Member postings for Andrew Johnston

Some points to note:

1. Lathes are top heavy, and if they fall off a pallet truck or trolley you're not going to stop them. If the driver can't, or won't, deliver to the door then there are a couple of choices. One, use scaffold poles and plenty of them. Two, looks like a farming area so can you borrow a JCB or similar? My comparable size lathe has a threaded hole in one of the bed cross members for a screw in eye for lifting.

2. Can you take the splashback off to get through the door without needing major surgery?

3. Once in the workshop you can inch it round using a pry bar and then small rollers to move into place. I've moved a 2 ton mill around in my workshop with a pry bar and short lengths of 3/4" aluminium rod.

Andrew

How can you do a phase comparison if the voltage measurement is DC?

All the smartmeter ICs I've used have measured voltage and current as AC signals.

Andrew

It's just one of the great model engineering myths.

Nick: Compound slide is the same as the top slide; the slide on top of the cross slide than can be swivelled for taper turning or screwcutting.

I've just had a quick look at the rear wheel hubs for my traction engines, which were bored in the lathe:

Tool is a Glanze 16mm boring bar and stick out is around 130mm. I measured both ends and as near as I can tell both readings are 1.629". I don't see why only measuring at both ends should lead to assumptions of tapering. Apart from a very short lead at the start the bore ought to be parallel, if the tool is being moved parallel, as the cutting forces should stay constant.

Andrew

It's all done in an integrated curcuit (IC). Voltage measurement is straightforward, simply a potential divider across live and neutral. Current measurement is done using a current transformer. These are a toroid with a multi-turn secondary. The primary, carrying the current to be measured, is a single wire through the centre of the toroid. A load resistor (usually a few tens of ohms) is connected across the secondary. The current in the load resistor is equal to the primary current divided by the number of turns on the secondary. The current transformer also provides isolation. Voltage and current are read by an analogue to digital converter many times a second. The IC can then calculate power factor, VA, real power and reactive power as well as kWh used. They're much more capable than the old electromechanical meters and, just as important, cheaper to make.

It's also easy to add comms so that the power companies can do you over without you knowing.

Andrew

Exactly, before rushing off to use a boring head the question that should be asked, and resolved, is why the bore is tapered when using the lathe? A difference of 0.2mm is huge. I might expect a thou or two difference due to tool spring, but no more, and after a couple of spring passes you should be able to achieve well under a thou. Tool spring should stay pretty constant throughout the cut, so I suspect the taper is caused by something else. Like feeding with the top slide when it is not set parallel to the lathe axis?

Andrew

I don't recall the SO239 being used much above a couple of hundred MHz due to non-constant impedance through the connector. Above 300MHz we used BNC and SMA, or waveguides!

Although the SO239 is labelled as a UHF connector apparently that is because it was developed in the 1930s when UHF meant over 30MHz, not the modern definition of UHF as 300MHz to 3GHz.

Andrew

I use Hysol XF from Castrol as flood coolant on multiple machines. As said above, when the water evaporates it leaves an oily film. There's one caveat, I've only seen surface rust on the lathe when I've let the concentration fall too low. Every time I top up the coolant I check the concentration with a refractometer and adjust as necessary. I generally run at around 7-8% concentation, in the middle of the manufacturer recommendations for turning and milling and the upper end for grinding.

Andrew

Been there, done that. Trying to fix an open frame contactor on the repetition lathe I got frustrated when it still chattered after the second disassembly and clean. So I took it apart for the third time - and then discovered I hadn't disconnected the 3-phase supply.

The switch on my M300 is still going after 40+years although it's possible that old age could be the cause of the failure. I doubt the problem is condensation. My lathe is in an unheated garage and condensation can be an issue in terms of flash rusting, but never had a problem with the 3-phase supply. I don't see why the converter should have had an effect either. Technically the item is a disconnector and isn't intended to make or break large currents like a switch.

The item no longer seems to be manufactured. My first port of call would be Harrison, although you'll need to sit down before getting a price. Alternatively it shouldn't be difficult to find an appropriately rated alternative.

Andrew

Too right, and triple check clearances at all positions of the saddle and slides before starting the spindle. Faceplates are really good for castings. In some cases mounting is simple:

But in other cases some ingenuity is needed, plus change gears for balance:

I'd agree with Hopper that it's a lot easier to initially mount the work with the faceplate horizontal. But I'd add a caveat. Make sure you know how you're going to lift the faceplate/work onto the spindle. The flywheel in the first picture was mounted with the faceplate horizontal on a wooden board on the lathe bed next to the spindle. But it was still an awkward lift onto the Camlock spindle. To the extent that I did myself a mischief resulting in one side of my body going numb and losing all feeling. Fortunately it went off after an hour or two. In retrospect I should have thought more carefully about the lifting. The faceplate is 18" diameter so the whole caboodle weighed 30kg or more.

Andrew

Edited By Andrew Johnston on 19/05/2021 11:19:30

Yuk! Depends what type of stainless, but most likely austenitic, ie, the 3xx series. Of these 303 and 316 are easy to machine although 316 has a propensity to work harden, but avoid 304 as it's 'orrid stuff. For tapping in stainless steel I drop the thread engagement to nearer 50%, so that gives 8.9mm for 3/8" UNF and 15.3mm for 5/8" UNEF. For external I'd definitely screwcut. But if dies must be used then ensure that the die is rigidly aligned with the work, at least to start with. Trying to start a die by hand in stainless steel is a receipe for disaster, or at least wonky threads.

The SO239 connectors are a blast from the past, must be 40 odd years since I've used one.

Andrew

The threads need to be better specified as does the material being used. I'd guess that the 3/8" thread is UNF and the 5/8" thread is UNEF and the material is brass?

For 3/8" UNF I'd be drilling 8.70mm giving a thread depth of about 70%. For 5/8" UNEF the minor diameter is 0.5799", giving a thread depth of 0.0226". For 70% thread engagement I'd drill 15.1mm.

For external threads I prefer to screwcut in the lathe, but you are correct that the nominal OD of the threads is 3/8" and 5/8" respectively. Barstock is normally a thou or two undersize which helps the die to cut.

Andrew (G8IUV)

Ok, I'd drop the speed to 250rpm and feed to 0.06mm per rev and use flood coolant.

Andrew

Depends what material you're cutting. For brass I'd be running at 500rpm and 0.1mm/rev and I wouldn't peck. Essentially the D-bit is a single flute reamer. You want to go in and out in one smooth movement with no faffing about.

Andrew

I made some tenons for my dividing head and tailstock, but I don't use tenons on the machine vice (although the slots are pre-machined) for three reasons. One, when not in use the machine vice often sits lengthwise on one of the other mills and I don't want to ding the table/tenons. Two, sometimes I need to set the vice at an odd angle. Three, the T-slots vary in width slightly across each table and from mill to mill, so I'd rather set the vice properly each time to eliminate the last couple of thou.

Andrew

I bolt down as the work is often on parallels, so I can drill through, and the cylinders would tilt when the work is tapped into contact:

Mid left above is a third cylinder, of a different size, used as a stop. I forgot that I made two short cylinders, mostly for stops on the CNC mill, but also used to align parts on the manual mill, see bottom right:

Andrew

For aligning the machine vice I set it roughly parallel using the bolt slots and a T-slot. Nip down the lefthand bolt and then indicate the rear of the fixed jaw. If the indicator moves tap the vice to bring the indicator back to the original reading. Repeat as needed. Tighten both bolts and do a sanity check pass. The whole operation takes less than minute to get within 1 thou in 6".

For aligning parts on the table I use two methods. One, a length of gauge plate in the T-slot as a fence. Two, I made a couple of cylinders with spigots that are a close fit in the T-slots. These can then be bolted as far apart as needed. The two cylinders were ground as a pair, so they are within a tenth of each other. My mill is industrial, so the T-slot is aligned with the ways. The methods don't work if the T-slots and ways are not aligned.

Andrew

..............I do have a level, does that make me weird?

No, but using the level across the tops of the prismatic guides doesn't tell you anything useful, as those surfaces play no part in controlling how the saddle moves, which is what you're really interested in. In addition the saddle is controlled by one prismatic guide, not by both.

Andrew

Not really, it depends upon the lathe. My secondhand lathe came bolted to the manufacturers cabinet. Early on I had issues with it turning tapered at the headstock, although strangely not when boring. The consensus on the internet was that it was a bad idea to fiddle with the lathe to cabinet bolts. Instead I spent ages shimming and fiddling with the cabinet bolt down points to no avail. In the end it turned out (just like Hopper mentioned above) that I hadn't been careful enough when replacing the gap piece. Having triple cleaned the gap piece and refitted it according to the instructions I loosened all the hold down bolts and just let the lathe sit on the concrete floor. The lathe now turns parallel to a couple of tenths at the tailstock and a thou or so at the headstock. Not bad for a lathe that is over 40 years old and is unshimmed.

Andrew

Mine was bought new, by me, some years ago and has definitely had very light use. The spindle is pretty loose, easily 20 thou. It's better if you hold the arm, but still a good few thou. Doesn't seem to affect it, so I assume it's normal.

Andrew

There is no right or wrong way to show prices. Generally consumer sites show VAT inclusive prices, since consumers are interested in the overall price they will pay. Sites aimed at business users generally show VAT exclusive prices as most businesses will be VAT registered and will offset the VAT paid out against VAT charged, so the net cost of an item is VAT exclusive. Shipping is usually plus VAT.

Andrew