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




awemawson:
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:
awemawson:
I was very fortunate recently in that I won for a modest sum a job lot of  VDI 40 tooling on eBay that included a Grippex Bar Puller.

Bar pullers are useful on a CNC lathe if doing repetitive work, in that you can automate the feed of the bar stock in the chuck between components. Advance the gripper over the bar, close it, grab the bar, release the chuck grip, pull bar out the length of the next component, close the chuck, release the gripper - all so nice and easy as it's automated  :thumbup:

Now this gripper sadly had one of it's hard steel 'talons' missing - never mind - spares still available for the not inconsiderable cost of £99 (inc postage and VAT) for a set of three - BUT you get the fixing screws AND an Allen key, so a bargain  :bang:

Biting my lip and remembering that these grippers cost £1400 new I shelled out my dosh and got the three spares.

Now I have a repetition job of 100 parts to do for a friend of a friend so time to mount it and play with some code. The gripper has a cylinder inside that can be operated by compressed air or coolant. No air service on this lathe so coolant it is. The sequence is, select the gripper, put it where you want it, turn the coolant on, do the pulling bit, then turn the coolant off again to release its grip.

Well, gripping works famously, but when the coolant is turned off it doesn't release. As the coolant is solenoid valve driven to the tool turret, coolant pressure is maintained in the line keeping the gripper firmly shut  :bang:

OK a modification is called for. Another solenoid valve working in anti-phase with the feed valve dumping pressure in the line to the sump. It would have been VERY easy if I could have sourced a 24 volt DC 1/2" BSP brass valve in a normally open configuration at a sensible price, but they are rare with the proper industrial ISO plug in connectors.

Never mind, use a normally closed valve, add a couple of lines to the PLC program to add another output for this valve in anti-phase to the feed valve and the job's a good 'un  :thumbup:

So valve and a few bits of plumbing have been ordered, and today I tweaked and tested the changes to the PLC program and now I'm just waiting for the bits to arrive .



AdeV:
A friend of mine is a CNC machinist by profession, I was talking about bar feeders to him one day, he said - don't bother... just turn up a piece of tube to be a 1 thou interference fit. Put a shallow taper in the front end just larger than your bar stock, so the end slips over. Now mount it in a toolholder. When you want to pull the bar; simply drive the tool onto the bar; release the chuck; pull the tool back the desired distance, close the chuck, then pull the tool off the bar... job done!

Obviously, you have to make one for every size of bar you want to pull; and it's no good if you need to pull something that's not plain bar; but it struck me as an elegant solution to the problem: Simple, cheap and reliable.

On the other hand... those grippers look cool!  :thumbup:
awemawson:
The Grippex gripper works on a large range of diameters and also will grip hex. I think mine covers 2 mm to 60 mm without adjustment.

There are parting tool holders that incorporate a push fit forked gripper that grabs the bar by pushing in the X direction rather than Z - their concept is quite clever in that usually you want to bar pull after parting off so this avoids an extra tool change and associated move to a safe place, but like your tube the range of sizes is severely limited.
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