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KEJR
12-18-2010, 06:52 PM
I'm going to be buying a new adjust true chuck soon and was wondering about the classic 6 jaw vs 3 jaw thing. I'd like to get a 3 jaw for simplicity and price.

My question is certainly not "which is better" but this: What do all you 3-jaw-chuck-only folks doing when you need to hold thinner tubing?

Do you just make plugs for smaller stuff? Does anybody grip tubes from the ID and then make an external "spider" to support the outer diameter from expanding?

I know you can machine down soft jaws to the diameter you are using, but for one off parts I can't see going through all that.

Any ideas?

darryl
12-18-2010, 08:16 PM
Done that both ways. Internal plug, and external ring. These days, my internal plugs are made from solid pvc. Though I save the plugs once I knock them out, I consider them to be expendable. The rings are often made from steel washers of suitable size. There's already a hole and usually all that's needed is to bore the hole to the appropriate size and deburr.

At one point I experimented with using mdf as a jig to hold tubing, etc. I layed out a triangular pattern and drilled three holes with a spade bit. These holes are placed over the jaws, then the jaws tightened- usually inwards. Then it's facing and truing to create a mounting rim or whatever for the tubing. I have found that these jigs remount quite well, as long as you mark the holes and jaws for mating, and use the same tightening sequence each time. You know, master pinion, etc-

Thanks for bringing this up- I have not as yet used this method with pvc, but I think it would work better than mdf. I think I'll make up a few discs like this from pvc and try it out. Maybe it's a lazy mans way of having a disposable faceplate or mounting adapter, since you don't have to remove the three jaw, just mount the plate in it- but I think it has its place.

KEJR
12-18-2010, 09:14 PM
Thanks Darryl,

My dilemna is that I've done alot of basic machining but had alot of high end tools to work with at the shop at my job. Now having machines at home it is difficult to retrain myself into the "Just get what you need" mentality. Surely making rings and plugs are fairly easy, maybe I just need to aquire more short bars of different scrap material, PVC, aluminum, etc.

I didn't quite get your idea involving the MDF jig. Any way you could post a sketch? I wasn't sure what you meant by a triangle layout and all.

I think also a good idea might be to make a 3 piece expanding arbor or something like that. It doesn't have to be perfect, just enough to be a backer for the jaw force as the tube wall collapses. I can envison a simple setup. I'm not sure its worth the effort to make a full set of these though for the odd tubes I'd be doing.

KEJR

Boucher
12-18-2010, 09:49 PM
After getting my six jaw I rarely use the three jaw. I probably dial things in less than 10% of the time. Next most useed are the 5C collets. The four jaw is used more for holding odd shapes or larger work. The relative importance kind of depends on your type of work. I have one friend that uses his three jaw 98% of the time and another that mostly works off a large faceplate. If I were buying a new three jaw I would definately go for the set true.

macona
12-18-2010, 10:01 PM
I also almost never use my 3 jaw and use the 6 all the time. And lately I have been using my Sjogren 2J collet chuck a whole lot.

Toolguy
12-18-2010, 10:05 PM
I mainly only use 6 jaw set-tru chucks and 5C collets like Boucher. They are worth the money. You can do so much more with a 6 jaw. For example, the jaws are straight across from each other like a 4 jaw so they grip tighter. If you have a part with one or two things sticking out perpendicular, you can take off one or two jaws to clear the protrusions. If doing tubing, they don't distort it. However, I know all about being on a tight budget and making do and getting by. For thin tubing using a 3 jaw, I just got a piece of steel, brass, or acetal and bored it out to a close slip fit to the tube OD and bandsawed or hacksawed a slit in the side. That makes a cheap and quick collet for the tube. Make sure the wall thickness of that piece is enough to not distort when clamped in the 3 jaw chuck. Position the slit 1/2 way between 2 jaws.

darryl
12-18-2010, 10:05 PM
Ok, here's a quick paint sketch. I'm calling it a puck, since that's the shape. The three recesses in the back fit over the chuck jaws, either inner or outer. After that, you create on the front whatever it takes to hold the workpiece. For tubing, you would machine a short stub that the tubing would press onto, then keep it in contact with pressure from the tailstock. This is good if you need to true up the outside of the tube to match the ID. Or you machine a recess to press the tubing into, in order to do a clean-up on the OD. Either way you would use pressure from the t/s to keep the tubing in place. If you want to machine the ID of a short section, you could make the tubing a press fit into a recess, making sure to not invade the jaws, then it's unencumbered by any clamping arrangement. If you do need to fasten the workpiece, just remember that these pucks are meant to be disposable, so you can drill, tap- whatever suits the job at hand.

http://img.photobucket.com/albums/v136/heinrich/puckfaceplate.jpg

These are meant to be mounted in a 3 jaw, thus the recesses for the jaws to fit into. If you clamp using outward jaw pressure, the recesses would likely be farther apart and the disc larger. In this case, you would be limited to the depth of the last step in the jaws- about 1/4 inch in my case. That leaves the rest of the thickness of the material to bore or machine to suit. When you mount this puck and face it, you'll see how much material you have left to work with to create any custom part mounting that would fit. You can take the puck out of the chuck and remount it- in my case it comes back almost perfectly centered.

If you just need to hold one end of some tubing without crushing it, the plug is the way to go. This puck method lets you do the equivalent of gripping from the OD, but without the plug being needed. You machine to suit a press fit of the tubing, and it leaves the ID clear. If it's the OD you need to be clear, you machine a stub and press the tubing onto that. The puck lets you make a relatively large diameter stub without requiring that the chuck be able to grip directly onto that diameter of stub.

Note that for workpieces of any real length, there needs to be support on its other end, and in many cases some pressure from the t/s. When I'm turning on some larger diameter tubing, I'll make up a centering disc first, so it can insert in the outboard end of the tubing, and the center hole in that disc gets controlled by a live center. I make the disc with a lip so it can't fall into the tubing.

Since reading this topic, I'm going to be making my future pucks from pvc, which so far I've made from mdf. I've made so much other stuff from pvc I can't count it. The section of city water pipe I came to own has been my source for stock in the 1 inch thick range. Pieces get heated in the oven, flattened, then table sawn into usable sizes, cut into discs if required (pucks) and strips, which eventually become round rod sections. Sometimes I'll take some of this and turn out several pucks in one go using various sizes of hole saw run on the mill. Where the diameter needs to be larger than my hole saws and mill can handle, they get cut out on the table saw. Thinner pvc materials I get from smaller diameter pvc pipe. For instance, a 6 inch diameter pipe is often 1/2 to 5/8 in thickness, 1/4 inch thick is available in many sizes, from 3 inch pipe to 20 odd inch- sewer, secondary water pipe sizes, drain pipe- the thinnest stuff I've found is 3/32 thick, and in pipe diameters of from 1 1/2 inch to about 3 inch. A visit to some building contractors should net you a source.

winchman
12-19-2010, 01:38 AM
Here's a fixture I made for holding thin-wall aluminum tubing so I could get the ends very square to the tube axis and the length just right.

http://img.photobucket.com/albums/1003/winchman/000_13122.jpg

http://img.photobucket.com/albums/1003/winchman/000_13112.jpg

It's marked so it always goes into the chuck with the same orientation to eliminate chucking error, and I use a threaded rod through the spindle to ensure it's seated against the chuck body.

The plastic inserts were machined in place so they would be true to the spindle axis. They're a tight slip fit on the tubing, and I don't need to tighten the two set screws for taking light cuts.

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