Member postings for Andrew Johnston

As per the drawing I'm using 1-5/8" diameter EN8 for the rear axle on my 4" Burrell. The finish of the bar as drawn is fine as far as I'm concerned. Of course I'll remove any dings and burrs, but as drawn it's probably better than the original. I dispensed with the bronze bearings in the final drive tube as well. So it's steel on cast iron.

Andrew

Well I wouldn't want to sully that thread by posting about fudge it and bodge it stuff.

Thus far the iron castings from John Rex have proved to be excellent; no hard spots or skin.However, I will use my insert face mill for the cylinder. In due course I'll test the 6" cutter shown on steel. The horizontal mill has a 5hp motor and I'd like to at least make it sound like it's doing some work. Don't suppose I'll ever have the nerve to stall it though. As far as I'm aware the Clarkson Dedlock system is totally obsolete. Which probably explains why there's been a glut of over-priced arbors on Ebay. I've bought a few cutters from Ebay over the years. One is a half way house - a steel body with HSS serrated inserts.

After a late session today all the spokes on the rear wheel have now been fettled. Riveting here we come!

Andrew

Edited By Andrew Johnston on 05/12/2019 22:48:09

Nitriding is all about forming nitrides. Nitrogen is quite soluble in iron, and iron nitrides give better corrosion resistance with modest increase in hardness. But they decompose at fairly low temperatures. Other metals such as aluminium, chromium, molybdenum, vanadium and tungsten form nitrides that are very hard and much more temperature resistant. Some of these metals are present in small amounts in nitriding steels, such as the EN4x series.

So, while nitrogen may well be absorbed during case hardening of unalloyed low carbon steel it will not do much for surface hardness.

Andrew

Good grief, isn't anyone else making anything?

The last rear wheel has now had the spokes fitted and the extra rivet holes drilled in the T-rings, using a spare spoke as a jig:

Next job to go round deburring and fitting the spokes permanently before riveting. Then fit the hub covers and job done. And I'll be glad to see the back of the wheels; four front and four rear wheels is enough for anybody.

Andrew

I suspect that may well be the case. Ideally you'd need an oscilloscope to check the waveform. Unlikely to be a ground loop, more likely to be inadequate smoothing capacitance after rectification. One test is to firmly hold a wooden dowel on various parts when the hum occurs. If the hum changes you've found what is oscillating, but not the why. But once you know the what the why is easier to track down.

Andrew

You can make an oscillator from a resistor, capacitor and a CMOS inverter. The frequency is set by the resistor and capacitor and, to some extent, the trigger levels of the inverter. Not a resonant circuit in sight.

Andrew

Using a low pass filter will ultimately produce a DC voltage, the value of which is proportional to the duty cycle of the PWM. Using a filter rather defeats the point of using PWM in the first place. Assuming a passive filter it will also require a physically large inductor, as it must carry the full motor current without saturating the core.

A fixed PWM signal will contain a fundamental frequency, which is the pulse repetition rate, and higher order harmonics. The amplitude of each harmonic will vary according to the duty cycle. There are no frequencies below the repetition rate of the pulse train. So for instance if the PWM frequency is 1kHz the spectrum will contain a frequency at 1kHz plus varying amplitudes of 2kHz, 3kHz, 4kHz and so on. There will be no component at, say, 100Hz.

Of course the above goes out of the window if the duty cycle of the PWM varies on a cycle by cycle basis, as in the output of the VFD. In that case the varying duty cycle is designed to produce a fundamental sine wave at a frequency below the repettion rate of the PWM. But for a DC motor the PWM will be fixed for all intents and purposes, unless one is playing silly duffers with the control knob.

I think I've discovered a new law:

Oscillation + ME = must be resonance

Just because something is oscillating doesn't necessarily mean it has to be at resonance.

Andrew

Now that I'm a member of the unwashed, aka unemployed, I've finally got time to look properly at items I bought years ago on Ebay. First, a Clarkson Dedlock chuck, shown here disassembled:

The shaft top left is interesting; a double start ground thread and it's a moot point if the next bit down is a multistart thread, a helical spline or a helical gear. It's one thing grinding the external "thread", but the internal "thread" would be more of a challenge. And here's the chuck reassembled with a cutter in place:

It works in a similar way to the Clarkson chucks for threaded cutters. If the cutter rotates slightly, due to cutting forces, the cutter is forced harder onto the shoulder of the chuck. Can't wait to give it a go and make the horizontal mill work for its supper. The question is; can I clamp the work down hard enough to resist the cutting forces?

I've also had a good look at the No.1 and No.2 Coventry die grinding fixtures. I see how they work now. There is the odd bit missing, but they can be made if required. Here's the No.1 fixture set up to grind the throat (cutting edge):

And to grind the rake:

That's enough excitement for one day. This evening I'll make a start on assembling the last of the four rear wheels for my traction engines.

Andrew

Never assume anything, ask the supplier for confirmation.

The Crusader looks a competent machine. A mate of mine (who was a professional machinist) has the Warco equivalent, and he's pretty happy with it, although not as nice as the Harrison M300 he really wanted. He mentioned two issues. One, the Camlock system isn't always quite as slick as it ought to be. Two, if you remove the gap piece it is not guaranteed to go back in exactly the same place.

I have a M300 so it'll be interesting to compare the specifications, Crusader to M300, where they differ:

Centre height, swing over bed, swing in gap and between centres values are about 10% smaller

Length in gap is significantly larger than the M300

Slide travels are slightly less as you'd expect

Tailstock barrel diameter and travel are about 20% less

The Crusader has more spindle speeds but over a smaller range. I can't see the top end being a problem. I never run my M300 at top speed (2500rpm) due to the noise, but 67rpm at the bottom end may be a problem when screwcutting, depending upon the reaction time of the operator

Feed rates are a slightly narrower range, but not significant. On the M300 cross feeds are half the longitudinal feed, on the Crusader it's more like a quarter

Metric threads are over a smaller range, fine and coarse pitch threads missing

Imperial threads are missing some coarse tpi, which I suspect won't bother the OP

Module threads are very similar and DP threads over a wider range, although again I don't suppose these are relevant to the OP

It would be well worth asking for a detailed list of the threads that can be cut - as always the devil is in the detail

Leadscrew pitch is half that of the metric M300

The motor power is half that of the M300. Should be adequate for making small bushes, but not for hogging. I've stalled my M300 when roughing, so beware. It's not clear from the spec whether the Crusader has a 415V 3-phase motor, or whether the OP has 3-phase available.

The Crusader weighs not much more than half the M300

I think the Crusader should be more than capable of the jobs the OP has, but I'd check everything with the supplier rather than get surprises after purchase. Ask about saddle and slide locks - the M300 has them, and they work, does the Crusader? I believe the new price for a M300 is around £20k, so the Crusader s a lot of lathe for the money.

Andrew

The experts seem to differ on the causes of the Tacoma Narrows bridge collapse. I think the general view now is that the cause was aeroelastic flutter exciting a previously unknown torsional oscillation, as opposed to the more common vertical movements seen while the bridge was being built, and after opening. The torsional movement was enough to overload the structure, which was unusually narrow and shallow for the span.

Andrew

I agree with JB, it's a waste of time going round twice. The only thing you achieve is to wear the cutter. This a is 5DP gear in cast iron cut in one pass:

I'll admit that the setup is pretty rigid; the mill didn't even break sweat when the cut was applied.

For larger gears, say 1 or 2DP, then two passes were often used. One used to be able to get roughing cutters for these, and larger, size gears.

Andrew

That's because nothing exists that meets all the requirements. A new industrial lathe will meet the turning requirements, but will bust the budget and will not be portable. A far eastern lathe will meet budget and portability, but may not meet requirements to work out of the box and make turning a pleasure. Some issues may be:

Ease of chainging spindle speed and feedrates. Of course many new machines have variable speed drives, but the price to be paid is lack of torque at low speed. Will they take decent cuts on stainless steel at slow speeds? I don't know, but wouldn't want to find out after purchase.

Ease of changing chucks. To me fiddling with bolts each time would be unacceptable.

Simple locking of saddle, cross and top slides, with locks that work.

How is the tailstock clamped, nut or proper lever locking.

We have no indication of accuracy requirements, but I suspect that moving a lathe around would not be conducive to accurate work, say a thou or so, or 0.02mm.

The basic problem is that nothing exists that meets all the requirements of the OP. So the requirements need to change.

Andrew

I didn't hear Buncefield as we were on our way back from gliding in Northumberland. Although it didn't affect us we wondered why there were lots of signs on the A1 announcing that the M1 was closed. My mum in Bedford claimed she heard/felt something at about the right time.

I heard my first sonic boom a few years ago, at the time of the London Olympics. I was in the workshop and there was a loud boom followed by a smaller boom. The garage door visibly shock. We don't have mains gas in the street so I wondered whose oil or propane tank had gone up. Half the street were outside looking to see which house was a smoking ruin. I told my neighbour it sounded like a sonic boom. She was very dismissive, said she'd heard one before and this boom wasn't right. Then the BBC news announced that two Typhoons had been scrambled to intercept a non-communicating aircraft, and had broken the sound barrier on the way down to London. My neighbour had to eat humble pie!

Andrew

The sums are easy if you use Newtons law of universal gravitation. Assuming a mean distance of the moon to earth I make the force on a 8000kg object due to the moon to be 0.265N. Otherwise known as not a lot.

It's more likely that movement due to the weight of water has an effect. But two of the longest items to be turned, propeller shafts and gun barrels, would have been done in naval shipyards. So if there was a problem I would have thought it would be better known?

Andrew

Neat idea to use a drilling vice, but not a new concept. Similar items are available commercially:

Albeit not suitable for hobby size mills. If you overtighten the vice there is a chance of distorting, or even cracking, the table.

Andrew

0BA?

Andrew

I'm not going to spark the sterile debate about new far Eastern versus old Uk or US.

I suspect that the choice will be influenced by the threads you need to screwcut. Are they metric, imperial or both? And what range of pitches or tpi? Some smaller far Eastern lathes have a fairly limited range of threads that can be cut out of the box, compared to a more expensive industrial lathe. Of course extra threads can be cut by playing with change gears (possibly involving making extra gears) but presumably you're not equipped to make gears, or want to spend the time doing so?

Andrew

I made these square thread serial taps:

to make the nuts for the brake shafts on my traction engines:

After I'd made them I cut a trial thread in brass which was easy. In contrast the bronze I used for the actual nuts was a total PITA.

Andrew

Edited By Andrew Johnston on 27/11/2019 22:22:12

I'm glad you posted that. I was going to say that my local tool emporium stocked reamers by 0.01mm as that is what I remembered. But I thought some smartypants would rubbish the idea. So I didn't!

Andrew

It's a question of finding the right tool shop. Some will stock a range of undersize reamers around an imperial value. One of my local tool warehouses stocks reamers in 0.01mm increments around common imperial and metric values. So when I wanted some imperial machine reamers for 1/4" I bought 6.35mm and for 3/8" I bought 9.53mm. For 1/2" I bought 1/2", as it was cheaper than a 12.7mm reamer!

Andrew