Author Topic: Bloomers and cock ups learning to cut thread on the lathe  (Read 16670 times)

Offline Stilldrillin

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #25 on: July 02, 2013, 03:54:18 AM »
Is it Me?  :scratch:

I was taught to screwcut in the apprentice school, 1960. Then, spent a lifetime machining.

I have NEVER have seen an angled compound, for screwcutting purposes......

David D
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Still modifying bits of metal... Occasionally, making an improvement!

Offline vtsteam

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #26 on: July 02, 2013, 09:39:52 AM »
Debate about this has appeared in the model engineering press for a long time. Not really debate, I guess, maybe more like discussion.

Anyway, I'll hazard a guess about why. Small lightly built and homemade lathes, like my Gingery lathe in its original form have low bed, spindle, and carriage stiffness and mass. Avoiding chatter in machining operations becomes a priority by comparison with manufactured cast iron hobbyist lathes, not to mention commercial and industrial practice. It means taking very light cuts, and a long time to do some things, and any procedure that can increase that cut depth or reduce that time is a boon.

Straight plunge cuts to any depth with form tools are often out of the question. So, methods become popular that reduce the contact cutting surface in plunge cutting. I'm guessing that's why the compound set over method was developed. It wouldn't be so important for a heavier lathe, and I can understand why commercial screw cutting machines and industrial lathes just cut straight on.
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Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #27 on: July 02, 2013, 10:43:21 AM »
Perhaps I should have worded my post differently, not sounding as if I was criticizing.
I have seen incorrect, sometimes unsafe advice given on machining sites.  Usually to novices.  I think we would all be served if we encouraged each other to learn the traditional (I do not want to say 'proper') manual machining methods first.  Then, when one feels that he has learned and is comfortable, make whatever changes he chooses.  I believe Bangkok Mick would benefit from at least reading instructions on 'how to cut a thread on a lathe'.  I suppose I have a problem with 'been there done that' advice as it does not exchange knowledge.

I was taught and do the opposite of Stilldriling concerning cutting screw threads on a manual lathe.

One thing I do differently is to grind the cutting tool with a top and back rake.  It makes a much cleaner cut with a better finish.

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #28 on: July 02, 2013, 01:06:21 PM »
It does seem to come down to the way you were taught. Where I worked there were three other machinists.  Non of them had even heard to the idea of setting over the topslide.  I had never heard of it until I started with my own lathe and began reading the hobby journals.

I suppose it is a case of whatever works for you.  you use.

Dave.

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #29 on: July 02, 2013, 11:08:41 PM »
Perhaps I should have worded my post differently, not sounding as if I was criticizing.
I have seen incorrect, sometimes unsafe advice given on machining sites.  Usually to novices.  I think we would all be served if we encouraged each other to learn the traditional (I do not want to say 'proper') manual machining methods first.  Then, when one feels that he has learned and is comfortable, make whatever changes he chooses.  I believe Bangkok Mick would benefit from at least reading instructions on 'how to cut a thread on a lathe'.  I suppose I have a problem with 'been there done that' advice as it does not exchange knowledge.

I was taught and do the opposite of Stilldriling concerning cutting screw threads on a manual lathe.

One thing I do differently is to grind the cutting tool with a top and back rake.  It makes a much cleaner cut with a better finish.

Just for clarity I am also reading up on and researching the internet as I go and trying to apply each different method to see what works best including safety.
I have tried setting the compound at 60deg. And this was a successful exercise but as I am cutting soft material such as aluminum and brass a parallel compound is also working out, still it is good to practice each way for future reference.

Thanks for all the feed back to this thread.

Offline unc1esteve

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Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #31 on: July 03, 2013, 10:49:06 PM »
I just ordered this.

http://www.bookdepository.com/Screw-cutting-Lathe-Martin-Cleeve/9780852428382


Thanks for the tip Steve, living in Thailand and with free shipping worldwide I just placed an order for the same with a couple more on mini lathes.

Cheers Mick

Offline andyf

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #32 on: July 04, 2013, 12:49:55 AM »
Well worth the money. An invaluable reference book, containing just about everything you might ever ask about single point threading. Being written in the UK when Myfords were the standard model engineering lathe, it leans a bit towards those and imperial leadsscrews, but if you want to know how to cut metric threads with those (and vice versa) it will tell you 101 ways of doing it without a 127T gear for an exact conversion.

Andy

PS Mick, if you want to practise threading, PVC pipe is cheap.

Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Jonny

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #33 on: July 04, 2013, 09:58:51 AM »
Firstly theres no right or wrong way as long as it works.

Its pretty much was I was inferring Vtsteam and Stilldrillin. You have books written by model engineers often self taught and then writing books, whos right.
One thing for certain any production based practice would need quality work at quickest amount of time.

I buy full form replaceable tips with relief already in them, no need to change any change wheels around I just dial it in with four knobs any pitch metric or imperial and would never ever contemplate looking at another lathe that I couldn't do that.

Offline vtsteam

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #34 on: July 04, 2013, 10:44:17 AM »
I'm happy that commercial outfits have needs that can be fulfilled for their purposes, and share those techniques, and that self taught hobbyist engineers also share their experiences and methods, even writing books about those. Seems everybody can learn a few new tricks from someone in a different line of experience and equipment. There's nothing wrong with being self taught, nor apprenticing 40 years ago in a production facility. And nothing wrong with a treadle lathe using gravers, nor a CNC 5 axis machine or anything in between. Attitude is the important thing, I get tired of forums with people who start pounding home right and wrong according to their singular experience.
I love it when a Plan B comes together!
Steve
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Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #35 on: July 18, 2013, 06:20:55 PM »
BangkokMick,
I received my book 'Screwcutting In The Lathe' and have skimmed through it several times.  Lots of good, useful information, especially for cutting a thread to specifications.  I have several other books from this series that I find useful.  I am an old man and I like referring to the hard copies.  I have used 'Gears and Gear Cutting' many times.
It did not, however, have a description of the procedures of cutting threads with the straight in method or the top slide method. 
Machine Shop Practice, volume 1, K E Moltrecht, has a step by step description of the two procedures.  How to books such as Machining Fundamentals, John R Walker, also explain the steps involved.  Books like Machine Shop Trade Secrets, James A. Harvey, add many useful tips.  Though I have not seen a reference to the way I sharpen my tool bit.
I have been thinking a lot about threading since I made my post.  It seems so easy for me to make a thread but Why is it easy?  I remember the first thread I cut.  1" x 8tpi. 
I just followed step 1, step 2, etc., after doing research, (reading).   But again, why is it easy?
I think about Stilldrilling's comment about never seeing a set over top slide.
George H Thomas, The Model Engineers Workshop Manual, gave a good description of thread cutting and also a quick, retracting tool holder.
I have no references from the gentleman that called himself Tubal Cain.  I would like to start collecting his books.
I have come to no conclusions.
But I am going to make a rapid retracting lever for my lathe's cross slide.  I think this would be of benefit for more than cutting threads.

Offline andyf

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #36 on: July 18, 2013, 07:23:50 PM »
BangkokMick,
I received my book 'Screwcutting In The Lathe' ....   It did not, however, have a description of the procedures of cutting threads with the straight in method or the top slide method. 


My copy does, Steve, though it doesn't take up much room - pages 136 to 140. A bit hard to notice after your brains have been boiled by the preceding pages of mathematics!

Andy.
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #37 on: July 18, 2013, 09:51:31 PM »
My copy was also waiting for me when I got home from work yesterday along with two other books on lathe works from the same series. I have only had time for a flip through each book last night but will look for the info on the straight in method on pages 136/140 when I get home today.

As I am using small diameter brass most of the time I guess this method will be a useful one to adopt but will also practice the 60 degree compound method for when I start cutting harder materials.

All in all from my cursory look through I see a lot of good tips and ideas in these books so will have some home reading to do over the next couple of weeks.

Cheers Mick

Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #38 on: July 18, 2013, 10:26:55 PM »
andyf, Mick,
I did read section 8, but it was not the kind of step by step instruction I was looking for to refer to.  I find threading to be no more or less difficult than any other process on the lathe.  It is just a mater of manipulating this lever or dial in a certain order.  Metrics on my lathe is just a matter of changing one gear.
What I am trying to understand are statements like Neotech's about learning to cut threads to be a 'damn struggle' when I do not find it a struggle.  I enjoy cutting threads and am thinking about his struggle.  For instance depth of cut.  I use a chart that was printed in a popular magazine that shows a standard depth for a standard number of threads.  Set the dial to zero and then cut to depth.
I am pleased that Mick finds my suggestion about 'Screwcutting In The Lathe' to be of benefit.
Mick,
I was in Thailand when I was in the Army many lifetimes ago.  A beautiful country with more beautiful women.  I was in Bangkok in '69'.  I can not remember being that young.
Bookdepository has several volumes by Tom Walshaw, aka Tubal Cain.  He was refereed to in a post I made about lathes cutting a concave.


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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #39 on: July 19, 2013, 03:09:25 AM »
Set over screw cutting well evan with a big Colchester lathe its still done, if you are un clear how the taper was cut he has a hydraulic tracer unit fitted

take a look

     


     


he explains it and shows how sets up the machine evan down to the reason for the position of the cross slide handle , also note the dial gage to show the total in feed
I do not know if its in one of the above but he get on his high horse about back lash his cross slide has about 1/4 inch slop yet he can hold a part to better than a thou , its how you do it

Stuart

Ps he has 310 video's all show some interesting machining , I am not to enamoured with the use of a file but its his work not mine
« Last Edit: July 19, 2013, 02:26:07 PM by dsquire »

Offline DavidA

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #40 on: July 19, 2013, 08:43:04 AM »
It is interesting how the set-over top slide  is being referred  to as the correct way to cut a thread.

At work we have two CNC lathes.  One is a Guildermeister (can't remember what the other is;  I don't use it) and this machine uses a straight in approach. It gradually reduces the depth of cut as it goes. Same goes for the other machine.

Can anyone recall a CNC thread cutting lathe that uses set-over ?

Not wishing to pour petrol on the fire here,  just curious.

Dave.

Offline Stilldrillin

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #41 on: July 19, 2013, 09:05:49 AM »
Can anyone recall a CNC thread cutting lathe that uses set-over ?

Haas, Mazak(x5!), Mori Seiki, Tos.  :thumbup: .........  Nope!  :scratch:

David D
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Still modifying bits of metal... Occasionally, making an improvement!

Offline mosey

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #42 on: July 19, 2013, 10:04:13 AM »
Beginner here!

On page 77 of "How to run a lathe", South Bend Lathe Co., it says under "position of compound rest for cutting screw threads". "in manufacturing plants where maximum production is desired, it is customary to place the compound rest of the lathe at an angle of 29  degrees for cutting screw threads."
This is obviously relevant to 60 degree threads.
Is this what you mean when you say "setting the top-slide over"?

It works for me. Also, in questioning several professional machinists, they've never used a threading stop. Curious. I find that stops frequently slip, ruining the thread.
 :med:
Mosey

Offline unc1esteve

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #43 on: August 02, 2013, 05:39:12 PM »
Bangkok Mick,
I purchased the book by Tom Walshaw, Model Engineer's Handbook from The Book Depository.
Thought he might have a step by step description of screw cutting but he did not.
I liked it so I purchased five more of his books.
This is a good source and the free world wide shipping is very good.

Habits are difficult to change.  I built a Bonelle T&C Grinder to sharpen tools but
find I still sharpen by hand.  The T&CG sharpened tool makes a much more smooth
and accurate cut.  I am forcing myself to use the Bonelle first, even if only for a touch up.

Offline Bangkok Mick

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #44 on: August 03, 2013, 09:06:35 AM »
Hi Steve,

I also used the Book Depositary and living in Bangkok appreciated the free postage service.

Cheers Mick

Offline JTisher

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Re: Bloomers and cock ups learning to cut thread on the lathe
« Reply #45 on: August 17, 2013, 09:14:50 PM »
  Hi all, It's been a long time sense I've posted ,or been on the site but I have to comment. I learned single point threading from the internet, not easy when know one's around to show you how.
  One thing I did learn though is on the east side of the pond know one offsets the compound. On the west side everyone thinks your an idiot if you don't offset the compound.
  I'm glade I don't care what people think of me.  ;)
  The thing is, learning online I've done both and they both work equally well ,sometimes (don,t ask :() so... do whatever works and that your comfortable with
   Joe
P.S. Be happy if you have a tight lathe and a threading dial