Hello CNC world

[robertodocc]

Hi guys,
I'm new reader, from Italy.
Great pleasure to be here to read your tips. I'd like to build a self made router to build wood objects.
A 4 axis...
Any suggestion where to begin from?

Thanks
Roberto, Florence

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[NIC 77]

Size of the parts you want to make, ie: cutting area? Expectations for performance, speed, depth of cut, etc?

What kind of equipment do you have available? Ie: Welder, bandsaw, drill press, mill? What kinds of materials are you comfortable working with to build this machine, ie: steel, aluminum, wood?

What is your budget? How much time do you want to spend building this?

All things that will help us to give you some relevant feedback.

The best thing to do on a first build is to find an example of a machine that works well and is within your capability to make, and do the same thing.

[robertodocc]

Size of the parts you want to make, ie: cutting area? Expectations for performance, speed, depth of cut, etc?

What kind of equipment do you have available? Ie: Welder, bandsaw, drill press, mill? What kinds of materials are you comfortable working with to build this machine, ie: steel, aluminum, wood?

What is your budget? How much time do you want to spend building this?

All things that will help us to give you some relevant feedback.

The best thing to do on a first build is to find an example of a machine that works well and is within your capability to make, and do the same thing.

Thank you NIC77
I like working with metal and wood. I have stick welder, drill press, circular saw for metal and wood, neither mill nor band saw.
The budget is low, as possible.
The real target I'd like is to build spear gun for fish in sea, so hard wood is the material I'll use.
The machine will be 1500 mm x 300-400 mm.
The first answer is: will I need a stepper motor for longitudinal moviment or a servo one?
And in first case, what is the torque I need (3Nm?). And for Y and Z and the fourth axis? And is better use a movement with ball screw or a tooth band for longitudinal movement?
Thanks again

[NIC 77]

With a good variable speed drill press, you should be able to drill holes in steel no problem.

It you build this out of steel it will be a project that will take significant time, whereas if you used something like T-Slot it could be done quite quickly.

I like my small mill because I can use it to make brackets where the holes are spaced perfectly to mount bearings, etc, however if you're careful you can do it all with a drill press.

The hardest thing about steel is getting it flat, so if you use steel you may need to use some epoxy leveling, however this isn't always the case.

For the size of movement you're talking about on the longer axis (1500mm = 59"), and the fact that you want to cut hardwood, I personally think you will be better off with rack and pinion for the X and Y drives. It should also be easier to make this way. However you could also use high lead ballscrews, but I don't see any added advantage in doing this.

I had a look at some spear fishing videos today. I like to swim with my fins and mask and will often swim out way farther than anyone else at the beach to the point where the people on shore loose sight of me. I'm fat, so there is little danger of drowning. .

How many of these do you want to make? Do they need to be 59" long? Does that include a little extra space at the ends to cut them free and the end, because you will need that.

Steppers should work just fine for you. That's what I'm using. No one can tell you exactly what size of motor you need at this point, and also the holding torque is not as important as the torque available at the max speed you plan to use them. You need to design it first. Nema 34s with low inductance values should be fine, however depending on how you orient your axis and how heavy you want to make this thing, you may get away with Nema 23's. A good stepper electronics system can also be not cheap.

For rack and pinion with a stepper motor you'll want a belt driven gear reducer with a ratio of 2:1 to 4:1. Look at the CNCRP (that's CNC Router Parts) kits to see what I mean there. But you don't have to use their parts, there are many different examples on here of how to do it.

You probably don't need a full rotary. If you are able to index at 90 degree increments, that will be enough. It depends on what you are willing to pay in money and time.

The best advice I could give you is to look at some other designs and build logs that people have posted and start drawing out some designs and come back with a design and ask for feedback on that. By looking at other designs you will get a feel for what materials you want to use, steel, aluminum, wood, and what you want to spend.

If you could buy a kit like a Saturn 2 from Fineline automation that was 2' x 6', that would be a good option for you, but it's not an available size. Then you could add a rotary. Have a look at their site to see what I mean.

With T-Slot you can make it whatever size you want and build from a kit, like the CNC router parts kit. The downside there is it can be quite pricey when you add everything together. To save money it's possible to build your own electronics and source your own T slot and rails locally, and just buy the parts you absolutely need from them.

[robertodocc]

Thank you for a so long and interesting answer.
The speargun is about 120 cm max so the 150 consider the extra space.
another question: would you use a spindle motor or a simple router?
and what you mean when say index at 90 degree: you unmount and re-mount the gun, rotating the piece at every 90 degree?

[awerby]

3-phase spindle motors, usually run with Variable Frequency Drives, are a much better choice for CNC than routers designed to be hand-held and used for short periods of time. They will run quieter, cut with more strength, and last much longer. They are more expensive, though. People who are trying to build a router on a tight budget sometimes start with a router and replace it with a spindle after the router dies from constant use.

If you're making a typical gantry router and want it to have a rotary 4th axis for doing things like your spear-gun without having to do all that mounting and remounting to cut each side, you might think about leaving an empty space in the table where the 4th axis assembly can fit, with the center of the axis at table height. Since you're only cutting on the top of the workpiece anyway, this uses your limited Z axis height to best advantage. Alternatively, you can mount it to one side of the table, but having it in the middle means you can span the gap with a large flat part when you're not using the 4th axis.

[robertodocc]

3-phase spindle motors, usually run with Variable Frequency Drives, are a much better choice for CNC than routers designed to be hand-held and used for short periods of time. They will run quieter, cut with more strength, and last much longer. They are more expensive, though. People who are trying to build a router on a tight budget sometimes start with a router and replace it with a spindle after the router dies from constant use.

If you're making a typical gantry router and want it to have a rotary 4th axis for doing things like your spear-gun without having to do all that mounting and remounting to cut each side, you might think about leaving an empty space in the table where the 4th axis assembly can fit, with the center of the axis at table height. Since you're only cutting on the top of the workpiece anyway, this uses your limited Z axis height to best advantage. Alternatively, you can mount it to one side of the table, but having it in the middle means you can span the gap with a large flat part when you're not using the 4th axis.

Thank you Awerby. Do you think that a motor 500W is strong enough?
I have another doubt: is it usual that a stepper motor loose a step or more? Is there a way to prevent this?

[awerby]

Thank you Awerby. Do you think that a motor 500W is strong enough?

Strong enough for what? For a spindle, that's at the bottom of the range, but it can be used for spindles cutting the traces on a PC board, or doing 3D work in light materials like foam. For making things out of hard wood, I wouldn't go much lighter than the 2.2 kw spindles that seem to be pretty popular around here.

I have another doubt: is it usual that a stepper motor loose a step or more? Is there a way to prevent this?

Stepper motors can lose steps if they are pushed too hard. They will also do it if they aren't getting sufficient power, if there's a mechanical problem, a failure of lubrication, or they aren't tuned correctly. You can avoid lost steps by switching to servo motors, but they have problems of their own, like trying to kill themselves if they hit an immovable object.