Author Topic: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)  (Read 48441 times)

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #850 on: June 04, 2019, 10:11:43 AM »
It was at this stage that I dug out my 'soft jaw clamping fixture' that I  had bought for similar service on the Traub lathe, only to find it was dinky compared to what was needed. I had been sure that it would work, but the difference between a 10" and a 6" chuck is rather a lot !

So what to do  :scratch: I could make something up for this one size, but this is going to be an ongoing requirement as jaws are changed in the future. Better to bite the bullet and get the right thing. A bit of ringing around  for best price set the dealers into a flutter, as behind the scene it turns out that they were ringing each other to see who had stock. Rotagrip won the day, and then minutes after I placed the order Cromwell Tools rang me back to say that their supplier had just sold their last one, and they were now on 8 weeks delivery. Yes says I, I just bought it  :lol:

Excellent next day delivery, so the clamp ring arrived this morning by Adrian with ParcelForce.

Now the theory is that you adjust the ring to such a size that the hydraulic chuck jaws bear down on it via pegs that go into the counter bores for the jaw mounting screws and it ends up clamped with a bit of 'meat' for you to bore out with a boring bar. It's actually quite a job juggling it, holding it in place, and operating the 'chuck close' button that is a fair distance away from the chuck.

It was at this stage I found that as these were new jaws and still fairly long, the clamping ring at its extreme would not clamp  :bang:

A bit of head scratching showed that as the clamp pegs are 18.5 mm and the chuck jaw counterbores are 25 mm, the slack was the problem. Quick solution, turn up some collars to slip over the pegs and sure enough we now have the correct travel to clamp, but we also have a pile of bits to hold in place at once while pressing that button, arm outstretched. Flying to my aid came some rare earth magnets, that not only held the collars on, but nicely held the clamp ring against the chuck jaws  :clap:
« Last Edit: June 04, 2019, 10:39:00 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #851 on: June 04, 2019, 10:30:26 AM »
So at long last boring could commence  :thumbup:

I'd turned up a plug gauge on the manual lathe with 24.5 and 25 mm diameters, as this boring was going to have to be done the old fashioned way - cut - measure - cut again. (The boring bar hasn't been measured and put in the tool offset table yet!)

So, cut a bit, measure, cut again measure with the bore gauge, get a finish depth of cut a whip it off. I used the jog facility and MPG rather than a program as the tool disk gets rather close to the chuck jaws as I wanted to minimise tool overhang.

. . . so what should have taken a couple of hours took a couple of days !
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #852 on: June 11, 2019, 06:48:38 AM »
Some of you may recall that I went to great efforts to mount a Renishaw MP12 probe, only to find that it's optics looked in the wrong direction being intended for a milling machine not a lathe.

I did an experiment with transmission through glass that proved that the IR wavelength used would pass, so ordered some prisms off eBay that have been on a slow boat from China, hoping to turn the beam through 90 degrees.

Well the boat has docked at last and would actually appear to have come from Malaysia. I had ordered four prisms, knowing that two would when joined cover the width of the optical window in the probe, and the others could be spares. Just as well, as two of them were chipped. Frankly unlikely to affect the passage of the IR much, just unsightly.

So experimenting with the two chipped ones - not worth sending them back at the price they were(n't) - I super-glued them together with  the smallest drop that I could decant, then fixed them temporarily to the MP12 with a tiny dab of hot melt glue that will be easy to remove without damage to the probe.

Lo and behold - they WORK  :clap: Now I just need to devise a more robust method of retaining them on the MP12 probe that looks less crude than the experimental set up - but definitely a success  :thumbup:

Andrew Mawson
East Sussex

Offline nrml

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #853 on: June 11, 2019, 08:47:55 AM »
A sung fitting 3D printed sleeve to go around the probe with a suitable mounting point for the prisms would do the trick.

Offline AdeV

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #854 on: June 11, 2019, 12:39:07 PM »
Lo and behold - they WORK  :clap: Now I just need to devise a more robust method of retaining them on the MP12 probe that looks less crude than the experimental set up - but definitely a success  :thumbup:

Something vacuum formed, perhaps?  :D
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
Skype: adev73

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #855 on: June 12, 2019, 09:23:00 AM »
Having had all the problems reaching over manually opening and closing the chuck to fit the jaw boring spider when I wanted to bore some soft jaws I went hunting for solutions.

Most commercial CNC lathes would have foot pedals to open and close the chuck so why not retro-fit some  :ddb:

I went hunting for spare digital inputs and some way of intercepting the drive to the 'open' and 'close' solenoids and drew up a simple schematic - it didn't even need any alterations to the PLC.

So, going to the termination strip for my selected input I was very surprised to find a wire already attached - it wasn't spare after all  :bang: So, attaching my 'tone tracer' to the wire I traced it all the way to the front hydraulic cabinet under the headstock and thence on to a socket on the side of the box that I'd never before noticed. Now this socket also has a double below it, and they are JUST where I would have put sockets for foot pedals . . . you don't suppose . . . no surely not . . . YES looking through the PLC code and relating it to the wiring diagram they are for foot pedals for the chuck and for the tailstock - whoopee  :clap: :clap:

Looking at the PLC code they both act on an already energised item - so if the tailstock barrel is pushed forward the foot switch will withdraw it until you take your foot off, where in it returns extended. Similarly a closed chuck will start to slowly open when your foot is depressed, and start closing when you take your foot off. EXCELLENT  :clap:

So I ordered up the appropriate connectors and a pair of sturdy foot switches and the later arrived at lunch time. OK cable them up and test them !

The foot switches are I think excellent value - cast aluminium with a proper heavy duty micro-switch. My only criticism of them is the cable management. The entry was a plain bush and a flimsy bent metal 'C' shaped clamp, but easily replaced by a proper cable restraint gland, and it's not so easy to route the cables so that they are not flexed each time the pedal is pressed, but it is possible.

OK Wired up, plugged in and tested - all works  :thumbup:




« Last Edit: June 12, 2019, 11:13:13 AM by awemawson »
Andrew Mawson
East Sussex

Offline awemawson

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Re: The Sequel - Oh Blimey I bought a CNC Lathe (Beaver TC 20)
« Reply #856 on: July 03, 2019, 05:28:24 AM »
I've been doing quite a bit of work recently with 1" and 25 mm bar stock, and not been able to use long pieces for fear of it whipping when run at speed. The solution to this is a 'spindle liner' to reduce the internal bore of the spindle to a reasonably snug fit around the stock thus preventing whip.

So I decided to print up three 'Pucks' on my 3D printer with an o/d of a tad under the 66 mm spindle bore, an i/d of a tad over 25 mm for the stock, with counter bores to receive two spacers made from domestic ABS waste water pipe. As the pucks were printed in ABS this made the gluing together simpler as I could just paint the bits with acetone.

I designed the puck with an outer groove to receive an 'O Ring' to give a bit of friction to discourage 'walk out' and hopefully prevent it rattling too much. Not having the correct O rings I glued some up using O ring cord.

In the event the cord was a bit too fat and prevented the pucks entering the  spindle bore so I will order up some slimmer ones, but in the mean time I did a full speed test working up from 500 rpm to 3500 and in practice there wasn't a 'walk out' tendency, but I shall still fit those smaller O rings when they arrive.

One side benefit was the ease of inserting a 4 foot long bar that was already aligned by the pucks to side between the chuck jaws :thumbup:
Andrew Mawson
East Sussex