I have a couple hundred pcs of 3/4 inch EMT conduit and I need to flatten them for an 1 1/2 inches on each end. I have a tire hammer but with little practice at this point getting one hit is still difficult. I also need the flattened ends in line with one another. I have flat dies and suppose I could fashion some sort of back stop but I am still not sure how I can align the flattened ends.

Any suggestions guys ?

Make a support with a horizontal cross bar at the top to stand on the floor, with the top about level with your hammers dies, and at an appropriate distance from your hammer.

Place the flattened end in contact with the horizontal bar and it should be in line ready to flatten the other end in the same horizontal plane, and in line.

its only 3/4? use a hand hammer, its much easier to control for people not used to using power hammers

What Steve said. I would do all of one end, then set up a jig to hold that new flat end in plane with the anvil. Lay them up and wail away. Check every 5th or 10th to make sure nothing shifted

Squeeze it closed in your vise.

I appreciate the suggestions guys. I am going to try Johns first. I can't see using the vise or a hammer. If I can't get the power hammer under control perhaps a cheap HF arbor press would work.

The vise Idea works i have done it.

I have experience here so I'll chime in. First make sure you do not flatten with the weld or the pipe will crack. I found keeping the pipe weld to a 45 of the the flattener works best. First go around I used a large vise and a jig to keep the flattened ends in line. Basicly a saw cut in a 4x4 wood post. Now I have a large arbor press that works a whole lot faster. It is a 6 ton and really couldn't recommend anything from HF. Anyway I have a self contained hammer with good control but could never get the results I wanted. Many ways to skin that cat just giving what worked for me.
One day a couple thousand lengths of 3/4 and 1" emt followed me home for the cost of scrap. I felt the need to build some geodesic domes. That's my story.

I'm up late tonight and soaking in the forum. My head is spinning as the new smithy is about built and I'm getting ready to move equipment in. So many ideas here what a great resource.

I would say to set up a good heavy stand like John B suggests. The nice thing about a hammer for this is its fast. I have a fabricator who comes to me with 3" pipes that he needs a section 4' long flattened to 1" thick. I set up a stopper on one end of the die. I hit one light blow to make sure I am flat on the dies then a second blow flattens them. He tried doing them on an anvil and not only was it a lot of work the city inspector didn't like the hammer marks which is kind of silly because the flattening is just to keep them from rotating or being pulled out of concrete. It is a nice little job, th e driver unloads one pipe hands it to me, I flatten it we exchange pipes and repeat. $5 each and I can make $50 in about 15-20 minutes

I am going to be part of a dome build Sky. Hence the flattened conduit.

I have experience using a brake press in this process. Schedule 40 pipe flattened on the ends for welding. Micro switches on the press. Outboard stand for indexing the ends to make even. I would think that some radiused top and bottom dies on an arbor press would work for the conduit. A depth stop inboard (fence) would give you the same length each time. you would need a comfortable stool to set on to make process friendly to yourself. Perhaps a spring return UP on the arbor press. YES pay attention to the weld on the tubing (pipe).

I have done several hundred pieces of pipe at a time in this brake press process. good luck.