Electrical Newbie....please help!

Hi

Sorry if this is a little off topic for this forum but its hard to find a suitable active forum with an experienced community and i thought i might be able to find some help here.

I have no experience with electrics but i am trying to learn the basics.

I am trying to build a jig for my wood lathe where i can make the lathe cutter move up and down the jig like it would on an engineers lathe.

I have a move-able fixed U channel gantry 1620mm in length with a 12mm threaded rod and square block that is tapped that hopefully will zip up and down the channel when it is powered by a motor. Lathe cutters will be attached to the moving block.

I currently have:

• 240v to 3-12v adapter with an attachment for wires (2A max load... perhaps i need a higher amp rating)
• PWM reversible controller for the speed
• 12v 1000rpm motor with 5amp cutout and 7.5kg/cm torque

The issue i am facing is the motor doesn't seem to have enough torque to turn the threaded rod and stalls before any turning, i need it to ideally run up to 1100rpm (but id prefer it to be variable hence the PWM controller)

I was wondering if anybody could point me in the correct direction for where to go with a motor suitable for the application, something like a cordless drill motor would probably be ideal but the shafts are geared and i was hoping to use a coupler with D Shaft.

The motor also needs to be reversible.

I know the motor i currently have works at different speeds under different voltages(i can change the voltage on my adapter) but some motors specify voltages and speeds

I can link my products if it helps but didnt want to break any forum rules i might not be aware of on my first post.

Thanks in advance for any help it would be greatly appreciated!

As a starting point:

Is the threaded rod a metric M12 threaded rod? if so what is the pitch on the 12mm rod? If it is standard 1.75mm, at 1000rpm you are going to be moving the tool at 1750mm/min. Is this the travel rate you are after?

What is the threaded rod made of? Stainless steel, brass, mild steel, hot dip galvanised steel or something else?

How straight is the threaded rod? What bearings is it running in? What is it driving, a standard nut or something else?

Is it a ball screw and ball nut?

What weight is being moved by the threaded rod?

What is the moving part running on? Smooth surfaces? Bearings? Something else?

Have you tried turning the rod by hand to see what effort is required to turn it?

The answers to these questions will give a starting point to work from to see if we can help you.

Martin C

Hi Martin thankyou for the reply.

Yes its a metric M12 threaded rod, i worked out the pitch and revolution so that i could get a full travel under 2mins i believe when i worked it out so wouldnt need to go faster than the 1100rpm ideal(but close to that is fine). I have the workings with the pitch/rpm/travel time on my PC at home but currently away on my laptop.

Its a stainless steel threaded rod
Stainless steel U channel
Mild steel threaded block
Aluminium bushings/stops/guides at either end for the rod(I do have some mild steel ones made too but wanted to try the softer aluminium first) (basically the 19x19x50mm block with a 12.5mm hole drilled through the center)

The U channel is perfectly straight and the rod sits perfectly straight into the U channel with the guide blocks at either end/threaded guide block in the center

I am not running it on any guides it is just U channel with 19.4mm clearance gap and 19mm mild steel block that is threaded....it slides up and down nicely and the threaded rod can be turned by hand to make it move (minimal resistance)

The mild steel travel block itself is very light maybe 100g? I havnt weighed it, it is 19x19x50mm

I have a coupler to drive the rod but when i know it is working i will probably drill the M3 grub screw holes all the way through and put a full m3 bolt through for a secure fixing

Hmm,

You don't need a variable voltage "adaptor" and a PWM controller. For inital testing just connect the power adaptor to the motor and vary the voltage. You can wire a change-over switch or just swap the leads to chang direction. I suspect that the power adaptor is not powerfull enough. If it is still slow without the PWM unit you need a bigger powersupply. The clue is 2A power adaptor and 5A motor. I suggest you need a 6 or 8A 12V fixed voltage power supply to drive this motor with the PWM controller. You could also try using the PWM adaptor with a 12V car battery instead of a mains supply.

Robert.

Hi Robert, thanks for the reply.

When i have tested it i did the testing without the PWM controller, just the adapter > wire > motor.

It does work when wired up and RPM changes at the different voltages(i can change from 1.5/3/6/9/12V with a dial on the back of the adapter plug).

However when i attach the motor to the rod the motor then stalls as i turn the power on - it makes a "motor noise(sorry cant describe it better than that lol)" and then tries to turn but doesn't and switches off.

Try running it off a car battery. I'm pretty sure your adaptor is not man enough.

Thanks ill give that a go. The original plan was to run it off of a 5amp motorbike battery but i came across the adapter on amazon and thought it might be more convenient. Ill order the motorbike battery and see if it works any better

Martin's approach will get the right answer, but I see the power supply is undersized. The motor probably draws more than 5A from stopped, and needs at least 5A amps to get up to speed. If the power supply can't deliver enough amps, the motor will stall.

I'd test the motor driving the lathe by connecting the motor to a car battery, which can provide at least 60A. Bit dangerous though, because accidentally shorting the battery will melt the wires - nasty burns and a fire risk.

In electrics:

• The system should usually be matched - do not connect a DC motor to an AC supply or vice versa
• The voltages must match - do not connect a 240V supply to a 12V motor
• The supply should be able to deliver enough amps to drive the motor - a 5A motor needs a 5A supply and a 5A fuse.
• The speed controller may be rated in Watts, which need to be 10 or 20% more than the load, The motor takes 5A at 12, which is 60W. The controller should be rated 66W or higher.
• Voltages below about 80V are unlikely to cause electrocution. UK 240v mains isn't a guaranteed widow-maker, but safer to assume it is! Note that metal machines and damp concrete floors multiply the shock hazard compared with standing on a dry carpet.

Try it with a bigger power supply, but gut feel is that 60W is on the low side. The power needed to drive the cutter is proportional to the feed rate and depth of cut. I doubt 60W will zip along - a motor that size will do the job, I expect it will slowed down with a gear or belt-drive. (Halving the speed with a gear doubles the torque.)

Dave

Thankyou Dave, do you know if the voltage can be "spikey" on car batteries? Im reading some reviews saying it can drop depending on the charge(some 12v batteries giving 6.3v outputs) which would affect the motor speed

I have seen geared planetary motors with high torque but they are all 200rpm or lower which would be super slow on the travel and take almost 10mins to do a full run.

I would be looking at taking off ~0.5-1mm per cut with the lathe cutters, i am in need of super straight accurate cuts which im unable to do by hand across the length of the spindle

Is it ok to link the products ive used on here or it is not allowed?

Ill put together some info i can gather from the product pages below

Motor:
DC 12v 1000rpm motor

• No-load current: 240 mA
• Stall current: 5.9 Amp
• Stall torque: 7.5 kg-cm

Wire:
22 AWG 0.32mm² Electrical Wire - 22 Gauge Silicone Cable Low Impedance, High Temperature Resistance Tinned Copper Wire

Adapter:
International Power Adapters Multifunctional Portable Power Transformers (Included USB),AC Supply Adapter 100-240V to DC 3V/4.5V/5V/6V/7.5V/9V/12V-MAX 2A (2000mA)+8 Different Plugs

• Has screw terminal connector for +/- wires

PWM Controller:

Brush Motor Speed Controller — DC12—60V /20A DC Motor Controller Forward/Reverse Electric Motor Speed Regulator

Features:
(DC Motor Controller supports stop and forward and reverse functions, making it more flexible and convenient to use.
Motor Speed Controller is made of high-quality electronic components with stable and reliable performance.
Motor Speed Governor is compact and easy to install in narrow space, simple control, it is easy to control the rotation of the motor with the knob.
The input voltage of the Electric Motor Speed Controller is within the range of DC 12-60V and the applicable current is within 10A.
Regulator Controller suitable for: DC brush motor)

• Voltage: DC 12V-60V
• Output current: 20A

Slightly nervous about Dave's last bulleted statement - perhaps I am reading it wrong :

240V mains IS a widow-maker potentially, (no pun intended). Any "electrical newbie" needs to be 100% aware of how dangerous the mains supply can be in the hands of someone who clearly knows nothing about electricity. Much lower voltages than 240 V can kill - hence why building sites, where it can obviously rain, use a centre tapped 110V supply for their power tools, resulting in only 55V between either conductor and earth.

UK mains can kill. Be under no doubt. Please be extremely careful. Better still, don't dabble with it.

PS, the wire you are proposing for the motor sounds much too thin. You need at least 10 Amp wire, which, (from memory, so please look it up), would be 1.5mm Sq cross section per conductor.

Edited By John Doe 2 on 11/05/2023 23:08:31

Agreed, I dont plan on playing with the mains directly Id always turn it off at the switchboard if i ever did. The adapter im using steps it down to 2amp/12v max and ive only been wiring it whilst disconnected lol. I have changed a few light fittings at home and had an unexpected buzz of of the light fittings before not recommended lol.

As others have said repeatedly, the fundamental problem is the power adapter.

You say

Motor:
DC 12v 1000rpm motor

• No-load current: 240 mA <------------ 2A adapter can supply this
• Stall current: 5.9 Amp <------------ This requirement is way beyond it.
• Stall torque: 7.5 kg-cm

Get a 6A or preferably 10A power supply and it should go.

The adapter you have is satisfactory for the No-load condition, but way too small for the stall current - which it will hit when starting up.

Thankyou, do you think i should try to find a similar adapter with a 5amp load then? And that should solve it? I think ill order the car battery as well and give both a go. I was thinking something like a cordless drill motor should do the job but when i looked for replacement parts they seem to have a toothed gear on the drive shaft which makes them slightly unsuitable for the use(well more unsuitable for my engineering aptitude lol). Would the motor not stall if i gave it a 10amp or 6+amp load?

Sorry to double-post. Ive just been trying to do a bit of research on the adapters, from what i can see the adapters dont force the ampage, its pulled by the source? So i am guessing the 10amp adapter would be fine as the motor should only draw up to 5.9amp from it? And the adapter will just cap the max amp draw at whatever it is rated to (10amp in this case)

This is what the description i am reading says:-
"【Strong Compatibility】 Works well with most of devices that draws less than 10A 12V, such as 5A / 6A / 7A / 8A, If your previous Adaptor was less than 10A then this will be a perfect replacement as amperage is NOT Forced. (Notice: This power adapter do not applicable to all Lithium / Acid Battery Products, and cannot replace or work for any Lead Acid Battery)"

Im just a bit worried about killing the motor as it was quite hard to get hold of

Just to clarify as well the motor does fully work without being connected to the threaded rod, it spins happily without stalling unless coupled to the threaded rod.

No offence, but I think you would probably be much better off using an actual battery drill to drive your lathe carriage.

You can sometimes buy second-hand DeWalt, Bosch, Makita battery drills from those high street shops. All the electrical supply, gearbox, speed control and reversing switch would be there as part of the drill. And they have high torque. You would simply need to fabricate a mounting to secure the drill onto your wood turning lathe carriage drive.

Without understanding electricity, you might spend a lot of time and money otherwise.

PS, Note : Domestic light fittings are still live even when the light they feed is switched off.

Edited By John Doe 2 on 12/05/2023 09:28:06

OP, with due respect, you are only telling us part of the problem.

What are you actually trying to make on the lathe?

Have you considered manual operation? It would just need a crank handle on the end of the leadscrew, and would be far more controllable than an electric drive in its simplest form.

You will also need some way of feeding the tool into the work, and that will normally require another leadscrew.

I do have plenty of drills but there isnt enough clearance between the jig and the tailstock to get the drill body behind the tailstock as the end cut is very close to the lathe center (4mm)

Right angle chuck adaptor on the drill ?

Disregarding the motor and power supply for the moment I would have serious concerns about spinning a 5 foot length of commercial threaded rod ar over 1000 RPM. The root diameter is a little over 10mm and whilst the nut will constrain it at some parts of the traverse there is always the potential to whip.

You mention using a lathe cutter but we dont know what you are machining. If this 'jig' has 1.5m of travel then presumably you have a lathe with a very long bed in which case why do you need the 'U' channel? Better would be to make a carriage that slides along the bed and (because a wood lathe does not have a leadscrew) pull the carriage along with a loop of timing belt stretched between two pulleys, one being driven by something like a car window motor.

Is the work in the lathe itself rotating whilst the cutter is travelling?

I see plenty of woodworkers use a router mounted on a carriage in order to remove stock with relatively low loads on the workpiece.

Ian P

Update - I got the 10amp power supply but the motor is still not strong enough to turn the threaded rod

A cordless drill does turn the rod nicely but the drill body doesnt have enough clearance from the tailstock to make it useable.

Ill need to find a motor as powerful as a cordless drill somehow, can anybody point me in the right direction? The cordless drill replacement motors come with a gear on the end that isn't suitable for the application (need a standard shaft or D-shaft ideally)