How to Properly Cut Lathe Soft Jaws — Part 2: ID Gripping, Re-cutting, and Adding a Taper

welcome to the lathe soft jaw video series brought to you by Haas Automation in our first video we learned about the fundamentals of cutting lathe soft jaws when we made two different sets of OD gripping jaws in this second video we are once again joined by Andrew who will now cover the important aspects of id gripping jaws using this ring cap as an example we also cover recutting your jaws as well as how and when to add a taper to jaws to achieve a perfect fit most often id gripping jaws are used to hold parts which must be completely profiled on the outside face of the part or where the OD geometry of the part makes the surface difficult to grip the ID bore and back face of this ring cap were completed while the work piece was OD gripped in the first operation and since we need to machine curved surfaces on the parts outer diameter we need to hold it with internal gripping jaws andrew is considering whether to use standard soft jaws or PI jaws to ID grip this part if he were to use regular soft jaws to hold this thin walled Park at higher holding pressures the ring would begin to distort during clamping PI jaws allow this part to be clamped in a more robust and consistent manner pie jaws are often used to hold thin wall parts that will deform easily without full support as shown in this graphic gripping force is distributed much more evenly over the surface area of our pie jaws than compared to a regular soft jaw as we covered in the previous video we have ensured the jaws are clean before mounting that the jaws are torqued in place and that the chuck was lubricated at the beginning of the day using this Chucky's grease remember with our jaws in position for cutting the t-nuts must be inside the chuck body since we'll be using these pie jaws to hold a large ID part we can't use this style of boring ring since it will block the cutting path instead andrew will use this style of boring ring spinning the boring ring counterclockwise moves the three threaded grippers outward so they can be removed andrew flips them around and inserts them back in the body matching the letters on the grippers to the correct letters on the slots the jaw grippers are now facing outward at the Chuck and replaces the outward-facing grippers into the screw holes in the pie jaws and clamps down however the jaw stroke is not at the center of travel so the boring ring will need to be adjusted to do this unclamp the jaws and rotate the threaded body of the boring ring to adjust the position of the grippers this time with the Chuck clamped the jaws are in the middle of their stroke right where they need to be to cut these jaws we set the clamping pressure to 100 psi and we'll keep the spindle speed below the recommended 900 rpm and just as we did with Odie gripping we will need to push the jaws in the same direction that we will be ID gripping the part this time outward against the boring ring take special note of how fast the spindle will be rotating during actual part machining as speeds increase over 1000 RPM centrifugal force acting on the jaws will begin to significantly increase gripping force as the jaws are forced outward Chuck pressure may need to be reduced to compensate for this added force this is another reason to consider using PI jaws with PI jaws the additional centrifugal jaw pressure will be spread evenly over the internal surface of the part regardless of what kind of ID gripping jaws you are using jaws holding the inside diameter of the workpiece should always be cut to match the nominal workpiece diameter with the jaws pushing outward against the boring ring at 100 psi the master jaws at mid stroke and our programs set to cut to the nominal part diameter these jaws are ready to cut you as recommended in the first video we make a narrow groove at the bottom of the jaws so that any workpiece with sharp edges will sit flush to the jaws back face we deburr the jaws as necessary now we're ready to make our part to demonstrate how uniformly the pie jaws grip the part andrew mounts an indicator to check how much run-out we have with our part gripped in these jaws at 250 psi clamp pressure our parts total indicated run-out using the pie jaws is 510 thousandths in contrast with a standard set of soft jaws cut to grip this part we see a total indicator run out of 15 thousandths at 250 psi here is another example of a part that we want to ID grip this pulley has sufficient wall thickness to allow us to use standard soft jaws however the parts inside diameter bore which we want to grip is so small that neither of our boring rings will fit inside of our cutting path in this illustration the red ring represents the cutting path needed to cut the jaws to support our pulley part we can't mount any of our traditional boring rings in this position because we plan to cut here one alternative is to make a custom ring to fit a groove or relief you cut into the face of the jaws this allows for adequate clearance of the cutting path while the jaws are pushing outward against the ring just as they will when holding the part although there are many factors that you should take into account when choosing regular versus PI jaws these examples represent two possible scenarios to consider when trying to properly support your part there are many reasons to go back and recut your soft jaws for example your jaws might be worn or damaged or maybe your parts are beginning to creep out of Tolerance andrew plans to reuse the jaws that were originally cut to hold our bearing housing part since he knows that he'll be using these same jaws on this same machine with this same Chuck in the future there is no need to recut before disassembly he finds a mark or feature on the master jaw and scribes a line on the soft jaws to locate them at this exact tooth position in the future then as he removes each jaw he numbers it to match the number of the corresponding master jaw on the Chuck in this way concentricity will be maintained without cutting the jaws again andrew packs his jaws away and powers down the machine as anyone who's worked in a machine shop knows tooling sometimes has a habit of disappearing at inopportune moments andrew needs to run this bearing housing again but he's found that his jaws have been used on a different machine in the shop after finding and retrieving the jaws he needs to recut them before he can run his parts again using the scribed reference marks andrew mounts the jaws in the exact same position as they were before the idea is to machine away material to correct the jaw inaccuracies we need to clamp OD gripping jaws to just slightly smaller than the workpiece outer diameter conversely ID gripping jaws should be positioned just slightly larger than the workpiece inner diameter we will use our part to set the initial position of the jaws as they clamp the boring ring we want to check what diameter the jaws are actually positioned at to do this we program a simple move going to x0 with the tool and offset we'll be using to recut the jaws press hand jog press current commands and press page up until you reach the position page with x-axis selected press origin to zero out the operator position field now that we know where x0 is for tool one and offset g54 let's find the jaw face diameter jog to a point very close to the face of the jaws use a slip of paper and bring the tool to the jaw face until the paper is pinched by the insert tip the x-axis operator field now shows us the diameter that our jaw faces are set to in our case we want to recut these jaws to the nominal part diameter of three point nine five zero inches with our jaws checked at a clamp location of three point nine three five we have set their positions such that an adequate amount of material will be removed from each jaw face we will also change our jaw cutting program to skim cut into the back face ten thousandths deep to clean up this face as well as the main bore always skim cut the jaws for complete cleanup but keep material removal to a minimum to get the most life out of your jaws now they are the correct bore size and once again concentric to the spindle you when clamping force increases so does the deformation of the jaws for this reason when cutting soft jaws it is important to try and use the same holding pressure that will be used when machining the production parts when the pressure needed to hold the part is much higher than the pressure that was used to cut the jaws the jaws will deflect away from the part particularly at extreme differences in clamping pressure and at very long jaw lengths to compensate for this deflection cutting a slight taper in the jaws may become necessary after the taper is cut and the correct force is applied to the workpiece the jaw faces will still be parallel to the workpiece despite jaw deflection let's look at some real-world scenarios this set of short steeljaw's was bored to one inch deep while being held at 100 psi when we clamped this accurately machined slug at 300 psi and check for deflection we find that we can't insert even a one thousandth of an inch feeler gauge at the jaw tips next we have these short aluminum jaws cut with a 1.5 inch deep bore also at 100 psi again we clamp the machined slug at 300 psi and although you might think with the softer material and different clamping height we might see significant deflection we still can't get the one thousandth of an inch feeler gauge in between the jaw and the workpiece to demonstrate a more extreme scenario we move on to these tall four inch aluminum jaws which were bored very deep at a clamping pressure of only 50 psi when we clamp the demonstration workpiece at a pressure of 400 psi jaw deflection becomes significant let's find out just how much taper should be added to the job or Andrew measures the space between the deflected jaw and the workpiece using the feeler gauges he finds a four thousandth of an inch space so he will start by adding a fourth thousandth taper to the jaws for both outside holding and inside holding jaws you should cut the taper to leave more material at the jaw tip than at the jaw base going back to his original program andrew changes the starting point of the cut from 0.05 to z zero to start right at the face of the part he inserts you 0.008 in front of the z-depth move this will taper the face so the bore is larger diameter at the bottom than at the top since you 0.008 is a diametrical adjustment it will taper each wall four thousandths of an inch andrew cuts the taper in the jaws with the taper cut and the workpiece clamped at full pressure feeler gauges will probably not fit in the remaining space however there may still be a small gap now Andrew uses a slow drying bluing compound to check if he needs to make another slight taper cut he clamps the workpiece in the jaws at full production pressure and applies a coat of the compound to the edge of the jaws where they meet the workpiece after allowing the bluing to dry andrew unclamped the jaws and finds that very little of the compound has seeped in between the jaws and the workpiece not even where the jaw tips contact the workpiece this indicates the jaws are gripping along their entire length now let's look at what too much and too little taper look like using our setup one thousandth of an inch too much taper results in a concentration of bluing at the base of the workpiece indicating the jaws are not contacting in this region the inverse of this is one thousandth of an inch too little taper which results in good contact only at the base of the jaw where it meets the workpiece in either case another pass can be made to either remove or add a slight amount of taper and thereby achieve the correct engagement thanks for watching this video and stay tuned for additional episodes covering other machining fundamentals

Channel: Haas Automation, Inc.

Views: 510,292

Keywords: lathe, soft jaws, cutting soft jaws, ID gripping, re-cutting, adding taper, taper, CNC machine tools, CNC machining, Gene Haas, Haas Automation, Haas CNC, CNC, Haas, haascnc, machining, manufacturing, boring, turning

Id: -AyMQNoaBjc

Length: 15min 45sec (945 seconds)

Published: Fri Jul 19 2013