Announcement

Collapse
No announcement yet.

workholding question

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

  • workholding question

    I have some plates i have to machine at different angles. I can get the angle i want by using the sin bar method but my problem is holding the metal to my table without it moving. I have your standard milling machine hold down kit.

    http://busybeetools.ca/cgi-bin/picture10?NTITEM=B054

    I know i can tip the head but i would like other technics as well.

    What do you guys use? Any tips or tricks for me?

    Rob

  • #2
    Rob,

    Can you describe a little better what kind of machining you're doing on the parts. Is it a flat plate-like part that you're doing a whole surface on? I presume you're not just machining an edge at an angle or you could hold it in the vise. I'm also guessing you don't have a sine plate with tapped holes for clamping your part or it would be straightforward to clamp the part to the plate and the plate to the table.

    Can it be clamped or screwed to a larger block which can itself be held in the vise?

    Jan
    .
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

    Comment


    • #3
      Hey Jan,

      Yeah i have to machine 8 1/4" x 2-1/4" x 3" flat plate. They need a 14° on the 2-1/4" end.

      Here is a picture.



      I have to weld the plate to the mechanical tube to make the pocket for the quick attach receiver. I can't get it bent at the local shop so i have to make it myself If i machine the angle fist my alignment will be alot cleaner and alot less grinding for me

      I hope you can read french! haha. I am too tired to go back into CAD and redo my layout. You can probably figure it all out anyways. I hope the picture helps



      Rob

      Comment


      • #4
        For that kind of stuff I just lay it out and scribe lines.Then setup to the lines and clamp.

        Shame you don't have a shop press.
        I just need one more tool,just one!

        Comment


        • #5
          Do you have a vice ?
          Do you have soft jaws ?
          Is it one off or multiple ?
          All affect the desired end point.

          If yes to the above
          Take the soft jaws off and layout the 14 degree angle, and drill two dowel holes in each Jaw. Mirror image.
          Lay your plate on the dowels and clamp, and mill
          Use a rigid stop on the table for length control
          Blocks can slip and move, pins will keep you in the same spot repeatedly
          Rich
          Green Bay, WI

          Comment


          • #6
            thats a bent part, seem silly to machine it at all.

            if you had an ironworker you could make a quick bending die and pound out parts like that every 2 seconds.

            also you could shear the angles with the ironworkers coper. so it would take 4 seconds to make the part.
            Last edited by ; 12-17-2009, 01:09 AM.

            Comment


            • #7
              Get a HF strap bender and a lager tip for your AO rig or a Rosebud and just bend them with the one inch die... set the stops after doing the first. Should take about 20 minute if that to do all 8 of them. After they are bent trim them to length on the bandsaw or mill flush after they are welded into the tube. Course you need to start with longer stock then needed... but that is how I would go about it.
              Wow... where did the time go. I could of swore I was only out there for an hour.

              Comment


              • #8
                I can read the phone number by standing above my LCD screen where the contrast is really high, haha.
                Never use black marker to blank out information to be posted online!
                Allways use a photo editing program to physicaly erase the pixels! it only takes one shade of 3 colors off to allow the origional text to be recovered.
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                Comment


                • #9
                  Originally posted by Black_Moons
                  I can read the phone number by standing above my LCD screen where the contrast is really high, haha.
                  Never use black marker to blank out information to be posted online!
                  Allways use a photo editing program to physicaly erase the pixels! it only takes one shade of 3 colors off to allow the origional text to be recovered.
                  It is as you say. Good thing to be aware of.

                  Jim

                  Comment


                  • #10
                    That seems like a LOT of extra work for what looks like a welded structural assembly. The tolerances for most of it can't be all that tight. If anything, you might need to do some milling to get the radius in the bottom of the two pockets to the desired size/location after all the welding is done. You'll be doing a bit of grinding to get all the edges prepped for welding, so the 14 degrees can't be all that critical.

                    Am I missing something?

                    Roger
                    Last edited by winchman; 12-17-2009, 03:40 AM.
                    Any products mentioned in my posts have been endorsed by their manufacturer.

                    Comment


                    • #11
                      More info

                      I went to the local shop to have it bent and they said it would take too much time / cost to me. They were being honest.

                      My plan was to take some mechanical tubing, cut it in half, machine the plates, and then weld them together. Smooth out the welds and voila. I have built these quick attaches before, and i spent alot of time shimming and checking my alingment. Not to mention grinding everything smooth. Having the correct angle already machined should make things better and quicker.

                      What i have done before was weld tabs on the sides of the plate with a reverse angle so when the part was shimed to give me the desired angle, the tabs were parallel to the table. Thus giving my clamps a flat surface to clamp on. I also put a stop at the bottom so the part would not move.

                      I am looking for different ideas. I machined some tool steel for a customer some time ago, and welding on it was not an option. Everything came out fine, but i am sure there is a better way then the way i did it. Just looking for suggestions

                      Tinkerer, Weird
                      I have a 20 ton press. I could probably weld a 1" round and press the part in between some rollers. 1/4" plate heated should bend pretty easily?

                      Rob

                      Comment


                      • #12
                        I think I would saw cut the flat plates and rig up some kind of angle device on the saw to do the angled ends. Then grind down just a bit to finished size.

                        If the outside edges after welding need to be more precise, I would mill them after welding the three pieces together to get better accuracy. At that point it would be easier to clamp. Perhaps let the radius rest in a slot with a 1" round to clamp it down.

                        But from the sketch of how they are used, I suspect high accuracy and milling is not really needed. There are no tolerances on the drawing. Could you assume +/- 1/16"?
                        Paul A.
                        SE Texas

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

                        Comment


                        • #13
                          Yep, weld it up and dress those ends on a grinder or disc sander.

                          Cheers,

                          BW
                          ---------------------------------------------------

                          http://www.cnccookbook.com/index.htm
                          Try G-Wizard Machinist's Calculator for free:
                          http://www.cnccookbook.com/CCGWizard.html

                          Comment


                          • #14
                            Originally posted by spkrman15
                            I went to the local shop to have it bent and they said it would take too much time / cost to me. They were being honest.
                            Time wise no... cost most likely at shop rate.



                            Originally posted by spkrman15
                            Tinkerer, Weird
                            I have a 20 ton press. I could probably weld a 1" round and press the part in between some rollers. 1/4" plate heated should bend pretty easily?

                            Rob
                            Rob a press should work for this and heat will make it much easier. Start with no less then nine inches of flat bar that should give you enough fudge factor. Once you have the basic shape you can adjust the angle in a large vise... of prudent use of a BFH.
                            Wow... where did the time go. I could of swore I was only out there for an hour.

                            Comment


                            • #15
                              Originally posted by spkrman15
                              Hey Jan,

                              Yeah i have to machine 8 1/4" x 2-1/4" x 3" flat plate. They need a 14° on the 2-1/4" end.
                              Rather than a 14 degree angle, it looks like they want a 90 degree angle from the center line of the part, 2.75" from the opposite side. I.E. the implicit spec here appears to not be 14degrees from the face but flush (both in angle and in depth) with the outer face of the work it will be assembled into (when the outer edge of the part is bent to the right profile). In other words, a smooth continuation of the original surface. 14 degrees never appears on the drawing. It is an artifact of the actual angle you want which is 90.

                              Drop the part in the vice with the radius flush with the bottom and centered up vertically, clamp and machine flat and parallel across the top 2.75" from the vice surface. The hard part is actually making the center line vertical, especially if your bend wasn't accurate. If your bend was perfect, you could just temporarily use a 78 degree angle block stack while setting the part in the vice. A jig with the right profile would (temporarily) bend the part to the correct profile for machining. Then if the part springs back, it will still have the right profile when squeezed into place.
                              This gets both the angle and the length right in one step. Jig could look like a vertical block with the outside profile machined into one side of it (or two, one on each side) and three cam locks: one near the center of the radius, and one near the end of each arm. Then, all you have to do is get the inside and outside radius (a function of thickness) and the total bend angle right and the simple machining step will bring all the other dimensions into compliance. Number of other ways to make the jig. One is to just clamp down the other part it will be mated with, drop a rod down into the bend and clamp down each end of the rod.

                              If there is any error on the angle of the overall bend, make it be too wide rather than too narrow. A wide angle will be self correcting when the part is clamped in place for welding but a narrow one will not be. Of course, you have a pretty big spring there so you don't want to need much correction.

                              I think it would also be a mistake to bevel the angles before bending. When bending, chances are the ends will come out uneven lengths. If you machine after the bend, then each will be trimmed to the correct length.

                              Also, since you are doing the welding yourself, I would machine to 2.750+x to give yourself a little bit of material to grind off for a flush surface so it looks like it all came from the same piece of metal.

                              I think the reason your other shop quoted so much on the bend was because you were doing the precise (machining) and imprecise (bending) operations in the wrong order which means that the bending operation needs to be done to machining tolerances. Getting the length on the arms right on a bender is likely an issue and the angle just right (with spring back etc). Just bending the metal probably no big deal. By having the length of the arms oversized and a slight under-bend which you take care of when machining and clamping for welding, respectively, you relax the tolerances on the bending operation which tends to be a less than precise fabrication step. Or it could be they don't have a bender which can handle 3" wide and would need to make a die set to do it in a press. Ignoring the issue of spring back, one die set could double as both a bending die and a machining jig.

                              That is my take on it, but ultimately you want to check with whoever you are making the part for and adapt to your shop, etc.

                              Comment

                              Working...
                              X