screw cutting dial

[AcieraF3]

Hi all,

Been busy moving back from the UK to the Netherlands, back to my machines!

On my Boley 5LZ lathe (metric) there is no screw cutting dial and I think that there is no possibility to mount one since the lead screw is placed in the centre of the lathe ways and completely covered. This lathe have a separate lead screw (for screw cutting) and "feed" screw (for automatic feeds during turning) is you now what I  mean.

My question is: is it possible to cut threads without a screw cutting dial and is there an other way than just not disengaging the half-nut.

Thanks in advance

Teun

[DaveH]

Teun,

My question is: is it possible to cut threads without a screw cutting dial and is there an other way than just not disengaging the half-nut.
Thanks in advance
Teun

The first part of your question is Yes you can cut threads without the dial (I very rarely use mine), but you have to leave the half nuts engaged all the time, until the thread is finished.

Your second part -sorry I'm not too sure what you are asking there - my brain cell can only handle one bit at a time

 
DaveH

[Lew_Merrick_PE]

Been busy moving back from the UK to the Netherlands, back to my machines!

On my Boley 5LZ lathe (metric) there is no screw cutting dial and I think that there is no possibility to mount one since the lead screw is placed in the centre of the lathe ways and completely covered. This lathe have a separate lead screw (for screw cutting) and "feed" screw (for automatic feeds during turning) is you now what I  mean.

Teun,

The point of a threading dial is to coordinate the position of your saddle (cutter) to a specific angular orientation of your leadscrew.  The mechanism to do this is a worm gear that is driven by your leadscrew, right?  It does not matter where the connection between the leadscrew and the worm gear is made so long as you can see the threading dial as you are working.  At the very simplest, a single index position will work for every pitch of screw-cutting you wish to do so long as you can close the half-nut when that marker lines up at your dial, right?

One thing to think about is a flex-shaft drive.  Once you have the worm gear mounted to your leadscrew, a flex-shaft can bring the rotation out to (just about) wherever you wish.  It only needs to be rigid enough to rotate the threading dial properly.

[Arnak]

Hi,

Have a look at this thread http://madmodder.net/index.php?topic=5439.0

It is a very simple to make thread cutting tool, with that you can leave the half nuts engaged all the time you are cutting the thread.

I have made one and can report that it works very well. 

You do not need to make the dovetail part as a rectangular piece of steel can be used instead to fit straight into an existing tool holder.

There is a good diagram in the latest issue of MEW.

Martin

[andyf]

The point of a threading dial is to coordinate the position of your saddle (cutter) to a specific angular orientation of your leadscrew.  The mechanism to do this is a worm gear that is driven by your leadscrew, right?  It does not matter where the connection between the leadscrew and the worm gear is made so long as you can see the threading dial as you are working.  At the very simplest, a single index position will work for every pitch of screw-cutting you wish to do so long as you can close the half-nut when that marker lines up at your dial, right?

Lew, what you say is true, and when cutting inch threads with an inch leadscrew it helps non-engineers like me who aren't in a hurry to use only one mark on the dial. But cutting metric threads on a metric lathe requires the worm wheel to be changed to suit the pitch being cut. 14, 15 and 16 teeth cover the common small metric threads up to M10 or so, and are often stacked on the same shaft, which can be moved axially to bring the right one into play. 

Teun's problem is that, with his concealed leadscrew, he can't easily change his worm wheel. One solution, if the construction of his lathe permits, would be to add an extension to his leadscrew at the tailstock end, threaded at the same pitch (though it needn't be the same diameter). Then, a threading dial could be mounted on the end of the bed, where he can get at it to change the worm wheel.

Andy

[loply]

Personally I never use the threading dial when threading.

Leave the half nuts engaged permanently until the entire job is done.

When I get to the end of a pass I kill the motor, wind out the cross slide one turn, reverse the lathe on the motor till I'm back at the start point, then wind the cross slide back in and repeat.

[BillTodd]

One solution, if the construction of his lathe permits, would be to add an extension to his leadscrew at the tailstock end, threaded at the same pitch (though it needn't be the same diameter). Then, a threading dial could be mounted on the end of the bed, where he can get at it to change the worm wheel.

I believe the dial has to move with the carriage to maintain sync with the lead-screw position.

[BillTodd]

Just read this in Tony's lathe site:

The clutch and brake lever also doubled to control the forward and reverse return of the carriage - and for setting semi or fully-automatic screwcutting cycles (though the latter required extra equipment in the form of the d32* threading accessory). When used for the batch production of threaded components the four-times accelerated reverse was especially useful and, of course, eliminated the need to disengage the clasp nuts. Unfortunately the electrical controls were clustered in a vertical line low down on the front face of the tailstock end plinth -thus leaving them conveniently out of reach as the operator was wound into the mechanism.
Screwcutting was by changewheels that, being fitted to large diameter studs and retained by quickly detachable locking discs, were easily dismounted and replaced. There was no option of a screwcutting gearbox, the makers deciding instead to offer the convenience of a well-thought-out power-feed system that enabled the operator to set the most appropriate cutting speed with the minimum of effort (a change in the power sliding or surfacing feed rate did not disturb the screwcutting setting)

This sounds like the machine has a Hardinge like screw cutting system You may not need a threading dial at all, just a user manual .

Bill

[andyf]

I believe the dial has to move with the carriage to maintain sync with the lead-screw position.

I hadn't thought it through, Bill; you're quite right.

Andy

[AcieraF3]

Thanks all,

Did some practice thread cutting with the half nut engaged and using the electric brake to forward and reverse the machine.......works great. Actually I do have a manual but it is in German 

[dmbasher]

Hi,
You need to have a dog clutch with only one "tooth" then you can open the leadscrew nuts and move saddle back and re-engage nuts without worrying about pick-up as this will be automatic.
Study ME/MEW forum where a very simple retractable threading toolholder is described with several different versions by various contributors.
I understand that EIM magazine will be publishing in Nov or Dec a series of articles on making a quick reversing system for a variety of different lathes. This system incorporates a single - tooth dog clutch. This should greatly speed up screwcutting. Maybe you should be patient and wait til you`ve seen these.
Hope above helps.
John.

[BillTodd]

Thanks all,

Did some practice thread cutting with the half nut engaged and using the electric brake to forward and reverse the machine.......works great. Actually I do have a manual but it is in German 

Phone Tony Griffiths  from lathe.co.uk, he may have a english manual or be able to explain how to thread with the boley system. (I suspect that, like my Hardinge, you can just reverse the lead screw without losing sync with the spindle.

Bill

[Philip Burman]

Hi Teun, I also have a Boley 5LZ.

Using the brake/clutch switch (C) to stop and then reverse the spindle at 4 times speed is the correct method for threading on the 5LZ. For short to medium length sections it's faster than disengaging the half-nut and using a thread dial.

I've had mine for a year and a half now and pretty much know my way around, although I'm not an expert.

I'm up for trading info and knowledge if you are interested. I have a complete English manual consisting of:

- Test Report BON 320/3E B1. 1
- Instruction BON 320/3 B1. 2
- Hints for fitting of Electric Multi-Disc Clutches
- Leaflet De 16
- Transport Instructions BON 715-6
- Erection Diagram BON 715 -7
- Controls and structural parts BON 715-8
- Headstock assembly drawing BON 715-9
- Leadscrew bearing BON 715-10
- Cutting Speeds in meters per min. BON 703 / 1
- Register of Change Gears BON 377/93
- Lubricating Instructions BON 705/1ae
- Instructions for d 32
- Wiring Diagram

Phil:)

Thanks all,

Did some practice thread cutting with the half nut engaged and using the electric brake to forward and reverse the machine.......works great. Actually I do have a manual but it is in German 

[hopefuldave]

[quote
Hi,
You need to have a dog clutch with only one "tooth" then you can open the leadscrew nuts and move saddle back and re-engage nuts without worrying about pick-up as this will be automatic.

/quote]


I believe you still have to leave the half-nuts engaged, but the spindle doesn't require reversing, just the leadscrew? On the Monarch 10EE and diverse Hendeys, Holbrooks etc. the apron control allows disengaging the dog-clutch and throwing it over *to reverse the leadscrew* when thread cutting, Monarch offered a (pretty rare) high-speed electrical reverse for the leadscrew complete with limit stops etc. I'm trying to come up with one for my machine (450W DC motor, pair of bevel gears, limit switches etc.) to hang on the end of the leadscrew... After the dog-clutch (rough sketch below) which is a fair project in itself (yes, pics will be forthcoming once I get the necessary Tuits!)

If the half-nuts are disengaged, particularly on "foreign" threads (e.g. anything other than tpi pitches on an Imperial lathe), although the dog-clutch ensures the same angular relationship between spindle and leadscrew (as it runs at spindle speed), releasing then closing the half-nuts could drop them into mesh any integeer number of turns out of step - fine if *and only if* the cut thread is divisible into the leadscrew pitch, not if (e.g.) cutting a Metric thread with a 6 tpi leadscrew...

Dave H. (the other one)

EDIT: although it may not look like it, that's a single-tooth clutch, as one dog's wider than the others...