Member postings for Andrew Johnston

Given the motor has a capacitor it'll be single phase. A VFD will not work with a single phase motor. They are designed to work with 3-phase motors. Cheap VFDs operate with constant torque as the frequency (aka motor speed) decreases. Since the speed decreases and the torque stays constant the power available decreases.

Andrew

You wouldn't need 126, you could use 63, 21, 7 or even 3!

It's a fundamental theorum of mathematics that any positive integer can be factored into primes, and only primes. So whatever the conversion factor there will be a need for a gear with a prime in it somewhere. It may have to be a multiple of a prime as small numbers of teeth wouldn't be practical.

Andrew

I don't agree with that. One disadvantage of using a single cutter is that one needs a 3D CAD model. But that model can be as accurate as needed. A hob forms the tooth shape via a series of facets. A single ballnose cutter also creates a series of facets, tending towards scallops as the cutter tends to perpendicularity. It is easier to control the facets/scallops in CAM than with a hob. A disadvantage of hobbing is a tendency to undercut gears with fewer teeth, the exact number of teeth being dependent upon pressure angle. With a single cutter the CAD model can easily be adapted to eliminate undercutting.

Getting back to the OP, while electronic leadscrews are versatile they're not on my list of things I want or need. My lathe will cut a wide range of TPI and (approximately) metric threads and DP/module worms. So far I've only needed one thread I couldn't screwcut - a 1 tpi lead 2 start worm. The coarsest thread my lathe will cut is 2 tpi. Although I subsequently dumped the two start arrangement by then I'd already set up the CNC mill for cutting the thread, so I stuck with that arrangement:

Andrew

The value of 127 is indeed tied to the definition of metric and imperial conversion, but the fact that it is prime is no coincidence. It's the result of decomposing the conversion value into its prime factors.

There's no need to hob gears on a CNC mill. Using a single cutter is simpler (no need to make a hob) and possibly more accurate, albeit slower:

And the finished pinion, made to test the fit with an internal gear, which was the purpose of the exercise:

Andrew

I remain unconvinced that when parting off brass the side forces would be sufficient to bend the tool. This is the tool I use for parting off (mostly steel) on my Britan repetition lathe:

The blade is 1/8" X 5/16" ( a little narrower at the sharp end) and has an angle on the end so no pip is left on the parted off item. Once the item is parted off the blade can be used to remove the remaining conical pip. While I haven't measured any concavity or convexity nothing is noticable.

I suspect something is moving, even though it shouldn't be. How good are locks? What top rake does the tool have? Has the tool ever worked in the past?

Andrew

Unlikely. Contrary to the statement made by SoD many inverters (especially cheaper ones) do not have built-in EMC filters. Even if the inverter had an EMC filter it is unlikely that it could be bypassed via a parameter as it wouldn't be simple to disable the filter electrically.

It's not clear from the post if a breaker (over-current) or RCD function is being triggered?

Andrew

That's easy, bin it and buy one that works properly.

As above I manually adjust the slides to make sure the indications are within range before powering the spindle. Although my indicator is marked on the dial that each division is 0.01mm measurement isn't mentioned in the manual. I've always treated the indication as relative rather than precise.

I can't imagine that a hole saw is going to leave a good surface to indicate on. When I've made panels with holes that are slightly too small I just use round and/or half round files in the hole until the instrument fits. Quick and simple, and any slight errors get hidden by the instrument bezel.

Andrew

May be the cheaper versions only work for holes? To be fair 90% plus of my usage is for holes. Hmmm, 600rpm is insane. Doesn't sound like an instructional video to me! I run at around 100rpm on the Bridgeport, horizontal and CNC mills.

Andrew

All my arbors, metric and imperial, have keyways. Small arbors, as used by clock makers, may dispense with the keyway but not otherwise. The bore of a cutter depends, to some extent, on the OD of the cutter. Smaller cutters have smaller bores so a sensible depth of cut can still be used. Are you sure it's INT50? That's a serious size taper normally found on large mills. My 3500lb horizontal mill is only INT40. Outer support is dependent upon the cut rather than taper size. i almost always use outer support on the horizontal mill, even with small slitting saws.

Andrew

I use a Centro from Haimer, although it's somewhat over the specified price:

The probe moves easily in one direction and the dial moves in sympathy. In the other direction the probe has almost no movement. If overloaded in either direction the probe will eventually slip. On the back of the body there is a rotating disc that sets the direction of probe movement, inwards or outwards for centring on holes or spigots. I don't remember any plastic rings, the Centro just worked out of the box. The Centro instructions list a maximum speed of 150rpm. I usually run around 100rpm, 170rpm seems too fast.

I'm not aware of any mid-price indicators. I suspect it's either hobby end or high end professional.

Andrew

Madness - the DRO on my vertical mill is by far the most useful workshop item I've ever bought.

Andrew

Let's start by saying that a condenser is not needed in order for an Uniflow engine to work properly. Of course if the exhaust is exiting into a partial vacuum due to a condenser then, as described by Leslie, the exhaust steam should be more completely scavenged. However, compression of any remaining exhaust stream is not always a bad thing. With conventional valve gear some exhaust steam is often left in the cylinder to be compressed on the return stroke. Although the compression uses energy it has two advantages. One, the compressed steam acts as a cushion to reduce the forces in the connecting rod needed to stop the piston. Second, the compressed steam increases in temperature due to the work done on it, which has two benefits. First, it reduces cooling of the inlet end of the cylinder and second it reduces cooling, and possible condensation, of the incoming steam.

It's not obvious what the trade offs are regarding condensers versus compression of exhaust steam prior to admission. It'll be interesting to see how any future models perform.

Andrew

Machining a thin walled cylinder is a tricky but avoidable problem. I bought my smokebox rolled and tack welded. I completed the seam weld, welded in a rolled length of BMS and machined the smokebox door ring to fit. I then drilled all the circumferential holes:

The ring was bolted to the smokebox and used to clamp the smokebox to the small faceplate so I could machine out the rolled BMS to the average diameter of the boiler:

Andrew

I would have thought they were pretty good? Presumably one wants a valve to open quickly, stay open for a time and then close quickly so that maximum steam can be passed in the minimum time. I'm also puzzled as to why the engine linked to worked without a condenser?

Regarding reamers, I'm a bit fussy and only use machine reamers in a machine tool. A general rule of thumb for reaming is half the speed and twice the feed used for drilling. But for brass the same speed and increased feed will be fine. The allowance left for reaming is dependent upon size. For reamers below 1/4" leave 6 to 8 thou, for reamers from 1/4" to 1/2" leave 8 to12 thou and above 1/2" leave up to 20 thou.

Andrew

Oh my word, we've failed to genuflect in the presence of genius.

The OP isn't the first new member to start by mouthing off about the stupidity of other forum members, and I don't suppose he'll be the last. Experience indicates that they normally calm down, or quickly disappear.

Andrew

I'd suspect the material, what are its antecedents?

Andrew

Welcome to the forum.

Here's a link, Advanced Uniflow to an advanced uniflow engine model. Interestingly it doesn't use, or need, a condenser.

Andrew

Increase the feedrate; I never part off at less than 4 thou per rev. Below that the tool rubs, cuts and repeat, leading to howling and vibration.

Andrew

Wouldn't we all like to know. He made a slightly intemperate post in another thread at about the same time. So may be he was having a bad day?

Andrew

Maybe, maybe not. In the UK domestic plug fuses are to BS1362 and are normally fast or medium speed. The BS specification states that the fuse should carry 160% rated current for a minimum of 30 minutes, but should blow within 30 minutes at 190% of rated current.

Fuses are thermal devices; they rely on heating of the element to melt the element and break the circuit. The current and time needed are dependent on the exact resistance of the element (which is not well controlled) and the external environment.

Looking at the datasheet for a 13A UK domestic fuse it will blow at 4 times overload (52A) somewhere between ~15ms and ~800ms.

Andrew