View Full Version : i keep on breaking bits???

03-22-2004, 08:47 PM
hi! i am new in the CNC industry and i have a lot of questions about it---i cant seem to find the answers, can someone please help me out. i am working on a CNC drilling/milling for the PCB industry and and i keep on breaking drills, of the hundreds of pages ive read on the web site i still cant find the recommended drilling speed and feed rate that is appropriate to this kind of application. what do you think is the right speed that i use in drilling holes in PCBs say for example a .8mm tool how fast should it run in drilling PCbs. the maximum speed in my CNC is 60000 rpm and i am using a carbide drill. thanks for all the help you can give me.

03-22-2004, 09:14 PM
How fast are you plunging the bit, try slowing it down.

03-22-2004, 09:35 PM
the feed rate that is set in the machine is 3200, i dont know what unit is that maybe mils per minute or what do you think? and the speed is at 60000rpm i really dont know what to do. you might have an idea on this since you work in woodworking, pcbs are not that different from wood only thing is that it is covered by a thin layer of copper---so wil have some adjustments on that part. if you drill a hole on a wood with similar density and thickness to a pcb using carbide drills what do you think is the speed and feed rate that i use. thnx

03-22-2004, 09:59 PM
3200 ipm, or is that pulses? What control/machine are you using?

03-22-2004, 10:28 PM
i use a bungard cnc drilling/milling machine from mega electronics

03-22-2004, 10:43 PM
Let's take a look at the 3200... if that's mm/min, then the feed speed is about 126 in/min. If that's mils/min, then the feed speed is 3.2 in/min. I'm guessing your feed speed may be in mm/min. if it's programmed in GCode. I don't have any experience with your control, so I'm kind of shooting in the dark here.

03-22-2004, 10:50 PM
i also think it is in mm/min feed rate. i ve read in an article that these carbide drills are quite durable and you can run them from 20000 to 100000 rpm and some say that the minimum rpm should be 30000 for a .8mm carbide bit, so it is just a matter of finding the right speed and feed rate for the machine that would strike a balance between efficiency and bit lifetime and i dont know much about that aspect.

03-23-2004, 04:28 AM
most carbide tools I've seen, especially coated ones, can handle very high temperatures, thus very high SFPM. I really have no idea of a recommended SFPM for carbide tools in PCB, but perhaps the tool manufacturer could give you more information.

To get you started, however, I would try keeping the spindle speed at 60,000 RPM and running at about 0.0002" per tooth, or 40 IPM for a 2-flute drillbit. Converting this to metric, you would be around 1016 mm/min, or about 1/3 of the feedrate that you're currently running at.

Realize that I have no references or experience with cutting PCB, this data is just an approximation from what I've seen from cutting aluminum. The best source for numbers would be from the drillbit manufacturer.

03-23-2004, 07:54 AM
Hi Joeyboy
I have also just got one of these Bungard systems and am having some difficulty setting it up to run reliably. The manual seems poor. How are your double sided boards working, I cant seem to get them to line up very accurately, and I have also broken bits, the feed rate seems to be very high on their default values. I am having better luck on my home built cheapy!

03-23-2004, 08:54 PM
thnx neomoses for that one you gave me an idea. from what ive read and my experience, i know that the feed rate is quite fast but i do not know just how much speed i should deduct in the feed rate. the drill bit is like hammering on the board at 3200 maybe that is the cause. 3200 feed rate i know is too much but that is what the setting that was used by the operator that i replaced. i think it was a deliberate a sabotage to the next users of the cnc like me. these settings got me into a lot of trouble. thnx

it is great to know that there is also someone out there who uses these bungard systems---like you spookie. the machine is basically a headache. in order to ensure that margin of error in these boards are low---meaning i got it drilling holes where i want it to even with boards that is just a few mms bigger than the entire drill dimensions---i use a test board and from then i know where the drill holes would fall. like what you said i think the manual is terrible. the problems with these boards is that when you put the surface with copper upside down(not mirrored) at the wrong feed rate and speed it generates holes with crater-like finish. a lot of problems. you said you have a home built machine, is that similar to a bungard cnc drillng machine? give me an idea how to make these things. thnx

03-24-2004, 12:47 AM
I have hand-drilled many PCB boards with a drill press. I am gathering that your machine is not actually routing the boards, or cutting it, they are "peck" drilling holes for ICs? If that is the case, 120ipm is much to fast! A bit spinning at 60,000rpm could probably cut that fast, but not a few times... I have broken many many bits doing it manually. Another possible problem is that if the bit moves even the slightest bit whle through a pcb, it will break. So, machine vibration could be a problem, or a noise stepper type issue where it is moving jsut slightly when stopped? Is the spindle & z axis at perfect 90degrees to the pcb?

any, if you want info on homebuilt machines, go look at the photo gallerys here, if you have any mechanical inclination, or have every built cabinets even, or screwed in a light bulb! you will be able to comprehend some of these beasts. there is one made of particle board, steel angle, and surplus stepper motors and stuff. there is even one made entirely of 3 old dotmatrix printers.

03-24-2004, 05:18 AM
there are some pictures of my machine at home here http://www.cnczone.com/forums/showthread.php?s=&threadid=2926 It is nothing like the bungard machine but more of a general machine. Made from an old spark eroder.
I have only had the PCB Mill for two weeks and we are slowly getting used to it. The routed groove for lining up double sided boards is off skew and we are now just moving the machine to an offset and machining the pegs into the base board, there seem to be some problems with repeatability, i.e the drills will drill all the way through on 1 board and without changing anything will drill only half way through on the next (or too deep). One thing I did find is that the board needs to be completely flat and held down (we use tape) for the drilling, because if it moves even slightly the drill will break ( and they are not cheap). The main problem seems to be with the software, it isn't very intuative, maybe I have been spoiled by using Mach2 at home.
But at the end of the day we have managed to get some nice little boards out, just not as quickly as I had led my boss to believe. Maybe with a bit more playing time we should get there. For >5k GBP I expected a machine that would come out of the box and work well.