On 6/25/2011 11:29 AM, David wrote: >>> So, it is like the most useless machine, where one flips a toggle and >>> then it immediately shuts itself off? The difference being that the >>> saw is a useful machine. >>> >> Yes, but that would be safe. ;-) >> >> My 7x12 horizontal bandsaw has the same setup as described. A tab of >> metal hangs down and contacts the on-off toggle switch when the saw >> swings down all of the way. >> >> It is very simple. >> >> Another way to do it electrically is to use a contactor to switch the >> motor power on and off and then construct a control circuit around the >> contact so pushing one button energized the contactor and seals it on >> with an auxilary contact, and then >> a stop button and a "saw off" switch break the seal on the contactor. >> The saw off switch would need to be normally closed, push to open etc. >> >> Here is an example of a seal-in circuit. >> http://www.allaboutcircuits.com/vol_4/chpt_6/4.html >> >> Push the Forward button and M1 stays on. Ignore the line below that >> has M2 as the output. >> >> Picture putting a normally closed stop pushbutton where the normally >> closed M2 contact is, and also put in series a normally closed saw stop >> switch. >> >> You lift the saw and push the start button, M1 comes on and stays on and >> the saw runs, you push the stop button or the saw closes (contacts the >> saw stop switch) and the saw goes off. >> >> The OL normally closed contact to the far right is the motor overload >> contact for M1, which is not needed to create the functionality you want. >> >> The wiring shows it being driven by L1 and L2 which normally means line >> voltage, usually 230 volts and up in the US, but the same thing could be >> done with 24 volts DC or AC. >> >> Dave >> > Hi, > > The original power switch arrangement used the toggle switch but had to be > changed when the requirement in certain jurisdictions became that the saw did > not restart after a power outage. > > The people making these saws changed the power switch to a double button > arrangement with a magnetically latching "ON" button and a separate "OFF" > button in a small plastic pod near where the toggle switch was previously > located. > > The action of these was arranged similar to the toggle switch with the saw > starting when the "ON" button was pressed and the tab of metal on the saw > frame pressed the "OFF" switch at the end of cut. > > This is somewhat less satisfactory when you need to switch the saw off from > the > button panel especially close to the end of cut. - better to switch off at the > power switch? > > If you wished to go all stops out the ultimate setup I saw on a site > recommending changes to the circuitry for use in schools saw a "Klockner > Moeller" surface mount emergency stop button (big red and about 150 mm dia) > mounted on the free end of the saw and a "Telemechanique" direct on line > starter (DOL) in surface mount on the frame above the hinge. The DOL starter > had on/ off buttons as part of the package. > > As this starter was a three phase unit, the usual arrangement of converting to > single phase use by looping the active through two poles of the contactor and > the neutral through the third would need to be adopted to defeat the single > phasing protection of the thermal cutout. > >
>>If you wished to go all stops out the ultimate setup I saw on a site recommending changes to the circuitry for use in schools saw a "Klockner Moeller" surface mount emergency stop button (big red and about 150 mm dia) << Ahh.... I could do much better than that....;-) How about a horn attached to the circuitry that beeps for 5 seconds warning all around that the saw is about to start up... then once the saw starts running a flashing yellow light comes on to warn people that the saw is actually running. We could even carry it a bit further by putting light curtains around the saw just in case an idiot tries to reach into the moving blade. That would require the addition of a brake on the saw so it could be stopped within a millisecond of the light curtain break. Seeing that it is a light curtain, a redundant safety PLC would be a good match to insure safety system operation. I recently programmed a Siemens Safety PLC that cost about $3000, a light curtain system could cost an easy $3000, box, buttons, pneumatic brake, framework for the light curtains, 24 volt power supply... I'm guessing we are talking about $10,000 including programming. The saw could be supplied by Harbor Freight and retrofit to the application. My saw cost $699. So the entire system, along with the idiot proofing would cost roughly $10699. :-) I know this sounds outrageous, but I work around safety systems like this all of the time. Dave ------------------------------------------------------------------------------ All of the data generated in your IT infrastructure is seriously valuable. Why? It contains a definitive record of application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-d2d-c2 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
