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What's wrong with my threading technique?

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  • Is the insert pictured supposed to be HSS material? If it is, it looks like it could be a sintered, or powdered metal product. That, and the rather odd positioning with the top face pitched down at such a high angle relative to the tool feed direction suggests that this may be a lower quality insert and holder combination. A low quality sintered insert is more apt to be brittle and therefor susceptible to breaking, and the cutting edge could be a little ragged too. Is this tool combination from the same manufacturer as the internal threading tool that was being used last week, at the beginning of this post? From what I see in the photos everything else appears to be capable of yielding good results, except for that threading tool. Also, have you invested in some thread measuring wires? From the description in the next to last photo, the major diameter at .495 should assure no clearance issues there, but the pitch diameter needs to be controlled accurately for a good fit, and that will require accurate measurement from either wires or a dedicated thread micrometer.

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    • As I mentioned earlier, the rake also changes the form of the thread being cut, So if the insert is INTENDED to be at that angle, it would be wrong if held straight, and if intended to be held straight, will be wrong at that angle.

      Looking at this http://www.arwarnerco.com/catalog%202014.pdf it appears that the insert is intended to be held straight, if indeed that IS a Warner insert and holder, which it may or may not be.

      Angling it will cause the v-groove to be shaped wrongly. So the thread will be no good, unless that insert, wherever it comes from, is intended to be used in that holder.
      CNC machines only go through the motions

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      • 192 posts (20 pages on my machine) to get to this point

        I have inserts and holders for that old type ... definitely wrong.

        Toss it. If you want to stay with carbide and inserts, buy a 16ER version from Shars. Upgrade if you want too later. heck, for $30 you can get the correct holder your insert (assuming you have a few of them).
        Last edited by lakeside53; 04-30-2018, 08:35 PM.

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        • I'd just like to make a comment that every one has helped a person that is learning is great, but i had a job the other day that would have made him run and hide, (I almost did) the thread was a triple lead 2 1/4" 4.5 pitch internal left hand.

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          • I'd pass that to my local machine shop! Trivial with CNC; not nice manually.

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            • Originally posted by duckman View Post
              I'd just like to make a comment that every one has helped a person that is learning is great, but i had a job the other day that would have made him run and hide, (I almost did) the thread was a triple lead 2 1/4" 4.5 pitch internal left hand.
              Nothing like a challenge to keep the brain cells sharp! Do you have photos of the job, or can you go into some detail about the setup and machine used?

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              • Honestly guys, like I said, I am acting totally on assumptions with this setup. I am assuming it's HSS from Warner because it looks like their product, and doesn't resemble any of the carbide I have. I could be totally wrong as I didn't purchase it directly. It was assembled in a small box with a similar holder that was neutral rake angle (flat on top) which I broke when I first started trying to thread stuff a few months ago. It was my fault, can't remember what I did exactly, but it was no fault of the tool's.

                On the up side, I recalibrated my DRO, cut a new thread with my carbide lay down insert and it turned out very well. I did learn today that I can get an amazingly nice finish out of my carbide tooling, but I've got to run more DOC. I've been trying to sneak up on a diameter, but today, I took heavy cuts, 40-50 thou per side, and the finish was great. Threading at 180rpm worked well too, but a bit nerve wracking, I think I'll stick to 60 for now (I've got nothing in between without releasing the motor tension and moving the belt).

                I may try ordering some HSS in the future and trying it, but for now, the carbide is working, I just needed to learn how to use it better. But then again, that's all I'm doing at this stage, learning how to use my machine. I wish I had someone to watch over my shoulder, but I don't know anyone in my area who does any machining. Central Texas isn't exactly known for machine shops, and the ones that are here, are 95% CNC.

                Sent from my SAMSUNG-SM-G891A using Tapatalk

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                • U-tube is your friend. Dig around; sometime it's better than being shown

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                  • Originally posted by lakeside53 View Post
                    U-tube is your friend. Dig around; sometime it's better than being shown
                    I watch YouTube for hours on end, that's how I've gotten this far.

                    Sent from my SAMSUNG-SM-G891A using Tapatalk

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                    • Please continue to ask questions. We are glad to help.

                      You'll note that the pictures of ALL the steps enabled several of us to see the problem immediately. I don't think you would have described the tool and it's holder properly without the pictures. This is because you are still building the vocabulary and learning about things. With digital camera's it's a breeze to snap a photo of all the control settings, the tool and the work, even if you don't post them.

                      BTW, youtube is a great source of information, but they don't always use the right terms and sometimes do things wrong. MrPete is a good source.

                      Key learning for today;

                      1) The top of the cutting edge will almost always be within a few degrees of pointing at the center of lathe's axis. (being on the same plane)
                      2) You can force a tool to "almost" work when it's maladjusted. It's worth learning what that sounded like as compared to when you were doing it right.

                      Dan
                      At the end of the project, there is a profound difference between spare parts and left over parts.

                      Location: SF East Bay.

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                      • To be fair to the OP, he DID state that the insert was presented at a negative rake last night back in post 183.

                        Agree, it might have been helpful to mention that earlier, IIRC he changed tools at some point in the process, I don't recall just where, but originally he was going in reverse on backside.

                        But, it is hard for people to guess what will be important information. If you can guess what is important to report, you may be on your way to a solution.

                        In many cases, just the idea that some piece of info might be important is enough to set off a solution to the problem, without ANY answers from others.... If negative rake is an important fact, that brings up the question of whether negative rake is correct.... which leads to the idea of trying a neutral rake, if that is possible.
                        Last edited by J Tiers; 04-30-2018, 11:51 PM.
                        CNC machines only go through the motions

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                        • Thanks for all the help so far guys. Keep in mind, I'm brand new to all this, and trying to make do with the tools I've got for now. I've bought a few and made a few, and done some upgrades to the machine (the DRO was a chore, but turned out really well), but this stuff is expensive, and I'm the type that doesn't want to buy junk only to have to replace it in a few months when I realize I've outgrown it. That's not to say that I need top of the line with everything, but why fuss around doing stuff the hard way when a tool is available that makes a 5 minute job into a 30 second job, so long as the results are of equal quality? Why spend money on thread wires, then have to keep up with all of them and do math to get the measurement, when Shar's sells a thread mic for around $50 that will give me the reading directly? In a few weeks, I'll be able to order more of the tools I need and want, and believe me, I've got a list already. Right now though, funds are tight due to paying 2 mortgages until I can get my rental house sold.

                          Everyone told me I'd spend more in tooling than I would on the machine, I just didn't think it would be this fast considering the machine came with a fair amount. The previous owner appears to have been really fond of triangle inserts......I seem to have better results from diamonds, both 80 degree and the smaller ones, 15 degrees? I've had good results turning aluminum and brass, but I've been struggling with steel, until today when I realized I could take bigger bites and get a good finish. I will probably order some HSS from Warner, along with their holders, just to try it out because I hear good things about it, and maybe (probably?) what I had that I thought came from them actually didn't. I know I'll eventually have to grind my own HSS blank for some specialty tool that doesn't exist as an insert, but for general use, I like inserts, not having to grind it myself, and being able to just bring another edge around when one gets dull or damaged, even though I haven't needed to index anything yet aside from that threading insert that I keep breaking.

                          Sent from my SAMSUNG-SM-G891A using Tapatalk

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                          • Keep in mind, the Way you presented the tool to the work, made it a much weaker edge.
                            Meaning that could be a lot of the reason you broke one edge.
                            And looking at the relief angles of that type of insert would be hard to hand grind, a thinner cutting tool is easier to make.

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                            • Blindingly obvious now we've seen the photos. Point of insert at centre height, flanks of insert way above centre height, no wonder they didn't cut, just rubbed.
                              Yes, carbide likes a decent speed and a deep cut, it doesn't respond well to lower speeds and 'sneaking up' on a finished size. HSS will do that though, and give you a decent finish if its sharp, preferably honed.
                              IMO, no way that insert is HSS. Mounted in a suitable holder, with zero or slightly positive top rake, the inserts will probably work quite well.

                              Like machining steel of unknown origins, theres always risks in using tooling of unknown origins.
                              'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                              • Originally posted by lakeside53 View Post
                                U-tube is your friend. Dig around; sometime it's better than being shown
                                yeah, can also be your enemy. There's no vetting of what gets posted and so many expand 15 seconds of content into 10 minutes of blabber. imo, one would be better off with a used high school senior or college machining text book that walk though it step by step. imo books are faster and vs the wild west, there's some quality control
                                in Toronto Ontario - where are you?

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