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SB-1001 (8K) Slows Down


Feb 20, 2022

Recently the Grizzly 1001 has exhibited a slowing down to almost a dead stop.

Grizzly and SB techs both say "loose belts."

Took the belt department on the machine completely apart and cleaned, adjusted and re-started and it slows down all by itself. The motor pulley slows down, too, so it's not slippage.

Decided to get into the electronics and look for loose connections, cold solder joints, out-of-spec measurements.

Found a questionable speed potentiometer and replaced it with an Allen-Bradley pot from an 800T speed control.

Am now on the way to reassembly, and I notice the schematic diagram is way different in several places than the way the machine was assembled, e.g., color codes are different, and the way things hook together do not match.

Please advise. If I blow it up it is being hauled to Recycling because both Grizzly and SB both say many parts are discontinued because of COVID-19.

Thank you for your commentary.


Hot Rolled
Jan 2, 2014
North Carolina
Looking at the wiring diagram for that lathe I'm tempted to conclude that the drive motor is DC since it only has two wires going to it. Now it could be some sort of shaded pole AC motor with some sort of Triac AC modifier but for the price of that thing I'd hope it's a DC drive with a PWM DC supply.

The fact that it slows down suggests that either it's not getting proper voltage to drive it and the culprit would be that "frequency drive board." OR it's the motor itself that has shucked a winding or two.

You might want to have a look at what voltage is being delivered to the motor as it's slowing down. If the voltage is up around 90-100 volts then the motor has a problem. If the voltage is down around 25-30 (for example) then there's something wrong with the drive board.

Depending on how much you love the lathe, you should be able to fix that by replacing their drive board with a commercial PWM DC drive. (That won't be cheap) Or you could replace the drive supply board with a less expensive SCR DC drive which should work but they tend to be a little "growely" under load.

OR you could replace the motor and the drive board with a nice 3 phase motor and VFD drive. It'll cost you a few hundred bucks but it's a "for sure" solution.

I have some experience converting Grizzly's bigger "gunsmith" lathe to a VFD variable speed drive. It's not a fun project because you have to figure out the somewhat bizarre logic inside the wiring cabinet. Yours should be somewhat simpler.


Feb 20, 2022
Stepinfettchit the lathe

Looking at the wiring diagram for that lathe I'm tempted to conclude that the drive motor is DC since it only has two wires going to it. Now it could be some sort of shaded pole AC motor with some sort of Triac AC modifier but for the price of that thing I'd hope it's a DC drive with a PWM DC supply.

The motor is supposedly DC. Inside the lathe control box is a heat sink-mounted Variable Frequency Drive module with a daughterboard Tachometer board that goes to a small liquid crystal numerical display.

The motor has two cables: A fat one and a skinny one. The fat bundle has five wires and three of them are labeled, "SA," "SB," and "SC." The skinny bundle gets messages from the FWD/STOP/REV switch, the speed potentiometer and some other stuff. All the wires are very skinny. So it looks like the
motor is a DC-based, 1100 watt, 14 ampere (rated) brushless being driven by three phase a.c.

There are no internal schematics for the module that I could dig up.
There are many websites with keyword "ANCER," but none of them are Chinese
Variable Frequency or Variable Speed manufacturers.

I've already sent an e-mail to K&S, and the FE left a message. I don't need to open my mouth and change feet anymore. There are certain diagnostic tests that are possible, but knowing how to identify the test points is
not a guessing game.

My favorite character on the Phil Silvers Show was Doberman. My dad and
I would watch that and Ernie Borgnine's Navy show all the time.

So thank you very much for your excellent advice and consideration. I like
the idea of using an Automation Direct micro vfd. That and a way to display turns. No DRO anything.



Hot Rolled
Jan 2, 2014
North Carolina
Well, I guess that shows the problem of taking Grizzly's "circuit diagram" as a circuit diagram and not just a picture of the inside of the control box. I should have known better!

Anyway, if it's a VFD problem with their hardware, just replace their hardware. Having a spindle speed readout might be a problem if you rely upon that. Personally I set spindle speed to be what the job needs based on what I see and hear, not what the numbers say.


Feb 20, 2022

Dear Sir,

I trained on a SB benchtop lathe with a leather belt going to a motor, no
readouts, no bells, no whistles.

Getting the right gears to match the work involved either asking someone how to do this or that, or finding it out the hard way.

It's just a shame with this machine. I jumped without asking anyone because it seemed small enough to just manage on its own. After working with it I saw it didn't hold any sort of precision and essentially it became something to wind solenoid coils with.

Now Daddy Sam Grizzly is exacting his punishment for believing that SB was actually okay.

The VFD module has been cleaned and deOx'd and I did find the little stickers showing the nomenclature for the various terminals. In addition I found EXTRA LITTLE PARTS in the electrical box, such as a 1" #4 self-tapping screw, an electrical terminal hold down screw with tiny clamp piece, and a red plastic cover for one of the relays on the VFD board
(all the relays are already covered and sealed)

I wrote to SB tech support.

In the e-mail I described what was going on and asked if I should completely disconnect
the wiring as I found it when disassembling, and rebuild it per the published "schematic,"
or just leave it connected the way I found it. It will be interesting to read their reply, if I ever get one.

I feel that many people at SB are not happy the 8K made its appearance these few years ago, as it has tarnished their reputation immeasurably.

But now, if I wanted to replace it after it goes out with the trash, what is there that's reliable?

Sincerely and respectfully.


Feb 20, 2022

Today's news concerning the Grizzly SB1001 South Bend 8K model lathe is not at all good.

On determining the way the lathe wiring was actually installed, meaning wire colors and what point-to-point connections were made that did not match the published wiring diagram that is available anywhere, I decided to uninstall what was in front of me and
to duplicate the printed road map as best I could.

The result was the Variable Frequency Drive, ANCER BLDC-750M has completely stopped
working, and there is no +/- 5 VDC buss output, the tachometer display has no backlight nor any digits, and the motor shaft continually spins at a low RPM with no effect from
the spindle direction switch or spindle speed potentiometer.

Grizzly wants $500.00 for the VFD assembly. If I buy it and something else is wrong in the lathe and the new part burns out there is no guarantee and I would be stuck.

So herein, gentlemen, I'm looking for a way to control the speed and direction of the spindle motor. It is a Huatian BLDC type motor Part number YK - 92 - BL - 001, and it is
rated at 1100 watts and 14 amperes.

I'm not interested in seeing the spindle RPM. All I wish to do is to somehow regulate the spindle speed Generally, and to make the motor go fwd or bkwrds. I am not averse to purchasing a 3rd part VFD with a 120 vac input, and mounting it somewhere near the guts.

I would welcome your comments and suggestions, and humbly submit these circumstances to you.


Feb 20, 2022

The lathe electronics failed, specifically for:

In the OEM Wiring layout, the Master Start Switch in the headstock casting, has two sets of contacts. A Normally Open set (1 to 2) is used to pull in the armature on the contactor,
and the other set (3 to 4) is Normally Closed and when STOP is pushed the circuit opens, allowing the armature to fall.

On paper it works.
In the real world of industrial electricians, the best way to run contactors is
to open the L2 ( or Neutral in a single-phase circuit, but "Neutral is a poor choice of words, it being single phase...) When the N wire is discontinued from the A.C. supply,
the magnet and the A.C. Hot all de-energize because the designer had them use the Auxiliary Set in the contactor.

Grizzly first of all has a contactor in this lathe WITH a set of AUX contacts. Grizzly second of all has a start/stop switch with the ability to run four different wires to it, PLUS a fifth and sixth to energize the bulb in all these switches.

Thirdly Grizzly uses silicon-plastic 21 gauge wiring, but only three (3) conductors go to the Start/Stop switch. The Hot A.C. is piggy-backed to the Hot terminal of the OFF set of contacts.

The result is the full a.c. load of the 8K goes through the Start/Stop Cheesy wires, and after a hundred or so operations the tiny set of actual contact points in the switch get hot and the metal's electrical resistance changes slightly. The result is firstly a
diminished voltage input to the contactor set of terminals. The second result is the Master Start/Stop switch Normally Closed set of contacts on the STOP set of switch contacts becomes intermittent.

All this was observed by monitoring the voltages with both a Simpson 260-8 analogue multimeter and a Fluke 89-4 digital recording voltmeter.

The lathe is spinning.
Switch set 3-4 points get hot.
Voltage to the contactor declines visibly.
Lathe spindle slows down.

The next operation was to completely disconnect all electrical
connections in the headstock and wiring cabinet, remove the motor
and the cabinet, then remove the master switch in the casting up
front, and then to individually operate every control and measure
the resistance across all contact points.

The Master Switch is defective. Intermittent visibly. Didn't even think of
spraying it with De-Oxit 5D because of how many steps it took to get to it
this one time. Grizzly part number 1001617.

The continual operations before the monitoring test affected the VFD module. The +5 Volt DC buss supply failed. One or more of the MOSFETS failed. There is no repair locally or with Grizzly. They had a new module, though, this one is "V2."

Needless-to-say the wiring design is now completely reworked into a higher ampacity version with 14AWG XHHW-2 Stranded, Gas & Oil resistant and 600 volt insulation. Using a set of colored Kennectit DIN rail splice terminals and soldered quick disconnects where
applicable. ALL bi-metallic connectorized or non-connectorized stubs and junctions get a dab of No-Ox-Id "A" (Special) anticorrosive paste. One molecule thick is enough for any connection. There just aren't any other lathes out there I could replace this with,
that have anywhere near the specs on the SB layout, and if I scrapped this, all the junk would have to go.

So if you are the proud owner of a Grizzly SB-1001 (8K) lathe, it might be in your best interest to rework the wiring and check the resistance of the master switch while you're at it.

Piece-by-piece, the spare parts at Grizzly are being distributed to 8K owners who need to repair. Grizzly themselves told me last week that they DO NOT plan on any 8K parts replenishment. Many line items are discontinued and the spares already sold.

Thank you to the members herein who afforded me ideas and assistance with making the decisions to address this.


Hal Mandel


Feb 8, 2015
Coral Springs, FL USA
You're talking schematics, but have yet to post any - so you're just talking to the wind.

If you trash this, give me a PM so that I can be at your curb on trash day to "help the trash men haul it off"!