Yet another CNC lathe project. Thoughts welcome (esp. Doc - it's a Logan)

[tyrone shewlaces]

Ever since I picked up a toy CNC mill a few months ago, I've been thinking on the next step. I thought maybe a CNC lathe would be handy so tried to outline some kind of features to work with.
At first I decided that a Hardinge chucker might be a good candidate due to the precision, rigidity and existing tool turret which might be relatively easy to automate.
Then this past week a Logan turret lathe came up on Craigslist for cheap - feel free to chime in Doc!
It has an 8-station tool turret similar to the Hardinge HC. I don't imagine it was built to the precision of the Hardinge, but it's got hardened ways which seem to be in good shape. Plus it's missing the tailstock, so between that and not having a compound in lieu of the turret, it's already not ideal for yer standard home shop lathe. It seems like a good candidate for a CNC conversion.
Whadda ya think for $200 in raw material?



The lathe has been partially disassembled but came with the parts needed to put it back together, but I figure it's prolly gonna get pretty well gutted then cobbled back together with CNC control.
My druthers is to go with servos. I've dealt with steppers several times in the past, and they can work, but having recently experienced servos on home-made stuff I'm pretty hooked. Sooo much nicer in several ways, albeit a bit more $$.
I'm somewhat committed on this as I have hauled it home already. But I'm gonna be swamped until winter I think so it will be a good cold-weather project I guess.

Thoughts?

A side note: I don't know if it will fit or even be useful on this, but I do have a fairly heavy-duty turret tailstock which may be made to fit this machine and expand it's capabilities. That can be added once everything else is totally complete and buttoned up though, so certainly only a side note. Worth mentioning maybe.

[Doc Nickel]

Well, lemme tell ya, if that were available within 300 miles of me for $200, I'd already be in the truck going to get it.

If you're thinking a CNC conversion, that's very likely an excellent start- depending, of course, on the condition of that particular machine, like headstock bearings and the like. Looks like it probably has an L00 taper which is nice and common, already has a 5C closer, and if you can figure out how to automate that turret, that'd be ideal for a CNC. (No idea how those flat turrets work though, so can't help ya there.)

I think those models had a vari-drive in the base, and between the empty holes and your note about it being partially gutted, makes me think that's been removed and it may be converted to direct drive. Which again, for a CNC build would probably actually be preferable. Set it up with a good 2HP or 3HP 3-phase and a quality VFD, belt it appropriately, and let 'er rip.

If you plan to do a permanent CNC conversion, that QC gearbox'll net you $300 to $500 on eBay.

As for the servo issue, split the difference and go with a set of something like Clearpaths. I probably should have on mine, though for the time being the closed-loop steppers and working just fine.

And as for the tailstock, as I recall those later Logans were either 12" or 14" swing- keep in mind the tailstock would have to match that, and the later ones are a lit more rare than the 10" and 11" ones like mine. And for CNC use with a turret like that, you really wouldn't be able to get much use out of a tailstock anyway, I think.

Doc.

[tyrone shewlaces]

Well other than the dirt & grime, the thing doesn't appear to be too bad on condition at all, so that's good. At first glance the picture does seem to look like it's got an L00 spindle, but after seeing it in person I suspect the nose is threaded and simply has a thread protector ring mounted, which is fine too. Well I guess in terms of making my own back plate, I guess threaded does make it simpler than L-type anyway. I do love the L-type design, but I guess it won't matter much in the long run. At any rate, fitting a chuck should be pretty straightforward. If it's threaded and I do get around to fitting a chuck, I'll design some kind of lock into it to resist accidental "automatic removal".

Yup on the vari-drive. But it did come with the parts as it was just disassembled and parts not lost to the ether, but I agree with you that converting to direct drive and CNC spindle control will be preferable anyway.

I do plan on a permanent CNC conversion and I hadn't had time to consider parting the excess out yet. Heck, the thing just got free! (maybe)

When I was looking into servos I was intrigued by the Clearpath line. They are indeed compact and kind of tidy, but a bit deeper research netted discovery of a couple other brands which provide more torque and speed for equal or less $$. I can't remember now of course but I'll find it again. I have a few months to work that out. They have standard separate drivers but I won't mind that. Only need to install it all once.

My turret tailstock is pretty large and might be "roughly" appropriate size for this lathe, but I also agree that the utility of a tailstock might not be there, other than simply being able to add 6 more tools that don't take up stations in the turret. Honestly I don't think I'll require more than 8 very often if ever, so that will probably be a wait & see.

[RB211]

Don't CNC it, do an ELS instead.

[Doc Nickel]

At first glance the picture does seem to look like it's got an L00 spindle, but after seeing it in person I suspect the nose is threaded and simply has a thread protector ring mounted[.]

-Yeah, it did look ikind of odd, not being able to see the L-series external locking ring. I suspect you're right, especially considering the collet closer is fitted.

If it's threaded and I do get around to fitting a chuck, I'll design some kind of lock into it to resist accidental "automatic removal".

-For CNC use, if you're going to use a controller capable of rigid tapping, it's basically a requirement. Unless you use the collet setup, which won't "unscrew" like that.

I do plan on a permanent CNC conversion and I hadn't had time to consider parting the excess out yet. Heck, the thing just got free! (maybe)

-Yep. I made my conversion "reversible", as I plan to upgrade from it to a purpose-built CNC lathe at some point, something with a proper turret. If I wasn't planning that, I could have sold my QCGB, old capstan-wheel turret, and binful of turret tooling, for a couple grand all together.

When I was looking into servos I was intrigued by the Clearpath line. They are indeed compact and kind of tidy, but a bit deeper research netted discovery of a couple other brands which provide more torque and speed for equal or less $$.

-Don't get too carried away, there's a limit to how much power and speed a conversion might need, especially if you're not looking for actual production-run speeds. For a homebrew unit like this, and in a home-shop setup, excess power and speed can cause more problems- read that as "crashes" ) than it solves.

In my case, my steppers aren't all that fast, but really, given a top spindle speed of just 1,300 RPM, unless I'm roughing something soft, like Delrin or Acrylic, the speed of the drives isn't the bottleneck.

My turret tailstock is pretty large and might be "roughly" appropriate size for this lathe, but I also agree that the utility of a tailstock might not be there, other than simply being able to add 6 more tools that don't take up stations in the turret.

-Oh, did you mean an actual handwheel type turret, the classic Warner-Swasey style ram turret? You won't be able to use that anyway- it won't clear the saddle and cross slide. You might be able to use a standard tailstock, for long, thin pieces, but I suspect you'll run into clearance issues there as well.

Doc.

[tyrone shewlaces]

Yeah my T.T. is the big hand wheel type. I haven't had a chance to look yet, but I believe you are correct and there won't be clearance anyway.

Checked our the spindle nose. It's 2-1/4 x 8 threaded.

Ways appear to be pretty good. Very minor wear.

Checked the cross slide and turret out a bit too. The cross slide gets pretty tight out at the X+ end. Only slightly disappointing since that was about 90% expected. I can fix it.
Turret works, but a bit goofy. Kind of overshoots and is overall a little clunky in operation. Need to check out the innards to see if it can be made to work snappier.

Spindle bearings seem smooth. But my luck never goes that way so not holding my breath there. Already used what luck I had on the purchase price. They certainly aren't trashed at least. Who knows? I might catch a break.

[mattthemuppet]

sounds like a fabulous project and plenty of experience on here to help you on your way. I'd start keeping an eye out for decent quality ground ball screws on eBay and the like, by all accounts they pop up every so often and you can get high quality screws for not much more than the basic rolled screws from China.

[Doc Nickel]

Yeah my T.T. is the big hand wheel type. I haven't had a chance to look yet, but I believe you are correct and there won't be clearance anyway.

-Really, in my admittedly limited experience with both manual turrets and CNC lathes, eight tools is generally plenty. I think the most tools I ever had set up in my manual turret was five. Six only if you count the material stop. And in that case, if it were a CNC, I could jhave used just two.

Eight in the primary turret is almost certainly more than enough for most day-to-day projects.

Turret works, but a bit goofy. Kind of overshoots and is overall a little clunky in operation. Need to check out the innards to see if it can be made to work snappier.

-The question will be how it works, and how that mechanism can be automated. Ideally, if you can just fit a stepper somewhere to actuate it, that's relatively easy. Worst case scenario, you might have to have a stepper and maybe a pneumatic ram or short linear actuator, and have to write a small macro.

I'd love to have a tool changer of some sort on mine, but I did the next best thing, and set mine up to use gang tooling. (I just need to build the actual tool holder, which I have to invent first.

Doc.

[Doc Nickel]

I'd start keeping an eye out for decent quality ground ball screws on eBay and the like[.]

-Definitely this. I went with the cheap Chinese rolled screws because they were cheap and available, and as I said, eventually I'll be returning this machine back to a manual turret, after I pick up a proper, purpose-built CNC lathe. But for a permanent, long-term machine, especially with fast servos, spring for the higher quality ground screws.

Doc.

[tyrone shewlaces]

eight tools is generally plenty

Yup I agree. Even back when I did production work, it was very rare to use more than 8. Even 8 would be a tapped hole and a counterbore if it required parting off, and even that is using the luxury (which is standard in production shops... but still) of separate rough and finish tools for both OD and boring.

Good to know about the ball screws. I have used cheap Chinese ball screws a couple times, but not on anything important so I didn't notice a problem. It would suck to cheap out only to find out too late that it ain't up to snuff. Fortunately I have a few months to be patient and watch for a good deal.

I was thinking if I could get the existing turret to work more smooth and consistent, I could just index with a simple actuator on the included lever. But I do see an advantage to hacking it with a constant driving motor for more intelligent indexing, i.e. for smoothly skipping over unused stations and maybe for indexing in either direction for efficiency rather than being stuck with sequential indexing. I could dream up some kind of 3-bit switch thing to keep track of the 8 positions. We'll see. I'll dig inside the thing and figure out what makes it tick first. I might tackle it in steps by utilizing what it has and keeping it simple at first, then get all fancy once the puzzle falls into place in my head. Heck, that's not a bad idea anyway since I'll certainly know what I want from it better once I've done a bit of work on it for a while.

I just need to build the actual tool holder, which I have to invent first.

Ahh. I see you like to do things the easy way too! Behold "the Wheel" !!

[Doc Nickel]

I was thinking if I could get the existing turret to work more smooth and consistent, I could just index with a simple actuator on the included lever.

-How does that turret work? Is it just a matter of flipping that handle with the red ball? One flip, which I assume is roughly half a rotation, to index one space? If that's the case, yeah, a couple of ways you could do that- a stepper would be easy, depending on the force needed, or a fat pneumatic ram. They even make small pneumatic rams with a built-in rack-and-pinion to produce a partial-rotation of a built-in shaft.

One thing to look into is how accurately the turret indexes. I know my manual turret was comparatively sloppy, particularly accurate work, I'd have to index it, then preload it by holding the turret rotated, and then tightening the clamping knob. Kinda takes the rhythm out of flippin' that handwheel around.

It may be worthwhile to more heavily modify the turret for more accurate indexing and locking.

Doc.

[J Tiers]

That turret is not the usual turret lathe type... might be better in some ways for CNC than the usual bed turret, but I'd like to see better pics to judge that.

[tyrone shewlaces]

-How does that turret work?

it's pretty much like you'd expect one to work. You move the lever up & back down and it indexes sequentially clockwise from one station to the next. Lifting the lever releases the turret and moves it to the adjacent station, lowering the lever locks it in place. The lock block is adjustable with a couple set screw things so you can tune it in. Basically it works just like the Hardinge HC turrets, but I don't know how either one is designed inside, so I can only say that externally they work similarly.
The turret has pretty deep wear dings at the spot for each station where it hits the back side of the lever thing, which is a stop for it. I'll have to build that up on all 8 stations if I want it to work better. It indexes as-is, but like I mentioned, it's movement is kind of klunky and inconsistent among the 8 stations. Once I take it apart further and peek at the innards I'll know a bit more.

At any rate, I think the thing will pretty much be on the back burner for some time. On the other hand, I do tend toward the obsessive and I'm sure between now and whenever I dive in for real, I'll occasionally explore the thing now & then to figure things out and strip things off in preparation for measuring and whatnot for the CNC fitments. I won't kill me to have a page full of numbers before I even start to look into which components might suit my druthers.

[mattthemuppet]

nothing wrong with mulling stuff over in your head for a while before you start. You can get through a lot of iterations of a project that way, before you even start.

[jmm03]

If you are going to keep the vari-drive, check the wear on the pulleys and the shaft. Once they get sloppy they induce a bunch of vibration into your drive train and they will fail. we had a conventional Logan at a place that I worked and I ended up pulling it all apart and sleeved and bushed it, Logan wants ridiculous prices for a new one.They are actually a very hardy machine. Jim