# Drilling/Cutting a 3/8" hole in a PCB.

#### WhatDoIKnow

Joined Apr 11, 2013
4
Hello all, this is my first post. This looks like the best place to ask this question.

I am working on a project that requires 3/8" holes to be cut into a fiberglass PCB. The only hole saws I can find that small are the diamond edged ones for cutting glass and ceramic. I am worried that these bits will create a very rough hole.

I would prefer something like a wood hole saw with a center mandrel bit, but am open to any suggestions as far as the best tool to use.

Any info is appreciated.

Thanks.

#### wayneh

Joined Sep 9, 2010
16,281
In wood, Forstner bits make a very nice hole. But I've never seen one as narrow as 3/8". I think one of your hole saws on a drill press would give a very nice result also. And if you sandwich your PCB between two pieces of wood clamped tightly, I think just about any drill bit will give a good result.

Just tossing out ideas.

#### WhatDoIKnow

Joined Apr 11, 2013
4
In wood, Forstner bits make a very nice hole. But I've never seen one as narrow as 3/8". I think one of your hole saws on a drill press would give a very nice result also. And if you sandwich your PCB between two pieces of wood clamped tightly, I think just about any drill bit will give a good result.

Just tossing out ideas.
The sandwich idea is a good one. Thanks.

#### JohnInTX

Joined Jun 26, 2012
3,987
These cut very smooth holes in all kinds of thin and/or flexible material. Get one whose step distance is longer than the mat'l thickness. You'll wonder how you ever got along without one. You can get cheapies at Harbor Freight but they are not as good.

#### gerty

Joined Aug 30, 2007
1,273
+1 JohnInTX you beat me to it.. Another tip, when using a bit like this, just wrap a piece of tape around the bit to mark the stopping depth.

#### WhatDoIKnow

Joined Apr 11, 2013
4
These cut very smooth holes in all kinds of thin and/or flexible material. Get one whose step distance is longer than the mat'l thickness. You'll wonder how you ever got along without one. You can get cheapies at Harbor Freight but they are not as good.
Great, I already have a set of those just wasn't sure how they would work with a fiberglass PCB.

#### #12

Joined Nov 30, 2010
18,190
That's what experimenting is for. I hope you have a few spares so you can learn what makes acceptable holes.

#### mcgyvr

Joined Oct 15, 2009
5,394
heck..ANY 3/8" drill will work..even a spade bit (using the sandwich method to prevent the backside from looking nasty).. Now if you need to drill hundreds of these holes thats a different story..

#### Metalmann

Joined Dec 8, 2012
703
Hello all, this is my first post. This looks like the best place to ask this question.

I am working on a project that requires 3/8" holes to be cut into a fiberglass PCB. The only hole saws I can find that small are the diamond edged ones for cutting glass and ceramic. I am worried that these bits will create a very rough hole.

I would prefer something like a wood hole saw with a center mandrel bit, but am open to any suggestions as far as the best tool to use.

Any info is appreciated.

Thanks.

Here is the ideal 3/8" tool for that job, and it's only $5.99.: http://www.rockler.com/product.cfm?page=19461 I don't know for sure how many holes it will drill before dulling, fiberglass is some abrasive stuff. Make sure your board is clamped down. If you don't, you'll have a very sharp board cutting into your left hand. Drill at low RPMs. Maybe 300 RPM, or so, to start. If you have a bunch of holes to drill, go for the more expensive bits. #### gerty Joined Aug 30, 2007 1,273 Here is the ideal 3/8" tool for that job, and it's only$5.99.:

http://www.rockler.com/product.cfm?page=19461

I don't know for sure how many holes it will drill before dulling, fiberglass is some abrasive stuff.

Make sure your board is clamped down.

If you don't, you'll have a very sharp board cutting into your left hand.

Drill at low RPMs. Maybe 300 RPM, or so, to start.

If you have a bunch of holes to drill, go for the more expensive bits.
This is one type of bit that works best in a drill press.

#### JohnInTX

Joined Jun 26, 2012
3,987
Great, I already have a set of those just wasn't sure how they would work with a fiberglass PCB.
I just used a unibit to drill to a .707" hole in .062" FR-4 to try it. At 540rpm, it went like buttah!

True, you can use a twist drill but they tend to snatch up thin material when they break through, unless you clamp and sandwich and even then sometimes. Plus you can get chips between the layers if you are drilling more than one hole which can throw things off. With the unibit, the hole is clean and round with no chance of snatching, even when hand held. At higher spindle speeds, the larger bit tended to chatter hence the 540RPM.

EDIT: I used a drill press.

#### WhatDoIKnow

Joined Apr 11, 2013
4
Lots of great replies, thanks. My instincts were good that this was the place to ask.

I do have a drill press that I can set for a slower RPM, and I do have some scrap PCB to experiment on. Wasn't finding suggestions via Google.

Will need 4 x 3/8" holes per board, so not all that many.

#### JohnInTX

Joined Jun 26, 2012
3,987
When it comes to this kind of stuff, Google is a snack, AAC is a sandwich!

#### wayneh

Joined Sep 9, 2010
16,281