Lathe Part Stop Essentials. Do You Know? – Haas Automation Tip of the Day

Hello and welcome to this Haas Tip of the Day. In today's video, we're going to talk all about lathe part stops and how those can be used to make parts more precisely with your pull-to-close collet chucks, with your push-to-close collet systems, like a dead-length, acculength, true-length type collet system. And to better understand how all of these things work together, we've got to explain how our draw tube assembly works with our draw tube and our hydraulic actuator. So stick around. We're going to show these things in a way that you may never have seen before. Everything for me begins with my setup tool. So check this out. I've got a block loaded up. Now, if you're tightening up those tools by hand... This, my friends, is a draw tube assembly out of one of our lathes, and it is amazing. When I press the foot pedal to close my chuck, a valve is opened, allowing pressurized hydraulic fluid to flow from our pump into our actuator. The fluid pushes against a piston that is fixed to our draw tube. The actuator piston pushes our draw tube to the left or the right with each push of our pedal. When the spindle and draw tube are turning at thousands of RPMs, the hydraulic actuator housing remains stationary, held by a bracket. Knowing how our draw tube works will help us make good decisions when it This is a typical pullback style collet chuck. With this style of collet chuck, our collets are pulled back by our draw tube. In fact, our collets often screw directly to our draw tube adapter, which is tightened onto our draw tube. As a collet is drawn back, the collet is force closed against our stock by the matching angle on the chuck body. This is a pull-to-close system. Now these chucks can be ideal for first operations and for bar feeder applications, but there are some drawbacks. Because the collet moves with the draw tube, any variance in our part's diameter will cause a proportional shift in our part z-axis position. Each type of collet has its own pullback ratio based on that collet's angle. In general, there are four different types of collets, or four different types of collets that we're going to talk about. Our C-style collets, like our 5C and 16C style, are simple and they can be found everywhere, and they typically have a threaded ID so they can receive collet stops. J-style collets have a slightly sharper angle to the collet, and they're a bit shorter than their 16C counterparts, and they have a little bit larger bar capacity. S-style collets have a master S collet with removable quick-change pads. Now these are popular with bar feed machines, and they come in different sizes like S20, 26, 30, and larger. Newer quick-grip styles of collets, like this one from Royal Products, have become really popular lately as well. They're quick to change, and they often come with high precision variants. Well, since this is a video about part length accuracy, we've got to show you these keyways that are in your collets. The 5Cs, 16C, 3Js, and even our S-style master collets have a keyway that is meant to receive an anti-rotation screw. After you place the collet into the collet chuck, you'll rotate it until the screw fits into the keyway. This will keep your collet from unscrewing itself. Okay, and if that collet becomes unscrewed, your Z length is going to vary. So make sure to check out the manual for your collet chuck. There's all different methods. There's a shoulder screw, which you tighten up all the way. There are set screws, which need a backup screw behind them. So look at your manual, figure out how these are used, and always use an anti-rotation set screw. With this 16C pullback style collet chuck, our parts repeat fairly well when held against a part stop mounted on our collet. But if our X diameter is shrinking at all, part variance, then our part is going to be moving along the Z axis by three times that X variance. That's a pullback ratio of one to three. It's important that you know the pullback ratio for the collet chuck that you're using. In this example, my orange part has varied by two thousandths of an inch in the X diameter. So we take that two thousandths of an inch, multiply it times our pullback ratio, and we end up with a pullback distance of six thousandths of an inch. Both 5C and 16C collets have a 10 degree tapered angle per side. That gives us a pullback ratio of one to three. That number isn't random, it's just the way the math works out at those angles. A 3J collet has a tapered angle of seven degrees per side. With those collets, we have a pullback ratio of one to four. If you're using an S style collet with pads, then we have a pullback ratio of one to 2.5. And that's the same value we'll use for our quick grip collet systems, one to 2.5. Just remember, our parts are going to move on us along the Z axis with any X diameter change in stock size. So, what's the pullback ratio for your chuck? If you don't know, you can use one to three as a general rule of thumb, or you can just look it up for your collet chuck. Now, on a first operation, that slight Z variance might not be too bad. We can just add in an extra facing pass. But on a second operation, it does matter. That's our finished part length. A dead-length collet chuck might be more appropriate for those second operations. Now, different manufacturers have different names for this style of collet chuck. You have dead-length, accu-length, true-length, fixed-length. And all these collet chucks are working really hard to keep our collets from moving when the draw tube moves. With push-to-close collet systems, our collets are fixed to the chuck body, which doesn't move, and not directly to our draw tube, which does move. The draw tube attaches to a clamping collar, which pushes against the stationary collet to force it closed. This leaves your part in the same Z location every time, even if your part diameter varies. We can tell the control which system we are running, pull-to-close or push-to-close, by selecting either OD or ID under setting 282 spindle chuck clamping. That is how our draw tube assembly works. Now we can take a look at some part stop examples, and you can guess as to how these will work with either a pull-back or a push-to-close dead-length style system. Are we stopping our parts against something that is moving or not? We've got some cool part stops for you here, and we're going to just walk through them quickly. Some you've seen, some you might not have. We'll start with our part stop of last resort, our calipers. And yes, using it for a stop could damage them, but you know you've done it. Don't do it. There are better ways to stop our parts. Using a stop-lock collet stop works in much the same way, but it doesn't damage our calipers. Here we have our collet stops, and these work really well. They were designed to screw into the back of our collets. They are available for different size collets like 5C, 16C and 3J, and you can purchase extension tubes that work with longer parts. But remember, if those collet stops are attached to your collet, and your collet is moving back and forth, then your stop is also moving. A really simple, easy-to-use collet stop is this extrusion from Mighty Bite. Cut it to length, slide it into your collet, and you have a stop. Programming a stop that is mounted in your turret can get you out of a pinch as well. With the chuck open, load some stock and then command our turret stop into position. Manually pull the bar to stop and clamp. Like many of these stops, this method is more accurate when used with a dead-length collet-style chuck or a 3J. A spindle stop like this one from Rovi Products can be mounted right inside of your draw tube. When you rotate the wrench, the stop expands, clamping firmly against the ID of the draw tube. Spindle stops like this one are a great way to locate first operations, where the parts are too long for a collet stop. Again, this style of stop moves with the draw tube, so remember those pullback ratios. If you have a Haas bar feeder like the one behind me, you can command the push rod to a known position using a V-axis command. Now, I really like this method because that push rod is held outside the machine and it does not move with your draw tube, meaning that it works great no matter what chuck you have. Many high-end collet chuck manufacturers actually make stops designed for their chucks, so check with your manufacturer. This is probably one of the better ways of stopping your parts, when it's designed right into your chuck. This video is primarily about pullback collet style chucks, but if you have a three jaw, there are some things to consider. If we locate our part stop on the draw tube, we kind of contend with that same pullback ratio. Most three jaw chucks have a mechanical advantage ratio of about 1 to 2.5. That's going to act in the same way as a pullback ratio of 1 to 2.5, if you locate your parts off the draw tube. So, it's a good idea to locate off the face of your chuck in some way. Now, there are magnetic stops that mount right to the face of the chucks, which are terrific, like this one from Royal. Beyond that, we've got stops like this one from Accustop for longer parts that, again, mount to the non-moving face of our chuck. For short parts, properly cutting your jaws is a great reliable way to ensure your part length. Be sure to check out our cutting soft jaws video for more info on that. We'll leave you a link in the description. And as always, you can try making your parts in one operation, running it from a piece of bar and using a cutoff tool to control your length, or run it on a machine that has a sub-spindle. We've given you some great methods on how to locate your parts, but here's one method that you need to avoid. Some shops have created their own stops that mount on the back of their actuators, and we don't want you to do that. That will void the warranty on your clamping union, and there's a couple reasons for this. Number one, some of these stops actually trap the coolant behind the actuator. That coolant has no place to go but inside the hydraulic union, contaminating your hydraulic fluid, which is a bad idea. Secondly, loading parts too firmly or using a pull-back style collet system can put a tremendous amount of force on our housing here, causing bearing damage or actually causing the union to crack or split. Well, that is it. Leave us your comments. Share your experience. We want to hear how you are locating your lathe parts. Thanks for letting us be a part of your success, and for watching this Haas Tip of the Day.