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

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awemawson:
Quoting Steve:

"OTOH the end arm looks severely twisted on the pivot in photo 5, but I'm assuming that's a camera distortion."

Yes Steve that is mainly the camera angle compounded with the angle that the arm is set.

The worst case is swinging the weight (chuck) out of the lathe - the centre arm pivot has to fold to clear the door opening then unfold so that the upper arms are in line but pointing out of the enclosure. In this direction the bracing of the upright post to the base plate is at it's weakest, and I expected the base plate to twist, but any twist is very minimal probably due to the close proximity of the right hand hold down bolt.

awemawson:
So - this morning's task is to work out how to attach the chuck to the hoist not only safely, but also so that it can be manipulated when refitting with enough accuracy to get things aligned. There are two 'O' rings squashed between the chuck and the back plate conveying the hydraulic oil, and I imagine it would be very easy to knock them off during installation as they just sit in small recesses.

I had thought to make up a rope net sling but that probably would give too much stretch :scratch:

So I intended to roll up an encircling sheet metal strap that could be bolted up tightly incorporating a lifting eye, and thinking that if I could perhaps pick up an indentation in the chuck periphery (the jaws for instance) it would be more secure from slipping on the metal to metal contact of chuck to strap.

Rotating the chuck by hand, what do I see but two 'bungs' screwed in the periphery, both stamped "1/8 NPS", in what would be an excellent place to screw a plate with a central lifting eye. Taking them out they obviously block oil ways, probably an artefact of the manufacturing process but the length of thread is pretty short - are they strong enough? Now 1/8" NPS (an American pipe thread I believe) is 27 TPI and approximately 10 mm o/d. Getting out my Imperial thread gauge to check that it IS 27 TPI I find that there is no 27 TPI blade, but there are two 26 TPI blades! This is a Moore and Wright No 800 thread gauge that I bought brand new when I was at school - I remember drooling over the tool shop window and convincing myself that I NEEDED that thread gauge set ! Now it just so happened that I acquired a second No 800 M&W thread gauges set in a job lot of tools last year, getting it out it didn't have 27 tpi going straight from 26 tpi to 28 tpi. ! However it DOES have a 25 TPI blade not in the other set !

Back to the chuck. Continuing rotating it by hand what do I find but ANOTHER bung about 180 degrees from the others, this time marked "1/2 UNC" - much more promising. Taking it out there is quite a long length of female thread and 1/2" UNC is reasonably strong - should be good to dangle 47 kgs off (I hope) BUT the position of the thread in the periphery of the chuck is far to far forward to be the centre of balance. However, on the face of the chuck in the same rotational alignment is another threaded hole that turns out to be 3/8" UNC. If I can make a stout bracket that is fixed by these two threaded holes, but extends further back to where I think the centre of balance is more likely to be, I maybe have a winner, and this will be far more secure than a strap wrapped round (I Hope)

. . . . Off to hunt for heavy section large angle iron !

awemawson:
My hunt for a bit of suitable heavy angle iron drew a blank - nothing with long enough webs - so I decided to bolt one together using some 1-1/8" square bar from the scrap bin.

Simple bit of cutting, guesstimate marking out, drilling and tapping - all went well except for breaking a brand new 3/8 UNC taper tap :bugeye:

. . . Why ? because I forgot when power tapping that the new motor on my Bridgeport hasn't got slow forwards and slow reverse next to each other on the rotary switch, it's slow forward and fast forwards !!!!!!!

All seems to fit nicely - I've stolen a 5/8 UNC lifting eye from the Eurospark sinker EDM for the present. It's skirt fouls the 1/2" UNC top fixing bolt so I'll have to make a stand off fat washer for it to screw down onto. But that's a job for tomorrow.

Of course I don't know that where I've put the lifting eye is on the centre of balance, but it's nearer to it than the single 1/2" UNC tapped hole.

awemawson:
Now that (theoretically!) I can lift the heavy chuck off there are a few steps that I need to accomplish first:

I have to decide what media I will use for test cuts of the A2-6 and A2-5 chuck registers - cast aluminium blank or machinable wax

I have to recess a set of jaws to grip the 170 mm blank, both the test ones and the final work

I have to draw up the profiles of the A2-6 and A2-5 spindle / chuck registers in FeatureCAM

So to help me decide what media to use I did some experimental turning with machinable wax from my stash - this is some that I made years ago and it's been maturing in a cupboard. The swarf that comes off tends to be long and stringy - on a manual lathe I can sucessfully hoover it up as it comes off by holding the suction nozzle to the lathe tool, but that's hardly possible on the CNC lathe So I turned both sides of a smaller puck that I had already cast and did some experiments. Yes it hoovers up nicely with the workshop vacuum cleaner. Why is this so important? - Well I suspect that if left in contact with the oils from way lubrication, and residuals that are in the enclose, it will make a sticky goo that could well block the various distribution pipes.

Now if I'm using M/W do I cut a blank from a slab that I have that is a bit thin (but it's only the faces that I'm interested in) or do I cast a custom blank from a rolled up mould. This stuff does take quite a while to get to moulding temperature as it has to have a very gentle heat, so I'll probably try with what I have to hand.

To cast a blank in aluminium would eliminate the 'sticky goo' issue but there's quite a volume to that blank and again a session of mould making would be needed.

So first off M/W it is !

tom osselton:
Nice stash of wax! Is there a recipe? :drool:

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