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

[Spurry]

I'm beginning to see why every good home should have a cnc plasma cutter.

[awemawson]

Oh yes, those upper pivots would be a right pain to do by hand, whereas they took about 45 minutes including drawing up in Autocad and steaming up the machine. (cutting time maybe 2 minutes !)

[Spurry]

An old friend, now deceased, bought me some labels for my machines, with EGHSO engraved thereon. "So what's Eggerso?", I asked. "Every Good Home Should Have One", he replied.

[awemawson]

I was wrong - that weight is only 20 kg not 56 lbs - but close! I added a second, and although the winch has no problem lifting the 40 kg (which is close enough to the 47 kg of the chuck for test purpose) it is of course still chewing it's gears. The worm is a two start one, and at 6 o'clock and 12 o'clock on the handle you can feel the starts of the worm hobbing the gear to shape 

I cut a pair of angle fillets for the main mast fore and aft (Z axis) reinforcement but there's not much room to add anything more to the abeam (X axis) direction. I think I'll weld together what I have and see how much flexing that I get, as I'm concerned that the whole thing is getting pretty heavy. Make it too heavy and it defeats the object of having  it !

To stop the base twisting I have both 3" and 4" box profile that I could weld on underneath, but it's the weight issue. If the twisting is too great I 'could' add a detachable outrigger resting on the floor 

No welding today - I have a fencer working and it's amazing how often he needs words. I've already straightened his Eastwing hammer on the 60 ton press  )

[mattinker]

Andrew,

How smooth is the worm? That's what's going to determine how long it lasts!

Cheers, Matthew

[awemawson]

Matthew, visually it looks OK but it's not the easiest of things to get a good view of. Once the start of the worm has meshed it feels pretty smooth, it's just the initial graunch as the start enters the spur gear.

I presume I'm right in thinking that even though the spur gear is canted over at an angle (lead angle of the worm?) a straight cut involute without crowning cannot be an exact fit, just an approximation, needing scallops out of the centre of the tooth width that use is generating 

Gear experts please comment !

[Spurry]

By no means an expert, but on a recent job, the gear definitely had hollowed teeth. Pic attached when trying to work out how to locate their respective centres.
Pete

[awemawson]

Now those (nylon?) teeth are cut at an angle to avoid canting the shaft but that's exactly the scalloping that my gear will end up with after not very long !

[WeldingRod]

Worm gear sets come in regular (what you have), single, and double enveloping.
Non enveloping has straight wheel teeth but with a spiral angle.  Single is when the wheel is grooved and the teeth are shaped into a curve: you can hob to get there.  Double enveloping has an hourglass shaped worm and a shaped wheel.  Load capacity goes up with number of envelopes.

You probably need to deburr the worm ends.  Also, the end of the worm should not be touching the wheel's teeth.  It may be installed in the wrong axial location.

If you want to wear.it.in, I would start with lower load or no load and wash the chips out regularly.  Might feed it some pumice mixed into grease.

Sent from my SM-G892A using Tapatalk

[Pete.]

Matthew, visually it looks OK but it's not the easiest of things to get a good view of. Once the start of the worm has meshed it feels pretty smooth, it's just the initial graunch as the start enters the spur gear.

I presume I'm right in thinking that even though the spur gear is canted over at an angle (lead angle of the worm?) a straight cut involute without crowning cannot be an exact fit, just an approximation, needing scallops out of the centre of the tooth width that use is generating 

Gear experts please comment !

It can be either way but the scalloped arrangemet gives more tooth engagement. The bigger problem as I see it is that the worm starts are engaging with the gear. That says to me that the worm is too short because the start of the worm should never be in engagement. Perhaps the worm can be moved along with spacers to move the end of the worm away from the gear centrline on the loaded side?

[vtsteam]

Cranking the handle there was an alarming graunching noise in a couple of places, and examining the gear on the handle shaft there is already visible wear and it looks horribly as though it's made from aluminium alloy - surely not 

Is it?

[awemawson]

Thanks for that Pete. Yes the worm is far too short and being welded to the spool shaft assembly cannot be moved. It'll just have to wear to it's comfort zone !

So today I welded the crane components together. I consider myself an 'occasional good welder' in the sense that occasionally I can do a good weld  But not consistently, especially on something like this with loads of 'out of position' welds. They are certainly strong enough, just not as pretty as I'd like! The box section is galvanised and I'd thought I'd ground off the zinc where I was welding, but it is obviously much thicker than I thought as it was popping and flaring at times.

Not cleaned anything up just now, I wanted to evaluate it on the lathe and see how much twist there is when lifting those two 20 kg weights. Answer surprisingly little  I'll sleep on it but at the moment I don't think that it needs further ribs below the  base though I have cut a pair of 60 mm diameter fat washers for the 30 mm holding down bolts to spread the load a bit.

I was able to lift the pair of weights - totalling 40 kg - without any alarming bends or creaking so at the moment I'm thinking just to clean it up, dress the welds, and move on.

The 60 mm thick slice of 170 mm EN24T has arrived to make the chuck adaptor so there's work to do !

[awemawson]

Steve, scratching the gear with a scriber I suspect that it is mild steel.

[vtsteam]

Andrew, it the worm is harder than the wheel and the lead-in of the worm isn't properly relieved and deburred, they won't wear together, the wheel will just keep being cut. Is the start of the worm relieved?

[Sea.dog]

I'm not sure that I'd like to hang those weights on that arrangement, at least not for very long.
I'd feel a lot happier with a double beam at the post end, one above, and one below the pivoting arm.

[vtsteam]

How would length of time matter? Also, the consequence of yielding doesn't look dire. If there was an issue it would, at worst sag.

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

[vtsteam]

Maybe the twist is real? There's not a lot of bearing surface between two square tubes because of their radiused corners.

In that case I'd get rid of the single bolt top pivot, then weld ears, top and bottom, on the main arm, and fit the swing arm between the ears and bolt/pivot through.

Similar to how you did the main post pivot. You can leave the swing arm longer inside the ears (for more bearing surface) if you don't cut off the arm square, but cut an arc with the pivot-end radius for closer clearance.

[vtsteam]

One other way of adding swing arm bearing surface would be to locate the swing arm pivot at the back (right side) of the main arm instead of the center, since the swing arm will mainly be used off to the left side. That would give twice the bearing surface of a center bolt plus more than twice the resisting lever arm.

[mattinker]

I think you'll see whether you need to modify in use! I think we all would have made our own versions! it works!

Cheers, Matthew

[awemawson]

It's surprisingly rigid, the main sag being from me having to slightly loosen the pivot bolt to be able to swing it. I may put a brass or PTFE shim between them to let it still move when a bit tighter.

This crane is probably only going to be used half a dozen times, mostly while machining the chuck registers on both sides of that billet of EN24T - it's not as though I'll be changing chucks every day !


. . . but thanks for your concerns - I certainly don't want to drop the 3 jaw - that's a beast of a chunk of expensive steel

[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

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 

 . . . 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?