Single point threadform tools?

I can just about make a passable threadform tool for 8tpi, but how on earth do you make such tools for smaller threads. Can you buy such things these days?

Or do you simply use a large pointed tool and forget about such niceties as thread profile? Triangular threads make me flinch!

Andrew.

Indexable inserts either partial profile or full form. internal and external ,available. in a vast array of thread forms.

Edited By Raymond Anderson on 29/12/2016 13:56:28

Andrew, don't worry about adding a radius to the tip then one cutter will do all. The crests of the thread can have a file run over them as the work slowly turns in the lathe to round them off if needed or run a die down the thread if you have one.

J

Hello John,

If you use a tool ground for 8tpi for a smaller thread, then the rounded formed shoulders of the tool never come into contact with the crest of the pitch. So you have a rounded transition at the bottom of the thread and triangular finish on the crests.

Is this what people put up with for the finer pitches?

Thanks Raymond, for letting me know that thread form inserts are widely available. I have not seen such things in my present incarnation as a model engineer. Obviously not looked in the correct places. I will shortly be buying some insert holders for my ML7 , so 6 to 8mm square. What type of inserts do you use. There are so many different types and I assume quality that I may as well buy insert holders and inserts that are recommended by some one on the forum. I don't want to relearn the wheel! help here any one?

Thanks again,

Andrew.

Andrew, Im not sure if there are holders as small as you mention [ for threading inserts ] I use all different types and sizes. You can also get ready ground HSS tools for metric and imperial threadforms. if you don't fancy having to grind one up. They are available in the sizes you mention, right up to 25mm square !

The "V " form is actually one of the easiest forms to cut,

As Jason has said a file (use a three square and you can do both sides at one pass) or a die to complete the thread. A thread on a component is in reality only a glorified bolt, that is unless you are making aircraft engine components that require that degree of finish. As has been said before if you go down the fully formed route you will need a tool for every size and thread form you intend to to cut, A very expensive way to go. On top of which you will not be able to regrind them.

Andrew the 11mm inserts should do you in the smallest holder you can find maybe 6mm shank but 8mm would be better provided you can get that into yout toolpost at ctr height. I use the partial form tools which cover a range of pitches and have the radius of the finest pitch so one or two inserts for metric and US 60deg is likely to be all you need and another one or two for 55deg form.

Edited By JasonB on 29/12/2016 16:06:53

Thanks gentlemen,

I do appreciate all the inputs that you give. It is really good to have such a formidable resource to hand when you are operating on your own.

A lot of written wisdom assumes that you have the basics under your belt, so quite often I find the written explanations to be wanting (or rather I am wanting!). Now I would never have thought of using a three corner file on the crests of the thread. Must be my age showing!

Thanks again,

Andrew.

I have a few 11mm partial profile inserts although the smallest toolholder for them is 10mm I think trying to get a 6mm shank for them would be a non starter, I think even 8 would be pushing it. but if they are out there [ and they may well be ] then the internet is your tool.

I think there is a US size holder SER 0310 H11 that has a 5/16" shank or in the case of an over size shank an insert milling cutter is more liekly to be your tool when it comes to skimming metal off the bottom of the holder.

If you are 'following the book' then you would have a tool ground for the specific thread and feed in from the reference point of first touching by the theoretical amount. Your tool will be either too short or too long so the infeed won't be as per the book. So forget the book. Just make a short test piece and keep trying a nut on it until it just fits. Make a note of the infeed you used then you can just use that up to the last couple of thou for 'fit'.

To right forget the the book, first thread i cut with a single point tool was 6 TPI internal square thread, and i reckon i spent more more time reading up on it than doing it ( and still reckoned most of what i read was wrong or at least could be done better,) a full 2 inches worth 12 t ( new nut for my shaper in pb ) the pb might be hard, but thread or screw cutting bit is not, its really not as hard as one may think.

It would be fair to say that most single point work is done in work shops like folk have on here ,

In industry one would just go down the stores and get 2 inch unc tap if that was what was required ( for example, but it could be any size ) male threads would usually be cut with a Coventry die head

There is very little single point screw cutting done in industry, time dosnt allow it !

After all think of all the bits of studding we all use to hold stuff together there"s nothing special about it despite its counterfeit endorsement it only fits where it touches ,( the nuts bought with the studding should fit better but often dont ).

I would bet any thread that any one made on their lathe in their workshop will fit better ! even if they have never screw cut any thing before.

Dont be put off screw cutting its one of the best bits of being able to make stuff.

Three corner files, bits of emery wrapped / laid over the edge of an old feeler gauge , plus many many more,these are all timed honored old wrinkles bods in sheds have been doing for ages

Trick is they do these things so effortlessly and without even thinking about it, so one tends not to notice just what they did do.!

This does not mean every thing ever written on this subject IS wrong, I do like GHTs idea of setting a finer angle of ( For Whitworth ) 25 deg instead of 27.5 deg so that a small part of the cut is transferred from the leading edge to the trailing edge of the tool, gives a very nice finish, there is a bit more to it , but one could buy the book ,

Sounds like a bit of a contradiction , but some books are better than others.........b

As for the first post in this thread , Take the time to learn how to grind HSS tool bits ! It will stand one in far better stead then dragging the plastic out every time........

The advantage of inserts is that they are consistent and when you wear/break a tip, a very quick change is possible. Partial profile only and then you need only 1 type per Metric or Imperial or BA or indeed ACME/Trapezoidal/.....

Use the plastic, that way you can buy time!

Satisfied customer of :-

**LINK**

Bodge has now got me all fired up , I WILL BE ABLE TO CUT THREADS ! I can face and surface..drill holes ,make holes bigger with a lathe tool, use power feed ( separate power feed shaft on a S&B ) but that long lead screw scares the crap out of me !!

I'm gonna assume a previous owner has already fitted suitable gears for threading...(because i haven't changed them in my ownership) and have a go at threading a bar tomorrow . I just checked out youtube for doing it without a dial gauge,because mines busted...the little gear is missing .. It'll be rubbish i know, but you've got to try , cheers Bodge!

If i slow it all down with back gear...will it make the lead screw slow as well...like the ratio's will be the same?

Edited By Hacksaw on 29/12/2016 23:20:34

Yes, back gear does not affect the ratio between the spindle and the lead screw, only between the spindle and the drive system. So go ahead and use backgear as per normal.

If you have no thread chaser dial, keep the half nuts engaged and reverse the lathe to run it back to the starting point. If you dont have a reversing switch, you can disengage the backgear and wind the chuck in reverse by hand until the carriage is back to the starting point.

Or for test purposes use a pitch of thread that is a multiple of the lead screw. Eg, if 8tpi leadscrew, you can cut 8, 16, 24, 32, 40 tpi without using a chaser dial. Engage the half nuts any time you like.

Not sure what all the fuss over special tools is all about. A piece of HSS ground to 60 or 55 degrees according to a standard screw cutting tool gauge that costs about ninepence hapenny will do the job. It is customary to rub the ground tool on an oil stone for a few strokes to round the end a tiny tiny bit - regardless of whether the theoretical thread profile calls for a radius, a flat or a point, simply because it cuts better and is less prone to the tip breaking off under load. One tool ground thus will cut all size threads from 40tpi or more up to a pitch equal to double the width of the tool at the wide end of the V, ie a quarter-inch wide piece of HSS sharpened to a V will cut up to 2tpi threads and down to at least 40tpi or more. Just be aware that the coarser the thread, the greater the helix angle and therefore the more clearance must be ground on the leading face of the tool bit.

Have fun!

Just to be pedantic CNC lathes single point all day long

OK J S, you got me on that one , & it Is the one place where the tipped tooling wins is CNC, COS it takes the monkey out of the equation , the damned things are even self replace tooling sensitive these days as soon as a sensor detects a drop in tool efficiency, it then self selects a new tip and that is where tip tooling scores , magazine fed and all exactly the same to a micron or two.

HSS cant even come close the speeds some of this stuff runs at . The place i worked at that was into the devolopment of high pressure fluid cutting, their tooling department couldnt put an edge on an HSS drill to save their life, stopped sending them when i sussed they no good , i used to do them myself by hand on a belt linisher in lots of about 80 to a 100 at a time ( four sizes 3/32 - 1/8 - 5/32 - long series, and 5/16 jobber, still got a few of each some are just stamped HS )

But if you think about this it is now to the point where tipped tooling is pressure formed and treated pretty much in a one hit process, and as usual its cheaper , therefor keeps board & the share holders happy ,and the money flowing., which comes down to the end user , and that is us

WHY,

Because we want next years model car at the year before last prices,

And that is how come the older type tooling can no longer compete on the shop floor,

Well i guess you will be safe enough in your life time , cos to replace you it would it mean mandatory scrapping of any thing that is worn out and compulsory purchase order to buy new

By this i mean the putting on machine , aka, the Mig ( or should that be Tig These days? ) and a bit HSS tooling to clean it up after,Well i think we have gone far off OPs original post for tonight , but i"m happy to come back to it some other time if you wish ,

I have got a bit more to say about screw cutting too , may be get back to it later , feeling a bit whacked out now , idont usual do this much typing
I blame J S he does two lines & i wind up doing half a chapter ..............b

Unless you are going into mass production, I for one would stick to HSS for the few screw cutting jobs in the home workshop. My first thread cutting tool was ground up from a bit of a broken square file, at back gear speeds carbon steel is no problem.

Ian S C

I don't think the reason CNC lathes do single point is because they are pedantic. I think it is because JS is being pedantic and the lathe is doing what it was set up for.

That's me being pedantic there. Happy new year your Lordship.