PDA

View Full Version : Multiple start threads



John K
08-02-2002, 03:41 PM
I need some technical help on how to machine a multiple start thread on a manual engine lathe. Do you actually index the part in the chuck by a certain number of degrees or what?
I have done this in a trade school about twenty five years ago but do not remember how the process worked. I thought that you split the threads per inch in two and then at the nominal thread per inch but I am not sure anymore. Help would be appreciated!

John Stevenson
08-02-2002, 04:47 PM
John,
First off you measure the thread with a set of normal pitch gauges. If it measures 8 tpi and it's a two start then the actual pitch is 4 tpi because you have two identical threads side by side.
Set your machine and screwcut the first thread as per normal.
For the second thread you mark oposite teeth on the spindle OR leadscrew gear. You need one that has an equal number of teeth. Pull the gear off and revolve the spindle or leadscrew until the opposite tooth lines back up. Tippex is good for this. What this will do is to place the tool 1/2 way between the thread you have already cut. Then you cut the second thread identical to the first.
HTH.

John S.

rbregn
08-02-2002, 07:01 PM
You can also turn your counpound so it is parallel with your piece. cut one thread, move your counpound half the pitch then cut the second thread. for 3 threads move 1/3 the pitch, etc. This is the easiest way I found.
Rob
sorry about the spelling. but I'm not a english teacher!

John Foster
08-02-2002, 08:44 PM
If you are using a double lead and a lathe dog,on centers, set the gear box to 4 as above, cut one thread to depth for 8 threads per inch. Take your part out of the lathe and rotate the piece so that the dog is now in to opposite slot of the drive plate and repeat (do not loosen the dog). You have now cut a double lead thread. Triple is just as easy but must be a multiple of 3 as the gear box must be set on 3 for 9, 4 for 12, 5 for 15, etc. Use the 3 jaw chuck with a piece chucked and turned to 60 degrees for a center and drive the lathe dog off the jaws.To make the nut, use the compound as suggested, cutting one thread, advance one pitch and repeat. John F

machine_rookie
08-28-2002, 10:04 PM
I know this one!!! In the book "How to run a Lathe" there is a concise description including pictures. I tried it on my Jet 818 and it worked. I've been using those examples and ruining good metal for months now....

------------------

David Hafnorske
09-21-2002, 11:03 AM
You do not need to take your piece out of the chuck. Just use your thredchasing dial. For instance, if you start the first thread on the number 1 and you want the second thread 180degrees from the first just engage your halfnuts on the nuber that is 180 degrees from number 1. Most likely the number 3.
<font face="Verdana, Arial" size="2">Originally posted by John K:
I need some technical help on how to machine a multiple start thread on a manual engine lathe. Do you actually index the part in the chuck by a certain number of degrees or what?
I have done this in a trade school about twenty five years ago but do not remember how the process worked. I thought that you split the threads per inch in two and then at the nominal thread per inch but I am not sure anymore. Help would be appreciated!</font>

John Foster
09-21-2002, 02:39 PM
A comment on Dave's suggestion. Most thread dials would continue to cut the same thread using 1 and 3 or 1,2,3 & 4, or even using the half marks for EVEN threads. But if you are cutting an ODD thread (7 on the gear box for 14 double lead) then cut one thread (lead) using the numbers and the second using the half numbers and you will have a double lead thread. You can do this by alternating between th etwo. Advance your tool, cut using the numbers, cut using the half marks and then advance the tool again and repeat. Also as I said above, turn the work half or third over using the lathe dog. Use the compoind rest for internal threads as mentioned. All of the methods work, some are easier than others.