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helical lathe prototype - choice of components

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Neil Wyatt14/07/2018 20:40:40
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You can disable the temperature settings. Many printers don't have heated beds, and these rigs are often used to make dual head printer/router machines.

Neil

john constable14/07/2018 20:52:29
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Posted by Neil Wyatt on 14/07/2018 20:40:40:

You can disable the temperature settings. Many printers don't have heated beds, and these rigs are often used to make dual head printer/router machines.

Neil

Thanks, Neil. So would that reduce the current requirement for a nema 23 low enough for one of these boards to cope?

john constable15/07/2018 18:35:08
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Posted by john constable on 14/07/2018 20:33:59:
Posted by Martin Connelly on 14/07/2018 18:41:02:

The problem of low torque stepper motors is if they get a small kick when a tool cuts a shaving or bit of swarf they can miss steps. Once out of position they keep on merrily moving things around in the wrong position until there is human intervention or the program stops having produced something that is not quite right. You don't get these types of force with 3D printers, there is no high speed tool spinning around.The other thing is you may be underestimating the amount of force needed to push a work piece and tool together for the cutting action to take place. These motors when used with 3D printers are often driving fine threaded studding which gives some mechanical advantage. Is this what you were thinking of using instead of ball screws? They are not used to push a cutting tool into a work piece either. The Gcode for what you want is trivial don't sweat over it but do get suitable equipment for what you propose otherwise you could be wasting money.

Gcode for a barley twist

G01 X0 Y0 Z0 A0 F50 (Move to starting position. Tool over the centre of the work piece at one end and just touching the work piece. Use A=180 for a second start 180° around from the first and add 180 to the A value below ie 360+180=540)

G01 Z-1 F25 (Move the tool down 1mm into the work piece)

G01 X250 A360 F50 (Move the tool 250mm along the work piece whilst rotating the work piece 360°. Change 250mm and 360° to suit your requirements.

G01 Z2 (Lift the tool away from the work piece)

G0 X0 A0 (Rapid move back to X=0

G01 Z-2 F25 (Lower the tool 1mm more than before to do a second cut)

Repeat with decreasing Z until you have got to the depth you want.

Martin C

Thanks, for all that Martin. It's been very useful. It's also my first look at real g-code!

can you recommend a good resource for learning g-code? G-code for dummies?

Martin Connelly16/07/2018 09:10:58
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CNC cookbook has some online training that would be a good start.

**LINK**

Martin C

Martin Connelly16/07/2018 09:15:28
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This site also has a short course on milling with Mach3 but part 1 seems to be off line, Neil please note, here is part 2.

**LINK**

Martin C

PS

I have found an alternative link to part 1 that seems to work.

https://www.model-engineer.co.uk/news/article/cnc-milling-with-mach-3--part-1/4787/

Martin C

Edited By Martin Connelly on 16/07/2018 09:18:31

john constable16/07/2018 14:50:25
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I found cncsimulator and its a fantastic free program with lots of tutorials and support. Last night I used it to write my first bit of g-code - yaaaaaaaaaaaaayyyyyyy! I actually cut a thread into the end of a rod on a metal lathe.

The problem is (and I think this might be an issue with all simulators) that my machine design is non-standard so it doesn't simulate properly. CNCsimulator does allow you to create a custom machine but it's a seriously advanced function and I think well beyond me.

XD 35116/07/2018 16:18:21
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Posted by john constable on 14/07/2018 20:52:29:
Posted by Neil Wyatt on 14/07/2018 20:40:40:

You can disable the temperature settings. Many printers don't have heated beds, and these rigs are often used to make dual head printer/router machines.

Neil

Thanks, Neil. So would that reduce the current requirement for a nema 23 low enough for one of these boards to cope?

On a ramps board the heating power controll is separate to the motor power so it wont make any difference , the motor controllers are designed for 17 sized motors with a 2 amp current and you will have to tune the controllers - plenty of stuff on the internet or youtube about that and it is fairly easy .

The main reason for disabling the heating is so the gcode doesnt hang waiting for something to heat up that isnt there or stall because of an alarm for overtemp / too long a heating time .

Martin Connelly20/07/2018 16:04:04
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I lashed up an A axis on my mill with a small stepper I had and the electronic driver board for it. I used a pen to mark a tube to show the result of rotating the A axis through 360° and at the same time traversing the X axis 150mm.

I then rotated the tube 45° and repeated to give 8 lines on the tube. If you imagine doing this with a piece of wood and a ball end milling cutter you can see how it is quite easy to produce decorative twists in round stock. I couldn't actually cut anything with this setup as the stepper motor was such low torque (0.7 amps per phase) that even with an axial gearbox on it torque to drive the workpiece around was very low and the motor stalled with both too high a speed or the slightest resistance in the set up.

CNC was done by manual data input in Mach3, no CAD or CAM required.

Martin C

img_20180720_143346.jpg

img_20180720_144821.jpg

john constable20/07/2018 16:48:06
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20180719_203006_resized copy.jpgThat's excellent Martin. It'll be exactly what I'm looking for. Although I might use a ball-end cutter for some effects, a point cutting roundover bit will give me a rope twist.

I've gradually been taking delivery of components and its its been my first chance to lay things out. My rotational axis is a rotating table and 4 jaw chuck. I can't remember how many turns per table rotation but its quite a lot so I hope the required torque wont be that much as a direct 1 to 1 ratio. Mind you. the reason I'm making a prototype first is so I can make these kind of mistakes and learn from them.

20180719_202711_resized copy.jpg

john constable20/07/2018 17:04:57
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did you use a tailstock martin?

Martin Connelly20/07/2018 17:11:49
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I run Mach3 on laptops with Widows XP on them. It does not require a fast computer or massive drives but does require a parallel port or a USB board that is provided with a driver program for Mach3. If you have an unused laptop lying around it would be good enough to run a couple of stepper motors. See this video Youtube video showing how minimal a setup can be for two steppers.

Martin C.

**LINK**.

john constable20/07/2018 17:17:43
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wow. I do have an old laptop but I dont think it has a parallel port. I'll have to check.

Would this setup run to 3 steppers?

Martin Connelly20/07/2018 18:42:03
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If you go to the website for Mach3 you can download the manual that shows the pinout for a parallel port. If you get a USB breakout board then you get the equivalent of two or three parallel ports. The manual shows the pinout in paragraph 4.4.1 and has outputs on pins 1-9, 14, 16 & 17. If you have enable, step and direction signals for each motor then you can run 4 motors but have no outputs for anything else. There are plenty of 5 axis breakout boards for Mach3 available which make connecting to a motor easier than using the parallel port and for a cost below £5. They are available as 5 axis so cover your needs.

No centre supporting the tube, I was only pressing on it with a pen. I would support both ends if machining.

Martin C

john constable20/07/2018 19:51:50
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thanks martin. Those 5 axis breakout boards you mention - are they usb or parallel?

Martin Connelly21/07/2018 11:22:27
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I think the cheap ones use the parallel port but have a USB socket to supply 5V for the control circuitry. If you want a full motion control system that gets its instructions from the USB link they cost more. Look up Smooth Stepper for an example. USB control instructions have the advantage of not relying on the speed of the computer to time everything. Having said that many people use the parallel port on older computers, including laptops, with no problem.

Martin C

Andy Pugh11/09/2018 11:17:58
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Am I too late to suggest LinuxCNC? (I should admit that I am a developer, but as it is free and open-source I derive no benefit from expanding the user base).

Another developer, Dewey Garrett makes beautiful things using a home-built ornamental lathe controlled by LinuxCNC. You can see his machine in the video at the bottom of this page:

http://www.deweygarrett.com/

 

 

Edited By Andy Pugh on 11/09/2018 11:18:32

john constable11/09/2018 12:08:31
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No you're not. I havent finished the hardware yet so software comes next.

I think I've decided that I dont need sophisticated tool control of the type needed to carve a design in 3D. I just need basic algorithmic control to move the the tool in and along the work and out again at a certain speed while rotating it slowly.

I think linux cnc is going to be excessive for that. I need something I can write and check my gcode in and if possible a simulator and I need to transfer my gcode to the arduino via usb.

still open to suggestions though.

Andy Pugh11/09/2018 12:18:03
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If you have already decided to use an Arduino then I am too late

(LinuxCNC won't run on an Arduino, and does the same job in the system as the code on your Arduino)

john constable11/09/2018 12:23:10
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thanks, Andy.

Nick Hulme04/11/2018 20:32:13
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Posted by Andy Pugh on 11/09/2018 11:17:58:

Am I too late to suggest LinuxCNC? (I should admit that I am a developer, but as it is free and open-source I derive no benefit from expanding the user base).

Without derailing the thread are you, as a developer, able to offer a brief synopsis of why Linux CNC never has any good functional mileposts which users can choose, the exact reason why Tormach had to spend money to get to a good usable system for 3/4 axis mill users developed without the need to for said users to "eat, collate and assimilate a ream of dispersed documentation" ?

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