My views on soft jaws
Posted: Sat Jan 25, 2003 4:10 pm
Running soft jaws is a great way to hold almost anything that you have need to chuck, be it a straight bar or a complex piece. The advantage is that you can chuck items time and again with precision with no effort aside from properly setting up the soft jaws. When properly prepared, soft jaws will generally repeat to within .0005" consistently. A further benefit of soft jaws is that you can hold delicate items without fear of marking, crushing or distortion because the jaws can be made to almost totally enclose your item. Using your imagination, soft jaws are nearly a perfect solution to almost any chucking problem. Even strange configurations can be held if you're willing to do your jaw machining on a mill. They are truly one of the best methods of holding parts.
How I came to run soft jaws routinely came about because of a negative experience with my 3 jaw shortly after I bought the lathe. I had the chuck on edge and turned to pick up my air hose to blow off the D1-4 mount before installing it in the lathe. The chuck rolled and hit the floor, landing on one of the jaws, shearing off the teeth. The scroll was apparently not hurt, for it is still in use to this day.
A new set of jaws was requested from the dealership. They were ordered, though never received. The dealer had a set of jaws on hand that had come from another chuck, which he offered to me while I waited (in vain) for the new jaws to come in. The dealer finally told me to keep the jaws I had borrowed. These used jaws had a considerable amount of runout, so I started using a set of soft jaws for gripping straight material.
My chuck came with three sets of jaws, the third set being the two piece type jaws that were already fitted with soft jaws. To this day, I generally have soft jaws in my chuck, though there are times when I do use the ill fitting jaws, along with the reverse gripping jaws that also came with the chuck. What I learned from that experience is that, in general, soft jaws are superior in almost every way to hardened jaws. They grip material very well, even for roughing operations, with the advantage of running far more precisely than the hardened counterparts.
If you're interested in trying soft jaws, your chuck must be fitted with the two piece jaws that permit reversing the top jaw. Instead of using the top jaws, a set of soft jaws is purchased or machined from steel or aluminum. I prefer steel, but aluminum has its place. Once the new soft jaws are installed in the chuck, the jaws are then bored to accommodate the form of the part to be held. This brief outline will be discussed in detail below so you can follow, step by step, the procedure to try them yourself.
A safety note: The larger the soft jaws are, the better the chance of getting clipped when running them. They stick out considerably farther than hard jaws, so you must exercise good work practice. They can be dangerous, but running machinery is dangerous business. Be ever aware of the spinning jaws, soft or otherwise.
To make soft jaws, consider these things:
The jaws you make should be a snug slip fit on top of the master jaws so they locate the same way each time they are installed, and can't shift under load. You should duplicate, in every detail, the mounting face of the soft jaws as compared to a hard jaw.
The larger you make the soft jaws, both in length and height, the longer life they will have. The wider you make them, the more area you will have gripping your part, something that can be important for thin pieces.
Wide jaws limit how far you can close your chuck. There is no good reason why you can't taper the jaws so they can close down farther. Just make sure you remove an identical amount from each jaw so they remain the same relative weight from jaw to jaw so the chuck runs in balance. I recommend wider jaws over narrow ones. They will serve you better in most instances. If you feel you will hold a lot of small parts, make more than one set while you're making them, and make one set as narrow as possible. Even tapering the portion where they come together so you can grip small diameters. Anything goes with these things as long as you keep them in balance.
Be certain that the ends of the jaws extend beyond the base jaws both inside and outside. There will be occasions when you bore through the jaws, so you must clear the base jaw to do so. You will have to do that in order to hold long items that will pass through the chuck body.
When you counterbore for the socket head cap screws, go deep enough that you can use the original screws. If you use longer screws, the life of your jaws will be restricted to the depth of the counterbore. Once you get to the screw, you can no longer machine the jaws. The counterbore should be no larger diameter than necessary.
Your jaws should be numbered so they can be placed on the same base jaw each time. Make your permanent mark by stamping, and do it below the area of the screws so you can't machine the number off inadvertently.
You MUST always use the same wrench hole when tightening your chuck. If you do not have one that is marked, mark one in a permanent way and use only this hole each time. Any other hole will yield runout. The scroll is loose enough in the chuck that it will load differently with each hole, giving more or less runout from hole to hole.
I have attached a photo of my chuck with one set of soft jaws partially installed, with various views of these jaws. These were made about 35 years ago for a specific purpose, but I have used them countless times since for gripping similar items.
Keep in mind that soft jaws can be reversed on the top jaw, so you can use both ends of the jaws for different configurations. Thus, each set is actually two sets of jaws. Those in the pic were used that way, plus the projecting jaw was also used to hold a part internally, so this set of jaws was used in three different ways.
When jaws have been machined until there is no more life in them, it is customary to weld on new stock and start over. They don't have to be pretty, and any precision that is demanded comes from the machining, not the welding.
I'll discuss boring the jaws in this post, and I'll discuss the making of the little adjustable spider in the following post directly under this one, along with a picture of it for clarification.
To begin boring soft jaws, once installed, set the jaws such that you can bore them by removing the absolute minimum of material to create the pocket that will hold your part. That way you will get the best mileage from your jaws. At that point, the jaws should be blocked by closing down on the spider, which has been pre-set to support the jaws at that particular location. The length of each of the stops in the spider should be identical, which can be measured from the straight face of the spider body by using a scale.
When you install the spider, it should be as close to the outside edge of the jaws as possible, just beyond the deepest point you will machine. If you are boring jaws straight through, you will locate the spider on the base jaw, just slightly beyond the end of the soft jaw so you can bore through but not hit the spider. Remember that the bulk of error in your chuck is because of slide distortion, so you want to load the jaws in the slide such that they can't move, and the loading will be identical to the loading in application. That's how you generate the high precision.
It is VERY important that the spider be at right angles, not cocked and running wonky. If you close your chuck on a piece that is not dead perpendicular, what it does is load the jaws differently from one another, yielding jaws that won't run on center. You'll be hard pressed to get your jaws to run under a thou that way. Be certain to also have the spider centered on the jaws so they aren't loaded to the side, which also yields jaws that don't run well. Tighten your chuck as tight as you feel you'll tighten it when you are actually running your part. Try to duplicate, as near as possible, the identical conditions that you will use when you are machining. That yields the highest degree of precision.
Once you have your spider properly located, bore your jaws to the exact size of your part. The part should start, but not necessarily go in when you try fitting for size. Approach size carefully, for an oversized bore will yield run-out. If you go oversize, you can reset the spider and close the jaws, then re-bore , so all is not lost.
Soft jaws run true because you machine the pocket to exact size of the part being held. If you advance the scroll beyond or retract it to a position before the one that it occupied when boring the soft jaws, there is no guarantee that the jaws will run concentric, and there will no longer be a match of holding surfaces, jaw to part. The soft jaws will grip only at their outer edges if the item is larger, and only in the center if the item is smaller. It takes very little to effect the fit, and also the runout
If you intend to use the bottom of the bore to register your part, bore your jaws to the desired depth, then face the back of the bore so you have a perfect right angle. It is always a good idea to slightly undercut the inside corner so it does not interfere with the part touching the shoulder. I generally use a relatively sharp pointed bar and just go slightly deeper in both depth and diameter at the corner, yielding some clearance so a sharp corner will clear. That seems to be adequate.
If you intend to hold a long item that won't bottom out in the jaws, bore them clear through, and to the diameter of the item to be held.
If you intend to make several parts, hold the chucking diameter as close as possible from part to part. Even a thou can change the way your chuck runs, so that is important.
Once bored to size, remove the spider, clean out the chuck as required, and carefully deburr the jaws so you can't roll over the burrs and trap them between the parts and the jaws. I make it a practice to draw my file away from the jaws so I don't roll any burrs inside, where they will mark your parts and create runout if you happen to miss them. It's a good policy to go over the edges with some abrasive cloth if you have parts that are finished and you don't want to mar them in any way.
Once you've cleaned up your jaws, put in a part and check it for runout with a DTI. If you aren't happy with how the part runs, repeat the operation. There are times when you may have to bore two or three times to get the runout down, a result of the spider not being located perfectly. Each re-bore need be only a thou or two in depth, just enough to clean up again and hit size. That will be determined by how you set the spider.
There is a follow up photo in the next post, showing a set of soft jaws made from aluminum. I generally make them without the step, but the piece of stock I used was tapered, so I cut the step to eliminate the taper. They normally would be rectangular in shape. That permits the most life and options of how you will machine the jaws. The step in this set of jaws will limit me in how I can use that end of the jaws, but the price was right!
Harold
How I came to run soft jaws routinely came about because of a negative experience with my 3 jaw shortly after I bought the lathe. I had the chuck on edge and turned to pick up my air hose to blow off the D1-4 mount before installing it in the lathe. The chuck rolled and hit the floor, landing on one of the jaws, shearing off the teeth. The scroll was apparently not hurt, for it is still in use to this day.
A new set of jaws was requested from the dealership. They were ordered, though never received. The dealer had a set of jaws on hand that had come from another chuck, which he offered to me while I waited (in vain) for the new jaws to come in. The dealer finally told me to keep the jaws I had borrowed. These used jaws had a considerable amount of runout, so I started using a set of soft jaws for gripping straight material.
My chuck came with three sets of jaws, the third set being the two piece type jaws that were already fitted with soft jaws. To this day, I generally have soft jaws in my chuck, though there are times when I do use the ill fitting jaws, along with the reverse gripping jaws that also came with the chuck. What I learned from that experience is that, in general, soft jaws are superior in almost every way to hardened jaws. They grip material very well, even for roughing operations, with the advantage of running far more precisely than the hardened counterparts.
If you're interested in trying soft jaws, your chuck must be fitted with the two piece jaws that permit reversing the top jaw. Instead of using the top jaws, a set of soft jaws is purchased or machined from steel or aluminum. I prefer steel, but aluminum has its place. Once the new soft jaws are installed in the chuck, the jaws are then bored to accommodate the form of the part to be held. This brief outline will be discussed in detail below so you can follow, step by step, the procedure to try them yourself.
A safety note: The larger the soft jaws are, the better the chance of getting clipped when running them. They stick out considerably farther than hard jaws, so you must exercise good work practice. They can be dangerous, but running machinery is dangerous business. Be ever aware of the spinning jaws, soft or otherwise.
To make soft jaws, consider these things:
The jaws you make should be a snug slip fit on top of the master jaws so they locate the same way each time they are installed, and can't shift under load. You should duplicate, in every detail, the mounting face of the soft jaws as compared to a hard jaw.
The larger you make the soft jaws, both in length and height, the longer life they will have. The wider you make them, the more area you will have gripping your part, something that can be important for thin pieces.
Wide jaws limit how far you can close your chuck. There is no good reason why you can't taper the jaws so they can close down farther. Just make sure you remove an identical amount from each jaw so they remain the same relative weight from jaw to jaw so the chuck runs in balance. I recommend wider jaws over narrow ones. They will serve you better in most instances. If you feel you will hold a lot of small parts, make more than one set while you're making them, and make one set as narrow as possible. Even tapering the portion where they come together so you can grip small diameters. Anything goes with these things as long as you keep them in balance.
Be certain that the ends of the jaws extend beyond the base jaws both inside and outside. There will be occasions when you bore through the jaws, so you must clear the base jaw to do so. You will have to do that in order to hold long items that will pass through the chuck body.
When you counterbore for the socket head cap screws, go deep enough that you can use the original screws. If you use longer screws, the life of your jaws will be restricted to the depth of the counterbore. Once you get to the screw, you can no longer machine the jaws. The counterbore should be no larger diameter than necessary.
Your jaws should be numbered so they can be placed on the same base jaw each time. Make your permanent mark by stamping, and do it below the area of the screws so you can't machine the number off inadvertently.
You MUST always use the same wrench hole when tightening your chuck. If you do not have one that is marked, mark one in a permanent way and use only this hole each time. Any other hole will yield runout. The scroll is loose enough in the chuck that it will load differently with each hole, giving more or less runout from hole to hole.
I have attached a photo of my chuck with one set of soft jaws partially installed, with various views of these jaws. These were made about 35 years ago for a specific purpose, but I have used them countless times since for gripping similar items.
Keep in mind that soft jaws can be reversed on the top jaw, so you can use both ends of the jaws for different configurations. Thus, each set is actually two sets of jaws. Those in the pic were used that way, plus the projecting jaw was also used to hold a part internally, so this set of jaws was used in three different ways.
When jaws have been machined until there is no more life in them, it is customary to weld on new stock and start over. They don't have to be pretty, and any precision that is demanded comes from the machining, not the welding.
I'll discuss boring the jaws in this post, and I'll discuss the making of the little adjustable spider in the following post directly under this one, along with a picture of it for clarification.
To begin boring soft jaws, once installed, set the jaws such that you can bore them by removing the absolute minimum of material to create the pocket that will hold your part. That way you will get the best mileage from your jaws. At that point, the jaws should be blocked by closing down on the spider, which has been pre-set to support the jaws at that particular location. The length of each of the stops in the spider should be identical, which can be measured from the straight face of the spider body by using a scale.
When you install the spider, it should be as close to the outside edge of the jaws as possible, just beyond the deepest point you will machine. If you are boring jaws straight through, you will locate the spider on the base jaw, just slightly beyond the end of the soft jaw so you can bore through but not hit the spider. Remember that the bulk of error in your chuck is because of slide distortion, so you want to load the jaws in the slide such that they can't move, and the loading will be identical to the loading in application. That's how you generate the high precision.
It is VERY important that the spider be at right angles, not cocked and running wonky. If you close your chuck on a piece that is not dead perpendicular, what it does is load the jaws differently from one another, yielding jaws that won't run on center. You'll be hard pressed to get your jaws to run under a thou that way. Be certain to also have the spider centered on the jaws so they aren't loaded to the side, which also yields jaws that don't run well. Tighten your chuck as tight as you feel you'll tighten it when you are actually running your part. Try to duplicate, as near as possible, the identical conditions that you will use when you are machining. That yields the highest degree of precision.
Once you have your spider properly located, bore your jaws to the exact size of your part. The part should start, but not necessarily go in when you try fitting for size. Approach size carefully, for an oversized bore will yield run-out. If you go oversize, you can reset the spider and close the jaws, then re-bore , so all is not lost.
Soft jaws run true because you machine the pocket to exact size of the part being held. If you advance the scroll beyond or retract it to a position before the one that it occupied when boring the soft jaws, there is no guarantee that the jaws will run concentric, and there will no longer be a match of holding surfaces, jaw to part. The soft jaws will grip only at their outer edges if the item is larger, and only in the center if the item is smaller. It takes very little to effect the fit, and also the runout
If you intend to use the bottom of the bore to register your part, bore your jaws to the desired depth, then face the back of the bore so you have a perfect right angle. It is always a good idea to slightly undercut the inside corner so it does not interfere with the part touching the shoulder. I generally use a relatively sharp pointed bar and just go slightly deeper in both depth and diameter at the corner, yielding some clearance so a sharp corner will clear. That seems to be adequate.
If you intend to hold a long item that won't bottom out in the jaws, bore them clear through, and to the diameter of the item to be held.
If you intend to make several parts, hold the chucking diameter as close as possible from part to part. Even a thou can change the way your chuck runs, so that is important.
Once bored to size, remove the spider, clean out the chuck as required, and carefully deburr the jaws so you can't roll over the burrs and trap them between the parts and the jaws. I make it a practice to draw my file away from the jaws so I don't roll any burrs inside, where they will mark your parts and create runout if you happen to miss them. It's a good policy to go over the edges with some abrasive cloth if you have parts that are finished and you don't want to mar them in any way.
Once you've cleaned up your jaws, put in a part and check it for runout with a DTI. If you aren't happy with how the part runs, repeat the operation. There are times when you may have to bore two or three times to get the runout down, a result of the spider not being located perfectly. Each re-bore need be only a thou or two in depth, just enough to clean up again and hit size. That will be determined by how you set the spider.
There is a follow up photo in the next post, showing a set of soft jaws made from aluminum. I generally make them without the step, but the piece of stock I used was tapered, so I cut the step to eliminate the taper. They normally would be rectangular in shape. That permits the most life and options of how you will machine the jaws. The step in this set of jaws will limit me in how I can use that end of the jaws, but the price was right!
Harold