Restrictor Tolerances

[Max Frohnen]

We recently finished machining our restrictors. They all came in around 19.95mm (about 2 thousandths of an inch under) and we are happy with that. That said with them so close to 20mm I am worried about tech and the possibility of their go no-go gauge not being spot on. How close (or how far over) have other teams been?

We have had issues with ours being way off in the past so I can't really use our experiences as good benchmarks.

[jlangholzj]

Originally posted by Max Frohnen:
We recently finished machining our restrictors. They all came in around 19.95mm (about 2 thousandths of an inch under) and we are happy with that. That said with them so close to 20mm I am worried about tech and the possibility of their go no-go gauge not being spot on. How close (or how far over) have other teams been?

We have had issues with ours being way off in the past so I can't really use our experiences as good benchmarks.

I'm assuming that they're not going to be too angry about your restrictor being too small....too large on the other hand....you should be okay but it never hurts to ask for a rules clarification from the smart folks.

[PatClarke]

Max,
There is no tolerance on restrictor diameter. There is an absolute maximum of 20mm (in your case) which is checked with a certified 'Go/No go' guage.

Your 19.95mm restrictor will be fine.

Pat

[Tim.Wright]

If you're that close, there's an easy fix if you are slightly over. We glued a piece of paper to the inside of our restrictor after we found our fibrglass moulded restrictor was slightly oversize.

Tim

[Max Frohnen]

Good point about the paper. Did you have to go through the tech line again or were you able to just do it there?

[coleasterling]

We passed tech last year at Lincoln just fine and I machined our restrictor to 19.995(yes, .995).

The tech people won't let you touch or see the gauge, nor tell you the tolerances. I suspect that they aren't that close themselves. We went through tech inspection twice since we were a top team in Endurance. The first time, the guy commented on how close it was and said it barely caught. There was a solid thud the second time.

That said, I made it that close because I could. There's no advantage to it over being two thousandths of an inch under.

[Owen Thomas]

Your 0.05mm under tolerance should be fine, but for anyone else reading this thread worrying about the same thing, keep your 20.000mm aluminum restrictor out of the hot sun before tech!

Most people are smart enough to build some insurance into such a rules critical item, but I just thought to throw that out there. It is worth doing.

[Tim.Wright]

Originally posted by Max Frohnen:
Good point about the paper. Did you have to go through the tech line again or were you able to just do it there?

We went through tech again only because we had a shoppinf list of other things to fix too (as usual).



Originally posted by coleasterling:
We passed tech last year at Lincoln just fine and I machined our restrictor to 19.995(yes, .995).

I'm actually more interested to know not how you made your 19.995mm restrictor but rather how you measured it.

[Warpspeed]

And just pray that the day on which it is measured is not a really hot day.

[coleasterling]

That's the easy part! I used a 20mm plug gauge that measured 20.000mm (my mics are only 0.001mm) as a no-go gauge and made another plug gauge that measures 19.995mm. I opened it up until the 19.995 gauge went and the 20.000mm gauge didn't. So it isn't exactly 19.995mm, but somewhere between 19.995mm and 20mm. Close enough for me. But you are correct, it isn't exactly 19.995mm.

[Warpspeed]

Just wished to point out, that at those tolerances, ambient temperature changes can eat right through your margin.

Coefficient of expansion of what you make it out of may also be worth thinking about if running that close.

[Tim.Wright]

Originally posted by Warpspeed:
Just wished to point out, that at those tolerances, ambient temperature changes can eat right through your margin.

No worries bro, ambient temperatures also expand the tech inspectors gauge http://fsae.com/groupee_common/emoticons/icon_cool.gif

[Michael Royce]

The tech inspectors' gauges are steel!

[Warpspeed]

I thought they used an official wooden school ruler.

[AxelRipper]

Simple, just wrap your hot side cooling line around the restrictor....

[Frank]

If you make the restrictor from a soft material, like SLS or plastic, then you are wise to leave it well undersize, like 19.92mm

It is not uncommon that the steel no-go gauge is pushed into the plastic restrictor, causing damage the restrictor.

[Michael Royce]

Another word of caution if you make your restrictor from a non-metallic material. Non-metallic restrictors can go slightly oval, and the scrutineers do check for ovality, (the restrictor gauges are not a complete circle). If the gauge goes through the restrictor even on one dimension, it will not pass.