CNC Lathe Build

vtcnc

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The gear hobber project is on hold for awhile. I've decided, for various reasons, that I need (no, no, no - not want, but need) a CNC lathe. I will spare you the long ranging logic behind my reasons for building a CNC lathe from scratch, but suffice to say it boils down to money and what I think I need.

Basic Requirements:
  • Minimum 1HP spindle
  • Potential for C-Axis control
  • AC Servo on XZ axes with beef to drive them
  • Software that has a good online community and staff support
  • NOT a small desktop CNC driven by small stepper motors
That's basically it. The design I've settled on relied on re-using some existing hardware. I had to search for what I thought would be adequate. The three main components for re-use I acquired are:
  • Hardinge HC headstock spindle
  • 7" dovetail bed to mount the headstock
  • Omniturn XZ stage
The headstock and bed were removed from an HC that was slated for the scrap yard. Those were free and only cost me elbow grease and lots of back pain.

1632660586209.png
Headstock prior to removal from the HC. 7" dovetail bed is what the headstock clamps to.

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Bottom side of the bed in all of its glory. Some cleanup to do!

1632661216668.png
And the OmniTurn XZ stage. Ballscrews and linear ways. I think they use 1/2 or 3/4hp servos on there machines. I'll be using 3/4hp DMM AC Servos.

If you know anything about OmniTurns, you know they are solid, slant bed, gang tool CNC lathes and from what I'm told - workhorses. Omni-Turn sells retrofit kits for Hardinge HLV, HC, etc. The nice thing about this mix of components is that the Omniturn stage is designed to clamp to a Hardinge dovetail bed. The convenience of not having to worry about headstock and stage alignment makes the design concept work in my mind. As I think you will see through this build most of my inspiration for this build comes from what I have researched on OmniTurns, Hardinge CNC conversions and through Centroid, which is the CNC control board and software I chose to go forward with.

Here is the conceptual design:

CNC Lathe Model.png
Headstock, bed and stage will be bolted to a welded "beam" structure made up of tubing and channel. That beam will then be filled with concrete for the purpose of vibration dampening. Then, the whole beam will be welded to the supporting frame structure below. Missing in the photo are leveling feet, panels, wiring, guarding, etc. - because I haven't designed all of that yet.

The bed is 43" long x 7" wide and ~3/4" thick. The frame is approx. 43" wide, 24" deep and approx. 36" high. I need to be able to fit this in my small shop. The footprint will consume a little over 2% of my shop floor - but it will feel like 25% of my shop if I get carried away with the design. Space is at a premium. So I may tighten up these dimensions while trying to increase mass and maintain stability.



Beam Structure Build

Materials used, 3" channel, 2" sq. x 3/16" tubing and a leftover 2"x5" steel tube from some long forgotten pack-ratty hoarding grab 20 years ago. I think it came from a semi-conductor machine I purchase before it was scrapped, I parted out a lot of the linear motion components that were mounted to this beam which was machine flat.

The 7" dovetail bed will be bolted through the channel webs with 5/16"-24 SHCS bolts. Lot's of fabrication work to do here and need to make sure things are nice and square, clamped flat.

Process Steps:
  • Cut materials
  • Tack weld channels to main beam
  • Layout dovetail hole pattern in channels
  • Drill 28, 21/64" clearance holes for bolts
  • Weld up the assembly
  • Clean-up
Pictures with captions:

1632661539334.png
Beam components clamped and stacked up prior to tack welding.

1632661625104.png
"Weld Me!"

1632661699415.png
Setup for tacking the channels to the main support beam. Fireball Tools "Minion" aluminum squares are really make setup easy.

1632662124069.png
Careful layout and marking of the hole centers. Thank you Hardinge for laying these holes out using fractional dimensions. I lettered the holes so that I could keep track of where I was when transferring the dimensions to the channels without making a mistake.

1632662249720.png
28, 21/64" holes drilled by hand. That was fun.

1632662758942.png
Next problem: bolt alignment on a 10deg surface. Most alignment washers correct for about 3deg.

1632662837956.png
No problem! I'll just cut a web off one of the channel drops and dice and drill them into 28 washers!

This took about 1/2hr.

1632663172513.png
I needed 28 washers. This piece was fortuitously 29" long. The fabrication gods were looking down on me today!

1632663246250.png
Perfect alignment. Now I just have to cut up the other 27 pieces, deburr and drill clearance holes.
 

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rwm

Robert
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Wow!
Hey are you concerned that the weldment might not be perfectly flat and then might pull the base out of geometry? Do yo have a plan to get this flat?
Robert
 

vtcnc

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Wow!
Hey are you concerned that the weldment might not be perfectly flat and then might pull the base out of geometry? Do yo have a plan to get this flat?
Robert
I'm not terribly concerned. The weldment will be clamped and welded as flat as possible. Any misalignment in bend (and I don't expect much if any) I plan to shim out. Once that is done any other alignment issues with the bed will be twist. The really nice advantage of using the clamp mounting style with the headstock and stage is that twist about the spindle axis doesn't really matter because the stage doesn't move once it is clamped onto the bed.
 

rwm

Robert
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Cool. I didn't consider shimming the base. That could work. I am not sure I follow what you are saying about twist. Twist in the bed will move the headstock one way and the tooling the other way and result in cutting a taper? I suppose you could try to level out any twist depending on how it is mounted. I guess for short pieces this would not be an issue anyway. Will this machine have a tailstock also?
I am excited to see this project!
Robert
 

vtcnc

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Cool. I didn't consider shimming the base. That could work. I am not sure I follow what you are saying about twist. Twist in the bed will move the headstock one way and the tooling the other way and result in cutting a taper? I suppose you could try to level out any twist depending on how it is mounted. I guess for short pieces this would not be an issue anyway. Will this machine have a tailstock also?
I am excited to see this project!
Robert
There are six possible degrees of freedom for misalignment. Looking at the headstock spindle from the tailstock: Left-to-Right bending, Up-to-Down and Axial Twist. In the case of the first two, I don't expect any Left-To-Right bending and I should be able to shim out any Up-Down Bending.

In the case of any axial twisting of the bed: even if the headstock rotated some amount about the axis of the bed, the stage doesn't move along the bed axis. It remains in one place since it is clamped to the bed, so any changes in any detectable twist in the bed are not translated to the axis of the stage. Hope this makes sense.

With all of that said, I don't expect there to be any real detectable alignment issues. Maybe that is my naivete speaking. We'll see! I'm wrong a lot!
 

rwm

Robert
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Obviously you have thought about this. I think you will be able to correct for twist pretty easily even if you get enough to interfere with your desired tolerance.
Now you have me cruising eBay for lathe beds!
Robert
 

Eddyde

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Curious to why you didn't use the original lathe base?
 

vtcnc

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Curious to why you didn't use the original lathe base?

Hi Eddyde, the main reason is that I don’t have a good mode of transportation for hauling equipment, let alone loading and unloading. It certainly would have been easier.

There was also the other “stuff” that comes along with the rest of the machine. I don’t really have the time nor do I want to prioritize my time to part out turrets, handles, speed control gear, etc., etc. The other problem with taking the whole machine is that the 5hp 3ph motor was bad. I also did not want to get stuck with that. Finally, I just don’t have room for all of it in the shop.

At the end of the day, came down to where I wanted to spend my time.


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Eddyde

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Ah, that makes sense. Reason I asked, I have a CNC lathe build project on the "if I live long enough" list. I was thinking of the same approach, using a Hardinge as a donor lathe.
Looks great so far!
 

vtcnc

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Ah, that makes sense. Reason I asked, I have a CNC lathe build project on the "if I live long enough" list. I was thinking of the same approach, using a Hardinge as a donor lathe.
Looks great so far!

If you have the space, it makes sense to use the donor lathe.


Sent from my iPhone using Tapatalk
 
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