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How long to make a part ??? (time, not distance long)

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  • How long to make a part ??? (time, not distance long)

    Last night I took a raw piece of annealed 4140 that was 5.1" long, 4.5" OD, and made a donut that was 4.95 inches long, 4.40 OD, and had a 1.45" hole lengthwise through it. Pretty simple piece. Sequence of operations and tooling shown in postscript.

    Anyway, I watch YouTube videos to help me learn (and for entertainment), and if feels like I must work incredibly slowly. Of course I know they edit out huge hunks of time, and some of the people use sped-up segments, but still it seems like I am a slow poke compared. In addition I know that I can't compare my output using a 1 HP Rockwell-Delta to somebody who has a 7 HP Monarch.

    SO -- how long do you think it would take you to make the same donut starting with that same bit of rough stock? Please include what type and HP of lathe you use. Also, how much of your speed is due to skill rather than just having better tools?

    Critiques, criticisms and "why the hell did you do that?" are all welcomed.
    Thanks

    SOO and Tooling:

    Mount in 4 jaw and center +/- .05 (since outside was rough).
    Face off end using MHC brazed carbide bit.
    Turn 1" from end down to 4.40 OD
    Reverse stock in 4 jaw and center turned portion +/- 0.002, then check that the end far from chuck has acceptable runout
    Face off end to length.
    Turn remainder of outside to 4.40 OD
    Spot drill face, and then use 1/4", 3/8" and 1/2" drills to make pilot hole about 3" deep
    Use 5/8", 7/8" and 1 3/16" drill to make hole about 3" deep
    Running out of drill bits, I use a 3/4" boring bar with carbide insert to widen the hole to 1.400" in 0.025" increments
    Flip stock in chuck, and go anal-retentive about centering in the 4 jaw.
    Drill the other half of the hole using the same tools as above.
    Make hole the final diameter 1.450 using 3x 0.015 cuts and a final 0.005 cut and a spring pass.
    (The two ends are within 0.002 of size. I have not yet had the courage to use a telescoping gauge to check if the hole is parallel or tapered.)




  • #2
    Space and time are the same thing, so really it does not matter which one.
    But for sure, the faster you go, the longer it gets.

    -D
    DZER

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    • #3
      7hp lathe, 1/2 hour.
      1hp lathe, 2 hours.

      But I don't step drill. Waste time.
      What does MHC stand for ?
      I couldn't mount something in a 4 jaw that was .050" out.
      Centering within .0005" takes me less than 2 min.



      -Doozer
      Last edited by Doozer; 07-13-2022, 04:40 PM.
      DZER

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      • #4
        Also depend on what level of precision you're shooting for. With "normal" tolerances that's a
        pretty simple job.

        My process would be:

        Mount in 3-jaw grabbing about an inch of stock.
        Face off one end.
        Turn OD to about .020" oversize.
        Spot drill.
        Pilot drill 3/8" diameter.
        Drill through 1-3/8".
        Finish bore- probably four passes.
        Chamfer edges on outer end.
        Mount a smaller piece of stock in chuck and quickly turn a 60 degree taper on it.
        Mount original workpiece using machined centre and live centre in tailstock.
        Finish turn OD.
        Chamfer edges.
        Done.
        Probably a half hour job but, realistically, closer to 3/4 of an hour with a clean start and no
        interruptions.

        My lathe is about 4 HP so power isn't an issue. I don't normally use a 4-jaw unless I really need
        to--it's extra work to change chucks. And I have a selection of turned centres that I use--all I have
        to do is stick one of the right size in the chuck and true it up.

        In the end there are many ways to do the same job; it depends on your machine size, skill level
        and tolerance required...
        Keith
        __________________________
        Just one project too many--that's what finally got him...

        Comment


        • #5
          I'd do roughly the same as Keith. But with some slight changes. My lathe is a 1HP 12x36 Asian import. I've also only got a 1" twist drill max. The two longer and heavier boring bars are 3/4" and 1" then the tools stick out a little from the OD of the bars. So a few passes with the 3/4" at around .02 to .03" DOC to open up the hole for the stiffer 1" bar. Then a few passes at .05DOC and finally the finish passes to sneak up on the size. Then some polishing if needed to give a good finish and size to suit whatever the tolerance needs. Plus with either chuck I'd be using the outside jaws due to the diameter of the raw stock.

          So my approach given the sizes involved and what I have on hand would be.....
          1. Chuck in the external jaws and adjust to run fairly true. 5 minutes
          2. Center drill the end and support with the tail stock and live center. 5 minutes
          3. Rough turn the OD to true up the majority of the the length and finish turn then polish a band to permit setting up the steady rest. I don't need something that big and heavy which only has the 7/16" of the outside jaws holding it flying away into the dark. So steady rest it is. 20 minutes
          4. Drill with a 3/8 pilot. 10 minutes
          5. Slow down the lathe and drill with 1" which is the biggest drill I have. I think the motor will do it if I don't feed it too fast..... 10 minutes
          6. Open up the bore .02 at a pass with my 3/4" boring bar until I can fit the 1" bar. Then open up the rest of the way with .5 or so .04 passes. This is slow going because they are HSS bars so low RPM. 20 to 25 minutes
          7. Final passes to size with measurements. 15 minutes
          8. Flip the stock and using a bull nose center for support turn away the last bit of rough OD. Fine turn and polish a new track for the steady rest. 15 minutes
          9. Face the end, measure for length and face off to length. 10 minutes
          10. Remove from chuck and switch jaws to permit chucking up a piece of 1.5" stock 8 minutes
          11. Using the 1.5" turn a stub mandrel with a 1° taper to give a drive fit on the OD of the stock. Use the bull nose center for tail support. 10 minutes
          12. Turn the OD with light passes and a final light finish pass. Due to the low RPM even with carbide inserts and need for lighter passes to avoid a high torque on the wedged drive grip this would probably be 4 to 5 passes of around 7 minutes each of around .015'ish per pass. So I'd use a right hand tool holder and make the passes from left to right towards the tail stock. I'd set a timer up to alert me at what I hope is when it's just about to reach the end or is only slightly past the end with lots of room still to go. 40 minutes?
          Adding up all the red times I get up around 160 minutes or 2 hrs and 40 minutes. I might be a touch generous on some of the times but I don't think by much. So perhaps 2hr 30mins? Or if all went faster than I think perhaps 2 hrs even? A lot depends on the DOC and feed rates that are possible. And that is dependent on the machine and tooling. Doozer's 7 HP lathe with burly large chuck would make doing it in 30 to 40 minutes more than possible. Especially the 1 3/8 drill which permits chucking up the heavy duty boring bar right off the bat. The lighter machines just won't handle that without loading the motor down far too much.

          I'm limited by my longer boring bars being HSS too. I can't run them as fast as one could run insert bars. But then with speed comes a higher likelihood of terminal chatter. So not sure about that.

          Any way we look at it a LOT of the time for doing this will be waiting for the passes. Fewer passes by having the mass to permit bigger DOC's and feed rates will count for a lot.

          If I did a video at 10x speed that would still be a 16 minute minimum video for my own lathe and tooling. More like 20 to 25 given the returns to real or double time while the voice over explained the reasons for each step setup during those slower parts. I think I'd drive myself to boredom watching it. Instead I'd do a lot of skipping ahead. I'd show like 2 seconds of the start of a pass then the last 2 seconds. No one wants to watch a cutter simply peeling swarf away even at 10x speed.
          Chilliwack BC, Canada

          Comment


          • #6
            Originally posted by Doozer View Post
            I couldn't mount something in a 4 jaw that was .050" out.
            Centering within .0005" takes me less than 2 min.

            -Doozer
            I don't know if the raw stock was egg shaped, oval, or had more bumps than a hootchy cootchy dancer at a carnival side show... but I know there was no way to ever get that close to even .005 ... Remember, I'm just a rank hobbyist, so I don't buy nice stock. I get drops and plops.... The throw-away ends that no professional would bother with.



            Comment


            • #7
              Spindle speed feed rate and Depth Of Cut.

              Every single operation has a time that can be easily calculated.

              At a given feed rate the advance is a fixed number, 1 revolution advances the tool say .010" at 1 RPM for instance.

              At 500 RPM spindle speed .01 x 500 = 5" per minute.

              At 2000 rpms it would 20" per minute.

              Choose wisely.
              Last edited by Bented; 07-13-2022, 07:07 PM.

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              • #8
                Originally posted by Doozer View Post
                7hp lathe, 1/2 hour.
                1hp lathe, 2 hours.

                But I don't step drill. Waste time.
                What does MHC stand for ?
                I couldn't mount something in a 4 jaw that was .050" out.
                Centering within .0005" takes me less than 2 min.



                -Doozer
                You are unusually talented Doozie.

                No one else can do what you do.

                Comment


                • #9
                  I made 2 parts today, 8 5/8" ID steel tubing bored to 8. 687" +.06 -.000.

                  26" through the bore.

                  Bored 13+ from each end in a cats head using a 16" long boring bar.

                  My employers time estimate was 2 1/2 hours including set up, I am now at 7 hours.

                  It is difficult to bore 13+" deep with a 16" long boring bar.

                  Comment


                  • #10
                    If it were a mill I'd start with checking the manual to find either the maximum material removal rate OR the largest hole that you should be able to drill. If you have something equivalent in your lathe's specifications I'd use that to determine how big the bit could be to rapidly remove the center of the donut.

                    I have found that most jobs take longer than expected, mostly due to my reluctance to take deep cuts. Even with my 7x12 mini lathe I can take cuts that create chips thick enough and hot enough to make the cutting fluid smoke.

                    With carbide inserts, you might need to keep the cuts a bit shallower on a small lathe but you can boost the speed to increase the removal rate.

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

                    Location: SF East Bay.

                    Comment


                    • #11
                      Originally posted by Bented View Post
                      I made 2 parts today, 8 5/8" ID steel tubing bored to 8. 687" +.06 -.000.

                      26" through the bore.

                      Bored 13+ from each end in a cats head using a 16" long boring bar.

                      My employers time estimate was 2 1/2 hours including set up, I am now at 7 hours.

                      It is difficult to bore 13+" deep with a 16" long boring bar.
                      Just out of curiosity, what is the diameter of your boring bar?
                      25 miles north of Buffalo NY, USA

                      Comment


                      • #12
                        Originally posted by BCRider View Post
                        I'd do roughly the same as Keith.

                        Using the 1.5" turn a stub mandrel with a 1° taper to give a drive fit on the OD of the stock. Use the bull nose center for tail support.
                        Turn the OD with light passes and a final light finish pass.
                        You guys are great. I would never have thought about turning between centers once the hole was bored. That will really help make sure everything is concentric. This forum is really excellent.

                        Thanks Keith and BCRider

                        Comment


                        • #13
                          How long to make a part ???

                          The question that plagues every manual job-shop owner.
                          Breaking it down step by step simply increases the likelihood and size of the error.
                          The error is NEVER in your favor.
                          It's all mind over matter.
                          If you don't mind, it don't matter.

                          Comment


                          • #14
                            Originally posted by nickel-city-fab View Post

                            Just out of curiosity, what is the diameter of your boring bar?
                            2 1/2"

                            Comment


                            • #15
                              I had to make a part yesterday for my lawn mower. It is 40mm outside diameter and needed a 32mm hole through the length of 100mm. The material was some type of stainless because it was just barely magnetic. I don't know what it was I got the piece from my neighbor. I didn't need to turn the outside as it was already 40mm. Drilling this material proved to be problematic for me. A normal HSS drill would not drill into the material. I managed to destroy three bits trying. I then took a carbide 16mm center cutting endmill and used it as a drill. 400rpm and hand feeding the end mill mounted in the tail stock. I had to swap ends on the part to get the through hole. Then I used a 16mm boring bar with carbide insert to bore the hole out to 22mm so I could use a larger diameter boring bar to bring the finished hole to 32mm. It took about 1 hour to make the part. The horsepower of the lathe really didn't play a part in making this part. My lathe has 14hp.
                              Location: The Black Forest in Germany

                              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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