Slant bed lathe, tool changer, pneumatic 5c drawbar, DYNOMOTION control, PICS!

[kn6za]

Wow! That is a beast compared to my rig! Sounds great!

The servos I am running are 100oz/in and I think I might get 400 lbs of axis force at stall. My machine is just a baby in comparison to yours.

My machine will be making delrin parts the size of a pencil eraser.

[kn6za]

Finished the operator panel fabrication and assembly, and dis-assembly, and assembly.

I think it came out better than engraving the text directly on the panel itself, and trying to fill the text with color.

[kn6za]

A shot from the back.

I was not sure how the ELO touch screen would end up being mounted when I got it. It was a used POS monitor that was decommissioned, and cheap.

After disassembling the bezel I noticed a nice land between the inner rim and outer perimeter of the front bezel. Just removing the back of the monitor, cutting a hole in the panel just larger than the inner rim but smaller than the outside perimeter, and making some aluminum tabs to anchor the monitor in place made it an easy fit up.

[hanermo]

Great stuff !

[Hezz]

Finished the operator panel fabrication and assembly, and dis-assembly, and assembly.

I think it came out better than engraving the text directly on the panel itself, and trying to fill the text with color.

I think it looks really good. I like the no nonsense industrial look. It's really nice to see someone build a DIY CNC with a complete
manual input control panel. It kind of makes working at the machine a little more fun then just using a mouse and monitor input.

It's a nicer human interface for the machine. There's nothing more fun than moving the axis with the hand wheel when your setting up
the machine. Makes it a lot easier to get things set up.

[kn6za]

Thanks Hezz!

[kn6za]

Time for limit switches, and getting the pulleys on the shafts.

I had this idea for an adjustable limit switch setup. I could never seem to place the limit switches exactly were I wanted them on my last machine build, so this setup gives an inch or so of adjustment to the final location. the delrin switch anchors slide down the track when the screws are loose, and lock up pretty good when tight.

There is an aluminum plate that hits the limit switches, this is epoxy glued to the side of the linear bearing.

I have one limit switch on each end that will be run into the advanced motion control 30a8t to disable + or - axis travel. There is also another limit switch on one end to locate the index mark for homing. This will wire into the dynomotion motion control board.

The belt is 10mm wide, 3mm tooth pitch. 25 tooth and 50 tooth. If I have problems with the belt being too flimsy, ill have to get creative with 20mm wide pulleys! Not much shaft left to work with.

Pulleys are mounted on the shaft, and clamped on a flat milled in the shaft. The pulley was machined off in the flat area, and a cap was made to fit. Both motor shaft and ball screw shafts have flats cut into them to accommodate this method of clamping, but the motor shaft does not have its flat on the end, but mid way down so that i could run the clamp behind the pulley.

At 14mm in diameter these motor shafts are a bit overkill for a 100oz in motor, but that gave me lots of potential flat to work with.

[kn6za]

On to the tool changer design and manufacture.

The design drawing is crude, but hopefully shows enough of the design to make operation understandable. The Hirth coupling locks the the turret rotation and axial position on the 30deg taper angle of the Hirth by air pressure. The springs return the turret to the forward unlocked position when air pressure is released.

The body side of the Hirth is made of A2 and can be heat treated as can the 4340 turret.

There is a cap on the end of the 2" shaft that will be driven round by the gear motor on the back of the tool changer, and forward/back with the piston and springs. The 4, 3/16 dowel pins are pressed into the drive hub, and loose fit into the shaft cap to allow the shaft to move forward and back relative to the drive hub with air pressure/spring action.

The gearbox will be servo driven to rotary position each tool change.

The shaft is 2" and the piston is 4" diameter.

The shop psi ranges from 100 to 150psi.

@ 100 psi the clamp force seen by the Hirth is ~942lbs and @ 150 psi the force is ~1413lbs

With a potential axis force of ~400lbs I think the ~1000 lb clamp force on the turret will be fine. Hope anyway!

Photos show the turret side of the Hirth being cut, and the A2 insert fit into the body. Both Hirth halves were cut in the little cnc machine shown.

The turret body bores, and o-ring grooves were cut in the manual lathe with a 4jaw chuck, its a 7"x5"x5" block of fortal aluminum. My shop is full of chips now, chips everywhere.

[kn6za]

Ok, so I screwed up. This is the gear motor I got for this project.

My initial plan was to extend the shaft so that it protrudes from the back through the case, so that an encoder could be attached and read the turret rotation directly.



like this


So whats the problem with this feedback arrangement? The backlash in the gear box is HUGE, and I think trying to close the servo loop through that much backlash will be a nightmare! The encoder will need to be moved to the motor shaft not the gearbox output shaft.

I never tested the first approach to find out it was not going to work, but it came to me in the middle of the night that this was a bad idea. At this point its an easy fix. I had the new motor on the shelf surplus from projects.

So I adapted the new motor shown in the last photo, and got rid of the old one because the main shaft in the old motor was about .125" diameter and I could not figure out how to make it longer to attach the encoder directly to the motor shaft.

The new motor has a 5mm shaft and I can add length to that without difficulty.

So I took one of the encoders that came out of the main axis motors and made a housing for it, and mounted it to the back end of the motor. Like this


I included some pics of the process. I put a photo that shows one of my line driver boards in the housing too.

[kn6za]

More progress has been made on the turret.

I got the orings made, and fitted into the body and piston grooves. I used 1/16 diameter buna-n oring by the foot, and cut them to length, then superglued the ends together to make the oring the fit the location. I did not take the time to make the oring grooves to fit off the shelf standard orings.

Now that the unit is assembled and air pressure is applied I can test oring seal and manual rotary movement. So far it feels great, no leaks that I can tell, and I can setup to start cutting the face and side of the turret.

With the Hirth cut into the back of the turret, I decided the best way to correctly time the machine work from the front of the turret to the machine work on the back of the turret would be to assemble the tool changer and apply air pressure to lock the unit, while clamped in the milling machine vise. I then just release the air pressure and index the turret to the next position. There is also work needing to be done on the side of the turret, and this is a photo of that operation.



While cutting the face of the turret I was impressed with how rigid the Hirth felt. I used a .625 carbide insert cutter to rough out most of the metal from the face. It did not complain with .100" depth of cut with full cutter width engagement passes.

I used a 10 deg. carbide single lip cutter to machine the wedge lock angle for the od cutting tool locations.

I included a photo of the tool changer parts all together but disassembled. I ended up putting 2 orings on the outside of the piston, just to keep the aluminum piston from ever touching the bore walls in the aluminum turret body. If the two come in contact there will be scoring and air leakage. Only time will tell if this method is successful.

[Hezz]

Nice work Kn6za, is it possible to put an encoder on the output of the gearbox as well as the motor and compare the two so the motor can make compensating adjustments. Actually, I'm pretty sure this could be done but I wonder if it is feasible for a DIY project. And how hard it would be to do. The majority of commercial lathe turrets use internal gears. I imagine that they are pretty high quality but they would still have some backlash. I wonder how they compensate for it.

[kn6za]

Thanks Hezz,

Well I could put an encoder in both locations, but it should not be necessary, even with lots of backlash.

The issue with the motor and encoder separated by the backlash came down to servo tuning and the backlash interfering with it. When the servo drive would try to close the position loop it would not know that the motor shaft was moving until it hit the edge of the backlash and started to read movement on the gear box output shaft encoder. By this time there could be significant motor shaft speed achieved. This would create an oscillation that would be difficult to stabilize.

Now that the encoder is mounted directly on the motor shaft no such oscillation is possible. The backlash can now be dealt with in software easily. I am not using the index motion to cut anything, so as long as I can reasonably accurately position the turret, I don't care how much backlash there is. Once the turret is locked, and it will always be locked before cutting starts, the backlash is no longer an issue.

One of the beautiful things about the Hirth coupling is that the servo does not need to have perfect rotational accuracy on index. The thing can take a few deg. of misalignment and correct it in the clamp up movement. Once clamp has occurred, the index servo is disabled. At this point If the servo thinks it is out of position, because of small errors, it wont even try to correct the error until it is re-enabled at the next tool change request.

Hope that cleared up my thinking on this.

[kn6za]

Got the ER16 collet chuck mounted to the center of the turret, and the tabs mounted for the remaining ER16 collet locations.

As far as the finishing the remaining ER16 collet locations, my plan is to wait until the wiring, and the alignment of the spindle and turret center lines is complete, then use the lathe to drill and bore the holes that I will press the collet chucks into.

I plan on chucking a milling machine boring head into the lathe spindle and cutting the bores on the machine.

The chucks are sold as ER16 motor shaft spindles extensions, but hey are perfect for this application.

[vidio1]

Is there a reason you build the turret to lock with air pressure? Not doubting your design, but Is would seem a fail-safe against air loss if it stayed locked until released by air pressure.

[kn6za]

Oh man! Vidio1, where were you when I was designing this thing?

Just kidding you.

Glad to have the design doubts expressed. I have some more of my own.

I locked with air as a compromise for manufacture. This is already a tough build and I did take some short cuts, this is one of them.

I considered locking the turret a few difrent ways, cost and difficulty of production worked me over to this current design.

The only safety measure I have implemented is a low air pressure e-stop alarm sensor. It will at least bring the machine to a halt while there is still enough pressure to keep it locked. While this is not a perfect scenario, it's better than nothing.

[pippin88]

I had the same thought. If you have good interlocks, like air pressure sensor, and a reliable air supply, you should be ok.

Most other turrets I've seen use springs, and air to unlock.

[kn6za]

I hope your right pippin88. Time will tell.

The worst-case scenario is a fitting blowout or line rupture. If this happens while in the cut there will be damage. Even with the machine being placed in e-stop durring the event, it could take longer to decelerate the spindle than unclamp the turret.

Slow leak down/compressor failure should not cause any problems, other than a disabled machine, and that's standard.

Either way it goes down, the machine will be in e-stop as the event unfolds, so damage will be minimized by that aspect.

I won't issue a redesign just yet

Sent from my SAMSUNG-SM-G900A using Tapatalk

[kn6za]

I have been collecting parts and pieces for over a year for this project. In that time, having not decided on a 5c closure method, I bid on and looked at countless lever acted closure mechanisms. Seems I was always skunked by other bidders or bad timing of auctions. I have seen the price range from $85 - $350 on a lever acting unit and new ones can be $1000.



So I started looking for a pneumatic closer.



In the process I found this drawing.



I was intrigued to think I could just build this myself, and after looking at the cost of the raw materials, I acquired everything needed to make it for about $150. I think building this will be an easier build than a lever acting unit, and ill take the power assist option over the manual any time.

The drawing has no dimensions, but it has bearing part numbers and snap ring numbers. I took the known measurements of those parts and scaled the rest of the drawing to get part dimensions. So while I wait for the remaining steel for the turret parts, I am going to start making the parts for the closer.

[DICKEYBIRD]

I wanna be just like you when I grow up Andrew; what a fabulous machine you're building!




( Birthday #69 is coming up 3 days from now so I guess it's too late to grow up. )

[kn6za]

Ha! Thanks Milton!

HaPpY BiRtHdAy!