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Musings on taps

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Ian P16/01/2020 21:48:39
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2412 forum posts
101 photos

The recent thread about 'driving taps' has prompted me to set out some other tap related matters that I have often wondered about. I could probably find answers to at least some of them if I used a search engine but I wondered if the things I have experienced have been seen by others.

'A'
Compared with the size range that (one example) of a typical bar type wrench can hold, I rarely find that the whole length of the squared end will enter far enough for the screw to bear somewhere near the middle, ie the squared section of the tap is to short (or the wrench too thick)

'B'
Plug taps with a 60 degree conical end are really not fit for purpose because they cannot really cut close to the bottom of a hole. Without tap re-sharpening facilities I just grind the point off.

'C'
If one breaks one of the first two serial taps, then presumably the whole set is compromised because, as far as I know, individual replacements are not sold.

'D'
Might be me, but I have not found any benefit in using serial taps. The tapping process take longer and is more of a faff and as far as I know it is less than ideal for cutting threads in tough materials. As I understand when cutting stainless steel is best to take a reasonably deep bite with the tap (say miss out the taper tap) so that whilst the cut is concentrated on fewer points, its better than multiple smaller cuts over the length of the taper tap.

'E'
When cutting a thread in material that is much shorter than the tap length I tend to let the tap pass almost as far as it will go (I tap under power at low speed with very limited torque) When reversing the tap out I find that when the tap is about half way disengaged the tap tightens up somewhat before then easing up and becoming as free to rotate as it was at the start of unscrewing. I see this with a whole range of thread and type and sizes but cannot fathom out what could cause it.

'F'
Despite the high quality and the 'ground all over' finish of some taps I have found some where the thread is off axis (even skewed) to the body, even with well known brands.

'G'
I'm just amazed that its possible to manufacture very small taps (like M2 and below) and incorporate the relief etc. The grinding wheels must be very small with even tinier features yet last long enough in a production environment.

Ian P

old mart16/01/2020 22:05:32
1921 forum posts
151 photos

You've got it pretty well sussed.

A. The wrench is probably made to be correct if using the biggest tap that will fit it.

B. Yes

C. Yes

D. I've never tried them, would prefer ist, second and bottoming myself.

E. Yes that seems to be common, no idea why.

F. I've never noticed.

G. Yes, they are miniature works of art.

Steviegtr16/01/2020 22:24:02
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1387 forum posts
148 photos

I would have thought that E: was due to the swarf bunging the thread a little on the way out.

Andrew Johnston16/01/2020 22:28:31
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5635 forum posts
652 photos

A. Never really noticed that

B. If needs be I do the same, but I rarely use plug taps, taper is fine for through holes. I use spiral flute taps a lot, you only need to buy one tap, not a set

C. No idea, never used serial taps for V-threads

D. C C. Serial taps can be useful for square and Acme threads. Here's a home made set for a square thread:

finished_taps.jpg

E. Never noticed it, but I use commercial tapping heads on the vertical mill and repetition lathe along with spiral flute taps, so reverse just happens. Depending upon tap size I'll run at 500 to 1000rpm

F. Not noticed it with professional taps, although I'm not convinced of size of some of the ME taps I've bought

G. The relief is fairly simple, it's how they get the thread form impressed into the grinding wheel that amazes me

Andrew

speelwerk16/01/2020 22:46:04
372 forum posts
5 photos

Perhaps it is only here in the Netherlands but I am shocked at the prices I have to pay for small sizes taps. I returned the M1.4 mm Bergeon ones when they arrived with an invoice of 98 euro ex. VAT. Ordered the same size from another supplier for 30 euro ex. VAT, made by Ritter which used to be a good German mark, they work but at close inspection are crudely made. Niko.

JA16/01/2020 23:22:41
962 forum posts
52 photos

A - Not worried.

B - I usually grind off the point on plugs. The last time I broke a tap was doing this.

C - I try to buy single taps from suppliers I trust.

D - I have tapped stainless steel without difficulty. I realise there are many different stainless steels but, I am told, you must cut and not rub. If you want real difficulties try Aluminium Bronze.

E - With mild steel, yes. I do not tap using power and consider 3/8" BSF very large!

F - I have not met this one - see C

G - That is what you pay for.

JA

JasonB17/01/2020 07:26:36
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Moderator
18659 forum posts
2049 photos
1 articles

A. Get a smaller wrench.

B. Yep grind the points off and not just the plug

C. You can get individual ones from Name brand suppliers but one will cost more than a set of three unbranded

D. No never found a benifit from the few that I have

E. Pass

F. Probably less noticable when hand tapping

G. I would not want to make ones that small.

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