Custom built CNC Lathe - Long term project

[pstockley]

I am looking into custom building a CNC lathe. The size would be somewhere in the 10 to 12" swing range. I don't want to convert an existing lathe because 60% of it would be scrap as I want to use precision linear ways and a variable speed spindle. Also, I want to make it as compact as possible.

For the bed I was considering welding up a webbed box section using a combination of 1/2" and 1" steel walls with 1/4" webbing. I would then get this normalized, milled and surface ground. To reduce resonance I was then considering filling it with something like concrete (any other suggestions would be welcome).

The big problem is the headstock. I don't want to make this as it is outside my capabilities. So I was thinking of either just buying a new headstock casting, backgear and spindle or getting one from a parted out machine. Does anyone have any suggestions? Within reason, I am not too concerned about the budget, I care more about ending up with a precision machine when I am finished.

[HuFlungDung]

If you buy the right machine, used, you could care less about the parts you have to scrap to make it into cnc. Perhaps even, you could sell off what you scrap, if it is one of the more popular machines.

The seperate headstock of a real lathe is not something that you are going to find all that easily, most likely, its going to come on a bed, etc.

I suppose you could even cabbage a set of linear ways on the sides of an old lathe bed, so that you could make use of the existing spindle and tailstock.

I think you would be far ahead to start with a used cnc lathe, and retrofit a new control on it. Consider the cost of two sets of linear ways, two ballscrews, high precision spindle bearings, a full cnc retrofit kit, building a carriage, tool turret, and a thousand and one other knick knacks. There is just no payback in starting from scratch.

Check out the machines at www.machinetools.com, if you are having a struggle finding something.

[pstockley]

I agree 100%, however there are a couple of reasons I don't want to go this route. The first and biggest problem is I don't have space to put an industrial CNC lathe.

Secondly, I am just as interested in this as a project as I am in the end result. I have always wanted to make a lathe.

The lathe would mostly be for model engineering so accuracy, versitility and swing is important. Of less importance is production throughput.

I was planning on getting as much of the linear components from eBay as I can. I have seen some very good deals on THK stuff.

[Bloy2004]

The way I see it, you are going to need a lathe to build one. Else you will be buying parts and basically assembling a lathe. You might consider getting a lathe that isn't quite to your liking and use that to make parts for your lathe.
..A mill would also be an asset .

This alone will be a "project"

...just my two cents...

John (Bloy)

P.S. I am just finishing a router I made and I couldn't have done it without my trusty Shoptask....which is a lathe and a mill combined (yeep!)
Shoptask lathe/mill:
http://www.cnczone.com/forums/showthread.php?t=2139
Router:
http://www.cnczone.com/forums/showthread.php?t=5049

[pstockley]

Just to clarify I have a lathe (Myford super 7) and CNC milling machine (Tormach) already.

Thinking about the bed, how about using continously cast iron as a basis. Obviously it would require machining and grinding. Places like versa-bar provide all kinds of shapes including hollow.

http://www.versa-bar.com/

I guess you could also get a custom die made but I bet this would be costly.

[Bloy2004]

Oh! Here in CNCzone is STEVIE who has built a lathe and is in the process of building a more massive one. You may gain some ideas from his threads:

http://www.cnczone.com/forums/showthread.php?t=8928.... the smaller one
and

http://www.cnczone.com/forums/showthread.php?t=13350 ....the bigger one

[NEATman]

Well, I you are looking for an accurate, stable flat base, you could always use a granite plate. They are already qualified, relitively cheap, and damp vibration well. The only problem is you have to epoxy in threaded inserts, and use a diamond grit coring drill to make the holes. Granite is used as a base for some of the most accurate lathes in the world. Also, for a slightly different configuration, you could mount both axes to the granite (as long as you don't need a tailstock), put the spindle on one carriage, and the cutting tool on the other.


Keith

[Ken_Shea]

In wanting to get into a CNC lathe as well I ended up going the used non CNC lathe route and scavenging all the usable parts. Got this Hardinge DV-59 second op lathe for $710 delivered (eBay of course). It has a very high precision head, 5C collet closer, HD cast iron bed, coolant pump and a incredibly HD stand, the doors are 3/16" thick, I just love old stuff It will be easily enclosable. These also do not have any of the extra stuff normally on a conventional lathe so the lines are clean. This seemed to be, for me at least a very easy and quick way of jump starting this project, spindles are easy to make, high quality spindle's are not.

The original V-way bed was removed and a 1" x 7" x 36" steel plate will replace it as the base for mounting the THK rails (eBay of course). It will have about a 8.5" swing but could easily be increased with a spacer as the head is a separate unit from the bed. I esentially have all the necessary mechanical and electrical components and at this point expect to end up spending about $2500 or so total.

[pstockley]

I like the granite idea. I did a little research and found

http://www.standridgegranite.com

They will custom make machine bases including slots and bonded in inserts. Thinking about it, I really need a slot down the middle to run the leadscrew in. I could use a flat plate and add risers for the rails to run on but from a rigidty point of view I don't really like this. I may mock up a drawing and get a ballpark quote from them to see if this is a feasible approach.

Ken, your deal is the kind of thing I am looking for. However, I wouldn't use anything but the headstock and maybe the bed. The tailstock and carriage and cross-slide would be custom.

[HuFlungDung]

Yes, the granite idea might be a good one. Perhaps if you could get a piece with a squared edge, you could fasten the ballscrew mounts along the perpendicular edge, which would create a similar torque position to the feed rack or leadscrew of a conventional lathe with the toolpost mounted on that same side.

Even my large slantbed lathe has the Z ballscrew back behind the bed, and the tool turret is back there, too. It may not be the best design to put the ballscrew down the center between the rails, but I do not know that for a fact.

[Stevie]

Originally Posted by HuFlungDung It may not be the best design to put the ballscrew down the center between the rails, but I do not know that for a fact.

works for my designs; the best part is the forces are inline with the axis center; a feedscrew off this axis centerline creates tangental force that jags the main slide

[pstockley]

That was my thinking as well steve. I have to believe most lathes with the leadscrew at the side do this purely to line up with the output from the screwcutting gearbox. They could build the output of the box to run down the center but I guess it would really complicate the headstock and encroch on space used for the spindle.