Thread: Screw cutting without Chasing Dial

Well the two other ways you could have been doing it is , with an instant stop foot brake lathe or a 3 phase instant reversing motor .
If you don't have either of these features you will need to disengauge the halfnuts to stop at the end of the cut. Then re-engauge with the thread chasing dial to start again.
However I think the AL 336D has an instant stop foot brake and a thread chasing dial but you will not really need a thread chasing dial with a foot brake lathe unless you have a tool breakage or tool movement that requires you to disengauge the half nuts to re-setup and start again.
It still would be a good idea to get the teacher to show you how to use a thread chasing dial just incase you have to disengauge the halfnuts for some reason.
There still is another adhock bodgie way of lining the tool back up into the thread form without using the thread chasing dial. With the lathe set at the right speed and thread feed engauge the half nuts . Run the lathe until the tool is oposite the half done thread . Adjust the compound slide until the tool is exactly opposite the thread v form and move a bit at a time cross slide and compound until the tool is just clear of the work but lined up in the v form. Then pull the lathe forward by hand watching how much back lash is present and readjust for the forward movement . Run the lathe backward to the start of the thread position and run it forward watching the tool travel along just clear of the work . If it is lined up well then run it back adjust in to a new cut depth and engauge forward.

Here we go again.

If you are now LEAVING the half nut engaged and are reversing the tool under power on the Colchester, then just do the bloody same thing on the Hafco lathe.

If you buy any lathe with a chasing dial fitted, just take that $tuffin' stupid confusing thing of the machine, chuck it in the draw and forget about it forever. Oh, remember where you chucked it, because when you sell the lathe, re-fit it then.

If you do happen to $tuff up when cutting the thread, do as Retromilling said to do, chase the half formed thread with the topslide and your away again.

Now the difference in threading on the Colchester and the Hafco is ZERO, it's all the bloody same thing, no matter what brand of lathe your using.

The reason that the chasing dial was thought of and fitted to lathes, was to utterly confuse ALL new comers, it's sole purpose in life is to make it 'effin' difficult to cut threads.

Chuck it away, you'll be much happier without it, life's hard enough now, without all this drama over a chasing dial.

Now print this answer off and take it to the school and show the teacher what I have written, then have an open class disscussion about this lot, you will be surprised at what the teacher say's.
If the teacher dissagrees with this lot, then please let me know the outcome.




regards radish

Radish is right , I studied up how to use a thread chasing dial way before I got a lathe but one time I was at a machine shop watching this guy belt this lathe back and forth cutting threads and never using a dial . I watched intently for a while and fell in what was going on. He was just wacking it into reverse each time . A light went on in my head and I realised if you have the right lathe you don't need the dial .

what radish says
leave your half nuts engaged and use the foot pedal to stop, withdraw the tool, reverse feed direction, start machine to run back to start of thread, stop again, change feed direction back, advance tool, start machine and take another cut.
another difference you will find I beleive is the hafco will have change gears whereas the colchester (i cant remember for sure) might have a universal gearbox where change gears not required. Its been a long time since I used a colchester so I cant be sure.
Change gears are used on some smaller lathes in order to get the feed rate right for thread pitches across the range of threads the machine can do.
Lastly, the AL-336 has an imperial leadscrew. The thread chasing dial will only work on imperial threads as with metric there will be a slight compounding error with the relationship between leadscrew pitch,thread form pitch and thread chasing dial drive sprocket pitch if cutting a metric thread that cannot be compensated for with the change gears. The change gears help get the feed rate right for your pitch, but the thread chasing dial drive sprocket running on the imperial leadscrew doesnt allow you to engage at the right point for cutting a metric thread if half nuts are to be disengaged then engaged again between cuts.
Basically, to cut metric threads on the AL-336 you will need to do what radish said anyway.

Guday Ben
Check out this post, it will explain everything you wish to know. I wrote this some time ago for newbie's wanting the best info on how to screwcut with the lathe. Also, study the attached drawing for the full details.
https://www.woodworkforums.com/showthread.php?t=86435

If you have any problems, send me a message and I will help you out. Regardless of all previous (negative) comments, the quickest and easiest way to screwcut is to use the Thread Dial. This is without a doubt, the most efficient and fastest method for locating where to "drop in" on the Leadscrew to position the tool. Unfortunately, the thread dial only works at its best when using an Imperial Lathe and cutting standard Imperial threads. For cutting any metric thread, the halfnuts must be left fully engaged and the lathe stopped and then reversed back to the start position. For a new beginner, the act of stopping and reversing the lathe can be very unnerving especialy when trying to stop the thread at a shoulder. If a lathe doesn't have a spindle brake, stopping at the exact spot is near impossible for a beginner. I have cut many threads at 200 rpm and never had to stop or reverse the lathe. You cant cut at this speed if you have to stop and reverse the lathe and keep the halfnuts engaged. You can also cut "Two-start" threads very quickly and easily if you use a thread dial indicator. This was a project I had my trainees in the USA perform and they did a perfect job. They made the bolt and then made the nut to fit.

Kody

that post sure is informative kody.
i didnt mean to sound negative. in truth, at least in my case, leaving half nuts engaged and crashing machine fwd to reverse where possible is a product of my looking for a shotcut.
In reality, on a small lathe where you cant do it, it is most likely easier to use the dial where you can because as you say it is hard to stop in the right spot for somebody who is new to it.

Ben, ultimately its up to you whichever way you find the easiest i suppose. Reading kodys post is going to be more helpful than my posts on this one

Originally Posted by Kody

Guday Ben
Check out this post, it will explain everything you wish to know. I wrote this some time ago for newbie's wanting the best info on how to screwcut with the lathe. Also, study the attached drawing for the full details.
https://www.woodworkforums.com/showthread.php?t=86435

If you have any problems, send me a message and I will help you out. Regardless of all previous (negative) comments, the quickest and easiest way to screwcut is to use the Thread Dial. This is without a doubt, the most efficient and fastest method for locating where to "drop in" on the Leadscrew to position the tool. Unfortunately, the thread dial only works at its best when using an Imperial Lathe and cutting standard Imperial threads. For cutting any metric thread, the halfnuts must be left fully engaged and the lathe stopped and then reversed back to the start position. For a new beginner, the act of stopping and reversing the lathe can be very unnerving especialy when trying to stop the thread at a shoulder. If a lathe doesn't have a spindle brake, stopping at the exact spot is near impossible for a beginner. I have cut many threads at 200 rpm and never had to stop or reverse the lathe. You cant cut at this speed if you have to stop and reverse the lathe and keep the halfnuts engaged. You can also cut "Two-start" threads very quickly and easily if you use a thread dial indicator. This was a project I had my trainees in the USA perform and they did a perfect job. They made the bolt and then made the nut to fit.

Kody

What do you mean negative comments . No one is putting forward any negative comments.
You can cut perfect threads with or without the dial gauge if you have the right lathe. End of story.

Keep it civil gentlemen.

Thanks for everyone's responses. Sorry for starting another Screw Cutting War

Just to clarify my earlier statement the TAFE lathes do have Chasing Dials, I just never noticed.

You're right Retromilling in saying that I should get the teacher to show me how to use it. I should at least know how to use it, even if I never do.

I hope you're right Radish and Brisbanefitter- That I don't really need it for most things and I can ignore it. I like the way I've been doing it on the Colchester. Although I haven't screw cut up to a shoulder yet.

I had read your guide for beginners Kody (very good article), just thought I'd ask the question to get it straight in my head.


Thanks again everyone.

hey there ben,
no problem at all, no war here.
there are really 2 different ways to cut a thread, with or without the chasing dial and you will always get opposite parties who prefer each method telling you what is the best.
To be totally honest, i was taught to use the dial at tafe, then when i got back to work was told thats not necessary and showed how to crash back and forth in feed direction and sworn black and blue by my old german boss that using the dial was rubbish and time wasting and so on etc etc etc (plus he had big boots that would have left a large imprint on my backside if he caught me doing anything other than what he said).
if cutting to a shoulder, if possible, its far less hairy to b able to use the dial and drop out of the feed at the point where you think its going to go bang, and not have to compensate for the slight overrun you will get when stopping spindle if leaving nuts engaged. Using the dial when you can might actually save you from the odd broken tool.
That said, I will still use the half nuts in crash me back and forth method to cut threads, only because I can and fell comfortable with it.

good luck and I hope you enjoy the life and times of what is a fitter and turner

It appears that there seems to be a bit of concern with threading up to a shoulder.
Most if not all threaded items with a shoulder that I have seen have an undercut at the shoulder.
This undercut appears to be at least 1 pitch wide and a little deeper than depth of thread.
This would I think then leave enough room to retract your threading tool before running into the shoulder,as well as removeing any stress,fatuige or fracture points from the item.

Ben I've seen that very lathe (well actually it it wasn't the D rather the standard version) demoed at H&F screw cutting using the thread chasing dial. It looks like a pretty nice lathe, well done. I'm surprised by those who claim it's faster to stop and reverse the lathe as personally I couldn't see much difference, you can wind the carriage back very quickly, so it seems more a case of swings and roundabouts from what I've seen.

Hi Pete, good to know I'm on the right track with equipment.

The way I've been screw cutting at TAFE so far is with an undercut. We've been running the tool into the undercut area, stopping the spindle and winding the cross slide out and then winding the carriage back to the start of the job. Then using the DRO to determine how far to wind the cross slide in for the next cut. Hence why I'm after the 336D, because DRO is awesome.

But you guys are saying that with a foot brake I can cut up to the shoulder (with or without an undercut), stop with the brake and just reverse the spindle with the tool in exactly the same position. Then just wind in on the cross slide for the next cut. Does the backlash in the leadscrew have any affect on reversing? Or is the pitch of the cut sufficient to compensate for the backlash as the tool starts to move backwards? Or am I dreaming?

Ben, hey I'm just starting down this path too so my opinion is worth about 9/10ths of bugger all, but I remember this lathe and have seen it used as described.

To cut metric threads on this machine you will definitely have to reverse the machine, but I've never used anything with a DRO so maybe it's possible to use that. I doubt it however as I believe the threads are not precisely metric, fine for typical short threads but the errors will accumulate.