Router Forums banner
1 - 20 of 20 Posts

·
Registered
Joined
·
36 Posts
Discussion Starter · #1 ·
What makes a good CNC router? The following is my opinion yours may vary.

I post this with some reservation as I don’t consider myself an expert but merely a user of CNC equipment and there are many folks out there that have a better understanding of CNC equipment. I am posting this for new user’s to be able to compare different machines and understand what you are getting for your money. This can also give you some talking points when talking to a manufacturer about their machines. Feel free to post any misinformation you feel I have made.

Let’s start with construction of the frame. The easiest way to make a frame is with pre-fabricated aluminum extrusions. All you need is a saw to cut the extrusions to length they make fittings to create most any angle you need. If you do not need to take heavy cuts this may make a good inexpensive solution.

Weldment frames are a step ahead of the extrusion route they create a more rigid frame with less flex. The next step up found in very expensive machines would be heavy cast iron bases thick machines in the $150K and up class way above what the average small business and hobby guy is going to have. These machines usually weigh around 12000#+. For this discussion I am not going to talk any more about the pure industrial machines.

Let’s talk about guides and rails this is the next place some manufacturers cheap out. My first CNC used a hardened rail with a guide bearing this is OK but not ideal. I have seen some cheap stuff that even use some sort of skateboard type wheel running on an aluminum structure. Linear guide rails are the best alternative in this level machine the give a higher precision fit.

Next how is the machine driven stepper motors or servos? There are many different strength steppers with different resolution you need to compare one machine to the next. Most inexpensive machines will run some level of stepper motor. What is the difference between steppers and servo motors? I will not try and explain the very construction of each but the basic difference in how they operate. In general a stepper motor is an open loop system now there may be some exceptions to this, open loop means a signal is sent to the driven motor to make a move in a direction and in so many steps. The better the stepper motor the more steps per revolution it makes giving it a better resolution. This is something you can compare the resolution in steps per revolution usually given in degrees per step. To recap the control sends out a signal for the stepper motor to take X amount of steps in one of 2 directions which will equal some distance you program needed to move.

Servo motors are usually closed loop but not necessarily. Closed loop means when a signal is sent to turn the servo a certain direction it also gets a signal back saying that it actually made that move. This does not happen in an open loop system the control assumes the stepper actually makes the move this where the term skipped steps comes from. Skipped steps or missed steps usually ruin whatever you are cutting. I have experienced this with my first machine my current machine is servo driven. Servo driven machines are going to cost much more than stepper driven machines. This is just a basic difference there is much more to this equation but I am trying to stick with basics speed is also picked up with the use of servo motors. I don’t believe you will find and entry level machines running servos. I also believe they make some closed loop stepper motors but I am not sure about this.

Now that we have the motors to move the machine and some sort of guide rails we need a drive system either gears in a rack and pinion system or acme screws or even better ball screws. This is where backlash comes into play and limits the ability of a machine to make high precision parts this is usually stated as repeatable resolution. What does that mean simply put how accurate is the machine is over a specified distance it is repeatable to some measurement usually stated in a multiple in a thousandths of an inch or MM.
A rack and pinion machine will have some level of backlash that will increase over age in fact everything starts to wear as soon as you start running it. Not all rack and pinion machines are created equal helical rack and pinion is better than a straight cut rack and pinion.
A acme screw is a heavy duty lead screw but they tend to have a fair amount of backlash sometimes they have a half nut that can be adjusted to try and remove most of the backlash as they wear especially in an area where the machines runs the most your backlash will increase because if you adjust it up close it will be too tight in areas the machine doesn’t run enough. Most manual machines use this type drive. They can make an acetal half nut that has very little backlash but it will never be as good as a ball screw and in my opinion due to wear not as good as a good helical rack and pinion. The acme screw is probably the cheapest route but in my opinion the least desirable of the 3 methods I am comparing.

Ball screw driven machines in my opinion are superior to the others but many manufacturers use this method and the level of quality of the ball screws comes into play also. A cheap machine with an extrusion frame and ball screws is not going to outperform a welded frame with very good helical cut rack and pinion and better quality stepper or servo motors.

Next let’s talk about control systems. I am not a fan of open source control systems but they are a way of keeping a machine inexpensive. I prefer a control that has a dedicated computer that is furnished with the machine and uses a separate board to control the machine rather than being a strictly windows machine running off the mother board. This is the area I have the least experience with so I am going to leave it short. The best control would be a dedicated professional control but no machine in the class being discussed would have that control would cost more than the rest of the machine.

Cutting with a hand router compared to a spindle. A spindle will have much less run out than a hand router and will have more of the rated HP throughout a larger range of RPM. The spindle is also very quiet compared to a hand router. If you live in town will your neighbors tolerate a noisy machine running for hours?

In finishing this I will say all components play a part how many of the better components that are discussed does the machine you are looking at have. Almost any CNC is better than none. The machine with no level of tech support is almost worthless in my opinion unless you are an expert you will be needing help a good user forum for the machine you are buying is great and free tech support a must. Large industrial machine manufacturers often charge for tech support by the minute so being an amateur just learning having free resources are a must.
 

·
Registered
Joined
·
351 Posts
Good points and glad you mentioned that there are variants in each of the categories that make comparing full machines tough. I would not say "Almost any CNC is better than none" as there are examples of people spending good money for extremely little value.

I lean toward the ball screw movement for reasons you mentioned, but have seen two CNC Routerparts machines with the tension mechanism for adjustment of gear to rack pre-loading that seems like real close competitor. PRO Rack and Pinion Drive, NEMA 34 | CNCRouterParts

The steppers offered today are much better than a decade ago and the servos have come down in price. I'm still inclined to steppers.

I've ran Mach3 with Gecko for over a decade and been satisfied with performance and support. That said, I know that I need to change in the next year or so with no real idea on what to.

Steve.
 

·
Registered
Theo
Joined
·
7,195 Posts
What makes a good CNC router? My vote would be one that can do what you bought it for.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #5 ·
I made this post to help people weed their way through the information and try and make an informed decision it was not made to be a slam on anyone's machine if you can make good parts on a low budget machine that is great. This was not meant to be anything but help for people looking at machines and trying to compare. There have been several people lately asking and I have had PM's and phone conversations about these topics I thought it would be nice to put it in one place and for others to add their thoughts.

Mike
 

·
Registered
Joined
·
487 Posts
What makes a good CNC router?
One that makes lots of dollars. Buckets full that is.

My vote would be one that can do what you bought it for.
Not true @JOAT. My intention was to do the same thing at work, make signs.
Yet, realizing there's much more to be made. So much more that ideas are endless.
I'm more into making the things that make things work better. I dig jig building.
Hell, maybe one day I might make a fortune making underwear hangers.

Btw @Gundawg

I've seen a few machines that now carry brushless (micro?) steppers. Any insights to those?
Or is it basically same concept just they last longer.
 

·
Registered
Joined
·
29 Posts
Mike,
A good start for a beginner's guide but there are plenty of worms in the can! As someone who has built and upgraded his own machine, with a tight budget being a critical part of the design decisions, I would make the following comments regarding budget, amateur level machines before donning my tin hat and ducking below the parapet...

The rigidity of the frame and linear rails is critical. The rigidity of the gantry especially so (according to a Brazilian manufacturer one of my friends visited recently). Sheer weight will reduce vibration but likely add cost and reduce speed from a given size of motor. Careful design is important here to maximise the capability of the materials used.

Stepper motors are cheap and effective. As long as the motors and their drivers are rated and adjusted correctly and you run your machine within sensible limits they work. You will suffer some missed steps (along with some broken tools) as part of the learning process regarding feeds and speeds but the value of timber ruined is unlikely to exceed the extra expense of using servo motors instead.
Most machines use NEMA32 sized steppers having 200 steps/rev, these are by far the most common type of stepper and are widely available. One of these motors on a 2mm/rev lead-screw gives 0.01mm resolution. Micro-stepping (a function of the driver not the motor) increases the resolution at the possible cost of reduced speed.

Stepper drivers, breakout boards for computers, external controllers and the bits that go with them vary in cost enormously. Personal experience tells me that you can assemble the electronics for a working 3-axis machine using an old junk PC and the cheapo bits available from China for about $80 the lot. For maximum speed plus minimum noise, vibration and heat plus customer support from the manufacturer add another nought.

ACME lead screws are way cheaper than ball-screws but both require careful construction and installation of the thrust bearing to avoid backlash. I'm about to upgrade my machine to use new ACME screws with DIY thrust bearings and delrin nuts, both of which will be adjustable to reduce backlash and to take up wear over time. Watch this space!

That's probably enough for now.

Kit
 

·
Administrator
David - Machinist in wood
Joined
·
4,362 Posts
Mike,
A good start for a beginner's guide but there are plenty of worms in the can! As someone who has built and upgraded his own machine, with a tight budget being a critical part of the design decisions, I would make the following comments regarding budget, amateur level machines before donning my tin hat and ducking below the parapet...

The rigidity of the frame and linear rails is critical. The rigidity of the gantry especially so (according to a Brazilian manufacturer one of my friends visited recently). Sheer weight will reduce vibration but likely add cost and reduce speed from a given size of motor. Careful design is important here to maximise the capability of the materials used.

Stepper motors are cheap and effective. As long as the motors and their drivers are rated and adjusted correctly and you run your machine within sensible limits they work. You will suffer some missed steps (along with some broken tools) as part of the learning process regarding feeds and speeds but the value of timber ruined is unlikely to exceed the extra expense of using servo motors instead.
Most machines use NEMA32 sized steppers having 200 steps/rev, these are by far the most common type of stepper and are widely available. One of these motors on a 2mm/rev lead-screw gives 0.01mm resolution. Micro-stepping (a function of the driver not the motor) increases the resolution at the possible cost of reduced speed.

Stepper drivers, breakout boards for computers, external controllers and the bits that go with them vary in cost enormously. Personal experience tells me that you can assemble the electronics for a working 3-axis machine using an old junk PC and the cheapo bits available from China for about $80 the lot. For maximum speed plus minimum noise, vibration and heat plus customer support from the manufacturer add another nought.

ACME lead screws are way cheaper than ball-screws but both require careful construction and installation of the thrust bearing to avoid backlash. I'm about to upgrade my machine to use new ACME screws with DIY thrust bearings and delrin nuts, both of which will be adjustable to reduce backlash and to take up wear over time. Watch this space!

That's probably enough for now.

Kit
Good points, Kit. But I think you meant NEMA 23 motors.

David
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #9 ·
One that makes lots of dollars. Buckets full that is.



Not true @JOAT. My intention was to do the same thing at work, make signs.
Yet, realizing there's much more to be made. So much more that ideas are endless.
I'm more into making the things that make things work better. I dig jig building.
Hell, maybe one day I might make a fortune making underwear hangers.

Btw @Gundawg

I've seen a few machines that now carry brushless (micro?) steppers. Any insights to those?
Or is it basically same concept just they last longer.
I have no info on the motors you speak about I am far from an expert I laid out my basic knowledge to try and help others in a constructive discussion is what I was hoping for thank you for your responses. I agree the operator makes a big difference but that was not what this was about it was strictly a discussion on the different attributes of machines for sale.

Those guys that built their own machines have a much better knowledge of how all the parts work. I have never built my own machine but when the time comes that I retire fully I will probably sell the big machine I have and I would probably make my hobby machine.

Thanks for adding your info Kit I was hoping for folks like you to do so.

Mike
 

·
Registered
Joined
·
29 Posts
David,
I did indeed mean NEMA 23 motors. Thanks for spotting that one.

Ronnie,
I've never heard of a stepper motor with brushes, are you possibly thinking about spindle motors? Traditional mains powered, hand operated routers will have an induction motor using carbon brushes as part of the mechanical commutator. Modern 'Brushless' motors use transistor based switching to perform the commutation function and tend to be less noisy as a result but usualy require an external controller and power supply. Stepper motors, as I understand them, are a form of brushless motor.

Kit
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #11 · (Edited)
Servo motors come both with brushes and without. Most of the newer machines run brushless AC servo motors. My CNC bed mill has brushes in the DC servos and my newer CNC router has brushless servos.

One thing my bed mill has is glass scales and gives very good resolution for an old machine 97 year model. The glass scales are very accurate and are not effected by any backlash in the drive system the position is read from the glass scales. I have often wondered why they don't use this system more often especially with CNC routers. The glass scales measure actual position and have nothing to do with the rotation of the motors. I asked the manufacturer of my router why they did not use scales he couldn't give me an answer.

Mike
 

·
Registered
Joined
·
487 Posts
...
Ronnie,
I've never heard of a stepper motor with brushes, are you possibly thinking about spindle motors? Traditional mains powered, hand operated routers will have an induction motor using carbon brushes as part of the mechanical commutator. Modern 'Brushless' motors use transistor based switching to perform the commutation function and tend to be less noisy as a result but usualy require an external controller and power supply. Stepper motors, as I understand them, are a form of brushless motor.

Kit
I seen it over at TechnoCNC, here:
Techno User Friendly CNC Router Hand Held Controller | HD CNC Routers

It sounded special being called a microstepper yada yada yada. :grin:
Thought maybe it was something new.

Anyways... thanks for you insight there. I know for sure that I wont
be building one down the road. Pretty intense stuff.
 

·
Registered
Joined
·
29 Posts
Ronnie,
That's one serious machine! Way out of my league. I think there's a bit of sales hype in them saying "The Techno HD Series CNC Router utilizes brushless microstepper motors" as this is true of all stepper motors in practice, even the ones in my humble machine.

On another point mentioned earlier in the thread: I think one of the reasons for using racks instead of leadscrews, especially on bigger machines, is that a long leadscrew would be prone to whip when spinning at high speed as it is unsuported along it's whole length. It may be cheaper to manufacture as well as a rack can be made in sections. The helical design as shown on the machine Ronnie linked to should be nice and smooth running.
 

·
Registered
Joined
·
36 Posts
Discussion Starter · #14 · (Edited)
In the case of my machine they don't spin the screw they spin the ball nut. I have 125" of Y travel and it is capable of 2100" IPM rapid according to the manufacturer mine is set to rapid at 1600" IPM. The wiping lead screw is why they spin the nut on the long ones that use ball screws. The stationary lead screw on mine is 1.25" in dia.

When I bought my machine I looked at the Techno but I thought the machine I bought to be better. I also looked at the Freedom machines they are also very nice.
 

·
Registered
Rick
Joined
·
17,593 Posts
Ronnie,
That's one serious machine! Way out of my league. I think there's a bit of sales hype in them saying "The Techno HD Series CNC Router utilizes brushless microstepper motors" as this is true of all stepper motors in practice, even the ones in my humble machine.

On another point mentioned earlier in the thread: I think one of the reasons for using racks instead of leadscrews, especially on bigger machines, is that a long leadscrew would be prone to whip when spinning at high speed as it is unsuported along it's whole length. It may be cheaper to manufacture as well as a rack can be made in sections. The helical design as shown on the machine Ronnie linked to should be nice and smooth running.
Liking the helical gear rack a lot , but not liking direct drive steppers . I’d like to know what there rated back lash is.
Be more expensive to replace also
 

·
Registered
Joined
·
487 Posts
...

When I bought my machine I looked at the Techno but I thought the machine I bought to be better.
I also looked at the Freedom machines they are also very nice.
Lol... thats a good one. I was back & forth w/ Brandon @ sabre only to learn that Techno is 9 miles away.
So I'll be a local PITA if anything goes hoohah.
I plan to do a visit after Christmas/NY's to get a better idea what the 4x4 HD-II (step) & HDS (Servo) looks like
and see for a summers delivery. Real Estate in me garage is only 12x20 and I think I can squeeze it in.
We'll find out.

Hey lets get back to our scheduled program, these are monster machines.

I'd like to build a small machine but I dont have the electrical component experience.
Where would a person like I start out from scratch not knowing the setup? I'm talking
connecting all the electrical parts. Leave out the physical parts build, extrusions etc.
Im sure there's others that are stumped.
 

·
Registered
Joined
·
1,273 Posts
I didn't find it difficult to learn and apply how steppers are wired to controllers. A google search and the instructions that came with my controller was all I needed. The needed signal to the controller depends on type, but that is usually over parallel or ethernet or USB cables. Power to the controller will either be a plug to stick into a wall socket or 2 or 3 (ground) leads from a power supply that has it's own plug for the wall socket. Limit and e-stop switches will have dedicated inputs on the controller.

For a small machine I suggest looking into the tinyG controller: https://synthetos.myshopify.com/products/tinyg
It can be controlled over a USB cable and run with free downloadable software that runs on a windows PC.
 

·
Registered
Joined
·
377 Posts
I'd like to build a small machine but I dont have the electrical component experience.
Where would a person like I start out from scratch not knowing the setup? I'm talking
connecting all the electrical parts. Leave out the physical parts build, extrusions etc.
Im sure there's others that are stumped.
You can do it in a number of different ways. I chose to go simple, with well documented components, and didn’t have any problems.

I went with a system using an Ethernet Smoothstepper (ESS). This is a small board that connects to the computer with a simple Ethernet cable (mine is about 20’ long). The ESS has essentially 3 parallel ports, and generates in its own hardware the step and direction signals usually done in the computer relieving the computer of this real-time duty. Anything designed to connect to a parallel port can connect to the ESS instead.

To drive my steppers, I used the Gecko 540, which connects to the ESS with a single ribbon cable (it is designed to connect to parallel port).
The Gecko is a single integrated unit that drives all 4 of my steppers (connected using purchased pre-made cables). My VFD connects to the Gecko with 3 wires, giving me speed control of the spindle. My estop connects across two other pins (actually acts as the enable), and my 3 home switches also connect here. A couple of wires to a power supply each for the Gecko and ESS and that is it! This was the simplest design I could come up with, and both the ESS and the Gecko have well written (native English!) instructions, and good support forums. All the electronics easily fit in a box a little bigger than a shoebox. Mine is wood with a plexiglass cover so I can see all the status lights inside for troubleshooting.

This system can handle any size cnc router using Nema 23 sized steppers, but probably is not enough for Nema 34 sized ones. But my machine using Nema 23 does 600 ipm rapids and cuts at 200 comfortably. One of these days I’ll have to see just how fast I can push it, but I think I can go considerably faster.
@difalkner did a beautiful job wiring his somewhat more involved electronics, documented in his build log. His shows what is involved when using separate stepper drivers for each stepper, and he controls power to his VFD, water pump and a few other items using relays. He installed proximity limit switches at each end of each axis. He also has 2 separate power supplies to power his Nema 34 sized steppers. While not the most complicated DIY I’ve seen, it is certainly more sophisticated than my approach and should be seen as covering just about everything one might want.
 

·
Registered
Joined
·
487 Posts
...

@difalkner did a beautiful job wiring his somewhat more involved electronics, documented in his build log. His shows what is involved when using separate stepper drivers for each stepper, and he controls power to his VFD, water pump and a few other items using relays. He installed proximity limit switches at each end of each axis. He also has 2 separate power supplies to power his Nema 34 sized steppers. While not the most complicated DIY I’ve seen, it is certainly more sophisticated than my approach and should be seen as covering just about everything one might want.
Hah! Thanx Balloon & 4D.... Sorry David, I had forgotten about your build.
I'll check into this and see what comes about.

After finding out the Techno HDS 4x4 is $65k... :nerd: Lol we'll see.

Palpitations..... mellloooooo melllloooooo ok
 

·
Registered
Rick
Joined
·
17,593 Posts
Hah! Thanx Balloon & 4D.... Sorry David, I had forgotten about your build.
I'll check into this and see what comes about.

After finding out the Techno HDS 4x4 is $65k... :nerd: Lol we'll see.

Palpitations..... mellloooooo melllloooooo ok
65K for a 4X4 , that’s a little expensive. It probably has every whistle and bell ,like multi tool change and vacuum table on it though .

I like this thread Mike , as it’s interesting hearing other people’s views on the subject .
In my case , after many hours spent on forums and other sites , I can’t really find any fault with CNCrouterparts 4x4 Pro version of there router table , other than it uses T-slot aluminum as opposed to steel .
Here’s the link to one I would like to purchace next year
http://www.cncrouterparts.com/pro4848-4-x-4-cnc-router-kit-p-251.html

Its $4100 US , and I think that’s very reasonable for what you get . Seeing as I’m on the east side of BC , I have no easy access to parts.
After I source out all the parts and pay shipping from several companies , any savings would be most likely lost . All I’d be left with is the headaches involved trying to scratch build it .
To save money , I am going to build the electronics myself , as I’ve worked with electronics in the past , so I’m not very intimidated by that aspect of it .
There plug and play system looks very solid , but by building it myself I feel it may help with future trouble shooting .
I also want to run a water cooled spindle . A spindle with tool change would be nice, but I nearly fell off my chair when I seen the price .

What I am also liking about CNCrouterparts Pro version , is it can be expanded to a larger size in the future . In my opinion, that’s a bonus knowing I have that option if the time ever comes .
They have also upgraded from V-bearings to Linear rails , as I wasn’t a big fan of the V-bearings , but it wasn’t a deal breaker.
 
1 - 20 of 20 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top