CNC PCB milling
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Dc aka brushed spindles run on constant (dc) current&voltage. They have some limits. Power it under minimum voltage and they will stall (stop rotating) and only one coil will be energised, heat up and blow. Over maximum voltage they overheat and burn (logically).
You can use a constant voltage source or pwm a maximum voltage since the electro-mechanical inertia will act as an integrator and smooth out the pwm pulses asuming pwm frequency is high enough. The driving circuit can be as simple as a high power FET or a complex constant dc voltage source. You control that circuit via a low power pwm or voltage signal. Pwm can be easily converted to dc by a low-pass RC filter. -
Brushless motors NEED a driver, same as steppers, since phases must be shifted in syncronisation to shaft speed and position. The control of the driving circuit is the same pwm or dc voltage talk as above.
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Dc aka brushed spindles run on constant (dc) current&voltage. They have some limits. Power it under minimum voltage and they will stall (stop rotating) and only one coil will be energised, heat up and blow. Over maximum voltage they overheat and burn (logically).
You can use a constant voltage source or pwm a maximum voltage since the electro-mechanical inertia will act as an integrator and smooth out the pwm pulses asuming pwm frequency is high enough. The driving circuit can be as simple as a high power FET or a complex constant dc voltage source. You control that circuit via a low power pwm or voltage signal. Pwm can be easily converted to dc by a low-pass RC filter. -
Brushless motors NEED a driver, same as steppers, since phases must be shifted in syncronisation to shaft speed and position. The control of the driving circuit is the same pwm or dc voltage talk as above.
@executivul Thanks makes sense and I just started to read simular explaination in other places, but yours helped.
How about rpm ? Is it generally considered that higher RPM is better, or at least not being limited by a low speed ? I've seen 1 300w spindle rated at 60,000rpm would this be better than a higher power slower spindle ?
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@NeverDie I use my 60k rpm spindle at 30-40k rpm most of the time. I manualy crank the vfd pot to max rpm, then slowly start lowering taking notes where the lowest harmonic resonance points are, then chose the highest acceptable one. Eg 100% rpm high noise, 94% rpm low noise, 93-84% rpm noise again, 83%rpm even lower noise, 82-xxx% noise again. I chose 83%. Most Vcarve milling bits are rated to 40k rpm anyways. This speed / resonance tuning must be done after every tool change, even a slight tightening of the tool a bit more can change balancing.
IMHO 24k rpm are enough for up to 1000mm/min pcb milling. -
@NeverDie I use my 60k rpm spindle at 30-40k rpm most of the time. I manualy crank the vfd pot to max rpm, then slowly start lowering taking notes where the lowest harmonic resonance points are, then chose the highest acceptable one. Eg 100% rpm high noise, 94% rpm low noise, 93-84% rpm noise again, 83%rpm even lower noise, 82-xxx% noise again. I chose 83%. Most Vcarve milling bits are rated to 40k rpm anyways. This speed / resonance tuning must be done after every tool change, even a slight tightening of the tool a bit more can change balancing.
IMHO 24k rpm are enough for up to 1000mm/min pcb milling.@executivul Which 60K rpm spindle is it that you are using? Are you generally happy with it, even if you tend to run in the 30-40K rpm range most of the time? i.e. would you buy it again, or would you maybe get something different?
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@executivul Thanks makes sense and I just started to read simular explaination in other places, but yours helped.
How about rpm ? Is it generally considered that higher RPM is better, or at least not being limited by a low speed ? I've seen 1 300w spindle rated at 60,000rpm would this be better than a higher power slower spindle ?
@rfm69 the honest answear: "It depends!"
I've had much better luck at higher rpm. I've even posted a gcode to determine the best feed/rpm in this thread.
To mathematically know for sure you would need a few hundred thousand dollars worth of equipment, engraving pcbs is not milling, so chipload calculators won't work. Lower rpm rips the copper leaving rough edges, too high of a rpm increases runout. As I've said IMHO 24-30k rpm is enough for our machines, you need a far better, stiffer frame, servos instead of steppers and a very good controller board to be able to go over 1000mm/s (400in/s). -
@executivul Which 60K rpm spindle is it that you are using? Are you generally happy with it, even if you tend to run in the 30-40K rpm range most of the time? i.e. would you buy it again, or would you maybe get something different?
@neverdie i would go for a 24k 800W water cooled spindle, far better "all around" tool, can mill wood or aluminium easier
The 60k is great for pcbs and that's about it.A larger wattage, lower max rpm spindle has a larger and heavier rotor, higher inertia, can withstand higher chiploads.
Remember, as in stepper's case, running a spindle at 50% of max rpm yelds far less than 50% of power, maybe as low as 10%. Going under 50% you get as low as 3-5% of max rated power. For pcbs that's no biggie, but for anything else... And you can't mill wood or metals at 60k rpm because of the feedrate needed to keep the chipload and the cooling needed not to burn the tool and stock.
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Quoting DavidSohlstrom from a thread on a different forum (https://discuss.inventables.com/t/runout-of-24v-dc-spindle/9984/11) in reference to vibration:
I've said it before and I'll say it again. This is a low cost DC motor that has a ER collet adapter attached to it. It is not a CNC spindle that incorporates the tool holder right into spindle with a minimum of stick out from the housing.
There is no bearing preload and the bearings are low cost bearings that have a lot of slop in them.
A bent motor shaft of just a couple of thou will cause a large run out at the tool.I notice that a lot of the available spindles are exactly that: a motor with an ER11 collet attached. So, the stickout is going to be greater. I haven't yet tried to find a proper CNC spindle like what he describes, where there's minimal stickout. In a perfect world, it sounds like that may be the way to go though.
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Quoting DavidSohlstrom from a thread on a different forum (https://discuss.inventables.com/t/runout-of-24v-dc-spindle/9984/11) in reference to vibration:
I've said it before and I'll say it again. This is a low cost DC motor that has a ER collet adapter attached to it. It is not a CNC spindle that incorporates the tool holder right into spindle with a minimum of stick out from the housing.
There is no bearing preload and the bearings are low cost bearings that have a lot of slop in them.
A bent motor shaft of just a couple of thou will cause a large run out at the tool.I notice that a lot of the available spindles are exactly that: a motor with an ER11 collet attached. So, the stickout is going to be greater. I haven't yet tried to find a proper CNC spindle like what he describes, where there's minimal stickout. In a perfect world, it sounds like that may be the way to go though.
@neverdie any half decent watercooled spindle should have the ER collet holder integrated. My 60k one has an ER8 and the default DC that came with the machine an ER11. Bought some ER high precision collets from ali, and some precision nuts and things got even better.
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This one would appear to fit @executivul 's criteria and also have a short stickout:
https://www.aliexpress.com/item/800W-electric-water-cooled-spindle-220V-ER11-with-65MM-diameter-158MM-length-for-cnc-router/32641099025.html?spm=2114.search0104.3.8.23ac8afeEe3r4S&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10151_10065_10344_10068_10130_10324_10342_10547_10325_10343_10546_10340_10548_10341_10545_10084_10083_10618_10307_5711211_10313_10059_10534_100031_10103_10627_10626_10624_10623_10622_10621_10620_5722415_5711313,searchweb201603_2,ppcSwitch_5&algo_expid=da6db481-06cd-4131-b9a1-e7278ac9d3f2-1&algo_pvid=da6db481-06cd-4131-b9a1-e7278ac9d3f2&transAbTest=ae803_5&priceBeautifyAB=0It would seem to need some kind of controller to go with it though, plus a water pump, water tubing, and fittings and all of that. Definitely a major upgrade.
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This one would appear to fit @executivul 's criteria and also have a short stickout:
https://www.aliexpress.com/item/800W-electric-water-cooled-spindle-220V-ER11-with-65MM-diameter-158MM-length-for-cnc-router/32641099025.html?spm=2114.search0104.3.8.23ac8afeEe3r4S&ws_ab_test=searchweb0_0,searchweb201602_5_10152_10151_10065_10344_10068_10130_10324_10342_10547_10325_10343_10546_10340_10548_10341_10545_10084_10083_10618_10307_5711211_10313_10059_10534_100031_10103_10627_10626_10624_10623_10622_10621_10620_5722415_5711313,searchweb201603_2,ppcSwitch_5&algo_expid=da6db481-06cd-4131-b9a1-e7278ac9d3f2-1&algo_pvid=da6db481-06cd-4131-b9a1-e7278ac9d3f2&transAbTest=ae803_5&priceBeautifyAB=0It would seem to need some kind of controller to go with it though, plus a water pump, water tubing, and fittings and all of that. Definitely a major upgrade.
@neverdie that's ok. Beware you need a VFD for it (driving circuit) and it's bettery to buy as a kit so they match, my 2c
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@neverdie any half decent watercooled spindle should have the ER collet holder integrated. My 60k one has an ER8 and the default DC that came with the machine an ER11. Bought some ER high precision collets from ali, and some precision nuts and things got even better.
@executivul said in CNC PCB milling:
Bought some ER high precision collets from ali, and some precision nuts and things got even better.
How can tell you tell if the collet and nuts are "high precision" or not?
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You can tell by the listing title or after doing some tests either with a dial gauge or by running it and listening.
Beware 2: diameter, my 3040 came with 53mm spindle holder, single piece with z carriage, so the 48mm only needed a 3d printed sleeve, but to add a 63mm or 80mm diameter spindle some heavy mods were needed so that's one of the reasons I didn't go with them
Beware 3: weight, the frame must support it without complaining, z drop, backlash or whatever
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My 10^5*2c: get a 6040cnc with supported rails and a 0.8-2kw water cooled spindle, will serve you good for anything from pcb to alu or bronze milling, even some light steel work on the 2kw one and will save you a lot of hassle in the long run.
LE. 3020 and 3040 don't have supported rails and many don't even have ballscrews
And if you're really anal about it get the ballscrew frame only from rattm on ebay, a set of hybrid servos, a spindle+vfd+pump, a controller of your choice and you can say you have the best tool in the entry class of router cncs.
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My 10^5*2c: get a 6040cnc with supported rails and a 0.8-2kw water cooled spindle, will serve you good for anything from pcb to alu or bronze milling, even some light steel work on the 2kw one and will save you a lot of hassle in the long run.
LE. 3020 and 3040 don't have supported rails and many don't even have ballscrews
And if you're really anal about it get the ballscrew frame only from rattm on ebay, a set of hybrid servos, a spindle+vfd+pump, a controller of your choice and you can say you have the best tool in the entry class of router cncs.
@executivul Maybe I've missed it, but none of the Chinese 6040's I've seen have had supported rails. They all seem to require that as some kind of DIY "upgrade".
For that reason, I've been considering a c-beam type design. There exists a relatively cheap Chinese clone of that:
https://www.aliexpress.com/store/product/C-Beam-machine-large-Mechanical-Kit-DIY-C-Beam-machine-Large-bundle-C-Beam-Frame-kit/1752067_32846185306.html?spm=2114.12010608.0.0.55bc1dafCeSt8dor maybe the WorkBee, which seems to be an upgrade to the OX CNC (though I'd prefer something where the screw holes are already tapped):
https://www.aliexpress.com/store/product/OX-CNC-Upgrade-Version-WorkBee-CNC-Router-Machine-CNC-Mechanical-Kit-with-Nema-23-Stepper-Motors/1752067_32850266842.html?spm=2114.12010608.0.0.36611dafYZdcH4 -
@executivul Maybe I've missed it, but none of the Chinese 6040's I've seen have had supported rails. They all seem to require that as some kind of DIY "upgrade".
For that reason, I've been considering a c-beam type design. There exists a relatively cheap Chinese clone of that:
https://www.aliexpress.com/store/product/C-Beam-machine-large-Mechanical-Kit-DIY-C-Beam-machine-Large-bundle-C-Beam-Frame-kit/1752067_32846185306.html?spm=2114.12010608.0.0.55bc1dafCeSt8dor maybe the WorkBee, which seems to be an upgrade to the OX CNC (though I'd prefer something where the screw holes are already tapped):
https://www.aliexpress.com/store/product/OX-CNC-Upgrade-Version-WorkBee-CNC-Router-Machine-CNC-Mechanical-Kit-with-Nema-23-Stepper-Motors/1752067_32850266842.html?spm=2114.12010608.0.0.36611dafYZdcH4@neverdie please search for the 6040 frame only from "rattm motor", it's not stated I believe but you can clearly see in the photos with the bed beams removed that y rails are supported. X are not, but they are high diameter and pretty stiff for 40cm wide span.
Imho wheels on rails will never ever ever be as stiff and have less flex than the lousiest linear bearing. Wheels on rails are for printers and lasers.
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@neverdie please search for the 6040 frame only from "rattm motor", it's not stated I believe but you can clearly see in the photos with the bed beams removed that y rails are supported. X are not, but they are high diameter and pretty stiff for 40cm wide span.
Imho wheels on rails will never ever ever be as stiff and have less flex than the lousiest linear bearing. Wheels on rails are for printers and lasers.
@executivul You're right:
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@neverdie please search for the 6040 frame only from "rattm motor", it's not stated I believe but you can clearly see in the photos with the bed beams removed that y rails are supported. X are not, but they are high diameter and pretty stiff for 40cm wide span.
Imho wheels on rails will never ever ever be as stiff and have less flex than the lousiest linear bearing. Wheels on rails are for printers and lasers.
@executivul said in CNC PCB milling:
Imho wheels on rails will never ever ever be as stiff and have less flex than the lousiest linear bearing. Wheels on rails are for printers and lasers.
Even in the case of the Rattm Motors 6040, where the z-axis is hanging off an X-axis that is dangling by unsupported smooth rod? Is it still better even then?
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@executivul said in CNC PCB milling:
Imho wheels on rails will never ever ever be as stiff and have less flex than the lousiest linear bearing. Wheels on rails are for printers and lasers.
Even in the case of the Rattm Motors 6040, where the z-axis is hanging off an X-axis that is dangling by unsupported smooth rod? Is it still better even then?
@neverdie it might be better than a rigid x axis aluminium profile dangling on some wheels all together. Then comes the profile joining piece dance.
On the cnczone forums people go like: linear rails are the best, round bars are good, wheels on rails are for toys. That is for normal milling on a small machine. These things are routers by the way, real mills are taig style and are small size and meant for steel and heavy metal milling (no pun intended). For wood, plastic, soft stuff it might be acceptable though.
For pcbs you need high precision, flatness, high rpm etc.
For wood you need large size, think of table or door pieces. Tolerances are not so tight. You won't go like: look! Your door engraving is 0.1mm off in that corner!
For metal you need precision, high rigidity and power at lower spindle speed.The classic ebay cnc is a good all around tool but excels at nothing 😁
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@neverdie it might be better than a rigid x axis aluminium profile dangling on some wheels all together. Then comes the profile joining piece dance.
On the cnczone forums people go like: linear rails are the best, round bars are good, wheels on rails are for toys. That is for normal milling on a small machine. These things are routers by the way, real mills are taig style and are small size and meant for steel and heavy metal milling (no pun intended). For wood, plastic, soft stuff it might be acceptable though.
For pcbs you need high precision, flatness, high rpm etc.
For wood you need large size, think of table or door pieces. Tolerances are not so tight. You won't go like: look! Your door engraving is 0.1mm off in that corner!
For metal you need precision, high rigidity and power at lower spindle speed.The classic ebay cnc is a good all around tool but excels at nothing 😁
@executivul
How thick is the aluminum that such a 6040 machine could mill? -
@executivul
How thick is the aluminum that such a 6040 machine could mill?@neverdie you must use a chipload calculator according to your spindle power at requested rpm, tool diameter and tool profile. Stock can be as thick as you want, the machine has about 100mm of z travel, you mill in multiple passes anyway so milling depth per pass is based on the results from calculator, experience or many broken tools.
