Page 2 of 4

Re: My views on soft jaws

Posted: Sat Jan 25, 2003 9:43 pm
by fredwhite
Thank you very much!

Re: Wow, that was Great!

Posted: Sat Jan 25, 2003 9:47 pm
by Harold_V
Hi Mark,
I wish I was able to tell you if additional jaws might be available for your chuck, but I am not. Considering you're in your chuck nothing, though, it sure leaves room for an expenditure to make it more useful if the jaws are available. If not, the chuck would certainly be a nice addition to a rotary table, if nothing else.

Making a set of master jaws could prove to be difficult, if for no other reason, the thread on the jaw that must mesh with the scroll. The rest could be managed with a surface grinder and some skill. If you're tempted to make them, the thread could be generated by a CNC, or they can be cut on a rotary table. Each face of each tooth would be a setup, but a small indexing fixture could be made to assist in cutting the teeth. It would be a time consuming project, but a lot of fun and a great challenge.

If you decide to tackle this project (making master jaws) be certain to index the scroll thread a function of 1/3 the lead difference on each jaw so they register properly with one another when you install them in the body. I would also strongly recommend commercial heat treating so you don't experience decarburization or excessive warping in heat treat.

I've always suggested to anyone in the market for a 3 jaw that they buy only a chuck equipped with two piece jaws, even if they come with two sets of permanent jaws. It's obvious why.

You fully grasped the value of running soft jaws. Running collets has its limitations, as you mentioned, and that includes step chucks. Soft jaws are truly a magic bullet.

Good luck, Mark, let us hear if you manage to find new jaws. It might be very encouraging for others.


Re: Wow, that was Great!

Posted: Sun Jan 26, 2003 1:08 am
by fredwhite
Mark - in case you don't know, the jaws from a 6 jaw work in a 3 jaw. Use either 1,3,and 5 or 2,4,and 6. Sometimes jaw sets come up for sale on eBay. Maybe you can find the other set somewhere.

Re: The "Spider"

Posted: Mon Jan 27, 2003 4:32 pm
by Harold_V
One of the places that soft jaws are outstanding is in holding short pieces such as a washer. If you find yourself in a position where you need to bore a thin object, of to face it off after parting, there's simply no better way than soft jaws. You can perform all necessary operations on the part, including turning it over and re-machining the first side should you find that necessary. A good imagination is all it takes to get full use from these great devices.

I have no idea when soft jaws were first used, but I've worked in shops that didn't run them. I even worked at a government installation that prohibited them, thanks to a fellow that had bid into his position as shop supervisor, having worked as a bean counter all his life. No offense to bean counters, none at all, but they shouldn't be making judgments like that when they don't have the expertise to understand proper application.


Re: The "Spider"

Posted: Mon Jan 27, 2003 8:05 pm
by Michael_Az
Harold, I can remember using soft jaws over thirty years ago.

Re: My views on soft jaws

Posted: Mon Jan 27, 2003 8:28 pm
by kap
That's an excellent writeup by somepne who knows.
Someone asked about adjust true chucks.
The adjust trues will mar the work sometimes because the jaw edges will sometmes
grip the work.
A soft jaw bored as Harold says to the grip diameter of the job, cannot mar the work.
I used to use Northfield Chucks with full wrap jaws.
In those you could hold tenths for aircraft engine components.
Nice writeup

Re: My views on soft jaws

Posted: Thu Feb 13, 2003 12:16 am
by Pat_S
Harold, good information on soft jaws. I am new to the site and I was reading the posts. I wanted to add that making softjaws and exact size can be difficult. If they are made .001" undersize the pressure could rest on the outside of the jaws which are usually not exactly spaced and thus the part may be held unevenly. I recommend that soft jaws be bored just a little large when the object is to hold the part accurately so the pressure is centered toward the center of the jaw. It also serves well to bore the jaws a little small to provide six point pressure when the goal is to hold the parts for roughing out. If you have a number of parts that require considerable stock removal you can bore the jaws undersize to rough the parts out and then bore the jaws slightly oversize to finish the parts.

Re: My views on soft jaws

Posted: Thu Feb 13, 2003 2:37 am
by Harold_V
Hi Pat,
Welcome aboard!

I read with considerable interest your comments on soft jaws. My philosophy varies only slightly.

When soft jaws are bored with the spider properly centered, the likelihood of the jaws not centering is small, but I agree that it exists. However, boring jaws oversized can have its own negative results, less precision in concentricity and deformation a minor consideration.

My experience with soft jaws, and I've used them extensively, is that boring to proper size is the best scenario, even for roughing. In truth, the parts being held will run the gamut of size, both larger and smaller than the ideal diameter, which, for me, has always been a very snug slip fit, with the part starting but not really entering the jaws. As a result, I shoot for the average diameter, but both of us know what that means. The fit may be tight or loose, rarely dead on. However, that way, the majority of the parts will be near the ideal size, yielding, on the average, a better running part. Understand that I'm talking about gripping a finished part where you don't want to damage the surface in this instance.

My experience with my chuck is such that I have achieved the best level of performance by employing that concept. The ability of jaws to load sideways enough to deflect a well fitting part is minimized in that fashion, the part fits the cavity with minimum distortion because of the maximum degree of support, and the jaws do not leave any marks of finished surfaces, something that smaller jaws have the potential to do, especially when chucking finished diameter aluminum and brass parts with steel jaws.

I've used straight bored soft jaws in place of hard jaws almost exclusively. I've found that I get good results, even for roughing cuts, regardless of the nature of the fit of the material as it relates to the jaws. It is only for deadly accurate running parts where I become concerned about fit, having discovered my soft jaws will generally run within .003" regardless of the diameter I choose to chuck. For bar stock, that degree of precision is generally acceptable because I normally always take a cut on all surfaces for uniformity and consistency of parts. When the setup demands more precise chucking, I will then bore the jaws to proper size.

I think you've presented some great points, Pat, points that each person that chooses to run soft jaws should consider in their particular case, to see if they will serve them better or worse than my proposed methods. I'm certain there are instances where they may have particular advantages. The most important thing, though, is to get set up for soft jaws, regardless of the method employed. Soft jaws open up a whole new world in parts handling. I'm sure all the readers appreciate your views and support of the concept.

Best regards,


Re: My views on soft jaws

Posted: Thu Feb 13, 2003 4:28 am
by Pat_S
I guess my concern comes from my experience at work were the steel soft jaws are made in shop by less experienced machinists who do not take the time to center the mounting of the jaws side for side all that well. I tend to take the side of eliminating as many possible problems as I can. Jaws usually have a lot of wiggle in their slides. When the angle of soft jaws are made so they will clamp small work, that also has to be well centered. I don't trust anybody else's work. You are right, I am talking about close tolerance work. If you have .005" or .010" to play with, it is not going to matter which method you use.

There is no doubt about it, soft jaws are the way to go for the vast majority of work. I don't understand why they sell chucks with one piece jaws.

Re: My views on soft jaws

Posted: Thu Feb 13, 2003 10:21 pm
by Harold_V
Hi Pat,
Actually, I have used my soft jaws where I had to hold less than a thou, and they do that very reliably. Like you, though, I do all my own work. I do not rely on the ability, or lack thereof, of others. My experience tells me that I have no trouble with side play, which I attribute to proper loading at the outset. If there is considerable side play in jaws and a device for loading them is used that applies pressure to the side, I'm inclined to agree with you. While I've never used it, there is a cam type device that is used for machining soft jaws. All one does is rotate it until it makes contact, at which time the jaws are tightened on the cam. Problem with that is it picks up the jaws on edges only, not in the center as the spider does. One might assume that the three jaws would deflect uniformly, still providing a center running pocket, but I can see where you'd be at the mercy of the degree of clearance from jaw slide to jaw slide, perhaps having one that is greater than the other two, resulting in side shift, which would equate to eccentricity. I've rarely had any trouble in that regard, though I can guarantee problems by rotating the spider from center, or cocking it sideways. Care must be exercised when using my method, but it yields excellent results, especially when boring your pocket to a tight slip fit on the average part as I've recommended.

In the distant past I was sole source for precision metering pumps for a blood analyzing machine. The pump components were turned from 1-7/8" dia. 303 S stainless. If one purchased domestic stock, it came centerless belt sanded, typically oversized by two or three thou (not true of import, which came cold rolled and slightly undersized from my source). Soft jaws, used as I applied them, allowed for a full cleanup and consistent chucking on the various parts that comprised the assembly, which consisted of three components. The parts were finish machined to 1.875" with no difficulty, the soft jaws ran that well consistently, which came as no surprise to me.

Funny, your statement about chucks coming only with one piece jaws. I guess you have to look at the economics for the manufacturers. You've likely seen the hard jaws that are reversible. They weaken the teeth on the jaws by cutting the radius on both sides, permitting the jaws to run in both positions in the scroll. Great for them, not as many items to produce, but it leaves the consumer with no ability to mount soft jaws. Not unless you buy another chuck, anyway! Do you suppose they have something in mind?


Question about soft jaws

Posted: Wed Aug 06, 2008 5:02 pm
by SteveR
I have read this January 25, 2003 posting about softjaws about 3 times now and I want to try this. Since I don't have two piece jaws, I need to figure out how to make some.

If you don't have two piece jaws, could you take the one piece jaws and machine off the top/jaw, just leaving the bottom/scroll section and adding the mounting holes for the new top/soft section?

Good points about numbering the jaws for locating on the same base jaw and numbering the wrench hole for tightening the same one every time - there are all these sources of variation that I just don't think about!

Thanks for your mentoring,

Posted: Wed Aug 06, 2008 5:26 pm
by BadDog
In my opinion, the best bet is to get a new chuck with 2 piece jaws (when you can find a deal on one). Second option is to find 2 piece lowers to fit your chuck, but this is far from ideal with respect to accuracy/repeatability, though doesn't really hurt soft jaws as much.

Avoiding all that, I saw where someone made some aluminum blocks to fit over the stepped one-piece jaws (secured with a set screw I believe) and then machined to suit the part. I seem to recall it was quite successful...