Best engineering practice to fit parts together?

Ladies and gentlemen of Her Majesty’s Royal Electrical and Mechanical Engineers (or anyone else reading the thread with ideas!), I seek some advice please.

I have a part for a kitchen mixer that I need to replace. This is the planetary gear assembly. There is a shaft coming down from the gearbox, that goes through the main mixer housing, and then into a receptacle in the planetary assy.

D8E77CAA-54B8-4B38-A618-9984B749E610.jpeg

The problem is that it appears to be an interference fit. As shown in the pic above, the shaft will go no further into the receptacle without doing something to either force it, or ease the fit. It has to go about 3/4” further in, so that I can insert the locking pin through the holes.

The receptacle is just cast into the mounting plate:

E8E2A4A4-083D-42E1-A8FB-24D214FAF8D7.jpeg


A few things have occurred to me:

1. Heat the receptacle hole with a heat gun. Tried that briefly last night, didn’t give me much of an improvement, maybe 1/8” further down. Also need to pack the gears with grease, and heat would be an issue there.
2. Press them together. I have a hydraulic press, but unless I get the holes aligned before pressing, I’m in trouble. No idea how to ensure the holes are exactly aligned.
3. Ream out the receptacle. My guess is it would require a very specific drill bit that I don’t necessarily have.
4. Reduce shaft diameter. I’m reluctant to do that, because the shaft is obviously machined, so is probably accurate. The hole is more likely the problem, at least to my eyes.

I could just get to it with a file or Dremel, but I don’t want to end up with a slack fit and it wallowing out.

I’m guessing you chaps spent many hours in SEME and then in the field doing exactly stuff like this, probably in the pissing rain under an MK in 3 inches of mud. So I’ve got it easy, that is recognised.

Virtual Yeller Handbag on offer to the DS solution here.

Thanks in advance!
 
Gazelle fenestron blades were frozen (with freezing spray) to fit them into the bearing sleeves. You could try the stuff plumbers use to freeze pipes and warm up the other part.
 
Can you lock off the gearbox end to stop it from spinning? Then use the bearing press and twist the black bit to line up the holes, then free the gearbox end again.

Either that or cool and heat but you'd still have the same alignment issues really.
 

Rab_C

LE
Have you googled it for any YouTube videos of “How To” I just googled kitchen aid planetary gear replacement and there was quite a bit, not sure what brand you have?
 

jinxy

LE
I spent a day bashing the **** out of crankcase cover. Having a seized motor on my DT 125R. I had brought replacement bearings from Yamaha. Only I missed the little letter at the end of the part number, .5 of a mill makes a big difference.
 
Can you lock off the gearbox end to stop it from spinning? Then use the bearing press and twist the black bit to line up the holes, then free the gearbox end again.

Either that or cool and heat but you'd still have the same alignment issues really.

I can’t see how to lock off the gearbox, sadly. It does spin if pushed hard enough.
 

theinventor

War Hero
Outer end in the oven, inner in the freezer (overnight) certainly helps with tight bearing fits. And remember to lubricate the hot part just before you fit it. And wear suitable gloves.
With one bit at - 25°C and t'other up to 75 you've got 100° variation which is close to 0.1% change in dimension for steel.
 
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Have you googled it for any YouTube videos of “How To” I just googled kitchen aid planetary gear replacement and there was quite a bit, not sure what brand you have?

I sure have. Sod’s law, there are three types. Tilt-head, AC motor. Bowl-lift, AC motor. Bowl-lift, DC motor. The first two are far more common. Of course mine is a bowl-lift, DC motor. And there’s only two vids I can see for that model, and the planetary just drops off. Which mine doesn’t. Shite :)
 
Outer end in the oven, inner in the freezer (overnight) certainly helps with tight bearing fits. And remember to lubricate the hot part just before you fit it. And wear suitable gloves.
Also watch out for the sudden appearance of Strange Smells and purple cloaks if applying oil based lubricant to hot objects (just saying, we all know You Know Who trawls aarse looking for opportunities)
 

Troy

LE
It has to go about 3/4” further in, so that I can insert the locking pin through the holes.
As it has this locking pin, the shaft won't have to be such a tight fit. I would turn the shaft down [even crudely with abrasive paper] until it fitted ok.
 

OneTenner

LE
Book Reviewer
Outer end in the oven, inner in the freezer (overnight) certainly helps with tight bearing fits. And remember to lubricate the hot part just before you fit it. And wear suitable gloves.
With one bit at - 25°C and t'other up to 75 you've got 100° variation which is close to 0.1% change in dimension for steel.
The outer doesn't look like Steel to me, it definitely sounds like an interference fit from the problem removing the old one.
@Roadster280 are you able to measure the parts with any accuracy?
Dependent upon the measurements, personally I'd chill both parts in a freezer and use Isopropyl alcohol as a lubricant when fitting (on the metal, not in me!)
 

OneTenner

LE
Book Reviewer
As it has this locking pin, the shaft won't have to be such a tight fit. I would turn the shaft down [even crudely with abrasive paper] until it fitted ok.
The shaft looks hardened, the casting is the softer bit and should be the part to 'give', only parts of equal hardness need to be a matched fit or have some sort of taper to allow for variations.
 
I spent a day bashing the **** out of crankcase cover. Having a seized motor on my DT 125R. I had brought replacement bearings from Yamaha. Only I missed the little letter at the end of the part number, .5 of a mill makes a big difference.

That's good advice, check you have the right part. Or newer parts might have gone Metric and be close but wrong. Don't know for sure, but I wouldn't expect an interference fit on consumer stuff like this - it's designed for quick easy cheap assembly, but you do say it was a bar steward to remove.
 
I spent a day bashing the **** out of crankcase cover. Having a seized motor on my DT 125R. I had brought replacement bearings from Yamaha. Only I missed the little letter at the end of the part number, .5 of a mill makes a big difference.
I should coco… 0.5mm is 20 thou…that’s proverbial bus territory
8)
 

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