Member postings for Andrew Johnston

Need to be cautious using twist drills to check measurements. Quality drills often have a shank that is a few tenths to a thou or more undersize. ideal would be to use a gauge block, or at least silver steel/gauge plate.

Andrew

I assume the micrometer is imperial and can read to a tenth of a thou. I'd read it as follows. The linear scale on the barrel gives tenths of an inch.The digit in the rectangular window gives hundreths of an inch. Assuming that the scale immediately to the right of the window doesn't move the two scales on thimble together look like a vernier and will give thousandths and ten thousandths of an inch.

Andrew

Some of the notes made by Ketan are a bit wide of the mark.

It is correct that the machine shown is ex-industrial, but it is a universal horizontal mill so does not have, or need, a horizontal attachment. Conversely I do have a horizontal attachment for my vertical mill:

But I wouldn't normally use it for gear cutting as it is a bit wobbly.

The horizontal mill shown has travels not that different from a SX2.7, 500mm in X and 200mm in Y, but it weighs about 15 times as much. I used the rotary table to cut the gear shown as the gear blank was too large to fit under arbor and cutter.

Andrew

Neither, but it will be tricky. it is normal to cut gears (at least in ME sizes) in one pass per tooth space. That means the cutter is working on a long mean path. So machine rigidity is your friend. With a 200mm diameter gear on a vertical mill the cutter will be sticking out about 100mm. That is an open invitation to chatter, which will get worse as the number of teeth get smaller and hence the spaces get bigger. What DP or Mod will be the largest you'll cut?

Of course gear cutting can be done on a vertical mill but it can be problematic. For manual spur gear cutting I prefer a horizontal mill. Far more rigid than a vertical mill and the arbor is supported at both ends:

Total cost of the setup above was less than half the stated budget, including a universal dividing head not shown above.

Andrew

Because they're South Cambs and are a bunch of ******. An official investigation some years back said they were too busy bullying each other to actually bother about running services.

Andrew

Almost always rolled, as it's cheaper and much faster than cutting. A caveat is that specialist fasteners, such as BA bolts, will probably be cut.

Andrew

Not really suitable for surface grinding. The top speed on my horizontal is 1200rpm and highest feedrate is 450mm/min, both of which are too slow for surface grinding. Plus I've got a Brown and Sharpe surface grinder.

I don't think there are any new far eastern hobby size horizontal mills; presumably as the market is too small. So you'd be limited to secondhand. In the UK Centec and Tom Senior seem to be popular. I have no practical experience of them, so I'll let others comment good or bad. i would be wary of smaller US secondhand models as some of them use proprietary tapers which are expensive at best and often non-existant.

Andrew

I'm all for horizontal mills. They're obsolete in industry but still useful in the home workshop. Mine was an impulse buy, albeit cheap at £175 plus £200 delivery. It has turned out to be more than useful. I use a lot of hot rolled steel on my engines and the horizontal mill is great for slicing up longways with a slitting saw. Once one has one it can be used in lots of applications:

Spur gear cutting:

Helical gears:

Horizontal borer:

Flycutting:

Compared to a vertical mill they can shift metal:

My horizontal knocks my Bridgeport into a cocked hat in terms of metal removal and rigidity.

Andrew

It's not just you; happened to me as well. They tend to be new or low post count members. I think they fire off messages scattergun and forget where and when they have posted. Now I send a one line response to see if they reply before creating a comprehensive reply.

Andrew

Small stuff, up to 3/4", I use a hacksaw. Bigger than that I've got a secondhand Axminster horizontal bandsaw. For sheet metal I use a guillotine which will cope up to 4ft wide and 1/8" thick. Above 1/8" I flame cut. For accurate straight lines on sheet/plate I guillotine/hacksaw and then file to a marked out line, or mill, depending upon work size and accuracy needed.

Andrew

Unfortunately it doesn't tell one anything of the sort. The fact that micrometer measurements are the same at each end implies that the lathe is turning parallel (probably, although the bar could be barrel shaped). The turned part of the work will be parallel to the axis of rotation. But nothing can be inferred about how the chuck is holding the work. If the bar is removed and replaced it is highly unlikely to still have zero runout.

It is very difficult to make measurements that highlight one, and only one, parameter. Assumptions about what is being measured are often incorrect. It helps to visualise the geometry and what is being measured beforehand.

Andrew

I rarely mark out, it's been superceded by using reference edges/circles and a DRO. Marking out is mainly used for sheet metalwork, done by hand, and the occasional reference mark for assemblies.

Andrew

They're diamond grinding pastes. The numbers refer to the size of the diamond particles, in microns.

Andrew

Fair point, although the motor will still run in star. Just that the power will be down as the phase currents will be lower than when running from 415VAC.

I've got two machines with 2-speed motors, the horizontal mill and the repetition lathe. The motor on the repetition lathe only changes the number of poles. Slow speed only halves the speed and hence is half the power, vis 1hp and 0.5hp.

The horizontal mill is rated 5hp in high speed and 4hp in low speed. So as well as doubling the number of poles it changes from star to delta when going from high to low range. I'm not convinced the motor is arranged according to Dahlander. I suggested this a while ago on the forum and was told in no uncertain terms that it was unlikely to be a Dahlander configuration. To change from high to low speed two knobs need to be changed. One standard electrical switch on the electrical box and one (which I an sure is electrical) on the column of the mill under the speed change levers.

Andrew

My experience of small centre drills is that you look at them, and ping the pilot snaps.

Andrew

I concur with some of the above. Use quality drills, and carbide drills are stiffer. Make sure that the setup is rigid and that the work is firmly clamped. For small drills spotting with a centre drill first is a waste of time; they leave a poorly defined indent that invites the following drill to wander. I find that letting the drill just "touch" the surface before applying cutting pressure allows the drill to form its own dimple. Here are two 0.8mm holes drilled 8mm deep in tungsten alloy, on the Bridgeport, using the above techniques:

Andrew

I can't see a problem running a 2-speed motor from a VFD, provided only one speed range is used. A potential problem arises if both speed ranges are needed, as one would need to change parameters in the VFD (number of poles and rated current as a minimum) each time the speed range was changed. I have a vague recollection that some VFDs allow multiple parameter sets which are selected via an external switch.

Andrew

Not really, similar hardware but different software and output waveforms.

A VFD usually drives an induction motor, which is asynchronous, ie, motor speed is not quite the same as would be expected from the applied frequency. The output waveforms from a VFD are PWM with a carrier frequency in the range of a few kHz to low 10s of kHz. The width of each pulse is different so that the underlying fundamental of the PWM is a sine wave of appropriate frequency (usually low Hz to 400Hz) for the required motor speed.

It is assumed that the propellor/drone motors are brushess DC. These are synchronous motors, ie, the motor runs exactly at a speed determined by the frequency of the applied signals. The output signals are a series of pulses, with the repetition rate being that needed for the required motor speed, ie, no PWM.

The signals required for a BLDC motor are simpler than for an induction motor, so the control algorithms and software complexity are also simpler.

Andrew

Never heard of them, but a quick search shows that they are still for sale in the US. It seems that they don't control the motor directly, but add an eddy current clutch on the motor output which can be controlled for speed or torque. So not as flexible as a VFD but presumably intended to maintain speed/torque on varying loads such as pumps and fans.

Andrew

I don't have wiring diagrams, or schematics, for the machine in question, so I can't offer specific help. The intention was to outline switch failures in general and make some comments on why the emergency switches may have failed with the characteristics seen. Never mind, serves me right for breaking my own rule of avoiding electronics dicussions on the forum.

Andrew