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November 13, 2018, 22:16:34 pm


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Author Topic: CNC Lathe Project  (Read 2211 times)
Bob La Londe
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« on: February 19, 2013, 02:56:03 am »

Ok, I am done.  The mini lathe is going to get stripepd and all the stupid plastic parts are going in the recycle bin.  I was turning some simple should bolts out of aluminum on it the other day, it just suddenly wasted several of the plastic gears.  Yes, I know I could buy a metal gear set for it, but I am tired of fixing it.  I just ordered some steppers, stepper controllers, and a project box for it.  Every plastic part on this machine is going in the bin.  So is the lead screw, the compound, and the cross slide screws. 

I have the heavier 8.5 by 18 that will remain my manual lathe for now.

I just have to decide what I want to use for a spindle motor.  It has a universal brush motor (running on DC) right now, but the speed varies pretty dramatically under from free spin to load.  I was thinking that maybe a DC servo might be an option.  I was also considering a small 3 phase motor and a small closed loop VFD. I suspect peak power on the current motor is around 300 watts (1/3 horsepower) and it only develops that at full speed. 

Suggestions? 

The plan is to make this one LinuxCNC based rather than Mach based just to force me to learn LinuxCNC setup. 

I ordered the steppers and controls today, but I may not have much time to make parts for it for a couple weeks.  I just signed a couple video installations last week, and I am going to be pretty busy. 
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Bob La Londe
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« Reply #1 on: February 19, 2013, 02:56:49 am »

I'll start with direct drive, but leave room to modify if I need to use a belt drive. 
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Bob La Londe
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« Reply #2 on: November 05, 2018, 15:52:16 pm »

I haven't worked on this project for a while.  I fitted a ball screw and motor to the Z and stopped. 

I want to run gang tooling on a t-slot table, but I struggled with exactly how to get it perfectly aligned on a very imperfect machine.  Then today I had one of those moments.  It doesn't matter.  You machine drill holders to fit, and manually set tool heights with a tool holder or shims, and then you set tool offsets in your tool table.  Nothing else really matters, and it doesn't have to be perfect.  Its not like I am going to be turning anything larger than 2 inches OD on it anyway.  In fact I have the spindle fitted with a 3C collet closer so most parts will be MUCH smaller. 
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stevehuckss396
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« Reply #3 on: November 05, 2018, 22:52:44 pm »

Any pictures?

I am in the middle of a conversion of a 9X20 lathe. I did a direct drive on the Z axis also and a 2:1 reduction belt drive on the X axis.

Would love to see some pictures of how you did things. Just curious I have a harbor freight 4X5 that might get done next.
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Bob La Londe
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« Reply #4 on: November 06, 2018, 00:24:20 am »

Any pictures?

I am in the middle of a conversion of a 9X20 lathe. I did a direct drive on the Z axis also and a 2:1 reduction belt drive on the X axis.

Would love to see some pictures of how you did things. Just curious I have a harbor freight 4X5 that might get done next.

I think there is a converting the mini lathe part one video on ( https://www.youtube.com/watch?v=bDG7WqT6uQY )YouTube, but after seeing another fellows 8 x 14 conversion going on CNC Zone ( https://www.cnczone.com/forums/mini-lathe/368174-cnc.html ) I've decided to scrap what I've done and start over.  He eliminated the V on the saddle and just put linear rails on his.  I can easily chuck the whole lathe up on one of the mills and do that.  Indicate off the V, machine it off, then machine slots and drill bolts holes for the rails.  



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« Reply #5 on: November 06, 2018, 20:12:02 pm »

Stay with the dove tail. It will take a lot of abuse and will never wear out unlike the trucks on the rail. Just put a motor on it with enough torque to move it with ease. I put a NEMA 34 with 600oz torque. With your lathe being smaller (i think) you wont need one as big. Much less to wear out and less money.

something to think about.
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lloydsp
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« Reply #6 on: November 06, 2018, 20:34:58 pm »

Although I have all the parts, I have not yet started my conversion.  But one of my goals is to retain manual operations, so I can use the machine under CNC control OR do simple ops by hand.

To that end, I'd keep the dovetail guides, too. (and the compound, even though it's not needed for CNC).

Lloyd
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Bob La Londe
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« Reply #7 on: November 07, 2018, 04:47:19 am »

You guys do know I have two bigger lathes right?
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lloydsp
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« Reply #8 on: November 07, 2018, 12:02:09 pm »

Yeah, Bob.  I have two, myself.  That's not my reason for doing it.

I want a machine on which I might run a fairly complex job under NC control, then perhaps do some 'touch up' or modifications to the routine's work, without having to re-chuck.

It's not a 'must have', just something I want to have.

Lloyd
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Bob La Londe
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« Reply #9 on: November 07, 2018, 16:05:17 pm »

I've gotten so used to CNCing parts I often just enter G-code at the MIDI command line for that sort of thing.  I get the right speed, feed, position, or corrective position.  Sometimes when I have to hit a tight spec I'll "manually" recut one part two or three times this way and mic the feature in between as I creep up on the dimension.  If its a more complex feature I'll likely have already created three or four code files to do the same thing.  I don't see where I would do it any differently on the lathe. 

I did some square steel boxes where two sides had tapered tabs that fit into tapered slots in the other two sides.  To hit both dimensions exactly the plate behind the tab had to pull down tight against the other plate, but only when the bolts were tightened hard.  This guaranteed consistent dimension of the inside of the box.  The straight side of the slot didn't change.  I just made multiple passes with a taper mill on the tapered side of the slot.  When it set in tight with a hair line gap between the flat mating faces it was perfect.  I also made the customer a brass hammer to knock them back apart.  LOL.  I would have just bought one, but because it was going out of the country I wanted to be able to label it made in USA.

I know a lot of old manual machinists like to put their hands on the wheels.  I've found some parts are easier to make manually too, but when its like you describe I'd CNC or "manual" CNC it.  No disrespect is intended to guys who have been turning hand wheels since they were still made out of hand chipped stone.   Grin
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Getting started on CNC?  In or passing through my area?
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lloydsp
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« Reply #10 on: November 07, 2018, 16:39:07 pm »

Yep!  'Been lathin' by hand since 1967, and it's hard to give up the wheels!

Lloyd
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Garyhlucas
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« Reply #11 on: November 07, 2018, 23:50:49 pm »

Our Servo 5000 bed mill has handwheels that work really well for an unusual reason. The servo motors are actually iron core varaiable reluctance motors that have zero detent forces. So you can’t even tell the motors are there when the motors are off. The Z axis handwheel is essentially useless, as on this machine it is up on top about 9’ above the floor! I’ve thought of using a flex shaft to bring it down where it can be reached. The DROs work while using the handwheels which is nice.
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Gary H. Lucas

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lloydsp
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« Reply #12 on: November 07, 2018, 23:57:33 pm »

Ooo!  Nice information, Gary!  Those aren't the motors I have, but I still haven't started the conversion!

Lloyd
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Bubba
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« Reply #13 on: November 08, 2018, 01:02:44 am »

Yep!  'Been lathin' by hand since 1967, and it's hard to give up the wheels!

Lloyd

 That's when I have served apprenticeship Grin.
Boy, time flew by..
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Garyhlucas
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« Reply #14 on: November 09, 2018, 00:10:06 am »

Ooo!  Nice information, Gary!  Those aren't the motors I have, but I still haven't started the conversion!

Lloyd
I  guess I should have mentioned the bad news.  Variable reluctance motors were going to be the next big thing in motion control back in the 90s.  However as best I can tell Servo is the only company that actually used them.  I just bought a spare motor off Ebay because Servo no longer makes them, but they do have rebuilds available.

However they are apparently still around, but not as motion control.

http://drivesncontrols.com/news/fullstory.php/aid/5661/Switched_reluctance_motor_aims_to_disrupt_the_market.html
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Gary H. Lucas

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