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Machinist questions

Posted by Stuart <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Stuart' width='330' height='300' border=0 style='border:none;'> on August 9, 2024, 5:59 am

Hi All,

1. Options for removing a broken tap from a hole (not blind hole)? I know of spark erosion and grinding, any other options? Asking for a friend ...

2. Cleaning out tapped (badge) holes in a couple of fuel tanks, if the cleaned holes aren't consistent - I'm having to do selective assembly with the screws - is the tap shagged, do I need a new one?

Regards,

Re: Machinist questions

Posted by Andy C <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Andy+C' width='330' height='300' border=0 style='border:none;'> on August 9, 2024, 7:55 am, in reply to "Machinist questions"

What size is the broken tap, and is the item it is stuck in "portable" i.e. could you take it to a machine shop?

Just thinking that might be the best way of getting it removed, depending on size wondering it you could break it down using a small chisel and then drill a new hole and helicoil - just thinking out loud on that one, probably impractical.

Could try: https://www.2linc.com/product/broken-tap-removal-tools/#:~:text=Remove%20Broken%20Taps%20using%20Solid,Armor%20Mills%20and%20Armor%20Drills.

Re the badge hole, are you saying that running a tap through the holes wont allow the screws to freely go in?

Stupid question, are the screw threads on the screws in good nick, and the right thread?

As you know more often that not running a tap through a knackered thread restores normality unless the thread is completely knackered, or of course the tap is past its's best.

Who needs a signature anyway......

Re: Machinist questions

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on August 9, 2024, 10:42 am, in reply to "Machinist questions"

If the tap is large enough you may be successful with a Walton tap extractor

These use 3 blades to engage with the flutes of the broken tap, allowing you to get a grip on it. The blades used to be available as spare parts, as they do tend to get mangled in use. These used to be held in the stores when I worked at Broadbent Machine Tools in the early '80s - handy, as I had something of a tendancy to break taps !

Broken taps can also be drilled out with carbide or Stellite drills, though this can't really be done free hand. Stellite drills especially rely upon heavy axial pressure to get them to "cut" - which isn't really cutting at all, more heating the material to be drilled by friction to soften it & allow it to be scraped off. I have had some success regrinding carbide masonary bits to metal cutting geometry of one-off jobs drilling hard bits - can't recall the specific jobs, but used slowly with a constant pressure and something like Rocol RTD cutting fluid, so probabaly a work-hardening material being drilled.

It is also possible to dissovle broken taps using a super saturated solution of alum (aluminium potassium sulphate, I believe). This method can be used if the tap is broken off in a non-ferrous material as it causes rapid oxidation of the steel tap - obviously it would also cause rapid oxidation of any ferrous metal the tap was broken off in as well. Read of this quite a bit, but never tried it.

I have occasionally had success in shattering a broken tap using a punch & then extracting the bits, though this can cause some damage to the hole.

Are the tank badge threads in chromed tanks ? Chrome plating in the threads can be hard on taps. Trying a new HSS tap from a reputable manufacturer would be something to try first ?

Nigel B.

Re: Machinist questions

Posted by Stuart <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Stuart' width='330' height='300' border=0 style='border:none;'> on August 10, 2024, 8:16 am, in reply to "Machinist questions"

Hi Andy, Nigel,

Thanks for replying:-

>What size is the broken tap

1/4"UNF.

>item it is stuck in "portable"

Clutch lever.

>break it down using a small chisel and then drill a new hole and helicoil

As I say, hole is less than 1/4" i.d.; lever is case-hardened steel.

>Could try

Again unfortunately, I don't have any way of grinding the remains of the broken tap flat so I could start a new hole centrally for that tool.

>badge hole, are you saying that running a tap through the holes wont allow the screws to freely go in?

Not all screws in any holes; I can get all screws in all holes but only with selective assembly.

>are the screw threads on the screws in good nick, and the right thread?

They came out of the tanks before painting, the job was initially just to clean up the threads in the tanks after painting. However, as they're only 8UNC, if I don't have a die already, I'll get one.

>As you know more often that not running a tap through a knackered thread restores normality unless the thread is completely knackered, or of course the tap is past its's best.

I'll die the screw threads but tap past its best is what I was wondering, although it's only ever been used for cleaning threads.

>Walton tap extractor

That's a generally Bloody Good Idea; unfortunately, on this occasion, the offending tap only has two flutes (No.1 tap).

Nevertheless, I'll spend some time with my mate Google, see if there's a 2-flute version.

>dissovle broken taps using a super saturated solution of alum

Unfortunately, this offending tap's in a steel clutch lever.

>tank badge threads in chromed tanks ?

Uh-uh, tanks just painted; the screws actually came out of the tanks, I was just cleaning the tank threads after painting, which is why I was surprised at the subsequent difficulty refitting the screws.

Once again, thanks for your time, guys.

Regards,

Re: Machinist questions

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on August 10, 2024, 10:46 am, in reply to "Re: Machinist questions"

the offending tap only has two flutes

That is a wierd one Stuart - I cannot recall ever coming across a 2 flute tap in the 45 years I spent working in engineering. Are there any makers marks on the tap ? Any idea how old it was before its demise ?

Nigel B.

Re: Machinist questions

Posted by MadMike <iframe src='https://members5.boardhost.com/classicbikemart/info/user=MadMike' width='330' height='300' border=0 style='border:none;'> on August 10, 2024, 1:52 pm, in reply to "Re: Machinist questions"

Like you Nigel, in 50 years of working in engineering based manufacturing I have never seen, or indeed heard if, a two flits tap. How would you keep it anywhere near straight or central when tapping by hand?

Other opinions may be available but this one is always correct.

(no subject)

Other opinions may be available but this one is always correct.

Re: Machinist questions

Posted by geoff the bonnie <iframe src='https://members5.boardhost.com/classicbikemart/info/user=geoff+the+bonnie' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 7:27 am, in reply to "Re: Machinist questions"

Maybe its not a tap. With two flutes, it could be a drill bit snapped off.

O ye of little faith ...

Posted by Stuart <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Stuart' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 9:36 am, in reply to "Machinist questions"

Re: O ye of little faith ...

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 11:01 am, in reply to "O ye of little faith ..."

Not suggesting that what you stated was incorrect, Stuart, just saying that such a tap configuration does not seem to be popular in UK industry.

Doing a bit of digging around, it seems that 2 flute taps are more used in the US for machine tapping certain materials - all the references to 2 flute taps were on US machinist websites & US manufacturers & most refered to their use for machine tapping. Maybe not the best type to use as a hand tap ?

In the UK machine tapping is usually done with spiral flute (for blind holes - swarf ejected backwards out of the hole) or spiral point (for through holes- swarf pushed forwards through the hole). A 2 flute tap has more space to accumulate swarf due to the larger gullets, where our usual 3 or 4 flute taps require a reverse rotation frequently to break the chips & stop them packing up in the smaller gullets - which usually leads to the tap breaking.

Still maintain that using a new HSS tap from a reputable manufacturer is the best way forward if you are having tapping problems. Unkown provenenace old taps - particularly those that have been rattling around for decades in an old tobacco tin ! - "no-name" autojumble specials in large sets made from "tungsten steel" (whatever that is !) and Ebay Chinese cheapies are far from guaranteed to give decent results. The cutting edges should feel sharp & easily make fine shavings with minimal pressure from your thumbnail - if a tap doesn't feel "proper sharp" when you touch it it is unlikely to cut well.

Taps can be resharpened like any other cutting tool & you may be able to improve one by hand using a small diameter round slip stone or "reamer" stone in the gullet. But for small taps they are best treated as disposable & replaced when they start to get blunt. Depending on the material you are tapping, life can be very short - I had one customer tapping 1/4" holes in a nimonic alloy casting who used a new tap on very hole. A new tap was almost guaranteed to complete one hole without issue, but it was 50:50 as to whether or not it would complete 2 without breaking. Given the casting concerned cost around £50k before machining (and that was around 1990), a couple of dozen taps per component was small beer compared to scrapping a part.

Nigel B.

Re: O ye of little faith ...

Posted by MadMike <iframe src='https://members5.boardhost.com/classicbikemart/info/user=MadMike' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 11:41 am, in reply to "O ye of little faith ..."

No lack of faith here, I merely commented that I had never seen or heard of a 2 flut tap. Interesting that they are used for machine tapping. Much more common in this country would be spiral taps.

Other opinions may be available but this one is always correct.

Re: O ye of little faith ...

Posted by Stuart <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Stuart' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 12:51 pm, in reply to "O ye of little faith ..."

Hi Nigel, Mike,

Not a "tobacco tin" tap; kept separately in its box with corresponding No.2 and bottom taps.

Says "Made In UK", is HSS like all my taps and dies; while I've probably had it thirty years (bought new from a tools supplier in NW London I'd used since I moved to the area in the late 1970's).

Before the break, can't remember ever using it for cutting a full thread from scratch, only extending existing threads. In this case, I was cleaning out a thread in a clutch lever after rechroming (Mike, same lever I couldn't enlarge the pivot hole with a hand-held electric drill a while back - as well as chromed, the lever is also case-hardened ... ). Was being used with cutting lubricant.

Hth.

Regards,

Re: O ye of little faith ...

Posted by Nigel B <iframe src='https://members5.boardhost.com/classicbikemart/info/user=Nigel+B' width='330' height='300' border=0 style='border:none;'> on August 12, 2024, 2:59 pm, in reply to "Re: O ye of little faith ..."

Hi Stuart,

Well you seem to have covered all the bases there with your tooling.

It would appear that the combination of chrome plating + case hardened lever (another strange item ? ) was too much for your HSS tap. I know from past experience that chrome plating is very hard, having had to grind off a built-up "lip" around the edges of some BMW exhaust pipes I had rechromed in the UK to get them to fit into the heads. Went though Dremel grinding bits like they were going out of fashion !

A quick search suggests that the hardened case layer of case hardened steel is very similar in hardness to that of HSS (around 62 HRC for case hardness, 62-65 HRC for HSS), with chrome being much harder than either at 68-72 HRC. I would expect the chrome layer to "machine" the HSS tap ! Probably explains also why you couldn't drill the chromed layer either.

On the odd bit of hard (as opposed to decorative) chroming I had done for work (usually building up worn tailstock barrels or spindles) the platers masked off areas such as threads with wax before palting to prevent the plating getting into those areas - presumably due to the difficulties that could be had trying to clean out the plating with cutting tools.

I have found references online to tap manufactures recommending carbide taps for materials up to 70 HRC - unlikely to be inexpensive & probably more brittle than HSS. And even more difficult to remove should you be unfortunate enough to break on in the part !

Nigel B.

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