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Member postings for Alan Charleston

Here is a list of all the postings Alan Charleston has made in our forums. Click on a thread name to jump to the thread.

Thread: Boxford Screwcutting box / Leadscrew binding
14/03/2019 05:17:28

Hi Andrew,

If you want to get the gearbox off you'll need to slacken off the bolts holding the headstock in place and slide it forward which will reveal the cap screws holding the gearbox in place.

This is not easy as the front bolt holding the headstock down is really awkward to get at and there's very little room to swing a spanner between the sides of the bed. I ended up buying a good quality 15mm ratchet ring spanner to get it out. Due to the restricted swing available, it needs to have a fine ratchet action so a cheap one won't do.

Regards,

Alan

Thread: Machining cork!
05/03/2019 05:02:07

Hi Maurice,

Moulding a silicone bung sounds a good idea. If that doesn't work try a scientific supply company. Rubber bungs are made from a small end diameter of a millimeter or so to huge (>100mm).

Regards,

Alan

Thread: metal spinning small bells
23/02/2019 05:24:07

Hi David,

You may have a problem trying to spin a bell. Whenever I've tried spinning brass I've found I need to keep annealing it to get it to flow evenly. I suspect annealed brass will be fairly dead as far as ringing goes so you are more likely to get something to ring by turning it from either a hard brass or bronze. Phosphor bronze may be a good candidate as it is hard and readily available in short lengths for bushings.

I actually have some brass which rings really well. It is 1" dia. and came from an old set of door chimes. Two different lengths were suspended from wooden plugs driven into the ends of them and a solenoid mounted between them hit first one then the other with a wooden striker giving a ding - dong noise. You might find some of this material in a junk shop.

Regards,

Alan

Thread: Quality issues with a SIEG SX2.7 mini mill
20/02/2019 05:43:53

Hi,

I have an SX2.7 mill and it has a peculiarity I'm not sure is a fault or not.

If there is a drill in the chuck but the mill is not turned on, and the quill is lowered using the handle on the right until the drill hits the work, it is possible to continue turning the handle a bit (say 2 degrees) until it comes to a hard stop. It's like the rack and pinion is really loose and a spring is used to keep the pinion at one end of the rack on the quill. This results in a tendency for the drill to suddenly drop a bit when the pressure comes off and grab when it breaks through the bottom of a hole. Is this normal. I did try to pull it apart to see if I could see what is wrong (if anything) but with the electrics in the handle to enable power tapping (a truly useless complication) I chickened out half way through and put it back together while I still could.

When I first got the mill, it came without the little bit of brass between the locking screw and the quill so I couldn't use it as a mill. The local supplier got onto Seig and as the part only weighed a few grams I expected them to mail the bit. No - they waited until they had a container full for the supplier - so it was about 3 months before I got it.

The other problem with the mill is the lack of oiling points. Unlike the SC4 lathe I was silly enough to buy which seems to have had a shotgun involved in the decision where to put the oilers, the SX2.7 only has one oiler - on the bushing end of the x axis screw for the table. It's really awkward trying to get the ways a screws lubricated.

Regards,

Alan

Thread: Anyone fitted a DRO to Sieg SC4?
10/02/2019 05:08:38

Hi Jim,

Rather than fit a DRO you may want to consider making a bracket to screw on the rear of the carriage and a DTI. DTIs are quite cheap through AliExpress and seem to be accurate.

sc4dti1.jpg

sc4dti2.jpg

Regards,

Alan

Thread: Filing A Curve
28/01/2019 06:47:43

Hi,

I was watching the video posted by Jason of the guy making a ring from a couple of brass nuts. I noticed he was filing the ring by starting with his left hand high, and following the curve with his left hand dropping as he pushed forward. This seems to be the usual procedure for most if not all of the people I see filing curves which is not surprising as it is the natural way of doing it.

When I was taught workshop practice at the Tech however, the tutor went to a lot of trouble to stop the class doing it that way. He taught us to start a cut with the left hand low, and to raise it as the file was pushed forward. There was a lot of muttering about it initially, but once the technique was mastered, it seemed to give better results, although this may have been because we were getting a lot of practice in filing.

Is the way I was taught the "correct" way or doesn't it matter which way it is done. The guy making the ring certainly ended up with a nice curve.

Regards,

Alan

Thread: The Diamond Tool Holder
21/01/2019 05:23:11

I've had a diamond tool holder for years and I love it. The surface finish I get on steel for general turning has improved no end.

I'm not great at grinding tools so in the past I've cut threads on the lathe using cutters with no top rake. The surface finishes were usually poor and needed finishing off with thread nuts to be useful. I was aware from their videos that the diamond tools could be used to cut threads but couldn't see how to grind them. I e-mailed Gary at Eccentric Engineering and he was kind enough to grind both 55 degree and 60 degree threading tools for me. They work brilliantly with the metal peeling smoothly off the work and giving a beautiful surface finish even on steel which is of dubious quality.

After seeing what the tools look like, and practising grinding them with key steel on the jig that came with the holders, I found it to be quite easy to do.

Regards,

Alan

Thread: nylon gib strip grub screws?
15/01/2019 04:58:37

Hi Peter,

Would wrapping a grubscrew in teflon tape give the same effect? You may need to roughen the thread surface by gripping it hard in a pair of pliers to stop the teflon slipping and experiment with the number of turns of tape but it should be possible to end up with a screw which is resistant to vibration turning.

Regards,

Alan

Thread: First attempt at threading on a bantam - all didn't go well
12/01/2019 05:24:44

Hi Mark,

If you can source or make a thread dial, you can use the half nut to stop the carriage even if you are cutting an imperial thread on a metric lathe. The method is as follows:

1) Engage the half nut when the thread gauge reads 0.

2) Disengage the half nut at the end of the thread and turn the lathe off. Back the tool off.

3) Start the lathe in reverse and engage the half nut when the thread gauge reads 0.

4) When the tool is clear of the work, stop the lathe, leaving the half nut engaged.

5) Reset the tool and start the lathe in the forward direction.

I made a thread gauge out of PVC for my old imperial Boxford lathe and turn metric threads quite happily using this procedure.

Regards,

Alan C.

Thread: Minnie Traction Engine
05/12/2018 05:08:46

Hi,

I've been casting around looking for a new project and thought I might like to give the "Minnie" traction engine a go. The snag is that the book by Leonard Mason is jaw droppingly expensive. It's no longer published and second hand ones go for upwards of $US100.

It was published by Model & Allied Publications (MAP) which over the years has morphed into Special Interest Model Books Ltd. I E-mailed them and asked if they would consider publishing it again. I received the following reply:

"We don’t have any plans to republish that particular title and in any case I would not know how to reach the author in order to clear the rights."

If anyone knows where Leonard Mason or his literary heirs are, you may wish to contact them and suggest they look at republication. Given the high price the used copies command, there's obviously a demand for it.

Regards,

Alan

Thread: Stepper Motor Identification
30/10/2018 01:26:12

Hi Joseph,

Thanks for putting me right as regards the motor resetting itself to the nearest step each time it powers up. I thought what I was doing was OK because I set the motor to run with 4800 pulses which resulted in the stepper motor rotating 3 times and the business end of the dividing head rotating 9 degrees which is what is needed for a 40 tooth gear. I set the head up to start at 0 degrees using the indexing pin, then went through the process of turning the Stepduino on and off 40 times. The indexing pin slid smoothly into the plate at 0 degrees, indicating an accurate process. The reason it worked, is that 4800 is divisible by 8 (the number of microsteps) so the rotor stopped at a full step rather than halfway through a step. My method would probably work if there was no microstepping, but the accuracy of the system would be less.

As far as the confusion regarding the steps/revolution is concerned, that was my fault. I could have set the steps/revolution to be 1600 (which is true) and the number of revolutions to be 3, but instead I set the steps/revolution to be 4800 (which is not true) and the number of revolutions to be 1 (which is also not true) but which also results in the stepper motor turning 3 times.

As far as the duration of the pulse to the motor goes, Dave had an ON time of 2 microseconds and an OFF time of 100 microseconds. I believe this gives a speed of about 375rpm. I found the motor was easily stalled. I wanted to reduce the speed and hence the acceleration at start-up and to increase the torque so I increased the ON time to 500 microseconds. The torque was much better and the speed went down to about 60 rpm. I ran the motor through 127 iterations when connected to the dividing head and the motor temperature didn't go up so I'm assuming I'm not damaging anything.

Hi Dave,

I loaded your first sketch into the Arduino and hooked the motor up to the dividing head. I set the head up to start at 0 degrees using the indexing pin, then applied power to the Stepduino and let it run until I counted 127 iterations. The indexing pin slid smoothly into the plate at 0 degrees so it looks like your solution works a treat.

Thanks for your latest sketch. There is a "Buttons" tutorial in an Arduino kit I've got so I'll work my way through it (again!) and see if I can get one to work with your sketch.

I'm really greatful for the help you've given me.

Regards,

Alan

29/10/2018 03:13:35

Hi,

Thanks for all your comments.

I'm not worried about plugging and unplugging the motor as the way I have it set up is that the power to the stepduino and motor is only on when the button is pressed i.e. the power is off, the button is pressed which supplies power, the motor advances the set number of steps, the button is released and the power is off again. I like this way of working as I can do as many teeth as I want then leave it and come back again the next day and continue where I left off. I'm not sure if that applies to the other programmes that are around.

I wasn't aware that each time I put the power to the system that it will restart at the beginning of a full step. I'm not sure that this matters however. As long as each pulse produces the expected rotation, and the number of pulses are correct to give the rotation required, I don't think it matters whether the new rotation restarts from the same stage during a step or from the beginning of a step.

Thanks for the sketch Dave. I put it into the Stepduino and it seems to make the motor rotate about the right amount. Is it supposed to stop after 127 iterations? I set a microscope above the pulley to see if it would return to the same point after 127 turns but it didn't stop. I'll have a closer look at the sketch and see if I can figure it out. I slowed it down to about 60 rpm by putting a 500 microsecond delay for the pulse HIGH time. This gave a much higher torque.

Regards,

Alan

28/10/2018 07:06:07

Hi,

Thanks for all the comments. I don't think lost steps are a problem. I've reduced the speed to about 60rpm to reduce the acceleration when starting each step and the registration pin on the head engaged the built in indexing plate at 0 degrees before and after 40 steps of 9 degrees each.

If I was confident of programming the Arduino I think I'd follow Duncan's approach and calculate the number of cumulative pulses for each tooth as the gear is cut, subtract the total for the previous tooth and round it to the nearest integer.

Alas I'm not. I have tried for years to get my head around programming the Arduino but I've got a teflon brain that nothing computer oriented will stick to. I'm in the frustrating position of understanding enough to see what can be done but not being able to do it.

That's one of the reasons I'm keen to stick with the simple solution I outlined in my last post. I take the point that it's probably not wise to do all the residual pulse correction on consecutive teeth but rather spread them out over the whole tooth. I can do that by using the two outputs from the Stepduino as I outlined earlier. I need some way of easily swapping between the two outputs as the gear is cut. My first thought was to have a plug from each of the outputs and switch the motor plug between the two at regular intervals throughout the cutting operation. It would be better however to have a rotary switch between the controller and a single plug. The operation of the switch would need to carry out the operation shown in the photo.

switch.jpg

It would need to switch the 4 wires of the motor between the 4 outlets from controller one and the 4 outlets of controller two. I don't know what the name of such a switch is which makes it hard to find out where to get one. Can anyone tell me?

Regards,

Alan

26/10/2018 07:07:57

Hi John,

I think I've come up with a working digital dividing head. I stripped out most of the Freetronics example sketch, leaving me with only the instructions required to run one motor a specified number of steps in one direction. The modified sketch is:

const int Stepper1Step = 5;

const int Stepper1Direction = 2;

const int StepsPerRev1 = 4800;

/**

* Set pin assignments

*/

void setup() {

pinMode(Stepper1Step, OUTPUT);

pinMode(Stepper1Direction, OUTPUT);

}

/**

* Main loop

*/

void loop() {

for(int i = 0; i < StepsPerRev1; i++)

{

stepper1Forward();

}

delay( 1000 );

for(int i = 0; i < StepsPerRev1; i++)

delay( 1000 );

}

/**

* Rotate stepper 1 forward by 1 step

*/

void stepper1Forward()

{

digitalWrite(Stepper1Direction, HIGH);

digitalWrite(Stepper1Step, HIGH);

delayMicroseconds(500); // 1uS minimum pulse duration for DRV8811

digitalWrite(Stepper1Step, LOW);

delayMicroseconds(100);

}

I slowed it down by increasing the pulse duration to 500 uS and set the motor to rotate 3 revolutions by setting the steps/revolution to 4800. I disconnected the USB connection to my PC and the external 18V supply to the controller. I found that when the external power supply was reconnected, the stepper motor rotated three revolutions and stopped. This is what is needed to turn my dividing head.

I connected the motor to the dividing head using a toothed belt and a 15 tooth pulley on the motor and a 45 tooth pulley on the dividing head. The gearing in the dividing head is 40X so the three revolutions of the stepper motor resulted in the dividing head rotating 9 degrees. I've included a couple of photos of the setup.

There is a indexing plate on the head with holes every 10 degrees which can be engaged by a pin on the main body. After setting the dividing head to 0 degrees, I applied the power to the controller from the battery 10 times and found the pin engaged the indexing plate perfectly at 90 degrees. The same thing happened at 180, 270 and back to 0 degrees again so the stepper motor is as accurate as the indexing plate.

This setting enables a 40 tooth gear to be cut. I can of course change that to any number of teeth I want by connecting the Stepduino to my PC and changing the number of Steps/Revolution in the sketch. This is probably not much more time consuming than setting it using the LCD screen with all the complications with the sketch and the hardware this would entail.

One thing worries me a bit. Given that it takes 1600 pulses to rotate the stepper motor 1 revolution and the gearing between the stepper motor and the business end of the dividing head (120:1) it requires 192,000 pulses to rotate the work one complete revolution. If, for example, I wanted to cut the ever popular 127 tooth gear, the number of steps/tooth required would be 1511.8 pulses. As the input to the sketch needs to be an integer, the StepsPerRev would need to be set at 1512. 1512 X 127 = 192,024pulses which is 24 pulses too many. This doesn't sound much but is 1.6% of the 1512 pulses/tooth. In other words, the final tooth will have 1.6% of its thickness removed and this will be worse if multiple passes are made when cutting a gear or if the decimal is closer to 0.5 rather than the .8 in this example.

One way around this would be to cut 103 teeth at 1512 StepsPerRevolution, then cut the remaining 24 teeth at 1511 StepsPerRevolution which would reduce the error to 0.07% for the last 24 teeth which is probably negligible. This can be done by reprogramming the sketch after cutting 103 teeth or, since I have the dual output stepduino, reactivate the Stepper Two output with the StepsPerRevolution set at 1511. After cutting 103 teeth the motor would be unplugged from output one and plugged into output two.

I hope this crude way of doing things doesn't cause too much offence.

Regards,

Alan

divhead1.jpgdivhead2.jpg

25/10/2018 03:25:19

Hi again,

Thanks to Michael and John.

I've managed to get the shaft of the stepper motor to spin using the example sketch shown on the Freetronics website!

The sketch wouldn't compile but I think the problem was at the end of the sketch where there was a section which froze the shaft in one position. I deleted that part of the sketch and the bit that was left which turned the shaft one revolution forward followed by one revolution in reverse compiled OK.

I had a bit of a hiccup when connecting the motor to the controller. There are six wires coming from the motor so it can be used as a unipolar motor. The controller has only four connectors so the motor needs to be connected in bipolar mode. I assumed that the centre tap wires would be ignored but the motor data sheet showed the connections to be from the centre taps to one end of each of the windings for bipolar operation. I tried this and the motor just buzzed so I connected the ends of the windings and left the centre tap wires loose. The motor then did what it was supposed to and rotated back and forth. I had a bit of a play with the sketch and changed the speeds.

Anyway, at least I've got the motor to turn, I know the motor works and how to connect it to a controller so I'm making progress. I think I'll take John's advice and revert to using a standard Arduino for the time being. When I get more proficient I may be able to make use of the Stepduino.

Regards,

Alan

24/10/2018 23:57:39

Hi Michael,

I've been to the Freetronics site but for a beginner like me it's not much use. I bought the Stepduino because I thought it would be easier to use for controlling a steeper motor because that's what it is designed to do. That doesn't seem to be the case.

Thanks John. I think I'll try hooking up the battery and using the sample sketch on the Freetronics website. If it works I'll have at least managed to get a stepper motor shaft to turn which will be a great leap forward. After that I think I'll use my standard Arduino and follow the multiple tutorials around on how to run stepper motors.

Thanks again,

Alan

24/10/2018 07:55:32

Hi John,

You seem to know a bit about the Stepduino so I'd like to pick your brains if I could.

I've managed to get the Arduino IDE talking to the Stepduino.

As I understand it, I'll need to provide an external power supply as the USB supply hasn't got the power required. I was intending to use the spare battery for my drill which is 18V. Is this OK? From what I can gather, the Input voltage can be 7 - 28V.

Can this power supply be connected when the Stepduino is connected to my PC via the USB port? I need the USB connection to download a sketch which will start to operate as soon as it is uploaded which will need the external power supply.

Do you know what the display screen is for? I can't see the point of it.

I may have made a mistake getting a StepDuino instead of using a basic Arduino with the required add-ons. There is virtually nothing around explaining how to use the StepDuino but heaps of information on how to run stepper motors using an Arduino.

If I can get the external power supply sorted out I may be able to run one of the sample sketches on the Freetronics website and maybe proceed from there.

Regards,

Alan

Thread: wood turning
23/10/2018 06:33:06

Hi ega,

Yes, Kanuka is a bigger version of Manuka (as per the honey).

Hi Nathan,

The tool angle on the ball turner is the same as on the diamond tool holder and the tool was ground using the jig which came with the holder. I don't suppose it's surprising the setup works well with wood as it's similar to how a gouge is presented to the work on a woodworking lathe. The wood peels off the work without tearing, even on end grain which makes it ideal for ball turning.

Regards,

Alan

22/10/2018 06:28:15

endgrain2.jpgHi Nathan,

I have found the Diamond Tool Cutter from Eccentric Engineering is excellent for turning wood, particularly if you use a round rather than a square tool. I have attached a couple of pictures showing the finish I got on the end grain of a piece of Kanuka wood. The finish is as good as that from a skew chisel but is of course dead flat. I use a similar cutter arrangement in my ball turner. There is very little sanding required after turning.endgrain1.jpgendgrain3.jpg

Thread: Stepper Motor Identification
20/10/2018 06:16:38

Thanks John. I've measured the resistance across the coils and figured out the configuration which happily coincides with the data sheet. Now for the bit I'm not looking forward to - relearning how to use the arduino. I wish people wouldn't keep on about how easy it is to use - it's not.

Regards,

Alan

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