PDA

View Full Version : Multi-lead threads on the lathe



bgray43050
01-25-2008, 12:52 PM
I am going to be cutting multi-lead threads on the lathe.

I understand the concept, but I'm unsure as to how I will designate the starting point of each individual thread...

Will I use the thread dial?

Is there a guide or article somewhere online?

Thanks.

BadDog
01-25-2008, 01:15 PM
2 ways I've seen.

1) With compound set parallel to the axis, move over by 1/2 lead for 2 start, 1/3 for 3 start, etc. But that makes the cut harder since you can't slide in sideways with the compound. Depending on thread form, may not matter.

2) By indexing the work piece. Generally between centers where you can just move the dog to the opposite (or next) slot on the dog driver plate to get the number of starts you need. Limited by your creativity at indexing the work piece. Can use a center in 3 jaw for 3 start and such. Can be done other ways with a standard chuck but more fiddly and perhaps less accurate.

Then just use the dial in the normal way.

GadgetBuilder
01-25-2008, 02:00 PM
"Screwcutting in the Lathe" by Martin Cleeve has a chapter on multistart threading where much of the material is dedicated to automatically sequencing through the multistart threads being cut so all are completed more or less simultaneously. Cleeve describes the requirements of the leadscrew vs the thread tpi which must be satisfied to use his technique; if you have some freedom in the tpi then this may work for you.

If you will be cutting more than one multistart threaded part then purchasing Cleeve's book would be worth considering - it is one of my favorites.

John

SGW
01-25-2008, 02:04 PM
A couple of other possibilities:

Disengage the geartrain and rotate the spindle the proper number of teeth to index the work, then re-engage the geartrain.

Depending on the pitch of the thread, you might be able to choose different starting marks on the thread dial. If the thread is a multiple of 8 (assuming an 8tp leadscrew) it won't work because you can engage the halfnuts anywhere, but with 12, 20, 28, 36, ... I think you could get a 2-start thread that way.

tony ennis
01-25-2008, 02:12 PM
Is the only point of a multi-start thread to allow the nut to move faster?

ptjw7uk
01-25-2008, 03:13 PM
Enable the nut to move faster and retain some strength and uniformity of thrust as in optics where you want smooth even motion although depth of thread is a lot shallower in multi start threads
Peter

thebusdweller
01-25-2008, 04:25 PM
the valve industry uses these also, for fast opening and closing. remember, if you need 8 tpi, you really are cutting two separate 4 tpi threads, 180 degrees apart, for a double lead thread. four separate 2tpi threads, 90 degrees apart for a quad lead. the acme threads that i've cut are standard depth. tom

bgray43050
01-25-2008, 08:16 PM
Is the only point of a multi-start thread to allow the nut to move faster?

My application is a pen.

www.pencraftonline.com

The multi-lead threads allow the cap to be removed with one turn or so, and still retain strength. Removing a pencap with three turns gets tedious!

Errol Groff
01-25-2008, 08:30 PM
Some years back I made up some samples of multi start threads to demonstrate the concept to my students. I took some pictures of them tonight and posted them here:

http://tiny.cc/a5FkN

I posted a link on another subject a few days ago which got truncated. Maybe this tiny url will work better.



Errol Groff

darryl
01-25-2008, 11:30 PM
I think you could index the final gear in the gear train, the one that is set on the leadscrew. Put a mark across the last gear and the gear that drives it. Then pull the gear, turn the leadscrew by hand until the gear can go back on with the appropriate tooth engagement. If it's a 30 tooth gear, for example, turn it 15 teeth to get a double start thread, or 10 teeth each time to get a three start thread.
If the final gear has 17 or 19 teeth, you're screwed :).

oldtiffie
01-26-2008, 08:24 AM
I am going to be cutting multi-lead threads on the lathe.

I understand the concept, but I'm unsure as to how I will designate the starting point of each individual thread...

Will I use the thread dial?

Is there a guide or article somewhere online?

Thanks.

Hi bg.

I will try to remember to post about 20 links to pics on the subject that will clarify things for you - in the next day or so.

To post pics at a limit of 4 pics per post requires 5 consecutive/sequential posts which is a PITA all round.

bgray43050
01-26-2008, 08:44 AM
Hi bg.

I will try to remember to post about 20 links to pics on the subject that will clarify things for you - in the next day or so.

To post pics at a limit of 4 pics per post requires 5 consecutive/sequential posts which is a PITA all round.

Thanks very much.

Of course, please post it here for everyone else to see, but if it's convenience issue, you can email it to...

brian@pencraftonline.com

oldtiffie
01-26-2008, 08:52 AM
Thanks very much.

Of course, please post it here for everyone else to see, but if it's convenience issue, you can email it to...

brian@pencraftonline.com

Thanks Brian.

Too easy.

The longest part is going to be photocopying them, scanning them ad uploading them to Photobucket.

After that I will insert the links into a post on this thread and then I will cut and paste the links into an email and send it off so you will get the links twice.

It will take a day or so.

oldtiffie
01-26-2008, 11:12 PM
I said that I would upload the details on "Screw-cutting in a lathe".

I have done that - see the 20 links at the end of this post.

I have read the posts to this thread again and I thought it both timely and hopefully beneficial if we were all to go back to basics as regards what threads and thread-cutting - single and multi-start etc. included - is.

The following links (20) will cover the theory and terminology.

I have used links instead of pics as it would require 5 posts (I am limited to 4 pics per post) and some will get bored sh*tless with up-loading the pics.

The links were scanned at 150 dpi after photo-copying them. The "roman" (serif) fonts lost a bit in the process. I would suggest that you copy the files to your computer and read them off-line as the images will be better -much. I use the "freebie" called "Irfanview" - works great.

Another perhaps better method is to click the link, place the mouse icon on the image when it loads and wait for the orange square with the expand/reduce arrows to appear at the bottom right of the image. Click that to "expand" the image and then use your mouse and the scroll-bars. It makes a huge difference and it improves legibility a lot.

The book I am using for this is authored and published in and by one of our Universities here in Australia - for Apprentices and Engineers, Drafters etc. etc. that have to do their "Work-shop" stuff (class-work, shop-work, assignment work etc.)both in the University and the wider community.

I continually find it an excellent reference as it covers the whole gamut/spectrum of Fitting and Machining (as we call/know it here).

It is pretty well the standard reference here.

It starts off at the basic level and progresses to intermediate level mainly - but often quite further on from that in parts.

It is also a "Primer" for "Machinery's Hand-Book" and the like later.

MHB assumes a good back-ground when it is being used - just as some software assumes a basic/good back-ground and competency in the use of "Windows" and computers generally.

The "path" may be seen as "crawl > "walk" > "run". That is the path I am taking here.

There are some here that are well into or past the "run" stage (and some that think they are but may not be).

There are others that are at the "crawl" and "training-wheel" stages.

They are the ones I am trying to help here.

Hopefully, when you have read this thread and posts in a lot more people will be better informed and a lot more confident in the use of their shop and "Machinery's Hand-Book" and similar references etc.

And in particular as it applies to threads and screw-cutting generally.

In reading these links please do understand that the principles in them are correct.

They are not necessarily the only or best way/s of doing it.

Other people will have other methods and points of view.

There is no one "right way".

But the best way is the one that you use that you feel best using.

I hope this helps.

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

oldtiffie
01-26-2008, 11:25 PM
Hi bg.

I will try to remember to post about 20 links to pics on the subject that will clarify things for you - in the next day or so.

To post pics at a limit of 4 pics per post requires 5 consecutive/sequential posts which is a PITA all round.


Thanks very much.

Hi Brian.

I have posted the links for threading - including multi-start - as I promised at:


Of course, please post it here for everyone else to see, but if it's convenience issue, you can email it to...

brian@pencraftonline.com

Hi Brian.

Task done.

I have posted a summary/explanation and 20 links at:
http://bbs.homeshopmachinist.net/showpost.php?p=329969&postcount=14

I hope it helps.

Mike Burdick
01-26-2008, 11:48 PM
Oldtiffie,

I made a pdf file out of your 20 jpeg files and if you want I can send it to you. If you can find someone to host the file it'll be a lot easier for people to download it

Send me your email address in a PM if you want it.

Mike

tattoomike68
01-26-2008, 11:50 PM
Oldtiffie,

I made a pdf file out of your 20 jpeg files and if you want I can send it to you. If you can find someone to host the file it'll be a lot easier for people to download it

Send me your email address in a PM if you want it.

Mike

I can host the pdf file.

Mike Burdick
01-26-2008, 11:54 PM
tattoomike68,

Okay...I'll email it to you. Please send me a PM to an email address.

S_J_H
01-26-2008, 11:58 PM
oldtiffie, thanks for taking the time to post these files, they are an excellent read!

A single PDF would be great!
Steve

tattoomike68
01-27-2008, 12:08 AM
oldtiffie, thanks for taking the time to post these files, they are an excellent read!

A single PDF would be great!
Steve

As soon as the e mail get here I will post a link to the pdf file.

tattoomike68
01-27-2008, 12:22 AM
I attached the PDF to a thread here, I have permissions set so anyone can download it.

http://www.homemodelenginemachinist.com/index.php?topic=1219.msg8744#msg8744

tony ennis
01-27-2008, 11:25 AM
(deleted )

Paul Alciatore
01-27-2008, 01:30 PM
There are lots of ways of doing this. You could do a search of the archives as it has been discussed at length before. I believe I posted some rules for what kinds of threads could be done with the threading dial.

Another way not mentioned above is to use a tool with multiple Vee shapes spaced at the thread's pitch distance while the lead screw is set for the thread's lead. This allows you to cut all the starts at once. Good time saver if many parts need to be made. Some have used broken taps to do this if the length to be threaded is short. The tap is held parallel to the work surface.