Threading is an important processing method that involves using a thread tap to cut the threaded part of a pair of matching metal fasteners. It has many uses, for example, manufacturers in the automotive and medical industries use threaded holes to hold parts together as it makes parts more compact and eases transportation and usage.
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There are many different types of tap machinists and engineers use and choosing the right thread tap determines the outcome of a project. In this article, there is a detailed explanation of what a thread tap is, how to use a tap for threading, and the considerations for choosing the right tap.
Though different tap types have distinct features, the following are the main components.
Body: This is the longest and most important part. The body of a tap is what does the cutting. It contains both the thread chamfers and the full threads. The number of these varies depending on the tap type.
Shank: The shank is located just above the body. It is smooth and has a cylindrical shape. The shank length differs according to tap type. This part has marks that indicate the distance between the threads.
Tang: This is the squared-shaped part above the shank. Based on the mode of operation (manual or automatic), manufacturers fix the tang on a holder to rotate the tap.
Flutes: Flutes are grooves on taps that accommodate and expel the chips during tapping. They come in different types and shapes based on the tap type. As a standard, a tap contains 2-4 flutes which can be angular, straight, or spiral.
Land: The land is the threaded part between the flutes.
Heel: This is the slanted area behind the threads.
Cutting Face: This is the surface of the tapping tool that comes in contact with the material.
Different tap types can cut different types of threads in holes. The following are the different taps for threads with their distinct feature
The taper tap, plug tap, and bottoming tap make up the complete set of hand taps.
This tap has 8-10 thread chamfers before the full cutting diameter. Hence, manufacturers use it as a starter tap for blind holes in hard materials. A taper tap offers a more delicate and gradual cutting motion. It is not ideal as the only tap for a project because it cannot thread to the bottom.
The use of a plug tap just after the taper tap is not uncommon. Plug taps give the desired depth and form to already drilled holes. It has 3-5 threads that taper from the tip. Hence, it gives a more forceful cutting action than the taper tap.
Manufacturers use bottoming tap as the last tap for a project. This is because it has 1-2 thread chamfers and does not align with the hole when used to begin a threading process. Also, as bottoming tap cuts, it cleans the already-cut threads.
The master tap is like the taper tap. The difference lies in the number of flutes. The master tap has 7-10 flutes with more cutting faces. Master taps are applicable in cutting clean threads in hard and strong materials.
Gas tap deeply cuts gas-type threads for merging hydraulic fittings and pipes. It has 1-2 thread chamfers that work perfectly with both cylindrical and conical-shaped holes.
In contrast to the tap types described above, machine tap is fully automated. It makes use of a tap drill machine, so lessens the occurrence of damage to the workpiece and the tap. Furthermore, this machine simplifies the threading process as the operation requires less human labor to complete a project.
This tap type is not fully automated. It is used with either a manual tap handle or a tap drill machine. Machine screw taps have 2-4 threads that taper from the tip. For this reason, they can thread deep holes manually in many material types. Manufacturers use machine screw taps for repairs, routine maintenance, and rethreading where accuracy and tight tolerance are not essential.
This tap type is like the hand taps. However, extension taps have a long shank above the body. Hence, it can reach holes that are considered inaccessible like the hub of a pulley.
Its distinct feature is a bent handle that extends from the tang. This allows for continuous tapping without stopping the drilling machine at intervals.
This tap is 15-20 inches in length and is used in the locomotive-broiler application. The stay bolt taps threads holes that match the diameter of the stay bolt nut.
Compared to conventional straight flutes, the flute in this tap is spiral-shaped. This feature aids in the easy removal of chips from the tapped hole. A spiral-fluted tap is perfect for soft metals and metals that produce short chips.
As the name implies, this taps type has threads throughout the body without flutes. Fluteless tap uses the pressure deformation technique to cut threads into holes without chip removal. This allows for faster-cutting speed and high-quality threads. However, it is only compatible with soft metals.
Tapping threads in a hole is a careful and stepwise process. Follow these steps to make high-quality threads.
Before drilling and tapping threads, it is important to hold the workpiece in place using a vice or other workholding tools. This is because proper clamping eases the drilling process. Any slight movement during drilling can result in flawed final parts. To do this:
Note: It is important to control the clamping force to avoid any form of damage.
To drill that perfect hole:
The bolt used will determine the size of the hole. Ideally, the diameter of the hole should be smaller. This is because the threading process further expands the hole. However, there is a standard chart(in the below section) that matches the size of the bolt to the diameter of the hole.
Note: One ought to be careful when drilling blind holes. The drilled hole should be a little deeper than the length of the bolt.
The process of tapping holes is straightforward. To do this:
There are many types of taps in the market. Choosing the right tap for a project determines the outcome of the threading process. Consider the following when selecting a thread tap.
Engineering materials have different levels of hardness. Hence, the tap type manufacturers use varies depending on how hard or soft the material is. Some taps have special features that make them more suitable for some materials. For instance, fluteless taps are ideal for soft metals while machine taps work better with harder materials because it is fully automated.
In general, taps are made of high-speed steel or carbide steel. The material one is working with determines which one to go for. Manufacturers use taps made from high-speed steel for soft metals like copper, lead, magnesium, aluminum, and related alloys. high-speed steel taps provide more controlled and slower cutting action.
On the other hand, carbide steel taps are strong and cut threads faster in very hard materials like cast iron, titanium, brass, stainless steel, nickel, and other hard alloys. This is because they can withstand the friction and heat generated when tapping threads.
The depth of the drilled hole determines the tap one would use. Different tap types have a varying number of thread chamfers. The thread chamfers serve as a support system to guide the tap as it threads. Only the full threads produce the cutting effect. Considering this, taps having 1-3 thread chamfers make deeper holes. This is especially important for blind holes.
Some tap types are specially created for use in high-speed production. If speed is a determining factor, spiral pointed taps, fluteless taps, or taps that are automatically operated may be ideal. For spiral-fluted taps, the spiral or helical-shaped flute pulls the chips away from the tapping direction. This reduces the time spent to remove the chip build-up. This advantage applies to fluteless taps that produce no chips.
I have used Tap-die in London for years, and am very sorry to see they’ve closed for good. Needing a new BSF set, I bought one sold (and marked) as HSS from another well known UK supplier. They don’t look as strong as the old T-D set (see photo – new one on right), but I was very surprised when the 1/4BSF taper lost some teeth at first use when I was using it to clean up an existing thread in a clevis pin fork. This was mild steel, and as ever I was using plenty of Trefolex. I’m not a professional engineer, but this seemed a bit odd to me. Is there a supplier out there of more durable tap and die sets?
There are many good suppliers. I use Avon Taps & Dies (because they are local) and Drill Service (Horley) Ltd. Both have good web sites. Don’t worry about them being industrial suppliers, they are more than happy to take your money.
Never buy used taps or dies. They are likely to be worn out and not cut to size.
JA
It looks like The Tap & Die Company (and stock ?? ) may have been bought out by a Sheffield company C R Tools Ltd
With competitive price and timely delivery, GSR sincerely hope to be your supplier and partner.
“Here at C R Tools we are proud to announce we have acquired The Tap & Die Co. Ltd from Zubin. With 49 years in the industry Zubin is well regarded and he has built up an amazing stock collection, along with a reputation for quality products.
We are now able to offer you Taps, Dies and Dienuts alongside our current range of tools which are all stocked in Sheffield UK, and we are committed to offering you the same excellent service as you experienced in the past.”
I’ve had no connection with them, so can’t pass comment on their products or trading practices.
Stocked Cutting Tools
Bill
On Said:….I use Avon Taps & Dies (because they are local) and Drill Service (Horley) Ltd.
…..
Never buy used taps or dies. They are likely to be worn out.
Beaten to it! I’ve been using Drill Service for many years, and have generally been very happy. I have just started using Avon, and so far I am impressed. I’ve just bought some 5BA taps from Avon, they cut very freely even in gummy black steel. I was never that impressed with Tap&Die; used them mostly for ME threads, to be used on brass.
I’ve got dozens of secondhand taps, and dies, and so far so good. If I need 3/4″BSW for a one off I’m not going to buy a new tap. To be fair I normally screwcut the external thread so can make it fit.
Andrew
Wow, what a very helpful forum! Thanks all, you your excellent replies. I have to admit to not following in my father’s footsteps as a model engineer, but put my Super 7 and Sieg to good use making bits for either an XK140 Jag or (more commonly) my Riley two-seater.
These recommendations are great – and glad to see that the T-D stock has not all gone in a skip somewhere, the thought of which filled me with dread. That said the folk in Avon might be worth contacting as the recommendations are very encouraging!
And now, back to my Girling rod-operated drum brakes,
Roger
Tony, as an amateur I’m a little reluctant to start naming suppliers as in my case it’s always possible I was doing something that could be considered as unreasonable (although that said, my tired old T&D tap finished the job the other had started with no trouble)! I have accounts with Zoro and Cromwell, but was looking for particular advice for users, which I’m very happy with.
I have bought many second hand taps and dies. The last lot I bought were 5 for £1 – certainly not warn out. My main metric ones came as a job lot for £10, at least 3 of each size 5 to 14mm plus – virtually all Presto or Dormer- and unused! plus a few dies and an assortment of vintage tap and die holders. However, I would not buy them online want to view them. I guess that where I buy them very few want them so go go for little money.
I have had a number of carbon steel taps and dies in uncommon-ish thread sizes from Tracy Tools for small lots of components for the railway, some in tougher materials. All have cut smoothly and accurately and have lasted the course without noticeable wear or blunting.
And certainly without spalling out whole teeth! >:-o
Further to JA (about seven messages up)
It is not always good advice not to buy used taps. It all depends on what you need them for. I use them a lot to hold threaded parts in a lathe for further operations, as they are strong, and generally dead straight and true. And how else can you hold a new-made nut to chamfer the ends, or add grooves, than by holding them on an accurate threaded part.
In my experience …
Tim
Hi All,
I have to say that we have sold literally dozens and dozens of various lots of Taps & Dies of all sorts in our EBay listings and never ever had a complaint.
We do make sure that they are all HSS and any where the size is unreadable or broken are binned.
They all have the flutes cleaned of old thick gunk etc and then into the ultrasonic cleaner.
We give clear close up pics of the items as well.
Mostly they come from model engineers workshops that have gone to auction so rarely heavily used and they certainly represent good value.
Just my two cents worth…
Cheers, Martin
Going to disagree with you Martin, prefer to buy them in their working cloths, gives a much better idea of how they were used / stored. but only buy them if I can handle them, gives a far better idea than a photo.
That might be just an effect of the flash I had to use to get rid of shadows in the photo. They’re actually still pretty sharp, as might be expected for only having been used once. That doesn’t answer the question about the fractured sections, though.
I had a look at the Avon site for box sets, and they do look rather like the one that has broken, with the waisted shank design. There’s no mention of who makes them, and I also can’t see any mention anywhere of whether or not these are HSS – going by other sites and their prices, I suspect not. I don’t need BSW but they do say they can build up sets to customers’ orders.
Ah yes, thanks – I did find a page that mentioned HSS, but it wasn’t easy to find through the ‘taps and dies’ drop down box. I can’t find any mention of where they’re made.
Could get expensive – I need sets containing taper and bottom taps ideally, don’t really need the second tap (which is the only one they have in their sets). Also a BSF-only set would be better than mixed BSF and BSW, so I’d need a custom set, most likely. s-s car restoration is a fussy business!
The problem with buying sets is you will likely end up with more tap wrenches and die stocks that you probably don’t need so may be better off just buying individual taps but if you do want a good quality set of just BSF then Volkel are good but not cheap, Rotagrip should have them in the UK.
Spiral flute taps are another option, you would just need the one of those, individual Volkel
This may be off subject. A fellow apprentice commented that when you buy a set of tool, in his case a socket set, all you are really buying is the box. I have always followed the advise, buy individual tools when needed.
And keep them in the little plastic containers they came in. Do not store cutters, taps and dies loose.
JA
These are all valid points, and I think it would make sense to stick with my various sets now and just buy good quality single replacements as they become necessary. I have plenty of boxes, and don’t need any more!
Now I have plenty of leads on suppliers too, so thanks again all.
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