Cnc Lathe For Shipbuilding: Where To Start

[bigjimslade]

I have been trying to make a more detailed post but it is being rejected as spam.

For ship building, I need identical parts turned on a lathe. For example a 16" gun barrel in 1:192 scale is about 4-1/2" long and tapes in steps from 1/4" to 1/8" diameter. A 5" barrel is 0.9" and tapers down to 0.04". Generally the material is brass.

There are a lot of similar parts I'd be interested in making.

I am trying to determine if a CNC lathe would be cost effective. However, I can find virtually no information on where to start.

What software is needed? What hardware interface?
Are there any reasonably priced lathes that can do this small type of work?
What add ons would I need?

 

[tmarks11]

Gun barrel like you describe would be easy to make on a manual lathe. No need for cnc to make that.

Make them identical? How identical? Cutting them to within 0.010" is simple. Cutting them to within 0.003"? Still easy for a novice. Closer then that just takes a bit more care.

Making identical parts to within 0.001" doesn't require CNC. Making parts with complex curves? That is where CNC comes into it's own.

In terms of lathe sizes: it isn't necessarily harder to make small parts on a bigger lathe. I have a 13x40 manual lathe and would have no problems with the parts you are describing. You could also turn them on a 10x22 lathe or even a 9x30. But the smaller you get, the less rigid the machine, the smaller depth cuts you can take, and the more surface finish can suffer and may require hand working to clean-up the finish.

 

[JimDawson]

I have been trying to make a more detailed post but it is being rejected as spam

Welcome Aboard! It takes about 3 posts before you can upload pictures if that's what you are trying to do.

In answer to your question, Tim pretty much said it all. The real question is do you NEED a CNC for this project as described......No.

But if you WANT a CNC lathe, do a google search for Tabletop CNC Lathe. That's a good place to start your search. It's not that I don't want to answer you question, but you need to see what's out there. Then we can help you narrow your search. The other option is to buy a manual machine, and do the CNC conversion yourself.

The next item to concider is budget. This is a biggie and is going to determine what you can buy. You might be able to find a small used CNC lathe. A quick Craigslist search turned up this one in New Jersey
http://newjersey.craigslist.org/hvo/5733620394.html

As far as software, you will need, CAD, CAM, and depending on what you buy, maybe controller software. A used machine might come with all of this.

This may help to get you started.

 

[bigjimslade]

Let me fill in some of the details. In this area, the machine has to be small.

I have a 3D printer, CAD software, and software to drive the printer. CAD: Create the model and export the model in STL. Driver: Convert the STL to GCODE and drive the print. I expected something like that would work for a lathe.
In the case of a 5" barrel, that could be turned by eye. It simply tapers. A 16" barrel tapers, has several segments, and even flares at the end. I can't really imagine creating sets of nine that are absolutely identical (and would be sitting next to each other).

What kind of specs should I be looking for? When I looking at 3D printers, this was easy to find (e.g., layer height, nozzle diameter, table size).

Maybe, being a total newb here, I through "CNC Lathe" meant a lathe controlled by numerics (i.e. a computer). Yet most of the lathes I see that are "CNC Lathes" clearly are not computer controlled.
When I search for "tabletop CNC Lathe" on Google nearly all of the results matching that are not tabletop units.

 

[JimDawson]

I have a 3D printer, CAD software, and software to drive the printer. CAD: Create the model and export the model in STL. Driver: Convert the STL to GCODE and drive the print.

STL files would not work well on a lathe. Most 3D printers have a STL interpreter built in to the operating software. For a lathe you would normally export a 2D DXF file to the CAM program then process that to create the G-code for the lathe controller. CamBam if my favorite CAM program. Depending on what CAD software you have, it may handle all of it. It is also possible that the lathe operating software could interpret a DXF file.

I can't really imagine creating sets of nine that are absolutely identical (and would be sitting next to each other).

This is totally doable manually, but is dependant on the skill of the operator.

What kind of specs should I be looking for?

Normally you would be looking for basic size parameters of swing and length. Spec'd something like 9 x 20 (in inches). Beyond that weight, horsepower, spindle through hole size, spindle mount type. Then it's a matter of how much money you want to spend. You could buy a Hardinge or Mazak on the top end to really cheap import stuff. Part of the equation is how much space do you have.

Yet most of the lathes I see that are "CNC Lathes" clearly are not computer controlled.

A Google search generally produces a lot of results that are not what you are looking for. You have to sort the the wheat from the chaff. But the initial search generally will lead you in the right direction for a deeper search.

 

[JimDawson]

Here is another example of a small CNC lathe that would work for your application. I don't know anything about the quality. http://seattle.craigslist.org/est/tls/5759807126.html

 

[John Hasler]

In the case of a 5" barrel, that could be turned by eye. It simply tapers. A 16" barrel tapers, has several segments, and even flares at the end. I can't really imagine creating sets of nine that are absolutely identical (and would be sitting next to each other).

Identical parts of that sort were made in volume before CNC. Form tools, templates, box tools, taper attachments...

 

[cs900]

http://binghamton.craigslist.org/tls/5674620063.html

 

[Boswell]

Let me fill in some of the details. In this area, the machine has to be small.

I have a 3D printer, CAD software, and software to drive the printer. CAD: Create the model and export the model in STL. Driver: Convert the STL to GCODE and drive the print. I expected something like that would work for a lathe.
In the case of a 5" barrel, that could be turned by eye. It simply tapers. A 16" barrel tapers, has several segments, and even flares at the end. I can't really imagine creating sets of nine that are absolutely identical (and would be sitting next to each other).

What kind of specs should I be looking for? When I looking at 3D printers, this was easy to find (e.g., layer height, nozzle diameter, table size).

Maybe, being a total newb here, I through "CNC Lathe" meant a lathe controlled by numerics (i.e. a computer). Yet most of the lathes I see that are "CNC Lathes" clearly are not computer controlled.
When I search for "tabletop CNC Lathe" on Google nearly all of the results matching that are not tabletop units.

I have a CNC Mill but a Manual Lathe so fair warning. I also have a 3D Printer. you are correct that the process is similar for machining (Subtractive) vs 3d Printing (Additive)
Both start with a 3d model in a CAD system

Both use a CAM system to turn the model into GCODE but with the 3d Printer this is largely a simple process where with machining it is much more interactive. You will need to learn the basics of machining so that you can tell the CAM system how you want to machine the part, this will include how fast to turn the spindle, what shape of cutting tool you are going to use, How deep of a cut to make on each pass. All this by the way applies to manual or CNC. There are lots books and I referenced several but just getting in and making chips was also a really good teacher. It allowed me to ask better questions on the forums and understand the answers better.

Both use a motion control program to take the GCODE and turn it into Stepper (or servo) control signals. In the 3D printer world this is almost always built into the printer but in the machining world it could be an integral part but for many hobby level systems it will be a combination of a program like MACH3 running on a PC (there are others) and a motion control system that is part of the Machine.

My observation is that most hobbyist hope to get +- 0.001 inch accuracy in the parts that they make but many are probably pretty happy with +-0.005. Manual machining has the advantage that skill and experience can compensate somewhat for a low quality machine. This is also somewhat true for CNC systems but on CNC systems the experience and skill are used in the CAM phase.

From the sound of what you want to do, I would think that you would be hard pressed to visually see the difference between two parts that were 0.005 or even 0.01 inch different. Remember the tighter the tolerance the more time and money you need to spend on measuring tools in addition to the machine tool. Try printing a couple of test samples on your 3d printer with different diameters by .01 or .025 and see if you can visually see the difference. If not then I bet most any hobby level CNC lathe will work.

Now you might want to spend more and get a better machine as a way of "future proofing" your purchase so you will be able to do higher precision work on your next project.
One of the many things that influences accuracy in a Mill or Lathe is how Rigid the machine is. In simple terms the Heavier and Stronger the machine is the more ridgid it will be but there are many other factors as well.

One final disclaimer that I am not a machinist and only started this hobby about 7 years ago. I am 100% self taught (well I get tons of help from this forum). So I am sure that I have simplified things too much or possibly completely have something wrong so keep reading. And when you see a lathe you think might work for you, post a link and let the super experienced group on this forum comment about specific pros and cons.

 

[fahrphrompuken]

I through "CNC Lathe" meant a lathe controlled by numerics (i.e. a computer). Yet most of the lathes I see that are "CNC Lathes" clearly are not computer controlled.

That all depends on what you mean by "computer". The typical CNC lathe, mill, etc. is usually comprised of a dedicated PLC, and intputs, outputs, and an operator interface.
Except for the latest controls, a regular PC desktop computer does not interact at all with the CNC control, other than sending NC programs, parameters, tool tables, etc to, and from the control.

I would say that I agree with the other guys, a manual lathe will get the job done, unless more complex moves are required. A CNC lathe is going to cost a LOT more than a manual lathe with the same size, and rigidity. And then there's the CAM software.
After I got my CNC mill, the CAM software cost me over $1k for basic 3-axis. Not to mention the broken cutters created during the learning process.....

The cool thing with the mill (Dynapath control) is the built-in conversational mode programming from canned cycles, that generate the program from the machine, and then can save them to a file.