How to use Power Lathe Chuck

[John3]

I've just begun using my newly acquired CNC engine lathe.

Its out fitted with a 10" HOWA 3-Jaw power chuck. I've got some soft jaws are ready to cut metal.

I have no experience with this type of chuck and am looking for pointers or user instructions. I'm sure I can muddle thru it, but I'm also sure that there's some hints and tricks that would help me.

Any suggestions on reading material or do's and don'ts about these chucks would by appreciated.

Specifically I'm wondering;

1. Do I really need those rings or circular fixtures to hold the jaws partially open for cutting or can I just let the chuck jaw travel run against its end stop, mount the jaws and cut them like that?

2. If I do the above, does it matter if I use the outside or inside travel stop?

3. Would I be better off investing the $600+ in a set of hard jaws or would I be better off just making soft jaws as I need them.

4. How do I determine the proper pressure for the hydraulic pump. How often do I have to mess with this setting? Is there a recommended PSI of jaw contact pressure? I normally turn aluminum, 303sst, and 1018crs.

5. The lathe spindle is A1-6, what's the best way to handle collets in this machine? A set of those trick power chuck jaws that hold 5C/16C collets, or remove the whole thing and use a different collet chuck? Anyone have experience with the collet holding power chuck jaws?

6. There are zerk fittings on the ends of the sliders for the chuck. What should I squirt into those and how often? Oil, light grease, heavy grease??

Thanks for any comments,

John

[Cruiser]

There are many ways to hold the jaws while you bore them, and much of it is pertainant to whether or not it is a through bore. I have numerous spiders that i made for just that. I have bored jaws for chucks up to 48" using spiders. if you must bore through then a good way is to put pins in the bolt holes and they must fit pretty good, then put a ring into these pins and close chuck. using differant size pins, rings, and shimms you can fit your jaws with good presision. it is imperitive to hold your jaws solid and bore them right to size, else your work could fly out of chuck with an improper fit. Good luck and have fun. oh and use a good quality chuck grease, and not too often, but when it is needed.

[Geof]

When machining soft jaws you do need the rings or something to load the jaws. During machining the jaws should be loaded as close as possible to the manner they will be loaded when in use. So obviously you need both inside and outside rings or plugs for inside and outside jaws.

$600 seems a lot for a set of hard jaws but if you need to grip hot rolled bar stock with a poor finish and poor dimensional tolerance you will find them useful.

We have a 10 Kitagawa and the maximum hydraulic pressure is around 350 psi. This seems to be limited by the capacity of the rotating seal on the cylinder rather than the chuck capacity. We rarely use less pressure than this on bar stock but gripping tubes it is easy to crush them. Back off the pressure just enough to avoid crushing for tube. I have seen tables relating hydraulic pressure to grip force but never used them.

To save time and effort changing chucks we machined a set of soft jaws to grip the outside of 5C and 2D collets. This works well but it is difficult to keep them better than around 0.005"TIR. It doesn't matter for us because nearly all our parts are fully machined.

The grease you need for the jaws is one with extreme pressure additives. Our Kitagawa manual says grease daily but we probably do it every week. If you were running cast iron frequent greasing might be a good idea.

[Newby2]

Forget about the hardend jaws. You may only have a small grip range with the chuck. Look closely at the #1 jaw and see if there are marks on it. There will also be a prick mark on the movable jaw. This will indicate the range the chuck will have the greatest holding power with a given hydraulic pressure. The maximum pressure should be indicated somewhere in the manuals. Also you will have to vary the pressure depending on whether the stock is solid or hollow. To much pressure will distort the ID of a hollow piece.
If you are holding raw material for turning, instead of size rings to clamp the jaws, step them outward from the end of the jaw toward the spindle, this will compensate for the jaw spread when it is clamped.
If you want to turn a finish surface, and hold concenticity, then the idea of clamping the jaws against a piece of stock prior to boring them smooth is proper. For OD's always bore the jaws in the open position for a good fit to the stock. The greater contact area of each jaw, the better the holding power.
As for the grease, I just use a multipurpose. I would advise against using a synthetic, especially if you are running coolant. 3 or 4 shots in each jaw every 30 or 40 hours will be sufficient.
This is what I do on 3 Mazak turning centers and have yet to have any problems.
Steve

[John3]

Thanks for the suggestions, sounds like I'll save my money on hard jaws and instead buy/make 5C collet holder jaws.

As far as fixturing the jaws for boring, What am I missing?

It seems I could just bolt the jaws at the right groove location with the chuck at its end of inward travel, bore the jaws, then move the jaws a few grooves closer to the center and they'd work.

When using the spiders, rings and other fixtures, how does one know that all jaws are loaded the same amount? For example, if the soft jaws are slightly different lengths (the ones I bought don't seem precision) they will have different loads if clamped on a ring, won't they? I think I'd be worse off than just using the end travel of the chuck to set my boring position wouldn't I?

.... a bit confused.......

John

[Geof]

Originally Posted by John3 Thanks for the suggestions, sounds like I'll save my money on hard jaws and instead buy/make 5C collet holder jaws. As far as fixturing the jaws for boring, What am I missing? It seems I could just bolt the jaws at the right groove location with the chuck at its end of inward travel, bore the jaws, then move the jaws a few grooves closer to the center and they'd work. When using the spiders, rings and other fixtures, how does one know that all jaws are loaded the same amount? For example, if the soft jaws are slightly different lengths (the ones I bought don't seem precision) they will have different loads if clamped on a ring, won't they? I think I'd be worse off than just using the end travel of the chuck to set my boring position wouldn't I? .... a bit confused....... John

Using the end travel will not work. Actually this means you do not know if all the jaws are loaded the same amount but gripping something in three jaws does load all the jaws equally. When three jaws are gripping something all three have to exert the same force; get someone to provide a third hand for you and pretend your hands are chuck jaws you will soon see what I mean.

The way to use a ring is position the jaws so they are slightly smaller than the intended ID size when the chuck is almost fully closed.

Make three pins that will be a nice fit in the counterbore of the bolt holes on each jaw.

Make a ring, it has to be quite sturdy, that has an OD size so that the chuck can be closed with the pins against the ring and the jaws are slightly smaller than the size they will be bored.

Now the forces acting on the jaws are the same as they will be when they are being used.

Bore the jaws to size, remove the ring and pins and they are ready for use.

Make sure the jaws are numbered and make a note of where they are on the serrations on the jaw base so they can be replaced in the same spot next time they are used.

[Newby2]

I usually bore the jaws at the outward limit. Also, once they are to the size I want, I stamp the jaw number on them to coinside with the chuck. I don't recommend moving them inward a few notches as the accuracy may not be the same at the new location. I run a few parts that have a TIR of +/- .0002" and a turned backface of +/- .0002" perpendicularity to the bore.
Even though the soft jaws may not be the same length, you can turn them to what you need to eliminate an out of balance condition. If they are that bad, turn the OD of the jaw first.
And always bore the soft jaws at the pressure you will be running the parts at.
Steve

[Newby2]

Geof...Not trying to confuse John3 with some of what I posted which may be contradictory to yours, but only offering my point of view. As one once told me, there is more than one way to do something as long as the end result is the same.
Steve

[lazza_1]

I usually "Free bore" Thru Jaws without using "spiders" and move the jaws in a couple of notches. This works fine as long as you have a good quality chuck with no play in the master jaws. I can even interchange the jaws to chucks on differnt machines and still have TIR of less than 0.0005". But on the other hand I will use Spiders if I am boring stepped jaws. I believe that it is not nessersary to Number Jaws on todays Modern chucks. It is just something that has been carried over from scroll chucks.

As for Hard Jaws I would invest in some. They will grip the work piece a lot tighter and you wont have work pieces push back in the chuck. You will save money in the long term as you will not constantly be having to rebore your expensive soft jaws just because you are working a different dia barstock.

[Geof]

Originally Posted by Newby2 I usually bore the jaws at the outward limit. .... I don't recommend moving them inward a few notches as the accuracy may not be the same at the new location. ....

If you always bore the jaws at the outward limit and don't move them inward a few notches how do you open the jaws to put in the stock?


lazza_1; When you are using the same chuck with the same hydraulic pressure how do hard jaws grip tighter than soft jaws. The gripping force is going to be exactly the same.

[lazza_1]

The Hard Jaws have serrations on the face that Bite into the material. It deforms the workpiece instead on the jaws. Only use the hard jaws on rough stock with high pressure.

[Geof]

Originally Posted by lazza_1 The Hard Jaws have serrations on the face that Bite into the material. It deforms the workpiece instead on the jaws. Only use the hard jaws on rough stock with high pressure.

Correct, I covered this, see my first post. But hard jaws do not substitute for machined to size soft jaws. When you are working with finished bar stock or soft material you may not want the workpiece deformed.