Throttle body balance rod adjustment knob

[Chuck]

Looks like a job for a printer if you need one made..

[Pressureangle]

2 hours ago, Chuck said:

Looks like a job for a printer if you need one made..

My son has a couple high quality 3d printers he's playing with, but hasn't developed the knowledge to reproduce a part from a sample.

[docc]

I noticed that when I assembled the knob back onto the rod that it threads on easily at first then has a distinctive resistance the rest of the way through. Is this accomplished with some change to the threads, a slightly smaller inside diameter, or how?

[Chuck]

*I'm only guessing* but I'd bet is a smaller pitch diameter.

[Lucky Phil]

6 hours ago, Chuck said:

*I'm only guessing* but I'd bet is a smaller pitch diameter.

I'm thinking more a tighter "class" of thread. Bit like cylinder stud fit the crankcases the first half of the thread is neat and they firm up after that due to the class of thread. If you run a std bottoming tap through them they end up loose all the way thats why I don't do that.

Ciao

[Pressureangle]

18 hours ago, docc said:

I noticed that when I assembled the knob back onto the rod that it threads on easily at first then has a distinctive resistance the rest of the way through. Is this accomplished with some change to the threads, a slightly smaller inside diameter, or how?

There are specific criteria and design to threads with intentional interference. I'm not familiar with all of them, but with a cast plastic part it's simple enough to alter half of them, or any portion. If I was an engineer (prone to over-thinking lol) I'd make the portion under the fingerknob regular to facilitate starting threads during assembly, and make those inside the snout to interference spec. <shrug> 
Whatever we end up with, it will be mechanically machined so we'll have to discover the properties; I suspect a standard tap through delrin will leave an interference, given plastic always springs back a little when machined. Alternatively, we can machine the snout with a little reverse taper, tap it first and when the tabs are brought parallel in the hole the threads will tighten up. Today's mission is to get my rod assembly off and shipped north to the shop. 

[docc]

So, the V11 snout screws easily onto the rod first. When it reaches the knob portion, the resistance begins.

[Speedfrog]

1 hour ago, Pressureangle said:

If I was an engineer (prone to over-thinking lol) I'd make the portion under the fingerknob regular to facilitate starting threads during assembly, and make those inside the snout to interference spec.

That seems backwards to the intended goal... 

[Pressureangle]

15 minutes ago, Speedfrog said:

That seems backwards to the intended goal... 

Are you making an inquiry, or asserting an opinion?

[Speedfrog]

6 minutes ago, Speedfrog said:

That seems backwards to the intended goal... 

WAIT, so going back to @Pressureangle first picture it looks like the knob is mounted in a reverse position on the rod as it is on the V11. Are we looking at the Sport 1100? Is it a different configuration between the Sport1100 and the V11?

[Speedfrog]

18 minutes ago, Pressureangle said:

Are you making an inquiry, or asserting an opinion?

When referring to the picture of your assembly, you’re right.

It just seems backwards when looking at the V11 assembly...

[Pressureangle]

11 minutes ago, Speedfrog said:

When referring to the picture of your assembly, you’re right.

It just seems backwards when looking at the V11 assembly...

Apparently (only apparently so far) they are the same part, but installed in reverse on the Sport and the V11.  I won't try to guess what the Italian engineers did with the threads in any case, I've been suckered and lost every bet so far.

[Speedfrog]

If it is indeed the same knob on both models, could it be that the friction is only provided by the split collet portion, which looks unthreaded on docc’s close up picture of the knob.

[docc]

Yes, the part(s) appear the same between the 1100 Sport-i and the V11, with the V11 assembled with the throttle connector inboard and the knob outboard. More accessible, for sure. Perhaps a different length (longer) throttle rod?

While the collet portion is not threaded, the "shaft" portion of the snout is were my "loose"/(normal?) threads are. And the tighter threads within the knob portion.

I initially thought the collets grip the shaft for the necessary set friction, but careful measurements and inspection say no. They are only there to capture the steel block and allow the knob to spin within it.

[Speedfrog]

24 minutes ago, docc said:

While the collet portion is not threaded, the "shaft" portion of the snout is were my "loose"/(normal?) threads are. And the tighter threads within the knob portion.

As described, that knob mounted backwards on the throttle rod of a Sport 1100 would have friction as soon as the threads engage on the rod then.

I’m not trying to make a case one way or another, it just doesn’t compute in my little backyard engineer brain.