Notching the tube is the final challenge before welding up the links. There are three basic methods for notching tube: tube notcher, chop-saw, and template. Using a tube notcher is the most obvious method – providing you have one. The only caution is that many notcher’s may have a difficult time getting through two inch diameter, half-inch wall tubing. If you use a hole-saw type notcher, be particularly careful of it catching in the cut and trying to break your wrists.
With a little patience and practice, you can cut excellent notches in tube using a chop saw. The first step is to mark the centerline of the tube in 2 places exactly 180* apart. Next, set the required angle on your chop saw and chuck the tube in the saw with the blade just touching the first centerline mark (Fig 2). Make the cut (fig 3), and the tube should then look like fig 4. Next, rotate the tube in the saw 180* until the blade just touches the opposite centerline mark (fig 5). Make the final cut, and you will be left with 2 small slivers of tube and a well-formed notch for joining to another tube (fig 6 & fig
. To make quality, accurate cuts you need to use a decent chop saw with a fairly rigid base and vice, and to use a quality abrasive cutting wheel designed for cutting tube. I prefer Walter brand cutting wheels as they are good quality, last well, and indicate on them with a little icon whether they are suited to cutting tube. The key to success with this method is how accurately you calculate and make the two cuts. Figure 9 illustrates the angle you are setting, and Table 3 gives some values for the cut angle for various sizes of tube. Generally, the larger the angle, the deeper and more narrow the notch. Figure 6 shows a notch cut at 30* and figure 7 shows a notch cut at 45*. Because all chop saws will vary a little and even the best are only capable of limited accuracy in angles the best results will be obtained from using the values in the table as a starting point and then proceeding to practice with your actual tube, keeping a 4.5” angle grinder handy to clean up the notches. After the initial cuts, test-fit the tubes and make any required touch-ups to the notch with the grinder (fig
. Note that the values in Table 3 are for joining two tubes at 90* to one another. If you want to join the two tubes at an angle (either to offset the link from the joint, or more likely in other tube work such as roll-cage building) you must adjust your cuts as follows. Take the angle at which you want to joint the two tubes, and then modify the initial cut angles by adding this value to one, and subtracting it from the other. For example, if I wanted to join a 2” tube to a 2” tube, the initial cut angle is 30*. If I wanted to join the tubes at a 15* angle, I would add 15* to one cut and subtract it from the other. In this way I would make one cut at 45* and the other at 15*. The values in the table were calculated and kindly provided to me by Marc "Tigweld" Googer. Marc notes that the figures given are for .120" wall tubing and that wall thickness can dramatically affect fit. Thicker walled tube will require either an adjustemnt to the figures shown or some post-cut cleanup with the angle grinder. The only limitation to the chop saw method of tube notching is the angle-capacity of the chop saw – most do not cut angles greater than 45*. NEVER ever be tempted to bypass the chop saw’s vice and simply hold the tube at a steep angle – no matter how strong you think you are there is a very good chance the blade will bind in the cut, rip the tube from your hands, possibly taking finger tips with it, and fling it across the shop with frightening force - as usual - ask me how I know this!. If in doubt about the angle to use, it is best to cut a little shallow (smaller angle) and finish the notch with a hand-held angle grinder.
Table 3 - cut angle for various sizes of tube
(Data kindly provided by Marc "Tigweld" Googer)
OD of tube
being notched (in)
OD of tube
joined to (in) Initial cut
angle (degrees)
2 2 30
1.75 1.75 28
1.5 1.5 26
1.25 1.25 22.5
1 1 20
1.75 2 25
1.75 1.25 45
1.25 1.75 20
1 2 12
The third method for notching a tube is to use a computer program that will allow you to enter the tube dimensions and will then calculate and print a template for your notch. You can then cut out this template, trace it onto the tube, and use any of several methods to cut along the lines of the notch (chop saw, 4.5” angle grinder with cutting disc, plasma cutter, etc.) Depending on how rough your cutting was, you can then clean up the notch with a 4.5” angle grinder to get a perfect fit. One such program available on the internet is Winmiter. It is a shareware program originally written for bicycle building enthusiasts. It accepts inputs of: large tube diameter, small tube diameter, angle of joint, and centerline offset, in metric or imperial units. It will then compute and display and/or print a simple template. I used this method for notching the 2” x 3/8” tube for my front lower links and it worked fairly well. Fig 10 shows the template cut out and taped to the tube, ready to be traced. After cutting the notch with a plasma cutter I then used a grinder to clean it up, pausing periodically to check the fit (fig 11).
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Fri Feb 01, 2008 11:16 am