How to hold 3 inch alumimun tube in lathe

dllewellyn

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I have a 6 inch long x 3 inch wide aluminum tube with 1/2 inch thickness. I am using a 13 inch Regal lathe that has a chuck with on set of jaws that are stepped inward and one stepped outward. I am trying to reduce the OD of the tube, but the lathe jaws only can clamp on about 1/2 inch of the tube no matter which way I set the jaws holding either from the inside or outstide. No matter how I try to hold the tube, it wobbles as soon as machine is started up. I have a steady rest, but that doesn't leave enough clearance to cut the tubes.

Maybe if I had a different chuck it would work, but finding new chucks don't have the thread to fit the Regal lathe.

So far, I can put the tube in a rotary table and turn it on the Bridgeport, but it would be far easier to do in a Lathe.
 

November X-ray

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I don't understand the jaws comment about two inward and one outward, can you post a picture? I've turned lots of tube or pipe and use a bull nose center. Depending on how accurate you need your dimensions you could cut a piece of wood and shape it with a taper that fits into the tube and a flat face that the center will fit into.
 

GK1918

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Im with November,,,chuck jaw with two inwards and one outward? I try to help but
I cant picture that. New to me. Chuck jaws suppose to all face the same way most
can chuck on the inside or outside. I just picture one being upside down for some
unknow reason. Just like xray said, no got bull center,, make from wood, dial it in
all is good then center drill the wood. Correct me a 3 inch OD amounts to inch and
a half jaw opening, three or four jaw dont matter. I am not a wise guy, but a 3x6"
piece of work should have been done already. I read it again and, no, this short
stock should not have a steady, it needs dead center. And then "1/2" grip it wobbles
yes, but thats all you need. Us guys are all here to help, some including me are
old timers or perhaps you have some kind of NASA chuck that I aint seen yet.
Please reply I just have to know as to this problem. ALSO if you have a 3 jaw and
some, turning jaws in and outwards thats a delicate proceedure they gotta be in
sync. four jaws doesnt matter. samuel d.
 

kd4gij

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I think what he has is a 3 jaw chuck 2 sets of 3 jaws one set for inside and one set for outside. Just make a plug with a center spot and use the inside jaws and the lale stock and have at it.
 

dllewellyn

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I think what he has is a 3 jaw chuck 2 sets of 3 jaws one set for inside and one set for outside. Just make a plug with a center spot and use the inside jaws and the lale stock and have at it.
Right. I have a 3 jaw chuck with with 2 sets of jaws. The jaw have three steps in them. One set has the steps in the center being the longest and the other set has the outer steps being the longest. However I try to hold the aluminum tube, it wobbles. I can only grip about 1/2 inch of the tub because of the size of the steps.

Here are some pictures of the two setups

IMG_0009.JPG IMG_0010.JPG
 

November X-ray

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Right. I have a 3 jaw chuck with with 2 sets of jaws. The jaw have three steps in them. One set has the steps in the center being the longest and the other set has the outer steps being the longest. However I try to hold the aluminum tube, it wobbles. I can only grip about 1/2 inch of the tub because of the size of the steps.

Here are some pictures of the two setups
Using the jaws in the picture to the right, close them all the way and see if the tube will fit over them and then open the jaws tight against the tube. If you do not have a bull nose center make a wooden piece that fits inside the other end and using a dial indicator, get the tube to run true then spot the center and install a center in the tailstock and use the tailstock to hold the end and push positive pressure against the chuck. Since it is aluminum and using sharp HSS tools, it should cut easily.
 

dllewellyn

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Using the jaws in the picture to the right, close them all the way and see if the tube will fit over them and then open the jaws tight against the tube. If you do not have a bull nose center make a wooden piece that fits inside the other end and using a dial indicator, get the tube to run true then spot the center and install a center in the tailstock and use the tailstock to hold the end and push positive pressure against the chuck. Since it is aluminum and using sharp HSS tools, it should cut easily.
I don't have a bull nose center, but will order one. To make a wood piece that fits inside, do you have any suggestions?
 

November X-ray

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You could cut a 2 x 4 with a hole saw of sufficient size to get a plug from, then chuck this up in your lathe, true it if need be and flip it around and true the portion beneath the jaws and turn a slight taper on it to allow one end to fit inside the tube. You could even spot the center in the 3 jaw after trueing it up. However it depends on how accurate your tube needs to be as you may want to obtain a bull nose center. (Or build one out of metal)
 

November X-ray

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However I try to hold the aluminum tube, it wobbles. I can only grip about 1/2 inch of the tub because of the size of the steps.

Here are some pictures of the two setups
Have you checked the run out of your chuck just to be sure it is concentric? Perhaps the jaws are placed out of order or in the wrong slots? Just a thought.
 

PurpLev

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are you using a pipe live center to stabilize the stock?
 

dllewellyn

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Have you checked the run out of your chuck just to be sure it is concentric? Perhaps the jaws are placed out of order or in the wrong slots? Just a thought.
The jaws are in the correct slot, but I haven't checked to see if they are all in the same spot. For smaller work, the chucks have worked fine. I think it is very easy to have the tube slightly cocked in the chuck which gets to be a big problem 6 inches later.

Supporting from the tailstock sounds like the right answer. I ordered a bull nose center. While I am waiting on it, I will see if I can use a wood plug with my live center in the tail stock.
 

Tony Wells

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Don't rely on the saw cut to run the bull nose center if you need good concentricity or roundness. If you push a center into a tube that is not faced square, and turn the OD, it won't be round when you pull the center out. And same general thinking on the chuck end. You can chuck the ID, but it will have 3 lobes where the jaw pressure expanded the tube.

How true must the product run and what is your size tolerance? What is the final wall thickness? Working in an oilfield machine shop, most everything is round, and hollow. I've suffered through learning how to make accurate thin walled cylindrical parts out of many different materials.
 

Charley Davidson

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If real precision is needed saw them close then mount them in your vise on a mill with a V block turned on its side but centered to the part and face off both ends
 

ScrapMetal

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If the inner diameter of aluminum tube is right at 2.5" you might be able to use a section of metal pipe from the hardware store. Cut a few inches from the pipe and slide it in the aluminum tube.

I was also thinking that you may be able to pour a lead/zinc slug in the end of the tube, in theory anyway, as I've never tried it.

-Ron
 

metalmaster

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we do parts like this at work all the time. first we face both ends, then we put a piece of solid stock in the chuck and turn a bull nose center.
use a bull nose in the tailstock and take light cuts if you don't have a bull nose for tailstock, turn a tight fitting plug with a shoulder to push against with a small center.


mike
 

rgray

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Nobody mentioned using a bump centering tool. To straighten up the pipe in the chuck. They work well and are easily made from a piece of bar stock and a small bearing. Just grip the tube semi lightly in the chuck and rotate while running the bearing in to the tube (bump center mounted to tool post) and it will straighten/center the tube right up. Then tighten the chuck. Light cuts could then be made but of course a center at the opposite end would be nice to.
I made a hexagonal "spider" that fits over my live center and set screws to it. It has three sides with 5/16 threads and 3 sides with 3/8" treads. Three appropriatly sized bolts are used and expanded out to touch and center large pipes. Worked well for 8" pipe but probably over kill for 3".
 

Brandon

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I use spiders on tubes also. Everything from 4 in. dia. To 18 in. They are pretty easy to make. Just a piece of round stock with 4 tapped holes in the OD, and center drilled. I back them up by sandwiching a chunk of wood between the spider an the chuck. Works good, but you have to be careful to balance safely holding the workpiece tight enough and deformation.
 

epanzella

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If you have some 1/4 inch alum plate, bolt 2 thicknesses together and center drill. Turn one side to the ID of your tube and the other to the OD. Stick it in the end of your tube and hold with a live center in your tailstock.
 

rwm

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Also, I have bought some structural tubing from McMaster that was pretty far out of round and had asymetric wall thickness FYI.
Robert
 

john.k

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The pipe is 3"dia,x1/2" wall x6": long, if it cant be securely held in a 3 jaw,I would say you have some serious taper in the jaws,and/or serious wear in the slots.....probably both.
 
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