Screw cutting Advice

Hi All,

I wonder if I could ask some advice on screw cutting please?

Firstly, I have ground and used my own HSS screw cutting tool before without too many problems, but I am currently remaking a grinder spindle, and would like the threads on there to be as clean as possible - I wondered in anyone uses the insert type threading tools, and if these produce better results? Example below:

LINK

Secondly, are these inserts suitable for RH and LH threads?

Thanks in advance,

James

Hi James,

I have just started to use an insert to cut a LH thread (square) to make a lead screw for my tail stock and was very plesently surprised at how easy it was to achieve a good quality thread

The inserts are handed so be sure to get the correct one

a new convert to inserts - well for threading anyway

Trevor

James,

I have found that using the threading tool in this set : **LINK** gives me an excellent finish - My one wasn't in this set but it looks identical. It is a preformed v tool (HSS) and saves any grinding! THese even worked really well on stainless steel. I also use Dormer Super Cut asa lubricant - its thick and sticky and stays on the thread well.

Matt

I use similar tips to those on top link for all my threading both internal and external, I get my tools and tips from Jenny, I think her company is called H&B tooling, a lot cheaper than the link, but I only see her at Auto jumbles Newark Ruforth etc, typical tool cost external about 20 quid, tips anywhere from a quid up, some tips are pitch specific and so have a depth gauge built in i.e. you machine down until the teltail just touches, however more general purpose tips are available, they chip very easily if you touch of to set your starting depth.

HTH

Shaun

Involute,

Correction, J B Tooling

Note to all,

Inserts are "partial" which cut correctly but do not shape the thread tips or "Full", profiles the tips BUT are for one pitch only!! So use Partial and run a die down or file to round off the tips.

Trevor,

Details of insert & supplier please.

Geoff - Heating on, but £80 to fit a thermal fuse

I always suggest APT carbide - as for instance their own threading insert holder is £24 plus vat. I've bought other holders off them and would have no hesitation at all about buying one. All so far have come with a key and if a screw gets messed up they sell those too. Most inserts come in packs of 10 but threading types singly and some useful hobby turning tips that are actually industrial but they sell them in pairs. Good way of trying them.

Which reminds me I must get another 16mm boring bar as the one I have doesn't hold the tip at a sensible angle.

Think I suggested apt to Trevor anyway.

One thing to add. I tend to use a chaser when I want an accurate form. Usually the hand type held in the tool post. The main problem is that they have several teeth on them, as do the machine types, so a bit more "fun" to use. That doesn't cause any problem at all on Boxford back plates as they can be run all of the way through. In other cases they have to be wound out at the end of the cut. They can still be used into a recess though just like single point tools. I've also cut imperial threads close to some metric ones and then corrected by hand with a chaser to save messing with change wheels.

John

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Edited By John W1 on 05/11/2015 15:46:09

Hi All,

Thanks for your comments / advice - I didn't realise there was a difference between partial and full form inserts, useful information.

I think I will try one of the insert tools and see how I get on!

James

James

Some of the tools I finished today, they are all for internal threading and use commercially available inserts that are available in all thread types and as you are advised full and partial thread forms. The largest tool has a 0.50mm insert the other 2 are just 60 deg cutting inserts that will cut up to 1.5mm threads. I had to make a replacement tool for 12mm ID threads and while set up it was simple to cut the additional 2 tools.

The 3 sizes are 08, 11 and 16 and are shown in order on the tools with diameters of 8mm, 10mm & 12mm. The seat is 60 degrees included and cut 30 degrees each side of the tool centreline.

Some more pictures in my Album.

One of the methods we adopted in the toolroom when making replacement lead screws with conventional ( not square or acme ) single start threads was to use a chaser that had all but the first two thread forms removed by grinding away.

The thread was roughed out by single pointing and as the thread neared depth the single point tool was replaced by fixing the machine ( or hand will do ) chaser in the tool post.

The chaser was first squared up and then lightly tapped over so that the trailing ( 2nd tooth ) thread form produced the lightest of cuts after the first ( thread/tooth ) had made its cut. Once you got the knack of this you usually ended up with a full thread form profile where the 2nd cutting tooth gave a semi burnished nice clean finish.

Inserts intended for Coventry Die Heads make a useful chaser if you must do it by hand.

Thanks again for your posts.

Emgee, those look good, I hadn't thought about making holders - have you mounted these flat, i.e. zero degrees in the holder? Do you need to worry about helix angles (I may be over-thinking this..!)

Regarding chasers, I have quite a good selection of hand chasers in various TPIs / forms that were given to me a few years ago, but I have never used these. To be honest I was never sure of the correct way to use them - should they be mounted in a toolpost and applied with the leadscrew, or are they really applied by hand? Should there be a support mounted in the toolpost?

Thanks again,

James

Edited By James Burden on 06/11/2015 13:30:42

Geoff, as John mentioned APT, not expensive and very quick delivery

well packaged as well - look for http://www.shop-apt.co.uk/threading-inserts.html

sorry but don't know how to do a "link"

cheers

James

Because the insert cutting surface is above the centre of the holder when viewed end-on, if the tool diameter will not pass in the bored hole, it will be necessary to rotate the tool in it's holder and cut the thread with negative rake. I haven't found this to be a problem with partial profile inserts, no different to using a boring bar with neg rake.

The N.16 insert is mounted on a 12mm shank to avoid using with neg rake as the tip is full tooth profile, normally the shank for this size insert is 16mm diameter.

The centre tool below has flats top and bottom for use in a standard toolholder, that gives an idea of the tool angle in use.

I normally use these tools in a rotary toolchanger so it is simple job to rotate the tip if required.

Regular readers will recall we covered a set of coventry inserts and a holder for chasing from Tracey Tools in MEW a few months back.

www.tracytools.com/thread-chasers

Neil

James, hand chasers can be used in a tool post just like a machine chaser but which is much thicker.

As the hand chaser is much thinner you need thicker packing blocks to get on centre height. Keep those supporting blocks up towards the cutting edges for support/rigity, else you will need loads of Spring passes.

Greenwood Tools are very expensive compared to JB Cutting Tools !.

There was some one on ebay selling those some time ago. I enquired about more pitches. None available. They said these are the iso standards ??????

John

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Rotate a boring tool so that it can go down a smaller hole with neg rake.

When tipped boring tool holders are bought the usually specify a min hole diameter that will be larger than the shank.Sometimes the difference is a lot, sometimes it's not eg

**LINK**

In fact the clearance needed on them over the bar size isn't all that great on any of the internal threading insert holders. Or the normal boring tool holders. They do it by having a larger diameter off set end to maintain strength.

Maybe get the end red hot and hit it with a hammer etc,

John

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You may find that if you are using inserts you will get better results when threading at higher speeds. That's true of non-insert tools too, of course, but more so with carbide inserts.

If you are using a partial-form insert, the extent to which you will need to deal with the shape of the thread crests afterwards will depend on which threadform you are cutting. Whitworth crests are rounded (unless you are cutting a truncated Whitworth form) while metric threads are flat-topped (although just a smidgeon of corner rounding is both allowable and helpful).

Using a chaser as described in earlier posts does improve the flanks and crests very effectively. My personal preference is to mount the chaser in a holder in the toolpost, for accuracy and fine control. It's too easy to lose the fine control of size, fit and finish when using a hand-held chaser (or at least that's my personal experience, so probably reflects my own tendencies). I use copious lubrication when chasing.

Marcus