Thread: ACME 1/2 - 8 LH rod available ?

oh i didn't really think about it on a safety standpoint.

[ame="http://www.youtube.com/watch?v=DgwsigIyz0c"]http://www.youtube.com/watch?v=DgwsigIyz0c[/ame]

Andre, my angry face wasn't directed at you but at the makers of the film, and the operator. I think it's ok to show the link, since the point has been made. Just my view.

Thanks for posting that Andre, great video, and a flash back to the days when machinist's wore ties...

I think all the key steps were covered pretty well, the only bit that could have been done better was comparing reversing with the half-nuts engaged (which is what I always do anyway) versus reversing by hand and using the thread chasing dial. It might be just my lathe but cutting metric threads I can't get consistency unless I keep the half nuts engaged.

Never mind Bryan, he's just jealous of the tie...

Regards
Ray

Something in that video I dont recall having seen before. Marking center height on the quill of the tailstock. 3.33

Stuart

Thanks for that Andre. I don't go on You tube to look at videos, and only see them if I am sent a link to a specific one like this.

I might be the only odd one out here , but I don't see any problem with that video and wear similar cloths myself in winter time. He is an experienced operator and he has probably done it his whole life wearing the same type of cloths without any accidents. It also looks like the lathe is probably only doing 20 rpm, if it was going to fast the wedge holding the lathe dog would fly out.

We are lucky over here with warm weather, but with some of the shops over their it could be snowing outside, so it is way to cold to roll up your sleeves.
I agree loose clothing around lathes is no good at all and should be taken off, but his sleeve looks to be buttoned up tight.

Ray,
My lathe is the same, you need to keep the half nuts engaged doing metric threads, but I would rather have the imperial lead screw, than be changing all those gears on the thread dial with a metric lead screw.

Stuart,
I checked the thread before posting this and see you picked up on the tailstock mark as well. A great idea as long as you have no movement in your tailstock quill, but not a problem on something like that lathe as it's a quality one.

Dave

Slight side track...
I suspect that I've thrown it out, but there was an article in MEW (I think) on thread indicator dials some time ago, where the writer went into the maths of it all. It came down to the fact that 5" was the smallest integer dimension between metric and inch measurement and so any lead screw indicator for thread cutting metric threads on an imperial lead screw lathe would have to have 127 teeth on it to indicate properly (as the indicator is really showing the points where the spindle and the lead screw are in the same angular relationship). For most jobs it's easier to keep the 1/2 nuts engaged.
I much prefer metric for calculations over fractional dimensions but tpi seems a lot easier than pitch for threading. If only when the metric system was first developed they had gone for 25mm=1", this stuff would be so much simpler.

Michael

Hi Michael,
That sounds like and interesting article, anyone have a copy?

Dave

Hi Michael,
That sounds interesting. My first thoughts are that on average you'd have to wait the amount of time that it takes to cut 7.5" of thread for pick up. So unless the job was longer than that, as you say it would be better reversing(though I do wonder on my sort of lathe just what the motor thinks of that idea)

Stuart

Originally Posted by PDW

If I was going to do it again, I'd cut the thread root first, same as a square thread, then clean up the flanks. That would be a lot easier and I think you'd get a cleaner thread.

PDW

I tend to agree with PDW on this point. It might be a bit more messing about, cutting the root then the two flanks separately, but unless you have an A grade machine in first class condition it will be difficult to cut an acme thread with a toolbit in the Acme form. The reason being is that as you advance the tool on each successive cut the toolbit has to cut at the front and two sides simultaneously,- not an easy task.

Hi Stuart,
Correct me if I am wrong, but if my calculation is right, having a 127 tooth gear on the thread dial with 8 TPI lead screw, would mean only being able to drop in ever 15,875 inches on the lead screw.

Or waiting to for the lead screw to turn 127 times, and at a threading speed of say 60 rpm cutting a 8 TPI thread would take around 2 minutes each time. That would give you plenty of time to reset the cross slide and dial in another cut on the compound, LOL
Still an interesting idea that I hadn't heard of before.

Dave

Hi Dave

Originally Posted by Dave J

, would mean only being able to drop in ever 15,875 inches on the lead screw.

Yes.. But, now and again you'll be lucky and not have to wait at all, other times you'll have to wait the a full turn. So the maxinum wait would be about two minutes. If you were cutting a 1mm pitch thread it would be closer to 7 minutes.

Stuart

Looks like the MEW article was April 2009 (see below for previous discussion) -
https://www.woodworkforums.com/f65/im...adscrew-97780/

Michael

I was here then, but don't remember it.

Stuart, reading that it looks like we have it all wrong, because setting it up off the lead screw it wont do part turns of the lead screw, where his set up was directly off the spindle with change gears for different pitches, just like you have to do with a metric lead screw.

Mike sorry for the OT, have you worked out which way your going to go. I am thinking of making a bit just for fun to see what it's like to cut.

Dave

Hello Dave

Been thinking about it . I will try and go ahead with it , but I need a follow rest for the Sheraton 9 , they are not cheap ( repro from tools4 cheap ) and its one of those things you use once in five years. Been reading up on them on that USA forum. They say roller bearings are the best tips rather than the plain brass tips , which wear quickly . I have a ACME thread gauge on the way ... in the post. Somebody did post about the roller bearing tips who was that ? MIKE