tips tolerances elbow

[reye]

Good evening to all, I ask an opinion of those who have some experience with the production of mechanical parts. My question is this: given the elbow crank in figure, what are the geometric and dimensional tolerances strictly necessary (I also mean for what concerns costs..) for the realization of the attached piece? I studied the tolerances on the chiron and came to mind 1000 options to quote in tolerance the piece. .
Thank you.

 

[meccanicamg]

If you are looking for any mechanical design book you find all the directions. I don't have mine right now. to tolerate everything that goes to make pins. geometric tolerances for the pins between them and any shoulder.perpendicular.

 

[reye]

and for dimensional tolerances?

 

[PierArg]

Hi.
if you look good in the forum there is a discussion (it is quite recent...robe of months) where they were placed files containing original drawings of the tree to elbows of the spear and alpha romeo.

Maybe you could take those as a reference

 

[PierArg]

I am too good today
http://www.cad3d.it/forum1/showthread.php?t=29884

 

[paulpaul]

and for dimensional tolerances?

where you have pins for bearings (as in this crank pin) you could use an h6. consider that for good behavior of a hydrodynamic bearing which are those of counter and biella the diametrical tree/internal diameter bearing must be about 1 per thousand of the nominal diameter of the coupling. combined with the specific pressure p/(bd) (p load, b bearing length) around the 20 mpa for trimetallic bronzine (can also be superior but personally recommend this value) you defined the coupling at least for a first dimensioning by selecting nominal and tolerances on tree, biella hole and bronze thickness accordingly. you can then check using for example the charts of raimondi and boyd and check based on t of work, speed and viscosity oil that the meate is at least 5 micron in the most unfavorable conditions (max t oil, min speed, max load, max diametral game) but in 90% of the cases the sizing is verified with these two simple parameters.
ra 0.2, polishing with cloth moving opposite to that of rotation of the tree to not have "creste" that in operation could destroy the meato.
very important among the geometrics the parallel between the rotation axis and the axis of the crank pin, otherwise your bearings will have asymmetric wear!
Bye!

 

[reye]

pierarg and paulpaul do not know how to thank you.. between geometric tolerances I could also insert a coaxiality between extreme diameters? I also wanted to ask: but that wonderful table of the tree to elbows launches on which wonderful text book is located? I've been in the open mouth, it's beautiful, but why don't they show me these masses at the table? would be very helpful

 

[PierArg]

pierarg and paulpaul do not know how to thank you.. between geometric tolerances I could also insert a coaxiality between extreme diameters? I also wanted to ask: but that wonderful table of the tree to elbows launches on which wonderful text book is located? I've been in the open mouth, it's beautiful, but why don't they show me these masses at the table? would be very helpful

Hi.
if you read all the discussion should be cited the book (if I do not remember badly). Try to read to the end.

For external diameters you said something right!
on one put a reference and on the other the tolerance of coaxiality. . They'd be where the bearings are staying.

As for the things called by paulpaul great straquoto! above all the parallelism between rod pins and rotation axis.
Besides parallelism are added, always on the same pins (in your case is only one), tolerances of circularity and cylindricality. on them mates the biella foot.. Imagine what would happen if the surfaces were not "perfectly" cylindrical.

 

[reye]

found, it is the strange consort thanks again

 

[PierArg]

found, it is the strange consort thanks again

Please, we're here on purpose:

 

[Ste_d]

found, it is the strange consort thanks again

I recommend this book to anyone who is approaching the mechanical design... use it to theitis and is very schooly as well as clear and exhaustive enough for a technical drawing course!