Tapping questions

Brendan,

In another life I used to have to hand tap M20 holes to 50 mm deep into the top of Injection Moulding machines to support Robots, I found that if the tap was straight to the hole and you had a decent sized tap wrench with tapping compound it was easy enough with standard taps.

Martin P

In article , anotherid writes

Yes, it would be hard work - I did some 1/2" BSW tapped holes by hand a few weeks ago. However, some things help.

(1) Use a tapping size drill to give the lowest thread engagement suitable for your application; unless there are reasons to the contrary,

65-70% thread engagement will be enough. The torque required will be less than half that for 100% engagement, and the strength will be more than adequate assuming at lest 1xD thread depth.

(2) Ensure you get a good perpendicular start to the thread; being measurably off perpendicular will be harder work, give a poor thread and possibly a broken tap.

(3) Use a suitably-sized tap wrench (obvious, really).

(4) For steel, I always use Trefolex cutting compound; normal cutting oil is markedly inferior. I have seen it said that normal soap is better than cutting oil, but I have never tried it.

Never used them; can't see why they would be easier to turn.

Yes and no respectively, for steel use Trefolex or similar. Paraffin is used on aluminium mostly to reduce metal welding on to the tool tip.

David

I have always found spiral fluted taps to be very easy to break, not sure if I have ever hand tapped a hole with one without breaking it.

The easiest turning taps are, I believe, the spiral pointed taps commonly known as gun taps because they push all the chips ahead of the tap. Taps with spiral points are available that do not have flutes, these are about as strong as you can get. This type of point sometimes needs to be pushed a bit when starting before it will pull itself or you get a ragged almost double cut thread. They are really intended to be used in a machine but can be used by hand.

Some descriptions.

*2ADifferent*types*of*taps

*2ADifferent*types*of*taps Good link, thanks! I now know more about taps (and reamers!) than I di ten minutes ago.

Brenda

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An M12 tap in steel with a 10.2mm hole is a piece of cake.It sounds as though you should be throwing your tap away and buying a new one.Also only use a taper tap to start a hole as it`s easier to keep it square then when you have a couple of threads done use a second (intermediate) tap.It`s easier to turn as it`s cutting over a shorter length than a taper tap. As you seem to be learning about tapping I would stay away from the spiral point and spiral flute taps for the time being although that`s all I use myself but there is a reason for that. Mark.

I meant to add,buy a tin of Trefolux tapping compound or a litre of neat cutting oil.Do not use lubricating oil as it`s designed to make things slip. Mark.

So all you need to know now is that Rocol RTD variants are your very best friend when it comes to tapping:

Tom

Brendan Hi, I think most aspects have been covered but I would emphasize the importance of the tapping drill size. If yours was a normal 12mm coarse thread then the most often recommended drill would be 10.2mm and if your drill is cutting accurately that should tap reasonably well. It is however producing a 95% thread form so will not be "easy". I must admit that unless that degree of thread engagement is necessary for steel I tend to go up a size on the tapping drill, for most uses 10.3 or 10.4mm will be perfectly satisfctory and much easier to tap. If the hole is relatively deep then the squareness of the tap is vital, most broken taps are the result of starting off square. I have a couple of spiral taps but have not noticed a huge difference in the effort required, I have though noticed a difference in my ability to start them square. That might be just the result of my experience being much greater with straight fluted taps.

Another issue where I agree with Davids comment is that with most sets of taps and dies the tap holder is always too short for the largest size of tap included. I have an expensive American set that goes up to

1/2" UNC and the tap holder is only 8" long, in steel that is OK but will always give the muscles a good workout.

As others have said tapping compound is worthwhile if you do a lot of tapping. You can get away with neat cutting oil for occaisional use but I have found Rocol or as David says Trefolex works well for steel.

Another issue would be is your taper tap sharp, it does most of the work in any set and is usually the first to dull. In my experience this is one of the areas where Carbon Steel is an advantage over HSS, it holds a really sharp edge better. Of course you pay as it is normally more brittle but you pays your money etc.

Best regards

Keith

If I have to hand tap anything of depth, I either use a square (123 block) or machine drill a block to use as a guide for the tap.

Taper taps are the worst as you can really get them started crooked. JMHO.

Wes

I have one of those cheap stand drills from ALDI. I whip the frive belt off undo the spring return and stick the tap in the chuck then turn the tap by turning the spindle pulley. If necessary (I've resorted to this yet) yu could grind three flats onto the tap to gove the drill chuck something to bite on.

12mm is hard work using a 10mm tapping hole.

I've used rocol tapping fluid, but I think it's a psychological benefit for one offs!

Steve

On or around 14 May 2007 15:00:44 -0700, " snipped-for-privacy@ems-fife.co.uk" enlightened us thusly:

is neat cutting oil better than having it mixed with water?

I've got a squirt-gun filled with mixed cutting fluid for aiming at things like the drill which don't have a built-in feed.

Cutting oil's expensive to use neat, mind.

On or around Tue, 15 May 2007 15:32:05 +0100, "Steve W" enlightened us thusly:

unless you're doing M12x1.75 then you're better off with 10.5mm.

Turns out you're exactly right! I got a new M12 tap today and I whizze through 10mm of mild steel in about twenty seconds. Easy-peasy, didn' even need to reverse.

I drilled another (10.2mm) hole and tried with the other tap and coul hardly make progress! This other tap came from a Maplin set - ther were about 30 pieces in the set and I paid about £30 for them. Look like I got sold a pup!

I also experimented with and without neat cutting oil, but couldn' honestly tell the difference. How does cutting oil work?

I notice that my lastest (RS) tap has a flat end, whereas the othe taps (and taps I've bought in the past from Chronos) have pointed ends which is OK for a drilled hole, but stops one getting to the bottom of blind bored hole. More to taps than at first meets the eye!

Brenda

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I've had problems finding a decent tap-holder. The ones I have fro Chronos really don't want to hold the tap square - I can easily spen two minutes swearing until I get the thing square. But, today I got tap from RS - it looked just the same as the Chinese (Chronos) ones bu cost about £10 more! However it worked a treat. It had a better holdin thingie and I could drop a tap in, screw it up and the tap staye square. Looks like you gets what you pays for!

Brenda

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I got a 20 litre drum of neat cutting oil for about £35 five years back. I'm still working on it. Nowadays you'd pay about £45 inc VAT for a similar drum of oil now.

Soluble oil is probably not a good thing to use neat.

I do sometimes use the neat cutting oil with taps, but generally I use a much heavier high sulphur oil for tapping.

Mark Rand RTFM

I've had the same experience with the Chronos tap wrenches (the 'replaceable jaw' types which they don't sell replacement jaws for), the small one's jaws broke after a few uses and the larger one comes loose after a couple of turns, so I spend more time removing the tap and re-tightening the wrench than I actually spend tapping holes. Martin

Great! :-) It at least increases your tool's life.

Nick

You can grind that off, except you want to give the tap to a t&c grinder who needs it for centering. But regrinding normally costs more than a new one.

Nick

On or around Tue, 15 May 2007 16:41:16 -0500, anotherid enlightened us thusly:

no, you bought a cheap set of taps and dies. decent taps, as you no doubt know by now, don't come for an average of about a quid each.

There are normally 3 taps in a set, no.1, no.2 and no.3.

No.1 has a pointy nose and a long taper - the first bit of the tap normally only cuts about 1/3 of a thread, and tapers up to near-full thread at the top - not all no.1s will cut a full thread. No.2 has a pointy nose and a short taper and a fair length of normal full thread. No.3 has a flat end and no notable taper, and is used for cutting most of the way to the bottom of a blind hole, although if you really want full thread right to the bottom, you might have to modify it.