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| Heart Transplant for a 3 in 1 machine |
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| John Rudd:
George, just for your enlightenment.... A remotely mounted vfd can be controlled via the keypad, if you move away from the machine to alter settings or it can be controlled via what folk typically call a pendant, built in stop/start and frequency or speed....then theres a comms protocol via RS485 usually from some sort of 'computer'..... |
| dvbydt:
Mounting the VFD inside back box seemed the easiest solution. Wiring to the motor and the control circuit could be kept short and it could be included the machine's safety system. Using the feed gears is unusual for most of what I make except for screw cutting. Lubrication of the gears is usually only a spot of Molybdenum loaded grease occasionally. Keeping swarf from entering via the spindle bore is cured by using a plastic plug with an "O" ring. I was more worried that the VFD would overheat from being enclosed,but it has inbuilt overheat protection and will cut out showing an error code, if it happens, I can always fit a computer extraction fan. As John said, a VFD can be controlled in many ways and interfaced to computer. My next post will show how I did it for the Centurion. Ian |
| dvbydt:
(I just had to watch the Crossrail London Underground program - utterly mind blowing!) Right, firstly safety. The next phase of this conversion involves dealing with 250Volts AC - it can KILL. If you have not been trained in electrical installation and you want to do something like this, give the job to someone who has! This topic is about how I altered the electrical controls on the Centurion, it is not meant as a step by step instruction of how to do it. As such I have omitted some details that would be obvious to an electrician. At all times, never work on an electrical system unless you have double checked that it is UNPLUGGED! Sorry about that, it sounds a bit elitist on rereading it, but it really can't be overemphasised. I totally removed the lathe motor and the FWD/REV switch connections. The VFD draws it's power from the machine main contactor and is earthed directly to the replacement 3 phase motor and the input mains earth. The control terminal connections are shown in the first picture. A 10K ohm variable resistor is connected to terminals 1,2,3 for the speed control. It looks fairly simple to control the direction, you need 24 Volts on pin 9 and 10 for forward and 24 Volts on pin 9 and 11 for reverse. This can easily be done with a centre off single pole switch. However I liked the multipole rotary switch that was fitted. Making and fitting a new cam to the first switch bank was fairly straightforward. The photos are a better explanation than my words. They show the original white plastic cam and my new one. A hex key was sacrificed to broach the hole. This rotary switch was easy to work on, blue ones defeat me. I do not have the manual dexterity they require to reassemble, springs and contacts end up in the great blue yonder. More next time. Ian |
| dvbydt:
So, if you look at the control inputs to the VFD, it needs a 24 volt drive enable signal and this is what my new cam provides in either FWD or REV. 24 Volts also has to be applied to the correct pins for FWD and REV. The switch was wired up and remounted. The "Live" light was repositioned next to the start push button and the speed pot took it's place. I attached a piece of card to the control knob and used a rev counter to mark the spindle speeds. Then I drew it up properly and laminated the print. That is what is shown in the front panel photo. Eventually, I will get a proper scale engraved. The carriage gib screws needed retightening far too often, so I made up some new ones that could be finely adjusted and locked in position. This has worked out much better. All in all I am happy with the Centurion. It's "Horses for Courses." It fits in my shed and so far has managed to do all I need for now. Does the lathe have torque like a geared head? No! But I can get more low speed torque with a smaller drive pulley on the motor. Is the mill as rigid as 626? No! But I am not trying to remove lots of metal quickly. The mill will probably get a 3 phase motor eventually, maybe even using this VFD if I can work out a safe way of switching it off, then using a changeover switch to the mill motor.(You are not supposed to have any switchgear between the VFD and the motor.) I'll finish this post next time with a "User Report" and some photos of what it has produced so far. Ian |
| dvbydt:
How has this all worked out? The first photo shows that at 350 rpm, 30 mm grotty steel can be cut at 5 mm DOC and 0.06 mm/rev - good enough. I have also turned some small wooden bowls, the rotary table allows me to cheat and get thin walls easily. Finish is three coats of Danish Oil then waxed. Screw cutting is very much easier because the spindle stops within in one second. The thread in the picture is 20 mm x 2 mm pitch, and the finished Arbor is part of my next project. (Have I bored you all or would you like a write up?) Criticisms :- Not that many because I had had a 3in1 before so I knew what to expect. The mill is not going to win any prizes at fast metal removal, I lock up the carriage and use the cross slide. The quill needs a depth stop, the return spring on the quill is TOO strong ( I have now adjusted it) and the quill fine feed knob needs replacing with a proper hand wheel. Apart from that, the scales are very clear, the alignments are good enough and it will do what I need but I would like to fit a two axis DRO eventually. Ian |
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