Drill,Tap Hole?

[tj309]

I am in the process of installing a themocouple for a pyrometer. I need to drill a hole into cast aluminum and then tap it to accept a 5/16 - 18 thread.

Question 1 - What size do I drill the initial hole?

Question 2 - Can I buy a single tap (5/16 x 18) at my local home improvement store (Lowe's) or do I have to buy the whole set?

Question 3 - Does a tap thread holes and a die thread rods? If not please excuse my ignorance and tell me how to die the hole.

Thanks, TJ

[bmax]

TJ , the drill size for a 5/16 tap , would be 9/32 . You should also use some form of lube on the tap . I quite often use grease , as it also picks up the filings . Go slow with the tap , and back up every full turn .

Yes you can buy both drills and taps individually . Bmax .

[tj309]

Thanks Bmax - that helps alot. And the grease instead of oil idea really makes sense.

[crazy horse]

The best size drill for 5/16-18 is a letter size F, That will give you 72-77% thread. You can go a little larger or a little smaller but a F drill is what I use. A tap is for internal thread and a die is for external threads. Make sure when you start tapping that your running straight down the center of your hole. Taps will run off if your not careful.

[Burke Kilgour]

Practice on something similar and unimportant first. Learning how to get a broken tap out is fairly difficult compared to learning how to tap a hole. ;)

[crazy horse]

Burke is right about practice, Brokin taps can screw up a really nice day fast. Also don't buy some cheap piece of junk tap. A good high speed steel tap will cut cleaner and be harder to break than a carbon steel or cheap import.

[riverrunner114]

they also make a bolt that replaces a exhaust bolt so you dont have to drill and tap into your mota. several vendors on this site sell them. the pyro screws into the special hollow bolt.