Here is a list of all the postings Billy Mills has made in our forums. Click on a thread name to jump to the thread.
|Thread: Hydrogen embrittlement|
Hi Hi There,
Invest in a trip down to the NEC for a two day Craft/Cookery/Dressmaking/Knitting exhibition for her and a friend then enjoy your shed time.
You might get extra fringe benefits like a nice knitted cover to keep your vertical mill warm, or a natty new pinny/manly overall to show off with.
It is possible that your attendance might be compulsory in which case you could drop a machine vice on your foot ( you don't really do this -you could damage the vice- just apply some blue and black to the tootsies) so that you can claim that you can't walk but you would not want to spoil her enjoyment would you?
The blue and black will rub off eventually. If the plan does not quite work don't worry too much, Hospitals don't keep anyone in for long these days.
Hope that helps!
|Thread: Boiler Feed Pump|
There is an almost infinite cold sink in the form of the "Lake" a few cm from the boiler so a condenser should not be tooooo difficult! However the real unknown is what the original problem is. So we are all speculating away-as we do- without any hard data.
It would be very good to know if the boiler leaked, a water pressure test would be a great help. Leaks elsewhere are very possible as is the issue of over firing. A running test- after the boiler safety test- is what we need.
Martin's memories are interesting. The idea of limiting the fuel flow by boiler pressure is not quite new but very sound, that's what stokers did by the Armstrong method!
Boiler topping by water level is a tad difficult as the sensor has to see a clear liquid, a simple beam break sensor would only work if dye was added to the boiler or a float fitted to the tube. However you could use the glass tube as a cylindrical lens with a dramatic change of focal length when clear water was inside.
You can invent servo systems to do almost anything useful /useless but they always introduce other issues that need to be thought about. For example, water level sensing in a stationary model is relatively easy but when moving about can become unstable.
So you put in a small leak to damp the level indicator, it furs up when someone uses tap water and the boiler runs dry.
Yes, there is enough material here to keep us all speculating away well into 2010!
You don't need to do the thermodynamics to top up the boiler- which seems to be the original concern. Simply that if you have lost 50mL of water from the boiler -49 mL of which is now condensate- you can return 49mL back to the boiler.
You only need a Bang Bang controller to do this, once you have a little condensate run the pump for a short pre-set time to return SOME (but not all) of the water to the boiler then wait till the level gets to the trip level before the next run. Simple.It adjusts itself, no complex algorithms needed! But it might not be what you need.
I appreciate that you are looking at some kind of advice on consumption rate however small heat engines will suffer from a very large number of losses from many different variables, any estimates may be a very long way out. Superheating greatly complicates matters, it puts in a lot of additional energy without increasing water consumption. I would suggest that after 50 years of non-use the boiler should be pressure tested then you can go for a test steam and quickly find out the magnitude of the problem. You may not have long enough trips to require boiler topping at all! If boiler water level went down too quickly all that time ago then steam loss might have be a problem or excessive heating and venting. It would be prudent to check these possibilities before working on a solution to another problem that may not exist.
Another kind of steamer was at the Sandown MEX last weekend, a Stanley Car. Did a quick Google and found a Stanley website, one model -not the one at Sandown- had two 4" pistons and a boiler max pressure of around 550psi, about 25HP when trundling along but 125HP before the pressure dropped. That was semi-flash steaming!
How about condensing the steam, collecting in a small tank then returning the water to the boiler when the tank level reaches a set amount? The recycling might not be 100% but you are not crossing the Atlantic.
|Thread: Fire Extinguishers For Small Workshops|
I'm not a FO but have Fire Risk Asesment experience in a commercial context and other stuff. Fire safety is more a state of mind than collecting extinguishers, it is about learning how to avoid needless risk and to reduce the impact of the unexpected. Only small fires can be tackled with an extinguisher, you also need to know how to use it!
Depending on the unexpected situation, the "window of opportunity" to put out a fire is often only a few seconds, in a small confined space the oxygen can be consumed in a matter of seconds so another form of extinguishing can happen.
Propane bottles should be outside, A defective valve or failure to shut off could create a potentially explosive gas/oxygen ratio, all you need is a spark ie the one you get when you switch the lights on.
Inflammable liquids should be in a steel cabinet, any wipers with flammable fluids on should be inside a suitable metal container or disposed.Only small quantities of flammables- this is one risk control method, if you can't avoid the risk then reduce the potential severity. One aspect of the metal cabinet concerns what happens when you have a fire, a Fireman may be inside an unknown building which contains roasting aerosol containers of highly flammable solvents- the least you can do is to minimise quantities and to have some metal containment.
Grinding is a particular risk, grinding Ali or other light metals is best not done at all. As was recently mentioned, linishing ali and rusty iron should never be attempted with the same belt or even with the same machine without removing the previous dust.
Grinding operations are a potential ignition hazard, consider where the sparks go!
Same goes for welding , gas or arc or plasma. The hot parts could also be an ignition source when placed on the wrong surface.
Smoking is also an ignition source to be considered, it is a very significant cause of domestic fires.
The workshop should be tidy -for a lot of safety reasons- no wood shavings or dust piled up and no oily rags. A rccd should be fitted, ideal to have power removed when the workshop is not in use.
The selection of fire extinguishers is a well known topic, there is a lot of published advice on what to use. A Carbon Dioxide extinguisher is useful in a variety of situations but should not be used on burning liquids. A Blanket extinguisher may be the best for slow burning liquids if you do not have a lid. Metal fires from light metals are best smothered with sand.
Anyone can call on the Fire Service for advice, they are normally pleased to advise people BEFORE they get into trouble.
Hope this helps someone sometime.
I would guess then that the two columns will hold the fixed electrode (job) at the btm. I have followed the same kind of tack but use two wide spaced leadscrews so that there is no risk of non-parallel movement. I used studding, there is no accuracy requirement-just smooth monotonic motion between the two electrodes. I insulate the top electrode.
The drilling of the tool and job is very sensible, why spend hours sparking metal that can be drilled away in seconds? You also gain from the flushing. Kerosene is popular but so is water! . The drawback with water is that it is more reactive so it needs more care in some ways than kerosene. Would smother a fire, not launch it!
The capacitor discharge concept was the first approach, it works well. The discharge melts a tiny bit off the job that then needs flushing out, the discharge time is of the order of 10's of uS for small particles. So electrically it's a relaxation oscillator (like a cap and neon bulb,) the C charges until sparkover, an ion channel forms , a tiny ball is detatched, the voltage falls too low to support the increased channel lenth and the V increases till the next channel forms.
So you get a very rough sawtooth across the C. A big C has a lot more 1/2CV squared so the channel current is higher and more energy is available for detaching bigger lumps off the job- hence a rougher finish. Now the peak current is High but the average low because once the channel is off the cap has to charge to the breakdown level.
This is one reason why cap discharge has been replaced by a pulse method, the supply is directly switched to the gap at well above breakdown voltage, the channel ionises quickly, the ball melts off and the voltage then removed. The switch is the simple bit, an oscillator sets the repetition rate, a monostable drives the gate of a bank of mosfets. This then gives V, F & t as more variables to play with! I am still learning about cap discharge.
Bear in mind that the peak current is very high, IF the inductance in the wiring is not minimised then you end up making a spark transmitter and ringing will then time the sparking. An obvious way of minimising these issues is to parallel smaller caps and wire them to the gap individually , feed through mini-ballast R's. Low Z caps are also good news, my fave is Rubycon ZL. You only need about 1uF for fine work at your voltage.
Glad the you are set up to take shots of the V and I ( symbols choice show age!) against T, think that you will find a new way of randomly producing numbers but the average instant V and I is the best way of understanding what is actually happening in the gap.
Current sensing resistors can be a problem I either parallel surface mount 1 ohm r's on a PC or use a length of insulated nichrome folded in half and twisted, inductance is a big issue here. Even Metal Film R's are spiral cut into inductors
I have been 'scoping for a long time, started using digital ten years back but still use Tek 7000 series a lot of the time. For one off events the digitals are great but if working with repeating signals I use a CRT job. Aliasing can get you into real capitol F trouble when working with high voltages, had a narrow escape once, however for EDM work digital is just what you need, certain that you will enjoy your new tool.
By the way, I did spend some time worrying about backlash in the screw drive as this can mess up the controller- i.e. retreat gets delayed as teeth move over to eventually reverse the final gear then you have to wait for the controller to close the gap. Ended up with belt drive, minimising the stages to one and using microstepping, the microstepping is not accurate beyond 4 or so steps as who knows the transfer params of the stepper? certainly not the drive. However it does not matter- all we want is monotonic.
One last thought , with a M6 1mm thread, 5:1 gear and a 200step stepper that is 1 micron per step. Microstepping at 2000 steps gives 0.1micron/step . So you could use a PIC to count U/D pulses to indicate how far and how fast things were going, that would be useful. By the way, I spark mini punch tools, what is your aim?
Best to run EDM closed loop, monitor the gap voltage with two comparitors eg 339's, when gap volts too low -retreat, when gap volts too high - advance. If you set up the thresholds at about 2/3 and 1/3 then you should get sensible stability.
It ain't optimal but gets you into the ball park. There are a vast array of variables in EDM so to get ANY cutting you have to stop reading and start sparking!
A simple set up is to pulse the counter when either comparitor says too much, the U/D line is driven by the retreat comparitor to reverse back a step or two. The basic aim is to get that gap set at the distance that maintains a steady rate of removal i.e. an almost constant current into the workpiece. This means that the advance rate equals removal rate.
The bit that some articles don't mention is the importance of good smooth movement without jerks or judder to get nice clean sides and a good finish, a sloppy slide will work for a "proof of concept", you need a nice slideway to control the gap between the electrodes- not just the position of the moving electrode!
As I am not looking at your circuit can only assume that the 0.1uF caps are across the stepper coils? When your TIP41's turn off the stored energy in the inductance of the coils has to go somewhere, this results in a massive damped sinusoid which could easily peak above the rated collector voltage of the TIP41 ie back EMF. The normal way of dumping this energy is to use a power zener rated about twice the supply voltage. This clips the peak to a safe level without "shorting" the coil with the normal reverse wired diode . If you are a total cheapskate then you can use a bunch of 1N4002's to connect the collectors to just one power zener around 30-36V wired to ground.That will lift your max step rate a little.
I am assuming that your set up is : a fullwave rectified supply of around 100-200V with a reservoir cap of around 100-330uF then a ballast resistor to limit the current to a safe value supplying the gap with a selected capacitor of say 1 to 100uF across the gap.
ONLY USE a transformer isolated supply!!!!! , keep the wiring from the gap capacitor and the gap short and flat i.e. minimise the inductance. This will help control the severe radio interference that you will produce.
Your dielectric fluid will get hot and filled with particles, pro EDM speeds up the rate by flushing the gap and filtering the fluid.
All for now, best regards, Alan
Sounds an unusual stepper, 18V suggests high inductance windings which would be slow with constant voltage drive. 48 steps is unusual these days too. Cannot say if 176 is sensible since more information is needed e.g. the motor type & drive. Is this a new build or an existing machine?
Most common steppers are 200 steps and around 5V voltage but it's the current rating that is of more interest. At high stepping rates the rate of change of current is limited by the winding inductance and the applied voltage, you hit a steeply declining torque when stepping quickly.This can then cause the motor to miss steps and "run rough".
The way around this is to use a much higher voltage but to limit the current to the rated value by modulating the on/off time of the drive- that's pulse width modulation PWM the speed improvement is roughly the overdrive voltage ratio- however it is a bit more complicated than that.
A second area of improvement is to increase the apparent number of steps from full stepping. Half stepping doubles the steps per rev by powering both coils between normal steps to produce a mid position. Microstepping allows a much larger number of steps by having many incremental steps of current to position the motor between full steps. ( although microstepping is not a strictly accurate angular interpolation) 8 usteps gives 1600 steps/rev on a 200 step motor ( 1600 steps is easy and a tad up on 48 steps/rev.
So a modern microstepping drive with PWM will drive the stepper much faster than simple whole step voltage drive and will not show the "resonance effect" where the motor fails to step at the driven rate. It also allows much finer control of rotation so that less gearing would be needed in an EDM application.
In an EDM application I can only assume that you are concerned with the advance and backing out rate since you would need a vast amount of power and cooling to spark out the metal that fast! But perhaps you have a gear train slowing the backing out, If so switching to a low voltage stepper with a microstepping drive could produce a substantial improvement and get rid of some of the gearbox.
Arc Euro Trade supply a good range of steppers and some inexpensive microstepping drives, their website also will lead you to the "Jones on Steppers" link, one of the best intros into stepper motors.
|Thread: HELP Wanted! Cutting Metal - But By What Means?|
My vote would be for the H/V bandsaw fitted with a bimetal blade. They are capable of chopping through thick lumps that you just would not want to hacksaw. With a few simple additions you can also do some quite fine sawing.
The vertical mode is useful for some sheet work however the wide blade rules out cutting mild steel jigsaws.
Do resist the temptation to fit a "metal" blade to a "woodworking" bandsaw if you want to saw mild steel. The metal cutting bandsaw really is a different animal, the frame is much stiffer to cope with the blade tension and thickness, the very important guides are much heavier and the blade speed slower.
The MachineMart website has a downloadable PDF manual for their CBS45MD which also includes the adjustment procedure.
When sawing metals for more than a min the blade can get very hot, I always use some kind of cutting/cooling fluid to extend the blade life and to be able to pick up the sawn parts after sawing without first aid.
After you have had a red/white/blue/green bandsaw around it becomes one of those tools that you don't want to be without when chopping a stock length of 50mm M/S into 30 bits 75mm long.
|Thread: Glanze Parting Blade - question|
The insert has shallow vees on two tapered faces, it pushes onto the holder which has matching vees. So any unexpected forces and it becomes an Unexpected Flying Object.
Of course this should not happen, the reaction from parting should be pushing the insert into the taper. So far I've been lucky with mine, but a good reason for having eye protection. You do need to make sure that the tool is at the centre height and cannot deflect downwards to then dig in.
It would be good to have a few words of advice with this tool as it is not as forgiving as the traditional parting tool.
|Thread: Wilf Baker's variable feed for mill|
Many wiper motors are self parking, when you switch the wipers off they run till at one end of the sweep. A switch may be fitted inside the motor on the output shaft so that it disconnects the motor at end of sweep, all you see sometimes is a springy arm wired to the motor.
The cheap way of arranging the switch is to insert it between a brush and the metalwork, the wiper switch grounds the common connection then the motor runs on to the stop position when the wiper switch is opened. Disconnecting the parking switch is easy on all of the wiper motors that I have seen. Putting it another way, wire directly to the two brushes disconnecting any other wire.
Another source of useful motors from the breakers yard is window winder motors, some of these are remarkably flat. They are not grounded since they have to be run with reverse polarity to close the window!
|Thread: Bandsaw question / Proxxon|
The 24tpi Swedish steel blade "for steel and brass" is now about £11.30 but the diamond job is now £101, the cooling stuff is another £46. The pics still show the nut and bolt sectioned but also show the cooling gear in place so what blade was used and how hard the bolt was is unknown. Axminster now list a bimetal blade that was not in the old cat.
I mostly use 14tpi blades -mainly for 3-10mm hardwoods- but the little bandsaw struggles with thicker wood soft or hard. The very important top guide has three races - like most other bandsaws- but the equally important lower guide is a slot in a cast post-no races. My top guide races need replacing frequently . So I don't cut metal on this machine, it gets used for curved cuts in thin wood or plastic and some modest rough shaping.
Axminster rate this machine as a "Hobby" tool - would not disagree, used gently on thinner softer materials the bandsaw is a useful miniature tool for light use but I would use other tools to cut any metal parts. ( the motor is very small, the steel blades 3-5 mm wide and 0.5-0.4 mm thick)
The H/V metal cutting bandsaw is a much more capable metalworking tool and about 80% of the price of the Proxxon bandsaw. It is a great help in chopping up mild steel, have used two from Draper over ten years to cut up large quantities of M/S and ally tube with bimetal blades.
You can fit a bimetal blade to many regular vertical bandsaws and cut a little M/S at a gentle rate - the most important bit is to listen to the machine, don't use a worn out blade or force the cut AND keep fingers and other bits away from the blade. Be prepared for a not perfectly straight cut- but that's another thread.
Chronos have a downloadable current Proxxon catalogue on their website.
I should add that we use several Proxxon tools in our hobby business and find them very suitable for some miniature jobs, the FKS/E table saw, DH40 thickneser and
the table router get a lot of use for working with around 0.1mm tol in hardwood.
regards to all,
Have had a Proxxon Bandsaw for around four years. Proxxon make a diamond coated blade that will go through steel HOWEVER it needs water cooling from a drip tank and is not quick. The regular blades will cope with Ali and soft metals but the bandsaw comes into its own when sawing thin plastic and wood on a small scale. It is NOT a heavy duty industrial tool but works for hobby and craft use.
Proxxon also make some very small chop saws which can be used on steel. They also make mini table saws, the larger machine being very useful for miniature work. It really flies when fitted with the carbide tipped blade which can be used on Aluminium, but forget steel. As with other Proxxon tools the top end models are capable tools for miniature light duty work and are cute.
If you need to cut much steel the imported Horizontal/Vertical metal cutting bandsaws that are sold by Machine Mart, Draper and many others are very useful machines and much more suited for tougher materials. Like any other sawing machine results very much depend on the blade and the user. A good bimetal blade used with cutting fluid will cut thick steel very nicely.
|Thread: Band saw blade comming off pulley|
Have had the same kind of fun with the imported metal cutting bandsaws, it's reassuring that others have problems too!. We have one at work which has cut tons of MS, it certainly works best with bimetal blades. After ten years the driven wheel has developed a rounded edge so the blade does slip off- time for a new one!
Be careful with the guides, the two ball races each side of the cutting region have to twist the blade to the vertical so they need a larger gap than you might think, the race positioning is via eccentric mounting bolts. If the races are too tight the blade will heat up and can jam then subsequently have a twisted backing. Badly worn bearings, too heavy down pressure, blunt blades and swarf can also cause jams. (This can also jam a conventional bandsaw and twist the blade back). One sign of twisted blades is a new clonking sound when the machine runs. Badly distorted blades then slip off the drive wheel.
When you get the saw it will normally cut vertically downwards however if it is Wednesday or you have changed the blade or fiddled with the races you will probably get a slanting cut showing that the twist is escaping past the races.
We use a scrap of 2x2 wood and try to get the blade cutting vertically at each side of the cut. It really is a matter of relaxing and making small adjustments until you hit the sweet spot. You can try using a straight edge held against the blade and adjusting for vertical with a stationary blade to get into the ball park then fine tune with the blade actually cutting.( Adjustments with the saw OFF please!).
Taking off the tension is a kindness to the rubber tyres that are fitted to the drive and idler wheels on good bandsaws, If you don't take the tension off then there is a risk of flats forming on the tyres. Some very nice machines have an over centre roller and lever so that you can "Knock off" the tension on the blade when you are finished.
|Thread: O-ring coming off pulley when motor power is cut|
Remove the grubscrew from the pulley, use a collar below the pulley to stop it dropping.
Fit a second collar above the pulley with a pivoting lever. Arrange for the lever to drop onto the top surface of the pulley at a shallow angle. When the pulley is driven the end of the lever will dig in and drive the shaft. When the pulley stops the lever will gently trail around the flange.
Improve the drive by cutting a few shallow slots in the flange if needed.
Get an electronic friend to build a darlington emitter follower to power the motor. Base has 100uF to ground and a preset 47K resistor across the capacitor. To run the motor the timer charges the capacitor to the supply voltage. When the timer times out the voltage to the motor is smoothly reduced to zero at a rate set by the preset.
Add a bit of friction to the disc to slow it more rapidly. Also you could have a solenoid wired across the motor pulling off a brake when the motor was running but stopping the disc quickly when timed out.
If you are making a coin operated machine then a good electronic coin mech would be a very good start. Go to your local coin-op company and shout abuse. They will then throw MS111 obsolete electronic mechs at you. Use enough abuse to also get the front plate mountings and the two orange plastic clips. You can set the mech to accept your wanted coin and reject ( return) all others. Otherwise build an impressive collection of dud coins.
|Thread: Finding the Centre of a Round Hole|
Hi Peter, Mount the DTI in the spindle above the rough centred hole with the dial facing you. Bring the DTI into contact with the hole wall closest to you and zero the DTI. Rotate the spindle 180 degrees then read the error. Move the table front or back to halve the error.
Rotate the spindle 90 degrees, zero the DTI and then rotate 180 degrees, read the error then move the table side to side to half error.
Repeat both axis trials a few times so that the opposite side readings are the same and you should be all centred up.
|Thread: B & Q Steel stock|
|Handy in an absolute emergency but the prices are high. Screwfix are much cheaper for fasteners and studding but are owned by the same group!|
Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!
You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.
Click THIS LINK for full contact details.
For subscription issues please see THIS LINK.