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I'm talking about IEC motors-gearbox alignement. Here are an example: enter image description here

enter image description here

enter image description here

I found the drawing in cross hydraulic website, so it's quite reliable. What i don't understand, is, how this design makes sure the perfect alignement of gearbox coupling and the motor?

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Bell housings are often fixed with bolts or studs, these are convenient and take the required loads but do not generally provide adequate precision in location. Threaded fasteners really need a certain amount of clearance otherwise there is a significant risk of damaging the threads or the through hole during assembly or at least making assembly much more difficult.

Instead additional matching sets of features will be machined onto both mating parts which are designed to provide alignment to the required tolerances. In some cases fine adjustment may be provided by shims or eccentric pins etc.

A fairly generic method is to use dowel pins, unlike bolts or studs, which generally require a certain amount of clearance to avoid damaging the threads these will be machined with a slight interference fit.

Other options include machining matching rings, steps or tapers onto both parts. Taper fits tend to be especially good at ensuring concentrically on standardised parts as they tend to be self aligning.

In some cases final machining with be carried out with both parts assembled together making them essentially a matched pair. This tends to give the best possible accuracy but makes parts non-interchangeable.

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  • $\begingroup$ i've thought about what you say a lot, but needed a confirmation. I think the creep phenomenon could also happen that results in displacement of flanges and ... $\endgroup$ Jul 27 '18 at 18:43
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Because they are both machined to a specified tolerance - you have the diagrams showing the information to choose the correct one for your application.

These are not the same as the manufacturing drawings,,,

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  • $\begingroup$ I thought so until i heard something about centring ring, it's not the same as the ring in drive wheels, but rather a specific part of bell housing, i added the third photo and marked something in red. Do you know something about the red area ? $\endgroup$ Jul 26 '18 at 16:23
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    $\begingroup$ Also known as a “register”... $\endgroup$
    – Solar Mike
    Jul 26 '18 at 16:28
  • $\begingroup$ Great! And why this register guarantees the perfect alignement but the bolted flange doesn't, however both of these circles are concentric to the hole at other end ? $\endgroup$ Jul 26 '18 at 18:06

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