Hydraulic-Powered Tubing Bender

I am a member of a organization called Willoughby and Baltic, based in Somerville, MA. With my membership I get access to three spaces, including a fully equipped wood and metal fab shop. I had already utilized the space for a couple small tasks, but I wanted to try something big to really get comfortable working with the machines, and to push the limits of my fab skills.

I decided to build a hydraulic tubing bender. I chose this because, one: I had some plans, but two: this thing is big. It is made from 1/4″ thick 2″ dia square steel tubing and some cold rolled 5/8″ thick by 2 1/2″ wide steel bar. It is operated with a 3 ton hydraulic ram. It is capable of bending up to 2″ dia 0.120″ wall DOM tubing.

The die around which the tubing is bent is availble to purchase for a couple hundred bucks, but there’s a Bridgeport milling machine in the shop, so I figured I’d go for broke and see if we couldn’t make it in-house.

a big piece of steel

Here’s a picture of the slab of steel that I found in the Bargain Barn at Logan Steel in Meriden, CT. That’s a 10″ dia 2 1/4″ thick plate…well actually it looks to be cut from bar stock. Very big bar stock.

Dave with Bridgeport

Here you can see Dave helping out Ian, another member. Dave spent literally dozens of hours milling this rusty hunk of steel into a beautiful precision tool. Actually it’s not quite done yet, but I’ll post pictures when it is. Just in case anyone is wondering, no it’s not worth making this piece yourself…that is unless you are as insane as Dave and want to spend hours poring over a milling machine just to make one piece of awesome metal that you can be proud of.

some pieces of steel

Here’s a picture of some tubing cut up. I made the first cut using a metal chop saw (it’s like a miter saw with an abrasive cut-off wheel). It was loud, messy, and took forever. To add insult to injury, the piece came out under-dimension.

close up of steel

Here’s a close up with a battery in the frame for size reference. If you’re not used to working with metal this thick (and i wasn’t) it is a whole different ballgame.

the horizontal band saw

Next I tried the horizontal band saw, which looks like it should be in a scrap heap. I love this tool. You have to stand there, applying oil and carefully lowering the saw, but the cuts were way better. The cuts were not completely square, but they were close enough for me.

close up of steel

Here’s a closeup of the saw right after I made a cut.

After I cut all the pieces I had to drill several large holes. I used calipers to scribe lines into the pieces which intersected at the hole locations. I then used a center punch to mark the center of the holes.

the drill press

Unfortunately there was one problem after another with the drill presses at the shop. Two were underpowered, and one was beefy enough, but the table was completely solid with no way to mount a workpiece. So I had to drill and tap some steel bar to insert a couple 3/8″ studs and then clamp the whole thing to the table so that I had something to hold down my work.

I’ve never had to drill 1″ diameter holes through over an inch of steel, so this was a learning experience for me. The procedure I used was to first put a 1/8″ drill bit into the drill press chuck and center the work piece under the bit. You can tell it’s centered if when you lower the bit into the dimple you made with the centerpunch, it doesn’t skew to one side or another. You will have to check this from two sides to make sure you’re completely center. When it was center, I drilled a 1/8″ hole, then changed the drill bit to 1/4″ and drilled a slightly larger hole, then kept stepping up 1/8″ each time til I got to the right diameter. Two tips I can give – use lots of cutting oil, and watch your RPM’s. For steel, you have to go pretty slow. Google “cutting speeds” and you should find lots of stuff on what RPM’s to use based on what size drill you’re using, etc. In my case, I would have liked to get the drill press to go slower, but I was at the lowest rpm’s already and so I had to just go really slow and put up with lots of smoke and chatter.

After having minimal success with the drill press, I was able to get some time on the Bridgeport and finish up the drilling. This was a WAY better solution. I was able to precisely place the workpiece and drill accurate holes at the right speed. This time I just put the piece in the vise and used the table to position it. I didn’t have to rely on the center punch marks that I made, although I found most to be pretty darn accurate. I started with a center drill bit to mark the piece, then drilled the same way as before, stepping up bits in 1/8″ increments. I found that the center drill was key – it’s a really short drill bit with a thick shank, meant to only make a dimple in the metal. If you just start with a small bit, like 1/8″, it will wander on the workpiece before it digs in, and your holes won’t be accurate.

Most of the cutting and drilling is done at this point. Here are the pieces, waiting to be welded up.

At this point, most of the frame is welded. This is really the first thing that I’ve welded, so I learned a lot along the way. When you weld, you’re literally liquifying metal. As that metal solidifies and cools, it contracts. It’s important to clamp down everything exactly where you want it, then tack-weld the pieces together for stability before you make your final welds. I had read a lot about this, but I didn’t know just how much metal will warp and how much force it exerts. I tacked a piece of metal across the two vertical posts that you see to hold them at the correct spacing. After I finished all my welds, I ground out the tack welds and the vertical posts went *TING*! They snapped out of place and ended up 1/4″ too close. You might notice some threaded rod going through the top set of holes on the vertical posts. I had to force them back apart so that I could then weld in a horizontal brace.

Here it is just about finished. Notice the brace welded along the diagonal supports. It was a proud moment when I installed the bending arm and hitch pins and everything fit!

In the background of the last picture you can see Doug preparing for the MIG welding class that I helped him teach that Saturday. Here he is cutting some metal pieces for the students to practice on, and then testing out the welder.

With the bender’s frame done, I then focused on the die and block that forms the tubing as it is bent. While at Logan Steel I also managed to find a perfect block of steel for the tubing guide. The dimensions were almost exactly what I needed except for the length – two times too long. I cut the piece in half with the horizontal band saw and will use the other half in the future for another size tubing. This block will be for 1.5″ diameter tubing. The cut with the bandsaw is far from square, so here you see I have milled the piece flat using the Bridgeport and a 3/4″ end mill.

I needed to remove a 4.5″ x 0.875″ section in the center, so I cut it out with the bandsaw and milled it to the proper dimensions. I first tried making the tubing groove by mounting the piece directly to the mill’s table and making passes with a 1″ convex radius cutter. The cutter could probably use some sharpening because it was slow and not so pretty. I made thousands of tiny shards of metal that were just attracted to my skin. I was still removing pieces of steel from my hands 2 weeks later. After this ordeal I switched tactics and mounted the block vertically to use a 1.5″ end mill. The finish was much nicer and the swarf wasn’t as dangerous.

drilling the mounting hole for the follower block

Here I am drilling the 7/8″ mounting hole. The ribbons I made look pretty, but they whip around with the bit and can cut you easily if you’re not careful. You can see they get long enough to reach the quill feed handles.

Here’s a closeup to show the razor sharp ribbons.

Dave did most of the work on the bending die, but I was left with the challenge of making a 1.5″ concave groove around the convex surface of the die. I only had a 1.5″ end mill with a flat bottom (not a ball end). The trick was to mount the die to a rotary table then mount the table vertically on the Bridgeport. I lined up the bottom of the end mill with the center line of the die, then rotated the die counterclockwise. This way I was able to use the bottom of the end mill to remove circular grooves about 25 thousands deep with each pass. When finished I was left with a groove slightly under 1.5″ diameter. End mill sizes are nominal and this one had a diameter smaller than it’s markings so I had to make a few finishing passes to enlarge the groove to 1.5″. The pattern you see on the groove is the result of vibrations during finishing passes. The vertically mounted rotary table wasn’t extremely rigid. Contrary to intuition, this wasn’t a problem when I was taking deeper passes. This is probably because I had a more constant cutting force that was in the same direction the whole time. Taking lighter finishing passes caused uneven cutting force and thus vibration.

This was the go/no-go step for the entire project. I wasn’t sure that I would be able to make this feature in the die, so with this piece done I was sure I would be able to finish the bender. These pictures were taken in my living room. I was so happy to have finished the die that I had to take it home with me to put on the coffee table.

It was a trivial matter to drill and tap the die to install the tubing clamp, so the next time I went to the shop I took care of this and then formed the clamp by heating some bar stock and bending it around a piece of tubing. You can probably see what I mean from the following pictures. When it was all put together, I placed a length of tubing in the machine and clamped it down. The two people in the shop with me stopped working to witness the historic event. I slowly jacked the hydraulic ram and the die pulled the tube around…and it bent! It came out almost perfect on the first try. The whole thing was actually a bit anti-climactic. After I made sure everything was working, I welded on a couple holders for an extra die and following block (should I ever buy/make another set) and then painted it. Here are some pictures:

I followed Dave’s suggestion and used “cat yellow.” I even painted the hydraulic ram black to match the other parts and make it resemble a piece of Caterpillar machinery.

And that’s it! A long project successfully completed. It’s not often I get to say this.

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