I'm replacing a few tendons as regular maintenance - Chinook tendons in a Chinook base. The holes in the tendon aren't quite aligning with the bolt holes. I'm off about 1 mm which doesn't sound like much but it doesn't allow the hex bolt to line up with the nut on the other side and the threads won't catch.
As there any reason I can't take an appropriate sized drill bit and straighten the hole? Don't want to do something that'll result in a swim.
Oddly, I've had this issue with all three tendons I bought which according to the stamped date are all from different lots.
Do you mean the tendon is not fitting into the uni housing fully i.e. the tendon hole needs to push in 1mm more. I have used Chinook unis & tendons forever and never had this issue but try pushing down on the end of tendon so it fully engages into the pin or base housing.
No, it fits properly that way, insertion. If you looked at the tendon from the top looking down, the hole for the retaining bolt isn't quite on the line of the diameter (ie the retaining bolt). If that doesn't make sense, I'll snap a pic in a while.
Appreciate it.
I just put it in the vice and twist a little as the bolt is inserted
Or is it misaligned even more than that?
Here it is. No amount of twisting seems to get it over enough. The nut is so shallow that trying to force the bolt into it seems like a recipe for just chewing up the threads. The nut seats pretty firmly into that square "hole" and doesn't seem to have any wiggle room. I've tried running a longer screw through there, seating the nut and then retrying the original socket screw but the misalignment persists.
I'm usually pretty good with wrenching things but this one has me.
Davox, you missed in the original post where I liberally sprinkled around the word chinook 
Select to expand quotePaducah said..
I'm replacing a few tendons as regular maintenance - Chinook tendons in a Chinook base. The holes in the tendon aren't quite aligning with the bolt holes. I'm off about 1 mm which doesn't sound like much but it doesn't allow the hex bolt to line up with the nut on the other side and the threads won't catch.
As there any reason I can't take an appropriate sized drill bit and straighten the hole? Don't want to do something that'll result in a swim.
Oddly, I've had this issue with all three tendons I bought which according to the stamped date are all from different lots.
If a longer screw works, I don't follow that the hole isn't aligned?
i would not hesitate to drill , which part are you contemplating drilling?
Select to expand quoteamirite said..
tendon is a little too long
cut it shorter by .......mm
It's a left right thing. The height is spot on.Select to expand quoteforceten said..Paducah said..
I'm replacing a few tendons as regular maintenance - Chinook tendons in a Chinook base. The holes in the tendon aren't quite aligning with the bolt holes. I'm off about 1 mm which doesn't sound like much but it doesn't allow the hex bolt to line up with the nut on the other side and the threads won't catch.
As there any reason I can't take an appropriate sized drill bit and straighten the hole? Don't want to do something that'll result in a swim.
Oddly, I've had this issue with all three tendons I bought which according to the stamped date are all from different lots.
If a longer screw works, I don't follow that the hole isn't aligned?
i would not hesitate to drill , which part are you contemplating drilling?
There's enough tolerance in the screw hole but not in the spot where the nut has to seat. It seats the nut by compressing the tendon just enough. But the socket screw that is supposed to go in there is so short, there's no way to force it over enough to get that small nut to thread on. There's a temptation if nothing else works to get a longer socket screw and then grind/cut off the excess. However, the one that goes in there as a smooth shaft and I don't know if that's important vs most that are threaded their entire length. I'm probably overthinking this but I'd rather ponder the issue now not during a 90 minute swim. 
I'm considering drilling the tendon itself to ovalize it just enough to get a straight shot out of the hole. I'm assumed the original holes were drilled.
I would definitely use a screw with a flat shaft part going through the tendon . Longer screws , usually over 50 mm start having flat shafts up to the head . So maybe a 70 mm one will work good . Thread it on , push it sideways and hacksaw the excess off .
Select to expand quotePaducah said..
Here it is. No amount of twisting seems to get it over enough. The nut is so shallow that trying to force the bolt into it seems like a recipe for just chewing up the threads. The nut seats pretty firmly into that square "hole" and doesn't seem to have any wiggle room. I've tried running a longer screw through there, seating the nut and then retrying the original socket screw but the misalignment persists.
I'm usually pretty good with wrenching things but this one has me.
Davox, you missed in the original post where I liberally sprinkled around the word chinook
Paducah,
Is that actually a Chinook uni as I've never seen one of theirs like this????? chinooksailing.com/collections/mast-bases-pin-style
EDIT - well I was wrong chinooksailing.com/collections/mast-base-parts-hardware/products/tendon-screw-and-nut-us-set
By chance is the bolt slightly bent as I've had this happen before? You can get replacement bolts from www.surfsailaustralia.com.au/product/surf-sail-australia-tendon-pin-locking-nut#surf-sail-clothing-hardware
Select to expand quotesausage said..Paducah said..
Here it is. No amount of twisting seems to get it over enough. The nut is so shallow that trying to force the bolt into it seems like a recipe for just chewing up the threads. The nut seats pretty firmly into that square "hole" and doesn't seem to have any wiggle room. I've tried running a longer screw through there, seating the nut and then retrying the original socket screw but the misalignment persists.
I'm usually pretty good with wrenching things but this one has me.
Davox, you missed in the original post where I liberally sprinkled around the word chinook
Paducah,
Is that actually a Chinook uni as I've never seen one of theirs like this????? chinooksailing.com/collections/mast-bases-pin-style
EDIT - well I was wrong chinooksailing.com/collections/mast-base-parts-hardware/products/tendon-screw-and-nut-us-set
By chance is the bolt slightly bent as I've had this happen before? You can get replacement bolts from www.surfsailaustralia.com.au/product/surf-sail-australia-tendon-pin-locking-nut#surf-sail-clothing-hardware
No worries. Bolt is straight. Otherwise, it would be off the other way every half turn Good theory to investigate, though. I love a challenge. I'll get this sorted. Appreciate all the help. I didn't want to reinvent something someone else had already figured out since there are so many here that are more clever than me.
Select to expand quoteImax1 said..
I would definitely use a screw with a flat shaft part going through the tendon . Longer screws , usually over 50 mm start having flat shafts up to the head . So maybe a 70 mm one will work good . Thread it on , push it sideways and hacksaw the excess off .
Hummm, some confusion here, a screw is what you drill and screw into wood, a bolt is what you put a nut on the end of like in the picture. A fastener with a shaft (i.e no thread for some of its length) is called a socket screw, a faster with a phillips head and threaded shaft is called a machine screw ....I know its confusing! Bolts machine screws and set screws can have various head configurations, hex, Allen socket, slot, Phillips Torx socket etc etc.
You might get a female sex screw through there and then you can wind the male half back into the female?
en.wikipedia.org/wiki/Sex_bolt
It's best to try and press the base together, possibly twist the tendon gently to line up the bolts and get the bolt through.
When the tendon is in as tightly as possible, there will be less stress on the holes. It will then last longer.
