DIY & Home Improvement
Related: About this forumNeed help understanding tap & die sizes
I have a piece of acrylic that is 5/16" (?) thick.
I want to tap four holes for screws with 1/4-20 thread
I believe the drill size I need to use is a #7.
But I can't figure out the tap size. I don't see any numbers that reference 1/4-20.
I have both metric and sae...
What am I not understanding?
amerikat
(4,987 posts)Available at any hardware store.
Nittersing
(6,818 posts)ret5hd
(21,309 posts)if i may make a suggestion:
if drilling by hand (as opposed to using a drill press or some other method that keeps your drill exactly perpendicular to the acrylic sheet)
use a #8 or even a #10 drill.
the acrylic sheet is soft enough
compared to steel etc
and using a hand drill
wobbly
the slightly smaller drill bit (#8 - #10) will give you a finished hole that will work perfectly.
dont expect the finished tapped holes to be particularly strong though
acrylic is brittle and your sheet isnt particularly thick.
Nittersing
(6,818 posts)Nittersing
(6,818 posts)ret5hd
(21,309 posts)i have decades of machine shop experience
i wouldnt buy one for one little job, but i know how to adjust things and methods to make sure i get an acceptable result (like the drill bit advice).
do what feels right
is this job a one-and-done? are you intending to start or add-to a tool collection for future projects? do you want to become a tool addict and spend hundreds or even thousands of dollars on tools that you now have to invent projects for? will your spouse/partner now expect you to remodel the entire house?
welcome to my world.
ret5hd
(21,309 posts)that item is used to hold screwdriver bits in a power drill
not what you might need.
i dont know why they would call that a drill guide.
usaf-vet
(6,802 posts).... taps and dies in the kit they came in.
Finally, take a known 1/4-20 bolt and physically put the bolt alongside the tap. Tip to tip (one is up, the other down), and match the bolt thread to the tap. It SHOULD be an exact match. They should fit together perfectly.
If you are going to do a lot of tapping, buy a plastic guide that includes all of the tap sizes. Also, buy a small can of CUTTING OIL to use when tapping metal.
And one more tip: if you tap metal, take a turn or two into the hole, THEN take a half turn back, which breaks the cut material free. Now continue 2 turns in 1/2 turn back.
Hope this helps!
Nittersing
(6,818 posts)Just going thru some acrylic... but thanks for the metal tips as well.
essaynnc
(863 posts)Use alcohol on the tapped hole to clean it. Tha acrylic will crack and craze and be ruined.
I speak by experience.
usonian
(13,470 posts)But I'm not a machinist, so what the heck.
https://www.littlemachineshop.com/images/Gallery/PDF/TapDrillSizes.pdf
So #7 is what you want for plastic.
1/4-20 thread is so common that it's easy to lose the tap.
Universal tripod thread for cameras.