Screw cutting Advice

[Nigel McBurney 1Participant @nigelmcburney1]

Instrument makers cut a lot of threads with chasers on plain lathes with chasing attachments,and the habit sticks,I have a lot of machine chasers ,metric ,whit and unified. I cut most of my threads from start to finish with chasers in non ferrous ,cast iron ,en 1A to En 8, its quicker, easier ,and an accurate thread form is achieved,just remember to withdraw the tool before disengaging the half nuts ,and check used chasers before purchase to ensure they are for right hand threads.I bought for next to nothing a lot of insert tooling (Kennametal) and in the lot there were metric and whit inserts plus tool holders ,the internal tools are useful as they can get down smaller holes than the usual internal chasers, though I would not buy insert thread tooling if I had to pay full price, though the inserts are very good on tough metals and stainless steel. I also obtained second hand some single tooth circular hss chasers with round shanks, for whit form internal threads, these are very good for deep internal threads,

[robjon44Participant @robjon44]

Hi all, if I may add my fourpennorth on screwcutting with insert tooling, firstly I am a died in the wool Sandvik fan, however these remarks apply generally, if you primarily screwcut metric threads there are only a limited number of pitches therefore full form inserts are the way to go, Whitworth threads are a different kettle of fish but as they are much used in model engineering & refurbishment of old british made vehicles & workshop machinery then you would have to decide how cost effective it would be for the task at hand, but bear in mind that the world is armpit deep in oddments of throw away tips of every kind. I have many leaflets from tip manufacturers, so here goes, when cutting coarse whitworth threads single point, rough out with a 55 degree rhombic V pointed turning tool, this gives you the options of finishing with full form insert, HSS tool, hand or machine chaser, or a split die. If single point threading with any imperial or metric full form insert machine down until the thread o/d is 0.005" or 0.15mm below nominal size measured with a micrometer, this saves all that faffing about ring gauges, thread calipers, & heaven forfend the 3 wire method. They also recommend stoning all round the V profile of the cutting edge with fine stone or diamond lap which prevents chatter before it has a chance to start more especially on relatively tough materials. Using these methods I have successfully cut many thousands of 1.5 inch double ended studs up to 8 or 9 inches long with no problems, whilst doing this I also discovered that regardless of the direction the tool is travelling in, toward or away from the chuck, I would have an old school rotating bar stop with a thrust bearing in it, from the days when bar autos fed bar without stopping the spindle, hard up against the front face off the stock, you can of course replicate this by fitting a simple cap over the nose of a revolving centre, saving the hassle of having a pip on the front with a centre in it. Please also factor into your calculations that certainly Mr. Sandviks screwcutting tools can be used to cut circlip & o ring grooves with the appropriate inserts & shims so they are far removed from being a one trick pony. P.S no I don't have shares in the company, but I wish I had!

regards Bob

[EmgeeParticipant @emgee]

Tools now heat treated/hardened, held at carrot for 1 minute then fully quenched in whale oil !!!!!

Good advice from Robjon re fully formed inserts and his method to form threads. More pics of the tools in my album.

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