Single point threading questions

[zeusrekning]

Marv...I'll delve into your treatise after I post this. It looks like a pretty fair read. I think I also just won a bet with Tim, due to your post....(grin). I bet him you'd have a prog-lette for the problem...LOL
Steve

Yeah , Yeah. I'm still looking for Marvs formula on the correct number of wipes to make after burrito night.

I really appreciate all the help with this. I agree with Greenie that the reverse method is the easiest. I also know that a lot of time the straight plunge method will work. But compound feeding is the more preferred way with most (most not meaning all) paid machinist. Our CNC's also feed in this way an they are very rigid machines .

Like I said earlier, on the Hardinge there was no thread dial you just reversed the spindle, best I remember. But does instantly reversing the spindle cause any damage internally?
Tim

 

[Bogstandard]

Mcgyver,

I didn't want to quote angles in my post, due mainly to the fact we now have a lot of UK members who work with the older UK threads, 55 degrees, and of course BA at 47.5 degrees, and whatever comes between. Whereas the US and Metric standard seems to be 60 deg. Just to prevent confusion to beginners.

Imagine one setting up his compound to, as you rightly say 29.5 (US or metric), then cutting a BA thread. Slight disappointment all round.

So just to put things straight on that score, you find the angle of the thread, halve it, subtract 0.5 degrees, and set your compound (topslide) over by that amount. But don't forget, you have to set the cutting tool square to the job using your fishtail threading gauge after you have set over the compound (topslide).

Just to reiterate my previous posts on the matter and to add a little more detail, touch on with your cross feed, zero your cross feed dial (if you can), if not, remember the 'touch on' setting. Put your cuts on using the compound (topslide), after the cut retract the cross feed to allow you to wind back to the start, advance your cross feed to zero or 'touch on' setting, then another compound feed and cut. Repeat until the nut starts on the thread but is tight. Then 0.0005" to 0.001" cut is put on using the cross feed, and a cut taken at this setting, to clean up the rear thread face. If the nut is still tight, take another cut with no settings changed. Try nut again, if still tight, try another 0.0005" cross feed cut. Do this until the nut goes on smooth. For a beginner, I would suggest dropping in on the same number each cut, after a bit more experience is gained, try the other numbers on the dial, by referring to previous posts to what number combinations you should be using. Marvs post on that bit is easy to understand.

John

 

[bentprop]

And now,just to upset the applecart,answer me this:
Why does my thread dial have only 3 marks,none of which is numbered?
FWIW,I tried cutting an 8tpi thread.Since this is the leadscrew pitch,I felt confident about cutting that thread.I did not disengage the half nuts,rather stopping the lathe,and reversing it back.What I ended up with looked more like 24 tpi than 8tpi,and rougher than a bears a*#e
Does this mean I have too much backlash in the leadscrew?,or could there be another reason for my dismal failure?
I did not use the thread dial,since the pitch I wanted was the same as the leadscrew.
Hans.

 

[DickDastardly40]

And now,just to upset the applecart,answer me this:
Why does my thread dial have only 3 marks,none of which is numbered?
FWIW,I tried cutting an 8tpi thread.Since this is the leadscrew pitch,I felt confident about cutting that thread.I did not disengage the half nuts,rather stopping the lathe,and reversing it back.What I ended up with looked more like 24 tpi than 8tpi,and rougher than a bears a*#e
Does this mean I have too much backlash in the leadscrew?,or could there be another reason for my dismal failure?
I did not use the thread dial,since the pitch I wanted was the same as the leadscrew.
Hans.

Hans,

The pitch of the leadscrew may be 8TPI, however the gears between the spindle and the leadscrew determine what the cut thread will become. If you adjust the gears/gearbox to a 1:1 ratio so for one rotation of the spindle you get one rotation of the leadscrew the lathe will cut an 8TPI thread.

Hope this helps

Al

 

[Bogstandard]

Hans,

The threading dial for your machine must be a specific type to your make and model, and this is the one time I will have to say, you would need to read up on it, and see how it is used with regards to dropping in.

With regards to the multistart thread, as you have said, maybe too much backlash in your gear train, or even the half nuts. I would also check your gear train, just to make sure it is set up for 8TPI, maybe you have a metric conversion one in there instead of an imperial.

John

 

[shred]

Shred
I didn't mean to state anything, but to present an observation, which was the reason for the questions. When Tim engaged at the #4, the resulting cut was a nice beginning for an 8TPI thread. When he next engaged, he engaged at #2. This set whole new path for the cutter which, from our OBSERVATION, was apparently dead center of the ridge of the first cut.

The questions we had were basically :
A.... Once you choose a number on the thread dial, should you continue using that number?

That's the safest-- see John's post previous, but as Marv demonstrated, there's more efficient options, depending on the thread pitch.

B... By engaging at the #2 of the second cut, did we actually begin a multi-start
thread?

If I understood right, for an 8TPI thread, it should have dropped right into the previously cut thread. I know I've used any-line on even threads and been ok with it.

The annoying one is when you forget and start the initial thread not on one of the lines. Often the books neglect to clearly mention that would be a good idea.

 

[mklotz]

Yeah , Yeah. I'm still looking for Marvs formula on the correct number of wipes to make after burrito night.

In your original post, you asked about learning how to use the threading dial. I attempted to answer that question. If my answer exceeded your patience level, just ignore it.

 

[lathe nut]

Bogstandard, I have a 14X40 got it a few months ago, I sure like it, it does have enough get it power, I am proud to say that I got the single point threading learned, got the bit sharpened right, angle right and after about 15 tries cutting some 1/2X13 threads got it, that is a real rewarding task to accomplish, thanks to you fellow for the information that I got here, Lathe Nut

 

[Cedge]

Marv
As usual, your post was informative and useful. It addressed severql points I was looking to clarify in my mind. I only ignore those posts which get too numerically challenging for my single remaining gray cell. Mother warned me about flashbacks....LOL

Steve

 

[zeusrekning]

In your original post, you asked about learning how to use the threading dial. I attempted to answer that question. If my answer exceeded your patience level, just ignore it.

Well I guess the humor was not relayed through text, so sorry.
Marv your help is always greatly appreciated and my patience level is easily exceeded.
My humor was more aimed to Steve b/c we always assume when we are stuck that you may have mathematically solved the problem on your site.
Grin it's easy.
Tim

 

[mklotz]

Ok, maybe I was a bit over-sensitive. Let me try to explain.

When someone asks me a question, I always attempt to give as complete an answer as I can. After all, if one understands the logic behind some of these processes, one is more likely to remember the technique. People who are looking for a quick and dirty answer to everything often find my responses too lengthy and don't want to take the time to read them. That's perfectly ok with me because I refuse to "dumb down" responses simply to achieve brevity. I don't do "sound bites". Einstein said, "Make everything as simple as possible, but no simpler."

As to "having a program for everything"... I've been helping machinists for a long time and I've come to understand that most machinists can't do the mathematics even if you show them what they need to do. The only way to help them is to provide a "plug and play" mechanism that will request the needed information, check the input for credibility, do the relevant math, and lay the answer out in a form they can understand - in other words, a program. As a result, many of the programs on my site are quite simplistic - the stuff any decently proficient math student would do in his head. Nevertheless, most of those programs have been requested by machinists so they represent stuff that some guys like us can't do by themselves.

 

[bentprop]

Sorry,Tim.I didn't mean to hi-jack your thread.But since I was referring to my "funny" thread dial,I thought it seemed relevant.
John and Al,your answers got me thinking a bit more about this,and I think I have it now.The geartrain is set up for metric,since that is what I use most.That's probably the reason for my "unique" thread on the part.Thanks again,chaps.

 

[zeusrekning]

After all, if one understands the logic behind some of these processes, one is more likely to remember the technique.

I agree with this 100%. When Steve was over I had to trig out what my compound feed @ 29.5 deg was actually taking in X. I can't remember the quick way of doing the math so I have to write it out and divide both sides by the same number to simplify the equation.
The only reason I remember the basics is b/c I had a math teacher in High school that explained what the math does and not just the formulas. I could settle for a simple "Start on this number for even threads" answer but I really need to understand how it works for it to get filed properly in my head and that is still hit or miss.

I actually have plans to put a computer in my shop mostly just to run your (Marvs) programs but understand I may have an ignorant question occasionally to understand what I need to do.

Back to the original question. If I am understanding correctly my method of always starting on the same number and using only that number will work. I also like to start at the same Z dimension (usually by marking the table with a white out pen).

Bentprop,you didn't highjack. But if you did I'm here to read so high jack my threads all you want.

I don't know anywhere else I could get this much help so quickly. Thanks to all that helped.
Tim

But what is everyones opinion on instantly reversing the spindle?

 

[mklotz]

Zeus,

Questions are always welcome. As are suggestions for programs to make your work easier. (That's how many of the programs originated - suggestions from machinists needing computational help.)

My lathe has a single phase motor so instantaneous reversing isn't a possibility. Nevertheless, even if it were, I wouldn't do it. If you're going to spend all that extra time watching the carriage plod to the right, the couple of extra seconds to let the motor coast to a complete stop isn't going to matter, right?

Starting each pass on the same number will always work but, per what I wrote, it's not necessary. If the lathe is running slowly (often a requirement when threading), you'll soon tire of "waiting for your number to come up".

Mentioned in all the books but I haven't seen it here and it's worth repeating. Always make your first pass a "scratch" pass and then use your fishtail gage to confirm that you are indeed cutting the pitch you wanted to. (Can't tell you how many near botches I've averted with that trick.)

 

[chuck foster]

this is a very interesting post...........it brought back memories of threading all types of stainless steel.

i used to work in a small shop that made boat propeller shaft, they were made out of 303,304,316 and
a very brutal one called acromat 22
acromat 22 required diamond tools to be used.
we did shafts up to 25 feet long and 10" in diameter, we had a lathe with a spindle bore of 18" and the bed was about 20 feet long.
we did all our threading with the compound set to 29 1/2 degrees (i think........25 years ago )
the threads were so big we never used threading dies to chase the finished thread, instead we used the three wire method to make sure they were spot on size.

one day the other guy that i worked with used the wrong size wire and made 10 or 15 big shafts with the wrong size threads.
thankfully the threaded portion was too big..........the bad part was i had to put them back in the lathe and pick up the thread and
re cut them to the right size.
it was no small job considering the size and weight of the shafting.

it would take all day to cut some of these bigger threads......i miss that job because every day we did some thing diffrent .

chuck

 

[Cedge]

Marv
I do hope no offense was taken due to the banter Tim and I have admitted to. While Tim was efficiently sorting out numbers I was the first to admit that what he was doing is beyond me. I did, however, bust him when he forgot to divide the results by 2....(grin)

You need to understand something. To those of us who are among the math deficient, you and your prog-lettes are a god send. When we joke about the fact that you probably already have one for the current problem, it's not derogatory in any manner. We've come to trust your offerings to the point where we really do assume you've already blazed the trail for us.

When we include you in a jest, it's just that... an inclusion into the fun. Rest assured, we might laugh with you and we might have a bit of fun with you, but no one here on the board would dare laugh at you or make fun of you. WE ain't a letting highly valued resource like you escape that easily...LOL

I have an acquaintance who has a MENSA level mind. A great guy, even if a little socially awkward. I learned long ago that he strained just as hard to reach my level in conversation as I sometimes struggled to follow him at his. The first time I popped of with some ribaldry, with him being the targeted subject, I nearly made the guy cry because he thought I was either mad at him or making fun of him. Neither being the case, I apologized and tried to "explain the comment". I'm not sure it ever clicked with him that day, but since then he sometimes stops me and asks if some particular statement was me being facetious again...LOL. It's probably not as tough being smart as it is being a little bit ignorant, but neither one is a total walk in the park.

Ya got our respect and our acceptance.. now relax and enjoy being "one of the boys"

Steve

 

[Circlip]

Zeus, go back to reply No 13 for instant reverse, and while I agree that the size/weight of Chuck's shafts presented a problem, why do some people panic about putting the job back in and picking the threads up again?? As long as the same gearing is selected, drop in the lathe nuts, power feed with the tool clear onto a threaded part to take up any backlash, stop the drive, reset with top and cross slides, zero dials,retract cross slide driveback and Robert is your Fathers Brother? No Problemo.
Regards Ian.

 

[zeusrekning]

we did shafts up to 25 feet long and 10" in diameter,chuck

Chuck you can have that job! What kind of wires would you use on a shaft that big? We used to do a lot of pump shafts and the ones used in corrosive environments were always 300series stainless and some were the duplex SS's.The customer once sent me a drawing to quote for some pumps in Texas (that help with hurricane flooding).These shafts were approx. 6" dia 10' long and almost the entire length had to have an acme thread cut on it. I stayed away from this one.
Tim