Drilling the correct size hole into plastic lattice?

Hi, I'm having a problem that I hope someone can help with. I'm attaching plastic end cap molding onto a piece of plastic lattice that I just purchased at Lowes. The directions say that the product will contract & expand, so you must pre-drill holes 1/8" larger to allow for contraction/expansion. My question is if I'm using a 3/16" drill bit, and I must drill the hole 1/8" larger than 3/16", what size drill bit do I use? Thanks so much for any help, Pam.
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1/8" = 2/16"

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So that means I'd add 2/16 + 3/16 and use a 5/16" drill bit? I'm sorry if this question sounds so simple and easy for you all, but I'm not very good in the "handyman" arena (in fact I'm lost.) Thanks so much for your help! Pam
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My son says "math bites", but really, it doesn't. It's 5/16", Pamela. If possible, take the material you're drilling to a real hardware store and have them give you the right type of bit. It's not THAT crucial, but it couldn't hurt. In some types of plastic, a bit may grab the material before it begins to make the hole. That could crack the plastic. But, not all plastics behave that way. A knowledgable person may fondle the plastic and recommend that you start with a smaller hole, maybe 1/8", and then continue with the final 5/16" bit.
If this type of thing may become a habit, get yourself an entire set of bits. Get brad-point bits for wood, and the "normal" kind for other materials. Good tools can be billed to your health insurance company. If you don't have the right tools, it's likely you'll injure yourself trying to use the wrong tool for the job. These things fall into the category of "preventative health measures", like stop-smoking or yoga classes.

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Thanks again, Doug! I thought it was 5/16" (I'm just little retarded, not too much! ha-ha!) It's just that I needed one of you pros to confirm as a 5/16" hole seems awfully large! Heck, if you drill a 5/16" hole next to a 3/16" hole, there is quite a difference! It just amazes me that this plastic lattice product needs _that_ much of an area to expand and contract!
And thank you for the tip on buying brad-point bits for wood and the normal kind for the other materials. I just took a look at the drill bits I'm using and found they're high-speed steel drill bits that I bought at Pic-n-Save! ha-ha! Time to invest in some appropriate tools! Thanks again! Pam
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Pamela, if they're still sharp, the bits you have are fine for plastic. No need to replace them.

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If they _really_ are HSS, they're reasonably good bits. A good HSS set from a hardware store costs a fair bit. Better than the common/cheapie carbon steel ones.
It's particularly important with plastic that the drill bits are sharp. Brad points can also be used with plastic. Just drill at a "good pace", and don't let up on the drilling pressure and stall in the middle. A good sharp bit will throw up two long streamers of "swarf" (in plastic or metal) when drilling at the right speed/pressure.
If you drill too slowly (or the bit is dull), you won't see the "streamers", and you risk melting the plastic.
Should also take into account temperature, when drilling oversize mounting holes for plastic.
If it's cold, you should install the screws to allow more in the way of expansion. If it's hot, you should install the screws to allow more in the way of contraction.
If it's in the middle temperature-wise, put the screws in the middle ;-)
If the screw heads seem a bit small for the holes you're drilling, you may need to get washers too.
I suggest stainless or galvanized screws and washers. Or maybe brass.
Do not drive the screws in tight - let the lattice slide a bit under the screw heads.

Vinyl siding is even worse. 1/4" or more movement over 12 feet. Which is why the holes are slotted.

--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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Pamela wrote:

I remember reading a story about a lady who was, uh, "unhandy." She had a deal with a bachelor neighbor. He'd complete the puttering on her list and she'd cook dinner. Each left the evening thinking:
He: "What a deal! A few of the right kind of screws and I get a home-made rack of lamb!"
She: "The towel rack is level and sturdy and all I had to do was pitch a few more potatoes in the pot."
They both left the encounter better off than before. Isn't that nice?
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Sounds about right. Depending on where you live, the material can see a temperature difference of 100 degrees over the seasons.
When siding is installed, the nails are put into slots on the siding and not driven home all the way for hte same reason. Ed snipped-for-privacy@snet.net http://pages.cthome.net/edhome
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You might find this chart useful: http://www.mrelectrician.tv/conversioncharts/drilltap.html
John Grabowski http://www.mrelectrician.tv

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On Thu, 29 Apr 2004 10:33:52 -0700, Peaches snipped-for-privacy@webtv.net (Pamela) wrote:

If this is math question ...
1/8 = 2/16 3/16 + 2/16 = 5/16"
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(Pamela)

It *was* a math question, but I think we were skirting the issue to minimize the chances of her math teacher being sued for negligence.
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