Member postings for Alan Charleston

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.

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

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

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

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

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

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

Hi 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.

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

Hi John,

Thanks for your reply. I haven't got as far as learning how to use the StepDuino yet as I thought I would need to know the motor characteristics first.I didn't realise you set the current instead of the voltage. I have attached a couple of pictures of the motor. The body is about 55mm across. I will go through the training exercises for the Arduino (again - I wish the information would stick) and then try using the stepduino.

Regards,

Alan

Hi,

A couple of years ago I bought a second hand stepper motor with the intention of using it to position my vertex dividing head and speed up cutting gears. I have a StepDuino to control it. It is a KH56 series motor with the first part of the serial number being KH56KM2. I have found a spec. sheet on line for this model but the last three numbers quoted are -911, -912 and -913 whereas the last part of the serial number on the motor is U037. I presume the U stands for Uni-Polar (there are 6 wires coming out) but the 037 doesn't correspond to what's on the spec sheet. The difference between the last three digits seems to be the motor voltage which changes from 2.3V (3.0A) to 3.6V (2.0A) and 6.71V(1.0A) with the power being about 7 watts for the three options.

Can anyone help me determine what voltage I should be applying to the motor? I'm a complete novice with these so don't assume I can see the obvious.

Regards,

Alan

Hi,

Can anyone tell me what the pressure angle of the gears in a Boxford AUD lathe apron is? I suspect it is 14.5degrees rather than 20 degrees but I want to be sure before I splash out on some cutters.

Regards,

Alan

Thanks for all the helpful advice. I agree that as far as the change gears are concerned, I don't need to be too fussy. They are DP 18 which is equivalent to Module 1.4111. I have a set of Module 1.5 cutters (20 degree P.A.) and I figured that the difference in the profile between Module 1.5 a 1.4111 would be small so I cut 3 extra change wheels using Module 1.4111 to calculate the OD and depth of cut. I made them from Delrin so I wouldn't damage the existing gears. The gears worked well. They seemed to mesh OK with the existing gears.

I then had a go at cutting a 14 tooth pinion on the handwheel shaft in the apron. The DP of the gears here are DP 20 which is equivalent to Module 1.27. I repeated what I did for the change gears using a Module 1.25 cutter (20 degree P.A.) and cutting a Module 1.27 pinion. I made the new shaft and pinion out of steel. It didn't mesh at all well with the second wheel in the apron train. This situation is quite different to the change gears as the shafts are in fixed positions and the clearance needs to be right which is why I was interested in getting some guidance on how to go about it. I managed to set the pinion up in the dividing head again and cut the pinion a bit deeper but the meshing was still not good, so I put the old one back in.

I concluded that the problem was the pressure angle so I'm looking to get a set of DP20 cutters with a P.A. of 14.5 degrees.

The reason I'm looking at working on this is that there is a lot of backlash in the handwheel on the apron although looking more closely at it I think the main wear could be on the pinion which engages with the rack on the bed. I'll pull it apart and measure the pinions and gears across pins but again, I need to know how to determine the backlash allowance so I can calculate what the correct across pins measurements should be.

Regards,

Alan

Hi,

In the past I have cut gears by making a blank with an OD of the pitch diameter plus twice the addendum and, using commercial cutters, cutting to a depth of 2.2 times the addendum.

This has worked OK but I watched a youtube video by Keith Rucker - https://www.youtube.com/watch?v=9Dl5J9b8GBw - where he used an excel spreadsheet he had devised to calculate the measurement across pins to ensure the gears were cut to the proper depth. A screenshot of the spreadsheet is shown at 36minutes into the video. There are two inputs which are the backlash which is defined as 0.040/P and the clearance which is defined as 0.157/P where P is the Diametral Pitch. He said he was going to publish the spreadsheet but I don't think he ever did.

I have found a calculater here - http://salemcompany.com/cgi-bin/cabAS.py?a=./gears/pages/Salem1501HS.html&b=./gears/pages/Spur1501S.html&c=./gears/pages/Salem1501FS.html .

There is a box labelled Backlash Allowance. If this is left empty, and the dp, pressure angle and number of teeth are entered and the calculater run, a recommended backlash allowance shows up in the results which I assume you can put into the front end and recalculate. There is no allowance for a clearance input.

The problem I have is that the recommended backlash allowance is quite different (higher) than the 0.040/P suggested by Keith Rucker.

Can anyone tell me if the backlash allowance worked out by the calculater is perhaps a combined backlash/clearance figure?

One of the reasons I am keen to measure gears across pins is that I have an old Boxford lathe and I want to make some more change gears for it. As I understand it, the pressure angle on these should be 14.5degrees but the two reversing gears at the top have 20P.A. stamped on them so I'm unsure as to whether the main train gears have 14.5 or 20 degree pressure angles. I've made a pair of dp18 racks with the two pressure angles but they both seem to mesh with the gears OK. That's when I came up with the bright idea of measuring the gears across pins. The problem is that if I use 0.040/P as the backlash allowance, they look like 20 degree gears and if I use the backlash allowance recommended by the calculater they look like 14.5 degree gears.

Can anyone help me?

Regards,

Alan

The seller has posted this:

My grandfather was a fitter and turner by trade and bought it with the intention of using it in his home workshop. However he lost interest in doing so and my father inherited it from him. While my father was also a fitter and turner by trade he never wanted or needed to use it so it had just sat in his garage all these years in its original crate. A great shame really. We'd love it to go to someone who is passionate about using it.

Regards,

Alan C.

Hi,

The maker posts updates on the HMEM website.

https://www.homemodelenginemachinist.com/threads/astro-skeleton-clock.26642/

Alan C.

Hi,

What about steel shim plate. Relatively cheap, readily available, flexible and should be easy enough to get paint to stick.

Regards,

Alan C.

Hi,

Gear cutters used to be a fearsome price but I have had good experiences with cheap cutters from Aliexpress. Here is a link for a full set (8 cutters) of DP24 14.5 degree pressure angle cutters for a bit over US$70. I can remember paying about that for one cutter about 20 years ago. The DP gears are hard to find on Aliexpress as most of them are module cutters but a search for "gear cutters 14.5 degrees" digs them out.

https://www.aliexpress.com/item/DP24-modulus-Pressure-Angle-14-5-degrees-1-8-8pcs-let-HSS-Gear-cutter-Gear-Milling/32825653274.html?spm=2114.search0604.3.26.7ba324c4dEKGwO&ws_ab_test=searchweb0_0,searchweb201602_3_10152_10151_10065_10344_10068_5722815_10342_10547_10325_10343_10546_10340_5722915_10548_10341_5722615_10696_10084_10083_10618_10307_5722715_10059_100031_10103_10624_10623_10622_5722515_10621_10620,searchweb201603_25,ppcSwitch_5&algo_expid=9eebc2d2-a942-49cb-b1a5-3847d5b60140-4&algo_pvid=9eebc2d2-a942-49cb-b1a5-3847d5b60140&priceBeautifyAB=0

Regards,

Alan C.

Hi Andrew,

Very interesting. Like everyone else I'd be interested in the motor and controller details.

Will the servo motor you're planning to drive the leadscrew with be linked to the headstock motor to allow screwcutting? If you can get that to work, then pretty much any knackered old lathe can be brought back to life with a bed grind.

Regards,

Alan

Hi Brett,

If you have a nice crisp break with the two bits fitting snugly together you might like to try gluing it together with an epoxy glue such as araldite. This can give a high strength joint which may be OK for your application.

Regards,

Alan

Hi All,

Sorry for the delay in letting all those who helped know how I got on.

The controller I settled on was a Series 9000 Vector Frequency Controller

After paying the motor supplier to install the cable between the controller and the motor, I installed the motor in the cabinet under the lathe (a real PIA) and was in the process of mounting the controller when the cable came out of the gland. I got in touch with the motor supplier and after we had passed through the “Well I've done hundreds of these and nobody's complained before!” phase it transpired that they had used glands designed for armoured cable rather than screened cable. So, (mutter, mutter) back under the lathe again to get the motor out and back to the supplier. The proper glands gave much more secure connections.

After the motor was reinstalled and the controller mounted, I started using the system and came across a couple of problems which centred on the motor deceleration time. The motor supplier had set this at 6 seconds which he said was standard for lathes as too short a time could result in the controller being burnt out.

The first problem I encountered was during threading. My usual practice is to cut a 3mm wide groove with a depth equal to the root diameter of the thread at the end of the thread. The tool is then run into the groove, the motor stopped, the tool withdrawn and then returned to the start point by running the motor in reverse. The half nuts remain engaged throughout. The delay between switching off the motor and the tool actually stopping, made it difficult to get it to stop in the groove. The lathe has an 8TPI lead screw and a Norton gearbox to cut imperial threads and a range of metric threads can be cut employing change gears. I didn't have a thread dial indicator with the lathe however I managed to make one which meant I could disengage the half nuts at the end of each cut which stopped the tool dead. So that was one problem sorted.

The second problem with the delay between pressing the STOP button and the lathe actually stopping is safety. If I get into trouble and press STOP, there will be a period of continued operation. It will be worse than a lathe continuing to rotate due to momentum as I suspect the ramp down period will be under power and will overcome the force produced as I am wound into the work.

The STOP button on the controller is a fairly small target to hit if you're in a hurry and I would like to install a larger STOP button. I presume this can be achieved by utilising a pair of the analogue input terminals and a switch but I can't make head or tail of the Manual. Can anyone help me with some advice regarding this?

After all this negativity, there are some aspects of the VFD that I like.

The ramp up time gives a very gentle start which is particularly good if the work has some weight.

I can do threading at 100rpm without having to engage the backgear.

When parting off, it is useful to be able to change the speed to get away from a resonant frequency if chattering becomes a problem.

The VFD reduces the number of pulley changes required which, given that they involve kneeling on the ground and fumbling around in the cabinet under the lathe is much appreciated.

On balance, given the hassles I had getting the VFD up and running and the safety concerns, I'm not sure if I would install a VFD and a 3 phase motor rather than a single phase motor and a reversing switch if I had the time over again. I suspect not.

This is the second time I have written this. The first time I made the mistake of trying to create an album of pictures to go with the words. When I returned to the post it had - of course - disappeared. I'm not making the same mistake again.

Regards,

Alan C.