Member postings for Les Jones 1

Hi Jason,
If it is the same as the Chester DB-10G (Which I suspect it is.) then the thread chart could give you the wrong value for the actual pitch. The DB-110G has a 48 tooth gear driving a 60 tooth gear which is where you put the first gear you can change for the gearing to the leadscrew. So though the actual pitch of the leadscrew is 2mm the effective pitch whencalculating the gearing is 1.5mm. I would suggest say turning the leadscrew exactly 10 turns and measuring how far the saddle has moved. (For Matt the pitch will then be one tenth of the distance that the saddle has moved.)

Les.

Hi Duncan,
I have to confess that I did not read you first post fully. I see no problem with what you propose. The only think I would say is that you will be running the 5 amp (60 W) power supply above it's rating. If we assume 80% efficiency in the boost converter then it will take 3/0.8 = 3.75 amps at 12 volts and the rest of your 12 volt load is 1.6 amps so 1.6 + 3.75 = 5,35 amps. I notice that the advert offers an 80 watt unit (6.66 amps.) so that would be a better choice. (And 50p cheaper)

Les.

I would suggest getting a 24 volts switch mode regulator of at least 3 amps rating and a switch mode regulator module such at this to regulate down to 12 volts. Using the switching regulator to drop the 24 volts down to 12 volts avoids having to disipate about 20 watts in a linear regulator. You can get these modules cheaper direct from China but it takes about 4 weeks.

Les.

Hi Neil,
I like the fact that the AVR chips have vectored interrups so that you don't have to sort out which type of event caused the interrupt as you have to do with a PIC. If you are interested in the source code for my interface that uses an ATtiny4313 then let me know and I will email it to you. (The current version is the one that also works with the Wixey type angle gauges. It supports 2 x 24 bit, 7-BCD, Bin6 and iGaging scales) It also gives the option of enabling fast sample mode on 2 x 24 bit scales.

Les.

Hi Dave,
It is only the 2 x 24 bit protocol scales that can be zeroed via the data and clock signals.Also they are the only ones that can be set to fast sample node. (Fast 40 samples per second normal 3 samples per second)
You need extra hardware in the interface to zero or set fast sample mode on 2 x 24 bit scales. The components in the grey area of my interface schematic are those that are only required to zero or set fast mode of 2 x 24 bit scales. I have only recently noticed that I have not put the resistor values (All 100R) and multiplexor part number (CD4051) on that part of the schematic.

Here are my notes on 2 x 24 bit protocol.

-------------------------------------------------------------------------
Scale protocol information.

2 * 24 bit scales

Data is sent as two groups of 24 bits.
Each group is a 24 bit binary number. The first bit received is the least significant bit.

Bits
are transferred LSB first! Also, data is 2's complement. (ie inverted Data signal at 0 volts = 1 at +1.5 volts = 0)

Static state of clock signal between frames Low
Time between start of frames 330 mS Normal mode 25 mS fast mode
Length of data frame 860 uS
Length of clock cycle about 14 uS
Time clock pulse is negative about 7 uS
Time clock pulse is positive about 7 uS
Initial high at start of frame about 52 uS
High in the middle of frame about 110 uS
High at end of frame about 80 uS

Clock in the data on the negative going edge.

The first group is the absolute position. It has some arbitary value at power on.
The second group is the relative position. This will be zero after the zero button is pressed.
Its value will be the difference between the absolute value when the zero button was pressed and
and the current absolute value.

48 bits in a frame of data

CPI 20480

-------------------------------------------------------------------------

Les.

Edited By Les Jones 1 on 09/08/2017 22:46:02

Edited By Les Jones 1 on 09/08/2017 22:48:20

Hi Paul,
The stainless steel would not be suitable for the winding as it would have too high a resistance. It would get just as hot as the blade part. The wire I used for the low voltage high current secondary was something like 6mm (6 square mm. not 6mm diameter.) mains wire. Using a number of strands of thinner wire in parallel should work just as well.

Les.

Hi Dave,
The waveform looks like 7 BCD protocol but the data is inverted. I can't remember if any versions of Yuriy's code support this protocol. This is a link to a website that shows the 7 BCD code. I have a powerfix caliper (From Lidle) but the one I have looks like 2 x 24 bit protocol.

This is some notes I made on the 7 BCD protocol on a set of calipers bought from Neto many years ago.

-------------------------------------------------------------------------
7 BCD Scales
LSB Sent first.

Static state of clock line between frames Low
Time between start of frames 330 mS
Length of data frame 820 uS
Interrecord gap 329 mS
Time between stat of nibbles within frame 110 uS
Length of clock cycle about 12 uS
Time clock pulse is negative about 6 uS
Time clock pulse is positive about 6 uS
High level at start of frame about 55 uS
High level between nibbles about 60 uS
High level at end of frame about 60 uS

Clock in the data on the negative going edge.

Top nibble
Bit 0: sign. L = +, H = -
Bit 1: in inch-mode H means +0,0005 inch, unused in mm-mode.
Bit 2: unit: mm/inch. H= mm; L= inch
Bit 3: unknown.

28 bits in a frame of data

CPI 2540 (Metric)
-------------------------------------------------------------------------

My interface design using an ATtiny4313 worked with this 7 BCD caliper. Let me know if you would like a copy of the source code (Written in assembler.) It may give you some ideas to write a version in "C" to run on the arduino.

Les.

I made a device similar to the one you describe for cutting grooves in expanded polystyrene to hold small cutters etc.
I uses the stainless steel strip removed from a windscreen wiper blade to form the U shaped blade. I did not use a temperature as high as 600 Deg. C but it may survive long enough to do the job. I just used a few turns of thick wire as the secondary on a toroidal transformer. (The transformer I used was one that the original primary had failed on. I removed the original primary and fed the original secondary from another low voltage transformer. (About 24 volts.) There would be enough room to wind an extra secondary on a good toroidal transformer to avoid using two transformers as I did.

Les.

Hi Bob,
I think the rorary encoder is a better solution than either of the angle gauge types. I have a design to display the output of a rotary encoder on an LCD display using a PIC16F690. Let me know if you want the schematic and code for the PIC. I have seen some 600 counts per rev encoders on ebay for less than £10.00 so one of them geared 6:1 to the telescope axis would give 0.1 degree resolution.

Les.

Hi Bob,
I have not taken that type of angle guage apart but I have just had a look at the on I have. If you peel the label off on top of the locking knob there is an alen screw which I suspect will allow yo to dismantle it. Have you considered the "Wixey" type angle gauges ? It is possible to display the data from these remotely and it should be possible to mechanically to the encoder. There is some information on these angle gauges on my website here.

Les.

It could also be the centrifugal switch. When you remove the wires from the capacitor measure the resistance between the wires that you removed from the capacitor. If the centrifugal switch is closed (Which it should be when the motor is stopped.) you should get a reading of about 10 to 20 ohms. this will be the resistance of the main winding in series with the start winding and the centrifugal switch. If you get a high reading then the centrifugal switch is not switching in the start winding and start capacitor. (An open circuit start winding would also give a high reading but it is not very likely to be the start winding.)

Les.

Hi Duncan,
I bought mine from Farnell but las time I looked they no longer listed them. Last November (Nov 16) I found a source of the three wire version which is simpler to interface than the two wire version on ebay. The part number is ATS667LSGTN This is a link to the data sheet. (I paid £3,88 each for them on ebay)

Les.

If you want to build a tachometer yourself there is a design on my website that might meet your needs. It can be set to cope with between 1 and 99 pulses per revolution so you can probably pick up pulses fron the teeth on an existing gear on the spindle using a hall effect gear tooth sensor. This is a link to the design. If you google DIY tachometer or rev counter you will find many designs.

Les.

Hi Lee,
You now have it wired correctly for 240 volt delta (Mesh) operation.

Les

Hi Robin,
Itis reasonable to have such a capacitor across the mains. (The X signifies that they are reated for this type of application.) They are used in that position to help filter out electrical noise. It could be to reduce external electrical noise getting into the equipment or to reduce electrical noise generated by the equipment from getting back into the mains. (A common source of this noise is from swtch mode power supplies. There is a reasonable chance that the rest of the equipment has not been damaged. The equipment should function with this capacitor removed. It sould be replaced with an X rated capacitor for long term use.

Les.

I agree with the previous two posts. The original switch may have provided a method to control the power to the start winding but with your lack of electrical knowledge I don't think you are capable of working out how the original switch works. I also do not think you are capable of rewinding the motor correctly as you do not seem to work out how to connect things. You just seem to swap wires around hoping that it will work.

Les.

Hi Nicholas,
It is very unusual to see a Myford fitted with a DC motor. First some questions. Have you checked the brushes ? Is the motor shunt wound or series wound (Also called universal.) ? What kind of rectifier is used, The old selenium type or a siicon diode bridge. ? Can you post a picture of the information plate on the motor ?

Les.

The Steve Bedair ball turning too discussed recently in this thread is worth considering. I have built one and it works well.

Les.

The power distribution system will almost certainly be at a higher voltage than 240 volts so a transformer will be required near the point where the power is used. The transformer primary will be delta wound so no neutral is required. The secondary can be star wound which provides a neutral. This neutral will probably be connected to earth at the substation. It could also be connected to earth where the power cable enters the building which it is supplying. The exact way it is done may vary between countries.

Les.

Hi John,
It is a result of looking at Dusty's problem that made me think that only the power supply was being used. I looked on the web (Which was not that simple as Warco's website is down at the moment.) to find a picture of the WM280 to confirm that it had a tachometer before posting the comment.

Les.