Jigging Tubing Before Weld

[SerpentEagle]

I'm looking to eliminate the need for gussets on many places on the robot next year, hopefully cutting fabrication time down by a good amount. I was wondering how teams jig together their frames prior to welding (other than using gussets). A good example that I could think of would be 254. Any ideas?

[s-neff]

You can do flat weldments laid out on plywood (with dummy shafts to preserve hole alignment). This was on 192, doing welded drivetrain module frames. As long as the board was flat, we didn't even really need to put much vertical constraint on the pieces - just using a pneumatic nail gun to put wood blocks in to hold everything in place was fine. We'd tack weld one side, then flip it over in the same jig to tack the other side, then finish the welds outside the jig. Some rework occasionally required for warp. All student welds, what do you expect.

On the Mini-Baja race car team in college, we ended up designing 3/4" particleboard jigs for the tube chassis with waterjetted cutouts in the exact design locations for each tube, and laying everything out before welding. It helped that we were using the same particleboard that our tube sponsor packaged the pieces with for transport (free), and that our waterjet time was free from the ME department in return for help with the upkeep.

[Cothron Theiss]

Originally Posted by SerpentEagle

I'm looking to eliminate the need for gussets on many places on the robot next year, hopefully cutting fabrication time down by a good amount. I was wondering how teams jig together their frames prior to welding (other than using gussets). A good example that I could think of would be 254. Any ideas?

Ok, so why exactly are you wanting to do away with gussets? In a lot of cases, gussets can be stronger than just a weld and if you want to change something or you need to remove a tube, gussets can taken off and re-assembled at a competition. I'm not saying welds are bad, just making sure you consider the pros and cons.
Also, many teams assemble their tubing with gussets and weld the gussets onto it. That ends that whole quick modifications thing, but it's a great way to do fabrication.

As for your actual question, there's tons of different ways to do jigs. I assume you're welding square and/or rectangle box tubing and not round tubing. The more you can know about what you're welding before hand, the easier you can make your jigs to use. You can make just a flat plate with pre-drilled holes. Use the holes to clamp down and/or insert pins to locate the different parts. You can set the pre-drilled to the angles you might commonly use, like 15, 20, 25, 30, and 45 degrees. You'll have to figure out what angles you'll want to use. It depends on what kind of tolerances you want to hold, and what equipment you have. Do you have a mill? If you can put some time and effort into the jig, you can get very tight tolerances on the angle itself.

Originally Posted by s-neff

On the Mini-Baja race car team in college, we ended up designing 3/4" particleboard jigs for the tube chassis with waterjetted cutouts in the exact design locations for each tube, and laying everything out before welding. It helped that we were using the same particleboard that our tube sponsor packaged the pieces with for transport (free), and that our waterjet time was free from the ME department in return for help with the upkeep.

I'm working on making jigs for our car this year. We often spend more time on the jigs than the welds themselves, especially when the angle of the weld is especially critical.

[GeeTwo]

Originally Posted by Cothron Theiss

We often spend more time on the jigs than the welds themselves...

I just had this same conversation about two hours ago by e-mail on a totally different topic -- cutting PVC to provide proper tension to blackout curtains in frames of temporary cubicles. About three months ago, I cut over 50 pieces to one length and 100 to another, but spent way more time on getting the jigs right than on the cutting. (Actually, I did these on opposite sides of the same piece of lumber.) Someone else is interested in copying my pattern - glad I didn't chuck that jig!

Back to the welding jigs -- we only did a welded chassis one year, and I only went to one welding session. I recall that Bruce had a pretty generic clamp that could do just about any weld on square/rectangular tubing or c-channel and sometimes angle, as long as the pieces were within the same plane, or (with spacers) nearby parallel planes. It was a long time ago, but it seems that it had two square j-hooks which could be put in holes spaced every inch or so along a "plank". It required manual alignment of the stock for each weld, but it secured the stock well for the weld.

[ajlapp]

I would say that 254 uses gussets extensively...they typically rivet their tube together with plate and then weld them in place.

See attachments. We regularly do the same thing.

[arc25565]

Our team primarily uses welding to attach parts together on out robot. To keep everything square I usually just clamp everything to the table or to a flat sheet of metal. I then do weld everything together and let it cool still clamped to the table. Vice grips are your friend.

[BrendanB]

1058 used an extensive amount of Versa Frame from Vexpro this year and a group of students welded our frame this year in house. We purchased a few packs of gussets from Vexpro that we could use to pre-assemble areas of the robot before sending it to the welding group.

It was quick and easy to replicate. After the first round of welding was complete the gussets were removed so the welders could finish the job.

[frcguy]

Originally Posted by ajlapp

I would say that 254 uses gussets extensively...they typically rivet their tube together with plate and then weld them in place.

See attachments. We regularly do the same thing.

We'll be doing this next season as well.

[Cory]

Originally Posted by SerpentEagle

I'm looking to eliminate the need for gussets on many places on the robot next year, hopefully cutting fabrication time down by a good amount. I was wondering how teams jig together their frames prior to welding (other than using gussets). A good example that I could think of would be 254. Any ideas?

As Anthony mentioned we use gussets almost exclusively for weld prep.

It saves so much time for us and the welder and it yields far superior results in terms of alignment/squareness/flatness/etc of the finished weldment.

[Richard Wallace]

Pre-weld assembly can be done in many ways as described by earlier posters. We have used all of the above.

When our design calls for an unusual weld angle or bearing location, we have also used jigs. Here is one: link.

[SerpentEagle]

Sorry for the late response, but thanks for all the replies! Very insightful!

[IKE]

Originally Posted by s-neff

You can do flat weldments laid out on plywood (with dummy shafts to preserve hole alignment). This was on 192, doing welded drivetrain module frames. As long as the board was flat, we didn't even really need to put much vertical constraint on the pieces - just using a pneumatic nail gun to put wood blocks in to hold everything in place was fine. We'd tack weld one side, then flip it over in the same jig to tack the other side, then finish the welds outside the jig. Some rework occasionally required for warp. All student welds, what do you expect.

On the Mini-Baja race car team in college, we ended up designing 3/4" particleboard jigs for the tube chassis with waterjetted cutouts in the exact design locations for each tube, and laying everything out before welding. It helped that we were using the same particleboard that our tube sponsor packaged the pieces with for transport (free), and that our waterjet time was free from the ME department in return for help with the upkeep.

I have used very similar method for years. Large flat piece of plywood, with a great deal of care on the layout. Wood blocks (pieces of 2x2) pre-drilled and screwed into position to hold the pieces in place.

One problem with this style is if the fixture isn't symmetric, you may want to apply more weld to one side than you should. Also, aluminum heat expansion can be pretty large if you try to do your welds fully within the weld fixture.

If you have the ability to do what 254 is doing with the rivet then weld gussets, I think this is superior joint and fixture. Often "butt" style welds can be compromised during the rigors of play in FRC. I have personally experienced as well as witnessed a lot of failures with this style of joint. Using a weld in place gusset/strap piece is usually the remedy most teams that weld employ into their future designs.

[Tom Line]

Our robot issues in the Michigan State Finals were directly due to multiple end-welds failing on our arm after a collision. Our long fix was to do exactly what 254 does - gussets welded in place. If you are into the physics of it, a simple free body diagram will show you how it decreases forces and torque on the weld by orders of magnitude.

Edit: And when you rivet the gussets in place, remember that it takes at least 3 rivets in a row to make a decent joint. 2 rivets in a row just makes for a wiggly mess.