I need a plan.

Transformer

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I am ok in English and wood but metal is a foreign language. I want to make 4.5" disks of 1/4 aluminum using my lathe. I was going to cut squares of say 4.75" drill a 1/2" hole in the centre, fasten a bolt, insert the bolt in the lathe and turn the circle. Firstly will this turn OK or will it be all off balanced and be a problem for that reason? Second if it turns OK in the chuck what kind of tool and procedure should I use? A cut off tool would not work because of the depth of the tool when I am approaching from the face. If I use a regular cutting tool I may have the same problem unless I cut a wide groove or ?? And what about when I finally cut through, will the picture frame left over jam on the tool post and the disk still in the chuck? So what is the best way to take a flat square piece and turn it into a flat round piece? All help appreciated.
 
I am ok in English and wood but metal is a foreign language. I want to make 4.5" disks of 1/4 aluminum using my lathe. I was going to cut squares of say 4.75" drill a 1/2" hole in the centre, fasten a bolt, insert the bolt in the lathe and turn the circle. Firstly will this turn OK or will it be all off balanced and be a problem for that reason? Second if it turns OK in the chuck what kind of tool and procedure should I use? A cut off tool would not work because of the depth of the tool when I am approaching from the face. If I use a regular cutting tool I may have the same problem unless I cut a wide groove or ?? And what about when I finally cut through, will the picture frame left over jam on the tool post and the disk still in the chuck? So what is the best way to take a flat square piece and turn it into a flat round piece? All help appreciated.

You can do that. The shaft that fits in the hole must fit tightly. It also helps to inscribe a circle and use a bandsaw to cut as much of the edges off to make the task go quicker. You'll want to have minimum extension on the shaft that's holding the disk.

For that diameter, you'll spin slowly -about 100 to 200 RPMs. For aluminum, it's OK to use a carbide bit but, you can use a sharp point HSS too. Just feed it across slowly and take about 10 thou depth cuts.

If you have a screw-on chuck, be careful that the chuck does not get hopelessly tightened onto the spindle as each little impact is tightening the chuck. Also, the shaft that you've got bolted in the center will get very tight too. -Just be apprised of that...

Ray
 
What your proposing is to cut through the face to trim off the outsize. I'm no pro but I don't think I'd try that on a lathe. If you were to try it, you would want a good solid backing plate to take up the force as you plunge in. Just don't do it is my opinion.

As mentioned, rough cut it on the band saw and then turn it down to diameter. Since your going to have a shaft on it, make a jig for the bandsaw with the centered pinned so you can rotate the aluminium plate and get a very close to finished cut.

Are you going to face off the aluminium? If so then again you may want a backing plate and not just a small shaft trying to hold the piece as you put force on the face. Or reverse your jaws and use that as backing.

What are the discs for?
 
I've done this on the lathe a few times. What works best for me is to make a mandrel from some scrap, say 1" od aluminum rod with the mandrel snout cut down to 1/2" od and about 0.005" shorter than the thickness of the work piece. Drill and tap the center for a bolt/screw and make a 1" od cap. Drill the blanks to fit the mandrel and rough cut the discs out on the bandsaw. Load them onto the mandrel and turn the edge to the desired size.

I have stacked four 1/4" thick plates like this and cut them at once without issues. I suggest using HSS and go slow, about 100-200 rpm if you can. Once you get the edge irregularities cut and are cutting smoothly then you can increase speed a bit to get a better finish.
 
I have done what mikey/Ray suggest and it works well. Getting as close to a circle with a saw will save you a lot of time. Even if you only have a hacksaw, you can lop off a lot of material in a short amount of time. Go slow until you get things round, then you can cut a little deeper once you are getting a consistent cut. I would recommend a normal turning too, nothing fancy. Should be no problem for that machine.
 
A long bolt can work well as a mandrel for this, if you get a 4 inch long bolt that is threaded 2 inches and cut the head off the bolt so it can be chucked by the unthreaded portion, the 2 inch threaded portion should be long enough for your four plates and a nut at each end, tighten your plates on between the 2 nuts, chuck the assembly by the unthreaded part of the bolt, drill a center in the end of the mandrel and use the tailstock with a center, the closer the plates are to round is better to save time but not necessary, make sure you give the whole thing a spin and check for your highest point when putting your fist cut on, use your feed for the cuts don't try to feed the carriage by hand, a sharp tool combined with intermittent cuts and a little to much pressure can make bad things happen.
 
I'd cut them on a drill press with a hole saw.. Stack all the flat pieces together on top of a piece of wood and clamp the whole aluminum sandwich down to the drill press table and drill away with a hole saw ID that gives you the dimension you need. Or use a fly cutter, same scenario.
 
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