Member postings for Andrew Johnston

Sadly not. I use Drill Service a lot, and they do LH stub drills and RH slow spiral stub drills, but not LH slow spiral stub drills.

Andrew

No chance of left hand, slow spiral, stub drills then? Can't find anybody that sells them.

Andrew

One factor no-one has mentioned is work holding. For a chuck with reversible jaws the steps that hold the inside diameter of work the conventional way round, and the outside diameter of the work in reverse, must be compromise shape that doesn't provide much holding capacity. Which is probably why reversible jaws normally appear on small chucks.

It's a moot point anyway, as 95+% of my turning on the main centre lathe is not with the 3-jaw chuck. Instead, in order, I use a collet chuck, 4-jaw independent, large faceplate and small faceplate.

Andrew

On all my industrial machine tools the contactors run phase to phase because a) I've measured the coil voltages and b) the machine inputs are 4 wires - three phases and earth - so there is no neutral.

Andrew

Hmmm, doesn't look like a rotary converter to me. A proper rotary converter uses a single phase motor to drive a 3-phase motor working as a generator. It provides a true 3-phase supply and can run multiple motors up to the total horsepower rating. The box illustrated by SoD looks more like a static converter that uses a capacitor in conjunction with the driven motor to create an artificial third phase. The give away are the switches on the front labelled in hp; used to switch in different values of capacitor for different loads. Note that a 3-phase motor will run on two phases, but is rather "lumpy". So that might be what the coolant pump is doing.

A static converter may, or may well not, run the contactors and other electrical items between the supply and motors depending upon how it is wired and the voltages required. Many 3-phase contactors run phase to phase (415V) not phase to neutral (240V).

In the absence of a 3-phase supply beg, steal or borrow a proper rotary converter. True rotary converters are pretty noisy, so you'l know if you have one!

Andrew

If the grooves are 5mm wide then the part is on the order of 70mm diameter. Speeds and feeds seem ok. What is the nose radius on the CCGT inserts? The CCGT inserts are much less sensitive to small DOC and fine feeds than CCMT inserts.

I'm with Hollowpoint, my bet is on the material, or rather less likely contaminated coolant.

Andrew

Much too slow yet again; that's what comes of checking facts and figures before posting.

Edited By Andrew Johnston on 25/11/2019 11:21:53

Mostly correct, although the real skill is knowing when BF&BI and a bigger hammer are the right solution.

Andrew

Welcome to the forum Sandra. What sort of apprenticeship are you thinking of doing? Way back in the 1970s I looked at doing an apprenticeship with W H Allens in Bedford. That would have been heavy engineering, as they made steam turbines, diesel engines and large pumps.

Andrew

Hmmm, 6082 ought to be easy-peasy.

The finish is poor everywhere; looks like tearing, but could possibly be chatter? First are we really sure that the material is 6082? And where did it come from, commercial stockholder or other?

Insert tooling or HSS? You can turn 6082 with CCMT inserts, but CCGT insert are way better and give a better finish. I use aluminium specific inserts for parting off, although they're not polished in the same way as a CCGT insert. However, parting inserts need to have a continuous feed, preferably greater than 4 thou per rev, otherwise they can chatter quite badly. For accurate (manual lathe) grooving I use HSS tooling.

I generally turn 6082 dry, except for parting off, and still get a good finish. The biggest problem with 6082 is birdsnesting of the swarf, which then dulls the finish. Note it dulls the finish, it doesn't produce the results seen.

Summary: given the poor finish everywhere look for a common factor, which is likely to be the material or machine.

Andrew

Should have specified a LH thread.

Andrew

Been there, done that. Ok for light work, like punching out small brass patterns for brackets to hold thermistors on battery terminals. But once I started using the flypress to its capacity cracks starting appearing; mainly in the bench top. Make any stand solid and then add more bracing and weight.

Andrew

Over the years I've used the following methods:

1. Filing buttons - I don't harden my buttons, but regard them as sacrifical

2. Clamped on a rotary table with the hole in the end of the rod over a pin in the centre of the rotary table. The centre hole in my rotary table is parallel, not Morse, so it's easy to make the pin

3. CNC milling

Of the three options 1 and 3 are the most used.

Andrew

Sounds a bit light to me. I'd use 2"/3" square thick wall tube and heavier plate. I'd also use proper diagonals, not just gussets. To save the trouble of searching here's what I did to repair my broken bench, note the hole to match the hole in the flypress:

And with the flypress in place:

The bench is on 3x3 uprights with cross bracing all held together with 3" coach screws. The rear of the bench is also bolted to the wall behind. My flypress is #3 and I still managed to crack the bench top. Although that was after closing several hundred steel rivets.

Andrew

NB: The hole in the flypress base is currently filled with a blank to support the rivet fixture while I'm riveting my traction engine wheels.

Having discovered that the top of my bench had broken due to over-enthusiastic operation of the flypress while riveting a rear wheel for my traction engine I've now fitted a 600x500x15 steel plate with M12 screws to stiffen things up:

And bolted the flypress back in place:

The whole set up feels pretty solid and is better than it was before.

Andrew

That's not my experience. Must mean I'm below average; and my workshop is in a garage, not a shed.

Brass and bronze can and do snatch a drill, to the extent of pulling out the Morse taper in the tailstock. For small drills, say less than 6mm, it doesn't seem to matter. But I run fairly heavy machine tools. Above 6mm if one goes up in small increments, say 1mm, there is not generally a problem. But I'm idle and I can't be a*rsed to keep changing the drill. I've bought a few slow spiral drills specifically for brass up to about 12mm. They work well and allow one to open out a hole in one pass with a sensible feedrate, around 10-20 thou per rev, if one can wind the handle that fast. Snatching seems to be worst when a pilot drill has been used. So I try and drill holes in one pass. I expect that the force needed to push the chisel edge into the work counteracts the force on the lips pulling the drill into the work. Above 12mm I'll bore if possible. Like wot the books say I tried stoning the lips on a standard drill. Didn't work for me; whereas the slow spiral drills do work without having to be careful.

On the manual lathe I use CCMT inserts for brass and bronze. For HSS specials, and on the repetition lathe, I'll use zero rake if grinding from scratch, but otherwise don't sweat about it. The only time I have a problem with swarf is when it birdsnests and/or gets trapped between the tool and work. Of the metals aluminium alloy is by far the worst for birdsnesting.

Andrew

Ooopsie," let battle commence" was intended to refer to the forum membership on the subject of how tooling cuts metal. Not me versus SoD, two falls, two submissions or a knockout to decide the winner.

Andrew

Edited By Andrew Johnston on 20/11/2019 18:40:57

Oh dear, yet again I'm going to disagree with SoD. I expect he's pee'd off with me by now.

I'm not convinced that HSS and insert tooling operate in different ways. Although I can't find a definitive explanation for HSS tools I think both operate by shearing off a ribbon of metal. The main differences are the angle between the work and top of the tool and how the swarf is handled.

To take the butter analogy. If a knife is pushed down on butter, sharp edge first, then the butter is cut. I'm not sure what the correct term for this is, but let's call it cleaving. I don't believe that any metal turning tool operates in this mode. Alternatively we can scrape the knife across the top of the butter with the blade near 90°, plus or minus a small angle. This will create a scroll of butter that is sheared off the butter. This is how I think turning tools work.

I am confident that insert tooling work by shearing, so let's consider HSS tooling. First take turning brass. The recommended side rake is zero, so the cutting edge is at 90° to the work. So the metal must be sheared off, and there's no doubt that it works. For steel the side rake is around 10°. The cutting edge is at 100° to the work, so not really cleaving, but more like shearing. For very soft materials such as aluminium the rake angles are larger, but still nothing like cleaving.

Let battle commence!

Andrew

Having read up a bit more I think SoD is wrong. Negative rake inserts create higher cutting forces, so for a given cutting speed they consume more power. However, as SoD says, negative rake inserts are stronger than positive rake inserts. So they allow one to increase DOC and feedrate. Of course that requires the machine to be rigid and have plenty of power available. But if one has such a machine then negative rake inserts allow one to utilise the machine to its maximum capacity and thus maximise volume of metal removed per unit time. That's advantageous for industry.

I won't be changing to negative rake inserts as I'm quite capable of stalling my lathe (3hp) using positive rake inserts.

Andrew

I think SoD is getting confused with units. Power per unit volume removed would be a better metric. Intuitively I'd think that negative rake would consume more power per unit volume, but I'm not sure without looking it up. However, it makes sense that less power per unit volume is used as cutting speed increases. That's due to increased heat in the cutting zone, so the metal is hotter, and softer, and shears with less force.

Andrew

Quite so. I knew it was a Shorts, but I had to search to find it was a Skyvan, which is why you beat me to the reply.

Andrew