# AL320G - Threading Dial



## joco-nz (Apr 9, 2017)

I've been looking at the threading dial on my AL320G and thinking it must be usable even though the "manual" that comes with the lathe doesn't tell you anything other than how to set up the change gears.

So first off some research into threading on the lathe by reading Workshop Practice Series #3: Screwcutting on the Lathe by Martin Cleeve.
Now this is pretty jolly complete and after reading things several times I felt I had enough of a handle on things to make the next steps.

So looking at the threading dial the gear is 20 teeth, the lead screw is a 3mm pitch and the dial has 4 "lines" or sectors on it.

So what does all this tell us ... well after some manual measurements the following ...
We get 60m travel of the saddle from a single rotation of the threading dial and the lead screw turns 20 times during that travel.
i.e. 20 teeth x 3mm pitch = 60mm travel.

So back to the book, specifically from pages 71 with specific attention to pages 81 and 82. So from reading this section it appears that the key to being able to use the threading dial is that the pitch of the thread needs to fit some rules with regard to:
[a] the thread pitch being a whole multiple of the leadscrew pitch
* the thread pitch being able to divide evenly into the amount of saddle travel represented by sectors on the dial

So armed with this hopefully correct info I built a chart to see what pitched threads I could use the dial for on the lathe and which I could not.  And that is the kicker with metric threads, not all of them will work with the threading dial without some changing in the threading dials gearing.

The calculated table of threads.  Blue lines show thread pitches not possible with the stock threading dial gearing.




Now to do a proof.   I picked a 1.5mm thread, setup the lathe gears, found some scrap and got it ready to do some light cuts.





So, set up the and ready to go I had the lathe running nice and slow (60rpm) and leadscrew turning and ready to engage the half-nut on a any whole sector line on the dial. Let it run a light scratch, disengaged the half-nut, pulled back the cross slide, brought the saddle back to start position, shutdown and checked with a gauge.  Photo's not the best but you can see that the scratch is bang on the 1.5mm pitch gauge.   So far so good.  Now for the moment of truth, can we get repeated pickup?




Well repeated the same process and engaged the half-nut on one of the whole sector lines. Not the same as the last one, just to make sure there was some more variability in the mix.  Re checked the slightly deeper cut, BINGO, bank on the same lines as last time.



Okay according to my understanding from the book learning I should be able to engage the half-nut at ANY point on the dial gauge as the 1.5mm is a whole multiple of the leadscrew pitch.  So thats what I did, engaged the half-nut at a point between the sector lines on the threading dial.



And the result was bang on!

I ran out of time tonight to do some more variations on threads, also will need to dig out some more scrap round to trial on.  But so far the math seems sounds and practical testing is lining up with the book learning.



Conclusion at this point is that while not all threads can be done using this method a good chunk of them can be so the threading dial is no longer looking like the useless appendage it seemed to be for metric threading.

I'll do some trials over the course of the week plus I want to look into what gearing would be needed on the thread dial to do the other threads and if that is even worth the hassle given the non-disengaged half-nut method will work just fine on those.

Cheers,
James.*


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## Journeyman (Apr 9, 2017)

Heres a bit of an article I wrote ages ago when having trouble cutting a 1.75mm (M12) pitch thread on my WM250, very similar to yours. It may or may not help!
The screw-cutting thread indicator dial meshes with the leadscrew via a  30 tooth gear. To get the indicator dial to rotate once the carriage has  to move 90mm (number of teeth x leadscrew pitch). Only those metric  pitches that divide exactly into 90 will be able to use the dial when  screw-cutting. Thus pitches of:-
  0.5, 0.6, 1.0, 1.25, 1.5, 2.0, 2.5 and 3 will work, pitches of 0.7, 0.8 and 1.75 won&#8242;t work.
  	Replacing the 30 tooth gear with a 28 tooth gear would work for the  missing pitches but not for all. With a 28 tooth gear the  	carriage has to move 84mm for a full turn of the indicator and 84 is  divisible by 0.7, 0.8, and 1.75. So either change the gear, make an  indicator that has both gears or just leave the leadscrew engaged and  reverse the lathe.​Cheers
John


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## joco-nz (Apr 9, 2017)

Thanks John.

I think on my leadscrew a 21 tooth gear on the dial indicator will get me the missing pitches. 21 * 3 = 63mm per full turn

For 0.45 pitch: 63 / 0.45 = 140.
For 0.7 pitch:   63 / 0.7 = 90.  
For 1.75 pitch: 63 / 1.75 = 36.

Therefore a 21 tooth gear will give these pitches on a full turn and half turn.  It will give the 1.75 and 0.45 on each quarter segment.

So I guess I need to source a 21 tooth gear.  :thumbup:


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## Journeyman (Apr 9, 2017)

James, I thought of putting both gears ie a 20 and 21 tooth in your case on the same shaft and find a method of sliding the indicator shaft up and down to engage the right gear. Never got around to it though as I don't do much in the way of screw-cutting on the lathe. Could make for an interesting lttle project though.

John


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## joco-nz (Apr 9, 2017)

Oh dear - another project for the list. :hDe:  Dang good idea though.


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## Blogwitch (Apr 9, 2017)

My drop in dial uses 3 separate gears to obtain the full range of metric threads on my machine (Chester Crusader), and it was a real PITA to swap them over when you went from one pitch to another.

http://www.homemodelenginemachinist.com/showthread.php?t=24110

Even when you have done this mod, by changing the gears (even single gears) it is a PITA to get the drop in lines to line up with the zero mark, so this is how I solved the problem and now only takes seconds to realign everything.

http://www.homemodelenginemachinist.com/showthread.php?t=24111

Hope this helps

John


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## joco-nz (Apr 9, 2017)

Blogwitch said:


> My drop in dial uses 3 separate gears to obtain the full range of metric threads on my machine (Chester Crusader), and it was a real PITA to swap them over when you went from one pitch to another.
> 
> http://www.homemodelenginemachinist.com/showthread.php?t=24110
> 
> ...



John - very nice and great pointer on how to approach that problem.


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## bazmak (Apr 9, 2017)

very interesting topic


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## joco-nz (Apr 10, 2017)

Managed to do a test this evening using a 2mm pitch and following what I have worked out got the thread restarts using the threading dial bang on each time.

The key of this test was that the restarts had to be done on a half turn.  Which I did and it worked perfectly.

I have updated the chart a bit on the basis I need a 21 tooth gear to get the extra pitches covered.

View attachment Hafco-AL320G-ChasserDial.pdf


Cheers,
J.


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## purpleknif (Apr 10, 2017)

Uhhh , why not just start at the same no. each time ?


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## joco-nz (Apr 11, 2017)

purpleknif said:


> Uhhh , why not just start at the same no. each time ?



Yes you could do that which would be a full turn restart which will work.  But you then have to wait that much longer for the dial to come into alignment before engaging the half-nut.

Cheers,
J.


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## Blogwitch (Apr 11, 2017)

That is why it is sometimes a lot better to use a permanently engaged leadscrew, no waiting about, just put the cut on and start the machine. It only works if you have fwd/reverse on your machine.

John


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## Journeyman (Apr 11, 2017)

A flip up tool holder is also a useful add-on for this. Saves having to wind the tool out and then back in again. I know John (Blogwitch) has a version of this but I can't find the post at the moment. (Might be on another forum)
John


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## goldstar31 (Apr 11, 2017)

Journeyman said:


> A flip up tool holder is also a useful add-on for this. Saves having to wind the tool out and then back in again. I know John (Blogwitch) has a version of this but I can't find the post at the moment. (Might be on another forum)
> John


 
You are thinking of the swing tool holder originally provisionally patented by Kenneth C Hart and writing as Martin Cleeve.

I think that my crude copy came out of Popular Mechanics but Cleeve certainly wrote modifications both in Model Engineer and also Engineering in Miniature.

Hemingway kits has the newest one which does boring but also screwcutting retraction.

I have the original tool but the new kit has yet to be started.

I hope that this helps

Norm


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## Journeyman (Apr 11, 2017)

Found the post I was thinking of by John, it's on Model Engine Maker. Useful bit of kit. Have a look at the videos to see it working. 
Who needs a thread cutting dial
Sorry James, you have another project!
John


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## Blogwitch (Apr 11, 2017)

About 2/3rds the way down that post I did a rough sketch on how to make one that just fits into a normal tool holder in the size you require.

I should have mentioned that little tool when I said you need a reversible machine to carry out that sort of permanently engaged lead screw.

John

BTW Norman,

"You are thinking of the swing tool holder originally provisionally patented by Kenneth C Hart and writing as Martin Cleeve."

He designed the tool to be retracted manually by cam action when doing the reverse operation, mine works in a different and more simple and economical way.

http://www.hemingwaykits.com/acatalog/Swing_Tool_Post.html

Mine uses a much more lightweight head swinging on a lowered pivot point that allows the cutter to lift itself automatically when in reverse, so no cutting action can take place, and in fact, the next cut can be put on before it reaches the end as the tip is well away from the surface of the job, and when it is sent in again it will start to cut straight away, fully automatically again without having to touch anything.


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## John S (Apr 11, 2017)

Don't worry John.

If is wasn't written by Hart, Cleeve, Thomas, Westbury then it's not worth considering.  Or should be according to a few diehards who never had a unique thought in their tiny brains and can only regurgitate the same old again and again.


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## joco-nz (Apr 12, 2017)

Thanks gents.

I'm aware of the swing/lifting tool holder for threading and even have a CAD model completed for one.

I also have done the permanently engaged half-nut with reverse threading model on my lathe and its very successful if a little on the slow side.

The challenge I have been looking to solve is when threading up to shoulder, either external or internal how to solve the challenges that brings when your lathe does not have a brake on it.   Even going slowly its all a bit nerve racking.  Heck thinking about it even a brake would still rattle my nerves.

I then found some very interesting discussions/videos on threading in reverse.  That is running the chuck in reverse with the tool suitably positioned to cope with the change in rotational direction.   The benefit of this being you could run at a higher rpm and the tool threads away from chuck.  Nice and safe, relaxed and no stress.  To do that easily having a working thread dial seemed to be very handy.   You could of course do a similar thing with a continually engaged leadscrew using the lathes forward/reverse.  It becomes even easier if your lathe has fully variable speed not gear based speed.  i.e. fast out threading and nice and slow and controlled back to start position.

Anyway the game plan was to get to a point that I could
(a) use the threading dial with confidence and know what threads I could use it for and what changes I might need to make to get the main threads I want covered.
(b) with the above under my belt I could then setup and do the "reverse" threading model and enjoy the lower stress, higher threading speed and extra safety this would deliver.

A reasonable video on the technique I am referring to is here:
https://youtu.be/Z-dqOi_z5bk

Anyway that was part of my thinking in beginning this research.  The other part was quite simply "why can't I use this blasted threading dial!?"


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## John S (Apr 12, 2017)

There are plenty of variations on the swing threading tool.
John has shown his and I have seen some where they use index-able tips to achieve the same result.

This is mine which has two tool holders. A normal single point one, made from a parting off tool, the red one, and a holder made to take one spare insert out of a Coventry die head.






Simple enough device as as Bogs says you have to have the pivot point below the tip of the tool, how much doesn't seem critical.

I also have machined a tenon inside the tool holder which mates with a key on the bottom plate to stop any sideways movement as you have to have some clearance in the pivot bush or it doesn't work.


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## joco-nz (Apr 12, 2017)

John - nice and chunky and solid looking.   They are a really smart tool for threading, no doubt about it.  :thumbup:


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## bazmak (Apr 12, 2017)

When single point threading I power feed to within a few threads and then turn the chuck by hand.Avoids hairy scarie


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## goldstar31 (Apr 26, 2017)

bazmak said:


> When single point threading I power feed to within a few threads and then turn the chuck by hand.Avoids hairy scarie


Apologies for the delay but the Victoria Cross  Memorial combined with the Anzac Day in London  sort of got in the way!

So my present thoughts  are the realisation that many small and new Far East lathes have a slowest speed of 100 rpm.   When push came to shove 'my' 918 actually ran at a mind boggling 130rpm which was too high to avoid nervous breakdowns.

OK, I tamed the beast by newer pulleys but the classic mandrel handle made life easier- and safer.

Just a constructive thought?

Norman


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## joco-nz (Apr 26, 2017)

Norman - yes the good old handle ala:
Picture from member albums on model-engineer.co.uk  (http://www.model-engineer.co.uk/sites/7/images/member_albums/45526/469416.jpg)






A very good option and even though my lathe will get down to 60rpm still a viable path if that extra bit of control is needed.


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## Tjimptjomp (Feb 23, 2021)

joco-nz said:


> I've been looking at the threading dial on my AL320G and thinking it must be usable even though the "manual" that comes with the lathe doesn't tell you anything other than how to set up the change gears.
> 
> So first off some research into threading on the lathe by reading Workshop Practice Series #3: Screwcutting on the Lathe by Martin Cleeve.
> Now this is pretty jolly complete and after reading things several times I felt I had enough of a handle on things to make the next steps.
> ...


Hi James!
I also have a lathe that has a 3mm pitch. Its an old weiler from 1952. It is missing the dial and i thought i’d build one. My question to you is if you know what module your 20 & 21 teeth gear are. Or if you coulde provide me with the diameter of the gears. That would help a lot!

cheers
Thomas


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## goldstar31 (Feb 23, 2021)

I have a Myford Super7B with a power cross feed similar or better than James's. So that is not a 3mm leadscrew but an * Threads per inch and WE, to convert our lathes to a metric function have to have a transposing gear of 127 correctly but workable substitutes of 63, or 21 are needed.  Again,   Myford gears for such purposes are not model pitches but are 20Diametrical pitch. 
So if you are Swedish and working in in Metric form  the reference to 21 is quite irrelevant
So what I deduce also having a Metric lathe( A Sieg c$) with a 3mm leadscrew is a set of  gears( the module is irrelevant- but will facrorize in multiples of 5. So a dial gauge to work in metric is  also in multiples of 5.

Going from a Metric Metric lathe to cut imperial threads it is prudent to gang a 127 transposing gear with a 120 one but you must leave the leadscrew permanently engaged and ignore a dial gauge if you have one. 

Again, with metric feed screws, it IS possible to approximate feeds without fitting a DRO.

'Cleeve' ie Kenneth C Hart is invaluable in such cases as he in Screwcutting in the Lathe book tries to cater for all possible problems but in it Professor Dennis H Chaddock explains the number of permautations into thousnds only usuning gears of multiples of 5.

So this is brief but heady stuff and I must remind you that Cleeve only had one lathe- but TWO leads-crews - or actually half a lathe- a ML7 driven by TWO motors.  So I synpathise with you. 
 But- and it might cloud the issue- Cleeve incorporated the dog clutch which was officially incorporated in some Myford ML10's. I had one.
Might I wish you the best of luck in what can be a very complicated problem.
Norman


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## joco-nz (Feb 23, 2021)

Tjimptjomp said:


> Hi James!
> I also have a lathe that has a 3mm pitch. Its an old weiler from 1952. It is missing the dial and i thought i’d build one. My question to you is if you know what module your 20 & 21 teeth gear are. Or if you coulde provide me with the diameter of the gears. That would help a lot!
> 
> cheers
> Thomas



Thomas - I sold the AL320 a while ago and replaced it with a larger and more capable AL346V.  Its still a metric leadscrew lathe but I have not had to work out what pitch etc as it has a thread dial chart already on the machine along with the quick change gear box.

After work today I will have a snoop and see if it is 3mm pitch and if so see what i can deduce about the gears for threading dial.

Having said that, the threading dial is just a convenience.  If I’m feeling lazy or a little tired I just keep the half nut engaged. There can be NO screw ups that way. And on short length threads its not really a material loss in time.

cheers - J.


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## joco-nz (Feb 24, 2021)

Lead screw is 3mm pitch.  had a look at the gears for the dial and they look to be Mod 1.  That is based on a visual inspection against the "to scale" profile pics in the "little black book" and by checking the measurement of the pitch on the gear.

An imperial 32 pitch looks to be too be a little big.


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## SmithDoor (Jul 23, 2022)

joco-nz said:


> I've been looking at the threading dial on my AL320G and thinking it must be usable even though the "manual" that comes with the lathe doesn't tell you anything other than how to set up the change gears.
> 
> So first off some research into threading on the lathe by reading Workshop Practice Series #3: Screwcutting on the Lathe by Martin Cleeve.
> Now this is pretty jolly complete and after reading things several times I felt I had enough of a handle on things to make the next steps.
> ...


The thread  dial for Metric threads has set gears for dial. 

A lot machinist just reverse the lathe.  

If you on a inch lathe cutting metric threads you can not use a thread dial only reverse.


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