"Hydraulic pump" issue fixed - senior moment!

Here's another illustration of the danger of letting The Stupid Fat Bloke loose in the workshop. As well as being the kind of idiot who knows it all and rushes in to do shit without thinking things through, he's also prone to simply forgetting simple things. He should be called The Stupid Old Fat Bloke.

The issue with the Tree installation isn't anything to do with the hydraulic pump motor or indeed a failure in any of the other mains powered components. It's simply because said SFB forgot to plug in the mains isolation transformer.

The issue is that I have a series of converters and inverters and EMC filters all leaking current into the chassis. Mainly, this is through their Y caps but also through the insulation in the motors, solenoids etc. Given that the consumer units in the house are mandated to have 30mA RCDs, there's a limit to how much cumulative Y caps can be tolerated before nuisance tripping becomes a major issue.

The mains in the UK seems to be climbing ever higher these days. I'm measuring 256Vrms on several DVMs and short of examining the actual waveform with a scope, I have no reason not to believe that's what we are seeing. This raises the leakage current from the nominal, which I think (from memory) is specified at nominal voltage.

The current is a Y cap with 230Vac across it is  

I = 2 πfCV         (where f = 50Hz & V = 230Vrms)

So, if we were to run leakage of 30mA entirely down to the Y capacitance, we'd be able to tolerate a value of ~415nF. Of course, that would be pretty stupid as it would allow no additional leakage anywhere downstream of the workshop consumer unit RCD.

Here's the Schaffner EMC filter that comes with the spindle VFD, which is a 4kW Yaskawa GA500:

They estimate ~5mA leakage for this filter. There's also some Y cap in the VFD itself. In the manual for the GA500, it says "If you turn on the internal EMC filter, the leakage current of the drive will be more than 3.5 mA"

"Use a high frequency RCM/RCD at the power input side of the drive and make sure that each drive has a minimum cumulative sensitivity amperage of 30 mA. The specialized breaker detects only the leakage current from frequency bands that are dangerous to humans.

If a device does not have protection against high frequencies, high frequency leakage currents can cause the device to malfunction. If you have a malfunction on a device that is not protected, decrease the carrier frequency of the drive, switch to a better breaker, or use an RCM/RCD with a minimum cumulative sensitivity amperage of 200 mA for each drive."

There's no mention of filter compt values or leakage currents in the Lichuan servo drives. The Meanwell SMPS PSUs claim <2mA each at 240V (there are 2 of them). 

Bottom line - measuring the capacitance between live and ground suggests a total of around 850-900nF, which will deliver a leakage current that is well above that nominal 30mA threshold. A measurement from neutral to ground wouldn't be relevant, as neutral is held at ground, so shouldn't normally be causing any significant leakage.

My solution to this was to run the lathe from an 230:230V isolation ("site") transformer - with a strong earth bond of course. Then, any leakage within the installation would be isolated from the workshop consumer unit.

What Fat Boy forgot to do was install that isolation transformer between the wall socket and the machine. It got misplaced when the machine was last moved a few months ago. This realisation struck me during the night (as it does) and today I've gone about convincing myself if / that this is what the issue was. After some buggering about with insulation and continuity testers, it's clearly what the problem was. With the transformer back in circuit, everything is fine. 

What now, Fatty?

So now, I have to reconnect the hydraulic pump assembly and and refit it into the machine. No harm done (hopefully I haven't nadgered any of the venerable hoses) but at least I know the thing appears to be in a reasonable state - and understand what I'm looking at.

Hydraulic pump repair or electrical issue? Tree CNC lathe tripping breakers

When I enable the circuit that powers the VFDs and servos, I'm finding that the main MCB and/or RCD trip. This seems to have been an intermittent feature of the hydraulic pump for some time now, as far as I could tell. But now I can't even get it to power up regardless. What's going on here - time to get to the bottom of it.

I reckon it's likely to be the pump motor. And access to the VFD wiring is a bit of a PITA, so perhaps the thing to do is simply remove the hydraulic "power pack" and see what's up - assuming that's there the problem is. Besides, I'd like to have a closer look at this part of the machine. (More later!!)

The front fixings for the oil tank are easily accessible. I hope TF there aren't any rear fixings, as this thing is tight against the wall and weighs several tonnes (thought to be around 3).

By stretching my arm to the back, I can see where any rear screws would be. Can't see anything, as it's too dark. Getting in to that area would be an absolute nightmare. The machine frame is solid cast iron with only a few apertures, mostly internal at that.

If I remove that adjustable foot bolt thing, perhaps the tank will pull clear?

Yes! Indeed, there's nothing holding it in at the back, so clearly there are no rear fixings - TFFT! Shouldn't need any, as it's not likely to walk on its own.

Regardless of whether there's anything wrong with it, let's have a look in more detail.

Here's the hydraulic pump block that is responsible for the operation of the turret and tailstock (I don't use the collet chuck). It's a Sperry Vickers H1J PVB6A-RS-20-0A-11 Can I find any specs for this? 

Oooof - bingo! There's an exact match available of the shelf (new old stock):

Let me just think about that price for a few seconds. Ok, done, now move on - I'm probably not going to cough up £2k for one of these. Besides, mine works fine, even if I think it's a bit noisy (and what would I know, that may be normal).

That's driven by a fairly straightforward 3-phase motor rated at 2hp / 1.5kW / 230V. It's 4 pole, so would run at 1800rpm in the US but 1500rpm in the UK, where it's been running fine - I set up the turret timing with the way it worked in this installation. It's pretty large by today's standards, given its limited power output but hey.

It seems to be a variable displacement pump, so presumably it regulates the displacement in order to regulate the output pressure. In this application, it spends most of its time simply providing a static head.

"The Sperry Vickers (Eaton) part number PVB6A-RS-20-0A-11 designates a variable displacement, inline axial piston hydraulic pump delivering a rated flow of 6 GPM (22.7 L/min) at 1800 RPM." That sounds like a swash plate type pump. I was expecting a "gerotor" type pump but this makes more sense, as it will avoid roasting the oil by recirculating it against a relief valve at full flow rate.

Here's an exploded view of the "pressure compensated inline piston pumps" and a parts list, with part number description:

And another site gives some blurb about how it's used:

The PVB6A-RS-20-CA-11 pump belongs to the PVB Piston Pumps series and is produced by Vickers for use in hydraulic automation circuits where controlled flow is required. It is an axial piston, variable-displacement unit, so delivered volume adjusts to system demand and reduces wasted input power. Clockwise shaft rotation aligns with common right-hand drive layouts found on mobile and industrial machinery. A geometric displacement of 13.81 cm³ per revolution establishes the fundamental output capacity, while a rated flow of 22.7 L/min is achieved at 1800 rpm for moderate actuator speeds. The rotating group tolerates a maximum shaft speed of 1800 rpm, allowing direct coupling to standard four-pole electric motors without gear reduction. Pressure regulation is handled by a pressure compensator control that trims displacement as the outlet approaches the 140 bar limit, preventing overload. System piping connects through 11/16-12 UNF-2B SAE O-ring main ports, providing reliable sealing for high-pressure service.

The swashplate operates on one side of center, giving a single-direction displacement zone that simplifies motion control logic in closed-loop circuits. Case drainage is routed through a 9/16-18 UNF-2B SAE O-ring port to keep housing pressure low and protect shaft seals. Suction conditions must remain under 1.0 bar absolute inlet pressure to avoid cavitation during high-speed operation. The pump is specified for ambient temperatures from −20 °C to +70 °C, accommodating both cold-start field equipment and warm factory floors. An operating viscosity window of 220 to 13 cSt is permissible, with a recommended range of 54 to 13 cSt offering optimum efficiency and reduced wear. Power transmission to the drive train uses a 4.8 mm square by 25.4 mm long shaft key, ensuring positive torque transfer to standard couplings without custom hardware.

Technical Specifications

Case Drain Port Thread

9/16-18 UNF-2B (SAE O-ring)

Control Type

Pressure Compensator (C)

Displacement Zone

One Side Of Center (S)

Geometric Displacement

13.81 cm³/rev (0.84 in³)

Main Port Thread

11/16-12 UNF-2B (SAE O-ring)

Max Ambient Temperature

+70 C

Max Inlet Pressure

1.0 bar (15 psi)

Max Outlet Pressure

140 bar (2000 psi)

Max Shaft Speed

1800 rpm

Min Ambient Temperature

-20 C

Pump Type

Axial Piston (Variable Displ.)

Rated Flow @1800 Rpm

22.7 L/min (6 gpm)

Shaft Key Size

4.8 mm sq x 25.4 mm long

Shaft Rotation

Clockwise (R)

Viscosity Range (operating)

220 to 13 cSt

Viscosity Range (recommended)

54 to 13 cSt

Anyway, enough of that. The pump's probably fine, so I need to just focus on the motor itself. First show that (if) the motor itself is the issue that is causing the RCD and MCBs to trip. I don't imagine I need anything like 1.5kW just to operate the turret....

The pump is driven by an Oldham coupling and of course, given this motor's parentage and vintage, it has a 1" shaft. That could be a royal PITA.

The motor itself is foot mounted, with a flange mount for the pump assembly. So if the motor is shagged, I'll need a foot and flange motor with imperial measurements. Enough doom scrolling - let's disconnect the motor and see if the fault has gone away - and the Yaskawa drive isn't buggered.

Good news and bad:

Turns out there's nothing wrong with the pump motor, it seems. Disconnected the motor entirely and the breakers trip when I close the switch to the VFDs and servos. I guess I can now start to disconnect the various branches from that node and see where the fault lies......

Machining the SFU3205 ballscrew on the Tree lathe - or not, as the case may be...

I need to machine down the ballscrew to fit the thrust bearing. The ballscrew OD is 32mm and the bore of the bearing is 25mm. I also need to machine some 17mm hex flats on the end so I can drive it with a socket, either on a handle or an impact driver.

The Bantam is barely man enough on a good day but on this occasion, it's not even a starter, as the through bore is just over 1" (25.4mm). So the Tree will come to the rescue, as it has a through bore of just over 50mm - probably 2" from memory.

The end of the shaft I will machine initially looks like this:

But to keep life simple, I'll create a simple model:

I'm going to use a "trigon" insert, as this will be a hardened ballscrew which could be tough on more delicate inserts. Note that these toolholders have been machined down to 19mm, due to the machine being an imperial relic on account of its US heritage, so an off the shelf 20mm tool will be 1mm too high.

Machine sort of flashed up OK - until I turned on the hydraulic pump, at which point the various circuit breakers tripped, depending which ones I reset, others would trip. I've previously had trouble with this motor and sort of bodged it by fitting a site transformer (voltage isolation) with a local RCD so that the consumer unit wouldn't trip out. It was clear that there was a lot of leakage somewhere, most likely the hydraulic pump motor, given that almost all the other mains stuff had been replaced.

I'm thinking that the motor insulation has finally broken down enough that the leakage current will trip anything in its path. I just hope I haven't fucked the Yaskawa drive that powers it.

Of course, access to the end of the machine that houses the pump isn't dead easy although that's due to the fact that I've got lots of crap piled up against it. In reality, access should be pretty reasonable once all that crap is moved out of the way.

I'm hoping that simply disconnecting the motor will clear / demonstrate the fault, in which case a new motor will be the solution. The hydraulic pump is pretty noisy, so it's possible I may also get myself a new pump in the process - how long's a piece of string?

Chips with Probe Basic Lathe Coversational!

Despite the AliExpress tracking info showing the ballscrew sitting at the China consignment hub, look what turned up a few days ago.

Yes, SFU3205 (single ballnut, 32mm OD, 5mm pitch). It even came with a transfer tube(?) to allow you to remove the ballnut without sowing the ball bearings across the length and breadth of the workshop.

Thusmost:

Anyway, time to drill the pilot hole in the stock for the bearing bracket. Centre drill, then 8mm drill, then 25.5mm drill.

There. Ready for the boring operations.

Then set up the first boring operation in the PBL Conversational screen (open out from 25.5mm to 50mm):

At this stage I was thinking I should check the spindle speed. This machine originally had a 1500 / 3000rpm motor and if you wanted the max spindle speed of 1600rpm, you needed the motor to be running at 3000rpm (that's the no-load, synchronous speed - slightly lower when under load).

The motor fitted to the machine is a 4 pole (ie 1500rpm) 3kW induction motor. That's a bit OTT but I had it kicking about and it saved having to buy another one. HWIW, it originally powered an air compressor on an electric urban bus to power the brakes and air suspension.

If I'm running this motor much above its 1500rpm base speed, it's going to be well down on power. And in the Linuxcnc .INI file, there's a spindle scaling factor that translates / scales the 0-10Vdc output from the Mesa 7i76 board to actual spindle speed. I've disable the I (and D) term in the PID controller so that the motor speed is a direct function of the analogue control voltage from the 7i76's digital potentiometer.

The only simple way to independently measure the spindle speed is using the "Machtach" device that I procured, built and installed on the machine some years ago. 

This uses an optical sensor to detect markers on the spindle nose and calculate the rpm. Those markers are still present on the spindle nose and the device itself seems to work once powered up.

True, there's an encoder on the spindle that reports back the actual speed but I'm not 100% convinced it's set up correctly - I suspect it is but now would be a good time to check.

You may notice that the motor pulley is rather larger than the original - it's actually the biggest I could fit under the cover. That's because I swapped it out when upgrading the motor. 

This was before, with the original, smaller pulley:

And after, with the oversized pulley:

The result is that I can actually get over 1500rpm at the spindle from this setup, with the motor operating below base speed ie not field weakened. And the scale factor is bang on - I'd clearly frigged it to get the exact correct values. And the reported spindle speed displayed (from the encoder) is sot on.

On with cutting chips, then. The operation is broken down into 2 steps - bore through at 50mm, then counterbore at 62mm. If I ran both operations together, I believe the conversational feature would merge them and avoid duplication (air cutting). However, this is the first time out for Chris Polanski's "Intuiturn" conversational macros, so one step at a time etc.

That seems to be going well so far: 

Oooof, even with the rear and top chip guards fitted, this was a painful business. Blue hot chips are flying out in all directions. Rather than stop the process, I grabbed a handy cardboard box and hid behind it.

That was almost manageable, containing perhaps 90% of the hot chips. And a good result. In fact, I must have screwed up the touch off step a bit, as the bore came out almost 0.4mm undersize. Easily managed by a final (manual) pass.

Good result.

So there we have it - the first use of the (Internal Turning) conversational macros. I need to fit a more sensible chip guard that will enclose the front of the machine, so I don't get burned and the workshop isn't sprayed in tiny chips.

Arguably it would be sensible to connect up the coolant pump but the same thing goes - I need a guard to contain the mess, so it's simpler to just run dry for now.

Setting up to test the rewired CNC Bantam and Probe Basic Lathe

Now that I've developed a ballscrew attachment for the JD TB3 tube bender, I need to prepare to get the new compts machined. This requires:

• Find suitable material for the 2 blocks., This should really be steel, as loominum isn't going to work so well, either in terms of strength or as a bearing material where it bears against the bender's arms. I seem to have a piece of 1" x 3" hot rolled steel of 190mm length. That's a bit shorter than I'd planned but I have little choice of material to start from. I can cut it into a 100mm length for the bearing bock and a 90mm length for the ballnut. I will modify the blocks in Fusion to suit the new reality.
• Cut the stock ready for machining. 
• Flash up some lathe tools in Fusion. Currently, most of the tools in my library are for the Tree ie LH tools, whereas I need RH tools. So to start with I will create a 25.5mm drill, a CCMT060204 tipped boring bar and a fairly conventional RH turning tool with DCMT11T304 insert, while I'm at it.
• Create the toolpaths in Fusion using the new tools.
• Export the tools from Fusion as a JSON file and import them into the PBL as the tool library.
• Import the g code for the boring operations into PBL.

I don't intend to do the predrilling as a CNC operation, as I will be using a tailstock mounted drill for that. Similarly I'm not sure I can be arsed to face off the front of the stock afterwards. So this will simply comprise the rough boring and finish boring operations.

Here's the modified bearing block. It's a fair bit thinner than before and instead of having pillars sticking out on top and bottom, I will insert short collared spacers or shouldered screws.

Similarly, the ballnut bracket has shorter pillars.

There should be enough info here for me to set up the machine:

Here's the boring bar setup:

And the turning tool:

For the CCMT060304, I will use 80m/min surface speed, 0.1mm per rev feedrate and 1mm depth of cut. This is a slender boring bar, albeit carbide, so I've erred on the cautious side.

For the DCMT11T304, I will use 150m/min surface speed, 0.1mm per rev feedrate and 2mm depth of cut. Or I would if I planned to use it here.

Note that there's no actual (internal) boring operation as such. Instead, you select Profile Roughing and Profile Finishing and by selecting the appropriate features you define a boring operation.

FFS, some of the Fusion turning toolpaths are a rite of passage. I struggled to get this done but finally found that turning "Rest Machining" off allowed the thing to generate non-empty toolpaths, which is quite helpful. The rough boring and finish boring operations, which make use of a pre-drilled 25.5mm hole:

The (not used facing operation):

The g code for the boring operations:

%

(3001)

(BRG BLOCK)

N10 G7

N11 G18

N12 G90

N13 G21

N14 G28 X0.

N15 G28 Z0.

(PROFILE ROUGHING2)

N16 T12 M6

N18 G54

N19 G97 S3500 M3

N20 G95

....

....

N127 G1 Z-16.9 F0.1

N128 X59.9

N129 X57.9 Z-15.9

N130 G0 X0.

N131 Z5.

N132 G97 S3500 M3

(PROFILE FINISHING2)

N133 M5

N134 M1

N135 G97 S2000 M3

N136 G95

N137 G0 X0. Z5.

N138 G96 D2000 S80 M3

N139 G0 Z1.014

N140 X58.922

N141 G1 X59.172 F0.1

N142 X62. Z-0.4

N143 Z-17.

N144 X50.

N145 X47.172 Z-15.586

N146 G0 X0.

N147 Z5.

N148 G97 S2000 M3

(PROFILE FINISHING3)

N149 M5

N150 M1

N151 G97 S2000 M3

N152 G95

N153 G0 X0. Z5.

N154 G96 D2000 S80 M3

N155 G0 Z-15.986

N156 X46.922

N157 G1 X47.172 F0.1

N158 X50. Z-17.4

N159 Z-25.4

N160 X46.

N161 G0 X0.

N162 Z5.

N163 G97 S2000 M3

N164 M5

N165 G28 X0.

N166 G28 Z0.

N167 M30

%

Let's get the stock set up in the 4 jaw and import the g code into PBL.

Ooof, those jaws are in the way of the boring toolpath. That's what happens when you allow The Stupid Fat Bloke to get ahead of himself and set stuff up before thinking things through. And it was all dialled in at this stage of course.

That's better. With a 4-jaw chuck you can remove 2 of the jaws and swap them round without removing the work, then do the same with the other 2 jaws. So it remains true and now has a helpful gap between the rear of the stock and the chuck and jaws. This method costs less in terms of inserts, carbide boring bars and chuck jaws.

Once I've imported the g code, I may be forced to actually machine this bearing block.....

Update Centroid Acorn Lathe to 5.4 - and modifying the PLC code to suit - sneaky gotcha!!

I've updated the Tree CNC lathe with Centroid CNC12 latest major version ie 5.42 at the time of writing. The process is still a bit clunky - you have to take screenshots of each setup screen, run the CNC12 installer (having backed up the current, working example under a different folder name), then use the Setup Wizard to replicate every option, item by item, screen by screen.

But as I also had to create a custom PLC program for my powered ATC turret, I'll need to modify the 5.42 PLC in a similar fashion. This turret doesn't use Gray Code to report its position - instead it has a single switch for each of the 8 positions. These come in via the Ether1616 expansion board. There's no default option for an "8-input" turret position feedback.

The edits I made are documented here and there was a minor edit that resulted from testing it out. I'll now need to replicate those changes. The main PLC code will almost certainly have changed since I made my changes back in August 2022.

It's worth noting that the inputs from the turret feedback signals that come in via the Ether1616 expansion board aren't set up by the Setup Wizard - they are effectively hard coded in the PLC code. If you don't make the PLC edits, the ATC turret isn't going to know correctly which tool is loaded.

The final step, after editing the SRC code file is to compile it. Using CMD window, change to the c:\cnct folder, then run the compile:

cd c:\cnct

mpu compile acorn_lathe_plc.src mpu.plc

This generates a new mpu.plc file that will be picked up by CNC12 and run.

The gotcha

Ooof.

c:\cnct>mpucomp acorn_lathe_plc.src mpu.plc

MPUCOMP v5.42 Rev 07 MPU11 PLC compiler

$Id: mpucompiler.cpp 21173 2025-07-21 17:11:10Z keith $

Copyright 2001-2018 Centroid Corp.

Input file : acorn_lathe_plc.src

Output file: mpu.plc

Error Line 6913 Col 4: Undefined label TRUE

IF TRUE THEN CurrentTurretPosition_W = 0

   ^

Error Line 6922 Col 4: Undefined label TRUE

IF TRUE THEN SV_PLC_CAROUSEL_POSITION = CurrentTurretPosition_W

   ^

Error Line 6913 Col 4: Bad Numerical Factor

IF TRUE THEN CurrentTurretPosition_W = 0

   ^

Error Line 6922 Col 4: Bad Numerical Factor

IF TRUE THEN SV_PLC_CAROUSEL_POSITION = CurrentTurretPosition_W

   ^

Compilation failed.

c:\cnct>

WTF?? Turns out they changed the rules slightly somewhere between v5.20 (my last working installation) and v5.42 (today's update):

According to Mr AI, "If you try to compile a legacy .SRC file (written during the CNC12 v4.xx era or earlier) using the new mpucomp compiler from v5.xx+, it will instantly flag IF TRUE as a compiler syntax error. To upgrade old logic to work under v5.xx software, open your old .SRC file and find/replace every instance of TRUE used in logic statements to TRUE_M."

There are only 2 instances of the IF TRUE statement, both of which I pasted in when updating the turret code using snippets of the v5.20 code:

;==============================================================================

                               ATCGrayCodeStage

;==============================================================================

; EME 2024-11-10 ATC control trials

; Input 1 on Ether1616 with A0 address = CNC12 input 33 etc

; IF Tool1Input THEN CurrentTurretPosition_W = 1

; IF Tool2Input THEN CurrentTurretPosition_W = 2

; etc...

IF TRUE THEN CurrentTurretPosition_W = 0

IF INP33 THEN CurrentTurretPosition_W = 1

IF INP34 THEN CurrentTurretPosition_W = 2

IF INP35 THEN CurrentTurretPosition_W = 3

IF INP36 THEN CurrentTurretPosition_W = 4

IF INP37 THEN CurrentTurretPosition_W = 5

IF INP38 THEN CurrentTurretPosition_W = 6

IF INP39 THEN CurrentTurretPosition_W = 7

IF INP40 THEN CurrentTurretPosition_W = 8

IF TRUE THEN SV_PLC_CAROUSEL_POSITION = CurrentTurretPosition_W

; EME end of substitution

Replaced both TRUE instances with TRUE_M. That's better:

c:\cnct>mpucomp acorn_lathe_plc.src mpu.plc

MPUCOMP v5.42 Rev 07 MPU11 PLC compiler

$Id: mpucompiler.cpp 21173 2025-07-21 17:11:10Z keith $

Copyright 2001-2018 Centroid Corp.

Input file : acorn_lathe_plc.src

Output file: mpu.plc

Compilation successful

Max stack depth = 7

Program size: 13475 tokens (82.2449% of max)

c:\cnct>

That should work. It compiles and runs OK although I'll leave the testing of the turret until tomorrow, as it's a pretty noisy, brutal mechanism and it's late and I'm supposed to be getting tired soon.

Ballscrew driver for tube bender?

Although I'm not 100% convinced the "JD Squared" tube bender is going to cut it for me with this particular exhaust task. However, it's pretty awkward to use, even with a long "helper" tube fitted to the actuator handle. Here are some observations about its use - and thoughts about how to add a power assist.

The default assumption in the US is that any man worth his salt will have compressed air in his (work)shop, so one of those "pneumatic to hydraulic" adaptors would be a fairly simple matter to connect up. This would allow a hydraulic cylinder to be fitted to the bender - and be operated from a compressed air supply. We don't do that over here so much and even if we did, there are every few of those "pneumatic to hydraulic" products available.

Here's a JD Squared (clone) bender fitted with a hydraulic cylinder. Note that although it says "$200", that price doesn't include any actual dies...

So, how about simply fitting a large Chinesium ballscrew and driving it with an impact driver? Just pulling specs out of my ass, I'm thinking a 32mm ballscrew with a 5mm pitch would suffice. Generally, these seem to rated at around 4 Chinese tonnes of dynamic load. 

Looking at a HLTNC (a semi reputable Chinese supplier of SFU3205?), I'm seeing a static load bearing capacity of ~50kN and a dynamic load of ~17kN. That's between 1.7 and 5 tonnes of force in street talk. With the kind of leverage we see on that bender of about 20:1 when fitted with a 1m helper bar (~5cm active length at the ratchet bar), I'd be needing to apply about 85kgf or 250kgf on the helper bar to exert a similar force manually. I'm pretty certain I've never come close to that, so as far as calculations go, I think we can leave it there - "an SFU3205 ballscrew will be man enough", even allowing for Chinese units of measure.

So what would it look like, this ballscrew power feeder thing?

Check the bearing loads - that looks adequate.

Here's the assembly with all joints working but not bothering with "real" pivots, fixings etc. I'm only interested in the ballnut, bearing and ballscrew at this stage.

That will do. Let's focus on making it happen.