Learning how to build Lotus Seven replicas...together!
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PostPosted: February 26, 2007, 12:52 pm 

Joined: January 22, 2007, 12:53 pm
Posts: 48
Location: ST. Clair Shores, MI
Figured I'd post this here as this method has saved my tons of headaches.
can be used with a chop saw or angle grinderor even a sawzall.

Chop Saw Mitering 101 (courtesy of PBB)

Cut Angle calculator: http://snip.awardspace.com/

Mechanically able, Monitarilly challenged

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PostPosted: November 18, 2007, 12:44 pm 

Joined: August 15, 2005, 10:13 pm
Posts: 7046
Location: Charleston, WV
So as not to tread all over their bandwidth, I will host the pic from their site. (Pirate4x4.com) I actually used this method to add some sidebars to a roll cage and it works great. Props those 4x4 guys for writing this up.

Next, what angle do you set the chopsaw to? Hint: It usually takes a pair of cuts between 20 and 30 degrees for a 90-degree "T" joint like the one in the above picture. Using two 45 degree cuts seems to make sense as a place to start, but is actually FAR too much and will leave large gaps if you try it.

I've seen this posted by various people on here so I don't know who to credit for posting it on PBB first. But here's the info:

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.

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*

What if instead of a "T" joint, I want the notched tube at a 15* angle with my first 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.

Written by Marc Googer
[Edited slightly for clarity by TNToy]

I used this to setup the cuts on the 1-5/8" tube in the top pictures (27* cut) and it came out very well.

chopsawmiter.jpg [ 26.07 KiB | Viewed 32904 times ]
chopsaw-notch-02.jpg [ 17.47 KiB | Viewed 32900 times ]
chopsaw-notch-03.jpg [ 23.57 KiB | Viewed 32902 times ]

He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.
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PostPosted: January 8, 2010, 4:33 pm 

Joined: August 19, 2009, 6:03 pm
Posts: 39
So therefore for measuring purposes, one must measure the total distance between, including approximately 1/3 diameter of each attaching tube as basis for initial cut? Is there a finite number for that?
Also, I seem to have misplaced link to round tube structural properties. Can anyone direct me to that link?

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PostPosted: January 8, 2010, 4:44 pm 
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Joined: November 14, 2009, 1:32 am
Posts: 700
Location: Rosser manitoba canada
Go to my thread in non traditional build logs and I will show you how to build your own tubing notcher from a piece of angle iron and a chopsaw. If the posts dont answer all your questions just ask more. :mrgreen:

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PostPosted: January 8, 2010, 9:29 pm 

Joined: January 5, 2010, 12:13 pm
Posts: 25
Location: Little Rock, AR
The examples are a bit counter-intuitive to me. I would think that joining same-size tubes should all require the same angle. In other words a 1" to a 1" should use the same angle as a 3" to a 3". Curious as to why this is not the case in the examples.

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Last edited by blueovalz on January 19, 2017, 10:32 pm, edited 1 time in total.

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PostPosted: January 9, 2010, 2:04 am 

Joined: January 14, 2009, 2:24 am
Posts: 505
Location: Edmonton, Alberta
The angle you use is dependant on the thickness of the tube, so I suspect his "base" angles are with a common size of tube. If the tubes had 0 thickness, then a 90 degree joint would mean cutting 45 degree angles on the tip. The thicker the tube, the less angle you want.

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