|Forum topic by ferstler||posted 11-27-2013 02:00 AM||783 views||0 times favorited||4 replies|
11-27-2013 02:00 AM
Most power switches used with moderately large stationary tools (contractor saws, drill presses, 6-inch jointers, thickness planers, etc.) and some mobile ones, too (jobsite saws, bench-top sanders, etc.), are dual-purpose items that have two sets of separate contacts: double pole, single throw. Four connector pins on the back.
The idea with the tool set up to work as a 240-volt arrangement is for the switch to simultaneously deal with both sides of the input. With 120-volt arrangements one set of contacts handles the hot side and the other handles the negative side. The latter is actually overkill, but the switches are dual purpose and it is easier to have them operate that way than to do a special wiring job on the tool, especially if it is designed to operate with either 240 or 120 volt inputs.
Some switches have only one set of connectors (single pole, single throw), and those are specifically designed for tools that can only handle 120-volt inputs, with the negative lead hard wired in place. Two connector pins on the back.
Most such switches are rated at 20 (or 19) amps at 125 volts or 12 amps at 250 volts, and the data will usually be clearly marked on the side of the switch. Most switches of this kind will be one of two types: a toggle type or a paddle type. I call the latter “slap switches,” because in a pinch their strong point is that you can quickly slap them for a shutdown, important with many tools. I am using a toggle type in my illustrations, and it is a single pole type with only two connector pins. Most here are quite aware of what the paddle types look like, and internally they are almost identical to the toggle type.
Anyway, with 240-volt arrangements the switches should hold up fairly well, because the initial arc as the contacts make connections are dealing with reasonably small current flows. However, with 120-volt set ups the initial arc is considerably stronger, and so the switch contact points can gradually pit and burn black, making the connection less than optimal. This also happens with the single pole types. I have had at least one toggle type switch that gets heavy use pit enough that the tool would not turn on. Another tool (an oscillating spindle sander) had erratic speed as the pitted connection was high enough in resistance to cut into the deliverable current flow.
Most of the time, if a switch begins to act up the user will opt to simply replace it. Grizzly sells replacement switches of both kinds (toggle and paddle), and they are generic enough to simply replace the vast bulk of dual-purpose power tool switches available. Even if the mounting plate on the paddle version is not the same as the one with the original tool, it is possible to remove the switch from the mounting plate and install it in the factory plate However, this might not be a viable solution if the user is in a hurry and does not have three to five days to wait for a new switch.
My solution has been to simply rebuild the switch. It is remarkably easy to do, taking maybe an hour if the switch is easy to get to from behind, and I assume that many on this site of ours have done the same thing, especially those with some electrical background training. However, some may not have, and so the info below may help them save both time and money. Note that with some tools getting to the back side of the switch may take more than an hour. However, I have yet to see a tool (and I have quite a few and have serviced the switches on most of the bigger ones) that did not have access of some kind from the back.
If you look at one of the switches, as mounted in a typical panel, it is possible to squeeze the four friction strips on each corner and ease it out of a panel mount on a tool. As noted above, with a lot of models, the original switch is installed in a plastic plate that is mounted to the panel with screws. These are usually the easiest to get to and rebuild, and if that is the case it is not necessary to remove the switch from the panel plate. Just unscrew the plastic plate and disconnect the two or four wires in the back that use standard male/female connectors. Pay attention to which wire goes where, needless to say.
With either a switch removed from a panel with the squeeze trick or with the switch still attached to a removable front plate, all you need to do then is use a screwdriver to pry the grippers on the ends of the friction strips that hold the front of the switch to the back. Most of the time the gripper ends are easy to pry apart, but I have seen those on some Ridgid tools that have an epoxy glue blocking the prying process. This is easy to overcome. Just use a small hack-type saw with a very fine blade to cut SLIGHTLY into the glue area. (Cut too much and you ruin the switch.) It does not take much cutting to make it possible to use a screwdriver to then pop the gripper loose from the rear section of the switch.
Once the grippers are slightly pried apart the switch will practically fall apart, and so it is important to keep the front facing upwards. Elsewise, the one or two (depending on whether it is double or single pole) little “rocker” connectors inside will flip out of position or fall out. You can of course pick them up, but if this is your first switch job it is a good idea to see just how they sit inside of the rear housing and how the housing orients itself to the front of the switch. This makes it easier to re-assemble correctly.
Most of the time the rocker(s) will be coated on one side with a silicone-type grease, with the other side having the contact tab. If you look at the tab you will see that if the tool has been used a lot it will be burned and pitted. To fix this, simply use a small jeweler’s file and buff it smooth. For best results, finish the job by using a diamond file that has a very fine grain. It is likely that metal fragments will get into the grease, and most of the time I just wipe all the grease off and leave it to the grease on the plastic pressure pins on the front section to carry forth the lubrication. Actually, even without lubrication it is likely that by the time that “dry” pressure pins wear out the tab will have been refurbished enough times by you that the switch will need replacing.
The tricky part is sanding off the pitting that will be down inside of the rear housing. I use a small rotary tool and a very narrow sanding or burnishing attachment to reach down into the housing and polish off the pitting. I then use a Q-Tip type swab and some alcohol to remove any metal residue.
Once this is done, the small metal rockers are re-installed into the rear housing, making sure that the contact points on those connectors match up to the housing tabs. This is one reason why it is important to be careful when you first get the unit apart so you can see just how they fit in. Also, pay attention to the way the front housing is oriented towards the rear housing. When the switch is “on” the pressure pins will be angled towards the rocker ends that have the contact tabs. Once you become adept at rebuilding switches this kind of super care during disassembly will not be needed.
The final tricky part is getting the front of the switch re-installed onto the rear housing. A bit of diddling is needed (and some fairly strong finger strength in some cases), and it is easy to jostle the rear section so that one or more of the rocker pieces jump out of position. Normally, I put the rear section in a vice (light pressure, please) and that keeps it from shaking as I carefully force the front section into place until the side grippers seat.
Once the grippers have a good hold on the rear section the switch is essentially fixed. Check it by using the continuity checker section of an electrical meter to make sure on is on and off is off, with both sides if it is a double-pole type. If you assembled the thing backwards you will have to disassemble and do the assembly again, with the section-orientation reversed.
It is easy to reinstall the switch into the front panel of the tool if you had to remove it that way. Just push it in from the front and the side tabs will grip the edges, Chinese finger torture style. Then, re-install the wire clips the way they were when you first viewed the back of the switch, and you are done. With the type that have a screw attachable mounting plate, just reinstall using the screws.
Stand back and turn the tool on to make sure the switch works properly. Even if it had not stopped working and you wanted to check the condition of the switch and spiff it up if needed, had it been strongly pitted it is possible that it will run a bit better than it did before, since the line resistance will be less.
Happy repairing, and if repairing is not in the cards for you make a point of ordering a spare switch or two for emergencies. If you have a special tool with a special mount, get the spare from the manufacturer. Otherwise, Grizzly sells generic types that can be adapted to just about any situation.