Advice regarding my worn nuts

[dieselsamurai]

Check Ali Express & Temu .. a few months ago I was about to make my own acme half nuts for my 1943 Atlas / sphere lathe I found the taps for the threads but was waiting till my next months mancupboard money was due ,

A few days later the clever Chinese worked out what lathe I had and produce the half nuts for it , they might soon produce the carriage acme screw nuts too .


Could you grind off half the cutting edge off the tap to leave you with a boring cutter that is tapered ?

The problem is I dont even know what tap I would start with , the leadscrew is an odd diameter

At least on the lathe I can test fit until the fit is good

 

[DAPPH]

Look up AMCE threads and profile info on line there are set standards for each diameter .

 

[Agroshield]

I'm guessing to do the left hand thread will be more tricky need to look into how to do that

The insert will be 16NL (or 16 IL) 10 ACME. It might also be called 3NL or 3IL. You will also need a left hand threading bar.

They are hard to find:

16IL10ACMEVTX ACME Internal Left Hand Vardex Thread Turning Insert, 16mm x 10mm TPI, Multi-Purpose Ground VTX Grade, TiAlN Coated (Vargus) - Ref: 3IL10ACMEVTX

Single point threading inserts (also known as screw cutting inserts) for internal left hand thread turning of ACME threads. These inserts have a high quality ground substrate with a TiAlN coated VTX grade for multi-purpose threading of Steel, Stainless Steel, Cast Iron, Non-Ferrous, Exotics and...

www.cutwel.co.uk

This will give you the code for the threading bar (the barcode):

SNR0008K11 SNR/L0010K11 SNR/L0016Q16 SNR0020R22 SNR0025S22 Internal Thread Turning Tool SER SEL Lathe Cutter bar CNC tool Holder - AliExpress 1420

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

 

[Agroshield]

...there are set standards for each diameter .

There are indeed set (common) standards for diameter and pitch but these are only adhered to when the ACME thread is used in a non-precision application (e.g. a scissor jack).

When used as a leadscrew, most manufacturers choose their own combination of diameter and pitch (and form). Think of the manufacturing advantages to the Chinese RF45 maker - if producing a metric machine, they cut a 2.5mm pitch TR thread onto a piece of rod of a particular diameter. When they want to make an imperial machine, they are not going to set up another machine with a different diameter piece of rod and a different shape of screwcutting insert. They will just flick a switch on the machine and cut a 10tpi (2.54mm pitch) TR thread on the same leadscrew blank.

Standards are for interchangeable manufacture (nuts and bolts). A leadscrew does not fall into this category of good.

 

[dieselsamurai]

The insert will be 16NL (or 16 IL) 10 ACME. It might also be called 3NL or 3IL. You will also need a left hand threading bar.

They are hard to find:

16IL10ACMEVTX ACME Internal Left Hand Vardex Thread Turning Insert, 16mm x 10mm TPI, Multi-Purpose Ground VTX Grade, TiAlN Coated (Vargus) - Ref: 3IL10ACMEVTX

Single point threading inserts (also known as screw cutting inserts) for internal left hand thread turning of ACME threads. These inserts have a high quality ground substrate with a TiAlN coated VTX grade for multi-purpose threading of Steel, Stainless Steel, Cast Iron, Non-Ferrous, Exotics and...

www.cutwel.co.uk

This will give you the code for the threading bar (the barcode):

SNR0008K11 SNR/L0010K11 SNR/L0016Q16 SNR0020R22 SNR0025S22 Internal Thread Turning Tool SER SEL Lathe Cutter bar CNC tool Holder - AliExpress 1420

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

I will check my boring bars i have a lot ive aquired hopefully one is lefthanded , sods law though....

 

[DAPPH]

Dasan Store
https://www.aliexpress.com/item/100...order_list.order_list_main.109.1ab01802IFS0Yf
10PCS 16ER 16NR 8 ACME 10ACME 12 ACME 14ACME 16ACME Lathe Carbide Threading Inserts Cutter Tools for Stainless Steel
DM10, 16ER, 10ACME
￡9.29
x1

Thanks or that Argo.
I've put up the info I had and IIRC there is also a chart showing the sizes & forms for imperial sizes and I'm fairly sure they were not screw jack thread ACME where one side that pusheds is of a flatter profile .

 

[dieselsamurai]

the most important size to me is the minor diameter as this is the size i start the thread at

 

[RichardM]

I used a piece of ground HSS in an old style boring bar when I did my vice, fortunately it was a square thread which I find easier to cut than acme.

 

[dieselsamurai]

well unfortunately no lefthanded boring bar most too big anyway



I did find some bronze but odd sizes.... 4" 2" and 1" plus an 8ft length of 2" i forgot I had!



1" is going to be too tight on the diameter as major is 0.920"

 

[Agroshield]

the most important size to me is the minor diameter

I would seek a second and third opinion on those numbers before cutting metal. Anywhere that quotes a tapping drill size to three decimal places of a millimetre is unrealistic.

A standard boring bar will not hold a screwcutting insert. You need the correct laydown threading bar so the angles are correct. The triangular insert is held so one edge is parallel to the face of the chuck/spindle so it can cut nearly to the bottom of a blind hole.

Every major insert manufacturer produces a technical guide on the laydown system. I am fond of the Seco one here:

https://fenntool.com/wp-content/uploads/2017/06/downloads-Seco-Threading_2016.pdf

That does not contain ACME data, but other manufacturers do. I think the Kennametal one has data in both imperial and metric, so that is useful. It tells you the total infeed, the number of passes to make and the infeed per pass so that you are cutting a constant volume of material each time.

 

[Pete.]

well unfortunately no lefthanded boring bar most too big anyway

View attachment 486358

I did find some bronze but odd sizes.... 4" 2" and 1" plus an 8ft length of 2" i forgot I had!

View attachment 486360View attachment 486359

1" is going to be too tight on the diameter as major is 0.920"

Sell that 8 foot length and buy a whole lathe with the proceeds

 

[dieselsamurai]

I would seek a second and third opinion on those numbers before cutting metal. Anywhere that quotes a tapping drill size to three decimal places of a millimetre is unrealistic.

A standard boring bar will not hold a screwcutting insert. You need the correct laydown threading bar so the angles are correct. The triangular insert is held so one edge is parallel to the face of the chuck/spindle so it can cut nearly to the bottom of a blind hole.

Every major insert manufacturer produces a technical guide on the laydown system. I am fond of the Seco one here:

https://fenntool.com/wp-content/uploads/2017/06/downloads-Seco-Threading_2016.pdf

That does not contain ACME data, but other manufacturers do. I think the Kennametal one has data in both imperial and metric, so that is useful. It tells you the total infeed, the number of passes to make and the infeed per pass so that you are cutting a constant volume of material each time.

Yeah i meant threading bar i realise they are different I have a couple but they are already in holders

the chart above was a rough guess at sizes while I was at work , i'll mike it before doing any boring to get an accurate idea

sods law cutting the 2" bar to a shorter length i heard the sound my bandsaw makes when a blades cracked so just had to fix that

the nut is roughly 32mm in diameter so i have to be careful how much to leave when boring it out and how much meat is on the threaded insert , if i leave 2.5mm on the nut it only gives me 2mm on the bush for threading that might not be enough ...

 

[dieselsamurai]

Sell that 8 foot length and buy a whole lathe with the proceeds

when i looked at a tiny length of bronze it was stupid money so i never really thought about it before but I guess it might be worth a bit ! I also a acquired a 4m length of 50x5mm brass angle god know what it was for but thats bloody heavy too

 

[dieselsamurai]

Ok done some checking and no need to buy a different bar left hand threads can accomplished using a standard one just start from the inside and thread cut away from the chuck obvious really just had to think about it

 

[dieselsamurai]

Got the bandsaw blade welded before the crack made it all the way through so much harder to do when they snap

2" bar cut in half as more manageable , just need to turn it down to 45mm so it will fit inside my for jaw chuck. Ran out of time as dad taxi service needed tonight

nice straight cut just weird how theres always an overlapping oval pattern in the cut only just visible

 

[Agroshield]

Ok done some checking and no need to buy a different bar left hand threads can accomplished using a standard one just start from the inside and thread cut away from the chuck

Please could you provide a reference for the place you have checked.

What you say is only half the story. So either the reference is being too light with its explanation or you may have neglected to read the small print.

Consider a cross-section of a right hand and left hand thread. Each thread wil have a helix angle. One 'leans forward' in the cross section; the other 'leans back'.

That means to cut each thread with the same insert geometry would require so much clearance on both sides of the insert (so that it does not rub) that it would be unworkably weak.

Instead, the insert is given a practical clearance and angled in its pocket roughly parallel the the helix angle of the thread (assume that angle is 2 degrees). Hence, going from a right hand to a left hand thread, the angle the insert presents to the work would need to change from +2 to -2. On high end tooling, that is done by means of a shim under the insert, available as a spare part from the tooling manufacturer. On affordable tooling, that shim is not available and it is cheaper to buy a left and right hand bar from Ali than a right hand bar and shim from Iscar.

Please study page 8 of the Seco handbook above. Pay very good attention to the small print after the asterisk at the bottom of that page plus the diagram at the bottom of the page.

 

[Agroshield]

...just weird how there's always an overlapping oval pattern in the cut...

They all do that, even the best-adjusted top end models.

Various theories here:

https://www.reddit.com/r/Machinists/comments/bwdp9p/what_causes_these_arcs_from_horizontal_band_saw

 

[dieselsamurai]

Please could you provide a reference for the place you have checked.

What you say is only half the story. So either the reference is being too light with its explanation or you may have neglected to read the small print.

Consider a cross-section of a right hand and left hand thread. Each thread wil have a helix angle. One 'leans forward' in the cross section; the other 'leans back'.

That means to cut each thread with the same insert geometry would require so much clearance on both sides of the insert (so that it does not rub) that it would be unworkably weak.

Instead, the insert is given a practical clearance and angled in its pocket roughly parallel the the helix angle of the thread (assume that angle is 2 degrees). Hence, going from a right hand to a left hand thread, the angle the insert presents to the work would need to change from +2 to -2. On high end tooling, that is done by means of a shim under the insert, available as a spare part from the tooling manufacturer. On affordable tooling, that shim is not available and it is cheaper to buy a left and right hand bar from Ali than a right hand bar and shim from Iscar.

Please study page 8 of the Seco handbook above. Pay very good attention to the small print after the asterisk at the bottom of that page plus the diagram at the bottom of the page.

I understand what you are saying as from what i can see the insert would be cutting on a face that was not profiled to do so but there are many people who do it this way

https://www.haas.co.uk/resources/better-techniques/turning-tips/how-to-cut-left-handed-threads/ (2nd option)

https://www.wisc-online.com/LearningContent/mtl12302/MLT12302.htm#Top (external threading but same principle)
https://www.practicalmachinist.com/...ight handed threads,moved in the +Z direction. (long discussion but many use the method i suggest)

 

[Agroshield]

I think you may be misinterpreting the information you have cited.

The Haas reference only tells half the story, as suggested above. We are not in dispute that it is possible, but are discussing the small but crucial details of what is required to make it possible.

The first video screenshot shows a left hand bar (listen at 9:43).

The wisc-online is using ground HSS tooling not inserts. Look at post #18 "this is the insert I think I need". See also Figure 15-3-4 and consider how you achieve both tools shown end-on in a single insert - you cannot so you have to tilt the insert itself.

The Practical Machinist discussion does not address the issue of using an insert nor does it talk about how an HSS tool must be ground differently for the two hands.

As above, every insert manufacturer (Sandvik, Vargus, Iscar, Seco, Kennametal) says the same thing in their technical literature. You can use a right hand insert and right hand bar for the left hand thread but you must change the angle of the insert.

Sandvik Coromant

www.sandvik.coromant.com

"Negative shims are used when turning left-hand threads with right-hand tools and vice versa"

Selecting a Shim for the MMT Series - Technical Info / Cutting Formula | MITSUBISHI MATERIALS CORPORATION

This page is about Mitsubishi Materials Corporation's technical information/calculation formulas. Detailed information on Selecting a Shim for the MMT Series. In addition to an overview of cutting

www.mmc-carbide.com

This one is worth bookmarking. I had not seen the information presented this way before and it is good. Note that in the shim reference table, right hand ones are given a positive value and left hand ones given a negative value.

From a practical and economic point of view, buying an overseas left hand bar and insert is cheaper in money and time than sourcing or making the necessary angle-changing shim.

 

[dieselsamurai]

I really appreciate your time and input on this subject and agree the best course of action is to get a left hand tool and insert , theres an APT SNL0016Q16 bar on Ebay at the moment with no bids for slightly more than the ALI ones that are mostly SNL0016M16 so the extra 20mm length may be useful in the future . Inserts seem to be less common but £10 should get one

As usual the internet is a minefield of conflicting information this was a way more complicated subject than I expected !

I have ordered a right hand thread insert and time dependant will turn down and bore a test piece ready for when it arrives for a trial fit