Thread tip information | Model Engineer & Workshop Magazine

Having just started using carbide tips for screw cutting ( I always used to make my own tools grind by hand. ) what tips do I need to buy ie do I need to buy a tip specific to thread dimensions or just get round it. I have only bought some 18 Whit tips so far but do I actually have to buy a tip for each thread size.

You can find more information on our web, so please take a look.

David

Please have a read of this to see the possibilities:

https://www.sandvik.coromant.com/en-gb/knowledge/threading/thread-turning/pages/how-to-choose-thread-turning-insert-and-shim.aspx

If you search for 'Seco threading guide', the pdf they give you is very good as it includes number of passes and infeed for each pass.

Every major insert manufacturer produces a similar guide, so pick any of them (Seco, Sandvik, Iscar. Pozithread).

For each thread form there are two types of insert, partial profile and full profile. A partial profile insert will cut a range of tpi/pitches. The root profile will be set for the largest tpi (smallest pitch) and will be too sharp for lower tpi (larger pitch). So some tweaking of DOC may be needed. In addition the crest will not be formed properly. In contrast a full profile insert will cut a full profile thread, including root and crest, thread but is limited to a single tpi/pitch value. Of course there are also variants for internal/external and LH/RH.

I screwcut a lot of the threads on the lathe, mostly imperial but also some metric. I prefer to buy full profile inserts. It makes life easier and forms a better thread profile. I buy inserts as needed. In practice I cut a fairly limited range of tpi/pitch values. For instance the majority of Whitworth threads I cut are 40, 32 and 19tpi.

For reference, a partial profile insert for metric threads:

A full profile insert for metric thread, 2mm pitch:

Internal and external inserts for Whitworth 19tpi:

Andrew

David, as has been said there are full form and partial form but think about what you did/do when you grind your own tools ? they are partial form and good enough for most jobs in the home workshop, one advantage you do have with home ground tools is you can add the correct root rad to the tool. As far as the crest goes the best way is to truncate the thread thus removing the need for a crest radii . This was standard practice in the 's and beyond and I was working in the Aero industry all cut threads were truncated.

I still use home ground tools but also tipped tools for these I purchase full form tips for each thread size/pitch

John

To be honest, I have given up using them and reverted to hand ground HSS. Whilst I initially thought they would make thread cutting a breeze, it was not so.

I just suffered so many breakages/chipping of the tips. Admittedly this was not the fault of the tooling but more my cack-handedness probably, I ended up spending more time trying to get the jobs done than before. I say not the fault of the tooling, but in at least one case I did suspect an 'economy' set from a large weel known supplier of tools.

With competitive price and timely delivery, GSR sincerely hope to be your supplier and partner.

Horses for courses as they say, and I'm sure most people find them a great boon, Personally, as I'm lucky enough to be able to grind toolbits quite well, I sticking with what I know (and saving a few bob in the bargain).

All the best. Mike

In the absence of any sophisticated threading equipment and undercut at the shoulder is the best way forward, as a rule of thumb the U/cut dia should be the thread root dia — .002" to — 0.005" and the width approx 1.5 x pitch. A small rad on the LH corner of the U/cut tool and the RH should be the thread flank angle.

You can also start in the undercut and run in reverse with the tool inverted [beware screw on chucks] also a useful technique when thread cutting into a blind hole.

John

Find some PeeDee thread wires or buy their thread wire kit. Works great if you want to make thread of a known pitch effective diameter. The full form external inserts are great and I use them to size the OD of the thread form. So on a M16X2 thread, I cut the thread until the OD is Ø15.95mm. I use 0.05mm in diameter on all the out side thread sizes down to 5mm. Then I reduce it to 0.02 for below M5.

Using the tread wires you can use a full form or a partial form to create the thread. Often I will make a short section and use that as the gauge for cutting the ID of the other thread, like a M20X1.5 for a nut or something. If making a thread gauge, I then make it +0.02mm to +0.04mm larger than the nominal diameter. So a M20x1.5 gauge would be 20.02mm to 20.04mm on the outside of a full form thread insert. Then when you cut the M20x1.5 and make it Ø19.95mm , it will definitely fit.

At the end of most threads I have a run out thread relief area. That makes it a lot easier to stop at the end of the threaded part.

Neil

There are many different styles of indexable thread turning tools, but a simple way to classify these tools are: laydown style, 'on-edge' tangentially mounted, and top clamped. Each style has its own benefits. Choosing the right tool requires a look at the benefits each style produces.

Lay down Style

Lay down style threading inserts are the most common threading system in the world today. The name comes from the insert ‘laying’ down on the holder. These are mostly interchangeable between different companies and have the advantage of selection and abundance in the market. The ability to utilize one holder on multiple style of threads is convenient and economical. The lay down style insert normally comes with 3 cutting edges to index, multiple inserts sizes for different pitches (larger inserts normally produce less TPI, threads per inch) and the inserts use a shim to protect your tool holder, extending not only tool life but also the holder life.

'on-edge' tangentially mounted style

On-edge threading inserts are tangentially mounted on a holder. Normally held by a screw, these provide a smaller footprint for smaller set-ups and additional strength. Many on-edge tooling systems also have a grooving counterpart, so a single holder may be able to handle multiple applications with a single holder. An on-edge style insert can hold a larger thread form that would not fit on a smaller lay down. With the advancement of technology, some of these on-edge inserts also produce more cutting edges than the typical three found on a lay down style. It’s not uncommon to see four or five cutting edges per insert with newer tooling. In certain situations, ergonomics drives the decision of a tool – in some slant bed lathes where the tool is upside down or the tool is at the back of the machine, on-edge style threading tools are used for the ease changing the inserts for the operator. Often, on-edge insert systems are proprietary and more expensive, and many times manufactures will not shim an on-edge insert holder.

Top Clamp Style

Top clamp style holders utilize a clamp to securely hold top clamp inserts via a groove on top of the insert. Top clamp inserts use a good amount of carbide and carbide shims, and can sometimes be provided on the insert holder, offering a strong and stable system for threading. One of the main benefits of top clamp style insert is the ability to switch from a grooving insert to a threading insert in the same holder, which can save on tool cost and set-up time. Many of these inserts are double sided, but because of the amount of carbide and grinding involved, these inserts can be costly.

SUMMARY

Many companies offer chip breakers on their inserts and these are useful when cutting long stringy materials like stainless steels, non-ferrous aluminum and certain heat-resistant alloys like titanium. Chip breaker styles also relieve tooling pressure at the tip of the insert. However, most chip breaker style inserts come in coated grades and not the ground and polished styles that are utilized in most aluminum applications. So, while they can be manufactured, you may have a hard time finding inventory.

If a dedicated threading tool is needed for aluminum, the lay down style threading tool is a cost-effective method to producing threads on aluminum. If applied with a partial profile insert, additional savings can be realized. Other factors such as the thread form, an existing tool holder, or ergonomics may lead you to an on-edge or top clamp style system. Regardless of the system, choose an insert that is uncoated, polished, and hard (wear resistant) to produce the best results in aluminum. Uncoated and polished inserts provide good resistance to BUE (built up edge). Utilize holders with coolant thru capabilities for additional benefits. Producing threads in a machine shop is almost inevitable, but with the right tools and approach, manufacturing threads can be quick and productive. Analyzing your application and available resources can help you quickly choose the best threading tool for the job!

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