Screw Threads

**Davidc** · 17-11-2022, 21:12

Originally Posted by Dick

There's always something new to learn, isn't there? I just got roped in to assist with tapping a lot of holes. The first batch will be 300 workpieces. Each will need eight holes to be tapped M3 (the holes will already be there) one hole to be drilled and tapped M3 and four 6mm holes to be drilled but not tapped. 300 x 9 = 2700 tapped threads. If the person who ordered the work successfully sells the items of which these pieces are a component, it could continue indefinitely. We surely can't tap 2700 holes by hand, so we bought a tapping head for use in a drill press. If you google "tapping head" there are several videos, the best being the demonstration of a Tapmatic tapping head in which the demonstrator says that a test run worked out at five seconds per hole.

While speed is the purpose of tapping heads, they are also designed to function in a way that minimises tap breakage. Yesterday I ran my first attempt and successfully tapped a dozen holes in a couple of minutes. That was slow because it was my first trial, but it tended to confirm that five seconds is realistic. It's not difficult but one needs to develop the right feel for the tap being used, so although my first threads are OK I'll need to tap 50 or 100 as a learning curve before attempting the real work. Its very interesting.

At what point will the tap be replaced? What is the average lifespan of a tap anyway? I never thought of that. Also what lubricant, Tapmatic (love the smell) or Barak type paste. Interesting subject.

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**Dick** · 17-11-2022, 22:06

Originally Posted by Davidc

At what point will the tap be replaced? What is the average lifespan of a tap anyway? I never thought of that. Also what lubricant, Tapmatic (love the smell) or Barak type paste. Interesting subject.

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Tap wear is one of those "how long is a piece of string?" questions. Depends on the material being tapped and the quality of the lubricant. I've had a few hand taps break but of course no way to know why. But its reasonable to assume too much torque because they were blunt. All my taps that broke were 3.50mm or smaller. I only broke one 6mm and I remember that it took a lot more than usual torque even with Tapmatic lube. I suspect that taps used by hobbyists don't last long, two or three hundred holes at best, but it hardly matters because few hobbyists will tap more holes than that in several years, so the cost of taps is hardly noticed.

Industrial use is another story in which cost matters, but its not only the tap - its that tap breakage stops production while it is replaced. We have been told to expect 1000 holes provided tap and lubricant quality are both good. The difficulty is that in machine tapping we can't feel the torque as we do in hand tapping. I suppose we'll start by working every tap until it breaks. If there's no consistency we'll have to continue doing that, but if we find that we get consistently close to 1000 we'll probably replace them at 900. We'll need to keep count of workpieces completed so we'll know how many holes every tap does.

**Sean KZN** · 19-11-2022, 16:48

Originally Posted by Davidc

At what point will the tap be replaced? What is the average lifespan of a tap anyway? I never thought of that. Also what lubricant, Tapmatic (love the smell) or Barak type paste. Interesting subject.

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On the paste, although in the past it was used and it is the compound I most remember as a do it all, something has changed, I think the paste.
For drilling, so so as it gets warmer, for sawing I find it hangs on to metal filings which don't make neat cuts and makes little difference on saw blade life, possibly the reverse.
On turning in a lathe you could do worse but easily better with proper stuff.

I have some very old sulphur lard, this works very well, Tapmatic is very good but does evaporate out of the tin, I can say this with confidence as I had a 3/4 tin evaporate on me over a few months, the refrigerant is volatile.
What is left after evaporation in a light sulphur oil which is as good as many. I am struggling to find sulphur powder to make my own, good for tapping,drilling and turning.

Taps break, especially small ones, just a torque issue. I've managed to break a 10mm tap many years ago, simply because I did not have the correct drill bit and tried anyway.
I've broken a brand new 6mm Alpine tap, no lubricant so took a chance, bad move.
When tapping a lot of holes by hand, I find that a tap is likely to break after you have tapped at least a fair number of holes as you have warmed up and don't gauge the torque properly. Frustration and rushing play a part.

**Koebelwagen** · 20-11-2022, 08:54

Originally Posted by Dick

There's always something new to learn, isn't there? I just got roped in to assist with tapping a lot of holes. The first batch will be 300 workpieces. Each will need eight holes to be tapped M3 (the holes will already be there) one hole to be drilled and tapped M3 and four 6mm holes to be drilled but not tapped. 300 x 9 = 2700 tapped threads. If the person who ordered the work successfully sells the items of which these pieces are a component, it could continue indefinitely. We surely can't tap 2700 holes by hand, so we bought a tapping head for use in a drill press. If you google "tapping head" there are several videos, the best being the demonstration of a Tapmatic tapping head in which the demonstrator says that a test run worked out at five seconds per hole.

While speed is the purpose of tapping heads, they are also designed to function in a way that minimises tap breakage. Yesterday I ran my first attempt and successfully tapped a dozen holes in a couple of minutes. That was slow because it was my first trial, but it tended to confirm that five seconds is realistic. It's not difficult but one needs to develop the right feel for the tap being used, so although my first threads are OK I'll need to tap 50 or 100 as a learning curve before attempting the real work. Its very interesting.

I once drilled and tapped 40 000 x M5 blind holes. The key aspects of long tool life is perfect alignment, sufficient cooling/ lubrication and correct spindle speed. The tapping head, when set up correctly makes the operation a breeze. If you are going to do this regularly, think about incorporating a flood coolant/ lubrication system, the spindle speed is generally low enough so cast-off is not an issue.

Good prep is 90% of the work done. If there is any way of building a jig to facilitate alignment, make one or a few, in machining, time is money, saving seconds add up.

**Sean KZN** · 20-11-2022, 17:00

I once drilled and tapped 40 000 x M5 blind holes.

Now that would be character building.

**oafpatroll** · 20-11-2022, 17:09

Originally Posted by Koebelwagen

I once drilled and tapped 40 000 x M5 blind holes.

Eyes bugging out of head! How long did that take?

**Koebelwagen** · 20-11-2022, 17:45

Originally Posted by Sean KZN

Now that would be character building.

Originally Posted by oafpatroll

Eyes bugging out of head! How long did that take?

3 or 4 full weeks. Joys of being lowest on the totem pole. Safe to say I understood a bit about thread tapping after that exercise.

Thread rolling on automotive parts was another one of my jobs, loved setting up those die boxes to produce crisp, sharp threads, rolling thousands of threads, not so much.

**Skaaphaas** · 20-11-2022, 22:20

Probably only tangentially on the topic. I had the misfortune of having to use my ez-out bits for the first time.

A Leupold weaver-style scope ring had a snapped mounting bolt head. Had to drill into the little 2mm screw body, and get the teeniest ez-out I’ve ever seen in there. With only a vice and a battery powered hand drillI was quite chuffed when I got it all sorted without damaging the thread.

Gunshop counter omie managed to find me a replacement screw in his box of screws, so happy days.

**atunguyd** · 20-11-2022, 23:38

Originally Posted by Skaaphaas

Probably only tangentially on the topic. I had the misfortune of having to use my ez-out bits for the first time.

A Leupold weaver-style scope ring had a snapped mounting bolt head. Had to drill into the little 2mm screw body, and get the teeniest ez-out I’ve ever seen in there. With only a vice and a battery powered hand drillI was quite chuffed when I got it all sorted without damaging the thread.

Gunshop counter omie managed to find me a replacement screw in his box of screws, so happy days.

Well done. I have had zero success with ez-out's I don't think they are easy at all

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**Wesley** · 21-11-2022, 02:13

Originally Posted by atunguyd

Well done. I have had zero success with ez-out's I don't think they are easy at all

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I once had a gentleman come and remove a cylinder head bolt for me on a machine. His trick was to use a Left Hand Drill bit. After struggling for a long time, it took him all but a few minutes. He drilled a hole in the centre of broken-off bolt, the friction of the counter rotating hole being drilled caused the bolt to screw out of its cavity.

It took me several years to come across a left hand drill bit set in a tool shop. They are not often used, but are very useful in events as described above.