Hello Guest it is July 20, 2019, 04:51:13 PM

Author Topic: BT30 spindle from scratch - with power drawbar and ATC of course  (Read 402209 times)

0 Members and 1 Guest are viewing this topic.

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #60 on: August 22, 2012, 06:31:21 AM »
Ha ha now that is naughty, editing quotes ;D

My PLC is a Koyo DL06 and I programme it with the graphical  ladder logic which I find very easy compared to script.
My solenoid can only act if the PLC is getting a zero speed signal from the spindle drive so it is partly hardware and partly software I suppose. Drive and PLC ladder being the software, drive output/plc input and relay output from the PLC being the hardware. I dont have it via Mach at all as I dont have an ATC so my drawbar is just via a button on the panel, that may change in the future if I get time to servo the knee or even better pick up a decent bedmill :)

The Spindles Enable is also via a switch on the panel which goes to the PLC. If the PLC is seeing that the draw bars relay is active then it will not pass the spindle enable signal to the drive.

If I rotate the spindle by hand when the drawbar is active it will drop out the solenoid right away, not that that is really any use but it shows the ladder is working as it should :)




Hood

Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #61 on: August 22, 2012, 10:36:09 AM »
Ha ha now that is naughty, editing quotes ;D
The Devil made me do it!     Actually it was the spell checker and an itchy trigger finger. Why the spell checker looks at quotes is something of a mystery.

Quote

My PLC is a Koyo DL06 and I programme it with the graphical  ladder logic which I find very easy compared to script.
My solenoid can only act if the PLC is getting a zero speed signal from the spindle drive so it is partly hardware and partly software I suppose. Drive and PLC ladder being the software, drive output/plc input and relay output from the PLC being the hardware. I dont have it via Mach at all as I dont have an ATC so my drawbar is just via a button on the panel, that may change in the future if I get time to servo the knee or even better pick up a decent bedmill :)
This is the type of thing I am looking to protect against; accidentally hitting a button, MACH or the PC misbehaving. I have a pneumatic lock on both the 4th axis and the spindle and when things go awry, sometimes I hear the familiar 'pop pop' which is harmless in this case, but would not be if the 'pop' was the drawbar releasing a tool. I plan to have the interlocks that you have wisely included on your mill and also have  . . .  uh . . I'll call it a 'lock' to differentiate from 'enable'. The lock will be engaged at all times via spring load. This will be a mechanical interference which will physically prevent the cylinder from contacting the drawbar. It will have to be retracted vie electric solenoid before the drawbar can be released.

The sequence will probably be something like:
*receive tool change command from MACH (or manual override)
*wait for spindle to stop rotating
* - - - 'disable' - - drive. This is a topic in itself, and could be:
  - engage spindle lock, disable drive
      - or-
 - leave drive enabled to hold spindle position and disconnect (via swapaxis board) the step stream so that the drive will not rotate
   
*enable Drawbar
*check sensors (including drive outputs - zero speed or equiv), drawbar position, and whatever else might be a good idea to check
*return tool
*sensor check - is tool in correct position?
*retract Drawbar safety lock
*release tool
*position commanded tool
*check elevations (Z axis or carousel) - is spindle nose all the way on the tool?
*grab tool
*Sensor check - is drawbar in correct position for a seated adapter?
*extend drawbar safety lock


Quote
The Spindles Enable is also via a switch on the panel which goes to the PLC. If the PLC is seeing that the draw bars relay is active then it will not pass the spindle enable signal to the drive.
If I rotate the spindle by hand when the drawbar is active it will drop out the solenoid right away, not that that is really any use but it shows the ladder is working as it should :)
From this I assume that your drive is disabled during a tool change? You press a panel button to disable the drive, then press another panel button to activate the (Pneumatic?) drawbar release, presumably while physically holding the adapter by hand? Swap tools manually, lining up the drive dogs by eye,  and then press a panel button to grab the new tool?

If I have that right, then I think this is also what Ray does with his new motor driven drawbar setup. Adding the ATC removes the human supervision that you have now. I'm just wondering what methods people use (or think about using) to replace the operator's eyes and good judgement when automating this particular process since it is potentially extremely dangerous. It will be a lot easier to incorporate in the design than to go back and add later.



Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #62 on: August 22, 2012, 10:50:43 AM »
When I press the drawbar button it automatically takes the enable away from the spindle drive so only one button needed to press.
The Spindle disable button is just used when I have my hands in about the work for any reason, have the same on the lathe. Both have brakes on the spindles and this unlocks the brake as well.
Drawbar is air over oil.
Hood
« Last Edit: August 22, 2012, 10:56:25 AM by Hood »

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #63 on: August 22, 2012, 10:55:39 AM »
Oh and if I ever get round to putting a servo on the knee and building an ATC then I will just use the homing feature of my drive to locate the spindle but if the drive didnt support that it would be easy enough just to home to an opto for me.
Hood

Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #64 on: August 22, 2012, 01:23:11 PM »
No surprise that your setup seems well thought out for a manual change power draw bar. Did you build it or did it come with?

Is your spindle motor a direct 1:1 drive or is there a reduction?

It seems to me that anything other than 1:1  1:2 or 2:1 would defeat the drive's homing as the spindle would stop at a random spot when the motor homed. My current temporary mill has odd ratios on the dual range head. I suppose they made sense at the time, but at this point  ???.  I will need to use the opto which is still there left over from tach duty quite some time ago.

For the new mill I am thinking about doing a 1:2 and 2:1 ratios for low and high. In this scheme, the motor can home on the encoder index and the tool will always be at the correct azimuth.  Those ratios would also provide a nice low range for big drills and big taps and about 7K max spindle speed.

How is the knee related to the ATC? Would you mount the tool holders on the table?

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #65 on: August 22, 2012, 01:44:51 PM »
The power drawbar was standard on the Beaver mills, the later ones than mine were single action intensifiers where mine was a bang bang type. It needed five or six pulses to get enough to release the tool and it took 3 or 4 seconds. I got a bigger intensifier from a friend and now mine is single acting and releases the tool in well under a second.
 I have an 8Kw servo on the spindle so I could have increased the speed, in fact I did at first but there is a gearbox that is to change between 1:1 and 10:1 ratios for main and  back gear. The gearbox didnt sound happy at the higher revs so I just put it back 1:1 on the pulley. I am thinking on the hoof here, the drive can be set to move any amount of encoder counts off of the index after homing so likely I could work out the amount needed even if I had a weird reduction ratio.
 Regarding the ATC, I would want the knee as an axis so I could drop the work well out the way so I could swing in a carousel or maybe even some form of dual arm changer, there just wouldnt be enough room without doing that as the quill only has 150mm of travel and some of the tools I use are longer, in fact a lot longer. The knee already has a motor on it, just an induction though, but it would be easy enough to fit a servo instead. I will do it at some point but just too many other things on the go at the moment. I will likely do away with the quill as the Z when I do or maybe just use it for picking up the tools. The great thing about the drawbar setup on mine is the cylinder moves with the quill so it can be operated at any position of the quill.

Hood
 

Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #66 on: August 22, 2012, 02:52:23 PM »
 It would be extremely unlikely for the encoder to happen to be in the correct position by chance, so  Degrees-off-of-index is needed to locate the actual desired home position relative to the random position of the physical encoder install, but I don't think it would be usefull in homing a spindle with reduction (other than the few ratios I cited).

For example, take a simple 3:1 reduction.

With the motor homed, the spindle could be at  0,120, or 240 degrees. Each position would require a different number of motor degrees to reach 0 (or 180) for a tool change, and I don't *think* the drive keeps track of encoder rolovers and even if it did, it would be a nightmare to extract that info . .  again that just 'on the hoof"  :P

Even with 1:1, 1:2, 2:1 etc, ratios, the degrees from index would still be useful to move the spindle from 'opto home' to the required tool change orientation. I think I have that feature on the Xenus, but now that you've brought it up and I've noodled over it a bit, I can see where it will be needed to operate the ATC from a PLC. I had to write some tracking code for my balancer and that encoder is absolute, so it was tolerable . .barely. I think I would prefer to get poked in the eye with a sharp stick to attempting that on a PLC with an incremental encoder. Kflop comes to mind because they have a lot of libraries. Perhaps I will take a peek at that.

What is clear is that this aspect of the process is going to need some more scrutiny.

Really I did not have an appreciation of how complex it would be to develop an ATC. Or more to the point a safe ATC. The mechanisms needed are only a small challenge, but the function will be a large one, methinks.  This is another of those cases where one of your random comments is going to probably save me a lot of headache down the road.  :-*

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #67 on: August 22, 2012, 05:17:05 PM »
My drives can be set up to roll over at any amount of encoder counts, it is in fact the way I use it for my lathes turret, it has a 20:1 gearbox on the motor so the drive is set up to roll over at 160,000 pulses. As the drive is also an indexing drive I can set up up to 64 positions and call any one of them from a combination of 6 inputs, life is easy :)

Big problem you have is you are trying to design in safety features and  you have no control over the hardware it is going to be fitted to. I think likely the best you are going to manage is to have a setup that requires certain signals and leave it up to the user to provide them whether that be by real signals or trickery. Either way you have done your best to make things safe and it will be the end user that has failed if they dont do as needed.

Hood

Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #68 on: August 28, 2012, 02:41:45 PM »
Hood; thanks for all of the info. You are a little over my head with the last post which only shows that I have a lot of study to do yet on the best way to skin this cat.

I have a tiny update and a short side trail for this thread. First the update: I have decided to go the cartridge route and make a complete housing for the spindle. This solves some problems and creates some problems. It seems DIY prefer aluminum for the housing, but I prefer steel for a number of reasons. The problem is that a chunk of steel large enough to create a flange and hold the massive lower bearing AND long enough is over US$200 and heavy as hell so shipping is also scary. IN the photo below, are the raw materials that I will be turning into a spindle. Purchasing an appropriate size piece of stock for the nose and the body of the cartridge put the cost under US$50, but it introduces the problem of attaching the two pieces together. After weighing options, I have decided to furnace braze the two pieces together. I have a furnace large enough to hold the parts and I have acquired a furnace brazing paste that contains flux and metal powder which is applied ti a specific slip fit between the parts. I am well aware of the furnace brazing process, but have never done it myself, so this will be interesting. If anyone has experience with this process, please post any tips or tricks, or specs on the slip clearance if you know what it is. I know there is a spec, but have been unable to find it so far.




Offline simpson36

*
  •  1,374 1,374
    • View Profile
Re: BT30 spindle from scratch - with power drawbar and ATC of course
« Reply #69 on: August 28, 2012, 03:03:51 PM »
OK now for the side trail. This is related to the BT30 spindle project because the device will end up inside the head of the new mill. For now, I have built the device and it will be installed under my current mill head.

Problem: need to drill bolt patterns in parts machined on the 4th axis. Taking the parts out and drilling the bolt pattern on the mill is a PIA, especially since the 4th axis has indexing capability and can easily rotate and hold any part for drilling. The mill had revolves and can face the 4th axis, but that is more time consuming than moving the part to the mill for drilling because the head has to be re trammed each time.

Solution: horizontal drilling spindle on (for now) or in (the new mill) the mill head.

To accomplish this, you first purchase one of these  - new:



The you grab one of these off Ebay for something less than the new price of US$285 plus something like $80 for the MT adapter. The chuck is the largest Jacobs 'Super Chuck' with capacity to 3/4". The huge MT adapter was trashed and unusable, but for my purposes, it was perfect because it was big enough to cut down to 20mm.



Next you reduce the diameter of the MT adapter to a 20mm press fit and duplicate the snap ring grooves and pin holes of the original shaft.

Move the bearings and gear over to the new shaft:



Rig a method to preload the bearings and reassemble. Now you have a horizontal drilling capability that can hold tools up to 3/4" and can drill and hard tap a workpiece held in the 4th axis. ONe of the first uses will be making the BT30 spindle housing.