Now the Headstock…

This is a big block of Aluminium – 150x200x100mm – I need a hole through the 100mm depth, 70mm diameter or so, so tried a hole saw – waste of time – just clogs up and takes forever. Drilling and boring out increasing each time was just too much, so I purchased an SDS drive concrete coring bit – 70mm OD. Turned a MT2 taper on the drive shaft ( very nice steel too, that drive shaft!) and sharpened the cemented carbide teeth on the core bit – gave them a good positive rake. Set up in the EMCO FB2 mill and drilled a core out the block – took 31 minutes…

SDS Coring bit – with taper machined on shaft

Teeth sharpened:

Front view of teeth:

Making the hole:

The cored piece..done from both sides – lots of chatter, etc..

Then boring out the hole and boring out for the bearings – rough bore first

The bearing boring had to be done from both sides, and I wanted the holes lined up to better than 0.005mm….

So a mill tramming took place, which is covered in Graham's FB2 thread – took 2 days with lots of effort – was worth it!

The idea then was to fit a locating boss to the table, which would snug up into the inner bore. fasten the block down to the table, bore the bearing hole out, and then rotate the block over 180deg, slip over the locating boss, and do the second bearing hole. The boss was made from a hard steel, polished, and 'just' fits in the inner bored hole – it is a real bugger to get the block down on it – cannot be slipped over even a little skew…

The boss:

The block slipped over the boss, and checking for center location before final boring of second bearing hole.

The headstock block bored out:

Bearings and spindle test fit:

Next up – Labyrinth seals…then the bed – in the shaper and more such fun..

More to come..

Joe

Martin,

You are quite correct – stupid idea – the remnant was still in my mind as I had thought of using toothed belts and pulleys originally, but decided against as that imparts unwanted vibration to the setup when run fast – ditched the idea but not the encoder location..I think that idea was flawed anyway, as even the toothed belts do move on the pulley when reversing, albeit slightly.

Kiwi – Bloke..

You know the old gauge-maker's trick of making a relief groove a little way along the gauge (=boss) – where the leading edge of the skewed block would try to dig in, as it binds?

No, I don't – please explain – I am keen to understand that – it seems like it can be a big help! It might not be evident in my photo, but that 'ridge' about 1/3 way down from the top surface of the gauge is the snug fit – the part above and below is 5-6 hundredths of a mm less, and then the 'ridge' is domed, like a torus with the peak diameter being the snug fit – gives some skew leniency, but not much!

Distance between bearings looks a bit mean, and drive belt between bearings might be preferable – albeit less convenient?

When you say 'mean' , do you mean close/narrow? The bearings are 40mm apart – that is narrow, but the bearing is also 90mm OD, so lots support in twist – also , its a 5C collet system, so there wont be any 100mm diameter workpiece in this lathe.. The headstock will be oil filled, bearings must run in oil for the speed, so belt down the center is hugely complicated..and I hope not needed!

John Haine,

Ok, now you have me going… I need to know a lot more about what you have said – it sounds very worth while, esp as I am making my best effort to make a very rigid, fast, and as accurate as possible a machine.. I can PM you, but would you mind if we discussed it here rather? Other folk may be interested and could learn something as well? And maybe it promotes further good ideas from participants as well!

The intent with this lathe is to make it a slant bed, with a tool changer, etc…So from the first rendered view I posted, the tool will sit on the cross slide table, away from the viewer – where is the better place for a hard contact reference? away from the viewer, ie, the rear of the cross slide?

Regarding Z reference to stock end – I am experimenting with a very low-impedance measuring device – basically an ohm-meter, with one contact on the headstock and one on the tool changer, which will then give some indeterminate reading ( 0.1ohm to 10ohm, who knows..-not important) and then detects the drop in resistance when the reference tool tip touches the stock. The ohm-meter is not conventional – its a synchronous detector looking at detection of a differential sinusoidal signal level, etc..capable of resolving a 2 milliohm change, between 10milliohms and 5 ohms.

Another thing I am looking at is a 27 hour day…( or more , if possible..)

Thank you to all for the kind comments – keep them coming – may help me make fewer stupid mistakes!

Joe

John, Thanks for all the photo's re homing/zero and tool setting sensors.

I am going to see how best to design in at this stage – maybe it ends up simpler that way!

The synchronous detector is worth pursuing – Basically a low level sine wave applied, say, to the tool and a sample of the same applied to a mixer. The second mixer input is from the contact point, ie, the setter in the chuck, and the signal then demodulated and detected for change – this is extended with a lock-in amplifier and can be very sensitive – reliable detection of contact can be with signals below AC mains noise , and other EMC, by 20dB or more…I am using an Analogue devices chip ADA2200 to trial and it looks good! If it works out, it means you can apply the excitation signal and sense point anywhere on any machine, without any electrical isolation of sensor, etc.

We will see..!

Now fighting Labyrinth seals – not easy getting the geometry correct, and even less easy machining the small and narrow tongues and grooves without CNC..

Joe

Some Progress on the lathe – Headstock is mostly done. Oil plug and breather hole still to do, and then pulley and collet closer..

The Lathe Concept slowly solidifying as well:

Exploded spindle with oil flinger rings and face flanges

Milling the headstock:

Drilling / Milling out the Face Flanges on the Automated Rotary table

Headstock parts ; Spindle, flingers and face flange ( seen from O ring oil seal side, below)

Assembled Headstock, collet end.

Test assembly Headstock, drive end.

More in a few weeks..

Joe

Another Installment…

Completed the ABZ Spindle Encoder assembly – using a magnetic encoder chip. The encoder is sat between the spindle drive belt, below the spindle assy in the above render.

Below the encoder parts – the toothed pully is 60mm diameter for scale reference.

Encoder partly assembled to test for fit before locktite of bearing.

Assembled Encoder – magnet shaft held in place with 3xM3 grub screws.

A similar pulley on the spindle shaft drives the pulley on the encoder in a 1:1 ratio.

Encoder chip on PCB, sits flipped in the cavity shown, chip over the magnet seen in the cavity.

Encoder gives 1024PPR, or 4096 edges, with an index.

Next up, the actual Lathe bed – bed is quite long, too long for my small Emco mill, and longer than the shaper stroke, so it was done in 2 halves on the shaper – that was interesting, to ensure ram alignment to the 1st half done…Judicious use of the dial gauge on the shaper Ram over its full stroke paid off – the finished bed has just been checked by a local Line-Boring company, on a granite table, and it would seem we are better than 0.01mm in width across the bed, and the sides are parallel to better than 0.01mm ! Blueing the bed flat top on the granite table showed contact over what looks like more than 95% of the flat surface. Some photos of the bed to follow in the next installment!

Flattening the bed top:

And then the sides:

Next up, the finished bed, and the bed base and mounting starts..

Joe

Not sure if I should start splitting the posts – would like to keep the build history in one place, but as I am visually vociferous the post becomes rather large…Will do what is suggested…

The Lathe bed turned out well, and the base framework is also started – The exercise now being to get the spindle motor positioned with regard to the drive belt, spindle, and motor tilt mechanism. The latter required as the motor will be fitted with a dual sheave pulley, one of 120mm OD and the step below , 80mm OD, giving max spindle RPM of 4000RPM and 2700RPM resp. I am hoping ( torque calcs indicate it is possible) that I will get away with just the 120mm pulley, and still have enough torque at low RPM's – sort of around 20RPM for some 'heavy' cuts.

the Motor specs 1PH and 3PH:

In the event that the smaller pulley is needed, the motor needs to be able to pivot to take up the belt slack, and the motor must slide back 20mm, to line the 80mm pulley up with the spindle pulley – this all to be a one lever movement exercise…

The motor is big for the lathe – 1.7KW @ 220VAC 1PH, and 2.9KW @ 230VAC 3PH.

It is a rather special motor – permanent Magnet rotor, and is actually a very high power closed loop 'stepper motor' dead silent in operation, no noise, no step feeling, etc. It is in essence a AC servo motor, driven by step and direction input. It is a closed loop control, with a 32000 count encoder.

The reason for using this motor is that it has full torque from 0 RPM and maintains the torque well up the RPM curve, esp if fed with 3Phase. In addition to driving the spindle for conventional turning, it serves as the lathe's C axis, with rotational position control capability to within 0.08 degrees, allowing use of live-tooling in the lathe to 'mill' the workpiece in the chuck ( Hex heads, High pitch 'threads' and anything else…) Holding torque is very high, so medium milling should be possible, and low speed toque is high, allowing full 'power' at low rpm's.

Below – The bed trial fitted to the base framework –

lots of effort went into straightening out the base frame after welding, all checked on a granite table..

The Lathe bed is as flat as the proverbial pancake, and once the base frame was straight, the lathe bed side supports were bolted to the bed, and then the side supports tacked onto the base frame. The welds were then tackled in short steps, alternating left/right and obliquely to help prevent the base frame from distorting. It Worked!

See how nice the bed shaped up!

The slides are 25mm square – nice and beefy..

Lots to do before the next post, so that may be in a good few weeks time!

Joe

Edited By Joseph Noci 1 on 24/12/2020 13:44:09

But you should, Michael! At least criticise a little – How else do I know where I am deluded in my doings??

Joe