Hafco al-960b thread dial problem

[steran50]

HI ALL,
OK Guys I am really stuck with this.
On Sunday I went to Cut a 7/16' - 14tpi BSW Thread on My Lathe (Hafco AL-960B) on a Part I was making for a Friend. It was to be first time that I had cut threads on the Lathe. I have had the Lathe from New and it is now 13 months old. When I first got the Lathe I swung the Thread Dial back out of the way, as I knew that I wouldn't be doing that much Thread Cutting (I certainly regret doing that now). I know from Memory that the Thread Dial rotated when the Carriage was wound Back & Forth by Hand, I can't remember about under Lead Screw Power though. The Leadscrew and the Thread Dial have never been used apart from initially working out the Gears, so neither can be worn.

What is going on is this: I repositioned the Thread Dial Gear against the Leadscrew, the Thread Dial rotates when the Carriage is wound back & forth by Hand. The Thread Dial also rotates when the Lathe is turned on and the Leadscrew is Turning. As soon as the Half Nuts are Engaged though the Thread Dial stops Rotating. I have tried repositioning the Thread Dial when the Half Nuts are engaged both with the Lathe turned on & off - it didn't make any difference the Dial still doesn't rotate.

I have even Physically held the Thread Dial in My Hand (Arms & Hands held stiffly or side of Hand aginst side of Carriage (Apron-Saddle) with its Gear against the Leadscrew, the Dial will still only rotate when the Half Nuts are Disengaged. I did not think Tonight to check if the Thread Dial rotates when the lathe is under Power Feed (using shaft with long keyway slot) - I will try and check this in the Morning before going to Work.

I Spoke to Grant at Hare & Forbes (Melbourne) on Monday Morning and He said that the Gear might be Slipping on the Shaft. I checked Tonight if the Gear might be slipping and it's not - the Gear is simply not rotating. According to the Manual the Gear is not Keyed to the Shaft of the Thread Dial. What I did notice though is that the Hole for the Socket Head Cap Screw that secures the Dial Indicator Casting to the side of the Carriage is larger than the shaft of the Screw.

I have not dismantled the Thread Dial Indicator to check for any rubbish in it as yet, but it seems to Rotate free enough. To Me it nearly seems like the teeth of the Gear aren't quite big enough, but yet the Thread Dial rotates when the Leadscrew is rotating. Has anyone else had this Problem or have any ideas on what might be wrong???.

[Bryan]

I don't use them but I think that's normal. Once the half nuts are engaged, the carriage and anything attached to it move at the rate of the leadscrew um, lead. So why would the dial turn? It turns to tell you when to engage, then stops, because it has to.

Edit: Watch the dial gear where it touches the leadscrew as you engage the half nuts and I think you will get it.

[Metmachmad]

I don't cut many threads but as I recall as you engage the 1/2 nut the chaser gauge stops rotating. so no problem, It's working as intended.

[Stustoys]

steran50,
That's how its meant to work.
The dial is telling you when the leadscrew is at the right angle(?) for the position carriage to be in sync. Once you engage the half nut the carriage starts to move in sync with the leadscrew, so the deal doesn't move. Make sense?

Stuart

p.s. on a slightly different note, do you have a metric or imperial leadscrew?

[steran50]

HI ALL,
It looks like You are all Correct and I was starting to think that My Lathe might be Broken. I was going to Post the same Question on Home Model Engine Machinist. I decided to do a search on their first and found the Answer ;

Qoute from HMEM 'Before you engage the half nuts, the leadscrew is driving the dial because the saddle isn't moving, when you engage the leadscrew the saddle then moves in sync with the leadscrew, so in effect the dial is not being driven any more, just one tooth is following the thread, so the dial actually stops turning. When you disengage the nuts, the saddle isn't moving in sync with the leadscrew any more, so with the saddle stopped the leadscrew is then driving the dial again.

The dial isn't disengaged at all during any cutting or moving back to the start. If you look at the dial as you go back to the start, it turns backwards, so showing it is still engaged with the leadscrew.' end Qoute.

Yes of course, how Dumb of Me. When the Carriage is stationary and the Leadscrew is turning the Thread Dial Rotates. When the Half Nuts are engaged the Carriage moves at the exact same speed as the Leadscrew, so of course the Thread Dial is going to stop turning until the Halfnuts are disengaged again.

Hi Stuart, the Leadscrew is Imperial. I thought I remembered that the Thread Dial on the 9" Hercus that I had kept rotating, but it couldn't have. I just found this Video [ame="http://www.youtube.com/watch?v=UjUfWq9j6fA&feature=related"]YouTube - ‪Single Point Threading‬‏[/ame] on Youtube where I was able to see the Thread Dial start and Stop as the Halfnuts were engaged and Disengaged.
Thanks Guys, I appreciate Your Replys.

[Stustoys]

Glad you're sorted.
I was just asking about the leadscrew to be sure you werent trying to pick up an imperial thread on a metric leadscrew.(not that that would effect the dial turning or not)

Stuart

[Dave J]

Hi Stewart,
Good to hear you have it sorted, don't worry it confuses a lot of people.
There will be a plate on your lathe telling you what numbers on the thread dial you can close the half nuts on for a particular thread.

OT
Many thanks for the emails/PMs guys very much appreciated.

My Grandfather gave us a scare as he had a slight stroke, so I have been busy with helping him and the family. He is 89 and still wanting to get back down the shed instead of being in the hospital bed, The first thing he asked me when I arrived at the hospital after the ambulance took him their, was how was my shed rearranging going, LOL.
I only started it because the week before he was over getting a job done for his home made metal lathe and it was getting a bit crowded and there where a few trip hazards I wanted out of the way him next time and we spoke about it, so his brain is fine, it's just his body letting him down.
He went home from hospital today so we will see what happens, it hasn't affected his arm very much, manly the right side of his face. He has speech and pysio therapy lined up to do.

It made me think that it wont be long before I am without him, I know it happens to all of us, but he is like my mate and has been my mentor since I was about 6 year old, as I never had a father.

Thanks again
Dave

[Stustoys]

Hi Dave,
Good to see you back, hope your grandfather continues to improve.

Now you have some catching up to do.

Stuart

[RayG]

Hi Dave,

Welcome back! we were getting worried about where you'd gotten to...

My friend's dad had a stroke last week, and so I have a bit of an idea what you are going through, I hope it works out for the best.

Just to stay on topic, I stopped using the thread dial a while back, and just leave it locked in and reverse back for each pass. Just have to remember to reverse past the backlash each time. It takes longer, but probably works out quicker if you factor in the times that I screw up.. (pun intended).

Regards
Ray