tap drill size

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Measure the core diameter of the tap and go down a bit for eccentricity and general wobbles. Alternately, try your larger drill on a scrap piece, tap the hole and then inspect it with a magnifier - if the threads are flat-topped you've gone too far.

Chris

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Do you have time to fight a broken tap out of the steel? Been there, done that, don't like it! Does the connection need all the strength of full threads? If not, drill the hole larger. If you don't drill the hole larger, at least use a good quality, sharp tap, there is a big difference. Either way, do use a proper lubricant. I'll be away, and won't bother you while your doing this, tell your wife to go away too! Mike

PS. Most of my experience is with 4-40, 6-32, and 8-32 in aluminum. I phased out the 4-40 without any regrets.

I would say that your tap is dull or you have soft steel. Chinese taps are horrible. If you don't need strength, you can go down to a 60% thread which I do in titanium, actually, 55% for some fasteners that hold a decorative plate.

.. Mark

qrk wrote in news: snipped-for-privacy@4ax.com:

You also don't state if you are using any lubricant. It makes a huge difference.

Doug White

The 0.201 (13/64") is for softer materials. You want to go to a 7/32" drill for harder materials. Also, you have to decide if you want 75% or 50% threads.

I was in manufacturing for 25+ years.

Bill

You can't beat PTFE lubricants - slick50 or Finish line grease from a bicycle shop.

--- IME it's not normal.

As someone else suggested, make sure your tap is sharp and use lube.

If you haven't done any tapping in a while, it may be that the tap isn't being held normal to the panel when it starts biting into the metal, which can cause it to bind up.

In order to make that go away, get or make a "tapping block" which is nothing more than a block with a 1/4" hole drilled through it perpendicular to the face being drilled, hold it against the panel, insert the tap into the hole and start the tap into the panel that way.

Works great!

JF

...Jim Thompson

Are you using lube ? Soap is Ok.

Are you using cutting oil?

Cheers

Phil Hobbs

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

You need some cutting oil, Kerosene or plain oil will do.

Cheers

Good idea! When I went out to get a larger bit, I bought a vanadium tap :-) ...Jim Thompson

Really good idea! When I can, I use my drill press to get a vertical start. In this case, it's free-hand, so your "tapping block" is a SUPER idea! Thanks! ...Jim Thompson

Of course not! I'm an EE :-( But I will ;-) ...Jim Thompson

What lubricant are you using? And is the tap sharp?

#7 bit.

I use my small cordless black&decker 3/8 drill in slip mode around 10 to drive the tap in, when it jams and the drill chatters, reverse it and then reenter. I do this all the time when making enclosure mounts etc..

P.S. If you don't have drill&tap oil around, use D-40 and use a start (tapered tip) tap not a bottom tap.

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

If you are doing through holes, what you really want is a "gun" tap. These push the chips out in front of the tap, so you don't have to do the "forward 3/4 turn, back up 1/4 turn" routine to bust off the chips. They just corkscrew out ahead of the tap.

A combination of:

2) a guide block

and you will be amazed at how easy it is to tap holes.

Doug White

That level of flexing is not normal. You risk snapping the tap off in the hole, which is a nuisance.

Lube, and, back the tap up a bit every half turn or so to break the chips (cuttings) loose as you go. That greatly reduces friction & cutting force. John's tapping block is another hot tip.

-- Cheers, James Arthur

Use lube. And back the tap up a quarter turn or so for every turn (once it starts cutting good thread) to clear the chips.