[g29cc]

I am curious , my sherline cnc lathe isnt what I thought it would be. Its definitely not what I was told it would be.

I bought one from IMserve. And I ll never recommend them to anyone.

But back to the point. I looked at a local 9x20 lathe and while I have a china 12x36 multi mill setup, the 9x20 seemed too small. My question is, while I wont be doing parts 36" long, I might be doing parts over 20" possibly and I am wanting this to be a one machine setup. In other words I dont want to have two lathes a cnc and manual. I would like both to be one machine.

Now on a 9x20 for instance, would my sherline equipment work on this satisfactory ?

It is a servo motor setup. Here is the link to the info from their site.

http://www.cadcamcadcam.com/index.as...PROD&ProdID=75

I would like something larger as a cnc lathe/manual lathe. But if I could take off my controls and setup and mount it to a new lathe even a 9x20 I would probably be a little happier then what I am working with now.

Thanks
Todd

[highspeedmazak]

I am not sure that is a large enough system for the 9x20 I am in the middle of converting a 9x20 to cnc right now. What size servos or steppers do you have?

I am curious , my sherline cnc lathe isnt what I thought it would be. Its definitely not what I was told it would be.

I bought one from IMserve. And I ll never recommend them to anyone.

But back to the point. I looked at a local 9x20 lathe and while I have a china 12x36 multi mill setup, the 9x20 seemed too small. My question is, while I wont be doing parts 36" long, I might be doing parts over 20" possibly and I am wanting this to be a one machine setup. In other words I dont want to have two lathes a cnc and manual. I would like both to be one machine.

Now on a 9x20 for instance, would my sherline equipment work on this satisfactory ?

It is a servo motor setup. Here is the link to the info from their site.

http://www.cadcamcadcam.com/index.as...PROD&ProdID=75

I would like something larger as a cnc lathe/manual lathe. But if I could take off my controls and setup and mount it to a new lathe even a 9x20 I would probably be a little happier then what I am working with now.

Thanks
Todd

[dareposte]

I did an analysis of what should be the minimum in terms of components for a 9x20 lathe, and am in the process of converting mine based on what I found.

In summary for Z axis + ballscrews you need a stepper (or servo) capable of producing 150 in-oz of torque at 300 rpm (at the screw). The X axis you could get away with less.

For the Z-axis + lead screw you need about twice that at the same RPM since the lead screw's efficiency is much less.

Honestly I don't think the sherline servo system would cut it, especially for the Z axis, but they don't have the motor torque curve (or any technical information for that matter) posted about them. If you geared it down and sped it up you might find it workable.

See the full analysis here: http://nerdulator.net/9x20/Engineering9x20_CNC.html

[g29cc]

What were the costs of the ball screws for a 9x20 ?


Here are the servo motor specs. I am new to building CNC equipment , so all the torque ratings and servo vs stepper pros and cons are all new to me as well. But I am very mechanically inclined. My biggest down fall is that I am using machines so much ( full time business started ) that I am looking to try and make things

A. Cheap ( of course )
B. Quick to convert and use
C. Reliable and able to cut stainless 1/2 material easily.

Globe motor (part 404052) with a timing belt reduction assembly. The assembly is a black enclosed box, with nema 23 stepper motor mounting holes, a .25 flatted shaft, and a shaft extension that can be used for a manual knob or lead screw handle. The reduction is approximately 2.8:1, resulting in an output shaft speed of 1000 rpm, 60 oz-in rated torque, and 500 oz-in stall torque.


This reducer is not designed to be used as a thrust bearing on an axis lead screw. Axis lead screw retention should be provided by another means. A flexible motor coupling is recommended to attach the output shaft from the reducer to the leadscrew of the driven axis.

The dimensions (in inches) of the reduction box are as follows:

Mounting 2.625 dia bolt circle, .195 dia holes, flat surface.
1/4 drive shaft extending approx 5/8 from mounting surface
Belt reducer assy is approx 1.25 x 2.25 by 6.25 long
Drive shaft is approx 1 7/8 in from endcap.

Setup data: The precise pulley ratio is slightly larger than 2.8:1. Use 5647.0588 steps per rev in quadrature mode (4X), and 1411.7647 in slot mode (1X).

[dareposte]

I orderd my ballscrews from Roton.com, and they were about $10.50/ft, plus $24/ball nut. Total was 4' of screw (1 36" section and 1 12" section) and 2 nuts. This is not anti backlash arrangement, and has about .005" backlash in the screw to nut. In my opinion for a lathe this is not a big problem, but you can ask Roton to pre-load them for you for an extra $10 per nut, and they will take out almost all the backlash. Total cost was about $85 for the ballscrew and ballnuts. They of course would need to be machined, but you can do that on your 9x20.

[dareposte]

For a servo system you really need about 120W or better for the 9x20. Since you already have what you have, why not try it out and let us know?

You can always bolt on another NEMA23 servo motor if it winds up too small, they make the BLDC and DC Servo's up to over 150W

[g29cc]

When saying 60 oz in torque at 1000 rpm and 500 oz in torque before stall, with the recomendation of 150 oz at 300 rpm, where does the stall power come from. The ball screw setup I wouldnt mind paying the money on a good set, but shoot at that price , and it is only a lathe, I can totally do that. I have a local almost new 9x20 jet lathe they want $600 for it, but I was thinking of offering $350-400 for it.

My main question though is this going to be tough enough to work with stainless and be used in small production runs ( I make small gun parts ). Thats mainly why I would be even looking at this setup.

I ll be getting a Tormach to replace the Sherline Mill since I do alot more with the mill then lathe. And I need something heavy duty ( and I know this will work ).

So if I could get out the door on the lathe for under $1000 that would be awesome. Heck if it would be easier to sell the CNC Sherline lathe as a package with everything , then I would do that and see about doing up the 9x20 or even larger with the extra cash. But I have about $2400 into the Sherline. (nuts)

Thanks
Todd

[dareposte]

The 9x20 should be fine for stainless steel if you are careful not to let it work harden. I'm not very experienced though so I'll let someone more knowledgeable handle that one.

The important torque is the torque at speed of the motor, not the stall torque. The two are usually related though, so buying a motor with a higher stall torque will usually (but not always) also give a higher torque at the operating speed. A higher stall torque will also give a machine with more grunt, especially with Servo systems. But in general for a CNC machine it's best to size the motor off the operating torque requirements, as the stall torque shouldn't be used often if at all for CNC. For example it doesn't do much good to have a 100W servo that operates at 15,000 rpm when you need to spin the ballscrew on a CNC machine at 300-500 rpm. You could either gear it down (and get backlash) or just operate very low in the speed curve The reason the manufacturers specify stall torque is 1) It's easy to measure, and 2) It sounds much more glamorous to claim "500 in-oz" instead of "150 in-oz @ 2000 pulse/sec". Motors can be built to operate most efficiently at a variety of speeds and torques, and there is an amazing number of optimizations out there. For specific examples look at linengineering.com or anaheimautomation.com, they both have pretty good reference material for steppers, and Anaheim has good information for BLDC and servo systems as well.

[g29cc]

The more I think about it , I dont do to many big parts, so I might be fine with a 9x20.

But I am just concerned about rigidity and accuracy out of the small lathe.

I was thinking of the Tormach duality lathe setup. If I am already going to get the Mill, the lathe setup might not be to bad to get also. But I do like the idea of having two machines so I can operate both at once.

Hmm.... decisions decisions...... my only real problem with doing a conversion is I need something now, plug and play pretty much. If could get someone to build one for me.......LOL

[dareposte]

The 9x20 can convert itself to CNC if you get a 4-jaw chuck with it and have a decent collection of hand tools. A drill press and/or mill makes it easier but aren't essential.

The basic plan to follow is 1) get a 9x20, 2) true it up so it does accurate work, 3) face all the X and Z axis brackets in the 4-jaw chuck, 4) measure the brackets and mark for boring, then bore in the 4-jaw chuck, 5) turn down the ballscrews and thread for locknuts, 6) tear the 9x20 down and install the CNC kit you just made. It might not be the prettiest but it should be plenty effective.

As to accuracy, if you take the time to true up a 9x20, and get it properly set up, then it is not too difficult to hold 0.001" in 10" with it. I got my 9x20 trued up to within 0.0005" in 14", and have had it hold 0.001" on a 12" test bar I cut out of drill rod. The key is to learn to grind and use HSS bits for it, and it will do good work. I have not had much luck with indexable insert tooling on it using carbite toolbits, I think it just isn't hoss enough to handle those.