need some help...anyone ever tap 4mm screw holes?
 

i'm making some 3mm screw holes into 4mm holes. i have the 4mm tap. they recommend using a #30 bit or a 3.3mm bit to drill it out. only, none of the stores i have carry metric bits. can i use a 1/8" which is 3.2 or will it screw up the holes i'm trying to thread?

can someone please lend me a hand?

3.3mm = .129", 1/8" is only .004" smaller- the tap will never know the difference.

100% safe :yes:

I should mention, always use at least a medium viscosity oil, (30W motor oil is ok in a pinch) but ideally some tapping fluid.

The conversion is .039" = 1mm, remember that and you'll be able to substitute SAE for metric almost anywhere.

Thanks! :yes:

Happy tappin!

Most important thing to remember when tapping. :rules: Gotta have the fluid, I always use one called tap magic. :intello:

Also go slow and make sure to go straight, and be sure to back out every few turns to get the chips out. Take your time and you'll have no problems

thanks guys. i'll get the oil tomorrow and thanks for mentioning that. i had never heard of needing to do so.

now tap that hole like a looter in a riot:surprised:

Advancing the tap half a trun of so and then backing it out is a great idea. I always do this. I like to clamp the item to be threaded under the drill press, drill the hole, then chuck the tap into the drill press and manually turn it in. The drill press keeps the tap straight and true to the hole, and you can focus on slowly cutting the hole and not breaking the tap off. Do not try to tap the hole with the drill press under power, I pull the plug and open the belt cover and use the pulleys to turn the drill chuck by hand. Works every time, in all metals.

thanks to everyone in the thread for all your help. i just tapped my first 4mm motor cover and it went great. it was alot easier than i thought it was going to be.
:yipi::party::yes:

one down, 5 more to go!