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  • Repairing drill press column bracket.

    I have been asked to fix a typical Chinese 16 speed drill press. My BIL has two of these in his injection mold shop where the table column clamp is cracked . The problem is the cast iron casting has had the broken piece lost.

    Is it possible to to use a 50 mm by 5mm flat bar strap and try to bolt it too the outer circumference of the clamp and using gas bend it too take the shape of the clamp and try to make pinch bolt strap of sorts. It seems sad to have to throw a machine away because of this.

    One of them just has a crack. Will brazing work on this and what type of rod will work.

    Another question.? I have one of these cheap drill presses and would like to change it to use a three phase using a vfd.
    But I see there is a conversion where you can by a jack shaft for this. The guy was explaining that a vfd just cannot provide sufficient torque on the slowest speeds when he is drilling a 25mm hole. Is this a real problem and does anyone here have a chinese press running on vfd and what are your thoughts.

  • #2
    This is a pic of one that could possibly be brazed/welded.It has a 6 inch machine vice attached to it.
    Click image for larger version

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    • #3
      I'd include a block of some sort to take the clamping bolt. Then weld that to a piece of suitable tubing or formed flat plate that extends over the casting surface by a fair bit of a third or so of the circumference. Then braze the snot out of it.

      And perhaps add a clamping limit screw so the gorillas he has working for him can't over tighten the part again and cause it to break somewhere else.
      Chilliwack BC, Canada

      Comment


      • #4
        I'm afraid his won't help you but might help someone else not get in this situation

        Clamp the table as you normally would and measure the gap
        then cobble up some hard plastic the right thickness so when someone
        comes along and cranks on it they get their satisfaction without destroying anything.
        (I do some work where folks are more enthusiastic than skilled)

        Think that if I were to braze that,
        I would also put a thin strap over, screwed to the part that is not broken,
        with the clamp pulling on the strap before stressing the brazed joint
        --
        Tom C
        ... nice weather eh?

        Comment


        • #5
          On the VFd issue. My answer is to use a big enough motor. It won't work with the typical overrated Chinese motor, but a real 1 or 1½hp motor probably will. I have 4 drill presses and a mill/drill on VFDs and drill most any size hole I want. The belts slip before the motor stalls. One "secret" is to use an 1140rpm motor. Full power at 1140rpm and then over speed it to say 2500 or even more. I run my mill drill up to 4,000 and it is a 1725 motor. The others I over speed about 50%. The power on a VFD is roughly as follows: HP is proportional to % of rated speed up to rated speed and then constant at rated HP. 50% speed = 50% HP, etc.
          Peter
          Grantham, New Hampshire

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          • #6
            The combination of hard, brittle, chinese cast iron and a highly stressed portion of the part seems pretty questionable, but a good welder could likely braze it. Might take preheat and so forth to prevent local hardening that might make it crack just to the side of the repair. At least there is some distance to the braze from the most stressed portion.

            My horizontal mill has repairs like that on it, and works fine. However, it is made of better old-time US cast iron, and was brazed by a person who was obviously quite experienced and good at that.

            The torque is definitely an issue. But a drill press that is intended to drill 25mm will already have the jack shaft setup to handle it. You should be able to just use the pulleys that are already on it for that.

            I am not sure why an added jack shaft would be needed, unless the guy has a quick shift setup with it just to avoid changing belts over. He might also have removed the original pulleys and setup, so that there is no other way to get slow speed by pulley.

            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              This is the jackshaft video Im referring to.
              https://www.youtube.com/watch?v=buIkQn4W9VI

              Comment


              • #8
                That guy is not taking advantage of his pulleys....even what he has. The middle pulley is driving, but the spindle pulley has the belt slipping. He needs to try it with the bottom pair of steps, which will improve (maybe not all the way) the spindle torque.

                Not having that bottom of the barrel link belt on it would help considerably, as the friction surface is better on a regular belt.

                That drill press may very likely not be made to do that drilling job to begin with, just because of the tiny pulleys. It is not "intended to drill 25mm" and does not "already have the jack shaft setup to handle it"

                My 18" Atlas Clausing is designed to do that, and the slowest speed spindle pulley is close to double the diameter. But I would definitely use the slowest speed pulley step pair to do it, VFD or no VFD.
                1601

                Keep eye on ball.
                Hashim Khan

                Comment


                • #9
                  Using a VFD is very conveniant, but in addition to the mechanical speeds provided by the pulleys. It shouldn't be a lazy persons way of not making any effort to change gearing.

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                  • #10
                    Originally posted by plunger View Post

                    Another question.? I have one of these cheap drill presses and would like to change it to use a three phase using a vfd.
                    But I see there is a conversion where you can by a jack shaft for this. The guy was explaining that a vfd just cannot provide sufficient torque on the slowest speeds when he is drilling a 25mm hole. Is this a real problem and does anyone here have a chinese press running on vfd and what are your thoughts.
                    Plunger, I got a different message from that video. I understood him to say that the VFD and motor were providing lots of torque. But the belt and pulley system on the drill press itself just were too flimsy to transmit all that torque to the 1" drill bit.
                    Lynn (Huntsville, AL)

                    Comment


                    • #11
                      Originally posted by lynnl View Post

                      Plunger, I got a different message from that video. I understood him to say that the VFD and motor were providing lots of torque. But the belt and pulley system on the drill press itself just were too flimsy to transmit all that torque to the 1" drill bit.
                      Perhaps you are right. I just want to know if a vfd is the bees knees on a chinesiam drill press or if its a waste of money.

                      Comment


                      • #12
                        It does what it does. If that's what you want, it may be perfect.

                        Slowing a motor with a VFD (or other means) does not typically reduce torque, but it does reduce power in proportion to speed. Reducing speed with pulleys increases torque and preserves power at the slower speed.

                        So you cannot say "hey, great, no more belts, I just twist this knob for any speed". Not and expect the same performance. But, you sure as heck can control spindle speed at any pulley setting.

                        I also saw the video as being more that the pulleys and that belt could not transmit the torque to the spindle. But the doofus running it did mot even put the belt on the best pulley groove for transmitting that torque. So even though I doubt the machine was intended to drill 1" holes in steel, it might have done better maybe a lot better, on the optimal pulley selection.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #13
                          Originally posted by plunger View Post
                          I have been asked to fix a typical Chinese 16 speed drill press. My BIL has two of these in his injection mold shop where the table column clamp is cracked . The problem is the cast iron casting has had the broken piece lost.

                          Is it possible to to use a 50 mm by 5mm flat bar strap and try to bolt it too the outer circumference of the clamp and using gas bend it too take the shape of the clamp and try to make pinch bolt strap of sorts. It seems sad to have to throw a machine away because of this.

                          One of them just has a crack. Will brazing work on this and what type of rod will work.

                          Another question.? I have one of these cheap drill presses and would like to change it to use a three phase using a vfd.
                          But I see there is a conversion where you can by a jack shaft for this. The guy was explaining that a vfd just cannot provide sufficient torque on the slowest speeds when he is drilling a 25mm hole. Is this a real problem and does anyone here have a chinese press running on vfd and what are your thoughts.
                          One thing you might consider is looking for replacement parts. I had a pair of Taiwanese generic DPs to refurbish and I wound up scrounging some parts from one to finish the other, so I have most of a drill press sitting around as loose parts. Measure your column diameter carefully - if it matches, I can probably furnish you a part to get one running again.

                          Here's the thing it seems a lot of people don't know about running a 3 phase motor with a VFD: if you cut the frequency by say a factor of five, you also reduce the available horsepower by that same factor. So you could oversize the motor and use a bigger VFD. But I suggest you buy a Dart controller and take apart free treadmills until you find one that will bolt right onto your machine. A DC motor can be slowed while still keeping full torque. That's why lots of guys upgrade their DPs to DC motors.

                          Drilling 1" holes in steel won't be easy on an import DP no matter what you do. But it's possible if you drill the hole in steps. It may be interesting to you to put a dial indicator up on the spindle somewhere, indicating distance to the table, and then put a lot of force downwards on the table and see how far it flexes. If you want a DP for doing large holes routinely, I suggest you look at an old camelback type. Those are hella strong and have power downfeed too.

                          metalmagpie

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                          • #14
                            I do get annoyed with belt changes but really,I seldom need to drill one inch holes.4mm to 18 mm is my max .I really would like the ability to tap and that is why I would be interested doing this conversion.I have a spare 1and a half horse power 3ph motor that i must see if it will fit on this machine of mine.

                            I am suprised I cant find any info on how to fix these cracked castings on the net . I am sure there are many that have cracked.

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                            • #15
                              Originally posted by metalmagpie View Post
                              Here's the thing it seems a lot of people don't know about running a 3 phase motor with a VFD: if you cut the frequency by say a factor of five, you also reduce the available horsepower by that same factor. So you could oversize the motor and use a bigger VFD. ... A DC motor can be slowed while still keeping full torque. That's why lots of guys upgrade their DPs to DC motors.
                              Just clarifying, you are describing them both as constant-torque (which is correct as far as I know). Torque is the same at all RPM, and power scales up with RPM. Is there a difference that you are trying to illustrate?

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