PDA

View Full Version : Thread cutting for Dummies



brian Rupnow
05-06-2008, 07:50 PM
When I bought my nice new craftex Lathe from Busy Bee, it came with a whole damn box of extra gears, and 2 sheets of poorly translated documentation.---None of which dealt with thread cutting. I have purchased an excellent book, "The Amateur's Lathe" by L.H. Sparey and read up on thread cutting, and there is a chart of sorts, (that I don't know how to read) on the face of the lathe. What book can I purchase that deals comprehensively with thread cutting, gear selection, how to read the gear/thread chart on the front of my lathe, and just where the heck these gears go on the inside of my gear cover on my lathe. I am slowly re-aquainting myself with turning, facing, boring---things which I did on a lathe during an engineering apprenticeship 40 years ago, but I don't think I ever did master setting up to cut threads even back then.---Brian

Fasttrack
05-06-2008, 08:13 PM
Unfortunantly, where the gears go and the appropriate gears to use are generally specific to the manufacturer.

Basically, your chart should have something like

. A B C D
18 H
27 L 27 64 72 13

(I just completely made up those numbers mind!)

Usually, you will have two TPI corresponding to either a high or a low on the gear box. Some gearboxes don't have the high/low feature so in those cases you'd just have one TPI listed. So, you find the TPI you want. For this imagninary lathe, lets pretend like we want 18 TPI.

We find the 18 TPI on the chart (it could appear more than once if there is a high/low feature) and then moving across the chart there are a bunch of numbers that correspond to the number of teeth on the change gears. The way my BS chart reads, a 27 tooth gear goes in location A, a 64 tooth gear goes in location B, etc. The letter locations should be listed near the chart, next to the place where you'll be sticking the change gears (crap whats that called?) or in your two page, changlish "user manual" :)

You can work through those gear ratios yourself, if you know the TPI of your leadscrew, any hidden gearing between the bull gear and the leadscrew and then the # of teeth on the change gears. That is generally a mess to do - you'll fill up a page of scribbled notes with a bunch of ratios fairly quickly.


<edit> hmm my chart looked alot more like a chart before ... Lets do it this way:

http://i108.photobucket.com/albums/n22/fasttrack237/ThreadingChart.jpg

http://i108.photobucket.com/albums/n22/fasttrack237/ThreadingChart2.jpg



In both of these images, you can see the table and the location of the gears. Looking at the ratios and the picture, I expect that the blank spots correspond to no gears used - but I'm not sure. That is not how my threading chart works; like I said it depends upon manufacturer.

franco
05-06-2008, 08:43 PM
Brian,

"Screwcutting in the Lathe" by Martin Cleeve, Book 3 in the Workshop Practice Series tells you everything you could possibly want to know about the subject, including how to work out the gear trains required for any thread from first principles. He has managed to write 173 pages on what seems on the surface to be a fairly simple process. It is well worth buying a copy.

franco.

oldtiffie
05-06-2008, 09:22 PM
When I bought my nice new craftex Lathe from Busy Bee, it came with a whole damn box of extra gears, and 2 sheets of poorly translated documentation.---None of which dealt with thread cutting. I have purchased an excellent book, "The Amateur's Lathe" by L.H. Sparey and read up on thread cutting, and there is a chart of sorts, (that I don't know how to read) on the face of the lathe. .---Brian

Hi Brian.

If my memory is correct. I have the same lathe as you do. Mine is the 3-in-1 (mill-drill-lathe).

I have the hand-book scanned in digital form.

I will post a pic of my head-stock panel for the set-up later in the day and will go through the set-up for metric and "inch" screw threading for you. That hand-book is pretty poor but if what I have is more than you do it will help. I will post the links and you can down-load it.

Just one thing - my lead-screw has a pitch of 3mm. Is this the same as yours or is yours a pitch of 1/8" (ie 8 tpi)?

I will get back to this later in the day or this evening.

These are pics on my 3-in-1 and may help in confirming whether the lathe is the same as yours:
http://i200.photobucket.com/albums/aa294/oldtiffie/AirSmith11.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathemill1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe1.jpg

miker
05-06-2008, 09:54 PM
Brian, I am pretty much in the same boat as you. I am just begining to read the book suggested by franco. It does look good.

http://img.photobucket.com/albums/v448/mikerr/Scan10724.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10725.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10727.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10728.jpg


If you want the Martin Cleeve book and can't get hold of it, let me know and I will try and get it and send to you, It is not an expensive book here, maye $18.00 AUD so no big deal to help you out.
I forgot the ISBN, 0-85242-838-3

Rgds

oldtiffie
05-06-2008, 10:22 PM
Brian, I am pretty much in the same boat as you. I am just begining to read the book suggested by franco. It does look good.

http://img.photobucket.com/albums/v448/mikerr/Scan10724.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10725.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10727.jpg

http://img.photobucket.com/albums/v448/mikerr/Scan10728.jpg

If you want the Martin Cleeve book and can't get hold of it, let me know and I will try and get it and send to you, It is not an expensive book here, maye $18.00 AUD so no big deal to help you out.
I forgot the ISBN, 0-85242-838-3

Rgds

Thanks Michael.

That looks to be a very handy book and very good value as well.

I am in OZ as well (Victoria).

Can you let me know (post to this thread, PM or email) where you sourced it in OZ and I will send for it.

Is it a part of a series?

miker
05-06-2008, 10:51 PM
I usually get mine from a local cut price bookseller. Can't always rely on what they will have in stock.
Plough books down in your neck of the woods should have it.

http://www.ploughbooksales.com.au/002766.htm

This is the series:

http://img.photobucket.com/albums/v448/mikerr/Scan10726.jpg

I have most of them.

Rgds

GadgetBuilder
05-06-2008, 10:51 PM
Hi Brian,

I believe the Craftex from Busy Bee is a 7x10 or 7x12 so you can get considerable documentation for this machine from a number of sources.

Basic setup for threading is covered in some detail on pg 24 of this guide from LMS:
http://www.littlemachineshop.com/Info/MiniLatheUsersGuide.pdf
(LMS also supplies parts and accessories for this machine.)

The guide has a nice picture of the gear end of the lathe that identifies the shafts where the change gears should be installed (helps make sense of the chart on the machine) plus lots of other threading information specific to the 7x machines.

"Screwcutting in the Lathe" is perhaps the best general reference available for threading and very well written - the jig for sharpening threading bits is worth the price of the book.

John

Duffy
05-06-2008, 11:21 PM
Brian:- I Know that Busy Bee sells at least SOME of the Workshop Practice series of books. Suggest that you call head office, since you are close.

Dunc
05-06-2008, 11:34 PM
Don't know about BB in Barrie but the Ottawa store stocks several of the books in the series. The Cleeve book is out of stock and "soon" for my copy has translated into many weeks. Not BB's fault.

Edit: Toronto Public Library, North York Central branch has this book. Call # 621.942 C . Should be an inter-library program to borrow it or just visit. To see the entry search the catalog using "screwcutting"

Edit 2: Go to www.littlemachineshop.com/default.php & click on "Learning Center" then "Mini Lathe Users Guide". Open/download (Adobe Acrobat Reader required) it and go to page 24 or 25. Pretty good explanation of what's involved.

R W
05-07-2008, 03:29 AM
I have a copy of "Screw Cutting in the Lathe" by Martin Cleeve
FOR SALE, Send a private message if interested.
R W

brian Rupnow
05-07-2008, 02:17 PM
http://i307.photobucket.com/albums/nn294/BrianRupnow/threadcutting001.jpgThe craftex lathe which I have is a 10" x 18", and is not classed as a "mini-lathe". This is a picture of it from the Busy Bee brochure.---Brian
http://i307.photobucket.com/albums/nn294/BrianRupnow/lathepics005.jpg
http://i307.photobucket.com/albums/nn294/BrianRupnow/lathepics003.jpg[/IMG]"] ("[IMG)

brian Rupnow
05-07-2008, 03:25 PM
And one last picture---
http://i307.photobucket.com/albums/nn294/BrianRupnow/lathepics003.jpg

pcarpenter
05-07-2008, 04:04 PM
I think the point was that more general information on the process of screwcutting could be had at littlemachineshop.com. I would add mini-lathe.com

Its probably not any more reasonable to expect your lathe manual to teach you to cut screws than it is to expect your car owner's manual to teach you to drive. The general assumption is that if you buy a machine tool you either will have or will get enough basic information on processes and practices (which are general and applicable to lots of machines). I think that its also generally assumed that owners of machine tools will have some basic mechanical aptitude too. You will find yourself applying that aptitude even after mastering the basics as its what helps you figure out the not-so-basic ways around more complicated problems. Change gear lathes have been around for over a century, making a basic text like "How to run a lathe" from South Bend (now out of print and available as a free .pdf) very useful. Once you get the basic understanding of end gear trains driving your lead screw which moves your carriage a fixed distance per turn down, the specifics of which combination of gears is needed for which thread pitch (as pictured in the gear chart on the front of the machine) will all make sense to you. I can see both a picture of the gear layout as well as the number of teeth on the gears for each thread represented in the chart in your picture edit (which is really all you need that is specific to your lathe).

mini-lathe.com is another good source...not because you have the same 7x lathe as depicted there since you don't, but rather because it shows some of the basics.

Paul

brian Rupnow
05-07-2008, 09:24 PM
Wow---I actually did it---cut my first thread. I figured out the change gears, and it seemed to be right. I didn't have a peice of 3/4" round bar stock, and I don't have a proper thread cutting tool. So---just to verify that I had figured out the change gears, I used a peice of 3/4" hardwood broom handle and a V shaped carbide tool. I didn't cut a deep thread, and it tore up the hardwood, but when I took it out of the lathe and measured it, it is cutting 10 threads per inch, like I had calculated. I am thrilled beyond measure!!! This weekend I will buy a proper shaped thread cutting tool and a setting gauge, and try this for real. Next challenge will be to figure out the thread cutting dial that lets you start a second cut in the same track.

oldtiffie
05-08-2008, 08:07 AM
Brian.

First of all, open up (down-load preferred) the 20 files at the end of this message. It covers screw cutting and the use of thread-chaser dials very well.

Even though it is metric the same principles apply for "inch".

When working through the gear trains you should add an extra "Driver/driven" = 4 as there is a 4:1 gear reduction within the geared-head before it appears at the small gear "A" in your gear train. This is a good idea as it keeps all the higher speed gears within the protected and lubricated geared-head.

One thing I did discover when checking out my lathe for my posts in this thread was that there is no "reverse/left-hand" thread capability. I am going to have to make a larger quadrant on which the change gears "A", "B", "C" and "D" are mounted on so that I can fit another adjustable spindle for an addition "idler" gear to provide the reversing option for left hand threads.

As previously advised, I have the hand-book for my lathe. It is in "Chinglish" as usual. The drawings, such as they are, are worse than the text!!. I have the hand-book scanned and can post the links to it if you require. It is OK if you persevere with it and it is better than nothing.

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting7.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting8.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting9.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting10.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting11.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting12.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting13.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting14.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting15.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting16.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting17.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting18.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting19.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Thread-cutting_lathe/Thread-cutting20.jpg

brian Rupnow
05-08-2008, 09:41 AM
Oldtiffie---A big than you from the heartland of Ontario, Canada. I am working on a new machine design today, but at the end of the day I will open and print all this good information. Thank You very much.---Brian

GadgetBuilder
05-08-2008, 11:22 AM
Oldtiffie,

I recently built a Geo. Thomas retracting threading tool which inclines the bit at 7 degrees, similar to the setup on pg 6 in your manual. Pg 6 indicates the 60 degree angle must be reduced to compensate for back rake but doesn't provide guidance on how much reduction is needed. I arbitrarily tried 55 degrees and this was clearly too much reduction. While I can use trial and error to arrive at a workable angle, it would be helpful to have a method to calculate the required angle. Any chance you have a reference that provides this info?

Also, what is the title of your reference? It looks like a good one.

Thanks, John

Tucker
05-08-2008, 01:53 PM
your extra gears for a craftex would not be for threading those are two go from standard to metric. easy machines for the threadinmg though what model do yoou run?

oldtiffie
05-08-2008, 07:34 PM
Oldtiffie,

I recently built a Geo. Thomas retracting threading tool which inclines the bit at 7 degrees, similar to the setup on pg 6 in your manual. Pg 6 indicates the 60 degree angle must be reduced to compensate for back rake but doesn't provide guidance on how much reduction is needed. I arbitrarily tried 55 degrees and this was clearly too much reduction. While I can use trial and error to arrive at a workable angle, it would be helpful to have a method to calculate the required angle. Any chance you have a reference that provides this info?

Also, what is the title of your reference? It looks like a good one.

Thanks, John

Hi John.

The book/reference is Australian (metric) written at the Technical and Further Education (TAFE) faculty of the RMIT University of Technology for Apprentices, Trainees as well as Engineers and Drafts-persons (I hate that "PC" stuff!!) that need to do some practical work-shop practice and theory. It is pretty well the default standard for the State Of Victoria where I live. It is the best manual I have ever seen in my 50+ years. It is written by practicing teaching Fitters and Machinists for practical work-shop people.

http://www.machineryhouse.com.au/Products?stockCode=L341

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurl_B1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Knurl_B2.jpg

It may seem expensive at AU$69 (~US$66.50). That includes 10% Australian Goods and Services Tax (GST). I don't know if the supplier ships to the US or the cost.

I will address the "compound angles" issue that you refer to in tilting your screw-cutting tool (in your case 7 degree)later in the day. The correction (ie additional to the usual 60 degree) is not much at all. I will try to have the figures etc. later today or tomorrow for you.

In the meantime, if you have a copy of Machinery's Handbook have a look at "Compound Angles". Its not much help but it will give you an idea of what the problem is.

oldtiffie
05-08-2008, 07:44 PM
Oldtiffie---A big than you from the heartland of Ontario, Canada. I am working on a new machine design today, but at the end of the day I will open and print all this good information. Thank You very much.---Brian

Hi Brian.

I really am pleased that the info was helpful to you.

The manual for my "metric" 3-in-1 machine of which your "inch" lathe is part is in the following links (Note: all sizes are in mm):

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_cover1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_contents1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page6.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page7.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page8.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page9.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page10.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page11.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page12.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page13.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page14.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page15.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page16.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page17.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Lathe_hand-book/Lathe_page18.jpg

brian Rupnow
05-08-2008, 08:54 PM
In regards to machine speed.---I have been playing at cutting a 3/4"-10 thread on my lathe, at the slowest possible setting of 115 RPM., on a mild steel round bar (cold rolled). Since I am a relative "Newby" at this business, I don't know if that is too fast or not. I do know this---when I am trying to take a second cut, having backed the cutting tool out, disengaged the half nuts, reset the carriage, and I am watching the thread indicator dial spin around, and trying to re-engage the half nut lever at an exact position on the dial---That damn dial seems to be spinning at 100 miles per hour!!! I managed to re-engage the half nut lever in the correct position for the first 3 cuts. Then on the fourth cut, I must have missed it, because I started cutting an entirely new thread in a different track!!! Ah Ha---this is just as tricky as I thought it would be!!! I tried the alternate method of stopping the lathe after each pass, backing out the tool, reversing the lathe, resetting the tool, un-reversing the lathe, then starting the lathe again for the next cut---without ever disengaging the half-nut lever. This works, but is infernally slow. those are my observations so far.---Any comments???

Lester
05-19-2008, 01:08 PM
If there is anything you need to know about lathe work, changewheels included, I have found that the site www.lathe.co.uk can provide the answer in very easy to understand language. It also has a programme for telling you which gears to use for the gears that you have. Very useful when like me you have a limited number available.
Best wishes.

Lester

Peter.
05-19-2008, 01:13 PM
Hi Lester.

Your links should be www.lathes.co.uk

brian Rupnow
05-19-2008, 01:40 PM
Thank you, Lester.

GrahamC
05-19-2008, 04:31 PM
hey Brian,

Nice to see you getting along with your Craftex B2227L.

If you are still struggling with threading and trying to re-engage when the thread dial is at the right place you can do as I do, stop the lathe when you reach the far left hand side of your thread (at 115rpm it stops pretty quick) and leave the carriage feed engaged, back out the cross slide OR the compound slide one full turn (but remember where you were at), put the lathe in reverese and start the lathe up and let the carriage traverse itself to the right to clear your work piece. Stop the lathe, turn the cross slide OR compound back to where it was when you finished the last pass plus the amount of your next cut and repeat til the thread is cut.

I cut threads all the time. Tried it the way you are doing it at first and it does work just fine but I find using the lathe's reverse much less error prone.

cheers, Graham in Embrun near Ottawa