CNC building

[Patuc]

Hello,
Immediately sorry for my broken english. So, I want to make 4th axis CNC mashine for mostly woodworking, but I wish that with this CNC I could do PCB milling and sometimes aluminum milling.
Working area 80 cm X axis, 70 cm Y axis, 30 cm Z axis.
I read a lot of information, but often information on the internet is wrong, therefore I appeal to you, as experts in CNC mashine field.
I hope you help me and you will be able to answer my questions.

So:
1 question – mashine frame. Which frame is better: aluminum or metal? I read that aluminum frames resonates, meanwhile metal frames not, it is true?
2 question - rack and pinion vs ball screw for X axis. Because I want to do PCB milling sometimes, CNC machine must be accurate. But most of the time I do woodworking. 80 cm is quite long axisis, I read that for long axis you need to use rack, but is rack enough accurate, what to choose?
3 question – linear block vs linear bearing. Linear block is more expensive, but or it is big accuracy difference comapring with linear bearing? What to choose?
4 qustion - spindle: air-cooled vs water cooled. I think 3 kw spindle should be enough, but air-cooled or water cooled?
5 question - nema 23 with reduction vs nema 34 without reduction. Is better nema 23 EU FreeShip 4axis Nema23 stepper motor 425oz-in 3ADualShaft driver CNC Engraving | eBay with reduction or nema 34 4Axis Nema34 Stepper Motor 1600oz 3.5A & Driver DM860A & Power CNC Router | eBay without reduction? What do you think about that nema 34 kit? I read that 60 VDC 350w power supply is too “weak“ for that nema 34, so stepper motors is workin half of their capacity, it is true? What do you choose?

6 question – how many motors to use for X axis? If using ball screw it is enough one screw in midle http://cdn.instructables.com/FPK/PB8...FCR.MEDIUM.jpg or better use two ball screws in two sides? https://idea2reallife.files.wordpres...axis-sbr16.jpg
7 question – 4 th axis. What would you recommend to use: belt reduction https://www.buildyourcnc.com/images/...tock_1-800.JPG or worm gear reduction http://img.tradeindia.com/fp/1/001/268/319.jpg ?
And which stepper motor is better for 4 th axis? It is enough nema 23, or better use nema 34?

Thank you very much for your time and sincere answers

Similar Threads:

• hi there building a new one
• Building my first CNC!
• OT, need a little help on a new mfg building
• Building a gun?
• building my own

[ger21]

1) All frames can resonate, but steel is abetter choice.

2) I'd use 2010 ballscrews.

3) Do you mean round shaft when you say linear bearing? Accuracy will be the same for both.
Hiwin or THK type profile bearings are much stiffer and stronger, and can provide better quality cuts.

4) If you'll be running at 20,000 rpm for long periods of time, then water cooled may be a better choice. But air cooled are much simpler, and work fine. They are louder, though.

5) It depends on the drive system you are using.
I would not buy either of those kits.
Motors should be the last thing you choose, after the design is complete, and you know all the components that you'll be using.

6) two motors.

7) belt reduction, but a single belt is usually not enough reduction. Worm gears will typically have too much backlash. Again, motor choice depends on exactly what components you're using, and the performance that you want to achieve.

[Patuc]

WOW, super, so quick response, thank you for straight answers

1. Thank you I will use steel then, but there may be problems with welding - metal bend.

2. 2010 ballscrews for all axis?
3. Yes - round shaft: http://www.ozak-linear.com/wpparts/cate/cg2.jpg so better to use this type: http://www.hiwin.com/images/linear_guideways_large.jpg
4. Thank you
5. Wouldint buy because there is bad drivers and big inductance? What do you buy? I think nema 34 is better, because metal frame would be heavy.
6. Thank you

[ger21]

1) Yes, you may need to have the frame machined after welding. Some people use epoxy to create flat rail mounting surfaces.

2) You can use a 1605 or 1610 on the Z axis.
Btw, 30cm is very high for a Z axis. You may want to go smaller.

3) Yes, Hiwin are better.

5) High inductance. Also, make sure to get digital drives.
With 2010 screws, a smaller Nema 34 is probably the best option. Something in the 400-600oz range, with low inductance and 6-7 amps rating.

[Patuc]

Thank you

3. Hiwin is expencive brand, maybe to look for analogies?

5. Thank you, what do you think: connect stepper motor directly with screw or through reduction?

[awerby]

Stepper motors exhibit their best torque at a standstill; as they go faster, they get weaker. So it's usually best to connect the motor to the screw without any belt reduction, since that would trade speed for torque. You don't want to connect them rigidly, though - use an Oldham-style coupler to transmit motion, or you risk snapping the motor shaft or screw if there's any misalignment.

[wizard]

I'm a little late to this thread but will try to provide more insight.

Hello,
Immediately sorry for my broken english. So, I want to make 4th axis CNC mashine for mostly woodworking, but I wish that with this CNC I could do PCB milling and sometimes aluminum milling.
Working area 80 cm X axis, 70 cm Y axis, 30 cm Z axis.

This isn't that big of a machine, it should be fairly easy to put it together.

I read a lot of information, but often information on the internet is wrong, therefore I appeal to you, as experts in CNC mashine field.

Sometimes the Internet is wrong but sometimes opinions don't agree.

I hope you help me and you will be able to answer my questions.

So:
1 question – mashine frame. Which frame is better: aluminum or metal? I read that aluminum frames resonates, meanwhile metal frames not, it is true?

Steel for most of the machine, certainly anything structural. I generally suggest steel because large cross section Aluminum extrusions can be very expensive comparatively. Further you will need to machine both materials if you want the ultimate in accuracy. On top of all of that it is highly unlikely that a steel frame will come unwelded. I have seen issues with Aluminum T-Slotted frames so if you go that route you need to implement a lot of gussets and lap plates.

2 question - rack and pinion vs ball screw for X axis. Because I want to do PCB milling sometimes, CNC machine must be accurate. But most of the time I do woodworking. 80 cm is quite long axisis, I read that for long axis you need to use rack, but is rack enough accurate, what to choose?

I'd go ball screw. First your machining isn't that big that rack drive is warranted. Second I find lead screw
Ions to be slightly less demanding construction wise. A long axis information a lead screw would be in the 2+ meter range.

3 question – linear block vs linear bearing. Linear block is more expensive, but or it is big accuracy difference comapring with linear bearing? What to choose?

If you mean profile bearings, such as THK makes, the I'd say go with linear blocks. Round rails and bearings can be very good in a machine but the little bit extra $$ to go with profile bearings will give you a stiffer machine.

4 qustion - spindle: air-cooled vs water cooled. I think 3 kw spindle should be enough, but air-cooled or water cooled?

Probably water cooled. The problem here is the wide range of tasks you have planned for the machine. PCB routing could be done on a smaller spindle possibly with a much higher max RPM. In fact I'd seriously consider a smaller task specific machine for PCB routing. I know that you probably don't want to go that route, but a small moving table machine can be very rigid and precise for such usage.

5 question - nema 23 with reduction vs nema 34 without reduction. Is better nema 23 EU FreeShip 4axis Nema23 stepper motor 425oz-in 3ADualShaft driver CNC Engraving | eBay with reduction or nema 34 4Axis Nema34 Stepper Motor 1600oz 3.5A & Driver DM860A & Power CNC Router | eBay without reduction? What do you think about that nema 34 kit? I read that 60 VDC 350w power supply is too “weak“ for that nema 34, so stepper motors is workin half of their capacity, it is true? What do you choose?

Hold off until you have the design finalized You will want to know how much mass must be moved around and any physical mounting restraints that migh crop up.

6 question – how many motors to use for X axis? If using ball screw it is enough one screw in midle http://cdn.instructables.com/FPK/PB8...FCR.MEDIUM.jpg or better use two ball screws in two sides? https://idea2reallife.files.wordpres...axis-sbr16.jpg

Well this hard to answer not knowing more about the design. For instance is this a moving table or moving gantry machine? A moving table design might be fine with a single ball screw.

7 question – 4 th axis. What would you recommend to use: belt reduction https://www.buildyourcnc.com/images/...tock_1-800.JPG or worm gear reduction http://img.tradeindia.com/fp/1/001/268/319.jpg ?

How about a harmonic drive? In the end it depends upon your expectations. You can make a perfectly good 4th axis with belt drive. However you need a fairly large motor to drive it and a fairly hefty belt.

And which stepper motor is better for 4 th axis? It is enough nema 23, or better use nema 34?

Again it depends upon usage and expectations. In general though neither a nema 23 nor a nema 34 will be big enough. You will need lots of holding torque to lock the 4 th in place.

Thank you very much for your time and sincere answers

As alluded to above a lot depends upon your expectations. This isn't a large machine but it might be considered large for PCB milling. Also make sure you really need the Z axis height as this impacts stiffness.

In any event explore multiple ideas for your design.

[wizard]

WOW, super, so quick response, thank you for straight answers

1. Thank you I will use steel then, but there may be problems with welding - metal bend.

In a perfect world your frame would be stress relieved and then machined on a large mill. A lot of us can't afford to do that though. There are alternatives such as epoxy leveling or replicating from a surface place. You could also hand scrap in the surfaces if you have a lot of time on your hands.

2. 2010 ballscrews for all axis?

Generally it is easier to use a common size as it avoids having to do a bunch of calculations for every axis. But this can lead to a less than optimal design.

3. Yes - round shaft: http://www.ozak-linear.com/wpparts/cate/cg2.jpg so better to use this type: http://www.hiwin.com/images/linear_guideways_large.jpg
4. Thank you
5. Wouldint buy because there is bad drivers and big inductance? What do you buy? I think nema 34 is better, because metal frame would be heavy.
6. Thank you

High inductance. Impacts stepper motor performance. To overcome the high inductance you often have to use a much higher voltage to the motor amplifier. This can out you into a different class of drive (expensive).

As for what to buy, steppers are a low cost solution to machine motion. If your budget permits there are all sorts of servo technologies out there. Brushed servos these days are fairly cheap but if you go with servos do yourself a favor and go brushless.

In any event designing with steppers requires keeping an eye on how torque rolls off with a specific motor/drive combo. You need enough torque to operate correctly at your expected max feed rate.

[louieatienza]

1 - All frames resonate... just some at a higher frequency than others. (Higher is better.)
2 - Your machine is small enough to use ball screws.
3- Profile rail is best, though round rail is pretty affordable. Whatever you choose, make sure you fully support it.
4 - I don't think it matters too much. Water cooled may be quieter, and you won't have the fan exhause helping to blow chips all over.
5 - If you go with finer pitch screws use NEMA23, faster pitch use NEMA34, generally. It is a rookie mistake to get the biggest stepper motor, as there are other issues related to them as far as top-end speed, cogging, even overcoming its own inertia and detent torque. Friction and mass as loads are good for a stepper because they'll mitigate resonance. I run my main machine with 1/2"-8, 8 start screw (1TPI) and 425in-oz steppers, and I can't stall my machine by holding an axis, and even snapped 1/4" carbide end mills by rapiding into a fixture. Also if you use a finer lead scrw, you won't need reduction. You may need reduction if you use servos.
6 - Two motors are usually used to keep the gantry from racking and share the load on the generally heavier axis.
7 - Worm gear reduction usually very slow (90:1). I'd find a planetary gearhead, though most on eBay are servo grade. Another idea would be a harmonic drive if you can find one NOS. You can use a small motor because of the mechanical advantage; it would be very difficult to backdrive a planetary gearhead or harmonic drive. Worm reduction is not backdriveable, but probably has more play and less accurate positioning than the other two.

[Patuc]

Thank you all for answers I'am leaving for few days, when I back, I will write as soon as I can

[Patuc]

Hello, I can not believe it has passed all the summer, I work and travel a lot. Now it is time to build a CNC machine I believe that you have build a lot of CNC machines, so maybe you can offer some CNC machine plans? I think about X axis 1 meter, Y axis 0.7 meter, about Z axis I'am still thinking.