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Power drawbar project (TTS system)

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  • #16
    Exactly, the point on the multi stage ones is to increase the surface (force) without increasingt the footprint. This one is equivalent to one with around 200mm diameter piston.

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    • #17
      I'm really amazed that you need that much force to tug on the drawbar. Not doubting you, you
      obviously know what you are doing. Just surprised.

      So your cylinder is going to have an inlet between every plate ?

      I would love a power drawbar .. but would prefer electric.

      Yours is the most complicated and ambitious one I have seen and can't wait to
      see how it turns out.
      John Titor, when are you.

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      • #18
        You could use an air over oil intensifier and a smaller hydraulic cylinder as a variation
        Mark

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        • #19
          I still don't understand how they can get more pressure unless they are in parallel. It seems like if they are end to end type of arrangement they would all max out the same as if there was only one cylinder.

          Anybody have an explanation of how they work? I looked at the fabco site and didn't see it explained.

          Brian
          OPEN EYES, OPEN EARS, OPEN MIND

          THINK HARDER

          BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

          MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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          • #20
            Originally posted by bborr01 View Post
            I still don't understand how they can get more pressure unless they are in parallel. It seems like if they are end to end type of arrangement they would all max out the same as if there was only one cylinder.

            Anybody have an explanation of how they work? I looked at the fabco site and didn't see it explained.

            Brian
            I'd appreciate an explanation also. With some sort of a sketch to show how the multicylinders add.
            ..lew...

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            • #21
              Presumably each section has to be a complete "half cylinder" in itself, with an end piece, rod seal and piston. The next cylinder's end piece would be the opposite end for each cylinder except the end one.

              Pressure is then developed between the non-moving end piece and the piston, for each cylinder, accounting for them adding up.

              How each gets linked to the rod without some feature that would foul up being fed through the seals might be interesting..........
              CNC machines only go through the motions

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              • #22
                Simple.
                Image two completely separate thru rod cylinders, on air each cylinder has a pull [ or push ] of 1,000 pounds.
                Put them side by side, body fixed and rod onto say a blade and there will be 2,000 pounds of force.
                Now stack the two cylinders, hold the body's and apply air and you still have 2,000 pounds of force.

                Each cylinder has to be added to the first.
                .

                Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                • #23
                  Electric drawbar

                  Couple of months ago our local ALDI had some 1/2" drive impact wrenches made to operate from 240v AC for £30 so I grabbed a couple.

                  Tried one on the Bligport with a 3/4" drive impact socket as supplied and it works fine. Nice feature on these is that loosening ir full force wheras tightening is torque limited. They are made for wheel nuts etc and they don't want anyone screwing a lug bolt off.

                  The idea of getting two was I wnat to butcher one to use just the guts and no handle, the switch being replaced by relays so I can use simple buttons on the side of the mill. Unlike full air ones I will have to pull this down onto the drawbar but at that point it it hit a micro switch to enable the buttons.

                  Reason I don't want to go to air is my big compressor is big and if I only want to do a simple quick job I have to wait for it to fill and then all the attendant noise.

                  Using electric is quick and a lot quieter.
                  .

                  Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                  • #24
                    Originally posted by John Stevenson View Post
                    Simple.
                    Image two completely separate thru rod cylinders, on air each cylinder has a pull [ or push ] of 1,000 pounds.
                    Put them side by side, body fixed and rod onto say a blade and there will be 2,000 pounds of force.
                    Now stack the two cylinders, hold the body's and apply air and you still have 2,000 pounds of force.

                    Each cylinder has to be added to the first.
                    Naturlich, aber.....

                    The mechanics of getting them stacked up and operating bidirectionally is the interesting part.
                    CNC machines only go through the motions

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                    • #25


                      Here is a cross section of a tandem cylinder. If you inyect air in A and C while B and D are conected to the atmosphere, you get twice the force. Then since I don't actually need force to retract the piston, I can only apply air to B or D, or even use a spring. NYCCNC has a great video disassembling his Tormach power drawbar that maybe helps explaining how it works. Of course the travel is way lower, on mine will be less than 15mm.

                      https://www.youtube.com/watch?v=gkE0vk_oDAU

                      Yeah Mike Amick, the cylinder have inlets for every piston. Think about it as several cylinders that then you just join their saft.

                      You are right bobslab, if fact I'm using this system in the brake I use in the lathe/4th axis headstock I'm finishing. It have a small pressure booster, an air cylinder conected to a samaller hydraulic one to generate 25 times more pressure. It's similar to what I coment on #5, but at first I try to avoid it since the maintenance of the hydraulic one is more critical. If one of the seals of the pneumatic one get damaged, it will just leak some air but it will keep working. If I have an oil leak I will stop working because it's a closed circuit. I can build an air powered hydraulic pump to use with an oil tank, but is way more complex.

                      The rods are already joined to the piston plates, J Tiers. I used anaerobic retainer to bond them together, I love that stuff. Instead of a long rod, like the one on the picture, each plate uses ist's own small rod. The first rod pushed the second, and so on.
                      Last edited by DEVILHUNTER; 08-09-2016, 06:15 PM.

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                      • #26
                        Originally posted by John Stevenson View Post
                        Reason I don't want to go to air is my big compressor is big and if I only want to do a simple quick job I have to wait for it to fill and then all the attendant noise.
                        That was similar to my thinking. Electric would be more convenient for me because I don't always have the compressor running. I also didn't have air near the mill. I have run air to it now. I will probably make a modification so that I can use it manually if needed. My compressor is small a quiet, but the power drawbar is loud.

                        Does anyone know why power drawbars are predominantly driven by air? Is there some benefit over using an electric motor?

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                        • #27
                          Basically cheap and simple on air.

                          I am going off air as being wasteful, noisy and not so convenient.

                          Some years ago I bout an air tapping head, the type on cantilever arms.



                          This set goes from 3mm up to 12mm and it works well on the smaller sizes but struggles a bit on the larger. On long jobs you do have to wait and I have a 15 cu.ft compressor.

                          What I found though was if I only has 3 or 4 holes to tap and the compressor hadn't been on I wouldn't bother and tap them by hand.
                          So one day I set about converting this.
                          Canabalised a 1/2" air drill to get the reduction drive and linked it to a 3/4 hp 3 phase motor so I could use single phase via a VFD for speed control.



                          Fair bit heavier so had to play about with some springs as well as the gas strut to achieve neutral buoyancy.
                          Works very well now and I can go up from M12 to M14 and it's available at the flick of a switch for just one or two tapped holes.

                          The lathe compressor hardly ever runs now and I rely on a small quiet dental type compressor for blowing parts out and the odd bit of air.
                          It's actually paid off quite well as I'm in the throws of a house move and workshop move to smaller premises and the big compressor can't go due to size, noise and no three phase.

                          All the old air tools have been given to one of my customers who does a lot of site work.
                          .

                          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                          • #28
                            Some updates. The last aluminium plates I needed and the steel one arrived this week. Also the toolholders, they are better than I expeted. Haven't checked the runout yet, though.



                            Unfortunatelly, when I was milling the last but one aluminium plate, the T-slot end mill broke. So now I'm waiting for the new tools to arrive.

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                            • #29
                              Originally posted by pinstripe View Post
                              Does anyone know why power drawbars are predominantly driven by air? Is there some benefit over using an electric motor?
                              Study the before/after photos of Mr Stevenson's tapping arm.

                              An air motor is a considerably simpler device than an electric motor - this has implications for cost, size, weight, power, speed, to name a few parameters.

                              With air, one centrally located prime mover can power air tools, pneumatic controls, sprayers and what-have-you. Going electric means a motor on each device; in the case of the tapper, a VFD, too.

                              .

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                              • #30
                                Well, It's been a while since last updated this topic, and a lot of things have happened. First of all I want to comment that I started having a lot of pullout problems and chatter, no matter how hard I screw the drawbar. I even got some of the safts a bit damaged. At first I though it was the quality of the toolholders, but finally I discovered that the problem came from the collet. It was only gripping on the top of the saft. Changed the collet for another one and no problem since then.

                                After finishing all the plates and bars that hold the power drawbar to my mill, It all fitted pretty well:



                                Unfortunatelly, soon after that my original DC motor got burnt. I was already expecting that, so I had been making a timming belt conversion, but couldn't finish it before it happened. To finish the HTD 5M spindle pulley and the 30x30mm bars that will support the new motor I had to use and old cordless drill that I had to connect to a power supply since it's battery was dead:



                                Using a router at the side of the headstock, made the plastic pulley and MDF adapters to an old washing machine motor:



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