taig and sherline mills to the UK

Stick with John and the other regulars, Milgo, you'll soon be able to sort the real engineers from the trolls.

Peter

-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:

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Reply to
Peter A Forbes
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"Airy R. Bean, village idiot" wrote his usual retarded crap in message news: snipped-for-privacy@uni-berlin.de... < retarded crap snipped >

You disappoint us AGAIN Airy. Just over a week ago you published a 'Valediction' on UKRA, and I thought the men in white coats had finally caught up with you. It now appears that your exodus was simply to another NG. ...(_!_)...

Reply to
Frank Turner-Smith G3VKI

[import it yourself]

I don't know about that story, but I've exchanged a few emails with Andrew Werby, a Taig reseller in the US (he's been so helpful I should mention his URL:

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who mentioned that there have been increasing customs problems with direct imports from the US for products without CE certs.

Having checked out the prices of direct imports and UK/European suppliers I really don't think it's worth importing yourself. Taig, Sherline, Xylotex and Gecko all have European distributors.

Tim

Reply to
Tim Auton

Lots of crap from mr Bean.

Please please if you are going to respond to Mr Bean please please ensure you snip ALL his post. I have killfiled him but you go and reply and post all his shit as well. That could become a qualification for a killfile entry for your good self, well eventually. 8-)

Reply to
use_valid_reply_to_address_but

"Airy R. Bean" wrote: [snip]

Care to elaborate on why a decent Real-Time OS running on a PC is inferior to an expensive custom board?

Tim

Reply to
Tim Auton

On Saturday 21 August 2004 19:32, the primordial soup was bombarded with cosmic radiation and a new life form of genus Frank Turner-Smith G3VKI emerged to test it's air breathing capabilities by gasping:

Come on, Frank, play fair. It's bad enough he gets talked about by those who have an obsession without this being cross-posted back into uk.r.a.

He's off the NG. Isn't that what you wanted? If he appears back here, he's fair game but for God's sake, leave him be until then. There must be something else you can talk about?

Reply to
MattD..

Yes using 5mm pitch HTD pullies and belts from RS. It's a 1:1 ratio using 24T pullies, it was done for two reasons. One was it is actually slightly cheaper to buy two pullies and a belt than an oldham coupling. Secondly I wanted to get the width and hight down, the genuine Taig CNC looks like Prince Charles. The mountings are just a piece of 3" x 1 1/2" box section, holes bored one side to fit the bed and the stepper mounting hole, 1.5" dia, and the 4 mounting holes are slotted to allow motor adjustment. I milled these on a full sized CNC but there is no reason they couldn't be done on the manual Taig as it's first job.

-- Regards,

John Stevenson Nottingham, England.

Reply to
John Stevenson

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Thinking about this thread on the way back from the supermarket this morning (sad), since the steppers are current devices, it probably makes good sense to avoid a regulated supply (a regulated supply is a constant voltage source) - big amps = big bucks, apart from being technically innapropriate.

Why not try an el cheapo battery charger (15 - 20 amps) install a bridge rectifier and a big fat capacitor?

Might want to consider some form of crowbar circuit to ensure over voltage conditions are protected against, but doesn't seem to be much point paying for heavy duty voltage regulation when its not required.

A 24v charger might exceed the 35v requirement with a simple arrangement and probably not available as "Aldi" specials.

Steve

Reply to
Steve

Couple of obvious reasons, one would be the ripple which a regulated PSU would take out, and the other is the overcurrent protection etc that you would get with regulation.

Voltage swings with varying load and input voltage, unregulated supplies are not normnally designed for good regulation, they are just built to do a job at a price.

Spikes and mush will get through a non-regulated unit easier than a regulated one.

"A cheap job is never cheap enough, while a good job is never too expensive"

Peter

-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:

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Reply to
Peter A Forbes

Worth looking out for a couple of cheap 13.8V regulated supplies to get round having to build one or mess around with battery chargers etc.

I picked up a 13.8V/5A linear regulated supply and a 13.8V/22A switcher, both new at a sale, for £3 and £10 respectively a couple of weeks ago. Strung in series with minor tweaking, I'm looking to get 30V DC @ 5A maximum which should cover the steppers I have right now (and probably meatier ones too).

For £13, I couldn't have bought the toroidal transformer to make a supply with. Precautions need to be taken if the neg side is grounded when stringing these in series though or it could get "interesting"....

Reply to
Duncan Munro

Yeah simply cnc recommended a transformer or car battery charger. But really I would like something I can just plug in and run. If I get something good quality then hopefully it will save me money in the long run. After some searching I came across some power supplies sold at rs components. A Lambda 24v 4.3amp psu, although it comes at a hefty £54, hopefully it will be worth it. So including that the whole cnc package will cost about £340 inc VAT and del. Whcih is still a large saving on the retail sets that are close to £600.

Reply to
milgo

But in this application a transformer, bridge rectifier and a BIG capacitor is totally adequate and all that's needed. NO need for regulated power supplies. If using a linear or regulated supply an additional large capacitor is highly advisable. The large capacitor is needed as a "flywheel". A few amps pulsed at 20KHz will eventually destroy a computer type switched mode or a linear power supply.

Reply to
Steve Blackmore

Very true Steve and some manufacturers of driver go as far as to say DON'T use switched or regulated power supplies.

An unregulated supply is needed to balance the system up over the two or three motors when one is decelerating

-- Regards,

John Stevenson Nottingham, England.

Reply to
John Stevenson

I don't see the logic of what you are saying, but I'm catching a plane at 05.30 in the morning so I'm off to get a coupkle of hours kip. I'll think it over on the flight.

Peter

-- Peter & Rita Forbes snipped-for-privacy@easynet.co.uk Engine pages for preservation info:

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Reply to
Peter A Forbes

The trick is not to send the recirculating chopper currents back into the PSU. You are absolutely right in what you say, sending a few amps of spikes back into the PSU will cause (potentially fatal) problems for any regulated supply.

I'm in 'debug mode' on the Xylotex boards at the moment, still getting some hash coming back which is causing steps to be lost through some of the recirculating current appearing on the supply leads. I checked it with a storage scope earlier on, the peak of the 'ring' between the chopper negative supply lead and digital ground is around 3V and enough to trip the inputs coming from the parallel port.

Why is nothing ever easy....

Reply to
Duncan Munro

If there is more than one motor on the power supply, normally these will absorb any back emf, but only to a point. The BIG cap is really essential, it acts like a reservoir and soaks up any nasty spikes. If your going to go to the expense of buying a big capacitor to add to your linear/regulated power supply, it would work out better,and probably cheaper in the long run, to just buy/scrounge/rescue a transformer and buy a £5 rectifier.

I've a power supply here, all new components, Transformer was £28, rectifier £5, Capacitor £16 - it's good for 76V at 12A.

Hash is generally from spindle motors - especially if your using a VFD. All power and returns need to be "star wired". All cables need to be screened and grounded at one end only and "star wired" to a common point. Avoid ground loops like the plague!

Lost steps are more normally caused by over driving motors, either top end, or, more subtly, accelerating too fast.

Never is ;)

Reply to
Steve Blackmore

Unfortunately this one screws up even when you try and jog it. It runs like the proverbial drunk; two steps forward one step back so I'm pretty sure it's not a 'greed with speed' issue. I've spent 6 hours on it tonight winding toroids and stuffing capacitors (electrolytic and ceramic) as near to the driver card as possible, and got absolutely nowhere.

Maybe hash was the wrong phrase for me to use Steve, these motors are not even mounted on the mill yet so no VFD/spindle to worry about. It's a damped ringing with the initial peak at about 3V referenced between the parallel port 0V and the negative supply to the chopper, unfortunately being picked up as a logic '1' to the driver card and causing it to reverse direction intermittently.

I'm going to order an 18V toroidal and a larger box tomorrow, and rebuild the thing in one package. At least I can star ground the DC power near the feed to the Xylotex cards and put the mains earth there too in order to kill the ground loop with the PC. With the switcher I've got about a metre of DC feed cable, and the high frequency ringing through that is causing the ground loop and subsequent tripping of the inputs from the parallel port.

It's tempting to snip to earth lead off the switching PSU to break the ground loop, but I'm not looking for a Darwin award just yet ;-)

Reply to
Duncan Munro

Err... I was on about the driver. Did you mean to say linear setpper motor drivers? If so, it depends: If you have a very high precision drive train with a large reduction or you arn't terribly worried about getting the smallest possible movement of the table, etc... then microstepping in general isn't necesary and linear or chopper will work about the same in full stepping mode.

Speed can be an issue in that situation because a stepper motor in full step mode will vibrate like all hell at top speed and heat and pull large amounts of power, etc... Read gekos white papers.

If your motors are strong enough, you have time to burn and everything is nice and tight, who cares? Use the tiny little stepper control chip and save on lower power transistors, etc..

But, if you need to get really fine motion, or really fast accelleration or drive the motor right to the edge of its torque rating, etc.. then you must microstep. And if you microstep with a chopper, then you will find that the motor is heating up and loosing power at high speeds, and still vibrating a bit, and if you really push it, you will loose a step here and there.

Then you need a linear controller. And you have to tweak it and tune it to the application. And then your old, cheap, underpowered stepper motors will turn fast, smooth, and clean and deliver very fine motion from a minimal drive system with nice accelleration.

And the linear controller doesn't have to cost an arm and a leg as long as the motor is anything less than a monster... ...You just need a MASSIVE heat sink for the power transistors, and larger than normal transistors at that. It helps if the controller can do some linear smoothing with an RC circuit. See:

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under "Current Ramping"

I guess the point is that you can run a smaller, older, cheaper stepper motor with a drive train that has less reduction with the linear controller. You can run a much larger motor with the same transistors in a chopper, but the cost of the motor increases faster than the cost of the transistors from what I have seen. Also the chopper will run much cooler, but since the controller is easier to cool than the motors, why not keep the motors cool and manage the heat back at the controllers?

In my mind, either go full step or, if you microstep, unless the torque requirements are massive, use a linear controller.

Does that answer your question? Does it make sense?

Reply to
James Newton

Because linear drive controllers have to be "dialed in" to the application. You have to tune them to get the best possible performance for a given load, speed, etc... Choppers also work well with modern stepper motors which have been engineered to avoid iron and copper losses. Linear works better with older, smaller motors. Choppers can drive much larger motors with less expensive power transistors and less heating in the controller. They are good, general purpose, quick and dirty systems. If I were mass producing a modern system, I would probably buy a slightly bigger stepper motor and put in a chopper. But I'm not. I'm a hobbiest (or amateur if you like ) and I have to use old, used stepper motors from eBay which are a bit smaller than I would like and I'm trying to push my machine faster and finer all the time.

I said modern is not ALWAYS better. Are cars better than horses? Sure, unless you are policing central park. Or running a ranch.

Absolutly not! A chopper type microstepping controller will still introduce vibration (not much I'll admit) and heat the motor at high speeds and loads. A tuned linear driver will provide constantly changing AC signals that smoothly transition from one microstep position to the next without motor heating even using an old, cheap motor.

Every word. Have you read:

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?

Reply to
James Newton

Generally, choppers systems will pull less supply current. The exception is at high speed especially with older "surplus" stepper motors. As per the geko white papers, iron losses increase greatly at high speed and the linear drivers reduce this by smoothing the signal getting to the motor.

Honestly, that is a fine point. In general, choppers are great. But there are places where a linear driver has advantages and saying that "old" "pathetic" systems are "out of date" and "modern" blah blah.. is just..

..I don't know, disrespectfull of those who came before us I guess. I'm advising people to keep an open mind, don't reject the wisdom of the ages just because it isn't "modern" and use the driver that is appropriate for your setup and needs.

Big new motors, lower speeds, precision drive train with good damping, nice airflow engineered into the motor housings, no time to mess with it: use a chopper.

Old surplus motors, wide speed range, minimal drive train, motors crammed in, willing to "dial it in": use a linear driver.

Reply to
James Newton

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