Homebrew PCBs

Any recommendations? Bit and Speed.

Thanks.

--- In Homebrew_PCBs@yahoogroups.com, "wayne.causey" <wayne.causey@...> wrote:
>
> Any recommendations? Bit and Speed.
> 
> Thanks.
>

I bought some of these: http://www.ebay.com/itm/10-2-00mm-0787-CHIPBREAKER-CARBIDE-ROUTER-BURRS-DP-Kyocera-Tycom-/380446241277 (Really good seller, too!)

And run them at top speed (20,000 RPM) in my Proxxon tool to cut FR4.


They also work very nice for cutting perspex, but on lowest (5000 RPM) or you start melting the plastic instead of cutting it.

I am no t sure about the best cutter, but have an almost free solution to the problem. I have been using a homemade cutter for PCBs recently, and it works fairly well. I have a number of solid carbide PCB drills that have broken, leaving a 1/8" diameter carbide drill rod about 1" long. I chucked these in my lathe and used an angle grinder with abrasive blade to grind a point on the end of the rod. I used an angle of about 45 degrees, but that is not critical. Then I carefully ground a flat on one side of the point, stopping as close to the exact center as possible. A diamond file was used to make the final flat as sharp as possible. The resulting cutter is capable of cutting the copper to about a .010-.015 width. The edges do have a bit of a burr, but this can be removed with an exacto knife or light sanding. An exacto knife may be required to remove any copper bits left in the cuts preventing shorted traces.

Bob


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OT warning....

On Fri, Jul 27, 2012 at 10:39 AM, Bob Butcher <bbutcher85@yahoo.com> wrote:

> I am no t sure about the best cutter, but have an almost free solution to the problem. I have been using a homemade cutter for PCBs recently, and it works fairly well. I have a number of solid carbide PCB drills that have broken, leaving a 1/8" diameter carbide drill rod about 1" long. I chucked these in my lathe and used an angle grinder with abrasive blade to grind a point on the end of the rod.

I have been told that carbide dust is quite dangerous.  Are these
concerns overblown?  Do you take precautions?

-p.

> fairly well. I have a number of solid carbide PCB drills that have broken,
leaving a
> 1/8" diameter carbide drill rod about 1" long. I chucked these in my lathe
and
> used an angle grinder with abrasive blade to grind a point on the end of
the rod.
> 
> I have been told that carbide dust is quite dangerous.  Are these concerns
> overblown?  Do you take precautions?


The boards are made from fibreglass, the dust from cutting it isn't overly
good for your health.  The particles are sharp and stick in your lungs, it
gives you something like from asbestos, silicosis (breathing in dust from
sand-blasting) etc.  Same goes for drilling holes. 

It'll take a while; the problem is that unlike most things that take a while
to build up (eg lead poisoning) and get flushed from your body in the
meantime, dust like this will happily sit in your lungs forever.  If you're
susceptible you'll find out in 20 years.

That's cutting the board itself, just cutting the copper will put out less
dust.

Some people prefer to 'score & snap', or cut it with shears.  That's not
always possible if you're cutting slots in the boards (HV isolation etc) or
funny shapes.

Tony

On 07/27/2012 04:39 PM, Bob Butcher wrote:
> I am no t sure about the best cutter, but have an almost free solution to the problem. I have been using a homemade cutter for PCBs recently, and it works fairly well. I have a number of solid carbide PCB drills that have broken, leaving a 1/8" diameter carbide drill rod about 1" long. I chucked these in my lathe and used an angle grinder with abrasive blade to grind a point on the end of the rod. I used an angle of about 45 degrees, but that is not critical. Then I carefully ground a flat on one side of the point, stopping as close to the exact center as possible. A diamond file was used to make the final flat as sharp as possible. The resulting cutter is capable of cutting the copper to about a .010-.015 width. The edges do have a bit of a burr, but this can be removed with an exacto knife or light sanding. An exacto knife may be required to remove any copper bits left in the cuts preventing shorted traces.
>
> Bob
>
>
> [Non-text portions of this message have been removed]
>
>
Do you can post some photo of that?

Tungsten carbide and fiberglass dust are allowed up to 5mg/m^3 in non-protected 8-hour work environments, day-after day. This is basically saying they are only twice as toxic as "non-classified dust".   Each 1 mm hole in a 0.064" PCB is about 2 mg of material.  If 10% floats away as fine dust in a smallish 20 m^3 room, then you need about 500 holes before a fan needs to be placed in a window. This matches well enough for our intuition.  The amount of drill bit metal that escapes, by comparision, is next to nothing, but if you wear out 0.1% of a 10 gram bit in a routing application in a small 20 m^3 room, you've met OSHA and ACGIH's max for daily 8 hour exposure.  The concern is usually with agressive sanding applications.  There is also cobalt in these blades that is 5 times more dangerous, but 10x to 30x less of it.

An interesting thing is that ACGIH says hardwood dust is 5 times more dangerous.  This isn't to say fiberglass isn't really unhealthy, but that you should take serious precautions to not breath hardwood dust, which goes against my intution, but I'll try to remember it.

This is not off topic because OSHA doesn't regulate DIY, so I think protecting ourselves is integral to our efforts.  BTW, weller says lead fumes result from soldering, and some rosin turns into benzene (a carcinogen). The ACGIH recommendation for rosin is not a value but "as low as possible".

zawy,

Thanks for the analytical data and regs pertaining to PCB dust, etc.

I have been curious about these topics for some time and your information is timely. I personally favor reasonable efforts to reduce PCB dust and solder fumes. For PCB dust, I use a vacuum cleaner with a drywall dust filter. For solder fumes, a small inline vent fan is used to exhaust to the outside.  Your information provides assurance that my efforts are more than sufficient and relieves further concern.

I also had considerable reservations about using lead based solder paste in the home shop with small children present.  Switching to no-lead solder paste alleviated those concerns.

Thanks again for the useful information.

Wayne

--- In Homebrew_PCBs@yahoogroups.com, "zawy" <zawy@...> wrote:

>
> Tungsten carbide and fiberglass dust are allowed up to 5mg/m^3 in non-protected 8-hour work environments, day-after day. This is basically saying they are only twice as toxic as "non-classified dust".   Each 1 mm hole in a 0.064" PCB is about 2 mg of material.  If 10% floats away as fine dust in a smallish 20 m^3 room, then you need about 500 holes before a fan needs to be placed in a window. This matches well enough for our intuition.  The amount of drill bit metal that escapes, by comparision, is next to nothing, but if you wear out 0.1% of a 10 gram bit in a routing application in a small 20 m^3 room, you've met OSHA and ACGIH's max for daily 8 hour exposure.  The concern is usually with agressive sanding applications.  There is also cobalt in these blades that is 5 times more dangerous, but 10x to 30x less of it.
> 
> An interesting thing is that ACGIH says hardwood dust is 5 times more dangerous.  This isn't to say fiberglass isn't really unhealthy, but that you should take serious precautions to not breath hardwood dust, which goes against my intution, but I'll try to remember it.
> 
> This is not off topic because OSHA doesn't regulate DIY, so I think protecting ourselves is integral to our efforts.  BTW, weller says lead fumes result from soldering, and some rosin turns into benzene (a carcinogen). The ACGIH recommendation for rosin is not a value but "as low as possible".
>

In article <jv6jen+v8b6@...>,
   zawy <zawy@...> wrote:
> An interesting thing is that ACGIH says hardwood dust is 5 times more
> dangerous.  This isn't to say fiberglass isn't really unhealthy, but
> that you should take serious precautions to not breath hardwood dust,
> which goes against my intution, but I'll try to remember it.

MDF is worst of all. I use

http://www.trend-uk.com/en/UK/product/AIR_PRO/4/178/airshield_pro_respirator_230v_uk_.html  

(usual disclaimer) (Also available in US)

when machining wood. I hadn't considered its use for drilling PCBs but I
do have my face pretty close to the drill bit in order to see what I am
doing so maybe I should.

> This is not off topic because OSHA doesn't regulate DIY, so I think
> protecting ourselves is integral to our efforts.  BTW, weller says lead
> fumes result from soldering, and some rosin turns into benzene (a
> carcinogen). The ACGIH recommendation for rosin is not a value but "as
> low as possible".

Concerns were expressed at the place I used to work; about half a dozen
guys in a smallish repair workshop with not particularly good ventilation.
An advisor was brought in but the outcome was that with the amount of
soldering done (probably about equivalent to what we might do at home) no
special precautions were needed. If it had been a production line it would
have been different but with repairs a good proportion of time is spent in
testing and fault diagnosis.

Check out  www.hse.gov.uk/pubns/indg249.pdf

-- 
Stuart Winsor

Only plain text for emails
http://www.asciiribbon.org

The amount of benzene, lead oxide, acetone, and hydrochloric acid produced will depend on the temperature of the tip, the amount of rosin in the solder, the amount of solder, the air currents, and how close the person is to the work.  So it's impossible to know how large a dose is received, and OSHA seems to fall in line with ACGIH and state "as low a dose as possible" which means good ventillation or respirators to block organics, acids, and metals.  Lead, cadmium, and mercury are not the only unhealthy metals, just the ones we've used a lot of in the past that turned out to be bad.  Rarer metals have risks that are not well known. Antinomy, tin, tellurium, vanadium, and nickel (as examples) are not safe, and almost any metal when heated to a high temp in the presence of rosin might be bad (tin organics can be really nasty and it melts at a lower temp than lead, so I would not assume the lead in rosin core solder is the most dangerous constituent and I would not trust any government agency to know otherwise (I was an air pollution regulator for 12 years)).  Toxicity for metal organics is bad and generally unknown.  The link you gave at the bottom is interesting in its comments on asthma.  I exposed myself to a lot of high temp rosin core soldering in an unventillated room because I had never heard there was a problem with home soldering. Now I can't breath it at all without having a strong irritation in my throat, and when I visit Lima I start gagging from I assume the sulfur dioxide that produces acid when it hits water in the throat and lungs, so I have to take a yellow cartridge respirator.  I think it might be the hydrochloric acid that does this if not the benzene, but my bigger risk might not be related to this irritation but a higher risk of lung cancer from other chemicals which is the largest cause of non-smokers cancer deaths from occupational exposure (perhaps 15,000 in U.S. per year....0.5% of all deaths) so my risk might now be 5% chance it gets me. If I can do 20 things to prevent that kind of risk, I'll live forever ;)  BTW, 10 years of holding a cell phone next to the head an hour a day causes 3 times more brain/nerve cancer in adults, 5 times more in children.  Studies showing no effect were lower doses not reaching statistical significance, so the public wrongly assumes (as usual) the studies are in contradiction.  It's like 5 years of smoking.  Congress knows it from hearings (see youtube), but there is no concern from the public to force them into action and of course you know where the lobbies stand.

I uploaded a couple of photos of one cutter as well as some cuts made with the cutter. Note that the cuts were made on a Bridgeport milling machine with a spindle speed of 2720 RPM. I think the cutter would work better if I had about 20,000 RPM. The cuts in the copper are not bad considering the rough finish and the slow speed. It appears that I needed to go about 1 mil deeper to get all the copper between traces however.
 
I ground the point on the carbide drill rod using a diamond "sanding drum" in a hand held Dremel tool. I made another one that I filed the point using diamond files (actually knife sharpners) using a coarse one for roughing and a fine one for the final finish. I will try to post some photos of that cutter when I get it finished.
 
Bob

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