Hey guys, I have a homier mini lathe and thinking about CNCing it.

After using the Bridgeport EasyPath CNC lathes at work and turning thousands of parts I have gotten an urge to convert mine, I woudl like it to be fully cnc and manual.

The main questions I have are what size steppers?

I had an idea for turning threads too, disingaging the spindle and driving the leadscrew and having the gear train to drive the spindle. Although it seems that would take tons of power.

Would a 300oz/in motor be enough for that? I would be hooking this up at the end of that screw and always have the halfnut engaged.

And for the X axis, I think i woudl only need about a 100oz/in motor right?

I was also thinking I might want to use a servo for the Z axis because if I miss steps, that would mean possibly throwing a rapid right into the chuck, that wouldnt be pretty;) for this I woudl definately use limit switches, kinda like how I should have on my mill;)


Let me know what you think.

Jon

I converted my 8x14 lathe to servo powered cnc, I using 360 oz-in motor on the z-axis, on a 3-1 reduction ratio. It has far too much power for that little lathe, but it was I had lying around at the time. The 3-1 reduction still gives me rapids of around 85 IPM, which again is far too fast. So yes, 300 oz/in will be fine, perhaps go for a 2-1 reduction depending on what speed you need.

alright, cool. I appreciate it. thats pretty much what I was thinking.

What do you think about threading like I have mentioned? will it have enough power to turn the spindle and move the axis?

I want to set mine up so that you can use it completely manually and completely cnc, thats what my goal is. when I get my mill set up again, Ill probably start working on it.

What did you use for your X axis?

-edit- The cnc lathes at work have like 3-400IPM rapids :eek: or thats what it reads before it says rapid on the screen.


Jon

Lol, 400IPM rapids on a mini lathe, I wonder how long the bed would last!
Seriously though, I am using Mach2 to control the lathe, with the aid of a tachometer fed into the software, cnc threading is possible. Mach2 will adapt the feed speed to maintain the proper pitch on the thread. Of course, I have not got that far yet since I have had no need to turn threads, but you may be able to use the info so the servo does not have to drive the spindle too.
As for my x-axis, I am using an unknown servo motor I picked up on ebay for about £5. It is a slow speed type - about 500 rpm, but bags of torque. I run it 1:1 ratio, and have never had it stall, even though I have some accidents with the work being pulled from the chuck. I guess 100 oz/in would be fine, our little lathes don't cut that fast, so you should be able to maintain the torque. Obviously, if you can get a more powerful one, it will be a bit of insurance against lost steps if you are going the stepper route.

thanx a ton man, Ill take a look at servos but if nothing comes up for a decent price, I will probably be using steppers. I know of a stepper motor that is 5v 1a but doesnt say anything about torque nor can I find it when I search the model number, if you know anything about how much it would have, let me know, otherwize Ill be looking around.

Jon

Those are fairly common numbers for 50-60 oz-in steppers.

I would say there is no way you can use the gears to run the spindle via the lead screw. You need to do it the way Kong mentioned by putting a simple tach on the spindle.

There used to be a fellow selling 114 oz-in steppers on ebay...can't seem to find him now. Someone else will pipe in with his ebay name...

Eric

Kong, I would be very interested in your 8x14 conversion. Is it documented anywhere on the zone? Pictures etc. I think my lathe is very similar, but I don't have the quick change gears. Either way I would love to see how yours was converted.

Eric

I think the guy is called deepgroove1 - I bought some steppers from him over a year ago now, so don't know if hes still around. Balsaman, ok I will get some piccies up, but it is a bit of a bodge job to be honest. I started buying the pulleys, then the company stopped selling the timing belts, so ended up buying bigger belts and using some crude bearings-on-bolts to take up the slack. I will get some photo's in the next couple of hours.;)

Here we go, some photos of my conversion. I hope you dont mind the thrad crash Jon, but hopefully they will help you out too.

So, in no particular order, the z-axis servo is mounted to a ali plate, which is bolted ontp the back of the lathe. I have used nuts as standoffs to align the pulleys. The large ali block in the foreground houses 2 deep-groove bearings - thrust would have been better, or even angular contacts. this conversion was done on the cheap!

http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0001.JPG
http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0002.JPG

The z-axis nut is delrin, 3" long, which should stop it from "squishing" undeer pressure.

Next is the extension I made to hold the x-axis bearings. the top was milled with my hacksaw and files to allow the x-axis to slide over the top. The leadscrew was replaced with a longer one, the nut was replaced with a bronze nut, and again, 2 deep-groove bearings on each end.

http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0003.JPG
http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0004.JPG

And next, the x-axis motor is mounted to an ali plate, which is offset to allow the motor to travel below the bed. The ali plate is mounted to a round ali block, which holds the leadscrew bearings. This, in turn, is bolted to the cross slide.

http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0005.JPG
http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0006.JPG

Lastly, a very simple control box holding two gecko 320's. Nothing fancy, simple engage/disengage switch, and power on/off.

http://www.btinternet.com/~jasonrsmith/Lathe/DSCN0007.JPG
Hope this helps. but like I said, could have been better if I had a few quid to spend. Perhaps when I get the wheels a rollin':D

Nice! So I take it you can no longer run it manually.

Eric

Nope, I use fly-by-wire! Hehe, jog it in Mach2 at a low feedrate.
You will know more than i do, but I think there are dangers of driving the servo motors with handwheels, don't they become generators or something? Are steppers different?

I know steppers are like that, I dont think servos are, they are mostly just dc motors arent they?


Jon

I want my pie and to eat it too, so I am planning ways to have both...

DC motors do beme generators when turned.

Eric

So, can you simply unplug the motor from the drive, or should there be some sort of resistor in there to soak up the generated voltage? It would be nice to have a manual cnc lathe, but I would want detatchable handwheels too.
Actually, there may a way to do it, but it would involve using rotary encoders as digital handwheels, so even then, you don't have the "feel" of the lathe.

As far as I know it does not hurt the 320 drives when the motor becomes a generator, so isolating the drives from the power supply should do it. Check with Marriss first.

I was thinking of ways to "disengage" the x axis from the drive mechanically, possibly using a new leadscrew to drive it and keeping the original intact allong with it's half nut and rack and pinion....not sure yet. Z-axis the options are more limited...

Eric

I was told that a DC motor would only become a generator if magnets were placed on the armature. I can't remember the last time that I took apart a DC motor, but I seem to remember that the armature is already magnetic, and that the windings are around it. Could anybody explain how the motor is made up so that I don't have to take any of my toys apart?

A "permanent magnet" motor does have magnets (obvious) and will act like a generator. Servo motors are of this type. The Ametek tape drive motors that many use in their CNC projects are also collected by renewable energy (windmills, etc.) folk.

You might be thinking of universal motors which are frequently retrofitted with magnets to become generators.

I made a small amount of progress on my lathe I drilled a hole in the end of the leadscrew, 1/4" and I made a 3/8 shaft with a .251" end that I press fit into the end, I made it long enough so I can still cut it down, turn it down or whatever I need to do. I also plan on putting a handwheel on the end of it along with a pully. I will be doing a 2:1 reduction for more torque with a japan servo motor 300oz/in stepper, same ones I have on my mill.

I need to find a 1-200oz/in stepper for the X axis still, I will do a similar thing to the x axis as I did with the z but I will be doing a 1:1 ratio and milling under the table thing for room for a small pully and offset the stepper downward or to the right.

Here are 2 pics of my progress so far:
http://jfettig.wc101.com/cnc/lathe/1cl.jpg
http://jfettig.wc101.com/cnc/lathe/2cl.jpg


I will be making either a brass bushing for the end plate so it has something to support the end with the pully and such, be using a ball bearing.

I plan on having the motor offset to the other side of the lathe and behind it.


-edit- what drives do you think I should get? I was thinking something along the lines of xyoltex but I need one that can do 4 amps for my 300oz motor. I only need 2 axises too.

Jon

Will you use the stock half nut, or a new nut to drive the x axis?

Im not really sure, maybe at first but I really should have a new one, I have the nuts from my mini mill still and I think they are the same, maybe Ill preload them just slightly or something.
-edit- dont forget to read my edit on the post before this one:D

Jon

Hi Jon,

I have some info on my minilathe conversions here:
http://www.wrathall.com/Interests/interests_index.htm

I replaced the leadscrews on mine with metric acme. Use 187 OzIn steppers on both axis with 2:1 reduction. The Z could do with a either a little more oomph (like say 300 Ozin steppers) or better yet, taking the time to file the undersurface of the bed so that the saddle doesn't have tight spots to bind on.

Thats pretty cool, nice work. I plan on setting up my X axis like that to to run multiple tool posts, today at work I had 3 tools going on cutting hosebarbs, was some pretty cool stuff!

I hope to get like 2 tools on mine at a time, or Ill make a rotary tool changer for it.

Jon

Thanks for the kind words Jon.

How are you intending to address backlash? I am not too happy with the preloaded brass nuts on X, as they need pretty regular adjustment. I wish you could fit a ball screw in the cross slide.

I really dont know what I will do about backlash, I think Ill worry about it when I get to that stage;)


Jon

Ballscrews are the way to go, but on a lathe, it is X which really needs to be backlash free. Z is less critical as you can do all finishing cuts in one direction for most work.

If you can fit a small ball screw in your saddle, you really should. Even a cheap rolled ball screw from McMaster-carr will be better than a preloaded AMCE setup. I realise that cheap rolled ballscrew is not that accurate at0.004"/foot, but then again you only have about 150mm travel so a bad screw will still keep you within 0.002" if you get unlucky.

I have looked at the 3/8" ball screw from McMaster where the nut has a 3/4" diameter, and it might fit. The slot in the saddle is about 20x20mm, but I think the leadscrew centerline is below the center.

I can highly recommend machining out the saddle to increase cross slide travel. If I had not done this, I would not have been able to use the Phase two Wedge type AXA tool post.

I'm following the cnc thread with interest, as I'm planning to cnc my 8x14 (Kong, you reading?) But I've yet to see a written-in-stone definition of which are the X, Y and Z axes on a lathe. What are the leadscrew, the cross slide and compound designations?
I suppose you never use the compound during CNC.

Larry

Ideally, the compund should be removed, which could allow for a more strurdy fixing of the tool post to the cross slide. Since I don't have a mill, I have no way to make a big ol' block of steel to the correct shape for this, so the compound has stayed.
As for the designations, the carriage itself is called the Z axis and the cross slide is the X axis. I guess these are related somehow to a plan view of a part drawn in CAD:confused:

Kong,
Your pictures don't show all, but your 8x14 lathe looks like our Lathemaster CQ6120x320. Is it?

Larry

Similar I think, it can be seen over here (http://www.axminster.co.uk/default.asp?part=BV20M) which is where I bought it from. Very nice lathe, shame to CNC it really, but needs must.

Nope, not the same. Still, a VERY nice looking lathe. You Brits sure have a lot more choices in machinery than we have in the states. Unfortunately, your prices are waaay high.

Im taking a look at this again, Im looking for leadscrews but not finding much for decent prices. I am looking for a 3/8" diameter leadcrew for the cross slide, the leadnuts seem to be the expencive part. Ill see if we have the stuff to turn them at work if I remember.

Im actually designing a replacement saddle and cross slide that will give me tons of travel.

I have 3 leadscrews from my mill(2 from my mill and another identical one) one has left hand thread, would work perfectly but too short, I have another Y axis screw and nut, but only one nut, it fits on the existing screw that is on the lathe, but then I would be lacking another if I used that screw.

I have looked around mcmaster quite a bit, if I was to get 5/8" ballscrew, it would cost me about $40 for the entire z axis screw and nut, I woudl have to figure out a way to cover it though.

I looked for leadscrew and nuts, the nuts I have found cost close to as much as 5/8" ballnuts. I was hoping that the 3/8" ballnuts were as cheap as the 5/8" nuts, I would use one of those for the cross slide.

Edit Now that I look at it, it appears that there is plenty of room in my desing for a 5/8" ballscrew and ballnut, I dont know if I want to mess with preloading them though, It would possibly remove a lot of travel and cost a great deal more.

Let me know if you know of any sources.
Jon

http://www.pro.com.sg/CNC.htm
Any good? :stickpoke