I met my Jerusalem-based tutor, who is also a klafim maker, and asked him for some yerios to get started. He asked, "so what size do you want and how many lines?", making me realize I had no idea of this key technicality. He told me the standard sizes are 45cm, 48cm or 50cm long klaf and since the table I use for writing is rather small I went for the smaller option, 45cm.
When I got back home in Europe, I realized I still needed a tikkun. And that's when things got really complicated.
Everyone I asked told me to call a Rabbi in Bnei Brak who's the authoritative tikkun-maker today, and I had a very interesting conversation with him. It turns out that until some 30 years ago, Sofrim didn't really have a good tikkun to copy from. They either used Chumashim, old codices like the Berdichev Codice or another Sefer Torah, until the renowed Sofer Davidovich took on himself to write a Tikkun for others to copy from, arranging all the Torah in Amudim of 42 lines. Now that's the important piece of information - 42 lines. In this arrangement, Davidovich's tikkun had 245 columns ("amudim"), and after some feedback from fellow Sofrim, who said that the lines where too "cramped", Davidovich made a longer, spaced up version of 247 Amudim.
Just a side point, it's important not to underestimate Davidovich's work - it was not easy to make the tikkun. In these days there was no PC and Davidovich had to arrange everything in his mind as he wrote - a work of a genius. And there are many rules to follow, for instance, we have a Mesora that some columns of the Torah must start with specific words - ביה שמו is the acronym for such columns (see in the right the column of "Yehuda Ata" which is one of these columns). Davidovich also followed the Minhag of starting all other columns with words containing a Vav as their first letter ("Vavei Amudim" - similar concept to the Hamelech Megillot) - further restricting the arrangement of the letters in the columns.
From then on, the 42-lined Tikkun became the standard tikkun all Sofrim used. For that reason, I understood why the Tikkun of 45cm I purchased from my tutor was also made for a 42 lines tikkun - this is virtually the case in all modern Sefer Torahs you will see.
This Rabbi told me that around five years ago, a Sofer asked him if he could supply him with an unusual 48 lines tikkun. He answered he only had the standard 42 lines arrangement but with the help of the computer and his experience, he could make a new one, although that would take time and money. The Sofer accepted it and because of him, now you can get a newer, more mehudar tikkun of 48 lines from this tikkun-maker. In other words, until five years ago there was no tikkun other than the 42 lines in the market for Ashkenazi scribes.
But why is the 48-lined tikkun better? Is it more Mehudar after all?
If you research deeper, you will realize that in Halacha, the 42 lined Tikkun is subject to debate. The most authoritative Sefer in Safrut, the Keset Hasofer, says (13:6):
(The Sofrim) have a custom of using (a tikkun) of not less than 48 lines and some say 42 lines and not more than 60 (...)
He comments further that the source is the Masechet Sofrim, an appendice to the Talmud, which says that the Amud should have at least 42 lines like the number of travels of the Hebrews in the desert. However, the Rambam (here), Tur and Rosh all say, based on the same source, that ideally the Amud should have no less than 48 lines and the Keset Hasofer concludes that they must have had a different version of this Masechet Sofrim, a very likely possibility as this Masechta is full of variant readings. But all in all, that's the reason why the new 48-lined tikkun this Rabbi has now is more mehudar.
The Keset Hasofer concludes that if it's possible one should write with at least 48 lines rather than 42. If it's too difficult, it's ok to write in 42 lines.
Interestingly, the Rambam also reveals that when he wrote his own Sefer Torah, he wrote in Amudim of 51 lines, which is within the ideal 48-60 bracket of how many lines a column should have. For this very reason, the Yemenite Jews to this day write their Torah with tikkunim of 51 lines in line with their custom of following all of the Rambam's rulings.
Bologna Torah has 48 lines, see on the right a 70-lines Torah, see here for 58 and see here for 55-lined examples); only the modern ones have the prevalent 42 that is the standard today.
My million dollar question is why Davidovich decided to write his Tikkun speicfically with 42 lines when he could have chosen to write with 48 or more lines. I don't know the answer to this question but one thing is for sure, the current 42-lines tikkun has 247 columns while a 48 lines tikkun has 213 or so - the extra columns of the 42 tikkun is extra money for the klafim-makers so perhaps they lobbied for this. Just a conspiracy theory...
Coming back to my case, I was thinking to give back the few yeriot of 42 lines I bought and make a special order of the unusal 48 lines klafim. I will only write one Sefer Torah and why not do it in the most Mehudar way?
My priority is to have the best, smoothest klaf possible - that's also a hiddur. When writing my 11-lined Megillah I got one bad yeria and it's really torture to write in bad klaf. If I make a special order for 48-lines klaf, I was afraid that since I couldn't pick and choose - special order means that the klaf is made to measure - I would surely get a few bad yerios without having the luxury of rejecting them. However if I went for a standard size, I could look around and be picky. So in one hand you have the hiddur of 48 lines without a guarantee of top klaf and in the other you have a 42 lines tikkun with a guarantee that you can always get the best klaf. Quite a paradox.
After another chat with my tutor, I learned that when making a special order you can request another hiddur - that the klaf should be "made without a tnai" i.e. that the person making this klaf has in mind that the klaf will be used for a Sefer Torah, and not for the lesser kedushot of Mezuza and Tefillin (normally he has in mind a condition - "tnai" - that he is making it for whatever purpose the sofer chooses - either for Torah or Tefillin or Mezuza).
So what did I decide? I will return the few yerios of 42 lines I got and make the special order for 48 lines klaf, taking a chance with the quality of the klaf. Maximum I will throw a few yerios away. Like this I have two extra hiddurim, 48 lines and klaf without tnai.
I will see in the coming weeks if all has worked out and if I end up receiving the new klaf. Wish me luck!