BASIC TUBE NOTCHING 101
TUBE NOTCHING MADE EASY USING A HOLESAW NOTCHER
Many a notcher manufacturer will demonstrate how a notch is made using their machine but that is the easy part of notching. It's the right placement that's critical and makes the difference between a good joint and one that requires either a lot of gap welding or in worse case, starting over again.
Making a wrong notch is costly in both time and money. Using a common holesaw type notcher such as the NotchMaster by JD2, we'll outline the following procedures to help simplify and hopefully make for a better and closer fitting notch for many a fabricator. These procedures work - regardless of the angle and regardless whether the joining tubes are parallel, divergent or skewed.
A basic notch starts with laying up the tube where you want the joint. Temporarily secure it so the tube can be easily marked so it can be correctly placed into the notcher. Position yourself to view both tubes at the intersection from a right angle perspective so you can accurately mark both the centerline of the tube (to be notched) and the intersecting point(s). The more accurate the marks - the better the resulting notch will fit. Always mark the point of intersection on the obtuse (or greater) angle side as shown in the picture.
A Centerline Finder may be helpful in locating centerline. Read more about the Finder below.
Record the acute angle(s). Know that most notchers consider a right angle notch as 0degrees so convert your measurement to a notching angle by subtracting them from 90degrees. For example: if the angle measures 70degrees then the notcher should be set at 20degrees.
A handy gadget that is helpful in marking the intersection is a snap-collar locator. It can be slid into position for accurate marking with a nice straight line and if the tube has to be rotated, when positioning the tube into the notcher, a snap-collar makes for an easy reference - especially if the tube has to be flipped over to notch from the opposite side. Snap collars can be purchased at: http://www.medfordtools.com/syncnotcher/snapcollar.html
Another important point is to make the tube the right length before you begin a notch. You don't want to leave the tube long and just 'plow' through the notch because doing so takes longer to notch and will put more wear on the holesaw - besides leaving a feathered edge that will need to be ground back. So before you place the tube into the notcher, cut it to proper length.
Set your notcher to the necessary angle. Position the tube into your notcher with the centerline mark showing at the very top. (In some cases the mark may end up on the bottom.) Regardless, this places the tube at 90degrees in relation to the center of the holesaw. The edge of the holesaw should be positioned in line with the intersection mark. If you're using a snap-collar be sure to slide or remove it out of harm's way. Make the notch.
In these two pictures you see that the edge of the holesaw is targeted to the intersecting mark. Note again the amount of tube that extends beyond the intersecting mark. For any angle 45degrees or greater there is no tube beyond the mark. For angles less than 45degree there should be some extra as explained above.
Quite often it becomes necessary to rotate the tube 180degree when notching at the opposite end. Using a snap-collar makes it easy for accurate referencing. Or just eyeball the end of the tube and mark it as close as you can. Remember, the more accurate the mark the better the fitting notch will be.
As was mention at the beginning, the basic procedures outlined above will work for all joints regardless if the joining tubes are parallel, divergent or skewed. Spanning between two tubes that are skewed (not in the same plane) is really no more of a challenge than working with any other span. What is important to know is that as long as the centerline of the tube to be notched is correctly marked in relation to the joining tubes - your notch will come out correct.
Just remember to position yourself so that the view is from a right angle perspective. Skewed angles can play with your eyes so it's important that each joint intersection be viewed separately. In other words don't try to mark both intersections while standing in one spot. Take the time to view each joint individually.
Purchase the Centerline Finder Here.
Now that the basic guidelines have been established, here is a short cut that can save you even more time.
Here's how: Simply lay up the tube as you would normally and record the angles as before. Don't bother to mark the centerline and intersecting points yet. Use a tape and measure the distance between the two spanning tubes and cut the tube somewhat longer.
Notch one of the ends at the measured angle without any regard to a centerline because at this point there is no need.
Take that tube and puzzle the notched end up against the tube to where that joint will be.
Secure the tube in place and follow the procedures for marking the other end as outlined previously, which, in summary are:
You can get a good idea of what the angle should be by laying a square-cut end of a tube up against the point of attachment and visualize the gap as an angle.
You can see where there is a bit of a gap where the tubes fail to meet.
One last notch we'll consider is where an additional member is to be joined at a 90degree junction. Typically the 90degree joint will already be welded together so the new notch may have to be relieved on the inside for a snug fit - the snugness will depend on the quality of the weld itself.
Lay up the tube and mark the intersections and centerline. Cut the tube to length with that length being about the diameter of the tube past the intersection (indicated by the dashed line).
Cut the tube to length at the dashed line.
Cut the second notch.
This particular notch, as shown, fits rather well without having to relieve the inside of the notched tube.