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View Full Version : 4th Axis with a twist, video



Evan
02-24-2008, 09:56 AM
I have made some additions to the 4th axis indexer unit. I mentioned already that the unit would be able to act as a lathe. Now it does. This is the first real part made on the machine with the indexing AND lathe capability. This show the unit with the part milled. I have used Lexan for a chip cover on the unit. This isn't ordinary clear Lexan, it's a product with a coating called MarGuard which is a very hard and tough coating almost like glass. It doesn't scratch easily and is extremely machinable. It also has a slight purple tint which is characteristic of machining Lexan.

http://www3.telus.net/metalshopborealis/pics4/twist1.jpg

I am making encoder wheels for a motion detection/e-stop system for the machine. Limit switches don't provide enough protection. More on that in another thread soon.

I have added a spindle motor to the indexer. It's a beer can size servo motor with ridiculous specs. It's rated up to 600 watts running over 3000 rpm up to 30 volts DC at 20 amps. Thats 3/4 horsepower in a beer can. It runs like it too. It will accelerate the spindle to 1200 rpm in maybe 200 milliseconds.

http://www3.telus.net/metalshopborealis/pics4/twist2.jpg

This is the machine running in lathe mode. I have temporarily mounted a turret tool holder on the side of the head but have something a little different in mind.

http://www3.telus.net/metalshopborealis/pics4/twist3.jpg

This is the finished part:

http://www3.telus.net/metalshopborealis/pics4/twist4.jpg

I recommend watching the video to see how easy it is to switch modes. I have also used magnets as part of the enclosure to make access easy and instant.

The videos are available from the new server so should download very quickly.

This is the low res version, 10 MB, 4.5 minutes
http://www3.telus.net/metalshopborealis/4_axis_twist_lo.wmv

Hi res, 20 MB
http://www3.telus.net/metalshopborealis/4_axis_twist_hi.wmv

DICKEYBIRD
02-24-2008, 10:07 AM
SWEET! I can only dream of such technology. That machine is going to make you some wonderful things.:)

A.K. Boomer
02-24-2008, 10:33 AM
Yup, looks just like an encoder disc, Very cool Ev, it really suprises me that your mill head is that solid to run a lathe tool off of, I never would have guessed, Thought it would be a chatter box but the part looks great:)

Evan
02-24-2008, 10:41 AM
It works fine on metal too, at least on aluminum. I haven't tried steel as I haven't built a speed controller for the spindle, yet.

A.K. Boomer
02-24-2008, 11:03 AM
Now I see the long ribbons, what type of plastic? (im still impressed by the way:) ) That peice looks metal esp. when your holding it after the part off.:o

I noticed you named her --- let me know when they hit E-bay and I'll see what the housing markets doing, I wonder if it makes chips hot enough to burn through the bottom of a tent? What an amazing little Mill...

pntrbl
02-24-2008, 11:14 AM
I thought the part was metal! Had me all confused for awhile there. What is it anyway?

SP

Evan
02-24-2008, 11:23 AM
Black acetal copolymer, Acetron by Quadrant.

John Stevenson
02-24-2008, 03:08 PM
Why does the spindle slow down when using the lathe tool ?

.

Your Old Dog
02-24-2008, 03:49 PM
I haven't been this green with envy since Lyle Lovett scored with Julia Roberts !! PFS.

HTRN
02-24-2008, 03:55 PM
Evan, I'm curious - is there a particular reason why you used a Minimill head over say, the headstock off of a 7" lathe?


HTRN

John Stevenson
02-24-2008, 03:57 PM
YOD,
It not new and is going to become more common in the future.

Greg Jackson of Tormach fame has got Seig to make him a special version of the C3 lathe to bolt direct to the bed of the Tormach.
I saw one of the prototypes when over in China at Christmas. Look just like a C3 but has larger feet that line up with the bed tee slots and has encoder drive to the spindle.

.

Evan
02-24-2008, 04:17 PM
The spindle slows down because the servo motor is running open loop right now. I don't have a controller for it but will build one.

The reason I used the mill headstock is because of a mixup by LMS back when I ordered it. They were supposed to send me an R-8 spindle but sent a MT3 instead. I called them and they shipped the correct part immediately with no questions and told me to keep the other as well.

John Stevenson
02-24-2008, 04:21 PM
The spindle slows down because the servo motor is running open loop right now. I don't have a controller for it but will build one.



Ahh makes sense now, thanks.

.

HTRN
02-24-2008, 04:57 PM
The reason I used the mill headstock is because of a mixup by LMS back when I ordered it. They were supposed to send me an R-8 spindle but sent a MT3 instead. I called them and they shipped the correct part immediately with no questions and told me to keep the other as well.

So it's a case "I had this lying around..".;)

Are you planning on adding a tailstock? It looks as though the LMS tailstocks could be easily adapted - even if they're a bit high, they're a "two piece" design, so removing the base and making a new one a bit thinner is easy enough..


HTRN

Evan
02-24-2008, 05:45 PM
A tailstock is planned. I have everthing I need to make one.

jim_geib
02-25-2008, 09:48 AM
Evan's,

Would it be possible to get more information on the spindle moter you are using. Name and Mfg.?

Evan
02-25-2008, 10:54 AM
http://vts.bc.ca/pics3/servomot.jpg

I point out that to get the full performance from this sort of motor you need a very stiff power supply that can supply the full instantaneous current it needs.

wierdscience
02-25-2008, 11:24 PM
Nice!

Limit switches and encoder limits,belt and suspenders good idea.

Have you run the mill spndle into the chuck jaws yet?:D

Evan
02-25-2008, 11:35 PM
Have you run the mill spndle into the chuck jaws yet?
No. But, while demonstrating to a neighbor yesterday I did manage to run the cutoff blade into the jaws. I thought I had it clamped securely but the chuck didn't think so. There is a reason I don't stand right in front. My friend was hiding behind the tempered glass. I think I'll make another Lexan shield that will fit the front with the 4th axis in place. 1/2" thick should do it. :D

I'll be mounting the lathe tooling on the front of the head. That way I can't easily run the spindle into the chuck. I have 8.5 inches of Y travel so it will still give me enough room.

Yep, I'll be making a system that detects whether the leadscrews are turning when commanded. It's not difficult to do. Each axis will have the step signal fed to a binary counter that counts up when step pulses are issued. The encoders will issue pulses when they turn that clear the binary counter each time the encoder advances. Direction doesn't matter. If the counter counts up to a selected value it issues an output tied to the e-stop. This same system is duplicated for each axis. The main consideration is that the counter must be allowed to count without generating a e-stop slightly more than 2 times the maximum number of counts that it will take to create a pulse from the leadscrew encoder. The system is foolproof as it doesn't care about backlash or the step rate at all and doesn't need an external reset. With a 50 tooth encoder on each leadscrew the system will e-stop automatically when no more than 1/25 of a rotation of the screw is detected as lost motion. With 10 tpi leadscrews that is .004" lost motion to cause an e-stop.

ZINOM
02-26-2008, 12:01 AM
That's some great work there....thanks for the video!

John