Need info on cutting threads and what is a dial indicator for

[Swagerman]

OK, I'm slowly working my self up to try and cut some threads on my HF mini-lathe.

So, we know with the proper cog wheel gears in place we should be able cut threads, but what in Billy blue blazes is the little dial indicator for...how does it work in relation to those mystery gears being in the proper places. (see photo of dial indicator on HF 7X10 lathe, its the little black square box)

http://i42.photobucket.com/albums/e321/44and45/Thread_dial_y.jpg

The dial indicator just sets there with a toothed shaft hanging down below it and no apparent connection to anything. The dial on top has 7 numbers with marks inbetween those numbers...it just spins by finger movement, what is its function???

Is this dial indicator missing some parts???

Any help would be appreciated.


Jim

[fishhawk]

well it's for (lack of a better word) timeing so when you make threads you watch the marks and engage the half nuts (or feed) at the same time every time

[R.M.]

It's pretty complicated to try and explain in a posting, but there will a screw going through the side of the so-called "indicator". You loosen it a bit, and you will be able to rotate the housing to engage the gear with the lead-screw. You only use this when cutting threads, and yes, it is used for timing you cut, so to speak. As your carridge is running down the ways, with the half-nuts engaged, the dial doesn't turn.

Hope this answers at least some of your questions.
R.M. (an old retired machinist)

[chevyiron420]

you cant cut the full depth of the thread at once. you have to take small cuts, over and over. you use that dial to time the feed engagement. i once threaded a barrel on a lathe without one! good greef!-phil

[fishhawk]

glad those guys are more "articulate" than i am

[Swagerman]

Wow! I can't tell you how much this has helped me understand that stinking little black box for what it is...after all the years I've had this mini-lathe. Harbor Freight is poor in sending any instructions with their product.

The lightbulb just went on between my ears, yes the lights are on and somebody is home.

That hex screw on the side of the black indicator box has to be loose to allow the indicator box shank to be moved against the lead-screw travel. Is that right? Then one tightens the hex screw again while the box is bears against the lead-screw.

At least that's the premise I'm going on until I actually test this out on the lathe.

Any other help out there...thanks to the above contributors.


Jim

[fishhawk]

from what i can see...YUP!

[Swagerman]

OK, you wonderful great knowledgible gents, my next question...

What dial setting on the indicator read-out should I have it set on for cutting 7/8X14 threads.

I'm assuming this indicator box and shank is what determines the depth of the thread cut.

Jim

[fishhawk]

not quite sure if i understand your quiestion. if your talking about the same thing we have been all thats for is a indicator of when to engage the self feed the number of threads per inch is set up in 2 ways either setting gears into the proper position or a "quick set" which is basicley setting the handel to the right position

[e15cap]

Get a copy of How To Run a Lathe by South Bend and it becomes much clearer. Try your local library.

[Swagerman]

not quite sure if i understand your quiestion. if your talking about the same thing we have been all thats for is a indicator of when to engage the self feed the number of threads per inch is set up in 2 ways either setting gears into the proper position or a "quick set" which is basicley setting the handel to the right position

================================================== =

Fishhawk, what is setting the handle to the right position? Which handle are you refering too.

I'm getting the feeling after testing the engaged dial indicator, that it really does nothing at all to mechanically operate the thread cutting. What's up with that???

Apparantly the only thing that does the thread cutting is changing the gears, (little cog wheels).

Here I was thinking I've finely hit on the mystery of thread cutting by utilizing the blasted dial indicator.

At this point I'm going to need some thread cutter bits, maybe some internal boring thread cutter bits. Then its off to the races...I hope.


Jim

[Buckshot]

...............It's a "Thread Chasing Dial". It has nothing to do with cutting the threads except to tell you when to engage the half nuts. Also:

1) Clean the swarf and chips out of the leadescrew threads. Easy to do. Get a piece of yarn and loop it around the leadscrew once. Wet it with oil and turn the leadescrew slowly, letting the yarn run down the screw while you hold the yarn.

2) Oil the leadescrew in the vacinity of where the halfnuts will run while engaged. I use 90 wt EP gearbox oil applied with a pump oiler, but an acid brush or similar works too. Any oil is better then none. There is considerable pressure on the flanks of the leadescrew-halfnut threads when engaged, as it is advancing the carriage plus cutting.

The thread chasing dial probably has 7 marks due to also covering those heathen communistic metric threads. For Imperial threads the dial will have 4 or 8 marks. Regardless, your dial will be useable and since you have no instructions with your lathe (probably print them off from Harbor Freights website) I'd just engage the half nuts at the same mark each time.

As was mentioned get that South Bend lathebook. It will explain and show photo's of setting the compound to 29* or 29.5* and why you do that. Why and how to zero out both the compound and crossfeed dials, and how to grind a 60* bit for threading.

Since the toolbit is a 60* angle, each side is 30*. You feed with the compound, and since it is at the angles mentioned, only one side of the bit cuts. Feeding directly in with the crossfeed cuts from both sides and the chips interfer with each other. Hpwever, when a thread is about done, you can feed in a half thou with the cross slide vs the compound to take a final finish pass. It's all in the book.

It may seem difficult to read about it, and very complicated. It is not and when you do it a couple times it will all falll together and you'll be a thread cutting maniac.

.................Buckshot

[grumpy one]

To use the chasing dial successfully you need to be cutting the same kind of thread (inch or metric) as your lead-screw has. You can cut inch threads with a metric lead screw and vice versa by using a 127 tooth gear in your gear train. However when you do so the chasing dial can't be used - you have to keep the half-nuts engaged and reverse the lathe to move back to your starting position. This is (IMO) a convenient way to operate anyway - my lathe, which started life in a German toolroom, was not designed to use a chasing dial and doesn't have one. I've never regretted the lack.

[e15cap]

Americanmachinetools.com has a section on how to use a lathe. Take a look and the clouds will clear. Roger

[45nut]

Swagerman I have the manuals from a long gone Smithy lathe I would be happy to send for the price of postage if you are interested.

[44man]

I have the Smithy and have to reverse it for the next cut. Talk about backlash! The only safe way is to back out the crossfeed a little or it will cut on the reverse path too. Even new half nuts didn't help. The whole machine is backlash city even after I worked it over. I don't know what I would do with a good machine!
I envy some of you guys.

[Swagerman]

.45Nut, sent you a PM with my name and address.

Man, this lathe info is like learning Greek. I seldom understand half the terms you guys are using.

Still trying to put together the concept on the dial indicator. Like when does one engage the lead screw, and what number on the dial indicator do I go for? Can you engange the lead screw while the lathe is running, that doesn't sound plausible.

What lathe speed should it be turning for threading work. What's with the direction lever on the back of the little lathe, how and when is that used...if its used in thread cutting.

Thanks, Jim

[44man]

I would never dis-engage the lead screw until the thread is done. Never take it out of gear. Just back off the cross feed a little, reverse back out and reset the cross feed for the next cut. If you miss by a few thousandths by going out of gear, the thread is screwed, hows that for a pun?
Shut the machine off at the end of the thread, back off the cross feed, hit the reverse button and turn the machine back on. The motor will keep moving a little after shutting it off, so allow for it by shutting off before the end of the thread is reached while in the foreward mode. In reverse you can stop anytime after going out of the material. Very tricky but I don't dare move anything or I will never get back in the thread.

[Jon K]

Read the South Bend book. Get a Machinery's Handbook. Do the math, Mark the Timer!, Mark the cross feed. Engaging the lead screw and backing off the cross feed is like pulling the trigger practice-practice-practice, you will get the hang of it, and it will become second nature, just like logging trigger time. Don't be afraid of it, and practice- practice- practice. Enroll in a class.
Also "make sure you're right before you go ahead", you can always take off more- hard to put it back on.

Have Fun,
Jon

[grumpy one]

44man, the backlash is normal - I always wind the crossfeed out to completely disengage the thread before stopping. I have an advantage over the small lathes in that mine uses clutches for forward and reverse, leaving the motor running at all times, so I can creep forward or backward by slipping the clutch as in a car. Disengage clutch, back out the crossfeed, all in one smooth motion, then reverse the spindle to go back for another cut. Check occasionally that the halfnut engagement lever stays all the way down. Reverse some way further than the start of the thread, stop, set the crossfeed screw to zero, increment the compound screw for the next cut, start the spindle forward again.

At the end of each cut it is essential that you back out the tool before the spindle stops or you will destroy the cutting tool. I have tested this repeatedly (in the interests of scientific investigation of course).

[44man]

Thanks for the idea of backing out the cutter. Much better then trying to stop the lathe before it reaches the end.
I was wearing out half nuts too fast when I first got it. I found they were not engaging well so I spring loaded it. Now it stays in full contact with the lead screw.
I still think .030" backlash on my cross feed and .052" on the lead screw is too much for precision work. I can't reduce it anymore.

[Buckshot]

.45Nut, sent you a PM with my name and address.

Man, this lathe info is like learning Greek. I seldom understand half the terms you guys are using.

You HAVE ordered the "How To Run a Lathe" by South Bend, right?

Still trying to put together the concept on the dial indicator.

It's a Thread Chasing Dial (TCD). A dial indicator is a measuring device :-)

Like when does one engage the lead screw, and what number on the dial indicator do I go for?

You engage the half nuts while the lathe is running. The half nuts WILL engage the leadescrew at each one of those marks on the TCD. However, for simplicities sake at this point, engage the half nuts at the SAME number each time.

The book will explain such things as when you can engage for cutting odd number threads, even number threads, threads which are multiples of the leadescrew's thread, metric threads, and how to setup for 2, 3, and 4 start threads etc. No sense typing it all out here.

Can you engange the lead screw while the lathe is running, that doesn't sound plausible.

Yes, you engage and dis-engage the half nuts while the lathe is running. The half nuts will only close when the threads of the leadescrew and halfnuts align.

What lathe speed should it be turning for threading work.

You could thread at the same speed as for cutting, because that is what you're doing. However that isn't practical for several reasons. You will generally get better threads the faster you cut. But there is a danger here in threading toward a shoulder and cutting fast. Possibilities of a good crash increase with your speed, as you have to react faster in opening the half nuts and winding the crossfeed out of the thread. My answer would be, thread as fast as you're comfortable threading.

What's with the direction lever on the back of the little lathe, how and when is that used...if its used in thread cutting.

I/m not that familiar with the controls on those 7" machines and it could be spindle direction or leadescrew direction. Usually the later is on the front of the lathe, but no reason it can't be on the back.

Thanks, Jim

Here's a real quick synopsis of threading. It's assumed that you have the correct change gears in place, and that the workpiece has a mark (like a ring made with a magic marker) where the thread is the length you want. and you have thread cutting oil, and the spindle speed is at a comfortable speed for threading:

1) Set compound to 29.5*, but the threading tool should be at 90* to the work piece's axis. So you slap the compound around to the mentioned 29.5* angle, then loosen the toolpost and turn it so the threading tool is perpendicular, or 90* to the work as below.

http://www.fototime.com/27DBAFBE166C54E/standard.jpg

I'm not threading here, but the compound is set at 29.5*. You see how the toolpost is, and is holding a tool at 90* to the work?

2) Now run the crossfeed in untill the tool touches, then zero the crossfeed dial. Also zero the compound's dial. If you cannot 'set' the compound's dial, crank in on the compound until the dial reads zero, and THEN run the crosslide up so the tool touhes the work and zero THAT dial.

3) Crank the carriage back toward the tailstock so it clears the work (assuming we're threading TOWARD the headstock).

4) Start the lathe and (to keep it simple) engage the halfnuts when the dial comes around to the #2 position. This will put a faint spiral on the workpiece so you can check the thread pitch. As the tool nears the chuck, and at the point you've chosen and marked on the work with a magic marker, dis-engage the half nuts and wind the crossfeed out a half turn.

5) If the thread pitch checks out, wind the carriage back down to the start.

6) Crank the corssfeed back in to zero, and feed in the COMPOUND (say) 0.015" acording to it's dial.

7) When the '2' comes back around on the TCD, engage the half nuts. The carriage begins to move toward the headstock.

8) The tool makes the first cut along the workpiece. At the depth mark you'd made with the magic marker, dis-engage the half nuts and crank out the crossfeed (the lathe remains running all this time).

9) Wind the carriage back to the beginning and crank the crossfeed backin to zero.

10) Now crank in .010" on the compound, and when the '2' comes back around on the TCD, engage the half nuts to make your second and deeper cut.

11) Repeat from #8. The lathe runs until you've completed your threading job.

NOTE: When you dis-engage the half nuts, the carriage will stop moving. If you do not wind the crossfeed out rapidly the bit will cut a groove at that location. Always keep your right hand on the half nut lever and your left on the crossfeed wheel.

Practice on scrap, allowing yourself a good inch or so from the chuck to dis-engage the half nuts and crank out the cross slide so it isn't so nerve wracking as you practice.

..................Buckshot

[Swagerman]

Holy Mackrel, Andy!

That is some synopsis you cranked out there. You even shouted it out so this old fart could see and hear it jump right off the screen...:mrgreen:

But it is very good info for myself to absorb, and I really appreciate you taking the time to clarify a few details...like that engaging the half-nut while the lathe is turning. Now that one is a mind blower, never would have guessed it.

Now to you old hands at lathe turning, this may seem like yesterday's news, but to me its new news and the kind you need when you trying to feel your way through the learning process.

Man, trying to learn threading is not for the faint of heart, its difficult...guess I'm getting too old to learn new tricks. But I'm still hanging in there.



Buckshot, you are a top hand when it comes to turning a lathe.

Thanks, Jim :-D

[Buckshot]

...................So. Have we cut any threads yet :-)?

................Buckshot

[Boomer Mikey]

This may clarify things some.

From Littlemachineshop.com:

http://www.littlemachineshop.com/Info/MiniLatheUsersGuide.pdf

Page 24 starts the section on cutting threads with this lathe.

Page 27 explains the threading dial and it's use.

The threading process description continues through page 30 of this user guide with a description of the threading tool and how to setup and align the tool.

Threading is intimidating at first but once you get the process clear in your mind it's no big deal.

BTW I own a Smithy 1324 and have no problems cutting threads on barrel shanks and anything else but learned the hard way that when cutting metric threads using a machine with an inch thread lead screw you can't disengage the half nut... you must reverse run the carriage back for each pass. Cutting an internal metric thread in a blind hole can get exciting but that's what they made dial indicators for.

Littlemachineshop.com has every gadget you coulld ever need for the Mini Lathe including replacement parts for the lathe. The plastic gears are very popular replacement parts.

Boomer :Fire:

[Swagerman]

Not yet, but have copied and printed all of you're synopsis...plus, have a wealth of information from the Smithy books I've recently acquired.

I have to acquire some thread cutting bits of 60* angle, some inside and outside cutting bits. Plus, a thread gauge. Will certainly let you know when this all comes together.

There are no local sources to buy these things from. Everything has to come from mail order.

Guess I'm really waiting for my area machinest to finish some job for me on the Lee Classic cut-off shellholder to take the Herter's shellholders...then gain some first hand insight on thread cutting if he feels inclined to relate.

I would have like to done that job myself but the little mini-lathe only has the rinky dink 3" chuck.

Jim