Member postings for Andrew Johnston

Steady on! Following on from the Don Valley comment it's not the moderators that are at fault but the dumb forum users.

Andrew

Don't see why it needs to be a curve. A plain taper and final parallel section would work just as well.

Andrew

Just as well I'm not a muddle engineer then; at least not like Chuck.

I've got full sets of steel imperial and metric slip gauges, both bought on Ebay some years ago. Both have old calibration certificates. The sets are accurate to at least two orders of magnitude better than I need. So even if they're a bit worn or not exactly at the right temperature any errors are still less than I can measure.

I use them for sanity checking micrometers, setting up sine bars and for measuring slots, both when machining and to get a size when I need to machine a mating part. I do not use them as parallels or packing.

Andrew

Based on the supplier specification I expect the finished engine to weigh about 500kg. The boiler alone is 90kg, so that's a good start.

Andrew

I'm not worried about the floor. It's B&Q plastic "wood", so the odd dent doesn't matter. It's got plenty of them already!

It will fit through the front door. When I had the door replaced a few years ago I calculated the width of the engine. Unfortunately the drawings, and my CAD model, gave several different values. In the end I went with my CAD model and chose to make the door 32" wide. The real engine is a bit over 29" wide, so it should go through the door with no probem.

Andrew

At last! I've finally finished making the wheels for my traction engines. Having completed the last rear wheel I was able to measure the real axle length and machine to the scribed line:

The drawing says the rear axle is 30" but check on the work. The real axle is a tad over 28", so gawd knows where 30" came from. I also fitted the key for the final drive gear, made from 5/16" keysteel:

Fitting was handraulic, using files and wet 'n' dry. The slot in the axle is pretty much bang on size. The slot in final drive gear needed some filing as I ground the slotting tool a couple of thou undersize. Here's the engine assembly with the straked rear wheels:

Note the other set of wheels under the table, ready to go off to have rubber tyres fitted. Paper chimney fitted too! That was to check the pattern. Seems to be a fairly good fit; but it's bound to need some fettling on the job. I've got the sheet steel for the chimney and the job for this afternoon is to cut to rough sizes the four 2m x 1m sheets of steel (3mm, 2mm and two times 1mm thick) that are stacked up down the side of the bungalow. I think Burrell often used cast chimneys, but I have a picture of a full size engine with two rows of rivets on the chimney. So obviously using an internal strap. That's what I plan to do; saves making a fixture to form a joggle in the chimney before rolling.

Andrew

Got to be a scam. Mind you I wouldn't give it house room even if it was free.

Andrew

If they are machine reamers they cut on the chamfer at the front, not on the flutes. So they should have only been sharpened on the chamfer. So the size on the flutes shouldn't have changed.

Andrew

Which is exactly what I said in the first place

Andrew

No mystery. It's basically a VFD, but digital in the sense that it uses vector control instead of an open loop v/f characteristic. While you may be able to run more than one motor they will all run at the same speed. So if you slow down the main spindle motor the coolant pump et al, will also slow down. The blurb specifically says you can't run electronics with the output unless you buy a sine wave converter. That's simply a lowpass filter that converts the PWM output of the VFD to a sine wave. Without the sine wave converter the output may well not drive contactors or any internal transformers for low voltage lighting or control circuitry. The VFD itself may be plug 'n' play but not in the sense that you can connect it to the 3-phase input to the machine tool and expect everything to work.

Andrew

I'd agree with Jason that rippa cutters are inappropriate. They're intended for large depth of cut and shallow width of cut, where they reduce cutting forces, not vice versa.

The casting may well be chilled, but a carbide cutter should cope without a problem. They'll cut HSS!

The main issue is a poor quality cutter. The picture of the cutter is a little fuzzy but it looks like all four edges meet in the middle and are not sharply defined. So the cutter will be rubbing rather than cutting. This is what professional 3 and 4 flute centre cutting mills should look like:

On the 4 flute cutter note that only two edges meet, the other two are gashed so they are not centre cutting. The meeting of the edges are crisp and well defined. I'd never buy RDG milling cutters, but I have used the ARC premium mills, and very good they are too. There are two rules for buying cutting tools:

1. Never buy cheap cutting tools

2. See Rule 1

Andrew

Bother, beaten to it by SoD!

But I bet he can't compete in the kitchen, sorry assembly shop, stakes. I used to have a lathe on the kitchen table, as well as a number of other engineering items in the kitchen:

Now that I've had a new kitchen fitted the engineering stuff has migrated to the hall and sitting room.

Andrew

I'd agree with the crowd; bin the toolpost. The angles of the toolbit are all wrong; you need more side rake.

I'd start with HSS toolbits and a bench grinder. You can ignore complicated grinding fixtures, a simple knife tool is only three angles, none of which are critical. Insert tooling can be tricky to get a good finish and is more expensive than HSS toolbits. I'd agree with SoD, know your material. If it's out of the scrap bin all bets are off; you may never get a good finish. Ideally start with EN1A; it's fairly simple to get a good finish. On the other hand EN3B, which is a common low carbon steel, can be difficult as it is slightly "sticky" and has a tendency to tear.

Andrew

Only true if the fluid is incompressible and Newtonian, and the flow is laminar. Water is a good approximation to the first two conditions, but we don't know if the flow is laminar without knowing the Reynold's number.

Andrew

That's unfair! The RS-232 4-40UNC screwlocks are useless. After fitting one gives it an extra little nip for security and the brass fitting snaps. No warning, no nothing! I always buy a spare pack when I'm fitting them.

Andrew

It's worse than that; tool steels are the wrong material. They have properties you don't need.

I'd agree with Emgee, use a medium carbon alloy steel like EN16T or EN24T.

The designators A2 and A4 for stainless steel fasteners refer to the grade of stainless steel; A2 is basically 304 and A4 is 316. For steel bolts the grading is based on mechanical properties. The common 8.8 grade is rather more than mild steel, or should be from a reputable supplier. The material should be a medium carbon steel quenched and tempered.

Andrew

I use the Burnerd collet chuck on my M300 about 80% of the time. The other 20% is almost all 4-jaw or small and large faceplates. I rarely use the 3-jaw chuck; whilst a quality make it is old and worn. I see little point in using a collet set that didn't allow one to make full use of the spindle bore.

I have a 2-axis DRO on my vertical mill and regard it as pretty much essential. I don't have a DRO on the M300 and have no plans to fit one. I simply don't need it.

Andrew

Ooopsie, missed that.

Andrew

The plot thickens. In the first picture of the motor terminals the motor is definitely connected in star. In the second picture it is now connected in delta.

Andrew

Indeed it has, but the pigeons are mobbing the cat.

The speed of an induction motor is determined mainly by the applied frequency, and to a much smaller extent by the load. The speed is unaffected by the motor being connected in star or delta. However, if you apply 240V to a motor in star, and designed to run at 415V, then the phase currents will be lower. In theory the currents will be lower by the square root of 3. To a first approximation the torque of an induction motor is proportional to phase current. Power is torque times angular velocity. So for a motor connected in star, but running at 240V instead of 415V, the angular velocity will be the same, but the torque, and hence power, will be reduced by a factor of root 3.

Summary: The motor should run fine on 240V, but the available torque and power will be reduced.

Andrew