Author Topic: Bloomers and cock ups learning to cut thread on the lathe  (Read 23047 times)

Offline Bangkok Mick

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Bloomers and cock ups learning to cut thread on the lathe
« on: June 28, 2013, 07:52:35 AM »
Well as the title indicates I have been persevering and honing my skills on my new lathe and decided to try my hand at threading with a one point cutter tool instead of the tap & die method.

Yesterday I have produced a couple of prototypes but could not get them to screw together no matter what I tried. I checked the pitch to insure my threads were straight and compared the diameter of both male and female threads and everything appeared to be at least a good effort for a beginner but nothing worked, as soon as I tried to screw one into another they bound up and joined one another crocked and simply did not behave as expected so I gave up and decided to try again with a fresh start tomorrow.

Getting home from work today I tackled the problem again and realized that by turning the male and female threads using the lathe in the same orientation and direction on both cuts I was producing one right hand thread and one left hand thread that of course simply could not screw together.

Having resolved this problem I have since turned and threaded a hollow brass bar that can be screwed together and the action is very smooth and satisfying.

Cheers Mick

Offline awemawson

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #1 on: June 28, 2013, 08:28:34 AM »
Well done - it's all a learning experience.
Andrew Mawson
East Sussex

Offline Jonny

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #2 on: June 28, 2013, 10:19:21 AM »
Good practice Mick and true its gratifying.
Sounds like wrong hand tool on female thread?

Done it all, wrong tips for thread on finished product to wrong pitch but right tip. Spindle startup 800 rpm on a short thread glad of foot brake. Check and check again no ones fallible.
Dare say you have realised now that you can actually make your own matching male and female thread up, one reason I like metric. Gets a bit tricky say UNC with metric pitch.


Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #3 on: June 28, 2013, 11:07:36 AM »
Thanks for the feed back guys, learning must be the best part.

Cheers Mick

Offline awemawson

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #4 on: June 28, 2013, 11:12:14 AM »
When you stop learning you must have either stopped doing or listening or both  :thumbup:
Andrew Mawson
East Sussex

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #5 on: June 28, 2013, 01:26:23 PM »
Not sure what is going on here.

To cut a left hand thread  (never done it ) don't you have to apply the cut while moving away from the chuck ?

Both internal and external right hand threats are made towards the chuck.

Or am I having a senior moment here ?

Dave :scratch:

Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #6 on: June 28, 2013, 04:49:09 PM »
You are correct.  The cross slide must also be re-positioned.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #7 on: June 28, 2013, 07:36:05 PM »
Mick,

What exactly do you mean by ...

..Getting home from work today I tackled the problem again and realized that by turning the male and female threads using the lathe in the same orientation and direction on both cuts I was producing one right hand thread and one left hand thread that of course simply could not screw together.

Sorry for the question,  but I can't visualize what you did.
Dave.

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #8 on: June 29, 2013, 03:59:04 AM »
I guess cutting a left hand thread away from the chuck is the correct way but I cut both internal and external threads towards the chuck and came up with opposing threads.

I had the lead screw engaged in revers so I could arrange the cutter on the far side of the internal thread so I would be able to see it cutting the thread as it proceeded. This also caused the thread to cut an opposing thread.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #9 on: June 29, 2013, 06:18:09 AM »
Still don't see how this would give you a left hand thread;  unless you were running the lathe mandrel in reverse.  But I'll let it go at that.
Clearly I need stronger coffee to clear my old brain.

Cheers,

Dave. :scratch:

Offline NeoTech

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #10 on: June 29, 2013, 06:53:07 AM »
He prob cut one thread from right to left and the inside thread from left to right.
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #11 on: June 29, 2013, 08:19:41 AM »
Neotech,

That is what I am trying to work out. But he (apparently) says not.

If the tool in the picture is the right way up,  and the lathe is turning in the conventional direction, then it wouldn't cut. So the tool has to be upside down.

But he writes,
.. turning the male and female threads using the lathe in the same orientation and direction on both cuts I was producing one right hand thread and one left hand thread ..

This and,

...I had the lead screw engaged in revers so I could arrange the cutter on the far side of the internal thread ...


If this means driving the saddle back towards the tailstock it would need the chuck to be turning clockwise (backwards to normal)  viewed from the front. This could unscrew it.

Very confusing.

Dave.

...

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #12 on: June 29, 2013, 08:34:48 AM »
Sorry, some clarification.

The chuck was turning backwards, “clockwise”  but I was also moving the tool towards the chuck with tool facing upwards, my first attempt so still learning the correct procedure.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #13 on: June 29, 2013, 08:47:12 AM »
Mick,

Thanks.  That clears it all up.  I think 'unconventional' is the term.

Dave.

Offline Meldonmech

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #14 on: June 29, 2013, 09:07:51 AM »
Hi Mick,

                 Well that is one lesson you will never forget, they say the best way to learn is by your mistakes.

                                       keep forging ahead ,         Cheers  David

Offline NeoTech

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #15 on: June 29, 2013, 10:54:58 AM »
Agreed, that would clear it up. But i imagine you learned your lesson from that. =)

Im a bit lazy when turning inside threads.. preventing tool crashes and such.. so i usually set it up so i cut from the bottom and out instead but reversing the chuck so it cuts the right hand thread in reverse (does that makes sense?). When i figured that one out i ended with having problems cutting internal threads where i couldnt see the bottom of the hole properly. =)
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline Jonny

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #16 on: June 30, 2013, 04:00:19 PM »
Exactly what I thought Mick, need opposite hand tool.

For an external left hand thread can start at chuck end or mount tool on opposite side and spin up clockwise.
No need to adjust compound the pros don't.

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #17 on: July 01, 2013, 02:31:13 AM »
Agreed, that would clear it up. But i imagine you learned your lesson from that. =)

Im a bit lazy when turning inside threads.. preventing tool crashes and such.. so i usually set it up so i cut from the bottom and out instead but reversing the chuck so it cuts the right hand thread in reverse (does that makes sense?). When i figured that one out i ended with having problems cutting internal threads where i couldnt see the bottom of the hole properly. =)

How can you bottom with no cross slide or compound adjustment for setting the depth of the cuts?

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #18 on: July 01, 2013, 02:34:20 AM »
Agreed, that would clear it up. But i imagine you learned your lesson from that. =)

Im a bit lazy when turning inside threads.. preventing tool crashes and such.. so i usually set it up so i cut from the bottom and out instead but reversing the chuck so it cuts the right hand thread in reverse (does that makes sense?). When i figured that one out i ended with having problems cutting internal threads where i couldnt see the bottom of the hole properly. =)

How can you bottom with no cross slide or compound adjustment for setting the depth of the cuts?

Offline NeoTech

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #19 on: July 01, 2013, 08:46:29 AM »
Cuz i dont cut threads with the compound, just a straight plunge cut, i havent bothered about setting angles and such. It works just goes slower. But i guess its not the recommended solution.
Make a  little "slot" in the bottom to start the thread from and just figure out how deep you are taking the cut by setting a dial indicator on the cross slide. And figure out forehand how deep your gonna make the thread.
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/

Offline Jonny

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #20 on: July 01, 2013, 10:20:31 AM »
Thats the conventional way of doing it Neo and how the pros do it for repetition work.

In fact its exactly how a high speed threading machine works, used an Elliot some years ago.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #21 on: July 01, 2013, 11:28:57 AM »
Same way I did it at work.  Just reduce the amount cut each pass as the cut gets deeper.

Dave.

Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #22 on: July 01, 2013, 04:21:18 PM »
Not trying to start an argument.
There have been many instructions from our predecessors about cutting threads.
Many articles in published books.
I am a 'pro'.
I strive for accuracy and efficiency.
I cut threads using the compound.  The depth of cut can be easily controlled.
I am not lazy so I use the procedures I was taught and have read about.
I am not in a hurry so I try to make the best thread I can so I do not have to do it over.
I believe that learning how to cut a thread by using the cross slide and a single point tool set at the correct angle will be of benefit.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #23 on: July 01, 2013, 04:36:20 PM »
I don't think anyone is arguing about anything.  Just discussing different ways of arriving at the same end.

All your points are valid.

Most of the time modellers tend to be cutting small pitch threads that don't seem to need the set-over method.

Dave.

Offline NeoTech

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #24 on: July 02, 2013, 03:03:18 AM »
Yeah, and most of us are not pros and have figured out how to cut thread by ourselves not fully understanding most books in the subject.. *at least not me*
I found it to be a damn struggle the first couple of times. And now i have found a way that suits me.. =)
Machinery: Optimum D320x920, Optimum BF20L, Aciera F3. -- I have not failed. I've just found 10,000 ways that won't work. http://www.roughedge.se/blogg/