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On this page you will find some general information about machining, NC'ing, g-codes etc.
It is information that we have found, been taught, experienced and discovered. Some of it has come from our forum, customers and suppliers.
We hope that you find plenty of useful info, food for thought and handy tips.
We don't consider ourselves to be the ultimate knowledge base in any respect - so if you find anything here which you know is not right, or have something you think should be added please send us an email.
Note that the page is in no particular order ... it's just snippets of information & notes as we think of them or come across them.
Servo's vs Steppers
Servo's are great ... no two ways about it ... but they require a far more expensive driver, require more power, are usually physically bigger and cannot position themselves ... in effect they are simple DC motors and that's why their controller is much more expensive as you need to have high resolution encoders on each axis to feed back to the system (eg Mach3) information about position. Servos are really just pure 'grunt' and RPM.
Steppers on the other hand are specifically designed for positional accuracy and require far less smarts behind them. As long as you can get a stepper to reliably 'step' then you can accurately know your position .. as long as they can do their step then they are totally obediant little servants. You can also marry steppers to hi-res encoders if you want/need positional feedback
Servos can run at high RPM which is why they are used in the high speed systems. Steppers will 'peak out' at a relatively low RPM - largely due to the fact that a rotation is a series of small steps.
What it all comes back to though is $$$$'s, balls & brains ... anybody telling you that you need servos on a small hand operated mill that is converted to NC has rocks in their heads ... THE limiting factor is simply SPINDLE SPEED ... without the RPM in the spindle you are limited with the speed at which you can push the tool through the work .... so putting big gutsy expensive servo's on a conversion is either due to having too much money to spare or being seriously anal retentive and following the 'in crowd' ... the only benifit you get with servos on these type of machines is faster rapids (ie when you move from one part of the job to another) - and they probably account for 3% of the movement in most jobs (so you might save a few seconds on a 1hr job) ... better off to use reliable steppers and put the extra cash into other tools that WILL make a differance.
Steppers on the other hand are specifically designed for positional accuracy and require far less smarts behind them. As long as you can get a stepper to reliably 'step' then you can accurately know your position .. as long as they can do their step then they are totally obediant little servants. You can also marry steppers to hi-res encoders if you want/need positional feedback
Servos can run at high RPM which is why they are used in the high speed systems. Steppers will 'peak out' at a relatively low RPM - largely due to the fact that a rotation is a series of small steps.
What it all comes back to though is $$$$'s, balls & brains ... anybody telling you that you need servos on a small hand operated mill that is converted to NC has rocks in their heads ... THE limiting factor is simply SPINDLE SPEED ... without the RPM in the spindle you are limited with the speed at which you can push the tool through the work .... so putting big gutsy expensive servo's on a conversion is either due to having too much money to spare or being seriously anal retentive and following the 'in crowd' ... the only benifit you get with servos on these type of machines is faster rapids (ie when you move from one part of the job to another) - and they probably account for 3% of the movement in most jobs (so you might save a few seconds on a 1hr job) ... better off to use reliable steppers and put the extra cash into other tools that WILL make a differance.
Please Note: This page is a 'Work In Progress'
It will grow gradually as we get the opportunity to add to/modify it.
X3 or Super X3???
(Also appears elsewhere on this site - but we get asked this one all the time so we put it here too...)
We recommend the X3 rather than the Super X3 for most customers.
Firstly ... although the X3 has a lower rated motor power it actually has a higher spindle speed which is good. Particularly for engraving etc as the higher the spindle speed the better - we are looking at producing an add-on kit that will take the X3 up to ~4000 RPM which is better and keeps a little headroom on the bearings (most standard bearings are only rated to 5000RPM). At 4000 RPM of course you drop a bit of torque however we've found that there's still enough power there to push a 10mm cutter full width at 2mm depth through aluminium.
Quill depth DRO ... becomes a bit irrelevant once the machine is NC'd as you end up with XY&Z DRO's. It could be useful for manual drilling but by the same token the standard X3 still has a scale on the quill handle.
Tapping feature .... from what we've read and been told it's a pretty good way to break taps!! You'd be better off saving the $$$'s and putting it towards a 'proper' tapping head attahment.
Tilting head .... if you really need to machine at angles then you would be better off with our TV6 kit on a 6" Vertex rotary table. We also belive that the 'non rotating' head of the X3 is more solid than the Supers rotating one. Finally (and most importantly) it is necessary to have your tools 'square' to the table. The process of machine alignment is called 'tramming' and takes anywhere from 30mins to 1hr to do properly - EVERY time you rotate the head you would need to re-tram the system otherwise parts won't be machined with square edges and facing would end up with a 'sawtooth' finish.
....but the Super X3 certainly looks nice
Firstly ... although the X3 has a lower rated motor power it actually has a higher spindle speed which is good. Particularly for engraving etc as the higher the spindle speed the better - we are looking at producing an add-on kit that will take the X3 up to ~4000 RPM which is better and keeps a little headroom on the bearings (most standard bearings are only rated to 5000RPM). At 4000 RPM of course you drop a bit of torque however we've found that there's still enough power there to push a 10mm cutter full width at 2mm depth through aluminium.
Quill depth DRO ... becomes a bit irrelevant once the machine is NC'd as you end up with XY&Z DRO's. It could be useful for manual drilling but by the same token the standard X3 still has a scale on the quill handle.
Tapping feature .... from what we've read and been told it's a pretty good way to break taps!! You'd be better off saving the $$$'s and putting it towards a 'proper' tapping head attahment.
Tilting head .... if you really need to machine at angles then you would be better off with our TV6 kit on a 6" Vertex rotary table. We also belive that the 'non rotating' head of the X3 is more solid than the Supers rotating one. Finally (and most importantly) it is necessary to have your tools 'square' to the table. The process of machine alignment is called 'tramming' and takes anywhere from 30mins to 1hr to do properly - EVERY time you rotate the head you would need to re-tram the system otherwise parts won't be machined with square edges and facing would end up with a 'sawtooth' finish.
....but the Super X3 certainly looks nice
Single or double ball nuts?
That's really going to depend on what you're wanting to do.
Good machining practice says to always come at the work from the same direction each time ... even on $300K systems. This completly eliminates any backlash error.
But for alot of people that is either too hard or inpracticle ... so the options are to go for dual ball nuts which adjust to take up the majority of the backlash or on a single ball nut system you can set up backlash compensation in Mach3 so that it will automatically apply the appropriate 'steps' to take up the backlash. It is virtually impossible on these types of machines to completely elliminate backlash. For example the X3 with it's square column - there's a 40Kg head hanging out in front of the column and it's lifted up and lowered down via a point only a few centimeters behind the gibbs. With the gibbs tight enough to prevent head wobble there will be a tendency for it to pivot about the gibb as the ball nut moves up/down. In extreme cases this can be seen as a judder as the head lowers or binding as the head raises -dual ball nuts go a long way to smoothing it out but there will always be some degree of backlash. Luckiliy most toolpaths lift the Z up to a retract height then bring it back down for the next cut ... so backlash is effectively removed anyway - and for toolpaths that don't do that then Mach3 (or other) is still able to apply backlash compensation which will work well.
Backlash can also effect the surface finish - particularly on the sides of jobs. If you imagine a cutter trying to force the stock away from itself then backlash gives it room to do that ... severe backlash can cause a rippling or wave effect as the stock/table pulses in/out back/forth with the forces on the tool.
But if this causes you to think that our single ball nut systems aren't good you need to 'think again'. Have a look at the photos below and you will see the surface finish on parts made on our single ball nut machine. Good quality 'made in USA' leadscrews can perform as well with a signle ball nut as some of the poorer quality double nut systems (or better!!!).
Good machining practice says to always come at the work from the same direction each time ... even on $300K systems. This completly eliminates any backlash error.
But for alot of people that is either too hard or inpracticle ... so the options are to go for dual ball nuts which adjust to take up the majority of the backlash or on a single ball nut system you can set up backlash compensation in Mach3 so that it will automatically apply the appropriate 'steps' to take up the backlash. It is virtually impossible on these types of machines to completely elliminate backlash. For example the X3 with it's square column - there's a 40Kg head hanging out in front of the column and it's lifted up and lowered down via a point only a few centimeters behind the gibbs. With the gibbs tight enough to prevent head wobble there will be a tendency for it to pivot about the gibb as the ball nut moves up/down. In extreme cases this can be seen as a judder as the head lowers or binding as the head raises -dual ball nuts go a long way to smoothing it out but there will always be some degree of backlash. Luckiliy most toolpaths lift the Z up to a retract height then bring it back down for the next cut ... so backlash is effectively removed anyway - and for toolpaths that don't do that then Mach3 (or other) is still able to apply backlash compensation which will work well.
Backlash can also effect the surface finish - particularly on the sides of jobs. If you imagine a cutter trying to force the stock away from itself then backlash gives it room to do that ... severe backlash can cause a rippling or wave effect as the stock/table pulses in/out back/forth with the forces on the tool.
But if this causes you to think that our single ball nut systems aren't good you need to 'think again'. Have a look at the photos below and you will see the surface finish on parts made on our single ball nut machine. Good quality 'made in USA' leadscrews can perform as well with a signle ball nut as some of the poorer quality double nut systems (or better!!!).
Cutting speeds
There's really two distinct speeds ... cutting speed and feedrate.
You need to try and get these reasonably correct. Too high in feedrate and you run the risk of breaking tools. Too slow in RPM/feed and you can actually case harden the stock and again break tools, get poor finishes etc.
Cutting speed is the speed of each tool 'tooth' (flute) through the work. It is calculated from the tool diameter and RPM with the formula
Cutting Speed = piDR/1000
Where pi =3.1415, D is the tool diameter (mm's), R is the rotational speed (RPM)
Here's a table that gives a very rough and general guide for various tool types/stock and their cutting speeds:
HSS CoHss TiNite TiN
Aluminium 40-60 50-70 60-80 70-90
Mild Steel 20-25 25-30 20-30 25-40 (derate all X 0.8 for Long Series cutters)
Please remember that those are pretty general figures which have been 'gleaned' off various tool manufacurers websites & data sheets. It is preferable to get the actual figures for the tool you want to cut with from the manufacturer/supplier.
Now to get the RPM you should be cutting at use this one:
RPM = (Cutting Speed X 1000)/piD
Where cutting speed is from the table above, pi is 3.14.15 and D is the tool diameter in mm's
Next we use the formula:
Feedrare (mm/min) = (Chipload per tooth) x (# of Flutes) x RPM
We have found that some of our 'fancier' tools actually need very high RPM to be working as they should so we created a simple spreadsheet using the formulas above to calculate the 'actual' feeds/speed and then applied that pro-rata for the RPM we had available. So if nothing else this info should at least give you a good starting point ... you may need to experiment and see if you need to go faster/slower.
See photo's above ... that reflective finish was achieved using these formulas. The tool was a TiCN 10mm 2 Flute end mill - going by our formulas and the manufacturers data we ran the job at a 2mm deep roughing cut, 350mm/min feedrate at 2600RPM, finish was at 100mm/min and 2600RPM taking off 0.1mm. This is just an example again of why high speed (& $$$) servos would have given us no benefit - even if the motors could move the table at 100000mm/min we had to cut at 350mm/min to suit the tool. Other times it will be limited by the spindle RPM - you are not likely to come across a tool/RPM combination that will be let down by available feedrate on MX3 kitted machines.
Sorry ...that's all for now !!
Quality kits and service (...and how it works against us!!)
One thing we hear from customers constantly is praise for the quality of our kits and both pre & post sales support - but let us explain how that works against us!!
Once you start researching CNC on the internet you will quickly become aware of forums like CNCZone.
CNCZone is fantastic - an absolute wealth of information with no shortage of people willing to help you with anything to do with CNC and machining. We are also members of that forum and use it ourselves when researching or when we come up against something that we've had little or no experience with. If you look there for what people are doing with their X3's you will very soon come across one of our competitors (Chinese). You'll see that they have their own forum 'group', there's hundreds of posts by many different people ... and the name becomes known.
The problem is that the reason so many people are on the forum talking about those kits is because there are so many people having issues with them. Issues with poorly made parts, parts that won't fit, dead electronics (which get replaced with more dead electronics!!) and so on. But all the talk acts like advertising (or false advertising) and the net effect of all this 'talk' is that the name gets known.
PROMiCA on the other hand is not splattered all over the forum ... and the reason why is because our customers are completely satisfied with their kits and are too busy 'making chips'. Plenty of our customers are CNCZone members - but they are the ones asking the "how do I machine titanium" type questions rather than the "how to I install my kit" type questions or even worse "how do I repair it".
From our perspective we'd much prefer to be unknown for the right reasons than known for the wrong ones... but having said that - if you do buy one of our kits PLEASE tell others how happy you are and help us become known for the right reasons.