499,715 active members
4,865 visitors online
Register for free
Login
Page 1 of 2 12
Results 1 to 12 of 13
  1. #1
    Registered
    Join Date
    Mar 2012
    Posts
    150

    Spindle speed 7000rpm ok?

    Will 7000rpm for spindle suffice for isolation milling / drilling / routing of PCB's?
    I have 400W spindle, it used to run @ 9000rpm but its power supply(48VDC) blew off and now I'm running at 36VDC and its running at around 7000rpm.
    I have heard that PCB drilling needs high rpms aronud 24K and above.

    I have some 30deg V bits, a few end mills and som drill bits.
    I plan to mill with the 30deg V and drill 0.8mm holes.

    What problems can I expect with doing the above operations @ 7000rpm. Broken drill bits?
    Would I need to modify the feed rate and plunge rate accordingly?

    Any suggestions would be appreciated!
    TIA

  2. #2
    Gold Member
    Join Date
    Apr 2013
    Posts
    1851

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by ZeroBacklash View Post
    Will 7000rpm for spindle suffice for isolation milling / drilling / routing of PCB's?
    Anything is possible, as long as you accept painfully slow speed.

    Quote Originally Posted by ZeroBacklash View Post
    I have 400W spindle, it used to run @ 9000rpm but its power supply(48VDC) blew off and now I'm running at 36VDC and its running at around 7000rpm.
    The problem is that the slower the RPM the less is the torque, so in your case, I'd get a new 48V supply, or connect a 12V in series with the 36V to get maximum RPM. Perhaps you can find a 12V supply in your drawer...? Just make sure it has enough power.

    Quote Originally Posted by ZeroBacklash View Post
    I have heard that PCB drilling needs high rpms aronud 24K and above.
    I run my 24k spindle at 22k to reduce noise and I don't think it would make much difference if I'd run it at 24k.

    https://youtu.be/nrW6Hq6V3VY


    Quote Originally Posted by ZeroBacklash View Post
    I have some 30deg V bits, a few end mills and som drill bits.
    I plan to mill with the 30deg V and drill 0.8mm holes.

    What problems can I expect with doing the above operations @ 7000rpm. Broken drill bits?
    Would I need to modify the feed rate and plunge rate accordingly?

    Any suggestions would be appreciated!
    TIA
    I am also using 30deg V bits and some drill bits made for PCB. You have to experiment optimal mill speed and plunge depth/speed. Yes, expect breaking V bits and drills until you get the feel. It is impossible to give good advice regarding speeds without knowing more about your machine. Milling speed depends on many other things, not only RPM. Yes, you should definitely modify your speeds, the reduction from 9k RPM to 7k is significant. Be careful when drilling, don't go too fast. On the other hand, if you go too slow, you'll burn the PCB and the drill...

  3. #3
    Registered
    Join Date
    Mar 2012
    Posts
    150

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by A_Camera View Post
    Anything is possible, as long as you accept painfully slow speed.



    The problem is that the slower the RPM the less is the torque, so in your case, I'd get a new 48V supply, or connect a 12V in series with the 36V to get maximum RPM. Perhaps you can find a 12V supply in your drawer...? Just make sure it has enough power.



    I run my 24k spindle at 22k to reduce noise and I don't think it would make much difference if I'd run it at 24k.

    https://youtu.be/nrW6Hq6V3VY




    I am also using 30deg V bits and some drill bits made for PCB. You have to experiment optimal mill speed and plunge depth/speed. Yes, expect breaking V bits and drills until you get the feel. It is impossible to give good advice regarding speeds without knowing more about your machine. Milling speed depends on many other things, not only RPM. Yes, you should definitely modify your speeds, the reduction from 9k RPM to 7k is significant. Be careful when drilling, don't go too fast. On the other hand, if you go too slow, you'll burn the PCB and the drill...
    Many Many Thanks!
    This is some pretty amazing information. I like the way you do multi pass milling, never thought about it before.
    How do you generate the multpasses does your gcode plugin do it for you or you just pause the program and run the whole thing again?

    Well lots of questions!
    1. How did you get your table absolutely level for accurate milling? I have been trying to use Autoleveller.
    2. How do you fix your pcb's to the table do you use double sided tape?
    3. What kind of clearances do you use when you design the PCB suitable for Isolation milling. I mean the width of traces and distance between traces?

    Have some 12V, 5A spare power supplies, but I guess that won't be sufficient power will probably have to use a PC ATX power supply and take 12V for those, I guess that are meant for high power.

    One again Many Thanks! Truly appreciate it!!

  4. #4
    Gold Member
    Join Date
    Apr 2013
    Posts
    1851

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by ZeroBacklash View Post
    Many Many Thanks!
    This is some pretty amazing information. I like the way you do multi pass milling, never thought about it before.
    How do you generate the multpasses does your gcode plugin do it for you or you just pause the program and run the whole thing again?
    The second pass is easy. Once you have the G-code for the first pass you just copy the text and change the parts you want to change, like feed rate and milling depth. The G-code is text, so it is easy to create the multipass milling file.

    Quote Originally Posted by ZeroBacklash View Post
    Well lots of questions!
    1. How did you get your table absolutely level for accurate milling? I have been trying to use Autoleveller.
    2. How do you fix your pcb's to the table do you use double sided tape?
    3. What kind of clearances do you use when you design the PCB suitable for Isolation milling. I mean the width of traces and distance between traces?

    4. Have some 12V, 5A spare power supplies, but I guess that won't be sufficient power will probably have to use a PC ATX power supply and take 12V for those, I guess that are meant for high power.

    One again Many Thanks! Truly appreciate it!!
    1. This did take some time, I levelled and squared the machine as well as I could when I built it. I also have a separate waste board fixed in a vice, which I surface mill before starting on a PCB to remove all unevenness as a result of drilling through previous PCB. I don't use any auto leveller, in my opinion that's not necessary if you level your table and use high quality PCB.

    2. Using only painters tape. I am not using double sided tape because it is not flat enough and the PCB is flexing slightly because of the thick tape.

    3. Sorry, I don't remember now. Anyway, I use as little as possible, or as large as necessary. The minimum clearance also depends on your machine and the bits you are using. In the example video, the depth is 0.07mm, so calculating that based on the 30 degree V bit gives 0.04mm. Note that this is calculated and is only in theory. In reality, it depends on how pointy your V bit is, because the Z zero is measured from the real tip of the V bit, which is never as pointy as this calculation. Never the less, if I see that the V bit is too flat or extreme accuracy is needed it should be taken into the calculation as well, or the bit must be changed. I think my bits have 0.1mm tips, so by taking that into account the separation is 0.14mm, which is more than enough for a normal PCB. There are plenty online calculators in case you are not familiar with triangle calculations, you can use this one, as an example if you want to calculate using your own values.

    4. You can always try. You motor doesn't really require all the power for this purpose, unless you stall the motor, so 12V 5A should be enough to "fill up" the needs. Worst that can happen is that the 12V PSU gets hot and the voltage drops, if you feel uncomfortable you can switch it off. The 400W motor is 400W from 48V, and that is 8.3 A, not that far from 5A, but again, the 400W is the maximum and I don't think you'll ever come close to that in this application.

  5. #5
    Registered
    Join Date
    Nov 2012
    Posts
    702

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by A_Camera View Post
    I'd get a new 48V supply, or connect a 12V in series with the 36V to get maximum RPM. Perhaps you can find a 12V supply in your drawer...? Just make sure it has enough power.
    As a rule, it is not a good idea to connect two random power supplies in series. At least when we are talking about hundreds of watts.

    Milling and drilling PCBs at 7000RPM is perfectly doable, just reduce your feed/plunge rate accordingly and make yourself more coffee to drink while you are waiting.

  6. #6
    Registered
    Join Date
    Mar 2012
    Posts
    150

    Re: Spindle speed 7000rpm ok?

    Thanks for the amazing suggestions A_Camera and Citizen of Dreams.
    I did a run of a test pcb with Autoleveler and then milling it.
    Twice the machine lost track of where it was and while the gcode view was showing some other position the machine was at some other co-ordinates. I later discovered that the Y axis coupler was loose and not driving the Y axis ball screw as required. But I'm not sure this problem is related to the one of the machine losing track.
    Am attaching a picture of the unfinished job.
    Click image for larger version. 

Name:	pcb.jpg 
Views:	0 
Size:	97.1 KB 
ID:	412368

  7. #7
    Registered
    Join Date
    Nov 2012
    Posts
    702

    Re: Spindle speed 7000rpm ok?

    Seems like you did not cut through the copper in a couple of places. Can you show us a picture with the dust blown off?

  8. #8
    Registered
    Join Date
    Mar 2012
    Posts
    150

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by CitizenOfDreams View Post
    Seems like you did not cut through the copper in a couple of places. Can you show us a picture with the dust blown off?
    Somehow the dust seems to be embedded into the PCB, I tried cleaning with a soft brush but the dust isn't coming off. Probably will need some water to get it off?

  9. #9
    Registered
    Join Date
    Nov 2012
    Posts
    702

    Re: Spindle speed 7000rpm ok?

    I usually spray some soft solvent (such as brake cleaner or flux remover) on the board. That both cleans the dust AND lets you clearly see all the traces (while the board is still wet).

  10. #10
    Registered
    Join Date
    Nov 2013
    Posts
    283

    Re: Spindle speed 7000rpm ok?

    Hi,
    I use a VFD and an asynchronous 24000 rpm spindle. I use 0.5mm endmills. When running at 24000 rpm at 1% feed per tooth per rev that works out
    to a federate of 400 mm/min. I halve that to 200mm/min plunge. I personally find the two flute endmills cut very much more cleanly than any engraving
    bit I have tried. In the first instance I used endmills because I have some VERY thick copper board (420um or 12 oz!) PCB and angled engraving
    bit just weren't going to do a good job in such thick copper. The minimum trace width was 0.4mm, so an angled cut would have been very poor.
    The results were so good that I have started using the tiny endmills on ordinary 1oz board as well. I get about 4-5 hours good clean cut with little
    or no burring per tool.

    https://www.ebay.com/itm/10-0-50mm-0...cAAOSwjjpbC1Xa

    If I slowed it down to 7000 rpm with the same chipload the feed rate would be down to 116mm/min and 58mm/min plunge....too slow for me.

    I use Autoleveller with very good results. My typical cut depth is 0.06mm (0.035mm copper) and get perfect isolation every time. I use double
    sided tape to hold the PCB blank down. I try to make the minimum cut depth I can and still achieve isolation. The less fiber glass in the chip stream
    the better the tool lasts.

    I've also found that my endmills last VASTLY LONGER if I use flood cooling. As a consequence I put some duct tape around the edge of the PCB blank
    to try to exclude the coolant from getting between the PCB blank and the spoil board and have the double sided tape adhesive fail before the board is complete.

    I use Eagle to design the boards and then use the U(ser)L(anguage)P(rogram) 'pcb-gcode' to generate the Gcode. It allow multiple passes. For example I specify
    I want 2mm isolation with a 0.2mm stepover the Gcode will have multiple passes (0.5+ 7 x0.2=8 passes) until the 2mm isolation is achieved.

    Craig

  11. #11
    Registered
    Join Date
    Mar 2012
    Posts
    150

    Re: Spindle speed 7000rpm ok?

    Quote Originally Posted by CitizenOfDreams View Post
    I usually spray some soft solvent (such as brake cleaner or flux remover) on the board. That both cleans the dust AND lets you clearly see all the traces (while the board is still wet).
    Thats a good idea will try that asap!

  12. #12
    Registered
    Join Date
    Nov 2012
    Posts
    702

    Re: Spindle speed 7000rpm ok?

    Unfortunately, 0.5mm end mills don't cut it (pun intended) for many electronic components. Even the old-as-dirt SOT package has 0.4mm between the pads; SOP needs 0.25mm or better. You can certainly do DIP chips, but without the ability to pass a trace between the pins.

    I personally use V-tip cutters with the effective width of 0.15mm or so. I set the cut width in CamBam (my CAD/CAM of choice) to 1mm so it makes multiple passes where needed. Then, if I want to, I remove the rest of the copper with a 1mm end mill. PreciseBits makes special "copper rubout" cutters just for that purpose: https://www.precisebits.com/products...bit-rubout.asp

Page 1 of 2 12

Similar Threads

  1. Replies: 0
    Last Post: 06-10-2016, 03:08 AM
  2. Replies: 1
    Last Post: 08-02-2013, 10:07 PM
  3. BPSeriesI / Centroid control- Spindle speed all out of whack with speed dial?
    By peter.blais in forum Bridgeport / Hardinge Mills
    Replies: 9
    Last Post: 08-08-2006, 09:29 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •