The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)

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awemawson:
Having packed up the RA17 and ordered it's collection I could get back to the coolant isse.

Firstly, I seems that the hose that blew on it's barb fitting is 5/8" bore Not 1/2" as marked :bang: but was on a 1/2" barb, so not really surprising that that is the one that went first. I replaced the barb.

Secondly, as I was working out where to put a Pressure Relief Valve and what thread sizes I needed, I looked closely at the pump and guess what I found - a Pressure Relief Valve. It was screwed all the way in so at it's highest setting, but I don't know what pressure that corresponds to as it is un-calibrated.

I unscrewed the PRV as far as I dared so it is at a much lower setting and sure enough all works, and when the Washdown Gun is closed off you can hear the PRV working - so a result :thumbup:

Sometime I'll put a pressure gauge on it and see what pressure it opens at. The wash is noticeably less vigorous.

Pete.:
When I was working in the Dartford Tunnel cutting out the road deck we had trouble with those hoses bursting right next to the jubilee clips. We were using the fire mains as a water supply but right at the bottom of the tunnel the extra pressure was too much for the hoses, but only where the clips were. We changed the jubilees for double-ear oetiker clips and the problem went away. The theory was that when tightening the jubilees it was dragging the top layer of the reinforced hoses round and causing it to tear where the braid was moulded into the hose.

Ever since then I have always favoured using those o-clips instead of jubilees wherever I can.

Pete W.:
:offtopic: :offtopic: :offtopic:

Many years ago, when I lived in Romford, I organised a guided tour of the Dartford Tunnel. (It was before the bridge was built - the Dartford & Purfleet Joint Tunnel Undertaking was the power in charge then.)

As part of the tour, we were taken beneath the road deck in one of the bores. The whole tour was very interesting and the staff spared no effort to make the tour a success.

It's many years since I crossed the Thames there so I'm well out of date with developments. Pete, why were you removing the road deck? Temporary or permanent?

awemawson:
Now I'm starting to use this machine in earnest I decided it was time to check and adjust the turret alignment.

Knowing that the turret had been driven into the tail stock at some time in its history, making that big dent in the cover that I had to re-fabricate, it was unlikely to be 'spot on' .

Two things are necessary:

Firstly that the tool disk front face is at right angles to the spindle axis, and parallel to the X axis movement.

Secondly that the bore that accepts the VDI tool spigots is accurately in line with the spindle centre line when X = 0 . This measurement can be 'out' either as X=0 has been incorrectly set for movement up and down of the X axis slide, or more likely that the turret rotational alignment has shifted in a crash.

Today's job was to check and correct the tool disk parallelism. I decided to use my Tesa electronic DTI, as it has the advantage of being able to be set to increasing sensitivity as the process proceeds, and also to have a long enough cable to be positioned at the operators console from where I'm moving the X slide.

The turret is held on by three massive cap head screws at the top and also the bottom, the bottom ones requiring that I remove the power tooling drive cover to gain access.

Loosening the screws then setting them to 'just nipping' I then installed the Tesa DTI head on a magnetic clamp on the face of the spindle (having locked the spindle to prevent rotation). Sure enough there was quite a large discrepancy as the tip of the DTI moved across the face of the tool disk - I didn't take accurate measurements but it was of the order of 5 thou in 2 inches! Then much like you would align a vice on the table of a milling machine, it was a case of judicious tapping with a soft dead blow hammer aiming to rotate the turret on it's mounting face with the X axis slide. After several iterations I got the error down to about 1/10 thou in 2 inches. Tightening the clamp bolts increased this to 2/10 but that's where I left it.

To check the rotational location of the tool disk I need to rig a ground pin in one tool position and swing the DTI round it. The Tool Disk is bolted to the Hurth Coupling that actually fixes it, and it will be a case of slackening the bolts and a bit more iterative tapping !

If I can find a suitable pin, then that's possibly a job for this afternoon.

awemawson:
One step forwards and three back - it seems that my various adjustments to the turret position have disturbed something within, and the turret no longer indexes properly :bang:

The turret on indexing brings the tool disk forwards, thus disengaging the front Hirth coupling and engaging the rear one that then allows the servo motor to rotate the turret to it's new position. Once there the system drives the tool disk back onto the front Hirth coupling locking it in place. BUT, it is not reliably getting to the right place, so when the Hirth moves to engage, it's two parts don't mesh correctly leaving the tool disk forwards and the system locks up awaiting the 'turret locked' signal, which it never gets.

Now it's a complicated control system. The PLC requests a tool change from the Baldor SMCC servo card, which controls the turret motor and takes in inputs from the Optical Incremental Encoder that is mounted on the servo motor shaft. Within the turret there is an Index proximity switch telling the SMCC card where zero is. As far as I can tell the program in the SMCC card knows how many encoder counts it needs to move to the requested tool position and homes in on that.

Now previously I had thought that the four way proximity switch block (that also monitors tool position) was what was being read by the servo, but now I realise that it cannot be, as when the tool disk is moved forwards for rotation, so are the protrusions on the 'hedgehog' that the proximity switches sense and are out of range. These four proximity switches are a confirmation to the PLC that the SMCC card has done what it was asked to do!

So I've been doing tests this morning, having first removed all the sheet steel covers off the turret to gain access yet again :bang:

It turns out that the direction of rotation of the turret influences things, so going from tool 5 to tool 9 might work fine, but going from tool 9 to tool 5 will often give the error.

Things that could influence this are possibly a loose encoder coupling, or a bias offset on the servo system. Now currently getting at the encoder coupling to check its fixings is proving a problem. I'm guessing that there are one or two grub screws on each side of it, and there are screw capped holes to give access at both ends where I expect the screws to be, but the shaft of the motor needs turning to get at the screws, and the motor has a brake that is engaged with the power off. Head scratching time working out how to just power the brake, as it's too dangerous working with my head round the back of the turret if the main servo systems are alive :scratch:

It probably just needs a 24 volt supply to pull the brake off.

As for the servo offset, this harks back to something I thought I'd noticed months ago when I first got the turret semi-working, but I'm short of documentation on the Siemens Simodrive AC servo card.

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