Announcement

Collapse
No announcement yet.

Old Paper Cutter Restoration & Blade Sharpening Question

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by JoeLee View Post
    ...The cutting board was in 3 pieces when I got it. Can you tell where the glue joints are??
    ...
    The one at 3-3/4 was pretty easy, the one at 9" is well hidden.

    Comment


    • #17
      Originally posted by Bob Engelhardt View Post

      The one at 3-3/4 was pretty easy, the one at 9" is well hidden.
      Yea, if you look close you can see the seam but that was before I sanded and painted it. Good eye for detail Bob !

      JL.................

      Comment


      • #18
        Finished it this morning.

        The only thing that I didn't repair is the return spring that is fitted between the handle and the pivot casting. Everyone of these with that "Auto Lift" feature has a broken spring, some even missing. I think the spring was too hard and couldn't take the required 90 degrees of rotational twist. It takes a lot of spring force to return that handle to vertical moving it from the pivot point.
        But I'm not worried about the handle falling down and loosing any fingers.

        Click image for larger version  Name:	IMG-20210227-152157.jpg Views:	0 Size:	307.3 KB ID:	1930878

        Click image for larger version  Name:	IMG-20210227-152337.jpg Views:	0 Size:	280.7 KB ID:	1930879

        JL................

        Comment


        • #19
          Your first photo in this post illustrates one thing that I am thinking about. As the cut proceeds, the upper blade MOVES OUTWARD. This means that the bolt that is holding it and that it rotates on also must move in that direction. The wear on your upper blade may have been intensified by a lack of lubrication on this bolt. I would suggest adding a few drops of a good lubricant to that bolt on a regular schedule. Wiping the blades with an oily rag may also help.



          Originally posted by JoeLee View Post
          Yes, the blades do preform a shear type cut but the contact angle of the two blades is a bit more radical than scissors as you can see by this picture. It's edge against edge and they tend to chew each other up. As I said previously, the lower blade has already developed a slight burr just from the few times I've played around testing it. It won't last long at this rate.

          The blades are not very hard, perhaps tempered to a degree. I can file them. They are just sheared sheet metal. The counter sink part of the screw holes is blue in color so that tells me that some heat treat process has been done, the edges are not blue. Maybe these were tempered, stamped out and then finish ground ?

          As far as the starting edge of the handle blade, no way I'm going to grind all of that blade to remove the hack up end. I would have to remove over .025 to clean that up.
          I may just polish it smooth. As along as it';s sharp and contacts the lower blade it will still cut. As long as the lower blade is straight my paper cut will be straight.

          Click image for larger version

Name:	IMG-20210225-101309.jpg
Views:	400
Size:	195.4 KB
ID:	1930470

          Here is a sketch of how the blade angles meet. The top drawing is how they are now. I ground the lower blade edge square.

          My other option is to grind a slight relief angle in it as shown in the lower sketch. By doing that it will just about put the two blade edges on the same plane and reduce that edge to edge contact. If it doesn't work out I can always grind it back square again.
          Originally, the lower edge looked like it had a slight bevel to it but as I said it was just a sheared edge and sheet metal shears have a tendency to cut that way.



          Click image for larger version

Name:	IMG-20210225-101112.jpg
Views:	404
Size:	136.9 KB
ID:	1930471

          JL.....................
          Paul A.
          SE Texas

          And if you look REAL close at an analog signal,
          You will find that it has discrete steps.

          Comment


          • #20
            Originally posted by Paul Alciatore View Post
            Your first photo in this post illustrates one thing that I am thinking about. As the cut proceeds, the upper blade MOVES OUTWARD. This means that the bolt that is holding it and that it rotates on also must move in that direction. The wear on your upper blade may have been intensified by a lack of lubrication on this bolt. I would suggest adding a few drops of a good lubricant to that bolt on a regular schedule. Wiping the blades with an oily rag may also help.




            Yes, the handle blade does move outward as it comes down. The coil spring keeps constant tension between the two blades. The handle blade doesn't run parallel with the lower blade, that's how they maintain the point contact between the two blades throughout the cut. The cast base part has a sort of cam shape that also pushes the handle shaft out as it moves down more or less relieving some of the force between the two blades.

            One thing I noticed today is the rabbit cut in the base where the lower blade sits is actually cut at about a 3 degree angle so the cutting edge of the lower blade is tipped slightly up. that's how they get away with not grinding a relief angle on the blade. I ground a relief in it anyway and in combination with the angle that it sits it worked out perfectly.

            You can see the handle cam here, and also the broken return or "auto lift" spring as they call it. Not going to bother to try and repair that as it wouldn't hold anyway.

            I spent a bit of time restoring that old ruler too, it was cracked and full of holes from previous repairs (which I didn't do). Had to doctor up all the graduations and numbers with a fine point marker followed by a light coat of polyurethane for protection.

            It gives a certain feel of satisfaction to restore something old to this degree of perfection.

            Click image for larger version

Name:	IMG-20200806-163900.jpg
Views:	155
Size:	187.4 KB
ID:	1930932

            JL..............

            Comment


            • #21
              Nice work JL. Very similar concept as reel mowers which I grind, lap and adjust every day. If I understand correctly the main issue there was the lack of relief on the bottom blade which was a result of normal wear. I wonder if that causes the drag to increase enough to break the return spring which you point out is a common problem.
              -Roland
              Golf Course Mechanic

              Bedminster NJ

              Comment


              • #22
                Originally posted by rmcphearson View Post
                Nice work JL. Very similar concept as reel mowers which I grind, lap and adjust every day. If I understand correctly the main issue there was the lack of relief on the bottom blade which was a result of normal wear. I wonder if that causes the drag to increase enough to break the return spring which you point out is a common problem.
                Thank you.

                The lack of relief after I ground the edge was one reason, but originally the lower blade was just sheared which leaves the cutting edge with a slight amount of relief just by nature of the shearing process. To add more relief the rabbit in the base was cut at a slight angle. When I ground the edge I ground it square to the face, no relief. When I saw that the blades were eating each other up I put about a 3 deg. relief on the edge. That did the trick.
                The handle blade has no relief cut, just a worn taper at the starting end which it needs to smoothly engage the lower blade.
                Who knows about the return spring ? several reasons why that may have broke. Like I said I've seen several pics of these and everyone has a broken spring. I just don't think the spring could take the 90 degrees of constant twist.

                Same principal as reel mower blades only much less complicated and no special grinding fixture needed.

                JL...............
                Last edited by JoeLee; 03-01-2021, 11:48 AM.

                Comment


                • #23
                  The springs break and the pivot end of the blade mangled because people tighten the spring. It is normal practice, IMHO, for the operator to apply enough sideways pressure to make the cut.
                  Last edited by The Artful Bodger; 03-01-2021, 02:26 PM.

                  Comment


                  • #24
                    Originally posted by The Artful Bodger View Post
                    The springs break and the pivot end of the blade mangled because people tighten the spring. It is normal practice, IMHO, for the operator to apply enough sideways pressure to make the cut.
                    Your correct. You and I may know this as it's common knowledge, but the average person has no clue.
                    I believe this thing originally came from a school.

                    JL..............

                    Comment


                    • #25
                      I don't know if adding additional relief to the bottom blade was a good idea. You have already seen wear of the upper blade near the pivot. Additional relief to the bottom blade may cause that wear to be on both the upper and lower blades. But I guess it is too late now.

                      I have one that is a lot like yours (13"?) and may be even older (50 years?) But I bought it new way back then and have been the only user, with light use at that. So far, the spring is OK. Lately I have been abusing it by cutting light gauge aluminum (0.040") with it. So far it is holding up well and it still cuts paper with nice, clean cuts. I am probably going to pay a bit more attention to lubrication after this. And lightly stone the edges from time to time. Right now I am trying to find the fence so I can cut some aluminum shim strips.



                      Originally posted by JoeLee View Post
                      Thank you.

                      The lack of relief after I ground the edge was one reason, but originally the lower blade was just sheared which leaves the cutting edge with a slight amount of relief just by nature of the shearing process. To add more relief the rabbit in the base was cut at a slight angle. When I ground the edge I ground it square to the face, no relief. When I saw that the blades were eating each other up I put about a 3 deg. relief on the edge. That did the trick.
                      The handle blade has no relief cut, just a worn taper at the starting end which it needs to smoothly engage the lower blade.
                      Who knows about the return spring ? several reasons why that may have broke. Like I said I've seen several pics of these and everyone has a broken spring. I just don't think the spring could take the 90 degrees of constant twist.

                      Same principal as reel mower blades only much less complicated and no special grinding fixture needed.

                      JL...............
                      Paul A.
                      SE Texas

                      And if you look REAL close at an analog signal,
                      You will find that it has discrete steps.

                      Comment


                      • #26
                        Originally posted by Paul Alciatore View Post
                        I don't know if adding additional relief to the bottom blade was a good idea. You have already seen wear of the upper blade near the pivot. Additional relief to the bottom blade may cause that wear to be on both the upper and lower blades. But I guess it is too late now.

                        I have one that is a lot like yours (13"?) and may be even older (50 years?) But I bought it new way back then and have been the only user, with light use at that. So far, the spring is OK. Lately I have been abusing it by cutting light gauge aluminum (0.040") with it. So far it is holding up well and it still cuts paper with nice, clean cuts. I am probably going to pay a bit more attention to lubrication after this. And lightly stone the edges from time to time. Right now I am trying to find the fence so I can cut some aluminum shim strips.




                        The wear that developed on the upper blade end may be part of the design because if you raise the blade to vertical and the two blades disengage from each other when you go to move the handle down the two blades would clash. So you need a tapered lead in edge. The top end of the lower blade was worn in about a 1/32" where it met the start of the handle blade. Years of use I guess. Everyone of these I've seen has about the same wear on the starting end of the upper blade.

                        When I ground the relief in the edge of the lower blade I stopped about .020 from the top. That did the trick. I've made a few dozen cuts with it and no burr forming on the edge of the lower blade like before. It even sounds much quieter. No more crunching sound. I guess I just got lucky.

                        Upper right hand sketch...........
                        Click image for larger version  Name:	IMG-20210301-184551.jpg Views:	0 Size:	169.7 KB ID:	1931322

                        I kind of shot myself in the foot when I reduced the width of the blade because I then had to file the cam on the cast iron pivot base and had to do a little filing on the mating spot on the handle.

                        The cam is supposed to move the handle outward as it's on the way down to keep equal pressure against the blades. How well does it work ? Don't know now. It was worn and gouged up to begin with. I had file both to get the two blades to touch again after shrinking the width of the lower blade. I tried to mate the surface of the cam with the mating high spot on the handle as you can see by the red ink. But that wasn't easy to do. I got it to where it's cutting perfectly.

                        Click image for larger version

Name:	IMG-20210301-184643.jpg
Views:	84
Size:	122.3 KB
ID:	1931323

                        On a final note..... I wouldn't stone the edge or your blade. Best thing to do is tape a piece of 400 grit wet / dry sandpaper to your face plate and with a little WD40 rub the flat surface of the blade until you get a good sharp edge.

                        JL.................



                        Comment


                        • #27
                          Seems to me that the pivot and the cam action have to be very close to factory in order to give a good result. Only a little wear would be enough to make it not work right. Good for you getting it working properly.

                          I'm thinking too that an EP lube might be best to use for this.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                          Comment


                          • #28
                            Several years ago back in the mid 80's I bought a small second hand paper cutter (very cheap) and I used it just to cut down sheets of sanding paper to fit my air powered sander. I quit painting after a few years and never used the thing since...until just recently to make labels out of various boxes (cereal boxes fo example) to fit my AKRO bins and others similar to them. It would never cut anything for the first 3/4" from the back guide and I had to resort to using a spacer to get the paper out to where it would cut. Today I decided to take a look at it and I found the little nubbin on the handle that slides along the rest thingy was holding it out too far, so I took it apart and ground it down a little until the moving blade just touches the stationary blade at the start of the downstroke. A bit of clean up, lubing and reassembling with a ~.010 spacer to increase the spring tension a tad and it cuts better than it ever has.
                            Location: Saskatoon, Saskatchewan, Canada

                            Comment


                            • #29
                              Originally posted by Arcane View Post
                              Several years ago back in the mid 80's I bought a small second hand paper cutter (very cheap) and I used it just to cut down sheets of sanding paper to fit my air powered sander. I quit painting after a few years and never used the thing since...until just recently to make labels out of various boxes (cereal boxes fo example) to fit my AKRO bins and others similar to them. It would never cut anything for the first 3/4" from the back guide and I had to resort to using a spacer to get the paper out to where it would cut. Today I decided to take a look at it and I found the little nubbin on the handle that slides along the rest thingy was holding it out too far, so I took it apart and ground it down a little until the moving blade just touches the stationary blade at the start of the downstroke. A bit of clean up, lubing and reassembling with a ~.010 spacer to increase the spring tension a tad and it cuts better than it ever has.
                              I think what has happened to yours is the same thing that happened to mine. The top of the lower blade has worn and no longer contacts the handle blade at the top or where your ruler is mounted.
                              It's not the nubby thing on the handle hub. Check to see how straight the lower cutting is. It;s only going to cut as straight as the lower blade is.
                              Shearing sandpaper doesn't help anything. Your going to have to file the nub on the handle hub to allow it to come into contact with the lower blade.
                              But before I do that I wold check the lower for straightness as I mentioned.

                              JL........

                              Comment


                              • #30
                                JL, I am sure it could be improved on but it's working more than good enough for what I want it to do...and I'm lazy. 🙂
                                Location: Saskatoon, Saskatchewan, Canada

                                Comment

                                Working...
                                X