Author Topic: PCB pad cutter  (Read 1154 times)

Offline Mike K

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PCB pad cutter
« on: January 06, 2021, 09:58:49 PM »
Hi guys,

I'm looking to do this:



YouTuber AndyDaviesByTheSea did it by grinding a broken 1/4" drill bit.  I went that route, but it grabbed too much for my liking.  And since I've made D bits in the past that worked well, I thought I could do similar for this.

I took some 1/4" drill rod, faced it, and drilled the end 0.200".  It's just a tube right now, but I'm thinking I can put the "D bit" angle on it?  What do you think?  It really only has to remove the top layer of copper (a few thou, I think).

-Mike

Offline russ57

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Re: PCB pad cutter
« Reply #1 on: January 07, 2021, 12:36:29 AM »
I'd think that you would need some "teeth" - just filed ought to work

-russ


Offline modeng200023

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Re: PCB pad cutter
« Reply #2 on: January 07, 2021, 02:04:30 AM »

Online awemawson

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Re: PCB pad cutter
« Reply #3 on: January 07, 2021, 03:36:55 AM »
Could you use a spot weld removing tool without the centering bit?


Andrew Mawson
East Sussex

Offline Mike K

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Re: PCB pad cutter
« Reply #4 on: January 07, 2021, 09:01:23 AM »
Yes, I know teeth, but I wasn't sure how best to do that.  That EEVBLOG thread helps.  Had considered a spot weld cutter, but OD and ID aren't what I want.

I'll give cutting the teeth a try.  I haven't done that before, it was why I asked.

Offline PekkaNF

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Re: PCB pad cutter
« Reply #5 on: January 07, 2021, 09:33:54 AM »
Interesting and very timely post for me! I have't seen island type construction, dead bug and Manhattan style I am familiar with.

I don't understand why diamond hole saw is not popular? Maybe it does not work well with manual tools, but I think tat it should work well with a mill/drill.

What ID/OD are you aiming at?

BR,
Pekka

Offline vtsteam

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Re: PCB pad cutter
« Reply #6 on: January 07, 2021, 09:38:31 AM »
The teeth(tooth if D bit) should have zero rake for copper to prevent grabbing. Basically they should act as scrapers. You don't need much relief either.
I love it when a Plan B comes together!
Steve
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Offline modeng200023

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Re: PCB pad cutter
« Reply #7 on: January 07, 2021, 02:49:26 PM »
RS Components used to sell pad cutters in two sizes but I can't see them now.

John

Offline timby

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Re: PCB pad cutter
« Reply #8 on: January 07, 2021, 04:36:08 PM »

Offline Mike K

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Re: PCB pad cutter
« Reply #9 on: January 07, 2021, 08:42:44 PM »
I made this:

 


Three teeth.  Done with a Dremel.  Heated, quenched, tempered, briefly honed.

Not terrible, but more tearing than I had hoped:
 


I drilled with my mini-mill at low RPM.  Didn't grab at all.

Offline vtsteam

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Re: PCB pad cutter
« Reply #10 on: January 07, 2021, 10:39:22 PM »
Why low rpm?

Also, are you clamping the board down?
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: PCB pad cutter
« Reply #11 on: January 07, 2021, 10:51:53 PM »
Pretty hard to tell what shape those teeth are or the angles in that photo. Looks like there's no clearance and finish is rough.

Try forming the teeth with a triangular file, smoothing the ID with a round file, and 1500 rpm. Tooth depth only needs to be a little more than copper thickness. Try 5 degrees end clearance.
« Last Edit: January 07, 2021, 11:18:13 PM by vtsteam »
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Mike K

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Re: PCB pad cutter
« Reply #12 on: January 07, 2021, 10:54:02 PM »
Low RPM so that I could just remove the copper without chewing down through the board in the blink of an eye.  Didn't need to clamp it down, the cutter didn't grab at all.

Offline Mike K

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Re: PCB pad cutter
« Reply #13 on: January 07, 2021, 10:59:15 PM »
I'll try to get a better picture; the lighting in that photo is terrible.

The teeth have no front rake and just a little clearance, probably a couple degrees.  Finish isn't rough, but not great.  I stoned the OD edge, diamond honed the top of the teeth briefly, and didn't have anything to clean up the ID edge.

Offline vtsteam

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Re: PCB pad cutter
« Reply #14 on: January 07, 2021, 11:22:20 PM »
Low RPM so that I could just remove the copper without chewing down through the board in the blink of an eye.  Didn't need to clamp it down, the cutter didn't grab at all.

From the appearance of the board, looks like it wandered one attempt, then grabbed the copper foil in the others, indicating feed too fast for the rpm and or board moving. Set a depth stop if over drilling is a problem, or add a collar as the user did in the post referenced earlier. 1500 rpm would be 100 sfpm on .25" which would be right for copper.
I love it when a Plan B comes together!
Steve
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Offline Joules

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Re: PCB pad cutter
« Reply #15 on: January 08, 2021, 05:01:57 AM »
I still like the idea of a small pilot drill, so you have a hole for though wires from the rear, think of it as custom Veroboard for fat fingers.   Will get in the workshop and make a tool, nice post by the way.
Honour your mentors, and pay it forward.

Offline vtsteam

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Re: PCB pad cutter
« Reply #16 on: January 08, 2021, 08:34:38 AM »
The point of these type cutters is to mount multiple leads on a single land, thus reducing the need for point to point jumpers. Or connected lands, which can't be cut with this kind of bit.. Mounting components from the non-foil side through a hole and trying to do the same thing would require a larger hole to accommodate multiple leads. Where a single lead is mounted into a too large hole the component tends to flop over or fall out with the board foil side up making soldering very difficult.

 If you do drill with an oversized drill, it would work better if the components were mounted through the hole on the foil side so they at least tend to stay in place while soldering. The advantage there over these non-pilot hole cutters would be that lead length does not have to be shortened before soldering, but excess leads can poke through the hole and be clipped off after soldering. And the self centering of the bit.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Mike K

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Re: PCB pad cutter
« Reply #17 on: January 08, 2021, 08:39:57 AM »
From the appearance of the board, looks like it wandered one attempt, then grabbed the copper foil in the others, indicating feed too fast for the rpm and or board moving.

That obvious one doesn't count; I didn't have the board resting flat.  The tearout one in the upper-left was never felt, it really tore easily...possibly due to being cheap board from China.

Offline Mike K

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Re: PCB pad cutter
« Reply #18 on: January 08, 2021, 08:44:33 AM »
By the way, the guy who's image is shown in post #1 used a sharpened broken drill bit with one tooth and got no tearout whatsoever.  Magnified images of his cuts look great.

His bit:

 


Maybe I should revisit my drill bit grind attempt.  Or maybe he's using better quality boards.

Offline vtsteam

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Re: PCB pad cutter
« Reply #19 on: January 08, 2021, 08:50:46 AM »
He ground proper tooth shape with flat rake and adequate end clearance angle, and likely proper radial angle (not visible). The same can be done on a homemade bit.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Mike K

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Re: PCB pad cutter
« Reply #20 on: January 08, 2021, 09:01:21 AM »
Other view of his bit:

 

Offline vtsteam

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Re: PCB pad cutter
« Reply #21 on: January 08, 2021, 09:02:55 AM »
That doesn't show any of the angles. An end view would show the radial angle.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: PCB pad cutter
« Reply #22 on: January 08, 2021, 09:12:33 AM »
Here's what I'm talking about. The end clearance angle is exaggerated because it recedes in the photo. The honed  flatting of the cutting edge is also normally done to conventional drill bits when drilling copper based metals.
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline Mike K

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Re: PCB pad cutter
« Reply #23 on: January 08, 2021, 03:38:41 PM »
I honed the cutter some more and made a board.  Still getting some tearout and raised burr edges.

 


Couldn't get a good closeup of the cutter.  I'll try again with a small tripod and better lighting.  Am now very impressed with AndyDaviesByTheSea results.