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1988 Jet JMD-18 with cracked head casting.

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  • 1988 Jet JMD-18 with cracked head casting.

    Hi,

    I recently acquired a used 1988 Jet JMD-18 Mill/Drill. I did not notice until disassembling the machine to haul it into my basement that the head casting was cracked near the lower head locking bolt. I don't think I got taken by the previous owner as he no longer needed a mill and all his tooling came with it.

    I now have to either attempt a repair or try and find a replacement part. Welding or brazing the casting is going to be difficult and time consuming at best, or expensive/impossible to have done professionally as I live in a remote area of MN. A new part would be expensive if I could even find one that would fit. From the text on the manual and a decal on the motor that says "RF-20.25.30" it seems as if the mill may be a rebadged genuine RF-30.





    http://i33.photobucket.com/albums/d6...z/100_0863.jpg (Link due to 4 picture rule)

    These two show the crack. It extends all the way from the vertical slot at the back of the head to where the pictures show it. The crack opens wider as you tighten the locking bolt.





    Here are my questions:

    1. From the pictures/ your experience, is this a genuine RF-30?

    2. Any chance that a head casting off an RF-31, newer JMD-18, G1006, or similar clone would fit and work with my mechanical parts?

    3. Any sources for said parts that are reasonable? (Best I've seen is $300 from Grizzly)

    4. Has anyone ever had a professional casting repair shop fix a similar crack? What was the repair bill?

    Since I am new here I'll provide a little background on myself. I have been around machining for the better part of my life. I came out of a very strong machining/manufacturing high school and continued taking machining classes in college as part of my major/minor (Technology Education/Industrial Technology)and served as a TA as well. I have worked as a research project machinist and have experience with most all manual machines as well as CNC. My present occupation is as a technology/industrial technology teacher in a 7-12 grade setting.

    Thanks in advance for your input/advice.

    ETA: Change picture links to actual images.
    Last edited by dkhntr04; 04-30-2009, 11:58 PM.

  • #2
    Manual in the 3rd photo, "Complex Machine."

    Comment


    • #3
      Possible quick and dirty fix- relocate the bolt?

      Comment


      • #4
        I don't think relocating would work too well. In between the bolts there are no flat surfaces to bear the head of the bolt and there is webbing.reinforcement around the factory holes for rigidity.

        Comment


        • #5
          Originally posted by tony ennis
          Manual in the 3rd photo, "Complex Machine."
          My favorite line from a Rong Fu manual ..."Do not put machine in the sunshine place."

          Comment


          • #6
            Originally posted by x39
            My favorite line from a Rong Fu manual ..."Do not put machine in the sunshine place."

            My manual says exactly that! Odds look good so far that it is a genuine Rong-Fu. Gotta love that Chinenglish!

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            • #7
              Originally posted by dkhntr04
              I don't think relocating would work too well. In between the bolts there are no flat surfaces to bear the head of the bolt and there is webbing.reinforcement around the factory holes for rigidity.
              Looks as if there is plenty of meat there, maybe you could cut a spot face for the bolt to bear against?

              Comment


              • #8
                I moved the motor and pulled off the lift/lower gear assembly. Unfortunately it doesn't look like it wants to stop even though it cracked through to an opening. you can barely see it in the picture, but there is a very fine crack leading straight down from the crack inside the lift/lower opening.



                Last edited by dkhntr04; 05-01-2009, 01:10 AM.

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                • #9
                  Originally posted by dkhntr04
                  I moved the motor and pulled off the lift/lower gear assembly. Unfortunately it dosn;t look like it wants to stop even though it cracked through to an opening. you can barely see it in the picture, but there is a very fine crack leading straight down from the crack inside the lift/lower opening.



                  I can't tell exactly from the pics...but have You thought about pinning it like is done for a head or block repair?
                  I did it years ago on a back gear casting on an old lathe and it worked out for for the guy I was helping.

                  Steve

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                  • #10
                    Steve,

                    I have only seen a few pictures here and there. Can you enlighten me?

                    Thanks

                    Comment


                    • #11
                      Originally posted by dkhntr04
                      Steve,

                      I have only seen a few pictures here and there. Can you enlighten me?

                      Thanks
                      Well they say a pic is worth a thousand words...I don't have a pic, so here goes.
                      The pins I used were tapered, cast iron , threaded with a square head.What You do is drill and tap on the crack. Then screw in the pin and cut flush. Overlapping the first pin and the crack, drill and tap again and screw in another pin.
                      Tedious ,but it does work providing the crack is where it can be accessed to be drilled and tapped.

                      Steve

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                      • #12
                        The pinning worked well on my FH Ford V8 FR engine but it seems as if it would tend to force the crack only wider in this application. I wonder if a close fitting splint with many small bolts might not hold things in alignment.
                        Jim

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                        • #13
                          I'd look around for a PROFESSIONAL weldor to do the repair. You will probably get a lead at a engine machining shop. They will know people who can successfully weld castings. There are always cracked heads.

                          Some people can do them and some people think they can do them. The engine machinists know the difference.

                          I have hear that these mills are OK so I'd invest the money.

                          If you want to see some casting weld Magic look at the threads started by castweld on WeldingWeb.
                          Last edited by RancherBill; 05-01-2009, 04:58 AM.

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                          • #14
                            Originally posted by dkhntr04
                            I don't think relocating would work too well. In between the bolts there are no flat surfaces to bear the head of the bolt and there is webbing.reinforcement around the factory holes for rigidity.
                            Looking at the images you posted of the inside of the casting, I'd say you're right. Looks like welding is the best option.

                            Comment


                            • #15
                              would this work?

                              http://www.locknstitch.com/

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