Representation of four start thread and manufacturing 2

Hello Group,,

Can I get any help from this group for the above issues? I'am badly stuck up with my design coz of this. Appreciate any response on this.

Thanks,

Sandy

You should only be concerned about
the full depth threads. If a tap with
4 thread lead cuts the threads,
you want to tap the depth of full thread.
Why do you need to show the excess
partial thread?

I'am sorry diamondjim, I really did'nt follow your question. I don't want to show the excess partial thread. Just want to know the standard representation of a four start thread on both male and a female part drawing.

And my second question is (I'am repeating this!) if this part is to be manufactured, is there any standard taps & dies that are available for 4 start threads, if yes, can you please provide me with manufacturers for this. Or Is there any standards or any other process to be followed for while manufacturing these special threads?

thanks,

If you have a 1/4" bolt with 20 threads per inch it would be 1/4-20 UNC-2B (Internal) and 1/4-20 UNC-2A (External). That is if, in fact, you have a unified screw thread. That being said, the American Standard for unified screw threads does not have any multiple start threads in it. Multiple start threads refer to Acme threads. There is a standard for designating multiple start threads, but it refers only to Acme type (ASME/ANSI B 1.5-1988). The smallest Acme thread is .25-16 ACME-2G. Perhaps that is what you have??? Place the tip of a pencil in one of the thread grooves of the bolt. Turn the bolt one revolution. If the tip of the pencil is in the next groove, then you have a single start screw. If there are three grooves between beginning and end then you have a four-start screw.

I'm confused why you would use such a thread.

If I understand you correctly you have a 1/4"-20 thread with a 4-start...(5) turns of the screw advances the nut 1"? I think this is a VERY bazaar thread.

Functionally you would get the same movement with a 1/4-5 ACME (which is not standard)...but a 1/4"-4 ACME is. Actually 1/4"-4 is really 1/4"-16 with 4 starts according to my favorite ACME supplier.
Your thread would be very fine and EASILY destroyed while an ACME thread is far more robust. If you would use a standard thread angle for your thread it would barely turn without locking up, much less supply any clamping force.

Please explain yourself more and explain why you would want to use such an animal.
I would suggest trying to use comercially available threaded rod and nuts since machine shops really charge a premium for this type of work.

First I want to verify what thread you are trying to make/use. The term of lead refers to the advance of the screw in one revolution. Your screw if I follow you will advance .200" per revolution. Pitch is the distance between adjacent thread forms or lead divided by number of starts which will be .050". If I were to show a multi-start thread I would represent it like any other thread with alternating lines crossing the area with shortened lines between the full width lines. I would call out the thread with a very complete note such as

.250-20UN-2A 4 start thread
.200 lead .050 pitch
Major Dia .2489/.2408
Pitch Dia .2164/.2127

I would use the UN designation trying to show a Unified Thread Form and the 2A to reference the tolerance range that I would want. I would then show the actual tolerances so there would be no questions of what you want. This may be not the proper method of calling out this thread but it will be understood by any competent machinist or supplier.

Look for "multiple lead", "quad lead" as well as "multipe start" threading tools.

Some examples:

From AMSME Y14.6-2001, Screw Thread Representation:

For 60 deg inch threads, the thread designation should include, in sequence, the nominal diameter in inches, the number of threads per inch, the letter symbol of the thread series, the number and letter of the thread class, and any qualifying information. For multiple start threads, replace the number of threads per inch with pitch in inches (P), lead in inches (L), and the number of starts in parentheses. An alternate designation method for multiple start threads retains the number of threads (pitches) per inch and adds lead in inches (L) and number of starts in parentheses following it.

Example:
Standard Unifìed Multiple Start Thread, Gaging System 21

.750-.0625P-.1875L(3 STARTS)UNF-2A(21)

or

3/4-16-.1875L(3 STARTS)UNF-2A(21)

That should have been "ASME" not "AMSME"...

You are not going to find any standard taps or dies for a four start (4 lead) thread. They can be made to order by any of the good tap and die manufacturers.

For those of you that are saying that this is a wierd thread, you are right, but I have seen much stranger ones. I actually was involved with a #10 four start thread that a customer wanted to use to speed up their assembly process (imagine: only one fourth numbers of rotations to seat a screw! What speed!). We were able to make the screws (roll thread dies from Reed) but the application didn't work well because the helix angle was so steep that the parts are terrible loosening issues.
(Tried to tell him.....)
There are a huge number of double helix threads in use. Many of the special plastics threads are double helix (HiLo and Twin helix Plastite are two examples).

Dick

Thanks a lot group for your valuable insights. I'am surely enlightened regarding the multi start threads.

It sure is a strange thread, but as Screwman said, there are even more wierd ones in the market!

Thanks again group,

adios

Sandy

Sandy, how did you get your pitch measurement? You say it looks like a fine thread, i wonder if maybe you have a 1/4-80, 4 start?

Hello Metalart,
I measured the pitch by counting the number of threads per inch. So there were 20 threads per inch, but, they were 4 starts. So it meant, it had only 5 threads per inch from one start. Hope this makes sense. I wonder why you would say that it would be a 1/4-80, 4 start.

Hope this clears everything.

Thanks,

Sandy

Hi Sandy,
I had seen your comment, when you said it looked like a fine thread. And a pitch of .200 to me doesn't look fine.So I was just running some numbers and came up with the 1/4-80, 4 start, which would have a pitch of .05, which to me would be a functional equivalent to a 1/4-20.
Funny thing is I found this web site because I am looking for information on a 6 start thread, so I have found all the comments great. I am trying to layout a Metallic Drive screw, #00, and get some screws made by Monday.