Been flat on my back most of the week. Literally. Readers will know I pulled a lower back muscle trying to move my top box about a week ago. Just starting to heal. I started training again, working in the walking pool, whirlpool and steam room.
As we last left our top box cart/workstation I was just starting the fitment and initial welding. To notch the tubing, or cope the tubing as some call it, I use a JD2 Notchmaster as show in this previous post. There are other notchers and methods as well. Some fabricators use chop saws and grinders to cope the tubing. Ant Fab did the 00 car using that method. I prefer a hole saw type notcher. I usually cut the pieces to length, going a shade over and then cope to fit the piece as I go. Bendtech software can provide cutting templates to use for the copes but I’ve not used them in production, only in testing. They seem to work well so I may use them as I finish the Miata cage later this year.
This is what you want a good cope to look like.
For MIG welding you can leave a bit of a gap, but not too much. Ultimately you want contact with the tubing wall all the way around. If you are TIG welding, it becomes much more critical because the GTAW, or TIG process as it is commonly known, does not handle gap filling as well as MIG. In the best of worlds you want no gaps no matter what process you are using. The edges of the cope get cleaned up with either a grinder or a disc or belt sander. I use an HF 6″ bench grinder, an HF 12″ bench disc sander, both great for the money. They’ve been champs for me. I use the sander most of the time to clean the copes. I use CGW grinding wheels and Norton sanding discs and stay away from the HF stock abrasives.
Here the welding has started. The frame is tacked together before any finish welding to minimize heat distortion and insure that everything fits. Sometimes getting the welder settings correct for a new material, joint or project take a couple of passes to set. Below, is one of the first finish welds. A bit too much wire speed (amps) and almost the right amount of “heat”, or volts. It’s ugly but it will hold. As you complete the finsih welds you “chase the heat”. That is, you weld on one end of the pice, then weld on an opposite end while the first joint cools. This is also a method to reduce heat distortion.
The end of the tube has been extended from almost the intersection of the cope. There was a measurement error and on a piece like this it’s OK to add some tube. I wouldn’t do that on something like a cage though I have seen others do it. In the race fab business it’s considered poor practice to extend cage tubing and some sanctions will not allow extended tubing. After the tack, each joint is hit with 120 grit flap wheel to knock off the mill scale and prep the joint. I then clean the joints with acetone. The method used to clean and prep the joints varies depending on the material and welding process. With mild steel and MIG this is acceptable. In fact, some won’t do the acetone wash. With TIG and aluminum or 4130 the prep process as well as the welding application will change. I’m using a Lincoln Pro MIG 180, 75/25 argon/CO2 gas at 30 cfm with ER70S-6 wire.
For the casters I wanted to use some 3/8″ studded casters I had left over from another project to save a bit of money. They are rated at 150 lbs each so they should be fine for the job. To mount the casters into the ends of the tube I fabricated bungs from 3/16″ plate. I looked for pre made bungs but didn’t find any locally with that thread size for 1″ tubing. Washers with nuts welded to the back weren’t going to cut it for this one.
First, I drilled the plate with a 1″ hole saw in a drill press. I’d been using the HF small press but after 6 years or so of light use, it burned up. It was replaced with a 10″ Craftsman bench top drill press. It’s held up well and is is a good size if you don’t have room for a floor mounted drill press.
And of course you’ll need some machinist’s Astroglide…
We end up with this…
Then weld them to the bottom of the tube, hand drill to the tapping size, tap the hole, add the caster. The reason I did it in that order instead of prefabbing the bungs was because I wasn’t sure of what sort of heat distortion and fitment I would get. If for some reason they weren’t exactly perpendicular to the tubing wall, I could fix that after the initial piece was welded in place.
Now that basic fab is almost complete, we’ve got expanded metal shelves, testing then finishing left for our final installment.