Power Feed Mechanism

Last Updated: 27 July 2007

The Metalmaster came from the factory equipped with a "Power Feed".  In the words of DoAll,

"The weight type power feed is an automatic feed which allows the operator to use both hands in guiding the work without exerting any sawing pressure manually.  This feed is actuated by a gravity fed weight carried along a beam.  The position of this weight along the beam simultaneously determines the rate of feed and the pressure at the point of sawing."

Is there any such thing as a non-"gravity fed weight"?  Anyway, what this is saying is that there's a simple counterweight mechanism designed to exert force on a couple chains or cables which are threaded up over the table to a large clamp.  When the weight is applied, it pulls on the chains and draws the clamp toward the saw blade.  This seems to me like more of a pain in the ass to set up and use than it's worth, but I give DoAll credit for coming up with a very inexpensive if not particularly clever mechanism to offer "power feed" to those on a budget.

Of course, I can't help but wonder what happens when the saw cuts through the last little bit of material and there's no longer any resistance to the counterweight throwing the entire assembly off the table and onto the ground.  The DoAll literature never addresses this.

Here (before disassembly and cleaning), you can see the counterweight, power feed rate adjustment screw (A), feed release chain (B), and external pulling cable attachment (C).  This mechanism is exceptionally simple.

The operator applies and removes tension on the cables by releasing or depressing the foot pedal (next picture).  The foot pedal is connected to the counterweight assembly via chain (B) in such a way that depressing the foot pedal raises the weight and releasing the foot pedal applies the weight.

The pressure (force) being applied to the self-feed cables (which are attached externally at lever arm (C)) is adjusted by turning the feed adjustment knob (next picture), which rotates threaded rod (A).

Threaded rod (A) is connected to the counterweight so that as the rod rotates the counterweight travels up or down the rod.  As the counterweight moves toward the operator, it's moment arm on the cable attachment (C) decreases, thereby decreasing the net force applied to the cable.  The opposite happens as the counterweight moves away from the operator.

The nut on the end of the threaded rod (A) prevents the counterweight being adjusted right off the end of the rod.  The counterweight weighs around 35 lb.

The amount of crud in the drivetrain housing would be impressive if it weren't so disgusting.  Most of it appears to be from the last shop that owned it, which apparently cut mostly plastics.  The remainder consists of oil leaked from the gearbox.

Here's the operator controls for the feed mechanism.


With the counterweight removed.

Here's the counterweight and its attachment.

So far, everything I've dismantled on this saw has come off with a minimum of force required.  Even though I know things on this saw should fall apart with a minimum of effort, old habits die hard.

A good example is the effort I went through trying to remove the self-feed pressure adjustment wheel.  I removed the set screw from it, then tried to pull it off.  And tried, and tried and tried.  I gradually worked my way up in force until I was using a nylon tie-down strap wrapped around the adjustor wheel to pound on it ("gently", of course) with a 14-lb sledge.

I kept thinking there was another set screw in there somewhere (having learned a lesson with the upper guide adjustment gear), but couldn't find it.  Well, thankfully I discovered what the problem was before I damaged anything: there are set screws and pins in the pressure adjustment assembly.  When I drove the pins out, the assembly fell apart.

So now I have to be on the lookout for set screws, multiple set screws, and pins.  I spent about 2 hours trying to pull this thing apart by force and 2 minutes punching out the pins.

Reassembly

Pictured at right is the entire self-feed mechanism cleaned, painted, lubricated, and installed.  There's not much to discuss about this, since the functionality is explained above.

Of course, since the casting that provides the pulleys through which the self-feed cables pass is broken and incomplete, this assembly can't actually be used.  I wouldn't even have installed it, except that it's convenient to "store" it in the saw rather than leaving it somewhere in the shop.

Note the self-feed pressure adjustment wheel has been chromed.  The lower wheel housing door handle, which has also been chromed, is visible in this photo too.

Note the front of the saw has been smoothed out (it was severely dented before).