Taptite - questions.

[Bellow]

Over on another forum I frequent, this has been posted:

''I've just received a brand new 700cc cylinder from Germany but only the camshaft cap holes and exhaust manifold holes have been threaded. So, the other 19 holes need to be threaded - 2 for thermostat, 2 for air con bracket, 6 for cam cover, 6 for inlet manifold and 3 for the engine mount.

Here's my problem - the three engine mount bolts are M8 so should have 6.8mm holes for tapping BUT they are actually 7.5mm and all the others are M6 which should have 5mm tapping holes BUT they're actually 5.5mm.''

Not the complete post but enough to highlight that the head in question does indeed require Taptite fixings.

The questions relate to the method of installing Taptite fixings eg, speed of operation, tools eg, electric, airline, or by hand (is manually, slowly, by hand viable?) and if any lubricant or compound should be used.

The guy has extensively searched the 'net for answers but suggestions more than answers are appearing - adding to the confusion.
Has anyone here experience of fitting Taptite into pre-drilled untapped holes? The head he has is for a smart fortwo/Roadster as 'engineered by Mercedes-Benz'. I'm guessing MB employ Taptite on other engines (components) not just smarts.
Any experience you can offer up and/or hints ant tips will be well received. TIA.

 

[Coruscator]

Over on another forum I frequent, this has been posted:

''I've just received a brand new 700cc cylinder from Germany but only the camshaft cap holes and exhaust manifold holes have been threaded. So, the other 19 holes need to be threaded - 2 for thermostat, 2 for air con bracket, 6 for cam cover, 6 for inlet manifold and 3 for the engine mount.

Here's my problem - the three engine mount bolts are M8 so should have 6.8mm holes for tapping BUT they are actually 7.5mm and all the others are M6 which should have 5mm tapping holes BUT they're actually 5.5mm.''

Not the complete post but enough to highlight that the head in question does indeed require Taptite fixings.

The questions relate to the method of installing Taptite fixings eg, speed of operation, tools eg, electric, airline, or by hand (is manually, slowly, by hand viable?) and if any lubricant or compound should be used.

The guy has extensively searched the 'net for answers but suggestions more than answers are appearing - adding to the confusion.
Has anyone here experience of fitting Taptite into pre-drilled untapped holes? The head he has is for a smart fortwo/Roadster as 'engineered by Mercedes-Benz'. I'm guessing MB employ Taptite on other engines (components) not just smarts.
Any experience you can offer up and/or hints ant tips will be well received. TIA.

Ive found if the holes are larger that required then the use of Heli-coils are a good option.

Im an engineer and we use these when an existing threaded hole has been stripped of its thread.

essentially you drill and tap the hole out one size bigger then insert the heli-coil to bring it
back down to the original thread size.

Screw the heli-coil into place with some locktight thread seal and they're as good as new, if not
better because the heli-coils are made from stainless steel.

 

[hotrodder]

Taptite are kinda posh 'self tappers' that roll their own thread? If i got that right then i've zero experience of using them but do use fluteless thread forming taps all the time as rolled threads are waaaaaaaaay better than cut threads... faster, stronger threads, no chips to clear up, taps are stronger as they don't need deep flutes for chip evacuation etc. While fluteless taps are designed around machine tools they do work by hand and are still easier/faster than thread cutting as no messing about backing the tap off to break the chip, just screw the thing in

Machine or hand tapping you want plenty of lubricant for rolled threads, ideally something with graphite or a neat cutting oil but any old oil will work if driving them by hand

All of that said the hole sizes given are only wrong for metric coarse... tapping drill size for an M8 x 0.5 is 7.5mm, M6 x 0.5 = 5.5mm tapping drill for cut threads. Rolled threads require different tapping drills as the material is plastically deformed to form the thread, drill chart here that covers various metric pitches and % thread engagement for rolled threads only http://www.guhring.com/documents/tech/charts/formtapdrill.pdf

Fairly obviously you can't rely on taps to self centre/guide themselves in straight, even with through holes where taps with a longer taper/lead can be used. Working by hand without a drill press or milling machine etc to set the parts up in can use a 'deck plate', basically a chunk of metal with an accurate hole drilled in it to support/guide the tap. Obviously no good when accuracy (properly perpendicular) is important but for an idea of the torque involved an M8 coarse roll tap can be driven into ally with a decent cordless drill as long the user hasn't got limp girly wrists

While helicoils have their place there are waaaaaaay better types of thread inserts about IMO, timeserts for example

ETA rolled threads require a slightly deeper counter sink/more edge breaking for flush threads due to the way they work i.e. because they 'squeeze' the material about if you don't break the edge of the hole enough the thread ends up proud

Oh, and while google will get you a tapping drill chart for metric fine cut threads all you need to do is subtract the pitch from the major diameter for example an M5 coarse has a 0.8mm pitch and the tapping drill is 4.2mm while M8 coarse has a 1.25 pitch and the usual 6.8mm drill size is a result of rounding up from 6.75

 

[Bellow]

Thanks HR - very useful post.
Just to pick up on one point though. Does this:

All of that said the hole sizes given are only wrong for metric coarse... tapping drill size for an M8 x 0.5 is 7.5mm, M6 x 0.5 = 5.5mm tapping drill for cut threads.

mean that what the guy has is correctly drilled but for metric fine not metric course? (Metric fine being 0.5mm pitch?)

If so, is the expectation that he uses conventional tapping methods and that there is some confusion because he has identified the holes as oversize - but only in relation to metric course threads?

 

[hotrodder]

Possibly, i dunno what thread pitch was used origionally and there are several different metric fine pitches for each diameter for example an M6 coarse is 1.00mm pitch and there are two fine pitches, 0.75mm and 0.50mm There are three fine pitches for M8 and even more for larger diameters

If the origional fasteners were definately metric coarse then the M6 hole size he's quoted is a pretty good match for rolled threads with a 72.5% thread engagement*. The 7.5mm hole is a match for an M8 x 1.00mm rolled thread or an M8 x 0.5 cut thread but doesn't make much sense if the origional bolts were m8 x 1.25 (coarse) unless inserts were used origionally in which case it's still undersized... 8.3 ish mm would be more like it to tap for an m8 coarse insert off the top of my head but exact size would depend on the flavour of insert?

Fine thread pitches are relatively common on automotive stuff, wheel bolts are a common one as are the bolts holding calipers on, both are m12 x 1.5 on 124s while m12 coarse has a 1.75mm pitch. MBs that use m14 wheel bolts have the same 1.5mm pitch, M14 coarse has a 2.0mm pitch. Makes for a stronger fastener (tension and shear) as the minor diameter is larger, they're less prone to loosening and develop more preload for a given torque

* % thread engagement being about diameter not length of engagement, 100% thread engagement would be an interference fit

Clear as mud? In his position i'd be questioning the supplier as when you buy something you don't usually expect to have to finish making it! If/when that got me nowhere and backing it for a refund isn't an option for whatever reason i'd change the bolt pitch to suit or if there's enough 'meat' enlarge the holes and fit timeserts

 

[Bellow]

Thanks HR. I'm figuring the guy will make sense of it.
Looking more and more like Taptite/rolled thread. The hole sizes - unlikely to be 0.5mm pitch at M8 size I reckon.
It is AFAIK a raw casting bought direct from supplier (MB/smart) and like you I'd expect it to be finished before it being handed over. Finishing for Taptite though is a one shot thread forming and component fitting so for them it is finished. Assuming they use Taptite during engine production assembly that is. I think, it was the supplier who first suggested Taptite and 'just drive them in'.
His choices appear then to be Taptite, or fluteless rolled thread and bolt. Hoping then he's familiar with fluteless taps as I wouldn't recognise one if it leapt from my alphabetti spaghetti and slapped me in the face.

 

[Ditch]

I have no experience of taptite and cant comment.

However for very similar proportions or differences I have , as an airframe fitter, successfully (and legitimately) used helicoils on aircraft and would recommend them.

They have the benefit of being a cinch to use with care

 

[hotrodder]

Looking more and more like Taptite/rolled thread. The hole sizes - unlikely to be 0.5mm pitch at M8 size I reckon.

Agreed, especially if it's an ally casting. I've just looked at that Guhring tapping drill chart again and 7.5mm is in the workable range for an M8 coarse... didn't notice before as i usually work to thread engagements in the 65 - 72.5% range with ally. With 58 - 60% engagement the thread would probably 'feel' a bit sloppy when screwing the fastener in by hand but it makes less difference to joint performance than you'd think a lot of the time and is relatively common with materials that are difficult to tap and/or are prone to galling

Hoping then he's familiar with fluteless taps as I wouldn't recognise one if it leapt from my alphabetti spaghetti and slapped me in the face.

If he isn't just tell him to google 'fluteless tap'. They look like they sound but aren't actually round in cross section, there's a very slight triangular or squareness (depending on diameter) to them which are the 'lobes' that do the forming. There's usually a few suppliers on the bay, random surplus Dormer etc as well as Rotogrip (machining suppliers) and someone else that sell unbranded taps that are pretty good. Don't think fluteless taps are listed on their site but Tracy Tools is another source for top quality (usually British made) gear that's often cheaper than branded cheapnese tat from the usual suspects. That's assuming you can't buy taptite fasteners in small quantities easily

 

[Bellow]

If he isn't just tell him to google 'fluteless tap'. They look like they sound but aren't actually round in cross section, there's a very slight triangular or squareness (depending on diameter) to them which are the 'lobes' that do the forming. There's usually a few suppliers on the bay, random surplus Dormer etc as well as Rotogrip (machining suppliers) and someone else that sell unbranded taps that are pretty good. Don't think fluteless taps are listed on their site but Tracy Tools is another source for top quality (usually British made) gear that's often cheaper than branded cheapnese tat from the usual suspects. That's assuming you can't buy taptite fasteners in small quantities easily

More questions! This time for my project.
Using a conventional cutting tap to tap 1/2'' UNC requires drilling to 11.5mm. But, the hole I am tapping into is already formed (read internal diameter of tube) and is slightly larger than 11.5mm (12.0mm > ID > 11.5mm, haven't (yet) got exact size but circa 11.8mm). A cut thread is giving a very sloppy fit for the bolt - no good!
Looking at the chart posted (linked) for threadforming with fluteless taps, the ID is between 12.07 and 12.14mm for 72.5 and 55% threads respectively. Have I got that right? What is the practical difference between 55% to 72.5% threads re security? Are formed threads just like cut threads and can accept any correctly sized male threaded fitting (eg Rose joint)? Anything else I should know or be thinking about? Can you recommend a supplier of a fluteless 1/2'' UNF tap? (I can't find them on Tracy Tools' website or hard copy catalogue).
I suppose the above is aimed at you Hotrodder - help!

 

[streethawk]

More questions! This time for my project.
Using a conventional cutting tap to tap 1/2'' UNC requires drilling to 11.5mm. But, the hole I am tapping into is already formed (read internal diameter of tube) and is slightly larger than 11.5mm (12.0mm > ID > 11.5mm, haven't (yet) got exact size but circa 11.8mm). A cut thread is giving a very sloppy fit for the bolt - no good!
Looking at the chart posted (linked) for threadforming with fluteless taps, the ID is between 12.07 and 12.14mm for 72.5 and 55% threads respectively. Have I got that right? What is the practical difference between 55% to 72.5% threads re security? Are formed threads just like cut threads and can accept any correctly sized male threaded fitting (eg Rose joint)? Anything else I should know or be thinking about? Can you recommend a supplier of a fluteless 1/2'' UNF tap? (I can't find them on Tracy Tools' website or hard copy catalogue).
I suppose the above is aimed at you Hotrodder - help!

Are you saying there is a thread already in the hole and that the minor diameter is already larger than 11.5mm dia. ? If so you can't go down with the 1/2 unf as there would be nothing left. Sounds like you need a helicoil or timesert.

 

[Bellow]

Are you saying there is a thread already in the hole and that the minor diameter is already larger than 11.5mm dia. ? If so you can't go down with the 1/2 unf as there would be nothing left. Sounds like you need a helicoil or timesert.

No thread other than one I trial cut. But the ID is larger than the specified 11.5mm for cutting so sloppy.
Formed threads require a larger diameter than cut, so that is the nature of the query - more info on formed/rolled threads.

 

[Bellow]

BUMP - as HR is around!

 

[hotrodder]

More questions! This time for my project.
Using a conventional cutting tap to tap 1/2'' UNC requires drilling to 11.5mm. But, the hole I am tapping into is already formed (read internal diameter of tube) and is slightly larger than 11.5mm (12.0mm > ID > 11.5mm, haven't (yet) got exact size but circa 11.8mm). A cut thread is giving a very sloppy fit for the bolt - no good!
Looking at the chart posted (linked) for threadforming with fluteless taps, the ID is between 12.07 and 12.14mm for 72.5 and 55% threads respectively. Have I got that right? What is the practical difference between 55% to 72.5% threads re security? Are formed threads just like cut threads and can accept any correctly sized male threaded fitting (eg Rose joint)? Anything else I should know or be thinking about? Can you recommend a supplier of a fluteless 1/2'' UNF tap? (I can't find them on Tracy Tools' website or hard copy catalogue).
I suppose the above is aimed at you Hotrodder - help!

I'm guessing it's UNF you're after as the tapping drill sizes correspond to 1/2" x 20tpi but both UNC and UNF were mentioned?
For a 72.5% rolled thread tapping drill is 12.07mm for a 1/2" x 20 (UNF). 12.14mm would give a 65% thread, 12.23mm would give a 55% thread

Yeah, formed threads are no different to cut threads with regards to what'll screw into them etc. Really large diameters aside virtually all commercially made male fasteners have rolled threads anyway but, that said, not all materials lend themselves to thread rolling. Moreso tapping female threads than rolling threads on male fasteners but as long we aren't talking about hard/high strength alloy steels you should be OK

Thread % is a bit like thread length engagement in many respects... a lot depends on the materials involved and what the joint has to put up with in service. OSG | Taps | End Mills | Drills | Indexable | Composite Tooling | Diamond Coating | Die Products and Tap Drill Size: Avoid Breaking Taps CNCCookbook may be useful/put your mind to ease.

That's about all i can say without knowing a bit more about the project and the materials involved... like i said before for flush/recessed threads holes need countersinking a bit deeper because of the way thread rolling works. Rolled threads don't tend to look as nice/crisp as cut threads for the same reasons. Moreso with less thread %

I suspect the reason no one is listing any stock in 1/2" is just lack of popularity? Smaller sizes are more popular/common for various reasons and obviously metric more common than imperial. I would have thought Tracy Tools would be able to get them and if not (or they're 'kin spendy) then i'd probably turn to the Septics... dunno if the link will go to the search results but Thread Forming Taps - MSCDirect.com have loads of 1/2 x 20 forming taps. Their UK site stops at 3/8 like everywhere else i looked

Dunno if you can weld or know any decent tame welders but welding in a threaded tube insert should be a chunk cheaper than a form tap and weird sized drill and is how suspension links for rod ends are usually made. Even if you can't buy the inserts cheaply 'cause you're working with ally or whatever

ETA, when it comes to things like enlarging hole sizes a little bit twist drills tend to make a mess as they're designed to make holes rather than enlarge them. Bit of a double whammy with roled threads as they're fussier about hole size and finish so you'd probably want to ream the tube rather than drill it to clean it up (seamed tube) and/or size it

 

[Bellow]

Thanks HR, much appreciated.
Yes, UNF at 20TPI (UNC a typo).
Material in question is mild steel and I want to tap straight into it without the need for welding (trying to avoid welding as much as possible) inserts.

I did find this >> Straight Flute UNF TiN Coated Roll Taps for General Purpose - UFS (P2SCUNF-T Series)

which I take to be a forming tap but haven't checked if available in 1/2'' yet.
I'll check out your links later - cheers.

 

[hotrodder]

Yeah, roll tap = forming tap. Also commonly called fluteless taps but sometimes they have shallow flutes for lubricant flow

1/2 x 20 is the second one down in the link, looks like they're all to order within 10 days

Massive pdf but if you goto pg 165 you'll find some useful info along with pics of under, over and ideal formed threads on 167 http://www.guhring.com/documents/catalog/litcart/400001035.pdf

 

[KennyN]

If it is just a 1/2" UNF x 20 tap you are looking for then i have a few here you can have FOC. They are 2 /3/ 4 flute types.

I found them in my toolbox that i brought from Rolls Royce.

Kenny

EDIT - just found another one making four , everything on an aero engine must have been 1/2" UNF

 

[Bellow]

Thanks KN but I already have cutting taps in the size but unfortunately I can't drill the hole from the 11.8mm it is to the 11.5mm required for cutting taps! Hence the need for forming taps which work at the larger ID.

 

[Bellow]

Yeah, roll tap = forming tap. Also commonly called fluteless taps but sometimes they have shallow flutes for lubricant flow

1/2 x 20 is the second one down in the link, looks like they're all to order within 10 days

Massive pdf but if you goto pg 165 you'll find some useful info along with pics of under, over and ideal formed threads on 167 http://www.guhring.com/documents/catalog/litcart/400001035.pdf

From the Guhring document:

''The spiral threaded, polygonal portion of the
fluteless tap is “screwed” into the pre-drilled workpiece with an
appropriate constant feed rate equal to the thread pitch.''

They work OK by 'hand' ? Yes?

 

[hotrodder]

Yep they work by hand in a normal tap wrench too. Haven't got any bigger than m10 x 1.5 but upto that size they're generally nicer/easier to use than regular straight flute cutting taps... they tend to guide themselves in straighter, no faffing about turning the thing back and forth to break the chip and no chips stuck in the threads afterwoods. Just screw the tap in with plenty of lube/neat cutting oil. About the only downsides to the things IMO are weird/uncommon tapping drill sizes and that they're fussier about hole accuracy/finish than 'regular' taps
Not gonna happen with anything bigger than m8 ish but when accuracy (properly perpendicular threads) isn't a big deal they work great with a cordless drill too although a cheapy might not have the torque to handle much over m5 or m6 depending on material and/or thread %

Given that a 1/2 UNF forming tap is likely gonna be special order and not dirt cheap personally i'd suggest buying a smaller example off the bay to have a play with... an m6 x 1.0 or 3/8 UNF will be under a tenner delivered and you'll already have some suitable drills, 5.5mm is close enough for m6 and 9.0mm spot on for the 3/8 UNF (both ~72.5% thread). If you've got some imperial and/or letter drills they would let you experiment as a 23/64" would result in ~55% thread with the 3/8 UNF, a letter T drill ~60% thread. A 7/32" drill would give you a 65% thread for the m6
Drill wise i suspect realistically your choices for the job proper are gonna be 12.1 or 12.2mm (cheap, even decent brands like Presto, Dormer, Guhring, whatever Tracy Tools send etc), maybe 12.15mm with some luck/more ££. More choice (and waaaaay better accuracy) with chucking reamers but a chunk more spendy i.e. 0.1mm increments but probably £40+ a pop. Another, albeit a bit tedius, way if you've only got a few holes to tap would be an adjustable reamer either to open the tube up or to clean up the scoring after taking the tube from 11.8 to 12.0 or 12.1mm with a drill

 

[Bellow]

Thanks HR.
Currently between two trains of thought. One is as has been discussed (with adjustable reamer) but the faff not too mention expense is starting to close it down. The other is to hassle my steel stockist into sourcing the tube I already have but in heavier gauge which would permit me to cut a thread at 11.5mm ID. Said tube is listed but I've been told it 'doesn't really exist'. We shall see....