Member postings for Muzzer

I know your game Andrew. You're just trying to look human and fallible by putting in a token tantalum. It'll still work perfectly I'm sure!

Murray

Tantalums are crap. They don't like any sort of ripple current and they fail short circuit if they get upset or see a tiny overvoltage, so they are utterly pointless - or worse. Any competent engineer will religiously avoid using them. Those who don't will struggle to give any compelling reason for their use. They are the sign of someone who needs to be in another job!

Murray

Before caps were fitted with vents, they could be lethal if they detonated. I once saw a 38mm diameter can punch a clean hole through the suspended ceiling above it. This was during an abnormal (overvoltage) test, so wasn't completely unexpected but it could have put someone in hospital (or a box) in different circumstances. Now they tend to vent in a more controlled (but still alarming) fashion!

Murray

And if it all gets a bit too serious, throw in a bit of Colin Furze!

Merry

One reason for using 2 x 200V caps in series was to be able to use the input rectifier in voltage doubling mode for 120V input, giving a 340Vdc bus. Those PSUs would typically have a 120/240 voltage selector switch on the side.

Modern PSUs tend to have a power factor corrector (PFC) which boosts the input voltage up to around 380-400Vdc regardless of the mains voltage. That's not a problem for electrolytics in itself.

Generally, when a bus cap goes, there will be several other key components taken out with it, like the inrush current limiter and the diode bridge - and the internal fuse. Your second hand PSU is definitely the way to go. Even a new one would cost very little and they seem to be very backwards compatible.

With time, the electrolytics dry out and this is often the cause for the PSU failing. As they dry out, their resistance goes up so they get hotter still and the ripple voltage increases. The cans are designed to vent in the case of an internal short.

If you replace the failed caps, you may find it fails again fairly soon due to the other caps having dried out. They were probably all designed(?) with a similar lifetime. Yes, I've been designing switched mode PSUs for some years now....

Murray

Bl**dy hell Jason, that's almost sickeningly good welding, not least given the restricted access! I've not done any copper TIG welding, only stainless, mild and aluminium but I don't expect it's any easier.

No doubt you did it entirely manually ie without a turntable.....

Murray

I run my Bantam coolant pump from the same VFD as the main motor. As long as you are running somewhere close to the nominal speed, like within +/- 50%, it operates OK. The flow obviously varies with the spindle speed but you can adjust it with the tap.

Generally speaking, if you are using coolant it probably means you are using some power in which case you should be in roughly the right gear and your motor should then be operating reasonably close to nominal.

As pointed out, the impeller is symmetrical, so it works equally well in either direction. At one point I had to dismantle the pump to free it up but otherwise it's pretty simple and looks almost bullet proof.

Murray

The penny's finally dropped for me I think. You appear to have attempted to braze (solder) a copper boiler using copper filler rods. However, you haven't heated it enough to actually fuse the parts together - if you did, we'd be looking at a large hole where the end plate had collapsed into a puddle of solid copper at the other end of the boiler.

For a small copper boiler, you'd need to possess TIG welding skills that very few people possess (and much smaller filler rods) or be using a solder (ie a filler with a lower melting point than the copper). I've never tried it myself but it looks as if you could silver solder using TIG if you were so inclined.

Realistically, unless I'm wrong and it's actually a steel boiler that can be brazed, you are going to have to revert to some form of soldering (silver?). I suspect the challenge now will be to try to recover something from what we see. I doubt the puddle of copper will come away easily, yet it can't be made into a sound joint. If you melt it enough to fuse, it will almost certainly collapse. I doubt you can silver solder it in its present form either.

I hope I'm wrong but TBH I suspect I'm not. It's a learning process from which only good can come!!

Murray

If it's a copper boiler then you are welding, if it's steel you are brazing. Hard to tell which in this case but I'm suspecting it's actually a copper vessel? The added silicon doesn't seem to affect the melting point, so it's essentially an almost pure copper rod.

Sounds as if you are TIG brazing, given the mention of SilCopper, so you shouldn't be seeing any penetration as such. Nice thing about TIG brazing is you don't need to use flux and you can control how fluid the copper gets quite easily.

I love TIG welding and brazing but practice is essential - and welding is quite a bit more difficult than brazing. With both, preparation and cleanliness are critical. You don't seem to have got very good wetting around the edges and there is quite a bit of oxidation of the parts so you may need to clean them up again and make sure you have enough gas flow.

Not an expert on boilers, as I've never made one, but leaving more of a protrusion would give better visibility of the wetting and you presumably need some meniscus to give the joint some strength.

Murray

3hp 3000rpm sounds pretty sensible. You should still be able to develop similar torque at low speeds to the original in low speed mode as well as being able to develop decent power at high speed. You can make more use of the variable speed and less of the gearbox if you have more power reserve like this. It's handy for varying the speed as you face off a workpiece with power feed, allowing you to keep the surface speed more constant.

With an inverter you can always overspeed it a bit as well, eg for small diameters. A bit of an overspeed isn't going to bother the bearings unduly, as the forces will be fairly light.

3-phase motors are smaller than the equivalent single-phase motors and there's plenty of space at the back of the machine anyway. My 3-phase motor is only something like 1.5 - 2hp and I've managed to bog it down a couple of times, so wish I'd been able to get hold of a larger example when I changed it. I have a 5.5kW inverter, although obviously I have set the limits to suit the actual motor nameplate ratings.

Murray

Of course, to get in the pocket properly, you need a set of drums and a degree of skill. And who better than Dennis Chambers to show how!

Merry

Technically this happened on Thursday last week but I've only just got my breath back and the network up and running again.

My workshop finally arrived back in Blighty after 4 years in Canada, accompanied by a new addition (the milling machine). Loading and unloading wasn't a trivial exercise but this time round we did it properly. These boys were very slick and professional - and great company too!

We loaded the gear into the container in Canada using a forklift but the Hiab / flatbed we used at the UK end was more versatile and capable. The Hiab crane is radio controlled, so the operator can stand right next to the load, inside the container etc. It struggled a bit to reach into the container but the tools were last in anyway. Apparently the boom can reach 16' beyond the end of the flatbed and lift something like 4 tonnes at this extent.

The tools were loaded onto the flatbed which was then backed down my mother's drive and unloaded next to the garage. The last stage was running them inside using dollies (note the steel plate to bridge the gutter).

More photos in my albums.

There was enough room remaining in the container to get our worldly possessions in (once I'd jettisoned a few things), which was a bonus!

Once we've found a more permanent job / house etc, I'll need to extract this stuff again. In the meantime, it's armchair engineering for me I'm afraid.....

Merry

UK building regs stipulate a minimum ventilation for the main building and you would be advised to avoid completely sealing your shed. You need fresh air to breath (solvents etc?) as well as controlling the humidity levels.

I used a "superquilt" type insulator in my loft conversion. There are several brands available but are fairly similar. The 40mm thickness provides broadly the same insulation as 200mm of rockwool and it's vapourproof on both sides, so no need to argue which way to put it(!!). That's quite a saving in terms of how much room you lose, if you can justify the extra cost. You should leave a breathing space (eg battens) on both sides no matter what you use, with any breathable membrane between that and the outside world - it's basically keeping rain, dirt and insects out..

The dew point will be situated somewhere within the insulation (unless you completely screwed up), so moisture vapour getting into the insulator from either side will be able to condense to liquid. Best to have impermeable layers on both sides or an impermeable insulator surely? The only way to completely avoid internal condensation is to keep the RH down and the minimum internal surface temperature above the resulting dew point. It may not always be possible - but if you have sources of vapour (coolant, tea, sweat, steam, kettles, towels etc), you need to control the RH by ensuring adequate ventilation, unless you like living in an oven. Hence the building regs Part F (pages 20-25?)....

Murray

Edited By Muzzer on 18/11/2014 12:02:49

Ian

Yes, it was fine. I made sure the section I removed didn't contain the index mark(!), scored the glass with a new carbide insert and snapped it over a cloth covered edge. The Chinese operative who assembled it had thoughtfully left his/her finger prints all over it and I cleaned these off before reassembling it. The glass is held into the extruded channel by several soft plastic slugs, so refitting it was simple.

The trickiest part was actually drilling the 4 holes on the end of the shortened housing that hold the end cap in place. The bogey is guided by something like 5 or 7 miniature ball bearings, biased against the glass by a spring. You can just about make that out in one of the photos.

Unless you are dismantling a full length scale (60-80cm), it's pretty low risk. Mine started out something like 30 cm long and I removed a couple of inches so it was an exact fit for the BP head. It's now sufficiently compact that I will be able to leave it in place when I install the CNC conversion parts, although arguably it would become redundant at that point.

Unless I ever try boring a cylinder block, I'll probably (almost) never use the knee scale, personally. Having said that, I may be fitting a spare power feed to the Z-axis knee at some point in which case you never know, I may make more use of it. Most of my precision (=DRO) work is within the 5" range of the quill.

Murray

I often use a single indexable boring bar for both the internal recess, the outside diameter and the internal and external chamfers. With the top slide at 45 degrees, you can turn and face using the cross and saddle power feeds, then use the top slide for the chamfers. No tool change required and obviously you should minimise the tool overhang as a matter of course.

The technique is to operate the machine in reverse with the tool behind the axis for (external) turning and in forward direction with the tool in front of the axis for boring. You can make both chamfers this way without disturbing the top slide or requiring a dedicated 45 degree chamfering tool.

With the right cutting speeds and feeds you can get excellent finishes. Using the micrometer dials, digital calipers and a bit of practice I can get finished dimensions within a thou or so.

Murray

Probably more risky breaking through endless drilled holes - you'll get some hairy transient loads on the cutters as they break through, which would be difficult to control and could prove expensive. I'd simply mill it the way Gary suggests, stepping down in stages and conventional milling ie working round clockwise to open it to the final dimensions.

With a bigger machine, you'd be able to climb mill the finish (for a better finish), having roughed it out in one pass. It's also worth using slot drills designed for aluminium cutting (faster helix, better cutting angle etc). Roughing (hogging) cutters allow you to remove material a lot quicker and are worth investing in - in my books at any rate. And I'd use WD40 if using steel cutters.

Murray

There are a couple of pics showing the internal construction in one of my albums. The glass scale is laser etched with deadly accuracy and the patterns are picked up by the travelling bogey thing, generating a quadrature output. There's also an "index" mark which is a sort of absolute origin point that allows you a repeatable datum on each scale.

Here are also some pics of my BP clone DRO installation. I actually fitted Z scales to both the quill and the knee but I have almost never used the knee scale. I'd strongly recommend you go for a quill scale - after all you don't tend to feed drills and cutters using the knee crank handle.

Really pleased with the DRO system - probably the best improvement I've made to date in the workshop. It transforms the speed, repeatability and accuracy of your work.

Don't think I've seen any scales in aluminium. The coeff of thermal expansion is quite a bit worse for aluminium than for glass, so not obvious to me what benefit would result.

Murray

They would be made of rubber if it were me! Or at least the underpants would be.

Slightly off topic but Borax (a salt of boric acid) is an excellent ant poison. Dissolve a half a teaspoonful in warm water along with as much sugar as you can dissolve and put a few spoonfuls of the resulting syrup in a jam jar with a hole in the lid (keeps larger animals from devouring your bait). Place it on its side on the path the ants follow into your house, as close to the nest as you can. As soon as they find it, they stop coming in the house and cart it back to the nest to feed to the rest of the colony. It acts as a slow poison and will kill off the whole colony in a few days. For more drastic results, apparently you can tip a bucket of hot borax solution into the nest.

Works every time for me, is almost harmless to humans (we could sprinkle the stuff on our cornflakes without danger) and is available at many pharmacies. It is lifted out of the ground in the Mojave Desert and used to be used for water softening for clothes washing purposes. The solubility is about 20g/L and the LD50 seems to be in the region of 2g/kg of body weight. Some new age tree huggers even take it as "medicine". It's pretty safe, unlike the industrial artificial pyrethroids.

Murray

Edited By Muzzer on 12/11/2014 12:33:26