Gonna drop this here to archive. This post probably rambles but it has lessons to be learned and wisdom you can share of your own if you choose.
Never did find the answer how to figure out or compensate for joint angle change in a part with rotation in multi-dimensions. Anything past 5*-8* requires special math that I haven’t learned yet. You can easily adjust by sight and the seat of your pants for the mentioned angles just off 0, 90, 180, etc
For this tube it had to be right the first time. I don’t have 3d modeling software yet so I had to model in real time. This crude setup is going to evolve into a table fixture system that I am building within the next year along with a notcher that I have designed that addresses a problem nothing on the market is capable of.
Notes:
Tube spans 46-3/4 between 2 parallels in a horizontal plane
Tube has a single 47* bend 9-1/2” outside offset
22* prescribed joint (2D)
Tube tips 14*
Tipping the bend 14* downward out of plane from the joint location increases the angle required at the joint. But how is this figured? Doesn’t matter anymore because I’ve had to model a few tubes in a similar manner. The setup time is worth the accuracy of placing a tube correctly the first time without adjustments. Now I know the euphoric feeling those with cam capabilities and who build cam produced chassis’s enjoy. I hate walking back and forth across the shop several times dialing in a part and fighting my grinders with their short cords and worn out plugs hogging up my extension cords.
The rotation increased the joint angle from 22 to 25*. How? Why? Don’t care anymore. Another interesting thing. Although the tube in plane is tipped 14*, the axial angle of each leg is 5*. Now, for reference once I placed the notcher back on the fab bench, instead of solving for rotation, I measured angle of the opposite leg. 10* was the reference. Now is that coincidence or the sum of the axial angle of 5*? Below you’ll see my improv fixture beam. This 2x4 has been very handy. I tacked a stop for the bend, squared the tube, tacked angle guides, tacked a reference tube for the protractor and the legs are supported with 1.5” tubing notched at 5*. Once the tube was squared and tipped to the prescribed 14* I could easily square up the notcher and transfer to the table where it is mounted. At that time the 10* leg angle was acquired
This project has presented several new challenges that I haven’t encountered when working with tube. I had to work through them and discover the answer or process the hard way. It’s been with great success. Of 200’ of material, less than 3’ cumulative drop. That’s a good tape measure and lots of paper drafting for ya.
Said tube of this post required a single bend located in the center. I’ve done this once before with 1.5” @ 10* but I can eyeball a 4.5 clr pretty easy. I have a lot more trust and experience with 1.5 and haven’t worked with my larger dies much and never with my 1.75. My 1.75” 90* was compromised as it became a template after the fact. It was a piece that was marked for data acquisition during a 60* bend but the trigger stuck and I went 1.5* over because my oily hands couldn’t release the locking hasp. So I removed it to see if the increased angle would work and it would not so I continued the markings and finished it to a 90*. The stupid hasp was murdered and thrown in the garbage like it should’ve been 3 years ago. So, very important people, if you’re actually reading this, when bending a 90 or 180 template, cost of material gauge, whatever, it must be one continuous bend and never removed from the die. Checking for spring back near your final angle is acceptable. If removed, you cannot collect any data to utilize in bend tech or similar.
This bend stumped me. I wanted to be a rock star and place the bend dead center with no adjustments and because it was my last piece on a couple of accounts with no room for error. I was missing values needed to solve the formula (bad order template). I’ve become familiar with bending tube in my head utilizing the info from a quality template. It’s fairly easy. I tried 2d drafting on the floor but I was approaching it “backwards”. Reached out for help but in doing so I studied Rob Parks guide and finally it clicked how it applied to what I was trying to accomplish. It’s basically what I’ve been doing already for multiple bends. Excited that I learned something new and dusted off the 3 year mental cobwebs. It’s linked on rme ages ago and it’s hard to find on pirate ( 🏴☠️ if you know where to look, there’s amazing tech - not in the forum) I’ll summarize. To make a circle you must first make a square. I drew a box on the floor with soapstone using my known constraints. Then connected my angles. 46-3/4 x 10. You can use inside, center or outside dimension references but don’t confuse yourself. I worked with outside dims. Now because of the bend radius I did lose approx 1/2” of my 10” offset but that’s ok because I had wiggle room there and it wasn’t worth compensating on my floor draft. Next I confirmed/collected the angle of 47*. This is what I had on paper. Slide the template into the corner of the angle and square the legs up with the constraints on the floor. Measure from your die reference to the end of the leg accounting for cut/notch length. 1/2” is typically the most efficient notch depth. All my tubes are calculated with a 1” minimum over length. Be sure to account for the inside length of the leg. In my case I had a 56” tube/28” legs to work with. You’ll see I determined 23-1/4 die reference location. Well I didn’t trust my math because I had already rambled a bunch of incorrect calcs to another forum member and wasn’t sure which way my compass was pointing so I erred on the side of caution that the leg behind the bend wouldn’t come up short. Well turns out I could’ve solved the formula and placed my C/L in the middle of the bend.
23-1/4 x 2 = 46-1/2
56- 46-1/2 = 9-1/2
9-1/2 / 2 = 4-3/4
28 - 23-1/4 = 4-3/4
4-3/4 / 2 = 2-3/8
A 47* bend on a 5.5” clr uses 4-3/4” of material. My 28” center of tube is off by 2-3/8” but now I know and am writing these damn notes down in a shop bible.