and a marker pen, measure and mark the bend points 19mm in from each end.
9. Set the bend tool former (the centre, non rotating grooved cylinder) to push or pull position. Leave just enough clearance to allow the RG402 cable to be inserted between the former and the 2 rotating rollers.
10. Insert the pre cut RG402 into the position described in Step 9, ensuring that the cable is within the constraints of the grooves.
11. Carefully align one of the bend point marks on the cable with the centre of the former. (See Figure 1)
12. Holding the tool in one hand or mounting it in a bench vice, rotate the knurled handle of the tool (cw if pushing or ccw if pulling) until the desired angle (in this example 90°) is achieved. Some “spring back effect” will be observed so you will need to go slightly past 90° to get the desired bend angle.
13. Release the cable by rotating the knurled handle in the opposite direction.
14. Repeat Steps 10, 11 and 12 for the other bend point, ensuring that, in this case, the first formed bend is parallel with the desired direction of the second bend.
15. Using recommended preparation tools for RG402, strip the outer jacket and PTFE dielectric, point the centre conductor, and solder or crimp SMA (M) connectors to each end of the now U shaped cable.
16. Test for accuracy of your bends by carefully aligning the completed cable assembly with the 2 mating connectors. There may be some final “tweaking” of the cable assembly to achieve perfect alignment. This is very easily achieved by using your thumbs to bring the cable assembly into final alignment.
For U shaped cable assemblies where the mating connectors and not in the same plane:
1. Measure the difference between the planes of the mating connectors: (As an example I will use the scenario where the two mating connector planes are 3mm different).
2. Use the same instructions described for connectors in the same plane but in Step 5, add another 3mm to the overall cutting length.
3. Amend Step 8 to “Using a steel rule and a marker pen, measure and mark the bend points 19mm in from one end and 19 +3 mm (22mm) from the other end.”
4. Follow Steps 9 to16 above.
Examples of bend capability
Acknowledgements
Mr David Dettmar for the original design of this very cleverly designed tool.