Lathe Threading Inserts

[mag_therm]

I have done  some threads on my South Bend 9A.
A straight 60 degree HS threading tool is for UNF and metric,
  or  the other end at 55 degree  for some camera threads ( metric Whitworth).

I tried the compound feed method, bu reverted to cross feed ( feeding the tool in at 90 degrees on each pass)
There are 2 reasons:
1) when using the compound feed, the back force is angled against its smaller feed screw so the cuts were not uniform.
The consistency is better when the compound is rotated so that the force is against the dove tail, and the gibs are tight.

2) The cross feed has a DRO, for better accuracy going into the thread depth.

I have done LH and RH threads eg the bike pedals and the straight tool seems to work OK

Tool holder was converted a few years ago to a quickchange tool post set similar to Tautech's intended set.
It saves a lot of tedious tool adjustment. With an extra holder purchase recently, the 2 most used tools ready to go.

[tautech]

I have done  some threads on my South Bend 9A.
A straight 60 degree HS threading tool is for UNF and metric,
  or  the other end at 55 degree  for some camera threads ( metric Whitworth).

I tried the compound feed method, bu reverted to cross feed ( feeding the tool in at 90 degrees on each pass)
There are 2 reasons:
1) when using the compound feed, the back force is angled against its smaller feed screw so the cuts were not uniform.
The consistency is better when the compound is rotated so that the force is against the dove tail, and the gibs are tight.

2) The cross feed has a DRO, for better accuracy going into the thread depth.

I have done LH and RH threads eg the bike pedals and the straight tool seems to work OK

Were you backing out with the cross slide then coming back to zero then advancing the compound ?

On the Harrison here the legend dials on each slide can be zeroed which makes returning to zero easy although with older worn lathes one needs return to a setting before zero and then advance to it.
For threading you sometimes see operators in videos do a scratch test with tooling by working the carriage back and forth to find the work OD zero.

Tool holder was converted a few years ago to a quickchange tool post set similar to Tautech's intended set.
It saves a lot of tedious tool adjustment. With an extra holder purchase recently, the 2 most used tools ready to go.

I've come to the conclusion I'm better of to polish my tool height setting processes and if that means upgrading some tooling to help with that so be it. One of the next things to turn is a tooling tip height setting gauge I mentioned a few posts back, something like this:

[mag_therm]

I leave the half nuts engaged for the whole thread cut.
Just back out tool by about 0.3mm when reversing back to start.
I only work in mm these days even when doing USA threads. Anyway the DRO is much easier than the scales.
Also DRO is reading the actual cross slide position, and to 0.01 mm
The depth by the DRO lines up with the micrometer more closely than when using the scales.

[tautech]

I leave the half nuts engaged for the whole thread cut.
Just back out tool by about 0.3mm when reversing back to start.
I only work in mm these days even when doing USA threads. Anyway the DRO is much easier than the scales.
Also DRO is reading the actual cross slide position, and to 0.01 mm
The depth by the DRO lines up with the micrometer more closely than when using the scales.

Likewise.
Although watching a treading vid recently I really need learn how to properly use the pitch engage indicator if only for it to look like I know what I'm doing. 

[tautech]

Bit the bullet and got this:
https://www.ebay.com/itm/285007111886

25mm shank tool holder plus 10x 60^o threading inserts.
Arrives early in the new year.

[Benta]

Looking at Harrison 12 pics, 25 mm seems a bit over the top, looks more like 16...20 mm to me. I'm judging by the four-way tool post and the width of the slot base supporting the holder.
But up to you.

[tautech]

Looking at Harrison 12 pics, 25 mm seems a bit over the top, looks more like 16...20 mm to me. I'm judging by the four-way tool post and the width of the slot base supporting the holder.
But up to you.

Yes, OEM tool post was too small for most of my tooling and I already had this larger tool post and nut that required minimal modification to fit. Will post up a pic of it maybe later today.

Therefore I'm staying with the larger shank tools that I have a small selection of. Some have been machined thinner which creates disparities in correctly setting tool height which was driving me towards investing in a QC tool post and a good # of holders that once correctly set makes changing tools a breeze.

However I can have 4 tools all correctly set but the shanks and shims need be short for tooling to be properly supported and as a lot of my work involves heavy cuts I only fit 2 tools to the tool post at one time, normally a LH and a parting tool and sometimes a boring bar instead.

Started on some mods yesterday to make a custom washer to fit the tool post fastening bolt/handle for the handle to be fully tight and facing more away from the workpiece where it really should be.
Turning done and only requires parting off....delayed as have been checking and adjusting gibs.   
Last parting job cost 2 inserts and gave up to use a 1mm cutoff wheel instead !

Then onto turning the tool height setting tool....another project I need have done months ago as it will be a great time saver despite requiring some time to build it.

[tautech]

Some pics....1st a shot of my preferred 125 x 40mm slot tool post with new custom washer to tighten ~90^o to the work, well outta the way !

2nd the OEM 80 x slot 30mm tool post with Tee slot nut and attached pivot shaft, top nut tightened. Its spanner is a gawd awful cobbled together thing with an old socket welded to a handle affair. Never liked it and never used it as it seemed the most ugly feature of the whole lathe. 

Standing unsupported nearby the tungsten insert is the new tip height gauge spun up today from shafting ex an automotive power steering rod with captured ball joint (worn out) parted off early in the build.

Benta
Dragging out the old tool post from within a deep corner in the lathe cabinet and dropping a ruler on it was quite a surprise it being the 80mm square with a 30mm slot, easily large enough to handle 25mm tooling.
Although I didn't measure some old HSS tool holders here it was plainly obvious they wouldn't fit in the OEM tool post but do in this other 125 x 40 beast so probably measure 1 1/4"(~32mm)

[tautech]

10-12 days to Auckland from China never ceases to amaze me for just parcel post !

Anyways the new 25mm shank threading tool and a 10pk of 16mm turning inserts arrived and while waiting the lathe got exposed from under several 20L buckets of swarf and 2 tip height tools made to assist with setting tip to center heights.
Not used in anger yet but hopefully soon some trial cuts to get the feel of threading with carbide using single and multipoint techniques.

[Bigfoot]

I notice you're using a negative rake insert and these require quite substantial rigidity in both spindle and cross slide arrangements on your lathe as well as a multi-horse power drive.  That is if you are aiming for a good finish. Now I'm not sure if you realize these inserts come with a specific cutting edge radius which is your minimum depth of cut or infeed.  These inserts peel rather than shear hence the need for the rigidity and horse power. Negative rake tooling is not always a good thing on a common home workshop type machine . You can get inserts for aluminium which have a sharp edge not a radiused edge and they work on many common alloys not just aluminium with caveats. Keep in mind that most insert tooling is very brittle , a sharp edge does not survive long under load.  This is why the cutting edge is radiused so that micro fracturing is minimized and tool life is extended. 

Insert threading tips also come in variants for specific thread pitches that is the tip radius depends on the thread pitch so 0.5mm pitch is a different tip than 1mm.  These tips always produce a rounded thread root proportional to the pitch and this can be a source of chatter. 

Brazed tip tooling is quite different, you can buy these and probably mainly targeted at the hobby market.  You can make these yourself and grind according to your needs.   

I recommend CoHSS  (Cobalt High Speed Steel) it's harder than standard HSS and performs similar to TC but not exactly. It's great for threading and machining tough alloys like 4140 steel.  It doesn't like intermittent cuts or shock loads as it fractures at the cutting edge just like TC or ceramic inserts. Also bear in mind that common HSS coming out of China is a softer alloy than what we normally call HSS, it requires constant resharpening.

On a  home workshop lathe it's common practice to use the set-over method for threading that is to set the compound to just under half the thread angle and feed in with the compound so the tool is cutting only on the leading edge. Another method particularly for tough alloys is to advance the compound (not set over) a thou or two ( 25micron) every other pass to reduce the tip load which increases geometrically as feed increases. The final pass in both methods is plunged to clean up the trailing edge.  The basic method is the straight plunge , OK for fine pitches and soft alloys . If you're lathe is flimsy or worn out you would need to implement the set over method regardless of the  cutting tool technology.

In the olden days we used to be able to buy leaded steel with the designation 12L14. This was called screw rod in several markets for obvious reasons. It was the preferred alloy for making screws , nuts and bolts on automatic screw lathes. It cuts like brass and takes a mirror finish with ease.  Mild steel these days is a broad range of alloys with minimal carbon and no lead but gives a ragged finish when turning and threading on small lathes. In the industrial workshops and factories modern machines can achieve a mirror finish in 4140 steel using those very inserts you are using but under highly controlled conditions.  I would not expect exceptional finishes with insert tooling on an old small lathe.

I would be using insert tooling for tough alloys and iron castings which the later I use a brazed tip tool to remove the skin in as few passes as possible then change to CoHSS for near mirror finish.  I generally thread with HSS  no top rake i.e. zero rake and sometimes if not feeling lazy I will use a retracting screw cutting tool holder in a QCTP to minimise adjusting the infeed.  I often cut ACME threads, the most recent 7/8"x5TPI 3ft long. The smallest thread I have cut is 0.4mm x0.1mm pitch on a watchmakers lathe for making a tap in silver steel.  For difficult or challenging pitches I cut them on a CNC lathe at 2000rpm where I can specify the pitch , half angle infeed  (simulated set over) number of passes , depth of each pass and the number of final spring passes.   On a manual lathe threading should be done in back gear or the lowest speed on the small chinese hobby lathes we see on the market. This will give the best finish and results. 

Cheers,
Peter.
 
 

[tautech]

Thanks very much Peter for sharing your knowledge.

What you call the set-over method is all I've done thus far using 5/16" HSS and threads mainly 1/2" UNC but wanting to get a bit more adventurous and go to carbide.
This Harrison 12 running 3hp on 3ph has no issues with heavy cuts and in the right work I'll happily take 60 thou (1.5mm) cuts with negative rake carbide or HSS although I've not pushed it any harder as dodging the purple swarf becomes an issue. 
I mainly turn dry or with some compound like Rocol RTD when in those awkward steels or needing to take big cuts.

But as a hobbyist turner I'm still learning how hard to push things and I notice a recent rush job taking large cuts has certainly dulled a carbide to where I can't get the same nice finish so it's time to turn in another corner.....the exact reason why I so like triangular double sided inserts. 

[Bigfoot]

With heavy cuts you may want to use some proper lubrication but it either has to be mist or flood. Carbide and ceramic wont tolerate, squirt , drip or brush as this causes shock stress. It's happy dry or constant lubed. Also keep in mind carbide has a limited life  it was mainly designed for the NC machines with auto tool changers . Try checking under a microscope next time you get a dulled carbide insert. This might give clues as to cause of failure. 1/8 or 1/4" cuts shouldn't be problem rigidity might be though.  Nothing wrong with pushing the envelope.   The purple swarf is an indication of ideal cutting parameters. It's not nice when you get it down your boot or down the front of your shirt.   There's no shame in wearing shock protectors or button up collars!

To get a nice finish with HSS it's worth ensuring you have ground the right tool geometry for the material and use a hard slip stone to stroke the cutting edges to a mirror finish and also hone a small radius at the very tip of the tool. This will make a massive difference to finish even without fine feed. 

Coolant systems can be a real bother, that stuff is messy at best if not contained.  Mist coolant can be inhaled which is not good for anyone. I mainly use soluble oil in a squirt bottle for HSS.  One of my mills has a built in flood coolant system but it needs a large catch skirt fitted which increases the footprint.

On small instrument lathes I use carbide almost exclusively when turning hardened carbon steel and quite often observing the cut under a microscope, you can see what's going on . Carbide produces a near mirror finish when honed correctly but any chatter will rapidly destroy the cutting edge and this also goes for full size lathes. QCTPs are not always rigid enough typically with excessive overhang since the deflection force is proportional to the 4th power of the overhang and then some of these QCTPs are not made well either particularly the piston type. Sometimes it pays to use a conventional turret toolpost especially when chatter is an issue as the tool is usually supported all the way down to the cross slide.

[tautech]

I notice you're using a negative rake insert and these require quite substantial rigidity in both spindle and cross slide arrangements on your lathe as well as a multi-horse power drive. 

Been at the lathe since I replied and checked the rake on the threading insert and while the tool holder is indeed negative rake the insert has a grind for it to be just slightly positive rake which of course being carbide can't be too positive as it will be too brittle.

With heavy cuts you may want to use some proper lubrication but it either has to be mist or flood. Carbide and ceramic wont tolerate, squirt , drip or brush as this causes shock stress. It's happy dry or constant lubed.

Ah, more gems, thank you !

Coolant systems can be a real bother, that stuff is messy at best if not contained.  Mist coolant can be inhaled which is not good for anyone. I mainly use soluble oil in a squirt bottle for HSS.  One of my mills has a built in flood coolant system but it needs a large catch skirt fitted which increases the footprint.

This Harrison has a suds pump although I've never used it and somewhat reluctant to with anything water soluble as the lathe is not in constant use and might not get used for a weeks at a time and I already have my hands full keeping atop of corrosion as it's in a shed and subject to Auckland extremes of temp which are certainly nothing bad but the humidity can be and I've seen it totally covered in a wet dew. 

I'm hoping that better tooling and cleaner cuts can help keep the lathe cleaner although some of the turning stock I have can only be called rusty old shit so a heavy first cut is called for to get under the rust in a single pass and it might just be I need keep atop of cleanliness and lube to keep the rust bunnies at bay.

If you have any suds recommendations I'm all ears.. 

[nctnico]

I use thick oil (for use in a car engine) to put a protective film on my metal working machines that are in cold shed as well. It works quite good to prevent excessive rust.  Doesn't look that pretty like your Harrison, but where there is oil/grease, there won't be rust.

[Bigfoot]

Traditional suds is soluble oil. We used to get this in cans to put in the car radiator but can be bought at places like Hare and Forbes if they are in NZ. A good machinery dealer should stock something like Garrick. I don't have a problem with soluble oil causing corrosion but it can get infected with metal eating bacteria and also cause dermatitis. Most industrial grade cutting oils stink and are not friendly to humans or the environment. I suggest a Rocol cutting oil  , they do make it, can't remember the name at the moment. If you are machining Aluminium then Low Odor kerosene brushed on is excellent followed by WD40 as second choice. This is not coolant  but merely a cutting lubricant and will smoke excessively if the chips are hot. 

 If you've done much Aluminium machining you'll know it welds to your cutting tools without a lubricant and will destroy carbide quickly.  The alloys used for enclosures is I believe high in zinc and throws chips rather than ribbons and machines nicely. There are certain alloys designed for machining and extruding.

With carbide inserts unless razor sharp are designed to peel and rub as mentioned previously hence the need to use a lubricating cutting oil under heavy loads.

A good oil to use for protecting exposed metal on a machine is chainsaw bar and chain oil. This is thick and designed to stay put and will not disperse readily . It's actually quite sticky stuff and not expensive.  There is Shell Ensis if they still make it which was designed for that purpose. I have some proper slideway oil , could be Ensis but it's similar in consistency to bar and chain oil.  WD40 has become unpopular for anything other than removing chewing gum but CRC seems to work well for protecting metal so if you use soluble oil you can always spray your machine down with CRC to disperse it but what I see is the water seems to evaporate out of the soluble oil leaving the oil behind.

I don't have a huge problem with rust in my workshop but cold machines are always at risk especially if fog rolls in or you get the spurious warm humid day when the machines are colder than ambient temperature.  Some people in cold climates keep a low wattage incandescent light under the machine to heat it above ambient.   

The double sided triangular inserts are a good thing for economy sake. You should expect them to last for the duration of the job or hours of turning before dulling. This would be a serious issue in the CNC world if they didn't. I

[nctnico]

For drilling/ milling Aluminium, I use Relton A9 as a lubricant. Works like a charm.

[tautech]

I'm starting to see the sense in different cutting aids and understanding the tooling shocks of the brush or occasional squirt compared to a continuous flow so I'm tempted to splash out and get a 5L of Rocol RTD Liquid that you can use neat/undiluted which should also give amazing rust protection.
https://nzsafetyblackwoods.co.nz/en/rocol-rtd-liquid-5l-each--04383406

Another alternative might be 35:1 Rocol but not thinned with water but some non/low flammable solvent.....but just what ? Washbath fluid ?
https://nzsafetyblackwoods.co.nz/en/rocol-35-1-longlife-soluble-oil-4l-each--07741858

Whatever I decide for suds I also need some good ol' RTD for all the normal drilling/tapping etc
https://nzsafetyblackwoods.co.nz/en/rocol-rtd-compound-500gm-tin-each--04461700

Recommended for this 1970 Harrison slideways and throughout gearcases is Shell TonnaT 68 however for hobbyist use where the lathe is not getting hot or even warm a 32 weight is generally recommended on the Harrison lathe forum.

Further investigations shows a TonnaT 32 crosses well with an ordinary 32 weight mineral hydraulic oil which is what I'm using currently but for slideways protection certainly a chain bar oil with its anti throw/stick properties would be an excellent Autumn/Winter protection solution and I use saws enough to always have a 20L on hand.

Never turned much alloy however I have worked a bit with magnesium alloys like used in saw crankcases which is amazing stuff to machine, drill and tap but never done enough in one batch so see it have an effect on tooling.
Tricky shit to weld but easier with TIG than oxy.

Now Water Displacement formula 40 has no place in our workshop as we prefer more useful preparations. 

[jpanhalt]

The machine shop at our institution moved from flood lubrication/cutting to mist that was directed right where the cutting took place.  It was a lot less messy.

[tautech]

Yes spotted this that Rocol call their Accu-lube range amongst their cutting fluids:
https://www.rocol.com/products

Still I'm not sure I want to work where there's a cutting compound mist, non toxic or not.

[jpanhalt]

From my experience in that machine shop, there was no more odor from misting than from flood cooling.  It doesn't take much mist.  It is not like using a vaporizer in your home.

[Ian.M]

You can get away with manually applied cutting compound/oil with insert tooling as long as you apply it evenly before starting the cut.  Once the tool touches the work, it heats up and you cant add any more without risking thermal shock damage, till the cut has stopped and the tool has cooled.   Also, because it has to be viscous enough  to stay on the surface, and the tool is cutting under the existing surface, very little of it gets to the actual cutting edge or the rubbing interface between chip and tool, so its typically considerably less effective than flood or mist coolant lubricant.

[tautech]

You can get away with manually applied cutting compound/oil with insert tooling as long as you apply it evenly before starting the cut. 

Yes that's exactly what I used to do

Once the tool touches the work, it heats up and you cant add any more without risking thermal shock damage, till the cut has stopped and the tool has cooled.

This is what I have just learned thanks to Bigfoot. So far it has only cost the the top efficiency of 1 of 6 edges on a double sided triangular insert. 
However I've also been having real problems parting that I'm now quite sure is due to insert thermal shock which these tiny 2mm parting inserts seem particularly susceptible to.
Did I get the wrong carbide parting tool for GP work ?
https://www.ebay.com/itm/282936006971?hash=item41e04cd93b:g:syMAAOSwybpboJYE

Also, because it has to be viscous enough  to stay on the surface, and the tool is cutting under the existing surface, very little of it gets to the actual cutting edge or the rubbing interface between chip and tool, so its typically considerably less effective than flood or mist coolant lubricant.

RTD paste has been my cutting aid of choice for ages but instead I've been using a cheap low speed tapping paste that I've never been particularly keen on from the first moment I used it turning.

[mushroom]

The ideal QCTP ! The best of the two worlds.

Made by Tripan. Takes different toolholders, up to 25mm (series 1, 2, and 3). And if overhang is a problem, it still is a conventional turret. Seems to me it was discontinued, and is now available for one toolholder size only. On the other lathe, much smaller than this 8HP beast, I also put a Tripan QCTP that fits the smaller toolholders (series 1), but has no "square style" side. After shimming the QCTP on the small lathe, the cardridges can go on one lathe or the other without needing any adjustments.
Not sure this QCTP is available worldwide, new or used... They are common on Shaublin toolmakers/clockmakers lathes.
Another advantage is that toolholders are easy to make, unlike the popular Multifix style.

Some folks just glue the shims under each tool. Some others attach them with electrical tape (not sure it's a great idea, never tried... I doubt the adhesive will last very long because of the oil)

NEVER EVER use WD40 on a lathe or any machine tool  ! Years ago I had the great idea to "protect" everything with that crap before I leave the machine unused for a couple of months. It evaporated, leaving a coat of brown waxes. Had to take the machine apart to clean it and it was a real pain. Chainsaw oil is known to be a good substitute to the classical ISO VG 64 way oil.

Years ago, I read on a forum (CNC Zone ? Practical Machinist ?) that ATF oil (Dexron) had the best anticorrosion properties because of its anti oxide additives, and was the best for long time protection. The author tested many oils in extreme conditions, with pictures and documented everything... Can't retrieve the thread.

I've been using mist on lathe, mill and bansaw, with a homemade system that worked well. Chronic sinusitis after a few months... Should not be used free air. But it worked well, and avoided most of chip recycling on the milling machine, in particular when side milling or machining pockets.

[nctnico]

ATF oil sounds like really nasty stuff. I always read the MSDS sheet before using chemicals and oils to see if these may pose any harm