Member postings for Clive Steer

Have managed to upload 4 pics of my Pultra with sewing machine motor.

Clive

I've just fitted a Brushless DC sewing machine motor to my Pultra lathe. I used some of the motor mount parts that came with the complete package at £99. The motor is more noisy than an induction motor but the level of torque and speed stability at low speeds is very good. The Pultra is ideal for having the motor mounted under the lathe but I elected to mount the motor behind the lathe with the controller to the left of the lathe so everything is above the bench. The only custom part I needed to make was a 16cm x 16cm mounting plate with 4 hole in it. Two to mount the plate to the base casting and two for the motor and belt tension adjuster. My plate was 15 mm thick Ali but only because I had some to hand and I'm sure something thinner would be fine. I used a 5mm V belt to link the motor pulley to that of the lathe and the pulley cover provide in the kit was used to guard the belt from stray items.

If anyone want to PM me I can send some pictures and meanwhile will try to post them to the site.

Clive

Internal combustion engines, although better than the steam engines that they superseded, are still appallingly inefficient and even a modest improvement would reduce fuel usage and pollution. So whether fuelled by petrol or hydrogen the issue is rather academic.

However electric traction, as demonstrated by very early transport showed excellent environmental benefits but until recently this has been a non-runner for personal transport which we can't seem to live without. If battery technology can be improved according to Moore's law then the future looks better. However there are issues with the "refuelling" of electric cars if provided by our current power distribution network as a huge amount of energy can be easily transported by a fuel tanker. When motor vehicles first came on the scene one refuelled at the chemist but the quite quickly the arrangement evolved and adapted and so it is likely to do for electric cars etc.

The main theme for future energy generation and usage must be towards better efficiency and not necessarily towards reduction although that might be a good this in the short term.

Although climate change is an important issue to be tackled the world population may be the largest Sword of Damocles that we face. As David Attenborough said "in his lifetime the worlds population had tripled" and I'm sure our consumption of the worlds resources to lift our standard of living has followed a similar curve which doesn't bode well for the future.

The meek might end up inheriting the earth and not have to pay the taxes as our "civilised" society may have self destructed. Hopefully the human race won't be stupid enough to let it get that far.

I have a picture in my head of Jeremy Clarkson using the last gallon of petrol in the world to show how fast he can drive around the test track at Dunsfold !

Clive

I think the majority of people just want a cheap reliable product. However when devices are rendered less usable because of poorly designed parts failing such as plastic fridge bootle trays the cost to the user and environment can be high.

Most manufacturers are continually redesigning their products to reduce cost or improve performance by using new technology or materials so having to stock or guarantee the availability of spare parts for 10 years can be a burden especially if the parts you are stocking are not the parts that end up being the ones that commonly fail. If manufacturers knew what parts would fail why don't they design them better in the first place.

In my experience the most likely parts to fail are stressed plastic, then mechanical and that includes electrical connectors and then electronics as least likely.

Although there are legal requirements for products to comply with various safety standards there are not, as far as I'm aware, any legal requirements for reliability. It is probably perceived that manufacturers wouldn't design an unreliable product. However given the number of products recalled because of safety issues through poor design or manufacturing control then I'm sure there may be many more with reliability issues.

How standards would be worded would be a challenge but the use of "appropriate" materials which are shown to provide longevity or easy of recycling may improve the situation.

Clive

I believe in the 1700's poor cider was sweetened by adding sugar of lead and the population suffered the consequences. However the rich could take "The cure" at Bath and a recent study has shown that with prolonged immersion in water, heavy metals are lost from the body. So if you think you have accumulated any lead, copper, nickel, cadmium etc bathe more frequently. However, and here is a health warning, prolonged immersion in water can lead to drowning so the cure can be more dangerous than the illness.

Imbibing plenty of the amber nectar can reduce the anxiety caused by unnecessarily informative labels and if you suffer from such anxieties never read the information provided with medication.

Clive

Hi Aaron

Welcome to the forum. I'm in Little Common and into precision engineering, clocks/watches and things electronic. Andrew Mawson, who's near Sedlescombe, is into all sorts of engineering and may still be into metal casting. You can find him on the Madmodder site.

If you are not aware already there is Harling foundries Ltd on the Ivylane industrial estate off the The Ridge, Hastings.

Clive

Stephen

Check out the recent thread regarding Brushless DC motor for mini lathe in the General section as this suggests the use of a Sewing machine motor and speed controller the comes as a complete plug&play package at a very reasonable price.

Clive

I've now reverse engineered the circuit of my Jack Sewing machine motor controller which uses a ATmega88 micro. Wanting to clip my scope to the circuit and mindful that it operates directly from the mains with no isolation I decided to see if it would operate off a bench power supply. So I connected my 60V/10A bench supply directly to the L & N pins of the mains plug and it started up OK. Surprisingly the controller didn't drop out till 20V and came back to life at 32V. At 60V and running at 200RPM no load the unit was drawing 200mA. The torque developed at this speed was wrist wrenchingly high but I didn't note the current being drawn but still a good contender for driving a lathe.

Clive

I wonder how long it will be before, as in I Robot, driving a car in "manual" mode becomes a criminal offence. Also would "disconnecting" certain safety features be classed as modifications and invalidate ones insurance. Like many manufacturers now if they can't make much profit from the manufacture they make up for that in making it impossible to get a service without using their service centres.

This is the way Rolex operate now as they control all their watch spares and a service at one of their centres cost £300 upwards. I suppose they figure that if you can afford to by a £3K watch you can afford to pay the service charge and it's all part of buying into the product name.

Clive

I wonder how long it will be before, as in I Robot, driving a car in "manual" mode becomes a criminal offence. Also would "disconnecting" certain safety features be classed as modifications and invalidate ones insurance. Like many manufacturers now if they can't make much profit from the manufacture they make up for that in making it impossible to get a service without using their service centres.

This is the way Rolex operate now as they control all their watch spares and a service at one of their centres cost £300 upwards. I suppose they figure that if you can afford to by a £3K watch you can afford to pay the service charge and it's all part of buying into the product name.

Clive

I believe some time ago there was a "problem" with a certain internet connected Asian made TV that without owner consent collected ones viewing habits. I'm sure it will not be long before we all become cast members of Googlebox if a TV with camera, supposedly there so you can control it with hand gestures, is the only type you can buy. In reality anything you buy that has software and connects to any network can be "updated" even though there may be a tick box in some menu to prevent automatic updates and the updates are not always to your benefit. Network products are a money making device and the software owners, either of Apps or the Operating system will squeeze all they can until the pips squeaks.

Clive

Bob's comment about being able to turn down the power doesn't strictly apply to the sewing machine motor and their controller as it is configured to act as a servo motor. This means the motor will maintain the set point speed irrespective of the applied mechanical load and the controllers do not provide programmable torque limit that are found in VFD's. A delicate mechanism being driven by high torque servo motor can be damaged unless there is a torque limiting device which could be the drive belt slipping or a shear pin. Having said that most lathes, even small watchmakers types, are grossly over-engineered in order to limit spindle deflection when cutting so may not be classed as delicate mechanisms although the parts being made on them may be.

Clive

Although I would like to present more details about the substitution of the pot for the Hall device it was just a way of exploring the controller functionality and not a recommended conversion. As an experienced electrical/electronics design engineer I understand the electrical safety issues but others may not have that understanding and in experimenting put themselves and others at risk.

Even commercial VFDs only have Basic insulation between high internal voltages and their control potentiometer input and any failure of this insulation could cause the Pot circuit to become live so supplementary insulation/isolation needs to be added externally in the way of putting the pot in say a plastic box and using a plastic knob.

In the case of the sewing machine motor controller the Hall circuit is directly connected to high voltage (160V DC) with regard to neutral or earth so supplementary insulation/isolation is imperative and needs to be done correctly.

The hall sensor can still be used but there may be mechanical limitations to the fineness of control achievable when zero to full scale output from the Hall device is brought about by a 3mm movement of the magnet. However fitting a shaped pole piece to the magnet may improve the situation and worthy of a try as the Hall device would be more reliable as there is no moving contact.

Clive

I've been investigating the use of Brushless DC motors for small machine operation and purchased an "Industrial Sewing machine motor conversion kit" to check them out given their described performance. They also appear to be excellent value for money compared to a 3 phase induction motor and VFD combination which doesn't come "plug and play". The other benefit of the BLDC motor is its small size and weight given the power and high torque it can provide. The high torque ( 3 N-m) aspect would allow a small lathe such as a Pultra to be directly driven without needing a countershaft/pulley system as BLDC motors can develop their full torque even at low speeds. The controllers of the sewing machine motors are described as providing servo speed control, which is needed for a sewing machines cyclic load variation and is a benefit for a lathe also. The down side is that a sewing machine is usually operated either off, slow speed for positioning and then full speed and the full speed is preset on the controller for what the machine or operator can cope with. The speed control unit has an operating lever connected by a rod to a foot operated treadle. Internally it has a linear Hall effect device so when the control lever is moved a magnet moves in a small arc above the Hall device. The Hall device is powered by 5V from the Motor control unit and produces an output from zero to about 4V when the operating lever is moved over its full range. From zero to 2.5V the motor is OFF, from 2.5V to 3V the motor operates at a fixed slow speed of around 200RPM and from 3V to 4V the motor speed varies linearly from slow to full speed. On my unit the full speed can be set from 500 RPM to 4500 RPM. If 500 RPM full speed is selected the 1V linear range of the Hall is used to proportionally control the speed from 200 RPM (jog) to 500 RPM. To check out what resolution the 3 - 4V proportional range was I replaced the Hall device with a 10 turn potentiometer and found that even for a high full speed setting, (200 - 4500 RPM range) the speed was essentially linear with no noticeable steps although I may test this further.

A word of warning !!! there is no isolation of the controller electronics including the speed control Hall device from the mains supply so adequate precaution should be taken to prevent contact with potentially live circuitry. The consequence of any error in this matter can be serious!!

I purchased a second similar unit from a different supplier and the motor used is a Permanent Magnet Synchronous Motor and works in a slightly different way to a BLDC motor.

Both motors are driven by sinusoidal waveforms so produce low torque ripple another plus for use with a lathe.

Being servo controllers when the manual speed control is moved to off from say full speed the motor is physically braked by the control and it stops almost instantly. I haven't explored this area of operation when the motor is loaded with significant rotational inertia. The controller also has the capability to position the output shaft which in a sewing machine relates to the needle position using another sensor which may be useful for a lathe ?

My investigations continue but so far they have the potential of being good for powering even larger lathes such as a Myford if this isn't heresy.

Clive

Hi Steven

I've fitted DRO scales to all three axis on my BCA Mk3 with X & Y being optical and the Z axis the much more compact magnetic type which are all relatively easy to fit without major alterations to the BCA. If you PM me I can send pics of how I did it.

Clive

Hi Duncan

I'm sorry I misinterpreted your reply. However I don't understand why, in the case of a Venturi , the pressure is the square of the velocity when the sensing port in the throat is at right angles to the flow so shouldn't be sensing any velocity component. My reasoning is that lift generated by an aircraft wings upper surface, which is effectively half a Venturi, is proportional to airspeed. I don't remember, a least in my aeroplane, ever experiencing a square law increase in lift with increase in airspeed although when fully loaded I wish I had.

I'm not trying to calibrate the ASI using a car but just to confirm the Venturi law and constant as I don't have a wind tunnel to hand. For checking the calibration of ASI's I use a published equation relating pitot pressure and airspeed together with a precision capacitance manometer and a certified ASI as a double check.

Clive

Many thanks Duncan for confirming that the relationship between inlet velocity and throat depression is linear and I'll try to use the Bernoulli equations to work out the Venturi constant from its dimensions.

I have tried a calibration using my car but the results were inconclusive due to turbulence. I might try using a pitot/static probe and ASI to gather with the Venturi and its associated ASI to compare one against the other. However I'm not sure my journey would be classed as essential.

I think I might have to steal a copy of BS 1042 as at £190 it's a bit steep for a one off calibration.

Many thanks again Clive

I have an original air speed indicator from a vintage Klemm aircraft which I need to check the calibration off. This ASI is unusual in that instead of being operated by the more common Pitot/Static probe it uses a Venturi tube that generates a vacuum. I've measured the relationship of the indicated airspeed to that of the vacuum pressure for the ASI and this appears to be largely linear. So this makes me believe that the vacuum pressure generated by a Venturi is largely proportional to air velocity. However I am finding it difficult to extract this information from the complex equations available which also usually deal with incompressible fluids rather than air. Another factor I'm struggling with is that, unlike a pitot/static probe whose performance is insensitive to port dimensions, a Venturi performance may depend on the max/min diameters. Venturi for aircraft are usually used to provide a vacuum for air powered gyro instruments so their vacuum pressure/airspeed relationship is not usually provided as a number but just that they are big enough to power one or two instrument.

If anyone has information about this or can point me in the right direction that would be greatly appreciated.

Clive

There is a lovely film made in the 70's by the BBC about the model flying scene called "Wings and Things" which can now be found on YouTube. It brings back fond memories of model flying starting with control line combat, single channel radio with a Super 60 and then on to much larger scale models with full proportional RC. My early model flying some times resulted in a "carrier bag" job but luckily we flew on a river flood plain with soft ground in Footscray Meadows. I also flew my models on Dartford Heath on the site of a WW2 Ack-Ack emplacement which had been demolished but the concrete access roads were left. I remember one guy returning his model to kit form by diving it into the concrete on his first attempt at RC flying.

My model making unfortunately escalated to full size with the rebuild of a Tipsy Nipper in my garage. I think my wife would have preferred I stayed with the models.

My worst model was a Giant bi-plane which we called the "Red Fletton" and my most fun one a "Panic" by Avicraft.

Clive

I have a Mk3 BCA with its original two speed 3 phase motor which unfortunately is specially wound and can only be operated on 440 volts.

Not having 3 phase available and also wanting the machine to have the capability of variable speed I have fitted it with a 440 volt inverter powered from the domestic mains through a 240v to 440V auto-transformer. I have fixed the motor in its low speed configuration and configured the inverter to provide 100Hz at max speed to recover the higher speeds. The original motor is quite capable and has all the necessary guards so unless it is faulty I saw no reason to change it and although the auto-transformer/VFD kit is more complicated it does transform the machine and enable less belt changing. There are VFDs available that produce 440v output from 240v but these are less common and can be much more expensive if fitted with the more capable Power Factor Correction (PFC) front booster stage.

If one doesn't want variable speed or the complication that goes with it then a static converter can provide the 440v 3 phase.

Clive