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feeding in or feeding out when facing

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  • feeding in or feeding out when facing

    Sounds like a song lyric doesn't it?

    Anyway, the "auto cross feed" thread reminded me of a question I've wanted to ask. What are the pros and cons of feeding in vs. feeding out while facing? Does it depend on the size of the machine or the type of material, or maybe the size of the material?

    Bob

    [This message has been edited by rmatel (edited 09-05-2004).]

  • #2
    My southbend book shows you to face feeding out. However I have always did it going in.
    I would think it would depend on your tools geometry more than anything else. I guess feeding in with a sharp angle would be good for roughing, and feeding out with a very small angle would be good for finishing.
    This is my educated guess.

    [This message has been edited by BillH (edited 09-05-2004).]

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    • #3
      The traditional fitting technique for engine lathes is to face flat to slightly convex. The theory is that slightly convex faces joint up and seal better than concave.

      If I want flat and the lathe faces convex I feed from the inside out counting on tool wear to flatten the convexity.

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      • #4
        I think this came up some time back, and the thing that totally sold me on feeding outwards is that if you goof up (and engage the cross feed when you shouldn't) you're not going to screw up the part. But, I guess it's kind of like those chuck keys with the springs on 'em - if you need the extra safety, you're probably an idiot anyways.

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        • #5
          If it's just a facing, I feed in for the rough cuts and then out on the last, finishing cut.

          Many times a facing cut is to an inside corner and meets a turned OD. I will turn the OD with a series of rough cuts that end about 0.020" from the desired face. Then when that section is within 0.005" or so, I will make a in cut on the face to bring it within about 0.005". Finally, I will make one more pass reducing the OD to the final size (perhaps a bit over for abrasive finish) and then a outward facing cut to do the same for the face. It seems to work well and produces a good finish on the face.

          Paul A.
          Paul A.
          SE Texas

          Make it fit.
          You can't win and there IS a penalty for trying!

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          • #6
            If a tube I'll face in to out. If solid I'll face out to in. But as always, nothin is set in concrete (cept Jimmy Hoffa). JR
            My old yahoo group. Bridgeport Mill Group

            https://groups.yahoo.com/neo/groups/...port_mill/info

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            • #7
              With me it all depends on where I'm at on a tool change,if I can turn the od then face to the center I go for it.If the part is a tube or has a bored hole I face out,simply because I don't want to roll a burr on the id.
              I just need one more tool,just one!

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              • #8
                So again, it depends on the cat skinner! Thanx 4 ur responses.
                Bob

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                • #9
                  Feeding in for the roughing, and out for the finishing- essentially you're scraping to a finish with a sharper edge feeding out. More of the edge is in contact with the work, evening out the irregulatities to a greater extent. There's a fine line though, if the edge starts to grab, the finish will be worse. While feeding in, you're digging rather than scraping, which will not leave as good a finish.
                  A good analogy is using a pencil. Dragging a pencil away from it's point will leave a better line than pushing it towards the point.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                  • #10
                    At my real job we make tire molds. When facing large heavy parts we feed out. With constant SFM enabled it takes less power since the table need to slows down as the tool moves out. These parts have a lot of inertia. We've done test and find we can take a heavier cut feeding out.

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                    • #11
                      you also have to consider the tool geometry-feedout with a right hand tool-feed in with a left hand tool

                      entoffice

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                      • #12
                        Forrest, I will have to call you on this. The traditional lathe faces from flat to slightly concave, not convex. Convex would produce a poor seat/fit/seal.

                        From the UK lathes website re: the Wade precision toolmakers lathe:

                        "Wade claimed very high standards of accuracy for the lathe: the taper hole in the nose of the spindle, and the chuck seat on the outside, concentric and true to within 0.00001". The spindle alignment with the guideways on the bed, carriage and tailstock to within a tolerance of 0.003" over 12" and a facing cut made across 8" in diameter would produce a surface within 0.0002" concave and 0.0000" convex."
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          yeah. I don't know jack but I have read on many occasion that lathes were supposed to be slightly concave. did you perhaps just transpose your terms Forrest?

                          Dan

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                          • #14
                            Maybe Forrest is having a senior moment!
                            Or, maybe it's me.

                            Or maybe, I'm out of the loop again.

                            mite

                            [This message has been edited by metal mite (edited 09-08-2004).]

                            [This message has been edited by metal mite (edited 09-08-2004).]

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                            • #15
                              darryl has it right, rough in finnish out.

                              the trick to high quality finish is always chip control, if chips pack into the workpeice & tool it will look bad and you will not get a flat face.

                              this pic will show you, you may have to mess with yahoo.

                              http://photos.groups.yahoo.com/group...iew=t&.hires=t

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