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Old Jun 01, 2015, 06:35 AM
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HF 8x12 CNC conversion

I have my trust Harbor Freight 8x12 mini lathe that I will be converting to CNC but I want to retain being able to run it manually.

I saw one that I liked but it was no able to run manually without a lot of work.

1 step at a time I will make the move to CNC.

My first step is a spindle tach. I will follow that with a motor upgrade and a VFD.

I figured that I would retain the leadscrew on the feed. and mount the servo in line with it and have a slide type mechanism to engage and disengage it. that leaves me with the cross slide and mounting the stepper so it's not in the way. this is the part I am scratching my head over... anyone gone this way before?
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Old Jun 01, 2015, 09:05 AM
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have to admit..this is where I would get a 2nd lathe but then, I could only copy what someone else had done to make a cnc conversion.
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Old Jun 02, 2015, 05:45 AM
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I never converted a Harbor Freight lathe. You can put the cross slide steppers on the back, using a longer screw. Or use a belt drive to get the stepper out of the way. A couple of examples of these two approaches. the first link has the stepper in the back, but was setup for cnc only. Most conversions remove the rack feed. So you lose the fast manual feed it can provide. Removable crank handles are nice so you don't have the danger of them spinning around.
http://cncfusion.com/images/7x12lathe/7xphotos.html
Manual or CNC with belt drive.
https://www.tacomaworld.com/threads/...s-here.139871/
Taig that is setup for manual, or cnc, with cross slide stepper in the back.
UNBOXING the CNC Taig Lathe (24 min 12 sec)
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Old Jun 03, 2015, 02:02 AM
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Quote:
Originally Posted by RCWorks View Post
I have my trust Harbor Freight 8x12 mini lathe that I will be converting to CNC but I want to retain being able to run it manually.......
My first choice would be an electronic hand wheel. Basically it is a full CNC machine which also has handles you can crank like a manual machine. The handles don't have a mechanical connection to the screws, they only send electronic signals to the computer. Also called a manual pulse generator. The computer then moves the screws with servos or stepper motors. The electronic hand wheels don't need to be mounted on the machine. They can be on a hand held control called a pendant. Google CNC pendant.

Here are a few links to 8x12 machines that have been converted.
http://www.cnczone.com/forums/mini-l...14881-cnc.html
http://www.cnczone.com/forums/mini-lathe/95419-cnc.html
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Old Jun 03, 2015, 06:12 AM
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My first choice would be an electronic hand wheel. Basically it is a full CNC machine which also has handles you can crank like a manual machine. The handles don't have a mechanical connection to the screws, they only send electronic signals to the computer. Also called a manual pulse generator. The computer then moves the screws with servos or stepper motors. The electronic hand wheels don't need to be mounted on the machine. They can be on a hand held control called a pendant. Google CNC pendant.

Here are a few links to 8x12 machines that have been converted.
http://www.cnczone.com/forums/mini-l...14881-cnc.html
http://www.cnczone.com/forums/mini-lathe/95419-cnc.html
Ronncat at CNCZone has done the tach and went to an AC motor with VFD, the same motor/controller I am looking at.

I don't want to tear up the apron and I don't want to buy ball screws(As nice as they may be.). I think if I were to go that far it would be on a bigger machine.
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Old Jun 03, 2015, 04:29 PM
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I haven't done any cnc conversions, but I hear if you replace manual lathe trapezoidal lead screws with ball screws anti-backlas nut for precision & reduced drag, that doesn't lend itself to manual machining. The ball screws are too good, they don't have sufficient resistance & the cutting tool can actually drift into the work & bad things happen. Likely discussed extensively in CNC zone or conversion projects, but that's what I thought I heard.
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Old Jun 03, 2015, 06:19 PM
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Quote:
Originally Posted by RCWorks View Post
Ronncat at CNCZone has done the tach and went to an AC motor with VFD, the same motor/controller I am looking at.
A VFD is an awesome upgrade even if you don't do a CNC conversion. I can't imagine going back to the factory setup. Too bad they don't sell machines without the motor,speed control, gearbox etc. and just let you add your own choices for that stuff.

Quote:
Originally Posted by RCWorks View Post
I don't want to tear up the apron and I don't want to buy ball screws(As nice as they may be.). I think if I were to go that far it would be on a bigger machine.
If I were starting over I would definitely consider a larger machine. Keep the 8x12 on hand to make parts for the CNC conversion of a larger machine and then sell the 8x12. Hindsight.......
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Old Jun 03, 2015, 07:01 PM
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Originally Posted by ptxman View Post
I haven't done any cnc conversions, but I hear if you replace manual lathe trapezoidal lead screws with ball screws anti-backlas nut for precision & reduced drag, that doesn't lend itself to manual machining. The ball screws are too good, they don't have sufficient resistance & the cutting tool can actually drift into the work & bad things happen. Likely discussed extensively in CNC zone or conversion projects, but that's what I thought I heard.
Most of that drift can be addressed by using "preloaded" ballnuts. The use a larger set of bearings to tighten them up and you will pay extra for that service.
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Old Jun 11, 2015, 06:19 AM
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Today I am finishing the soldering of the parts in the tachometer chassis.

As you can see by my current avatar the magnetic part of my hall effect sensor is ready to mount to the spindle. I ended up cutting the ring with a bandsaw. I do not yet own an arbor or slotting saw blade. However since it's mounted where no one will see it except to service it or rebuild the headstock I think I can live with it.
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Old Aug 12, 2015, 07:55 PM
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The tachometer for the spindle is compete and operational.

Now to put some $$$ together for a 1 hp motor and VFD.

The original motor is 5/8ths horse and I think they were generous with that rating.

Once I have the new motor in the old one will be sold complete with harness and switches.
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Old Aug 21, 2015, 01:17 AM
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....The original motor is 5/8ths horse and I think they were generous with that rating....
Very likely true on the hp rating.

The lathe can easily handle 1 hp but I'm not sure about the drive belts. With a 2 hp motor the toothed belt lasts about 15 minutes. PM me if you need a spare belt. I have an unused one I will never use. It's yours for the price of shipping.
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Old Aug 21, 2015, 04:12 AM
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Very likely true on the hp rating.

The lathe can easily handle 1 hp but I'm not sure about the drive belts. With a 2 hp motor the toothed belt lasts about 15 minutes. PM me if you need a spare belt. I have an unused one I will never use. It's yours for the price of shipping.
When you do this you eliminate the first belt and pulley from the motor.
The spindle is driven right off the motor.
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Old Aug 21, 2015, 04:21 AM
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While stacking up a pile-o-bucks for the motor and VFD I have some time to figure how to setup my steppers so I can go CNC or manual cutting without it being a pain in the butt to switch over but still be reliable.

Running the lead screw and letting it be driven off of the spindle seams easy enough.

I will need to look at making a coupling on the back side of the screw for the slide that would be easy to engage and disengage. I'll figure something out.
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Old Aug 21, 2015, 10:21 PM
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I don't know if you have looked into it but I used a treadmill motor on my wood lathe and my small Craftsmen lathe I have for my son, the most I have payed for one is $5.00, of course thy are small motors, but work on the small lathes I used them on.

Mike
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Old Aug 22, 2015, 03:05 AM
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I don't know if you have looked into it but I used a treadmill motor on my wood lathe and my small Craftsmen lathe I have for my son, the most I have payed for one is $5.00, of course thy are small motors, but work on the small lathes I used them on.

Mike
I use my lathe a lot, I'd rather have something I can mount in the first custom mounting I had to make rather than make another... It's a bit different when you sell parts for something you sold someone 2 years ago. The machine has to work, if not it has to be repaired in short order.
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