Single thread or musti start?

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Dan_F

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I would like to know the pros and cons of each type of threads for pens. Please discuss...

Here is what I know (or believe) as of this moment, based on my very limited experience:

Multi starts can be a pain in the butt, especially if you have several new pens and can't remember where to position the cap on each one as you close it so that it aligns properly with the other half.

Multi starts require fancy (expensive) taps ind dies.

Multi starts make it particularly challenging to assemble a Little Havana fountain pen, and be able to get the cap to align in both closed and posted position.

So, are there any benefits to balance out the disadvantages?

One negative comment I've heard about a single start pen, the Berea El Toro, is that the cap has to be turned over three revolutions to close. Is that a requirement of single start threads, to need more turns to be secure?

Please enlighten me.

Dan
 
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DCBluesman

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A single start thread provides the advantage over a multi-start thread of offering greater resistance to unscrewing after the spigot (the part with the male threads) has been inserted tightly into the socket (the part with the female threads). The steeper helix angle of a multi-start thread enables a spigot of any given length to be inserted into the socket with less rotation and, therefore, faster. Additionally, a multi-start thread reduces the amount of rotation required on average to engage the thread when starting from a random orientation. Also, because a multi-start thread is deeper cut than a single start thread, the shear strength of the threads can be greater. A shorter spigot length is therefore possible.
 

skiprat

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Originally posted by DCBluesman

A single start thread provides the advantage over a multi-start thread of offering greater resistance to unscrewing.....
I agree 100%. For 'normal' nuts and bolts you don't want them to come apart easily. However, I believe that for pen caps, the lesser resistance to unscrewing is an advantage. You can easily tighten a single thread, by hand, so that you struggle to un-do it.

The steeper the helix angle, the easier it will be to undo. Naturally, the helix angle increases as the number of starts is increased. Of course, you could over do it by having so many starts that each thread is almost parallel to the spigot.
 

Chuck Key

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There are many trade offs as in this photo:






The lead is the same in all three examples. You have to ask yourself which is more appropriate for the appliation at hand. For pens I would just as soon use the less aggressive four start thread on the right since there is a possibility that I would have physical contact with the threads. Also, trying to put the example on the left as a cap thread would leave a rather large step to the nib and would be quite unsightly in my view. If I were building a battleship and need to join two thick metal plates the thread on the left might be the better choice.

A second point. Multi start threads can be made with out expensive taps and dies on most metal lathes.

Chuckie
 

Dan_F

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Thanks for responding.

If I were to go with single thread, would 2 turns of thread be sufficient, as opposed to the 3+ turns used on the El Toro? It would be very convenient to be able to do exactly 2, and be able to line up the cap in the same position to start as it will end up.

So far, I haven't heard of any complaints about El Toro caps locking up, has anyone actually experienced this?

Dan
 

bgray

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Just as a heads up, Very rarely will pen collectors prefer single start threads.

There are only one pen manufacturer that sometimes puts single-start threads on their pens that I'm aware of, and that's Dani Trio.
 

rherrell

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What's so dismal? These guys are talking about selling to collectors and the "tradition" of the fountain pen.
Do you plan on selling your pens to "collectors"?
Do you WANT to make a traditional pen?
If not, go for it. If it turns out like c#@p then you'll have learned something. If it doesn't, then you'll have learned something too, tradition ain't all it's cracked up to be.:D
 

Chuck Key

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Ok, so you have decided to break with tradition and go with a single lead thread. Will a commercial tap and die be used? Will it be 3/8, 7/16 or 1/2 inch standard thread? You might grab a 1/2 bolt by the threads as you would hold a pen and see if it feels right before spending alot of time and money buying the tap and dye and preparing the blank. If it feels right you are good to go.

Chuckie
 

Dan_F

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Well, between the fact that the general opinion is they are not very sturdy and are difficult to sell, the outlook isn't exactly encouraging.:D

At this point I'm just considering options. I have one of the multi thread tap and die sets coming from the group buy, but would like not to be limited to El Grande sections.

I'm thinking about a mini metal lathe, but can't find much in the way of info on cutting MS threads with it. I have no experience with such things.

Dan
 

Texatdurango

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Originally posted by Dan_F

... I have one of the multi thread tap and die sets coming from the group buy, but would like not to be limited to El Grande sections...
Hi Dan, Either I am misunderstanding you or you are misunderstanding what you can do with your new tap and die set.

For starters, the threads the tap and die set will make are indeed the same as the threads on an El-Grande pen kit but that's where the similarity can end. Many pen makers chose this particular thread because th El-Grande is a popular pen to modify. This DOES NOT mean that you have to make El-Grande compatible pens or use any El-Grande kit parts when using this tap and die set.

I have made a few dozen different pens whose threads have been cut with the tap and die set mentioned and if you've noticed any photos I have posted lately, none of them come close to an El-Grande! I start with an acrylic blank, do some drilling and tapping, a little notching here and there, grab some silver stock and add a center band and an accent ring or two, add a clip and call it a pen!

You are free to design any kind of pen you want. The only constraints you have using a tap and die is that the cap and body diameters must accommodating the threads.
 

PenWorks

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Dan, I wouldn't be so down either. I made these single thread designs well over 3 years ago and they work just fine. The black one closes in one turn and the red one takes two turns. As for collectors. I have never sold a pen to a collector that has asked if it is a multi start thread [:0] They either like how the cap screws on or they don't. I say go for it, these were just cut with a standard fine tap & die set, nothin fancy.







 

RussFairfield

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OOOOps, I deleted my previous message when the power went off in the middle of revising it. Here it is again with some additional comment.

It is all a matter of the shear strength of the threaded parts. The more threads engaged the higher the shrear strength of the thread. 5 full threads is a commonly used rule for thread design. Most pens have somewhere between 4 and 5 full threads engaged when the cap is on the pen.

A pen cap that requires less than 2 full turns to screw it on the pen is a lot more "user friendly" than one that requires 5 turns to accomplish the same thing.

A single thread with only 2 or 3 threads will be a weaker thread, and more likely to be damaged.

Then, as Lou said, the steeper lead angle of the multi-lead thread also requires less effort to screw on and off and break the seal when it is removed.

There is also the matter of "tradition" for fountain pens. Like pens with caps that don't post, it is all but impossible to sell a pen without a multiple-lead thread and something close to 5 full threads between the pen and its cap. Most buyers don't like things that are different from what they are used to seeing. However, you will find this preference will be different in different markets, if you are selling pens.

We can use any size and number of threads we want if we are our own customer. We will have to alter our design to meet the needs of someone else if they are the custopmer

Having said all of this, the bottom line is - it has nothing to do with the thread size, how many threads are engaged, or how many twists it takes to put the cap on the pen. Within reasonable limits. if it works, stays on, and doesn't wear out, the customer will like it and buy it, even if it doesn't have any threads at all. Yes, there is a case to be made for the "slip fit" cap.

"Reasonable limits" would dictate that I don't use a 1/2" coarse thread, but I might be inclined to use one of the fine or extra-fine thread series taps and dies for cap threads. Quite often, a metric thread is better suited, and again, taps and dies are available.

And, don't give up on the ElGrande tap and die set. It can be used for a lot more than duplicating the cap threads on an ElGrande. I would not be surprized if you couldn't make a postable cap for a Baron with these threads. Or, you can design your own pen, and forget about the kit.
 

PenWorks

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Another way to look at single lead threads, the Michel Perchin rep was in today. I was foundling the new Limited Edition Red Cross pen, retail around $4,500.00 As I was unscrewing the cap, which I was doing very slowly, turning, turning & turning seemed to go on forever...........:)

As if you were slowly unwraping a present you knew would be amazing once you opened it.
Sometimes, that is how a fine pen should be, why are we always in a hurry. Like fine wine, most of us don't beer bong a $100.00 bottle of wine :D

$4,500.00 pen, single lead thread, I would say it is a collectable pen [8D]
 

Chuck Key

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I think we are getting back to one of Dan F's concerns expressed in his original post. That being "fancy (expensive) taps and dies" but now we are talking about single start taps and dies.

I looked at the pen that Anthony mentioned. It looks like a one lead and pitch thread at about maybe 25% depth. That would difinately be a special order item.

The el Grande tap and dies are 12mm x 0.8 three start. A 12mm x .8 single start would also be a special order item as far as I know. That size would translate to about a 1/2 inch x 32 tap and die which again would again be custom. Some of you may know where to get these special sizes off the shelf and I would like to know where they are located:)

Chuckie
 

Dan_F

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OK, I guess the news is out, I do get a bit confused form time to time.[:0]. I keep associating the tap and die set with the section instead of the cap.

My initial post was born of the the frustration of dealing with a four start thread set for a Little Havana kit, on which I wanted to have the blank line up in a certain way. Since this is a pen that virtually requires the cap to be posted for use, as the body is so short, it needs to align correctly when capped as well as when posted, or the clip will digging into the hand when writing. That makes is necessary to remember two sets of landmarks to start the threads for closing or capping the pen. Multiply this by a hand full of pens, and that's a lot to remember, particularly for one who is prone to "senior moments"

So if there was a cheaper, simpler way of doing things, that would be good as far as I'm concerned. I would love to see some ideas on friction or snap fit caps too, as that's the direction I'd rather move in.

Anthony---What size of tap and die set did you use for the pens you posted?

Texatdurango---Yes, I have seen your pens, and in spite of that, for some reason my brain simply reverts to following the pattern of the kits. Just force of habit I guess. Thanks for reminding me.

Russ---Thanks for clarifying your previous post. I would like to come up with something like a closed end Little Havana, with beefy, non coved, similarly weighted section, but a much lighter friction fit cap. I would think that this could be made to balance reasonably well with the cap posted. I'm not a fan of feather weight pens, though find the full sized CSUSA pens such as the Gent a bit too heavy. In fact, I 'm not completely happy with any of the FP kits I've done, between issues of weight, balance, comfort of section, and nib.

Well enough rambling, thanks again to all who have contributed.

Dan
 

bitshird

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Originally posted by Chuck Key



The el Grande tap and dies are 12mm x 0.8 three start. A 12mm x .8 single start would also be a special order item as far as I know. That size would translate to about a 1/2 inch x 32 tap and die which again would again be custom. Some of you may know where to get these special sizes off the shelf and I would like to know where they are located:)

Chuckie
Chuckie; MSC has 1/2-32 in an H3, they also offer a 12 x.5 pitch, I'm not to up on DIN class but it was D6 so it's probably a bout the same as our class 3, prices weren't that bad,
 

Chuck Key

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Excellent! Thanks. I found out Victor Machine also has a good selection also including a 7/16 x 64 tpi. Can you imagine, put just 1/8th inch of threads on the cap and it would take eight turns to tighten the cap :D

Chuckie
 
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