Homebrew PCBs

Hello twb8899,

19. January 2003, 21:48:33, you wrote:

ttyc> Zoran,

ttyc> There are calculations we used for the various feeds and speeds but 
ttyc> most of this was done automatically by the machine. What you need to 
ttyc> know is the chip load for the bit size you are using. The chip load 
ttyc> is how many mils (.001" = 1 mil) the bit goes into the board per 
ttyc> revolution. Your feed rate is then calculated by multiplying the chip 
ttyc> load by the spindle speed. For example, a bit requiring a 3 mil chip 
ttyc> load at 60,000 rpm equals 180 inches per minute feed rate. 

ttyc> There are more calculations required to arrive at the surface feet 
ttyc> per minute for a bit size etc. I don't know how to post these 
ttyc> equations in this message because they are complex. There is a chart 
ttyc> with all of this information on it and perhaps I can photograph or 
ttyc> scan it into the Photos section. The bottom line on all of this is to 
ttyc> just get your machine going any way you can and adjust the speeds for 
ttyc> what works and sounds good to you. 

ttyc> The Excellon drilling machines have a built in software page called 
ttyc> a "Diameter Page" which contains drill bit size and feed rate 
ttyc> information. This chart can be user edited to get the results you 
ttyc> want. The machine looks at this chart and adjusts the spindle 
ttyc> parameters as needed. These charts are set up in ranges such as .020" 
ttyc> to .030" etc. Every size in this range will have the same feed and 
ttyc> speed. If needed, the Diameter Page data could include a feed and 
ttyc> speed record for every drill size you wanted to enter.

ttyc> Some CNC drill programs contain the feed and speed data from the CAD 
ttyc> system and the drilling machine will use that info. The problem with 
ttyc> this is I never once saw a CAD system that could get even close to 
ttyc> having the correct feeds and speeds. So we always edited that part of 
ttyc> the program and let the machine take over. 

ttyc> An experienced machine operator will always tweak the spindle speed 
ttyc> while the spindles are drilling until everything sounds right. You 
ttyc> can actually hear the difference as you change the speed so you just 
ttyc> keep tweaking until the spindles are "singing". The only time we got 
ttyc> out all the charts and did calculations was when a customer was 
ttyc> hanging around. This way they thought we really knew our stuff and 
ttyc> were getting their money's worth! As soon as they left we went back 
ttyc> to "winging" it!!  We bent a lot of rules in those days to get the 
ttyc> jobs out the door. It really was a lot of fun back in the old days. 
ttyc> Anyone in the PWB business can tell you similar stories.

ttyc> Tom






ttyc> --- In Homebrew_PCBs@yahoogroups.com, "Zoran A. Scepanovic" 
ttyc> <zasto@y...> wrote:
>>   Hi all,
>> 
>>   I'm on the way of making PCB drillin machine, and I would like to 
ttyc> get some
>>   info  on  the  spindle speeds and feed rates for different drill 
ttyc> diameters
>>   needed for drilling FR-4/FR-10 boards.
>> 
>>   (Maybe Tom has the answer!)
>> 
>> -- 
>>  Sincerely,
>>  Zoran A. Scepanovic
>>  zasto@y...
>> 
>> [Non-text portions of this message have been removed]


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And I replied:

Tnx for info! I'll have to experiment!

-- 
 Best Regards,
 Zoran
 mailto:zasto@...