Mating a Browning Bushing to a hub GD&T --- H, P, Q, & R Bushings

[ingallspw]

We have several similar parts that need to mate up to Browning's H, P, Q, & R Bushings. I've been looking everywhere to tell me what is too much GD&T and what is not enough to mate with both pages of the attached pdf.

We currently have these parts in production at an outside source. They were bought off by placing a bushing into the hub... if it fit, it was good. But in an effort to cut back on cost we are soon to making these in house. For years they have gone by without question. Now we are taking a closer look and having questions about the parallel spec, thread depth, clocking, etc. and we have been unable to find any information to tell us how to design and manufacture these parts efficiently.

Any help would be greatly appreciated!

Thanks!!!!

Keegan

 

[NomLaser]

First off I would ditch any surface callout that is 125 and greater. No need to call them out (125 & 250) unless they are critical.

Parallel callouts usually don't have a per inch descriptor. You offset a line 0.00025 on each side of the nominal dimension and the surface that you are measuring can't break it (assuming your 0.0005 limit).

I would call out your keyway to the opposite face and not the center of the bore. With a taper that makes it even harder to find the center.

Undercut looks fine but you may want to call it out as a MIN

You might want a concentric callout on the taper bore to the straight hub. I don't know what your target application is so I can't really give you any advice on how tight.

The Ø4.002-Ø3.998" might be better served on the section view to know where exactly you are measuring. You might need to add or adjust your section to get rid of the keyway.

Everything looks pretty good and I have had experience designing similar hubs in the past. Just be sure that you are familiar with runout vs total runout. I always had to double check the definition to keep them straight.

 

[fsincox]

Is this replacing the bushing or mating with the bushing?
Usally isn't the keyway it in the bushing itself? What does it do?

 

[ingallspw]

It's mating with the bushing.

And yes the key-way is a part of the bushing... as far as what it does, it actually does very little. Most of the stress is transferred through clamp load on the taper surprisingly.


This all seems a bit simple in a way because I'm sure browning has some sort of recommendation out there but I am unable to find it..

 

[fsincox]

ingallspw,
Sorry, I know you said that in your original statement but I was not visuallizing it right. Datum "A" is some type of pilot?

 

[ingallspw]

You are correct. Datum A is a piloting feature.

 

[fsincox]

I would be interested in any remarks on the parallellism of the centerplane to datum B (datum B being one of the surfaces creating the centerplane, itself), comments? I have something similar I am exploring.

 

[ingallspw]

Thank you all for your responses so far! I am bring up NomLaser's comments in a meeting soon and we'll see if people agree.

Does anyone have experience with putting key-ways in tapered bores? Does the .0005 seems a bit extreme? I am amusing it's a typo and it should have been .005 possibly even .05 but I usually just draw the things and I don't have much experience applying GD&T. Reading it yes, but not engineering it...

The final application of the hub/spacer will be a 80 - 96" fan. Some of these prints were created in the 80's and updated a few years ago with new tolerances. (The old 80's print barley had ant significant call outs.) Now again several are questioning the prints.

I almost want to say "If it ain't broke, Don't fix it!" but like most companies, we like money or hate spending it so again all your help is appreciated!

 

[fsincox]

ingallspw,
I must disagree with NormLaser on his approach to finishes, I believe, he is assuming they will be automatic with process, I disagree with that philosophy of drawing practice.
Keyways are generally held pretty tight as they are intended to take thrust loads and not slip alot. Your tolerance is .0005/in the key length is 2.25 in so .0011
over all. I do not think .005 is right. My guess would be there was a company standard somewhere in your past that said all keyways shall be held within .0005/in.
I prefer position (RFS in this case) or concentricity on the taper but that is a whole discussion in itself, (reference other threads).
Do you have a reason that you call out the parallelism of the centerplane. Without an assembly it is hard to really judge these things.

 

[NormCrawford]

IF datum feature A is truly a "pilot feature" so be it. At first I was wondering why not have the taper itself as the datum feature.
I would position the keyway with a parallel refinement.
I question runout for datum feature B. Why not just use perpendicluarity? Is datum feature B rotating while against another surface?
I would control the .531 locating dimension with a dual single segment FCF of profile and the parallel refinement. But does it really have to be refined parallel to B or to A?
I would not use concentricy at all if you are trying to save money. Runout on the taper is most likely sufficient. Total runout is an option but more difficult to inspect for a taper.
The B/Ammc DRF for the hole pattern is very questionable. If Datum Feature A is truly a "pilot" feature, isn't that feature going to constrain the rotational degrees of freedom? Is datum feature A a clearance fit?
I suggest using profile to control the 2.25 locating dimension unless this truly functions as a feature of size. Or otherwise, you may want to make a not that Rule #1 does not apply. Trying to save money.
The outside dia needs a position control.
I would question the .010 position tolerance value on the two hole patterns. It looks a little cut and paste and so I suggest someone double check the Vc calculations.
I personally would control the top surface of the keyway with profile. You guys no how I am about those +/- dimensions. But typically not a critical feature, some things I just learned to let go of.

Norm Crawford
GDTP-S
Applied Geometrics, Inc.

http://www.GDandT.com

 

[fsincox]

Norm Crawford,
Thanks, I agree with you completely on the taper as datum,I avoided that, here, hoping someone else would bring it in. If the function is as I would believe, the taper should be a datum for the key at least. The bushing is going to follow the taper wheither people want it to or not , unless the keyway is just clearance for the key, but then the parallelism WOULD be extreme.
This is the kind of thing I see all of the time: "lets call it out to the 5.999 dia because it's easier for manufacturing", EVEN THOUGH IT DOES NOT FUNCTION THAT WAY!

 

[NormCrawford]

The key way makes perfectly good mechanical sense to me if orientation (timing) of the mating part is needed or to carry shear loads for rotation (stopping rotation). I can't tell if this is a solid stationary bushing or rotating.

In any case, the bushing (taper) is what actual mates to the mating part, right? The rest of it is just a housing, isn't it?

Norm Crawford
GDTP-S
Applied Geometrics, Inc.

http://www.GDandT.com

 

[ingallspw]

Thanks all, you have given me a lot to go by.

The bushing, hub, and fan assembly all mate to a rotating shaft from an engine or hydraulic motor. The hub's housing also acts as a spacer in this case.

I've not seen a company standard for key-ways tolerances as we do not truly have many parts that rely on the key-way.

And you were right about the top of that key-way not being critical. That is why we have it as +/-. Also, we are having troubles getting people to put it in the first place because of safety concerns with the broach.

Thanks again!