Simple workshop technique that shows how to straighten Microbore copper tube using basic workshop tools
This post shows a technique I’ve used to straighten 10mm Microbore copper tube and forms one of a series of video’s I’ve made to show how I’ve constructed my Quadrifiliar Helix antenna or QFH as it’s more commonly known.
- Tube cutter
- Mold grips
- Lump hammer
- Fine grade file
- Flat file of smooth grade
- Marker pen
- Straight edge
- Bench vice
This technique is not 100% efficient and will produce some waste but at the same time it does produce some good results using some basic workshop tools.
PURCHASING MICROBORE COPPER TUBE
10mm Microbore tube is usually sold in coils rather than straight lengths.
The first thing I do is carefully uncoil the tube by hand and lay it out on the floor. Despite best efforts it is very difficult to fully straighten the tube.
MEASURING THE MICROBORE TUBE
For one part of the antenna I need a piece of tube that’s 182mm long so I’ve added an additional 100mm and cut a piece that’s 282mm long from the uncoiled tube.
The reason I’ve added the additional 100mm is because this technique requires each end of the tube to be squeezed and the squeezing causes some distortion to the tube as you can see in the picture below.
SQUEEZING & BENDING THE TUBE
I place one end of the tube in the vice to a depth of approximately 10mm and tighten up the vice to squeeze the end.
I do the same for the other end of the tube and bend the tube 90 degrees.
STRAIGHTENING THE MICROBORE COPPER TUBE
I attach some mole grips to one end of the tube and strike the mold grips hard using a lump hammer three or four times. You’ll usually feel the copper stretch out on the first or second hit. You need to be careful not to overstretch the tube.
CHECKING THE STRAIGHTNESS OF THE MICROBORE TUBE
I remove the tube from the vice and check the straightness using a straight edge. If your not happy with the straightness of the tube you can repeat the last step again.
MARKING THE MICROBORE TUBE READY FOR CUTTING
Happy with the straightness of my tube I place it in the vice and tighten up just enough to hold the tube in place.
Using a marker pen I mark one end of the tube approximately 15mm from where the distortion finishes.
CUTTING THE MICROBORE TUBE
Using a tube cutter I cut off one the end of the tube.
USING CALIPERS TO MAKE PRECISE MEASUREMENT OF THE TUBE
Using calipers I make a precise measurement of 182mm from the end of the tube.
CUTTING THE MICROBORE TUBE
Using a tube cutter I cut off the other end of the tube.
Using a straight edge I check the straightness of the tube.
And that’s it, with the process now complete I now have a straight piece of tube 182mm long and can now use this for constructing my antenna.
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73 de M0NWK