Need help with boring and tapping CI

[Mike Heidrick]

I need to tap the shaper for the power feeder - table is cast iron of course.

Instruction say I need to bore 10.3-10.5mm and then tap M12 X P1.75

What is a plug tap? - is that what I need?

Any good links to the bit and tap that I need to do this?

Anyone want to lend me these for an hour or two - or rent them to me??

Anyone have advice on how to do this? Says I should punch this and then bore - is that with a small center punch (small pointy punch)?

I have never done this so go easy on me. I am new to drilling CI all together, much less tapping it.

Mike

[Kyle Kraft]

Mike,

I may be able to help. First off don't be afraid of drilling and tapping CI. For drilling, you can use the 10.2mm drill, or the more widely available letter "Y" drill. To spot the hole from the workpiece, a transfer punch will get you dead on center. A transfer punch is a cylindrical punch with a small 90 degree tit in the middle which will make a dent in your table when hit with a hammer. Short of a transfer punch, you can scribe around the mounting hole and carefully eyeball the center and ding it with a center punch. To drill, first start with a small drill like 3/32" and go all the way through. You can drill and tap CI dry or use kerosene as a cutting fluid if you wish. There is enough "free" carbon in CI which allows dry machining, and in industry usually a water base coolant is used mostly to keep down the dust.

Finish drilling with the "Y" drill. You should be able to get a Y drill and your tap at your local industrial supply house or Fastenal for a few bucks each.

There a many different styles of taps available, but the top three styles are Taper, Plug, and Bottom taps. A taper tap has the teeth ground in a taper from the tip to the shank back about 10 teeth. A plug tap has a taper ground back about 5 teeth. A bottom tap has only the first tooth ground back.

If you use a four flute hand tap, you usually have to turn the tap one rev. or so and back up to break the chips, continuing this motion on through the hole. A two flute spiral point tap can be ran down to the bottom without backing up as it runs the chips toward the bottom of the hole. Cast Iron produces discontinuous chips which are "crumbly" so backing up isn't an issue no matter which tap you use.

Hope this answers your questions

[Bernhard Lampert]

One hint to add: May want to consider renting a magnetic base drill to get a nice straight and perpendiculat hole. Alternatively, place a square right in front of the drill and have a second person spot you, so the hole goes in straight.
Cheers,
Bernhard

[Carl Eyman]

But to emphasize, you only need the bottoming (or plug) tap if you have a blind hole. If your hole goes clean through, the taper tap will thread the entire depth of hole.

One more caveat - DON"T BREAK THE TAP damhikt

[Al Willits]

I found a little lube helped in ease of tapping, also used a air hose to blow out the chips and I would make a small jig to make sure I was straight, people that don't do much of this usually get it crooked, not sure how accurate you need to be but a crooked tap looks like heck.

For a jig I'd take a block of aluminum (now that I'm a woodworker, a block of hardwood would work..) about 4" square and 2" high and bore a hole just large enough so the tap would go though it, the use that block to make sure the tap is straight.
Height of the block depends on length of tap, but it should be tall enough to keep the tap straight and yet get 6 or 7 threads cut before removing it to complete you tapping....
Just a thought.
Not sure where your from, but I wouldn't doubt I have one, prob cheaper to just buy one though.

I'll repeat the, do not break the tap, suggestion.

Al....who thinks drilling out taps is a challenge he doesn't care for.

[Frank Chaffee]

Mike, in addition to the above, I suggest you do a number of practice holes on a plate of scrap steel.

[Matt Day]

I drilled and tapped a couple holes in my old TS for a new fence and it was easy as pie. As others have said, just take some precautions like using as square to make sure you're straight with the bit. And as always, use a lot of lube when cutting the treads with the tap. Do at most a couple full turns at a time with the tap, back it out, clean the tap, relube it, repeat.

[Jason Roehl]

If you're going to just be tapping this one hole, buy the tap. And don't buy cheap. I have two sets of taps--one was $30, the other was $130. I twisted the collet on the $30 set trying to tap into my (CI) engine block after about a half-hour of intense effort. With the $130 set, it was like a hot knife through butter, and it took me about 5 minutes to finish that hole and do the next. The more expensive set was high speed steel, if I recall. So, for one tap, you should be looking at about $10 to get a usable one.