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  • really basic

    I'm brand new at the whole lathe thing, so on the recomendations of a coulpe of people from this post I've gotten some books and done some reading. The formula for rpm is 4 x cutting speed, divided by diameter. So I figure 1" shaft should be spinning at about 168 rpm with a cutting speed of 60 thou per revolution....am I close?????
    Shorty

  • #2
    I almost forgot....What is a safe amount to take of per cut? I've been taking off about 30-40 thousanths but it sure seems slow to me. No "curly peels" either. Gotta have "curly peels" right???
    Dave

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    • #3
      No answer to that question, without knowing what kind of lathe and material.

      A 16" Monarch will bite a lot more off than a 6" Atlas!

      Grind of the cutter also affects it, as a "peeling" cutter will take off more per rev than a straight-top like a typical threading cutter.

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      • #4
        The lathe is an 18" Stanley and the material is shaft for hydraulic cylinders.
        I'm using a right hand turning tool. I should correct myself. 90 rpm, ..03-.04 per cut, and 70 fpm feed is actually what I'm using for settings. Also, I think I may have been using a left hand roughing tool to do a right handed operation.
        So many variables but what the heck, the lathe just sits there and calls to me(heh, heh, heh) so I've got to try, right??
        Shorty

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        • #5
          Stanley 18" lathe. The stock is (I assume) carbon steel for hydraulic shafts.
          I have to correct myself. 90 rpm, .30-.40 per cut and 70 fpm feed. The tool will be a left hand turning tool as I have to cut away from a corner, however I think I've been using a right hand facing tool up to this point. Right direction but the wrong tool.This is the first time I've actually run a lathe but it's just sitting there waithing for an ambitious welder like me to take advantage of it.
          Shorty

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          • #6
            Speeds and feeds often are the hardest thing to learn. First lets get the terminologies correct.

            Surface speed is the actual speed that the tool is contacting at. It is the speed of the outside of the shaft when turning in lathe, or the outside of the cutter when using the mill. Think of a bandsaw, speed that the wheels are turning really don't matter, it's the speed that the blade moves, a saw with big diameter wheels don't turn as fast as a small saw for a given surface speed of the blade.

            Surface speed is measured in feet per minute. Remember this is the speed that the cutter is cutting at.

            Feed rates are classed 2 ways, lathe work is classed at inches per revolution, ditto for a mill spindle when boring. Mill rates are classed at inches per minute. Doesn't have anything to do with how fast the spindle is turning, but speeds do determine allowable feed rates.

            Feed is geared to the spindle on a lathe, unless you have a Hardinge tool room lathe or such. Increase the rpm of the lathe spindle, if feed rate was .008 before, it will still be .008 after the speed change. Mill feed rates are independent of the speeds, got to do some calculations, rpm, number of teeth of cutter, chip load per tooth, etc. Then feed rate is set at inches per minute.

            Calculation you were refering to is Surface feet per minute x 4/diameter= RPM

            So, with that 1" diameter shafting, probably 1045, it's common, 50 surface feet per minute is a good rate to start at with HSS. 50x4/1= 200rpm.

            Don't know exactly what kind of shafting you are dealing with for sure, I've ran accros some of this stuff that was nasty to cut. Got to watch some of that stuff, I've ran across some German made cylinder shafts that had some heat treat to them, case hardened to boot.

            Feed rates will vary, depending on tooling, lathe, material, and desired finish.

            Depth of cut will also vary, I often cut .100 per side of .200 total on Clausing at work. Machine can handle more but the worn out chuck won't. 1/4 per side is not that uncommon on larger machines. I'll take about .050 per side with my little Logan. Just depends how big of horse you have. Finish cuts are less of course.

            Hope this helps.

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            • #7
              Shorty,

              One more thing, some back rake, side rake, and some lead angle and those chips will curl. Makes for nice finishes. I kinda like chip breakers, more pounds of chips will fit in barrel, easier to clean up, can use a shovel instead of a fork or hook.

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              • #8
                Thanx halfnut,
                Surface speed = the point on the shaft that the cutter contacts....feet per minute(so this changes as the work gets smaller, does a guy half to make allowances for that)
                Feed Rate = how much the cutter moves down the shaft with every revolution( measured in thousanths??)Rough cut uses a courser feed, finishing cut a finer feed.
                Is this right so far?
                .100 off each side is o.k.?(.200 or just more than 3/16 total) The size of the machine dictates the size of cut you're able to take. The machine at work has an 18" four jaw chuck, as well as a bunch of other attachments for turning smaller than 1" material which is the smallest the chuck will accept. It doesn't seem to be bothered by .30-.40 so I'm assumening that I can take a larger cut safely ( baby steps of course)
                The .008 feed rate you refered to is 8 thou' per revolution, right?? How does this calculate out to surface feet per minute ie. 50?
                We've got some cutters that are gold coloured trianguler shaped as well as some hss cutters that have been sharpened, how well I don't know. There are guidelines in my reference book for side rake and clearance so I'll have to take a closer look at the hss ones that have been "sharpened".
                Oh yeah,what's a chip breaker?? Gotta learn the lingo eh
                thanx again,

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                • #9
                  I was just looking through my book (Machine Tool Operation Part 1) and found the feed in thousands, I didn't realize it was right there with the threading settings. Beleive it or not I'm goint to try cutting threads Tueasday or Wednesday this week.
                  Fortunately I saw a post here so I'll have to take a good look at the Q&A's there. Any beginner tips would be really appreciated though.

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                  • #10
                    Your best bet is to just experiment a little...There is a lot of stuff to learn, and just doing it will teach you more than anyone on this board can tell you...

                    Just remember, the finer the finish, the slower your feed rate should be, (i.e. .002-.004 per rev), roughing could be from ( .008-.016 per rev),

                    tool nose radius is a big deal...do not have a sharp nose, have aprroximately about .007 to .032 radius at the tip...if you are using 1045, then I would suggest if you are using HSS then to go about 350 rpm's and about .006 per rev for finishing with a .015 radius at the tip of tool...these are just numbers to get started.....you will need to adjust accordingly...

                    The smaller the workpiece gets, the faster your rpm's should be...this is not very practical with a manual lathe, you would have to change the speed every so often...what a pain....

                    lets take an example...if you start out with a 1" shaft, then use the formula for a 1" shaft...don't worry about changing the speeds unless you are turning down to about a 1/2 or so...then I would double your rpms when you get close to the 1/2 dia....

                    going too slow usually just affects production time, so if you are at home doing this stuff, then don't worry too much about feeds and speeds....I believe that you said that you are a "rookie"??? if so, then start out by going slow until you get confidence and experience first...ten fingers are a good thing to keep...remind my sometime to tell you about "left arm Louie"....Think SAFETY....good luck

                    brent

                    Comment


                    • #11
                      Shorty,

                      Those gold triangular things are probably TIN coated carbide inserts. Do they have bumps or little grooves just back of the edge, those are chip breakers.

                      18" 4 jaw, this ain't a whimpy machine, how much horsepower does it have. What flavor is the machine. We wants to know, curious bunch we are.

                      The carbide will need to be ran quite a bit faster than the HSS. Sometimes older machines are a bit underpowered and slow to take advantage of carbide to it's fullest potential.

                      Keep your nose in that book, sounds like you are starting to absorb some, and make some chips. As Brent says, watch those fingers and other body parts.

                      Comment


                      • #12
                        thanx guys,
                        The machine is an old Stanley(made in England).I looked for model/serial etc...but couldn't find anything but I didn't check for the horses. There's a pump for coolant that I'm going to try and get going this week.
                        Question: Where's agood place for the coolant to be fed to (before tool, on cutting edge, opposite cutting edge....?)
                        Also, is there some kind of gauge for measuring existing threads so I can reproduce them on a new shaft?
                        "LEFT ARM LOUIE"!!!!!! Sounds like a campfire story to me, what a visual.....

                        Comment


                        • #13
                          Hi Shorty

                          <font face="Verdana, Arial" size="2">Originally posted by shorty:
                          thanx guys,
                          Also, is there some kind of gauge for measuring existing threads so I can reproduce them on a new shaft?
                          </font>
                          Yes there is. A screw pitch gauge. It is a set of blades similar to a feeler gauge. There is a thread pitch cut into each blade.

                          They are available in different pitches or combinations of pitches ie Whitworth, UN, or metric etc.



                          ------------------
                          Kind regards

                          Peter
                          Kind regards

                          Peter

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                          • #14

                            I actually cut threads today thanx to you guys. Had to chase them with a die but I'm sure they'll get better. Anyway, just wanted to say thanx and if you're ever in my neck of the woods (Alberta) lets go for a cold one.

                            Comment


                            • #15
                              shorty:
                              Where in Alberta are you? I am in Edmonton.

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