multi start threads

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babyblues

babyblues

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I'm not sure I understand the math involved here. For example, what do the numbers mean for the tap and die group buy that's going on currently - "M12.0x0.8Px2.4L"

How would you know if it's a multi start tap and if so how many? I feel kinda clueless, but I'd like to learn.
 
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I will take a shot but am not entirely sure as I am not as familiar with metric taps and dies as I am with Fractional.
M12.0X0.8X2.4L"
M= Metric (my best guess anyway)
12.0= bolt or screw diameter like 1/2 inch etc in this case it is 12.0mm
X= By like in 2X4 (two by four)
0.8= this one I am not completely sure of in this case but this number should be number of threads per inch. since I think the P means Pitch then 0.8 would be the threads measured by pitch. again sort fo a guess here.
P= I think pitch
2.4= not sure of this one either unless it has something to do with the depth to which the tap will cut threads. that one is a real guess as I have never seen the third number added to a tap or die.
 
I'll have a go at answering this.

On a metric thread the pitch is normally equal to the lead. Except on a multi start thread.
Commonly you would see M12.0 X 0.8 only. This would be a single metric fine thread. The clue here is the 2.4L though

M12.0 is the diameter of the thread
0.8P is the pitch. So the thread is 0.8mm deep
2.4L is the lead. So one rotation of the 0.8mm cut would have a length of 2.4mm.
So if you started the cut at say 12 o'clock on the bit you were threading, then the next time the cut was at 12 o'clock then you would have traveled 2.4mm along the material. 3 x 0.8mm cuts set at 120 degs apart will be 2.4mm. So you know it's a 3 start tool.

If the spec on the tap was say M12.0 x 0.8P x 3.2L then it would be 4 start etc

Hope I didn't confuse you more:smile:
 
I looked this up recently.

12 is the diameter in mm of the part being threaded with a Die. For the tap, you need it to be smaller, about 10.2 mm

.8 is the distance in mm from one crown of thread to the next (or any part of a thread to the same point on the next adjacent thread)

2.4 is the overall distance of the threading. Or the distance from the peak of a thread to the next peak of the same thread. Remember that we have three threads going around this thing.

So a 12x.8x2.4 is a 12 mm shanked piece with threads spaced .8mm apart with 3 starts (.8*3=2.4)
 
There is hope!!!
At least that sounds right to me. I was starting to get lost there for a minute. Not sure Iwill remember it the next time I need it though.
 
Mike, you made me laugh, thanks. I always think of threads in T.P.I. this is the first time i have had Pitch explained in a way that I got it. makes since though, at least to me so you both did a good job at clearing it up. I do have a side line question but will tell you why.
I am sort fo poking around to see if these taps and dies can be gotten at a lower price. maybe a much lower price. I am not sure at all that this will go over as there are a lot of issues.
First there are already Bulk Buys that get done out there and I do not like to step on toes. I do not know what sort of deals that buy has made with suppliers, friends etc in order to make those buys work.
second the source has a lot of concerns about not only quality but being able to verify that quality etc.
and finally I know a lot more about drill bits and saw blades than I do Taps and Dies. I am sort of shopping for something that I don't really even know how to look for or ask about. I have found a source for taps and Dies as is the standard type, and am waiting to hear if they can even make a triple start set.
now for my question.
What sort of taps are needed to make threads on pens? are there different sizes etc? or does the one pretty much cover it. I also noticed that the group buy that is going on offers different types such as taper, bottoming or plug. is any one of these the.
best. what I am up against is that same old Min Order thing so narrowing the offering to just one type is pretty much a must.
 
I'm not aware of differences in the Dies, but the different types of taps are for different situations.

tapered - easiest to start. 5-6 of the first threads are ground at a bevel so you don't get a full cut until the 7th thread hits.

plug - the standard. 3-4 of the first threads are ground at a bevel. first full cut on the 5th thread.

bottoming - used when you need full threads all the way to the bottom of a hole. Very difficult to start (only 1-2 threads are ground) and as such is usually used in conjunction with one of the others. Start with a plug tap, and finish with the bottoming tap.
 
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