New Taps Breaking

J.Hainen · Dec 2, 2020

We use a specialist tap for producing a coarse thread inside of a connector - thread is a 3-start 5/16 by 5TPI, square modified profile. We recently purchased some taps from a new supplier after the previous went bust. We successfully tapped the parts for many years with the taps from the previous supplier. The new taps however, have broken on first use, under our usual procedures. The tap is a tapered tap with three straight flutes, carbon steel. We are tapping a mild steel.

We have attempted tapping on a small lathe with a floating head, and also on a CNC lathe with pitch control set up. Sulphurised cutting oil has been used, we have tried different speeds, as well as correct and oversized pilot holes for the tap. Very frustrating as we have never had issues until now!

Any advice on the tap, procedure, or anything else would be greatly appreciated!

Thanks
Joe

Limy Sami · Dec 2, 2020

Chuck em back at the manufacturer!

Just a thought 1 - you did use the right size drill, ......the new supplier didn't alter the thread form in any way??????
Just a thought 2 - who made them?

Milland · Dec 2, 2020

Limy Sami said:
Chuck em back at the manufacturer!

Just a thought 1 - you did use the right size drill, ......the new supplier didn't alter the thread form in any way??????
Just a thought 2 - who made them?

Along with Limy:

1) Carbon steel? This isn't 1915, at a minimum a "generic" high-speed steel should be used.

2) Confirm heat treating of the taps was done right, and threads were ground correctly afterwards.

3) Do you have any of the older taps still around? Even if dull, compare torque required against the new taps when hand tapping (with appropriate alignment guides) a couple correctly sized test holes in a steel bar. If the older, worn taps cut with less torque than the new ones, the new manufacturer's grinding is no good.

3A) Please tell me these were ground, not cut taps.

4) Did your steel supplier change, or did they ship a different grade this time than you used before?

5) When in doubt, check the old and new taps under a microscope to see if anything else is notably different between the two taps. Maybe the new taps have a smaller minor diameter, or they left too sharp a root corner from thread form to minor.

6) Materials! (bears repeating). If they buggered the heat treat to get sufficient hardness on the carbon taps, then they're likely more brittle than a proper HSS tap.

J.Hainen · Dec 2, 2020

Milland said:
Along with Limy:

1) Carbon steel? This isn't 1915, at a minimum a "generic" high-speed steel should be used.

2) Confirm heat treating of the taps was done right, and threads were ground correctly afterwards.

3) Do you have any of the older taps still around? Even if dull, compare torque required against the new taps when hand tapping (with appropriate alignment guides) a couple correctly sized test holes in a steel bar. If the older, worn taps cut with less torque than the new ones, the new manufacturer's grinding is no good.

3A) Please tell me these were ground, not cut taps.

4) Did your steel supplier change, or did they ship a different grade this time than you used before?

5) When in doubt, check the old and new taps under a microscope to see if anything else is notably different between the two taps. Maybe the new taps have a smaller minor diameter, or they left too sharp a root corner from thread form to minor.

6) Materials! (bears repeating). If they buggered the heat treat to get sufficient hardness on the carbon taps, then they're likely more brittle than a proper HSS tap.

Thanks for all of your input on this issue.

I must agree, I was surprised to find that the taps had been made in a carbon-steel, as opposed to a HSS.

Unfortunately, all of the old taps from the previous supplier are gone. We sent away piece of an old tap to the new supplier for their reference, unfortunately it seems to have been 'misplaced', so it wont be possible to compare the two. From memory, the new and old taps look visually very similar, granted it is not a guarantee that they are the same.

In regards to whether the taps were cut or ground, i assumed they would be ground, however, i will pose the question when i next speak to the person dealing with our taps.

The steel we use has been from the same supplier for years, and the grade has never been changed.

When you say "too sharp a root corner from thread form to minor", what exactly would i look for on the tap to confirm if this is an issue?

The way that the taps have broken, it does indicate a possibility of an overly brittle tap.

A little more information to ponder over, 3 of the broken taps have all broken just at the point where the taper ends and the tap reaches full diameter. Could this indicate a specific issue?

I appreciate all of the pointers,

Thanks
Joe

BT Fabrication · Dec 2, 2020

my guess from that is as it hits full diameter that the load is the greatest. i would wonder about the hardness being too hard or like others said that the threads aren't fully in line at the end and has the wrong tpi.

J.Hainen · Dec 2, 2020

BT Fabrication said:
my guess from that is as it hits full diameter that the load is the greatest. i would wonder about the hardness being too hard or like others said that the threads aren't fully in line at the end and has the wrong tpi.

Is it possible that an an over-hardened tap can break with such a relatively small amount of force being applied to it? We tried an oversized pilot hole yesterday, meaning that the tap was only cutting approximately 0.3mm of material at full diameter. For me, it seems as though there must be more to the issue than just a hardening issue if the tap breaks with such a little amount of resistance.

boslab · Dec 2, 2020

Heat treatment fault?, get a heat treater to re do and cryogenic perhaps
Mark

michiganbuck · Dec 2, 2020

Agree on the heat treat and perhaps the kind of steel used, also consider the geometry and the gullet radius and flute spacing...

Lucky perhaps the original vendor had it all together and so made a tap that fit your needs to a T.

You may have to bite the bullet and go to a high-speed steel tap. Might pay double, but might also get better tool life from the better tap.

Qt; [ if the tap breaks with such a little amount of resistance.] Everything matters even the sharpness.

You might get a HSS tap and a simple end sharpening grinder to get double the life with the higher-priced tap.

A Royal Oak grinder setup for one job, the tap would do nicely.
https://www.ebay.com/i/224219210884...1291&msclkid=ff2b831b33411a1f7ff5dcdca1c1ec1e

DDoug · Dec 2, 2020

Grinder burn ?

michiganbuck · Dec 2, 2020

QT:[just at the point where the taper ends and the tap reaches full diameter. Could this indicate a specific issue?]

Bottom out and change feed direction but I'm sure you addressed that. Also the direction the flute geometry as to how it pulls in the chip or pushes it/some forward. Forward chips can fill the expected bottom space.

Holding fixture can be an issue with a change of holding ability at the change of forces, but you are using the same set-up so likely that is not an issue.

Another tap sharpening method is to use the inside arc of a cup wheel on the simplest TC grinder. The position at the wheel provides the clearance and radil relief with no changing set-up. Just grind all flute ends to the same in feed. less than 5 minutes a tap and you get a second life of the tap.

Yes HSS taps grind better than carbon taps.

BT Fabrication · Dec 2, 2020

J.Hainen said:
Is it possible that an an over-hardened tap can break with such a relatively small amount of force being applied to it? We tried an oversized pilot hole yesterday, meaning that the tap was only cutting approximately 0.3mm of material at full diameter. For me, it seems as though there must be more to the issue than just a hardening issue if the tap breaks with such a little amount of resistance.

is there a picture of said broken taps?

Shawnrs · Dec 2, 2020

I would check to see if you have an old used tap from the previous vender and test it out on the same material you are using now. I would think that the taps you are using are probably different in some aspect than the previous ones you had. Are the taps coated?

dgfoster · Dec 2, 2020

One other point. Is there a reason this should be a cutting tap? A form tap produces a stronger thread but requires less torque. At three starts this tap cuts much more steeply than the single-start. So, torque is much greater in the three-start.

Denis

J.Hainen · Dec 2, 2020

Thanks for all the responses.

The tap should be set up to push the chips forward, as the component being tapped is effectively a tube which connects two drive-line components together. We haven't been able to observe whether this is happening because the tap breaks so quickly, before any substantial cutting is done.

Unfortunately we have none of the old taps from previous supplier. All were broken, and the piece that was saved was lost by the new supplier when it was sent to them for reference. The taps are coated.

I think a form tap would likely struggle because of how coarse the thread is, and the shape of the thread - simply too much material to deform.

Would it be worth considering a serial tap set to try and reduce loading.

I will try to get a photo of one of the broken taps today.

Thanks again all.

Joe

michiganbuck · Dec 2, 2020

Here in the States, we have many companies that make special taps.

I think to try HSS and then gather a bunch perhaps 12 dull and have them resharpened is the way to go.

Very often the OD of a HSS tap will resharpen one to three times with still make a good thread.
Sharpening is 1/2 or less the cost of the original price.

DDoug · Dec 2, 2020

michiganbuck said:
Here in the States, we have many companies that make special taps.

I think to try HSS and then gather a bunch perhaps 12 dull and have them resharpened is the way to go.

Very often the OD of a HSS tap will resharpen one to three times with still make a good thread.
Sharpening is 1/2 or less the cost of the original price.

Good point.

Why not try a vendor over here, and shipping should be minimal.

michiganbuck · Dec 2, 2020

I thought they were out of business but here is a web site, I knew guys who worked here and still have a tub of center-drills from them up in my Kellyroadcamp tool shop.
might you try their number?

Special Taps, Off Standard & Standard Taps | Cheboygan Tap & Tool

Want me to call them I will. ( 3-start 5/16 by 5TPI, square modified profile.)
likely need to order 12+ to get that better price
Buck

Web site last edit 2011 they may be closed?

Other specials USA shop. (Germany likely has many such shops.)
Special Thread Taps, Special Size Threading Taps, Made to Order Thread Taps

Milland · Dec 2, 2020

Hi Joe,
From the further comments it sounds like an over-hard situation, or some other manifestation of bad tap material and heat treating.

If you can post some good pictures of broken and unused taps, we can try to see if there's any other factor that might be an issue, but unless this company is totally incompetent it's unlikely they got the thread form wrong or used a "cut" process rather than grinding.

As stated, the torque will be highest when full engagement of the tap is reached, presuming there's no "packing" of chips ahead of the tap to further increase load. That's unlikely with a through hole, but not impossible. Pics of the lead/taper of the tap will help with figuring this out, it should be a "gun" style.

BTW, you can resharpen taps, but I'd suggest only the lead be reground, not the OD. Basically, you just "push" the taper further down the tap, reducing its length.

Bobw · Dec 2, 2020

My 2 cents.

I'm surprised you found somebody that would even make a carbon steel tap, I thought
you could only buy those in hardware stores now a days.

You are saying that it takes little force to break them, I'm going with a buggered
heat treat and the "carbon steel" is loaded with cracks.

If they were taking a lot of force to break, I would say a bad grind, or no relief.

Are Taps the thing these people do, like Balax, or are they a custom tool/sharpening
shop and they decided to take on your rather complicated tap.

J.Hainen · Dec 2, 2020

Hi all

I have attached pictures of one of the broken taps. There is a small piece missing, did a disappearing act somewhere on the shop floor! Unfortunately I have no pictures of the old taps, as they have all been disposed of prior to now.

The company making this tap specialise in this type of work. The rep that i spoke to seemed to have some concerns about getting a tap of this format to work properly, but as stated here, we used taps from a different supplier without issue for several years.

New Taps Breaking

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Titanium

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Stainless

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