Member postings for Muzzer

Around about the time I bought my first lathe as a boy in the mid 70s (a Portass Model S), I found a book about lathe operation in the local library that wasn't written or published by the South Bend Lathe Co but had many photos that were attributed to them. A constant theme that struck me was the continuous, spiralled swarf that came off the tool, something you don't see these days. There was clearly nothing unique about their machines that would cause this effect so it was evidently down to common practice at the time. Recently I bought a copy of South Bend's "How To Run A Lathe" which is still readily available to buy or download off the internet. Most of the content dates from the war years give or take a couple of decades. What are often described these days as "clever" techniques like the use of the cross slide to draw the tool in and out while screwcutting with the topslide at 29 degrees are simply stated as the way it should be done - and this before most of us were born.

In the photos, that evocative swarf is there in abundance. It got me thinking...and experimenting.

With some consideration, a few things seemed clear:

· Cutting speeds must have been pretty modest, otherwise these spirals would have been lethal. Also, coolant was generally applied by brush (lard oil etc!), so heat generation must have been low. It all points to slow RPMs.

· Feed per turn must have been fairly modest too, otherwise the power and rigidity required would have been significant.

· The angle and offset of the cutting edge relative to the work piece are critical. It's got to be presented at a significant angle to the radial direction to generate a continuous spiralled swarf. This is achieved by angling the toolbit at about 30 degrees to the horizontal and where possible gaining another 5 degrees by deliberately raising the tip of the toolbit above the centreline. It’s rather like planing a piece of wood with the plane at an angle to the direction of travel.

I managed to buy an Indian or Chinese copy of one of those "American" toolbit holders after a bit of searching (they are out of fashion these days), cut and welded it to better follow the angles shown in the SB book and ground up a couple of 5/16" HSS bits as recommended therein.

I did some trials on my Bantam using a piece of scrap 1" dia mild steel. With 120RPM, 2.4''' per rev and 6mm width of cut, I was soon making some fine spirals. Lowering the tool tip reduces the pitch of the spiral (bunching it up), while raising it increases the pitch as you might expect. Raising the speed to 180rpm caused chattering despite tailstock support and coolant. I tried a second bit with a longer cutting edge and managed to get a ~10mm width of cut but of course I couldn't generate a decent vertical offset with this tool turning a 1" dia workpiece, so the swarf had a very short pitch - I'd drilled a 1/4" dia pilot hole for it to work into. I'd need a 2" or so diameter piece to allow me to raise the tip of tool enough to lengthen the spiral pitch to the point where it is flexible enough to clear the tool holder and flow from the work cleanly.

That's it. Probably nothing of any great practical value but an interesting experiment to me at least. The feed rates are a lot lower than we tend to use these days with the prevalence of carbide tools, pumped coolant and high power high speed machinery. Note that I had to fit a larger 60t gear on my Bantam geabox to get the feedrate low enough.

Hope you find this interesting!

Muzzer

Any semi-decent DRO system should be specified over a reasonably wide temperature range that ideally would cover the range of expected working temperatures. Here's what Mutitoyo have to say about it. They specify their accuracy over the whole range 0-45C.Beyond that you might suffer operator malfunction!

You'd have to look up the spec of the system you actually have but hopefully it covers a sensible range too.

**LINK**

Merry

When you start looking at requirements for products that you intend to sell for use anywhere in the world, you rapidly discover that there is no real level of standardisation, even within the EU. In some places like parts of Australia you see over 250V, in other countries less than 200V. And then there's Japan, where you may find 50 or 60Hz and anywhere from 85-120V. And that's just talking single phase. But we do love to knock the EU!

No, haven't changed it, it's still the old Xtravert from PDL Electronics who still appear to be in business. Hasn't been a bad unit, 15 years out. Rated at something like 6kW but of course set up for a smaller machine, probably around 2kW, I forget. Apart from the bizarre delay it has all the features you'd want and expect of a modern VFD - plus a noisy fan. Similar unit also on the drilling machine but without the speed control pot etc. It has a 3-phase motor too and this was the simplest way to operate it at home.

Murray

"If your lathe has a screw on chuck or faceplate I think a rapid stop could cause the chuck to unscrew."

Michael - I believe this is why the "Camlock" spindle was developed. The Americans seemed to like to switch their machines into reverse whilst running at full speed - without anything fancy like an inverter in the way. Time is money I suppose! The Camlock (as used on my Bantam for instance) doesn't care which direction it turns as the chuck is driven by pins and held on by cams. That's quite a bit worse than starting direct on line but they must have been rated for it presumably. Must have taken a nice gollup of current out of the mains, mind!

My lathe inverter has an annoying 1 second delay that can't be avoided. Even pushing the e-stop results in that delay which seems bizarre. Can't imagine what they were thinking of.

Merry

(1) Re : Electrical equipment .

**LINK**

All supply companies have a similar guidance document .

This is for industrial users requesting the utility company make a new connection for their facility. I think generally speaking, there will be very few plonkers in sheds that find their existing connection inadequate.

Meanwhile, the regulations governing the development and sale of electrical equipment address these concerns, so said plonkers will struggle to find equipment that cause those kinds of issues in the first place. Unless said sheds contain some very impressive experimental electrical equipment!

Those regulations cover the issues in the link (flicker, harmonics, EMC etc), as well as the concern in (2). You can start with EN61000 but there are quite a few others to be met as well. And that's before you even start on safety certification..... **LINK**

Merry

Edited By Murray Edington on 18/03/2013 18:36:53

Billy - "The peak current without a choke can be very high, if you want to draw 10A DC then the peak current goes towards hundreds of amps for a mS or so." That's an old chestnut (myth). The theory is actually very simple and the worst case current (even with a hard supply and ideal components) is actually part of a (modest) cosine waveform, not a peak of indeterminate amplitude. I know, having spent many years in this field.

"It is certainly the case that many -if not most- PC's are badly made, leave out EMC filtering parts and put people at risk. That is how you can get an ATX PSU for £7.00 trade in the UK." It's illegal to sell PSUs (or any other potentially hazardous electrical equipment) in the EU that doesn't meet a whole raft of EMC and safety standards. If it's got a CE (or UL or CSA) mark, then you can be fairly certain it's significantly compliant. If you find that someone's selling such a component with the marking on but that you think isn't compliant, you should contact trading stds etc.

Nothing personal but we need to get a few things straight!

Interestingly, "passive PFCs" are simply large inductors on the input of passive diode rectified capacitive filter PSUs that smooth out the input current so that it's much closer to a sine wave. Of course, it doesn't actually lead to a very good power factor but it's cheaper than an active PFC for small (<300W) loads. The filter sections at the front of PSUs are actually aimed at preventing the switching voltage (noise) being conducted back into the mains and generally have very little effect on the current waveform. The legislated limits for conducted noise are of the order of millivolts and cover all frequencies up to 30MHz.

Merry

Ken

1/ American house have "2-phase" in the sense that you get 2 x 120V withneutral centere tap. You can connect a load across the "ends" to get 240V. Call it what you want but 2-phase seems fairly sensible?

2/ Not sure what you mean. The voltages in all cases are sinusoidal. In fact, "single phase" in a typical home or factory is simply one of the 3 phases.

3/ You mean 180 degrees apart.

9/ The PF (angle) may be good but the harmonics (distortion) is pretty poor. Which means you are taking a higher RMS current than you would for the same outcome. And which you pay for literally.

10/ Isn't this scheme called a rotary phase converter?

To answer an earlier point, reactive (imaginary) power involves a real quantity of real energy flowing through the circuit. A purely reactive (ie capacitive or inductive) load can generate a very significant current. The current and voltage are 90 degrees out of phase. You pay for the current but get no benefit from it in terms of heat or shaft power (which is what "real" power results in). "Real" and "imaginary" are the formal words you'll find in the text books for describing resistive and reactive impedences and currents. "Imaginary" doesn't mean it doesn't exist....

Merry

In N America, the simplest 3-phase is "208V" phase-to-phase voltage, which is formed by 3 phases of 120V phase-to-neutral, in the same way that the 240V in Europe translates to "415V" 3-phase. Just as in Europe, higher power (proper?) loads use a variety of higher voltages like 480V or 600V, as 208V isn't much of a voltage.

Domestic wiring in N America provides 2 "opposite" phases of 120V nominal, giving 240V for high power loads (cookers, driers, kitchen receptacles, workshops etc). If you move over from the UK, you can use your 240V gear with a bit of rewiring. All my stuff was fine, it just spins a bit faster!

In Europe, if you have a poor power factor, you are paying for power you aren't using, so the utility companies aren't too bothered. If you don' t like paying for that, you can fit your own remedies.

There are regulations governing the manufacture of high power equipment that limits the distortion (=harmonics) and power factor (angle), so unless some incredibly high power homebrew system gets connected up the the network there really isn't a problem. Some guy in a shed isn't going to even register on the radar.

I believe more than 50% of motors produced nowadays are inverter-driven unless I completely misremember. There's no real disadvantage to them apart from the initial cost, yet the benefits are several. For home users with no 3-phase, they are the obvious solution. The main requirement is that you need to connect your 3-phase motor in delta (240V) instead of star (415V). Some machines can't be reconnected this way. However, 3-phase motors are quite a bit more compact than single phase motors, so replacing one with a modern motor and inverter may still make a lot of sense.

Merry

You use a collar / spacer to clear the 127t gear. If you don't have one, it's easy to make one up. Same width as the gears. As I said, I did this exact setup myself just a few weeks ago. Took me very little time and effort. The machine is designed to take the 120/127t combination otherwise they wouldn't supply them....

The manual would cut out a lot of trial and error

There you are then - thanks John. So if you use the right gears and gearbox settings, you should theroretically achieve zero error. PM me if you want me to send you the Bantam manual in PDF with the settup information.

Murray

Hi Trevor

Have you got the manual for the Bantam? It has all the setup info for cutting metric on an imperial machine. I don't know if your problem is basically a lack of a manual or whether you are really needing to cut a deadly accurate pitch. If it's the former, I can help - let me know if you'd like me to send you the section on setting up the Bantam for metric cutting.

I did this myself 2 weeks ago and the recommended gears were 35 (headstock), 30 (gearbox), 120 (meshing with gearbox) / 127 (meshing with headstock) to cut a 3mm pitch. However, you also need to set the 2 gearbox knobs to positions 5 and B for this example. I don't know what pitch you are trying to cut.

I don't know what the theoretical error is but doubtess HH's article will tell you. However, as it was a internal/external threaded chuck adaptor I actually wanted a degree of slop so that the chuck and adaptor would engage with the register - my kind of thread!

You also have to get the thread profile right. If the peaks of your thread are too pointy or your valleys are too wide, they may bottom out in your "nut".

Murray

Yes, I had one of these. You need a steel rod that fits the round holes in the knurled ring. If you had a back gear, you could engage that (with the bull gear still locked to the pulley) as a convenient way of locking the mandrel . Looks as if somebody's tightened it up good and proper in the past using a Manchester Screwdriver.

Murray

You can indeed use Google. But try searching for say "johnston", as if you were hoping to see what posts our good friend Andy has perpetrated recently. Sure enough, you'll get plenty of hits back but if you try to follow any of them, you won't have any luck unless said gent is responsible for the very last post on that page (try it) - not much use as a search tool really.

To search the web page quickly for a key word (in this case "johnston", you can hit control+F and enter the key word in the box. Usually this comes up blank.

Perhaps I'm missing something?

Come on David

The forum is impossible to search, which puts it in a league of its own. I know there are postings in there I want to find but short of spending hours randomly and fruitlessly diving in and out of likely-looking threads, there's no way of finding them. I can't even search by author. I challenge you to find a posting unless you already know exactly where to look for it.

If the search returns too many results, then the normal reaction is to make the search more specific. That's how they work and therein lies the power of the search tool.

Would there be any harm in having the search facility available? If it's really that useless we could always not use it. It would be nice to have the choice.

Please enable the search function and let us decide whether to use it or not. It could only improve our experience of the forums.

Pretty please?

Murray

There are and I forget which. Got a feeling some Drummond and Myford ones will mate. However, you have to get the tooth pitch (module) right as well as the bore of the hole through the middle and the keyway - Drummond used pins instead of Woodruff keys. You'll only need a full-ish set if you want to do loads of screwcutting. I used mine for this and mine had 90% of the gears but I must point out it's not an easy lathe for screwcutting.

I agree about using bronze bushes for now. You might also need to get the headstock mandrel ground parallel if it's badly worn, otherwise it may be loose in the new bearings once installed and a pig to get in there to start with. Wouldn't be surprised if yours is badly worn.

Merry

Hi Oli

I have one of these that I've owned for about 35 years. Mine's got "Portass" cast into the front face, otherwise it's pretty much identical to the Bond's Maximus which looks as if it was a rebadged Portass anyway. Haven't used mine for the last 25 years but it served me well when I was a boy and I did all kinds of stuff with it. What it lacked in features I made up with enthusiasm!

Like mine, your headstock bearing looks as if it has been overtightened and the cast iron fracture has some form of repair. The top slide / cross slide is missing as are the back gears. The Bond's Maximus article gives the best idea of what yours should look like in terms of missing parts etc. You have only a few change wheels but I think they are a fairly common pitch.

My leadscrew nut was stripped, so I bored it out and fitted 2 brass machine screws that mated with the square threaded lead screw.

The only difference I can see is the fact that yours has vee-belt pulleys. Mine came with flats and I machined vees into them later.

Looks as if yours has had a hard life!

Murray Edington