Member postings for Andrew Johnston

It's badly worded but I think the comment refers to the four magnets referenced by SoD. The answer is it gives four pulses per rev.That can mean a number of things:

* Faster response to a change of speed

* Same update rate but better averaging

^ Better S/N ratio equals more robust in the event of noise

Andrew

Postscript: Beaten to it

Edited By Andrew Johnston on 13/07/2022 21:08:05

Speak for yourself, don't presume to speak for me. My aim is to make good parts with the least expenditure of time.

For the thread size concerned, especially in brass, I just use a plug tap or screwcut. No need to use taper/second taps.

Andrew

Looking at the picture the thread is definitely Acme/trapezoidal, not square. Forget Wikipedia, Acme style threads can be whatever the manufacturer decides, although there are standards for the shape of the thread form.

Looking at the picture can we assume that the screw mates with a gear? If so then the flank angle of the thread should match the pressure angle of the gear. Furthermore the depth of the thread will be determined by the addendum and dedendum of the mating gear.

Andrew

That's a new one on me. I've designed the battery management hardware for a number of electric vehicle battery packs, including regen capability. But this was always for the main battery pack, not the SLI battery?

It turns out that regen is not as useful as one might think, not least because the battery needs to be at a relatively low SOC to accept the short term high currents without being over-voltaged.

Andrew

Not so, hydrogen is explosive in air from 4% to 74%. When I first started working on electric vehicles in the early 90s we were using lead acid batteries. We had to have hydrogen sensors fitted in our battey room and in each vehicle. One of the experimental battery packs we were asked to look at had clearly had an internal fire, suspiciously just above the battery vent.

Andrew

Many car batteries these days are sealed, so they shouldn't vent hydrogen unless grossly overcharged. So no risk of explosion. I always connect my charger across the battery terminals.

Andrew

No idea what you're trying to say, but the reliefs on the tap are being ground on the periphery of the wheel, as shown in the Clarkson manual.

Andrew

Armchair - check

Popcorn - check

Beer - check

Let battle between hardened rollers and soft rollers begin!

I don't have a filing rest, but when using filing buttons I regard them as consumables and leave them soft.

Andrew

The proper way to grind reliefs on taps:

Andrew

Modelling a diode as having a resistance, or trying to measure same isn't useful. The forward characteristic of a diode is exponential. The forward voltage drop of a diode varies with current, temperature and the particular diode. The theoretical value (at an arbitrary current) is set by the semiconductor physics of the precise materials and doping levels used.

Most multimeters have a diode symbol on the dial, in which position the forward voltage drop of the diode can be measured. No measured drop means the diode is the wrong way round, or is duff.

From a practical stance the most important number for a power diode is the forward voltage drop at rated current as this will determine device dissipation and voltage loss for the following circuit. The drop at rated current is usually several times the nominal voltage drop.

I would agree with the above comments that a signal diode isn't the best choice; a power Schottky, say 1A rated, would be better.

On other points I'd also agree that running diodes in parallel is frowned upon. But sometimes needs must; a rule of thumb is that each diode should be rated for two thirds of total current. The only time resistance and diodes go together is when looking at the slope of the breakdown voltage with current in Zener diodes. The 'resistance' in breakdown is often listed on datasheets. The name Zener diode is a bit of a misnomer, as at higher voltages the breakdown mechanism is dominated by avalanche breakdown, not the Zener effect.

Andrew

This is what steel swarf looks like when using an insert parting tool:

The swarf is slightly narrower than the insert and considerably thicker than the selected feedrate.

See this discussion: Parting Off

Andrew

Edit: Messed up the link

Edited By Andrew Johnston on 09/07/2022 11:59:16

I've decided it's not appropriate to outline the mathematical basis of gears in what is essentially a practical thread.The only thing I will add is don't get your hopes up about Tracy Tools or Home and Workshop. When I was looking for a range of 5 and 6DP involute cutters for the gears on my traction engines they never seemed to have anything in stock. I was able to buy a job lot of cutters on Ebay, from the US, that covered all the spur gear tooth counts I needed, except one. For that I bought a new cutter from Victornet in the US.

Andrew

No, that is incorrect. I have to go out now, syndicate meeting about our broken sailplane, but will try and explain in more detail later.

Andrew

I'll second the book by Ivan Law. Good on the fundamentals of spur gears but weaker on more advanced types of gear. The maths isn't complicated, early secondary school level.

Which gear cutter to use for a spur gear is easy. For each cutter the range of teeth it wil cut is specified. Simply pick the cutter that covers the tooth count desired. The form of the cutter is exact for the lowest tooth count in the range and gets progressively less accurate as the tooth count increases. The errors are small and don't concern us in most ME applications.

Be aware that the numbering of cutters in the Module system is the the reverse of that in the DP system. So a number 1 cutter in Module will cut a gear of 12 or 13 teeth. In the DP system a number 8 cutter will cut a gear of 12 or 13 teeth.

Andrew

Give me some credit; the decision was made on direct personal experience. I did visit a local club but it seemed to be full of whining old men. I also made the mistake of saying I was a professional engineer; you'd have thought I had farted in a lift given the response.

Andrew

Which is precisely why I don't belong to a model engineering club.

Andrew

See this recent thread:

QC Toolposts

Personally I don't use them, almost. A 4-way does for me for most turning and is more rigid, although I do run my lathe to the limits.

I would also agree with Tony, it is an unanwerable, and rather lazy, question. You might just as well say what is the best car to buy without giving any details.

Andrew

Before the advent of inserts brazed carbide was recommended for iron castings to get under the skin, complete with sand, and to get through chilled area. i've got a few industrial ones from way back but haven't used them for decades. Carbide inserts work well, even for tough and hard materials. Plus the castings for my engines seem to be old school as they have never had any hard spots.

Andrew

The tapered recess is just that, tapered not parallel. So once in place the insert does not move any further. I gently tap a new insert in place with a nylon hammer. I use 3mm inserts, but I use a relatively large industrial lathe:

On a smaller lathe I'd use a narrower insert, probably 2mm if you go the insert route, narrower still if using HSS.

Andrew

Personally I wouldn't buy sets. Buy HSS blanks and grind your own tools. For carbide I use CCMT inserts for 80% of my centre lathe turning. My repetition lathe was designed to use 5/16" square HSS blanks so that is what I use. I suspect the Logan won't allow the best to be got from carbide.

For threading I use full form inserts, except for specials where I grind a HSS blank.

Andrew