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 Post subject: Good L-Style Protractor?
PostPosted: August 30, 2013, 12:19 pm 
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Joined: November 26, 2012, 2:29 pm
Posts: 71
Location: Sioux Falls, SD
Does anyone know of any good and inexpensive protractors that have a good edge on the backside? granted I could just subtract 2 degrees off every measurement I make to account for the error but I like to be as exact as possible (ocd much?)

http://www.sears.com/general-tools-ultr ... 934847000P
This is the one I have currently and it works okay but not perfect since the steel tubing has slightly rounded edges it isn't perfect and my angles are always off by a bit.

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PostPosted: August 31, 2013, 10:21 am 
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I doubt any of us cut material and weld to within 2 degrees.


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PostPosted: August 31, 2013, 10:49 am 
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Joined: July 7, 2011, 12:17 am
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Miatav8,MstrASE,A&P,F wrote:
I doubt any of us cut material and weld to within 2 degrees.

I machine my tubes to +/- 1/2 degree. On purpose :-D

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PostPosted: August 31, 2013, 4:13 pm 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
CodySimonson wrote:
Does anyone know of any good and inexpensive protractors that have a good edge on the backside? granted I could just subtract 2 degrees off every measurement I make to account for the error but I like to be as exact as possible (ocd much?)

http://www.sears.com/general-tools-ultr ... 934847000P
This is the one I have currently and it works okay but not perfect since the steel tubing has slightly rounded edges it isn't perfect and my angles are always off by a bit.


Are you trying to mark the tubes for cutting, Cody? If so, you might be better off setting the blade of your cutting machine (miter on a bandsaw or blade angle on an abrasive cut-off saw) using a simple, manual protractor with a set screw to hold the angle. Here is one that I've used successfully on both of the above devices. It has 1/2 degree marks, but it is very difficult to get that accuracy in real life (machining excluded).

Simple metal protractor ==> http://www.homedepot.com/p/Empire-Stain ... iJFXT8VWOE

Protractor in use on my bandsaw:
Attachment:
Simple-Protractor-at-Bandsaw.jpg
Simple-Protractor-at-Bandsaw.jpg [ 179.21 KiB | Viewed 1945 times ]


If you're cutting by hand using a hack saw, the above will not be useful except for marking a rough cut by eye, which you can get good at pretty quick. If you use the simple protractor to mark a cut ~ 1/16" to 1/8" (depending on context) longer than the final piece needs to be, you can hand file the surplus to fit pretty precisely. It's more work, and you have to have a good set of files, plus a vice to hold the tubes securely while you file and good lighting, but it can be done if you're patient. Below is an example of a complex tubular joint done using the metal protractor to mark a rough cut (typically within a degree with practice) and and hand filing.

I use 0.7 mm, red and blue, Sharpie markers to indicate where I need to file as I make the joints fit precisely. Otherwise, I found it too confusing to file accurately when you have the tube out and in a vice out of it's installed orientation in space.

Attachment:
File comment: Complex tubular junction done by hand with protractor, hacksaw and files.
Simple-Cut-with-File-Finish.jpg
Simple-Cut-with-File-Finish.jpg [ 154.65 KiB | Viewed 1945 times ]


Here is an inexpensive file set similar to what I use ==> http://www.harborfreight.com/5-piece-12 ... 60368.html

Now, I'm not the most advanced metal worker on this site and there are probably a half dozen better ways to do it than my way, but it's what I could figure out and do with the tools I had on hand at that time in my build. Let's see if the "horror" of my post motivates the better ones to respond. :lol:

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: September 2, 2013, 9:33 am 
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Location: Tallahassee, FL (The Center of the Known Universe)
Here at Team Slotus, we used a device that I think is properly called a "Carpenter's Triangle" a lot. It quickly became known in Slotus Speak as a Confuse-A-Cat, because that's what it did for the most part.
Attachment:
Confuse A Cat.jpg
Confuse A Cat.jpg [ 683.1 KiB | Viewed 1918 times ]
I can't tell you how many times it was rescued from the pine trees and weeds along the property line. The usual procedure was to lay it down on the piece one was working on, realize it was turned the wrong way, flip it over, realize it was still turned the wrong way, repeat one more time and then throw it like a boomerang into the bushes. (It never came back of its own free will.)

Look closely at the lower right corner and you can see the shiny places where I cut a bit too close to it with the jig saw. There's a blob of epoxy resin near the top-most corner, and several scratches in the surface from encounters with tree branches and rocks and such.

We also used the degree marks on the deck of James' ancient chop saw, otherwise known as "The Antichrist." The saw was called that, not James. Although... Well, never mind...

Team Slotus is happy to assist our fellow Locosters by providing a baseline for others to evaluate their methods by. :mrgreen:
:cheers:
JD "Bad Example" Kemp

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PostPosted: September 2, 2013, 3:36 pm 
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I'm not sure I understand your proble,. Is the protractor off calibration? Or is it difficult to get a good edge on round tube to align with your protractor? If it is the latter, then using a piece of 1/2" x 1/2" or so, angle iron about 4" long should help as a guide to square up with the tube. Something similar should work too. Just lay it on the tube, it will self-align to the tube. Then the protractor should have a nice sharp edge to fit against.

If your problem is the former, then ??????

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PostPosted: September 2, 2013, 6:03 pm 
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Joined: June 24, 2007, 6:04 pm
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rx7locost wrote:
I'm not sure I understand your proble,. Is the protractor off calibration? Or is it difficult to get a good edge on round tube to align with your protractor? If it is the latter, then using a piece of 1/2" x 1/2" or so, angle iron about 4" long should help as a guide to square up with the tube. Something similar should work too. Just lay it on the tube, it will self-align to the tube. Then the protractor should have a nice sharp edge to fit against.

If your problem is the former, then ??????


I am not sure either, I just a cheap plastic ' Empire' and it did everything I needed.

Al

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