Member postings for Andrew Johnston

I prefer to use full form inserts, partial form inserts are just a pain. I screwcut a lot of Whitworth threads and it is much easier with full form inserts. The root and crest are properly formed and cleaned up. Partial form inserts leave the crest unformed so it ineeds cleaning up seperately. In addition thread depths are as per theory with full form inserts. Whereas for partial form one has to account for an incorrect root radius. In this picture partial form on the left, full form Whitworth middle and full form metric right:

I buy my threading imserts from Cutwel.

Andrew

The 163E series collets are dead length collets so intended for operation where speed of operation is paramount. As old mart says it should be lever one way clamps the work in the collet, lever the other way releases the work from the collet. During operation the collet should not move axially. It should be possible to clamp work, machine, release work and insert next workpiece without stopping the spindle.

If the above isn't true then either something is missing, is misadjusted or is damaged.

Andrew

It was drawn by my grandfather in indian ink and watercolour wash, dated March 1908. He was chief draughtsman at Westland Aircraft in Yeovil from 1925 to 1939, when he moved to Airspeed, also as chief draughtsman. At Airspeed he knew Neville Shute Norway very well.

Andrew

The only purpose of the fuel gas when cutting is to get the metal cherry red. Once at temperature the cutting process does not need a fuel gas, as the reaction between hot iron and oxygen is exothermic. Once started the cutting process is self-sustaining. So oxy-propane is fine for cutting, and is widely used commercially as propane is cheaper and easier to handle than acetylene.

Andrew

It was a rather odd post. The phraseology was not English, more US. The OP ignored the replies and just asked for recommendations. I suspect something suspicious caused the mods to delete it.

Andrew

Find someone with the right equipment. If you are near Cambridge you can borrow my box and pan folder.

Andrew

Some people do cut out Vs before bending to remove excess material. But probably more common when using steel as the sections can be easily welded together afterwards.

Andrew

Just to be clear I formed my plates while the metal was red hot. Presumably by heating the brass this evening and hammering tomorrow the heating was only intended to anneal the brass?

Personally I'd use steel for the tender sides. Much cheaper and better behaved when forming. This is an oiler tray made from 1mm cold rolled sheet formed hot on the same former as the spectacle plate for convenience:

Andrew

It's not clear what the material is, but once the material has kinked it will be very difficult to get the kinks out by hammering alone. It might just be possible by heating to red hot and using a wooden mallet.

I haven't flanged my tender sides yet. The former is made and the blanks machined. I will be forming red hot and the job is made easier as my tender sides have a large radius on the flange.

When I made the spectacle plates for my engines I formed them red hot over a steel former. The plates were made from 3mm cold rolled steel sheet and have fairly sharp internal corners:

This is the former:

And the partial former, a test piece and home made wooden mallet:

To summarise; the tender sides really need to be formed hot, and avoid kinks at all costs. For convex curves, as shown, the metal has to compress, or increase in depth, as it is folded over. Trying to bend cold makes that very difficult indeed. On the test piece note that the depth of metal on the curve is larger than the straight flanges although the blank started uniformly oversize.

Andrew

Yes they can! All the electric vehicle drives I have worked on used regen braking irrespective of whether an induction motor or a BLDC motor was used. A bigger problem is charge acceptance by the battery without damaging it, normally by over-voltage.

The last big power system I designed was a 3-phase boost converter that took the output from a 3-phase generator, driven by a diesel engine, and created a 600V DC link. Conversely the 600V DC link could be used by the power electronics to generate 3-phase PWM signals (just like a VFD) to drive the generator, as an induction motor, to start the diesel engine.

Andrew

The term 3-phase motor generally refers to an induction motor, running on a 3-phase supply. Brushless DC motors generally have three sets of coils which are switched in sequence, but it isn't 3-phase in the generally understood meaning of the term.

Andrew

I wouldn't bother mucking about with the port spacing in the cylinder at this stage, although I would make them longer. I'd alter the slide valve width and cavity, and eccentric throw, to achieve sensible valve events. That way there are fewer parts to make and they are simpler parts.

Andrew

The gears look a bit worn, but there don't seem to be any dings or damage that would cause intermittent action.

Skew helical gears are not the best choice in this appication as there is significant sliding action rather than simple rolling action of the teeth. The flanks of the lower right gear appear to be quite worn. A gentle pass over the tooth flanks with needle files or wet 'n' dry may help remove any small imperfections due to wear.

Andrew

The gears look ok to me; I'd be looking for a problem elsewhere.

Andrew

If a M6 screw is loose then a 7/32" screw will be even looser. Try 1/4" BSF, at 26tpi it is close to the 1mm pitch of M6 screws.

Andrew

I'd ignore it; it's a hang over from the days when most people didn't have access to micrometers but relied on plain calipers and rules. Just make it to size, or maybe a thou or two smaller if the part needs to fit in a hole.

Andrew

The spacing and number of harmonics are dependent upon pulse repetition rate and pulse width. How high the harmonics go, at a detectable level, is mainly controlled by the speed of the pulse edges. The faster the edge the higher the frequency of detectable harmonic.

Andrew

Welcome to the forum.

I've not used the Clarkson for sharpening drills thus far, but have used it for grinding the relief on some home made square thread taps:

Andrew

No-one is suggesting that one would control the 3-phase bridge directly. On VFDs I have used the basic functions such as on/off, forward/reverse and frequency can be controlled from the front panel, via external components such as switches and potentiometers or from an external controller, usually via a comms link.

Conceptually the 3-phase control signals are simple. How the values are arrived at can be simple or complicated depending upon the control algorithm. Simple V/f control only needs a microcontroller but vector control ideally needs a DSP, preferably floating point to simplify the software.

Andrew

That is incorrect, a VFD is just a variable frequency drive. The output frequency can be varied by several means. Could be a PLC, but I expect most people on here just twiddle a knob on the unit or use a remote potentiometer to provide an analogue voltage input. Alternatively a VFD can just be used to provide a 50Hz 3-phase output.

If the OP is planning to move then I would agree that installing 3-phase isn’t sensible.

Andrew