Thursday, November 19, 2015

Harbor Freight Chop/Miter Saw modifications

I acquired a new Harbor Freight chop/miter saw and was not all that impressed right off.   No cut stop, and a hokey safety device that prevents the saw from being able to be lowered unless pressed.

For me the first thing was to take the thing apart, and remove the "safety catch".  I had a low profile red momentary on switch that I mounted on the handle where the "safety" tab emerged, and wired it into one side of the power switch which now functions as a Master Arm switch.  Turn it on, and press the button and the saw runs until you let the button go.  This is an improvement in the ability to use the saw.

I will say though, that when you take yours apart should you choose to emulate this modification, be very careful and lose or break nothing...

----   Note - these photos were taken after I had done the electrical modification, but had failed to photo document the process, which I repeated here.


Slide up the blade and belt covers and remove.

Next using a small Allen wrench that will fit through the hole underneath remove the blade.  The Allen wrench is to keep the shaft from turning and fits through a hole in the shaft.  

I removed the blade after disassembly, but it would be safer to do it at this step.

Use a piece of thin wire like a cord tie wrap and from the rear loop it around the long arm (upper) of the spring, and secure it to the cord so you don't put out an eye or lose the spring when it pops out.

Remove one C clip washer from the cord side of the pivot pin and put it somewhere safe.

Using a similarly sized rod or bolt drive the pin through to the other side.  I used another 3/16" stainless rod from the typewriter scavenge because it is smaller than the pin and easily removed.

At this point you remove the pin and the rod you used to drive it out, which releases the spring.

Take the base off and set it aside.

Remove the screws from the underside of the handle and the body and set aside.
Remove the top and set it alongside the bottom.

Remove the orange safety arm and discard unless you can think of a use someday for it.

What you have at this point is a black motor with two wires leading to the switch, red and white.  Using a number 11 blade or a multi flute reamer, enlarge the hole the orange thing went through on the handle to 1/2" or just until the new switch can be dropped through it.

Radio Shack has a N.O. (normally open - or OFF) low profile button switch similar to what I used here.
Part Number 275-0646.  You will find it in a drawer and not on the wall.

Remove the plastic nut before you drop it through the new hole in the handle.

You will need two short (2" will do) pieces of wire, probably same color as the wire you are going to cut would be less confusing.  Choose one of the motor wires (I chose white) and cut it in the middle so you can remove a little (1/4" or so) insulation from the cut ends.   I used  pieces of red and black wire which is visually confusing.  

Strip 1/4" insulation from each end of the two new wires and solder one end of the two short wires to each of the terminals on the new switch.  If it is easier you can solder these on before you insert the switch into the handle.  

Insert the new switch wires first trough the new hole in the handle and secure it from the underside with the plastic nut.  It may be a snug fit and require some fine needle nose pliers or forceps to tighten it.

Cut some pieces of small heat shrink tubing and slide over the new switch wires.  Solder each of the new wires to the cut ends of the motor to switch wire you cut earlier, slide the heat shrink tubing up over this new splice and heat them with a match or lighter.

You should now have one wire directly from the motor to the original switch, and one wire from the motor to the new switch and one wire from the other terminal of the new switch to the original switch wire on the other side of it. 

To test the new circuit, plug the saw in, and with the original switch in the off position (O down), press the new button.  Nothing should happen.  

Turn on the original switch, ( - down), which has now become a master arming switch, and press the new button.  The motor should start when you press and stop when you let go.  If this is the case tidy up and make sure all connections are insulated and replace the cover making sure the wires fit into their slot between the switches. If it is not the case look at your wiring again and be sure you have the new switch wired between the motor and the original switch. 

Remate the two halves with the pivot pin through one side and the other pin or rod through the other leaving the gap in the middle for the spring.

Grab the long end of the spring which is still tethered.  You might want to lengthen the tether a bit first though.  Using vise grips 90 degrees from the orientation of this picture, press the spring in long arm up until you can slip a pin through the center of the spring.  Drive the pivot pin all the way through gently, remove the vise grip and tether.

Replace the C clip you removed earlier and you should have a saw that moves up and down against spring pressure as before.  Plug it back in and test the electrical function.  Master on, momentary push button down should spin the motor and letting the button go should stop it.


Insert the Allen wrench back into the hole in the bottom and rotate the shaft until the holes line up.  Replace the blade.  The thick washer goes on first and the hole in the blade has to center around the raised portion of the washer.  Make sure the blade will rotate downwards towards you, place the thinner washer and screw on the shaft and do not totally tighten until you are certain the blade is centered on the back washer.

Remove the Allen wrench if it has not fallen out already, and replace the side guard pieces.  Engage the rear of the belt cover first and the front will engage easier.

You now have a saw that is a little more user friendly in my estimation, and as long as you are not pressing the new button, the blade will not turn, no matter the orientation of the master switch, although the master should always be off if you are not using the saw.

I thought about using a lever switch to automatically start the blade when the top is lowered, but discarded that idea as being stupidly unsafe.


It was still less than useful at this point and needed some improvements.

I had some uneven aluminum angle and decided on making an extended table with backstop.   The left hand piece had a piece trimmed out to snugly fit the vise jaw width, and the backstop was then super glued to the fixed jaw (rear) of the vise.   The remainder of the bottom part to the right of the vise was trimmed off with the saw and a hand saw in a miter box as the trim saw did not appreciate trying to cut through the horizontal flat of the angle aluminum. 

The saw was mounted on a piece of oak using the two screw holes on the base, and a second piece of oak glued butted up against the right side of the base to mount the angle to.   A couple pieces of same width aluminum bar stock were cut to fit the right angle to raise it up to the same level as the left angle. 

This sandwich was superglued together in a magnetic glue jig, and when set had the ends sanded to 90 degrees. 

This was marked for drilling and countersinking a couple of brass screws for mounting to the oak base.  Some cardboard shims were used on both sides to level out the base of the tracks, and a straightedge clamped during marking the oak for drilling for alignment.  When that time came, the right side was slid up to the lowered blade and clamped into place for drilling the oak base for the screws.

I added an oak endpiece drilled for a 3/16" diam stainless rod I scavenged years ago from a typewriter.  It is internally threaded at both ends so I was able to drill and countersink for a screw to mount a rosewood stop block, and threaded the oak endpiece for a thumbscrew.

Setting the stop with digital calipers gets a cut within .010" which can be further accurized until exact measurements are achieved.  In the photo below the master switch is on, and awaits only the pressing of the red go button to start the blade.

The masterr is off and the low profile go button is not being pressed for the photo below, which is included to show the full cut available with the modification.

While this is a vast improvement to the saw, I can see where having the rosewood stop block replaced with aluminum, drilled and tapped for the screw in the end of the rod so that micro adjustments could be easily made.   Having visualized this I may update this post after it is done.

The miter base can still swivel, but the rear of the new fence interferes with the upper half, so an adjustment may have to be made, but to be honest, I do not need multiple angle cuts and can use a hand miter saw for those if I do.

I hope this makes sense and that will gide you safely through this modification and turn that inexpensive saw into a real tool!