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Thread: Screw Threads
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17-11-2022, 21:12 #21
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17-11-2022, 22:06 #22
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Re: Screw Threads
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.
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19-11-2022, 16:48 #23
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Re: Screw Threads
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.
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20-11-2022, 08:54 #24
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Re: Screw Threads
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.
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20-11-2022, 17:00 #25
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Re: Screw Threads
I once drilled and tapped 40 000 x M5 blind holes.
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20-11-2022, 17:09 #26
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20-11-2022, 17:45 #27
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Re: Screw Threads
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.
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20-11-2022, 22:20 #28
Re: Screw Threads
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.Sent electronically, thus not signed.
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20-11-2022, 23:38 #29
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21-11-2022, 02:13 #30
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Re: Screw Threads
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.
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