chop saw notching?

[andyr354]

Have heard it mentioned a bunch of times, but have yet to find a decription of the process.

Any writups anywhere on how to go about it? It is either this or buy a HF notcher for the time being to get by.

[guidolyons]

Here is one from Marc Googer on www.Offroadfabnet.com :

The chop saw method, if understood, is a science. With known tube size and joint angle, tube can be notched with great accuracy. The notch is achieved by cutting two opposing angles on one end of a piece of tube, to form a point. The cross-section of this cut will be an elliptical cut due to the shape of the tube. Changes in both of the two angled cuts must be made for the intersection angle and the size of the two tubes being joined. The only real limitation is the max angle of the chop saw.

You start with what I call the base angle. This is the angle of both cuts if the joint was 90*. For an example, I am fitting Two tubes together that are both 1.75", at an 90* joint. The base angle, or the angle of both cuts is 28*. These two cuts must meet at a point, and the point must also be centered on the tube.

What if I want a 15* joint with my 1.75" tube???? You must start with your base angle, which was 28* for 1.75"(remember above), and subtract 15* from one cut, and add 15* to the other cut to form a perfect notch. So now I must make a 13* cut and an 43* cut with the point centered on the tube. Perfect coped joint, with no grinding.

Remember your base angle will change with the tube being cut and the tube that you are fitting to.

Here are a few examples of base angles...

2.0" to 2.0" tube, base angle of 30*

1.75" to 1.75" tube, base angle of 28*

1.5" to 1.5" tube, base angle of 26*

1.25" to 1.25" tube, base angle of 22.5*

1" to 1" tube, Base angle of 20*

Now to fit different size tubes together

1.75" to 2" tube, base angle of 25*

1.75" to 1.25" tube, base angle of 45*

1.25" to 1.75 tube, base angle of 20*

1" to 2" tube, base angle of 12*


Written by Marc Googer

[chumly2071]

Another (http://www.pirate4x4.com/forum/showthread.php?t=293993) thread detailing this method.

[guidolyons]

Yeah that's other thread I was thinking of...just couldnot remember where I had seen it before, and I had the other link handy. Lots of good info.

[tennessee rockhumper]

nice post, guidolyons. thank you for the info. im gonna apply the money i was about to spend on a new notcher to a miter band saw to make that easy.

[tsm1mt]

I finally got this thing down last weekend.

Biggest mistake I made in the past was this "make two cuts" thing.. I always wanted to make a "V" INTO my tube (imagine the tube coming up from below) and then use a grinder to clean up the "V" into a "U" sort of shape.

Never worked well.

So I used the hole-saw a lot. Even bought a hole-saw notcher that I've never used, and might not ever use now.

I hole-saw notched a tube and then I was rolling it around in my hand and finally noticed the trick to the "chop-saw" method.

Take your notched tube and roll it so the "ear/lip" is up and down, with the notches to the "sides".. and suddenly it looks like..

/ \

(not the V cut)

Ah-hah!

I actually use my band-saw to make the cuts.

I use a web app that makes some lines/elipses on the screen that you print and wrap around the tube and use a marker to trace the lines.

If you were patient, you could cut this with a hack-saw or plasma or something.. but you can also take it and just lay it on it's side, so to speak, imagining a line running from the "not notched" ear to ear and set that line vertical.

Then line the bandsaw up with the marked lines, and let it make a "straight" cut through the tube.. and it's notched.

I'll try to get some pictures next weekend.

[TNToy]

Basically, what they said...Yeah.

Lop off the corners of the tube at an angle so that the tube changes like this:

From this: (Ignore all of the periods - they're just to space the lines out properly)

-------
|........|
|........|
|........|

To this:
.....--
../......\
/..........\
|...........|

In other words, instead of cutting a V-notch INTO the tube, cut the end to a point. Turned sideways, it's a nice smooth curve that will closely follow the other tube once you get the angle right. You also have to round the point off with a grinder. :)