1+ for what Hopper says, this is a sketch I prepared earlier where someone needed to swing the topslide round more to the 29deg position

With inserts there is no point in canting over the top slide, just leave it parallel to the spindle axis and leave it alone. That way the cross slide reads thread depth directly. Threading inserts are symmetric and cut on both flanks, so no need to cant the top slide so as to cut on one flank.

Andrew

JB do partial form inserts which as well as their overall size differences will cut a range of pitches and have clearance for those pitches unless you are doing something odd like 2.0mm pitch on a 5mm dia shaft. These may leave the peaks pointed and they will possibly need dressing with a needle file run along the thread

You can also but "full Form" inserts which are ground to suit one specific pitch and thread form and will round the peaks and valleys as needed. Again available in different O/A sizes to suit your holder.

JB don't give a lot of info but if you look at an industrial tooling site they will give the pitch range for a specific insert

Edited By JasonB on 02/08/2018 09:14:37

The reason for putting the cut on with the compound slide when half-angle screwcutting is that if plunge-cutting, two swarf streams collide on the top surface of the tool, and some chips will be deflected back to the surface about to be cut, trapped inside the swarf-curl and cause scuffing of the flank surface.

In some conditions that doesn't occur enough to matter, in others it does.

Notice that Ruby here:-

**LINK**

…is applying a heavyish plunge cut directly from the crosslide and has a single stream of dull red swarf coming off. I wonder if she's offsetting each cut by a calculated longitudinal value to achieve that.

Ah. Simple, tidy solution – thanks for sharing.

Reckon that's maybe what Ruby was doing.

This picture shows a full profile insert for a 2.0mm ISO (metric) thread:

The insert is designed to cut ISO threads only with a 2mm pitch. Note that the profile will form, at the full depth, the correct curved root profile and the truncated crest profile.

This picture shows a partial profile insert for ISO threads:

Obviously the thread angle is 60°, and the insert will cut a range of ISO pitches. There are two points to note. The root radius is set by the smallest pitch the insert can cut, and is incorrect for larger pitches. The insert does not form the crest, so the work OD needs to be correct beforehand. The incorrect root radius means that the actual thread depth for proper mating may not be the same as the theoretical depth.

I've screwcut almost all my V-threads using full profile inserts and plunge cutting. I don't recall ever having had a problem with swarf getting trapped. The process just works. Mind you I cut fairly fast, several hundred rpm, so that may help with swarf ejection.

Andrew

Confirm what Andrew says, i always use full profile tips daily on quality aftermarket items. Not once seen two edges collide on any pitch from 0.5mm to 3mm pitch or imperial to 11 tpi in any metal aluminiums, plastics, manganese bronze, steel to titaniums.

What i suspect is those that get a bad finish are super imposing rather than addressing or acknowledging the issue of tool, machine flex or actual poor tips used.
I do have a pack of cheap AG60 tips £25, to get a tolerable finish with brings out the machinist in you resorting to additional measures.

Said it often, theres no substitire for quality tools as hard as it is to muster. By that i dont mean shop branded stuff.
First choice of screw cutting inserts for me are Iscar approx £5-6 each, not far behind are Stelram and Seco. If not convinced try one.

Other downside is partial profile tips will cut a lot deeper at the non root that is created, every thread has some form of radius to it. Therefore not ideal when wanting two parts to join up exact with no runout. Will require a full profile tip for every pitch created, double that if doing internal threading, adds up but can buy singularly.