Member postings for Andrew Johnston

As you know I don't believe in pussyfooting about.

I've stalled both the Bridgeport and CNC mill without the R8 taper slipping.

Andrew

Can I assume that what you are trying to do is similar to this:

The relieved section will be about 2" long and is 3/16" thick. I did it in two steps, each about an inch long. Trying to do the full length in one pass caused too much chatter. I've just measured the thickness variation on the finished part - about 3 tenths of a thou. Some pointers:

The cutter is a 6mm professional quality 3-flute carbide endmill and is razor sharp

I took a couple of spring passes which removed extra slivers of material

The cut shown is conventional milling, but on the reverse side the cutter was climb milling - it's not something I sweat over

Material was hot rolled steel

The DRO helps to move the cutter back to exactly the same position

The rear jaw of the vice is set with a DTI to be less than 0.01mm out over 150mm

Andrew

Are the measured phase to phase voltages off load? If so what do they measure on load, on both the lathe and mill.

Andrew

The peg is intended to stop the arbor rotating while the drawbar is tightened. It provides no drive capability; that's due to friction on the taper. Both my R8 mills have no, or broken, pegs and they work fine.

Andrew

There are rotary converters, and then there are rotary converters. The simplest (but expensive) ones use a single phase motor to drive a 3-phase motor, which generates a true balanced 3-phase output. But there are also ones that use an idler motor to generate a psuedo 3-phase output.

It would help to have more details of the mill. My universal horizontal mill also has a 5hp motor. But it also has two speed ranges. In high range the motor is wired in star and produces 5hp. In low range the windings are arranged to double the number of poles and hence halve the speed. That would normally also mean half the power. But the motor is also reconfigured to be in delta with a corresponding increase in phase current. So the power in low speed is halved due to the speed reduction but increased by root 3 due to the increased phase current giving a power of about 4hp.

If the OPs mill is similar it may be that the converter cannot supply the increased current, although nominally within it's power rating.

Andrew

Never seen one, so possibly not; mine is INT40:

From a practical point of view I suspect most R8 fitted mills wouldn't be capable of utilising a Dedlock cutter. I certainly wouldn't use this cutter on my Bridgeport:

Andrew

That takes me back to the great zero-one controversy. Many years ago when I was designing active noise control systems I labelled microphone inputs and speaker outputs from 1 to N whereas the softies labelled them 0 to N-1. For the first system I designed N was 64. That's a lot of hardware when the boards were wirewrapped or point to point wired using the expensive Verospeed system.

Andrew

Bother, when I was posting I had a premonition that I was going to end up looking a wally. And so it came to pass.

Andrew

What's a domestic 3-phase supply? I've got 3-phase in my domestic garage and it's definitely 415V phase to phase.

Andrew

Crankshaft bearings are split horizontally. Otherwise it would be difficult to assemble the engine.

Andrew

Here are the results of some turning trials. Material was 25mm diameter EN1A and a CCMT insert. Spindle rpm was 1200rpm,and depth of cut 0.1". I did two tests, one with a feedrate of 4 thou/rev and one at 8 thou/rev. I then measured the width and thickness of the swarf:

4 thou/rev width = 0.098" thickness = 0.007"

8 thou/rev width = 0.117" thickness = 0.010"

Somewhat inconclusive on width, but we can say that the chips do not get thinner. It would seem strange if they did as it's not clear what force would be pulling the chip away faster than it is being generated.

I also looked at the swarf generated by a 3mm wide insert parting tool:

The insert curves the swarf and in particular curls the edges to make a shallow channel. The width of the swarf was about 0.117". So only a gnats wotsit less than 3mm.

As an aside all the swarf was quite brittle, which is not a quality one would associate with EN1A. May be it's a consequence of the shearing action?

I'm aware of the claimed advantages of rear toolpost parting; my question to David was about why the forces are different in parting off as opposed to turning. If we assume a square parting tool I would expect the force vector to resolve to two orthogonal forces. There should be no force parallel to the axis of the work. Depending upon material and tool shape there might be a force perpendicular to the work axis pulling, or pushing, the tool into, or away from, the work. But the main force will be downwards. It seems all wrong to react that force upwards trying to pull the cross slide off the saddle and the saddle off the bed. The machine designer has gone to a lot of trouble to make the bed stiff in order to resist downward forces so why not make use of it?

A claimed advantage of rear toolpost parting is that the swarf falls away. That may well be true for brass and cast iron but for steel where the swarf may be slightly wider than the tool the swarf is so light that the force on it due to gravity will be negligible.

Front parting works fine for me so I'll stick with it.

Andrew

After the interregnum caused by the horizontal mill feed gearbox 'noise' both cylinders now have four faces machined square and to consistent dimensions, plus the sides of the flange have been cleaned up:

It's now over to the vertical mill (and DRO) to machine one more reference surface and then start machining cutouts, bores and tapped holes for studs.

It turned out that the loose motor cooling fan was the cause of the gearbox 'noise'. That's a relief in one sense, as it was an easy no cost fix. But if I'd known that from the start I wouldn't have needed to dismantle everything. I could have got to the fan simply by removing the sheet metal cover round the motor.

Not sure when I'll get back to the cylinders as it looks like the weekend is going to disappear with glider surveys and airworthiness reviews.

Andrew

The two most common causes of poor finish are the material and the tooling. So I'd make the following points:

Don't buy material from Ebay unless you know what you're doing and don't care about finish. The quality of material varies widely even for nominally the same specification. Proper EN1A is one of the more forgiving steels and should give a good finish.

HSS tooling should produce a good finish, but is dependent upon how it is ground. You do not need fancy guides and setups to grind HSS (I hand grind my tools) but the shape needs to be roughly correct with proper clearance.

Insert tooling can be fussier about cutting conditions. It's possible that a small lathe simply won't have the speed and power to get the best from inserts. The same caveat applies to inserts as to materials; cheap inserts may not perform as well as more expensive branded ones.

A stick out of 60/70mm without tailstock support is quite ambitious on a small lathe.

Recutting on the way back to the tailstock is normal, even on industrial lathes. It's due to work and tool deflection, and the cutting process itself. It will become second nature to simply withdraw the tool, wind back and reset the tool position.

For HSS tooling and 12mm diameter EN1A I'd be running at about 800rpm (100 feet per minute surface speed). For insert tooling you can easily be three or more times that.

Andrew

Because there are a lot of Bridgeport mills, and clones, in Europe. Some real Bridgeports, including mine, were built in the UK. Tooling with R8 tapers has been available in the UK from commercial suppliers from long before the hobbyists started using it. Popularity is dictated by the commercial market not the home one.

Of course R8 is power limited, I think around 2hp is regarded as the maximum it can cope with. Another plus compared to Morse tapers is that it is, in theory, self-releasing, so no stuck tooling. It's a bit dinky, but it suffices on two of my mills. The third mill uses INT40 which is in a different league.

Andrew

Not the same as turning but I've measured some chips created when milling with my new Arc face mills. In all cases the cutter was running at 900rpm and the feedrate was 430mm/min. With 5 inserts that gives a chip load of 0.096mm.

For aluminium (6082) I used a depth of cut of 5mm. The resultant chip measures 5.00mm wide and 0.35mm thick. It's interesting to note that the chip is tapered at one end. That implies that the chip gets thicker as the cut gets going and conditions stabilise.

For steel (hot rolled) I used a depth of cut of 4.5mm. The resultant chip measures 4.55mm wide and 0.19mm thick. The chip is also tapered at one end.

Andrew

Can you explain that please.

Andrew

This morning I did a grocery shop and delivery run for my mum.

This afternoon I made a new tie rod for the feed motor on the horizontal mill. Fortunately I had a 3/16" BSF die to hand. This evening I reassembled the motor and gearbox. Fixing the motor fan may have cured the problem, although the feed seems a bit noiser than I remember. We'll find out tomorrow when I recommence machining the cylinder. Out of interest here's a picture of the internals of the feed gearbox:

Seems logical; horizontal input shaft at the top and two sets of three gears to drive the lower shaft which then drives the vertical shaft via skew gears. That seems a bit odd as the drive must be transfered to the swivel point of the table to drive the leadscrew. It's many years since I've had the table off the mill so I can't remember the details.

Andrew

Not sure I agree with that. For ductile materials at least, like low carbon steel, I think the chips are thicker than the feedrate might suggest and about the same width as the depth of cut.

Andrew

It was raining when I got up, equals double yippee. One, because the garden really, really needs it and two, because I can play in the workshop.

I decided to true up the second cylinder block. Having machined two surfaces square I started machining one of the faces perpendicular to the bores, with the casting slightly twisted to get the best alignment. I will true up the reference surface afterwards as there is still a lot of metal to remove from it. I was just starting the cuts with the second iteration of the twist when the power feed starting making intermittent noises. The immediate reaction was to ignore it. But if I do it'll only get worse, and there are no spares if something breaks. So I top up the gearbox from the motor to the feed gearbox - not much change. So next I fill up the feed gearbox, which due to poor design means I have to swivel the table (and lose my setup) to get to the filler. Do that and still not much change. The noise definitely sounds as if it is coming from the motor/gearbox. So take off the motor and gearbox combination:

A big gear on the feed gearbox input can just be seen to the left of the two levers that select the feedrate. It's a really messy job. Not only is the gearbox stripped, so was I as I don't want to get oil all over my decent shirt. On looking more closely I notice that the motor fan is loose as the bolt has unscrewed. The fan cover is removed and the fan is fixed. I ran the motor in this configuration and it "seemed" better. But annoyingly I damaged one of the rods holding the motor together. By the way the feed motor is 1hp.

The next tasks are to make a new rod, re-assemble the motor, refit the motor and gearbox and try it out. Then I might be able to get back to what I was doing.

At least the weather is going to be poor over the next few days. Which makes me glad I flew the big glider yesterday for a few hours of local soaring. It all went rather well given I haven't flown this glider for nine months. And I didn't make any boo-boos, which is a bonus.

Andrew

This is the threading/feed plate from my M300:

The gear train seems to be slightly different, although the last two gears also need to be reversed to get the coarser threads and feeds. The note bottom left clearly states facing is half sliding. Looking at the exploded diagram of the apron in the manual there is a 5 tooth low helix skew gear which might be involved in the feeds. That would be expensive to make. That could explain why import lathes use simpler alternatives, but leading to a higher ratio.

Some other points to make are:

In light of a recent thread on an odd 7mm and 1.1mm pitch thread it's interesting to note that 1.1mm pitch is listed.

In the manual the chart is extended to allow cutting DP and Mod worms using a 56 tooth gear in the drive train rather than 44 tooth.

My lathe is definitely power limited. With a decent cut I can hear the motor slowing as the cut comes on. I've pushed it far enough to stall the motor more than once. Calculations showed that I was trying to remove about 3 cubic inches of steel per minute. So the old rule of thumb is about right.

Andrew