Member postings for Muzzer

Well spotted Russell - senior moment etc!

Looking at typical voltages for alkaline and silver oxide batteries, the silver oxide seems to be typically around 1.6V (SR44) and the alkaline about 1.2V (LR44). Although they are physically the same size, the LR44 probably struggles to operate the circuit in the calipers unless it's almost new. And the smaller capacity of the LR44 gives a very short life (in my experience) relative to the specified SR44. Together, the experience is not satisfying.

Murray

Never used an ACME die to cut threads but is it possible that it's supposed to look like this ie different teeth cut different parts of the thread? The ACME thread form has deep valleys and sharp corners, so a different approach may have been taken. Have you tried using it? Could you be thinking too much?

Murray

Sorry - I see you DID try it. May be crap finish but still supposed to (otherwise) look like this.

Edited By Muzzer on 14/01/2015 09:24:13

I think we are (almost) all furiously agreeing here - you need to reduce the field (rotor) current to speed the motor up once it is moving, otherwise it will reach a (slow) speed and stay there. Whether you put one or more resistors in series with the field winding to achieve that or control the field current with a PWM controller (or even a linear one), the effect should be the same.

Murray

Make sure you have a silver oxide battery fitted (SR44), NOT a lithium one like the LR44 etc. They both fit but the silver ones have a life that is 10-20 times longer and are what is recommended for these devices.

Murray

Regardless of whether the label says Mutitoyo or Xmas Cracker, I habitually check the zero reading before and after critical measurements and periodically check a known reference piece. This will certainly show up any significant inconsistencies, without needing any fancy calibration equipment. My generic digital calipers seem to be pretty reliable but there again, if they hadn't been, I would have kept looking until I found some that were.

When I took one of my glass DRO scales apart to shorten it, I found nice finger prints all over it from when it was manufactured - obviously I took the opportunity to clean it, although it hadn't been causing a problem. They need to be able to tolerate a certain amount of contamination but like any tool you depend on it pays to periodically clean, check and inspect them.

Murray

If you are controlling a shunt wound generator (like a car dynamo), the output current will increase with the field (wound rotor) current. The battery is pretty much a constant voltage in this case. Similarly, if you are driving a shunt wound / wound field motor (which is essentially the same electrical machine as the dynamo above), the maximum speed will occur at minimum field current and the maximum torque will occur at maximum field current and low speed.

I think I've got that right - and I think it's what Russell is saying. Intuitively, if the field current is cranked right up, the back emf generated in the armature reaches battery voltage at a low speed and you can't then drive any current into the armature (current = torque). Backing the field current off reduces the back emf and allows current to be driven into the armature at a higher speed.

Murray

Edited By Muzzer on 13/01/2015 10:57:01

IIRC, the mechanism that causes asbestosis is repeated scarring of the lung tissues due to the unique particle (fibre) size of asbestos, particularly the blue variety. For other materials, smaller particles are caught in the mucus lining the lungs and cleared by the natural ejection of sputum. Larger particles are caught by the cilia etc in the respiratory passage and are prevented from getting down to the lungs. Unfortunately, asbestos has a rather unique particle size that defeats both mechanisms and can get permanently lodged in the lungs where it repeatedly injures the surrounding cells. Eventually the scar tissue builds up and causes problems including increased risk of cancer and mesothelioma. The fibres themselves are actually inert.

No idea how talc compares with asbestos in terms of particle size or if it's a chemical hazard but breathing anything other than clean air can't be a benefit. Presumably it's a very wide range of sizes but the smaller particles seem to be able to work their way almost anywhere in the body.

Time may tell how healthy it really is to inhale clouds of propylene glycol aerosol ("vaping". Although it's got to be better than inhaling any kind of proper smoke, it must condense back again in the lungs and get expelled out again eventually, or ingested. It's been used for years in "smoke" machines and is presumably well understood but not at these high concentrations.

Merry

The builder was out to nickel and dime you if you so much as farted. Any change in spec came out as a cost increase. Once I'd got him to finish the roof and the end wall I did the rest myself. Of course, I had to dig out all the rubbish he'd kindly secreted under the flooring. I expect he'd have wanted to charge me for removing that too. He also laid the first 3 sheets of tongue and groove chipboard upside down, the clue being "this side down" visible on the top face. Luckily I turfed him out before he messed anything else up.

Murray

In Morrison's today and they are selling tubs of pork dripping near the cooked meats. Looks about 75% white fat with 25% brown jelly.

Originally, margarine was made from beef fat although it's been exclusively vegetarian for years AFAIK, apart from that stuff "you can't believe" which includes cream (Milk Marketing Board wheeze).

Murray

Gordon - good luck with the waterproofing etc. If you can't completely keep out the water, you can at least try to control where it goes to some degree.

I got a local "builder" to do some roofing on my last house in the UK some years back and obviously we chose to do the work in the winter when it was pretty wet. Luckily he let us rent a large tarpaulin from him that covered the whole roof to keep the rain out when the tiles were off. It may have been a good tarp when he bought it, in the days of the ark but not when we needed it. Chocolate teapots come to mind.

There was no way of stopping the rain coming in, so I had to simply control where it went and prevent it damaging things that needed to stray dry. Using proper (waterproof!) tarps, I formed large funnels in the areas where water was coming in and punched holes in the plasterboard to release the water into them, then collected it in plastic crates which I emptied periodically. Saved the books, piano, filing cabinets etc that way and prevented a flood in the house. Worth thinking about in your situation.

Murray

Neil - where did you buy your little flute? The only source for the kit of parts is in the US, so wondering if you found anywhere closer, given that there was a recent workshop in Eindhoven.

Tempting to get one of these and force my boys to build it.

Murray

Yes, the heads on these things fairly fly about, yet it still seems to take forever to knock out parts, particularly if you are watching. The nozzle diameter is tiny, so you can imagine how many passes are needed to complete a layer, even with a lot of honeycombing inside the model.

Some CNC routers have 3D printer heads too. But these are much lighter and faster machines than proper machine tools.

The subset of g-codes used in 3D printing is supported by the free, open-source software that converts the .STL file to machine paths. For a 3D milling machine however, you'd have a bigger set of operations supported and the CAM software would tend to be a lot more complicated (expensive).

Murray

You'd better write to all the schools and universities around the world to let them know then, as it's been taught for many decades - and continues to be. When in Rome...

Merry

At the risk of collectively losing the will to live, IIRC the Van Der Waals forces can be sufficient to provide significant cohesive forces between (sufficiently) smooth parallel faces. In the extreme it is possible to join surfaces of similar material without the need for adhesives. The force is inversely proportional to the cube of the distance and obviously also proportional to the area. The "weak" VdW forces are more long range than the direct interatomic forces holding the atoms together.

Microscopically, the surfaces of even the finest pair of gauge blocks will be fairly rough but with enough surfaces in close proximity to generate some degree of VdW pressure. There is clearly some gap size at which they begin to come into effect and it looks as if the very fine end of the gauge block quality range (master blocks?) may be in that zone. The effective gap will be a function of the surface roughness and the residual crap (oil etc) left on the surfaces. Of course, if the surfaces are not almost perfectly clean, there will be surface tension and other effects resisting the wringing movement as a result of oil and contaminants.

Sitting in my armchair with my flak jacket on...

Jason - sounded as if Neil was planning on developing his own driver but it's not simple. Stepper drivers are switched mode constant current drivers integrated with gating logic and an up/down counter, so pretty sensible to buy it rather than develop it yourself.

If this is for tracking planets, the idea of using a piezo or crystal controlled micro makes sense and a single micro board can be had for peanuts in whatever flavour you like.

BTW, Minebea are the Rolls Royce of small BLDC and stepper motors. The life of steppers and fans is determined by the quality of the bearings and seals (and when the oil runs out). IIRC, Minebea (Nippon Miniature Bearings) actually make and supply the bearings to the majority of the other motor manufacturers.

Murray

The Arduino etc "shields" simply contain an off the shelf stepper driver IC but then require a micro to generate the drive pulses. I did this myself not so long ago with an MSP430 starter kit but it's cracking a nut with a sledgehammer.

You could get your own stepper driver board and simply drive it with a pulse train eg from the old 555. Something like this. The clever bits are already taken care of and they cost peanuts on ebay.

The high voltage is required to allow a sensibly fast speed from the motor. If you put resistors in series, you'll end up with no torque - it's not the right solution. There's really no point trying to drive the motor directly or making your own driver circuit.

Murray

Weathering raw castings is an established practice and there is some logic behind it. It seems that the process normalises the material so that they are better able to withstand stresses. Famously, the BMW Formula 1 engines of the 1980s turbo era were made from raw production castings that had been weathered for many years, as they found them to be more durable. The engines used a std block. I recall that from the time although now it's entering internet folklore territory and is now in danger of becoming an urban myth.

Murray

PS - as ever, it's already been done on this forum. Bad echo in here!

Edited By Muzzer on 08/01/2015 15:53:42

I'd be surprised if it doesn't have oil nipples on all the main external bearings. My (Colchester) Bantam has them on the saddle, slides, tailstock, apron, leadscrews etc. Brass with spring loaded ball, requiring an oiler. I use the same oil for the gearbox, nipples and slides ie ISO-32 hydraulic oil, modern equivalent of the Telus oil recommended in the manual.

Have you got the manual for your machine? It will tell you how to lubricate the various parts, as this is something they will recommend you do frequently. There is bound to be some means for doing it.

Murray

From the manual for this inverter, it is only rated at IP20 ie prevents fingers from being inserted but has no protection against swarf or water. You need to mount it away from swarf and coolant, which I find gets everywhere, possibly also fitting a shield to further improve the level of protection.

Some inverters have a removable front panel which you can mount next to the machine but this one doesn't. However, you can wire up a remote box that has start / stop / direction / job / speed etc controls. This might only need 2 toggle switches and a pot, depending what you want to control. The control signal are safe and low voltage, so nothing special is required for safety.

I wouldn't mount the controls above and behind the machine, as you would need to lean across the rotating machinery to turn it on / off etc - really not recommended! You should also think about wiring up one or more large red e-stops or incorporating a kick switch.

If you have a cabinet, you could even mount the main inverter inside it, assuming there is some reasonable degree of ventilation.

Murray

It's a bacterium, not a virus.

Murray