Member postings for John Haine

Before I got the Myford collet set I lucked on a Myford collet closer to fit the nose in the odds&sods bit at a show. I discovered that actualy you could use it with a standard MT2 finger collet though of course wouldn't have the convenience of the "self extracting" since they don't have the groove. I do wonder if it would be possible to modify a standard finger collet, possibly by grinding a groove near the end to fit the groove and taking a bit off the length at the nose if necessary.

As I understand it the Myford company either went into administration or receivership and the assets were sold, many of them being acquired by RDG including the brand. Lots of people bought bits in a sale of stuff they didn't want - I recall SirJS writing about a part assembled VMB he bought to modify for CNC. I suspect, though I am not sure, that RDG bought a lot of Super 7 lathe components such as bed castings etc and these are being finished and assembled for sale. My apologies if I misunderstand.

It would be very interesting to know just how big the market is for these small/medium sized lathes, UK-wide, EU-wide, worldwide. I doubt that the UK home workshop market is more than a couple of thousand a year, which is not going to yield much revenue to cover development. There used to be a big market for this style of lathe in model shops in industry and academia, but these days with modern CAD/CAM even for one-offs it's better to design in CAD and make on a machine. I think the only manual machines in our university workshop are the ones in student workshops.

The tail at the left is because the run started at a lower amplitude which built up to a steady-state value about 20,000 seconds in.

I think I bought a few of them from Myford so they must have made the grade. IIRC there was an MEW article that described making the collets - was that you Chris? I have a copy somewhere...

Found it!!

https://www.haythornthwaite.com/collet%20myford.html

https://www.haythornthwaite.com/collet%20myford.html

Edited By John Haine on 01/05/2023 11:57:46

And here's the histogram of the period.

Now have first results from the lash-up, without amplitude control other than varying the drive voltage to the L298 that drives the Helmholtz coils. The trailing edge of the centre opto pulse clocks a D-type which is connected as a divide-by-2. The Q and nQ outputs are connected to the L298 control inputs to set the drive direction. The D-type toggles on the trailing (+ve going) pulse edge. The amplitude opto at the moment is just driving the "set" input of the D so that it "knows" which side the pendulum is. Initial tests were done with the supply voltage set to 7.5v which is a bit more than the minimum value to make sure that the 5v regulator that feeds the logic and picPET works. This proved to be more than enough to drive the pendulum to a maximum amplitude of 34mm (target 20mm) so plenty of drive in hand - I think I need some resistance in the coils to reduce the current. As the L298 drops nearly 2v in both sides of the drive the coil voltage is ~3v and current about 60mA. Should be around 40mA at target amplitude. The plot above shows the standard deviation of the pendulum period averaged over 100 successive measurements. Here the values are significantly less than 10us and of the same order as I was seeing in run-down tests without impulsing. The combination of the new spring, more rigid pendulum rod, and revised impulsing method seems to have done the trick. Now I can make progress!

A quick update. I have made a new CF pendulum rod of 10mm diameter, and a new wider single-leaf suspension spring. The new rod again has embedded magnets and uses the Helmholtz coils for impulse - I'm hoping that the much more rigid rod and improved spring will much reduce any spurious resonance ("dreaded rod wobble" ). The larger diameter rod means that I can use a larger magnet - actually 2 6.35x9.5mm stuck together - which should increase their magnetic moment from ~0.1Nm/Tesla to 0.6Nm/Tesla, which will also decrease the drive current by a factor 6. I have also changed the drive method - rather than generating a short pulse from the BDC opto signal I apply a constant current to the coils but reverse its direction at the trailing edge of the pulse. This will be a sort of EM equivalent of a recoil escapement. Also rather than hit-and-miss amplitude control, i.e. give the pendulum a kick when its amplitude doesn't quite reach the set level, I will control the magnitude of the current and impulse on each beat so that any "escapement deviation" will be the same for every cycle.

Edited By John Haine on 01/05/2023 10:40:47

And ER collets fit a range of sizes, Myford ones only their nominal size.

Myford collets of the type that close in an MT2 bore and have a groove that engages with the clamp/removal nut are hen's teeth. I do have a set that I bought incomplete years ago and managed to fill in the gaps before the "old" Myford went bust. As Martin said, better to get an ER type that will fit on the spindle nose. Myford used to sell one but no longer seem to and nor do RDG who now own the Myford brand. Arc sell collet chucks that will bold to a backplate and they also sell plain backplates which would need machining to fit the chuck. Better to do this than use an MT2 fitting collet chuck which will limit the length of stock you can fit and would need a drawbar.. If you can accept a drawbar (just a bit of studding will do) then you can also use MT2 finger collets in the spindle.

John B, somewhere here there's a thread that links to tables of change gears needed to make metric threads without using the "exact" gears. The resulting errors are minimal for all practical purposes, likely less than the error in the leadscrew itself. Also I think there's a spreadsheet to calculate them if the table doesn't cover what you need.

Or of course you could fit an "electronic leadscrew" in which case you'd never need to worry!

Another eyelet crimper?

Probably cost the thick end of a million to design and develop and the same to set up production. How many would they sell? Not a chance it would make business sense. Might have been a good idea 25 years back to develop a relationship with Sieg and badge Myford version of one of their lathes but too late now.

Edited By John Haine on 28/04/2023 17:10:13

Also you may be over-ambitious with microstepping. The torque increment when you apply a microstep can be very small and not enough to move the screw. Trying to improve resolution by setting the microstepping too high can be self defeating.

I think the crank sensor have a built-in magnet, the toothed disc creates a magnetic circuit with varying reluctance.

The 7 series lathes are very basic as you say, being designed I think in the 1940s or early 50s with a lot of DNA that dates back decades from then. Even the latest S7 has a plain bearing on the business end of the headstock. The bed design is not very good, there's a reason why nearly all industrial lathes have a prismatic bed. The drive system is stupidly complex with modern motors. They are nicely finished and have cult status. Myford never adapted to modern standards and paid the price. I have a S7 and a VMB mill, both I bought new. I chose the latter as it had/has more daylight under the quill than any other small machine at the time and I was looking at making a launch engine. Myford fitted a rather agricultural UK made motor but otherwise the machine was made in the Far East. When it was time to tram the head I discovered one of the hold-down bolts was held in the casting by paint! But having said that I have had good service from both machines but wouldn't choose to buy another.

If you mean this type of device:

**LINK**

...then they look intriguing and I hadn't come across them before. Essentially they are a board with a stepper driver plus a rotary encoder chip, of the type now available that can sense the rotational position of a small magnet on a shaft held just above the chip. The chip seems to be mounted on the centre of the track side of the PCB and the board is fixed to the back of the motor. The motor therefore needs to have a shaft extension at the back for the magnet to fit on. Joe Noci has written about these sensors on another thread. The boards completely substitute the standard drivers and in effect give you a closed loop stepper servo.

If your motors have a rear shaft extension then you could try one, but if not and you'd need to change the motors anyway it would be safer I think to invest in a servo or stepper-servo which would probably be about the same cost as one of these boards plus a new motor. All the "system integration" would be done for you.

As Emgee says though, if your problem is just occasional lost steps then maybe some mechanical attention to the machine and motor tuning would do the job.  What machine & control system is it?

Edited By John Haine on 28/04/2023 06:31:12

Good grief! Worse than I thought.

I think you'll find it at least comes with the motor! But yes Myfords are expensive. I bought a new S7 many years ago and though it's a nice lathe, knowing what I do now I wouldn't buy another.

I think you need encoders on the motors to close the loop?

Seems to me that there is a paradox here. Anti-vibration implies compliance, i.e. springiness. Unlikely to be in the horizontal plane as that is very difficult to arrange. If in the vertical plane they will not be very good for levelling! Do we just mean adjustable feet!

There used to be an electroless plate called Niculoy for aluminium.  As the name implies it adds a layer of copper and nickel.

Aha! It still exists

It also works on non-metallic surfaces. One place I worked, we made RF enclosures by slicing an aluminium extrusion into short lengths, plating after ultrasonic and vapour-phase cleaning, then screen printed solder paste onto the appropriate surfaces in a jig, applied pressed plated lids, and vapour-phase soldered the lids on using a standard electronics solder. As I recall we bought the plating fluid from RS.

Edited By John Haine on 27/04/2023 10:57:13