Sander troubleshooting

[Carl Beckett]

The wide belt is not coming up to speed. It behaves as if a 'startup' issue.

Note it is a 7.5hp three phase running on a Phoenix rotary phase converter. It has always spiked amps at startup but the settles once up to speed.

But now it does not make it to speed. The feed motor works (at least unloaded it does). And if I take the belt off the main motor jumps right to speed. So appears to be load related.

Am doing the usual internet search, but posting here because a wealth of knowledge and if ever sorted out the post helps others someday.

This is a 'jet 16/32 widebelt' - I believe identical to a powermatic of similar brand.

It requires air supply for the tracking system, but I also noticed this pneumatic cylinder attached to a lever on the motor itself. Wonder if that is a cap start mechanism that needs to engage.... appears to be missing the linkage bolt. (note from what I can tell the cylinder is not moving at startup so this is part of the research to figure out purpose of)

IMG_7313.jpg

edit: a quick search suggests this pnematic lever is a motor brake. Do not believe it has ever worked in the time I have owned it, given the slowness in winding down when shut off

[Steve Jenkins]

Check voltage on all three phases.

[Carl Beckett]

SOLVED:

Thanks Steve - did check the voltages and they were fine.

Turns out this sander has a plenum that has a graphite pad on it. The graphite had worn through (I have been using it hard lately with some 36 grit to essentially act as a planer on some contrary wood I got into). Which meant the back side of the belt was running on aluminum. The aluminum is fine so glad I caught it before it wore through, but friction against aluminum pulls much more current.

Replaced plenum graphite.

Works perfectly again.

PLBCAK: Problem Lies Between Chair And Keyboard...

[Bill Dufour]

Platen?
Bill D.

[Carl Beckett]

Platen?
Bill D.

YES!

(yet another brain fart, not my day...)

[Richard Coers]

If a 7,5hp motors drags down from dragging the back of the belt against aluminum, I wouldn't be too confident that you have found the problem.

[Carl Beckett]

If a 7,5hp motors drags down from dragging the back of the belt against aluminum, I wouldn't be too confident that you have found the problem.

Fair point! I havent pushed it hard yet. We will see...

[Carl Beckett]

Yep. Still trips.

Gets up to about 20amps (per the meter) on a load - runs a few seconds - then trips and shuts down.

Voltage in seems consistent. Running under no load for several minutes no problem.

Note that it does not turn back on immediately. I have to kill the power and wait a few seconds for everything to reset (perhaps the phase converter winding down and discharging) - or maybe this is just how magnetic relays work. Then it will turn on again from scratch.

There is always power to the machine and the feed motor works no issues.

Pic of the inside of the control panel below - seems pretty straightfoward.

20amps does not seem outrageous.

Do relays go bad and not hold (with current...?). Not obvious to me why it wouldnt hold with load but be fine unloaded.

Motor thermal switch... maybe. Then quickly resetting after shutting down.

Or - perhaps I should be chasing the phase converter although the feed motor stays on. It is 'only' the main motor

IMG_7318.jpg

Next step: test if any legs show grounded...

[Carl Beckett]

No legs shorted to ground.

From leg to leg reads .6ohm for every combination

[Kevin Jenness]

Do the motor, drum and idler spin freely without belts in place? If the sander's rotating parts are not dragging more than before, perhaps the problem is with the phase converter. Have you contacted the mfr?

Is there an adjustable overload in the main motor starter, and is that adjusted to match the max. amperage draw?

As for the platen, that should be used only for finish passes and either removed or adjusted to take it out of play otherwise.

[Carl Beckett]

Turns out this last trip was due to the belt tracking. After replacing the graphite pad, the belt tracking needed adjusted. I just missed it.

Loaded it up today and it runs fine. All is good again. (thought about whether the original failure was due to belt tracking and am pretty confident it was not)

[Bill Dufour]

Voltage? 440 will be 1/2 of 220.
Bill D

[Carl Beckett]

As for the platen, that should be used only for finish passes and either removed or adjusted to take it out of play otherwise.

Chased this around a bit and resolved the tripping.

But this comment was triggering... mine doesnt do this.

I bought this sander second hand. Turns out the previous owner machined a much thicker platen such that it doesnt lift out of the way - ever. By a lot (1/2" or more)

And the feed pressure rollers had been moved down.

So I am in process of putting this all back to factory setup. Will leave the platen out for now and see how it goes, while I machine this home made platen back to original dimensions.

Anyone that has a powermatic 1632 widebelt and can pull a dimension of the platen thickness send a note, else I will have to do some measuring to come up with a value.