The Home Machinist!

Hi,
Need some help here. I need to cut off two 1.5" long rings from an 11" length of 6" OD 1/8" wall aluminum pipe stock. The critical part is the cut plain must be square to the tube axis and thus parallel to each other. The length only needs to be within +/- .050. The lathe seems the only logical choice as the band saw just wouldn't cut accurate enough.

So the question is how do I chuck this in the lathe with out distorting it? There has got to be some clever simple tricks to this. I have a 10" Logan with a 6" 3 Jaw and 8" 4 Jaw chuck.

One option I though of was to true up one end on the lathe then cut off the ring with the band saw and finally cleaning up the band saw cut on the mill, but I still have to chuck it in the lathe.


Craig

I don't think you'll want to try to "true it" on the lathe first. It's too long and too flexy.

I guess it would depend on tolerance of square/parallel. If tight, I guess I would be thinking band saw over size, then mount in soft jaws on the lathe. To prevent distortion, pie jaws if possible, or some shop made over-size top jaws for that 3 jaw. But since you are only facing, distortion wouldn't be a big an issue as if you were turning the OD or boring.

If the 3 jaw is not 2 piece, then the 4 jaw would likely be my next choice, particularly since only facing, and use relatively light cuts. I've also got a HD (wide thick jaws) 8" Cushman 4 jaw that I use to hold stuff like this on the mill, so I might also consider fly cutting it using that 4 jaw.

Now lets see what the more knowledgeable guys come up with.

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Russ
Master Floor Sweeper

The pipe probably isn't perfectly round in the first place. However, if it's close, what about turning a slug that will fit snug inside the ID? Maybe with a bit of taper on the leading edge to help insert it in the pipe. Then you would have something to oppose the force of the chuck jaws when gripping the pipe.

Or maybe this is a good excuse to go buy that 6-jaw chuck you've always wanted ever since it was mentioned earlier in this sentence.

I do nearly the identical job with the same dimensions. One difference is that I use a larger more rigid lathe that has never had any difficulty parting anything. I see many posts regarding parting problems using smaller lathes, so there may be issues there.

I have a shouldered (OD smaller than the tube OD) plug that fits snugly in one end of the tube so the chick jaws have something to grip against and not distort the tube. I also use a six jaw, but would use soft jaws if I didn't. The far end gets a similar plug that has been center drilled. The tube is chucked and the tailstock with a live center used. The key is not to have any real pressure on the tailstock center. I snug up the tailstock in the normal fashion when tightening the chuck jaws, but then release the tension after that. I then start the spindle and rest my finger on the live center and adjust the tension until the center just starts spinning with the part, no tighter. By using minimum tension the parting blade does not get pinched when it cuts through. I do all of this with just saw cut ends that are close to square. Next I make a parting cut about a quarter inch from the tailstock end to get a nice square end on the tube. Then the tube is reversed in the spindle and the whole process done again. Now you have nicely machined square ends on the tube and you can start parting off the 1.5" sections from the headstock end moving the plug with each cut. I have done it by parting then off from the tailstock end as well, but you may be better off parting close to the chuck.

The whole key is not to have tension on the live center causing the parting tool to bind in the cut.

I hesitate to post this as it is sort of a finesse job, but with care and proper lube (flood coolant), I have parted off many rings, but as I stated my lathe is fairly stout. I have a 12" bench late as well, but have never tried using it for this job.

It all depends on finesse and having a bit of lathe experience, so be very careful, as if the parting tool grabs, it won't be pretty!

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Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

Since the question is "how would YOU cut this?" I would cut off about 3½ inches on the band saw, mount it in the 3 jaw (gripping internaly), keeping concentricity with the axis as best possible. Face one end, turn it around and face the other. I would then part it off (it's only 3+ inches long and your parting tool would only be 1½+ inches from the chuck face or first step in the jaws).
Then I'd face each piece to 1½" and be done.
Sometimes overthinking a task can make it more difficult.

Fill it with wood!!

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Cheers Twin

Bench saw my friend...
Set the fence 1 1/2 inches from the blade, install two guides the hold the tube square to the fence, with the blade down slide the tube in the guides against the fence, raise the blade 1/2 inch or so and rotate the tube. Perfect rings every time.
Hope this helps
Claude

Thanks for the suggestions. I think I am going to make about a 4" long snug fitting plug from some laminated MDF mounted on a 1" dia CR shaft. Then mount the plug between the chuck and the live center. Will include a taper or just use paper shims to fit a seciton of the stock to the plug. If necessary I guess I can hot glue it on or just insert some wood screws on the end of the plug near the surface to expand the MDF a little.

For those wondering, the ring will be the wall of a short throw 6" dia pneumatic cylinder. Initially, the ring was to be sealed to the pressure side end plate with an o-ring but have since changed it to be expoxy bonded into a groove in the end plate.

Craig

There are a million ways to do it! just ask everyone and they will give you a different way.
this is just one option, especialy if you where making a pile of them.

just cut the stock off in the saw a little long for machining,

A quick and easy fixture , make a spud that is a nice easy slip fit to the ID, but as close as you can, the clearance you give it determines the final runout. then mill a slot down the length of the spud with one side open as shown in the picture. make it so a common dowel pin works.
to use, put the spud in the lathe and indicate it in. slide your part blank onto the spud. slide in the dowel pin and rotate the part on the spud so the dowel rolls out and cam locks the ring. machine both front and back sides and any outside diameter work you want, all in one holding. if runnout is a problem indicate the od of your part in after it is locked on the spud. just turn only in the forward rotation. if you turn the spindle in reverse the part will become loose.
once done grab the part and rotate it backwards which rolls the dowel out of locking position. some times you need to tap it to loosen. you can not take heavy roughing cuts as you might over power the locking strength or get it spun.
basically you are using a one way roller bearing, I used to make a ton of pipe welding coupons for a school program, cut the pipe, place on fixture , face and turn the chamfer. roll the chuck over to the slot was straight up and down, tap above the dowl pin, it would slide down. pull the pipe off, slide the next one on and roll it back up. 4 inch pipe and we would do about 30 an hour on a manual lathe.