More Machining Adventures
May 31st, 2009Parting Works!
I parted one of my aluminum bars tonight. I guess that will seem boring to most people, but I was in the garage for three hours, and they passed like ten minutes. I had a blast.
I fixed up most of the wiring on the lathe so I could push it back against the wall. This is not something you want to do every day with an 1100-pound machine. I had left the machine pretty far out because the wiring wasn’t done.
I decided to use plain old Alumaflex conduit instead of the expensive waterproof stuff. The upper end of the conduit was going to be open toward the front of the lathe, so it wasn’t going to stop fluids, and I have no plans to hose down the lathe anyway. And I already had a box of conduit.
I tried out my new 11″ back plate to see if it would clear the metal panel I made for the VFD, and I had like an inch of clearance. More than enough. That was a good Ebay score.
Once I got the lathe back closer to the wall, I decided it was time to try out the parting advice I had received. I tried indicating the 8″ aluminum bar, but just like last time, it was hopeless. It’s so heavy the weight pulls it out of line when you loosen the chuck jaws. I had to give up and mount the three-jaw chuck. Carrying that 4-jaw job around and holding it while trying to get the spindle threads to catch is not much fun, so I really did not want to take it off.
I mounted my new cobalt blade in my toolpost with around 1 1/4″ extending out. I had to do that, because the work was 2″ thick. I put the lathe in back gear, got the angle as close to 90° as I could, and fired the motor up.
My only problem was that the blade wasn’t rigid enough to cut perfectly. When I got close to the center of the work, the blade flexed enough to sink under the work and leave a 1/8″ nipple on it. I suppose this is only a problem when you part something fairly thick.
I’ve been told to avoid parting things, because it’s slow and likely to break tools and mess up workpieces. I may get a cheapo portable band saw. There is no way I’d use my wood band saw on aluminum. I’d have to get a special blade and change the speed, and it would be a pain. The saw is supposed to be good for both wood and metal, but that doesn’t mean I have to use it on metal.
When the parting was done, I put a new face on the work with an AR tool. The face was gorgeous. You couldn’t get a prettier finish without polishing it. Then I turned the dial two thousandths and turned the whole cylinder down, to within 1/8″ of the chuck. I did this at about 1350 RPMs. The finish was not good. Lots of vertical lines. Maybe this is not the best tool for the job. I could grind a radiused HSS tool. I guess if I moved slower, the finish would be better, but it would take a week to go three inches.
I turned the post 45° and chamfered the work with the AR tool. I hope that’s kosher.
I love machining. It’s as much fun as using a good table saw, only without the sawdust.
I have to find out whether turning the dial one thousandth reduces the diameter by one thousandth or two. I didn’t see that information in the manual. I guess the calipers will tell me.
May 31st, 2009 at 10:02 PM
The “lines” in your OD cut are because of using a sharp tool. You need to surface with a tool that has a nose radius, and perhaps even wipes. Best surface finish is with larger diameter tool noses.
Parting tools should be actually somewhat above the centerline because of the issue you discussed. Also, a parting tool should not flex. If you have one that is flexing it’s probably installed/adjusted wrong. Keep trying. Lots of fun, innit? Now use the 3 jaw chuck and the piece you took off the boat chair and bore through the center of it.
June 1st, 2009 at 8:55 AM
The dial on the compound will move the tool .001″, so if the compound is at 0 degrees, the diameter will be reduced by .002″. The cross-slide is a different story: most industrial lathes, which yours is, will reduce the diameter by .001″ when you crank it one .001″ division. Smaller, cheaper lathes like an Atlas or my little 7X10 Mini-Lathe will have a .002″ reduction on the diameter for .001″ on the cross-slide dial. It’s no big deal either way, once you know.
Parting off: the tool must be sharp and square at the end. It also must be perfectly square to the workpiece; I usually square the toolpost to the chuck by using a 123 block. It’ll almost always leave a little tit on one piece or the other, however.
You’re correct about needing a slight radius on the end of the tool, plus you might try some WD-40 on the part. You don’t need to flood it, just spray/brush it on before beginning the pass.
June 1st, 2009 at 3:16 PM
Why not build a frame to hold a hacksaw blade on the lathe, and use the rotary motion to cut the stock under hand pressure?
June 1st, 2009 at 3:21 PM
You really have to see how little effect a hacksaw has on T6 in order to understand.
June 1st, 2009 at 7:02 PM
Actually, a hacksaw goes through 6061 T6 like butter- but you have to have the right blade, and you have to understand that slow is much better than fast.
But of course, a Do-All bandsaw with a metal cutting blade would be just the thing.
June 1st, 2009 at 7:04 PM
Try it with my Ace Hardware blade, if you want a challenge. The teeth are so close together, they fill with aluminum in about half a second. My guess is that I would have to go to Enco or MSC to find a blade that would actually work.
June 1st, 2009 at 9:49 PM
I tend to choose a blade appropriate for the material. You should have on hand a dozen or so each of 10 tooth, 12 tooth, 18 tooth, 24 tooth, 32 tooth. Welded edge blades from Starret are nice, Nicholson makes good ones, and Eclipse are nice too. Cutting something properly with a hacksaw is a difficult skill to acquire and a useful one. I’ve seen a firearm made entirely with hacksaws and files, and no, it wasn’t some hacked up piece of zipgun crap, it was a gorgeous falling block rifle. Hell, the very first M1 carbine was made with a hacksaw and files.
June 2nd, 2009 at 9:37 AM
A more esoteric cutting device would be a fluid-cooled abrasive wheel saw. Great for cutting 6061-T6, Hardened Steel, Rocks, etc. They don’t make cutting Cast Iron easier though. Nothing does.
June 2nd, 2009 at 9:42 AM
I couldn’t find any good abasive wet saws. Did find this amputation-grade device.
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