Position Tolerance for Pressed-In Bushings/Pins

[Guest0527211403]

Hi all

I've done a few searches on this and didn't come up with anything.

I've got a few machined castings in aluminum that have hardened steel locator bushings and pins pressed in to them.

We want our suppliers to press in these bushings during machining, and deliver to us or our customers a part that's ready to be loaded on the machine.

Currently my drawings have positional tolerances on the hole into which the bushing/pins are pressed, along with a note to the effect of "VENDOR MUST SUPPLY AND INSTALL BUSHING XYZ123". The hole diameter is toleranced based on a press fit with the bushing or pin.

Now, we're sending these drawings to a few different machine shops and I'd like to leave it up to the vendor how they get the bushing/pin in the right location. I'm OK with it if they put a looser fit on the hole and used a locking compound (like green loctite) to hold in the bushings/pins, provided they can maintain position to the other datums using a fixture or some other means. These elements provide location only so I don't need a heavy press fit, but they are part of a component that may be changed frequently so I don't want them falling out with frequent use.

So, would it be appropriate to place a note under my FCF on the hole's position tolerance that states "POSITION TOLERANCE APPLIES TO INSIDE DIAMETER OF BUSHINGS" and leave it up to them how to achieve it?

Thanks in advance

 

[pmarc]

I would say your print should show what you require and get from your supplier in reality, that is casting with bushings installed. Positional tolerance should be applied directly to inside diameter of bushings and it should be left up to the vendor how to produce holes in the casting and how to mount bushings in it if this is not critical for you.

Is there anything that stops you from doing it this way?

 

[CheckerHater]

Justkeepgiviner,

Everything you are trying to do is perfectly in-line with the letter and spirit of the Standard.

First, your drawing should show the final state of the part; so if you want your supplier to give you part with bushings in it, you produce drawing of part with bushings.

Second, use of GD&T is not limited to parts; if necessary it can be applied to the assembly, and your case is a textbook example. On your drawing of part with bushing you apply GD&T to ID of the bushings.

This way you explain what the final result should be and leave manufacturing details to the supplier.
Will you, for example, accept part with bushings secured with something like set-screws and re-bored after assembly as long as bushing ID size and position are according to your print?

 

[Guest0527211403]

Thanks for the responses.

This was my feeling as well but I've been fielding questions from suppliers lately and I've been second guessing what goes on some of our drawings. Some suppliers want us to spell out every detail of the process for each tapped hole/helicoil/bushing, where others can understand what the drawings mean and produce a part that meets the spec. We're trying to avoid having drawings made to suit the requirements of one vendor over another, but naturally there's all sorts of push back from sources internal and external.

As for anything that stops me from doing it this way, it's the inevitable emails from (some) suppliers asking us to work out the manufacturing details for them. And so the dance continues!

 

[KENAT]

I'd detail it as an inseperable assembly - that's how I do parts with dowel pins press fitted.

So I'd attach the positional tolerance to the ID of the bushings, not anything to do with your hole that the bushings go into. Are the bushings off the shelf or detailed on the same pring?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Guest0527211403]

The bushings are off the shelf (misumi) components. It really is a simple assembly procedure, and I was overthinking things last friday when I posted, probably a consequence of responding to these inquiries from suppliers.

It really comes down to the fact that our purchasing dept. gets feedback from vendors, and then they put pressure on us to change our drawings to suit the vendor. In some cases (ie. where the vendor is doing special operations) this makes sense but for an bushing or pin as simple as this I agree we need to start stripping out manufacturing details from drawings.

Thanks all for the sanity check.

 

[KENAT]

Since they're off the shelf I'd make the ID a reference dimension and apply the FCF to it.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​