Internal threading using laydown inserts

Please could someone confirm, deny or comment on the following statements in relation to internal threading using laydown inserts.

NR16 inserts are 16mm across, so will, at best, enter a 16mm dia. hole. That means the smallest ISO metric coarse thead an NR16 insert will cut is M20.

NR11 inserts are 11mm across, so might enter an 11mm dia. hole. Smallest ISO metric coarse thread possible with NR11 is M14.

Partial profile inserts come as A60 (0.5mm to 1.5mm pitch) and AG60 (0.5mm to 3.0mm pitch).

Having looked at a few manufacturer's catalogues, AG60 does not exist in 11 size. For full profile inserts, 11 size goes up to 2.0mm pitch.

Thus, the only way to cut pitches coarser than 1.5mm using an 11-series insert (e.g. M14 x 2.0, M16 x 2.0) is to use a full-profile insert.

M18 x 2.5 does not seem possible using either 11-series or 16-series inserts.

The only way to use a laydown insert to cut an old Dremel thread (3/4"-12 UN) is to use an 11 NR 12 UN full profile insert.

Thanks.

I get around it by using the NFTG series of inserts, and regrind the insert to become an insert to cover up to 2.5mm pitch and put the radius required on the end, so not sharp tipped. They are available from Sandvik, and some others too. The inserts sit on a 3 point tapered seat. They come in 12mm and 16mm shank holders in steel and carbide. I use them for all the threads under 20mm diameter. Just another option. Not sure of the thread insert pitches available that they do make. M10 and under I sue a special tap that has a pilot to guide it from the bore to keep it concentric if required. Sometimes I use the carbide small threading tools, but they only have a very limited reach, hence for the pilot tap option.

Not sure what your overall criterion are but I cut my Dremel thread with one of these from RGD:

**LINK**

HTH,

Rod

Have a look on here.

https://www.shop-apt.co.uk/snr-internal-threading-bars-apt/c10psnr-11-apt-carbide-shank-threading-bar.html

David

Thanks. Could you expand a little on how you did this. The insert that is supplied with it goes up to 1.5mm pitch. The thread on my Dremel is 12 tpi (it is an older one - newer ones have 16 tpi, within the range of the tool you show).

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David: please could you explain how that tool could assist. It is identical to that which I have and takes a standard 11NR insert.

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Neil, thanks for the suggestion.

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Seco's handbook shows how you can reduce the diameter of the standard bars for smaller bores. I might try that with a 16-series bar and also knock the back corner off the insert (so I can only ever use two out of the three edges on inserts fitted to it).

You can always rough the Dremel thread with a partial 0.5-1.5 and then run a tap down the hole, seem to remember that is how I did mine though may have been an HSS tool to do the roughing. Advance the tool with the topslide set parallel so you get the width then the tap just cleans out the valley.

M14 and M18 coarse are non preferred sizes so less likely to be catered for but if you have a need to regularly cut them then buying the few full forms, doing the modifications you mention or using a different shape of insert (or hss) would seem the way to go.

No. I'm talking bollocks. I will have done as Jason suggested. I was thinking of the 3/4" UNF. As a matter of interest, the height of the cutting tip on the tool is measured at 1.25mm.

Rod

I would think that M18 x 2.5 is possible with an insert. I will check the bar size with a 2.5 TR insert in it. I could probably lend you inserts and a boring bar to do it. I'm not sure of the length of the tool until tomorrow.

Check out my thread "new knee nut for Tom Senior" for extreme internal threading.

Edited By old mart on 29/07/2022 13:45:23

M18 x 2.5 has a tapping drill size of 15.5mm when the conventional diameter minus pitch formula is used. An NR16 insert is 16mm nominal dimension.

In the one above linked to by David George, it says minimum hole dia. for an 11-bar is 13mm. My rough measurements with a 16-bar show 17+mm min. hole.

I think the insert manufacturers also quote an inscribed circle diameter for each size, so the difference between nominal dim. and inscribed dia. set an upper limit on depth of thread that can be cut.

Thanks for all the suggestions. Don't tell anyone but I'm going to use a 3/4 BSF tap.

I do not have any pressing need for any of the metric threads, but the 'dead band' in the laydown threading capability was new to me and I have not seen it mentioned anywhere. It would appear that there is a similar gap when you move down from an 11-series insert to an 08-series. M12 x 1.75 would not seem to be possible. M10 x 1.5 (8.5mm tap drill) would be challenging.

Everything above is writen in metric, but I guess the same applies to imperial, maybe marginally worse.

Just to show you what is possible with an unaltered 2.5 TR size 16 insert. The tool will pass through a 15.02mm bore and this one cancut 36mm length of thread.

Edited By old mart on 30/07/2022 17:28:24

It is often done to sacrifice one tool for smaller shorter work. At 36mm of a working length is starting to really be pushing the boundaries of diameter to length ratio, as the support material under the insert is where it is the thinnest. I have a Mitsubishi bar that I modified to get to 45mm deep and really it should have been a carbide bar, as the tool does chatter more than I like to see in a thread form. Sadly there was no tap readily available for the thread being made on the repair. So both parts were screw cut. Swarf or chip evacuation is the biggest problem when the bar to bore gets very close. So just have to watch the depths of cut or volume of material being removed. Some materials make fine chips and they can be lodged between the bar and the minor diameter. So coolant or a vacuum cleaner running with a nozzle very near by does hlep.

That is an interesting insert holder with a single angled slice removed to provide the insert socket. Much easier to make than the usual type.

Doug

It is good for a one off but if we were to look at it from a strictly engineerng point of view, it has some shortcomings.

In a standard holder, the X-Y (plan) location of the insert is assured by the two shoulders on the holder. The screw pushing the insert against the flat seat assures location in the Z direction. In the one shown the screw is doing more than one thing.

This is not meant as a criticism of a good solution to a tricky problem, more as an example to make the brain cells work - the insert has six degrees of freedom, so what is the easiest (cheapest) way to fully- but not over- constrain it?

The screw in my shop made holder is displaced about 0.005" from the centre of the insert. This holds it tightly against the shoulder. With a close fit in the bore, it is essential to blow away the chips after every pass. The material the bar is made of is not steel.