making threads: tap bit size vs drill bit size

[neskusen]

If you don't understand that chart then search for something easier for
YOU to understand rather that being a jerk....

Well I apologise for being a jerk but it doesn't seem like you read my post. You suggest to search for another chart that is easier to understand, but the issue is I can't find any and I made it clear in that post you say you have read:

There are charts listing tap bit sizes and corresponding drill bit sizes but there are more numbers in the charts I am not sure what mean. I'd be thankful if someone would help me with this.

So thanks for suggesting to use Google, but I'm not stupid to not know that I can use Google to find the info I need on the internet.

Yes, that's exactly it.

Thanks!

[Draco]

One thing that do is buy the taps with the matching drill bit, the local hardware store sells the dewalt brand with the bit and tap in the same package. i know lubrication has been covered but not using lubrication can snap the tap off in the hole and they are not fun to "try" and remove, when it's in a blind hole i drill into the metal far deeper then the tap would go so i don't bottom it out or have to get the different tap sets as mentioned. I store the taps with the matching bit to make things a bit less complicated for my self, a ratcheting handle for the tap helps me a lot, or just a normal tap handle as i do it by hand. the linked tap/drill bit in one looks kinda neat, i wonder how reliable they are?

[kitatit]

Hi neskusen,

Good questions. The guys have covered most of it well.

I'll lay out an example so you can use it to search and learn more.

"What is the tapping drill size?"
Yes, you are correct, that's the drill size you need to drill before you tap the hole.

Say you wanted to screw two pieces of aluminium plate together with an M4 screw. First you would drill say a 4.5mm hole in the top plate so the screw drops through. This is called a clearance hole. Then you drill a 3.3mm hole in the bottom plate which is the tapping drill size (4mm-0.7mm pitch).

Regarding the different taps types, I listed them below as they get called different things and may get a little confusing.

1st = starter tap
2nd = intermediate tap
Plug = bottoming tap

The main benefit of a starter tap is that the end of the the tap is smaller than the tapping hole and you will notice that the taper is very gentle. This allows the tap to "bite" in easily while only applying small force. The tap will pull itself into the tapping hole easily.

When you start out, practice with say an M6. It's very hard to snap an M6. Be careful with M3 and very careful with M2.
As you may have already read, you should start tapping the hole then after a few revolutions, revere the direction say half a evolution. This will stop the tap from jaming.... And snapping.

On small taps you will feel the tap twist and flex, this is normal but it has a limit and pushed too far it will snap.

I have snapped many taps and I should know better but as its quiet a boring job I can day dream....... Snap!

Also, as mentioned before, the ratchet T handle tap wrenches are very good.

Oh, different metric thread pitches. Here are the standard thread pitched that you will use 95% of the time;

https://www.boltdepot.com/fastener-i...ead-pitch.aspx

The only non standard metric thread you are likely to come across in laser work on a regular basis is M9x 0.5mm for lens barrels.

Good luck and have fun.

Kit