Author Topic: Small Flash Single  (Read 1430 times)

Online vtsteam

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Re: Small Flash Single
« Reply #30 on: December 03, 2022, 06:15:35 PM »
I decided to just try it out on a spare bearing to see what it "feels" like to try dimpling it for a set screw. The bearing is actually a 6201RS not an R8 as mentioned previously, with seals removed. I measured ~0.10" in max shell thickness, though the ball grooves reduce that to about 0.075".



I ground a very small dimple in the outer race with a Dremel tool, and found a 1/8 x 40 set screw:



The screw set in the dimple well, and I "feel" like this will be okay as long as no hard pressure is applied. The only purpose is to prevent rotation of the race assuming a close slip fit in the shaft housing.


Offline Admiral_dk

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Re: Small Flash Single
« Reply #31 on: December 03, 2022, 07:52:07 PM »
I have never build a steam Engine - just to be clear .... but there are a number of ways to secure the crank on the bearing. One of them is to have either an angle on the Crank outside the bearing (or Cam for that matter) and an equal angled 'female' that is 'Mated to' the other one with a nut. The angle bit can also sit 'loosely' on the Crank against a 'step in diameter' - again tightened with a matching opposite.
You see this methode all the time on small IC Engines for model aeroplanes - where the Prop is tigthned against the 'female part'. This way the Crank can move a tiny bit sideways in the Bearing.

You can argue that if you don't need the 'Play' - it's even easier - just let a nut (maybe Lock-Nut) hold it.

Best wishes

Per

Online vtsteam

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Re: Small Flash Single
« Reply #32 on: December 04, 2022, 03:22:43 AM »
Thanks Per :cheers:

I think I'm clear on how to secure the crank and retain the bearings axially. I was just thinking about securing the inner bearing circumfrentially (against spinning in the housing). That's because the inner bearing has to be a slip fit in the housing. It can't be Loctited or interference fitted because it needs to be easily removable, so the crankshaft can be disassembled.

I'm going with the set screw and dimple for that.

Today's work.... Drilling out clearance space in the front plate/bearing housing:
« Last Edit: December 04, 2022, 02:36:47 PM by vtsteam »

Online vtsteam

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Re: Small Flash Single
« Reply #33 on: December 04, 2022, 03:24:32 AM »
Boring the inner bearing recess:


Online vtsteam

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Re: Small Flash Single
« Reply #34 on: December 04, 2022, 03:25:56 AM »
Inner bearing mounted:


Offline john mills

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Re: Small Flash Single
« Reply #35 on: December 04, 2022, 05:31:47 AM »
normally in that case the fit should be a push fit so you can push it together by hand but not loose never seen plain  ball bearings held with a grub screw.
John   .

Online vtsteam

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Re: Small Flash Single
« Reply #36 on: December 04, 2022, 02:09:32 PM »
Thanks, It is a push fit.

I nevertheless was worried it might spin in place, since, there is no retainer against the outer rim. Maybe it wasn't necessary.

Online vtsteam

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Re: Small Flash Single
« Reply #37 on: December 04, 2022, 02:56:46 PM »
I actually still haven't put it in yet, so still thinking about this. Maybe you guys can explain.

The only thing preventing rotation with a slip fit in the housing is the axial pressure against the bearing's rim. Without a retainer, I can only increase that pressure by how tight the crankshaft pulls the whole bearing into the housing (pre-loading) -- assuming it can be tightened with a nut at the outer end of the crankshaft.

But with ordinary ball bearings, I thought that you wanted to avoid pre-loading axially -- not like tapered roller bearings or angular contact ball bearings. Is that right?

Or am I over-thinking this?
« Last Edit: December 04, 2022, 03:01:42 PM by vtsteam »

Offline RReid

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Re: Small Flash Single
« Reply #38 on: December 04, 2022, 03:25:47 PM »
If the bearing fits in the housing with a push fit, i.e. one that requires just a bit of thumb pressure to push it into place, then friction will be more than enough to keep the outer race from spinning unless the bearings seize. But you do need to provide some way to push or pull it back out. A couple of small through holes to allow getting at it with a drift to tap it out would be one possibility.

Looks like you're having fun, keep up the good work! :ThumbsUp:
Regards,
Ron

Online vtsteam

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Re: Small Flash Single
« Reply #39 on: December 04, 2022, 03:39:36 PM »
Thanks RReid. :cheers:

It's a slip fit, but wiggle free. I can twist the outer rim once seated, but I can't push it sideways.

Hard to explain by words this stuff! Better to make it and take a photo. But I'll try....there will be an outer ball bearing at the other end of the housing. and both bearings can be preloaded towards each other by tightening the nut at the outer end of the crank shaft.

Between the two bearings inside the tubular housing is a cam lobe which will not pass through either bearing (it is trapped between them inside the housing).

To prevent spinning I guess it could just be the preload holding the bearing in place.....  Reading all about pre-load online... :atcomputer:

So it looks like I do want some preload, even though these are just deep groove ball bearings. Not true that it applies only to tapered roller or angular contact ball bearings. I was wrong there.

So that could take care of the worry about the bearing spinning, and a set screw may not be needed.

Ahhh, ....I might put it in anyway. With the high case temps involved in flash steam, tolerances can change, and it won't hurt to have a positive lock on that bearing.  :zap:

Online vtsteam

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Re: Small Flash Single
« Reply #40 on: Today at 07:25:40 PM »
Today I shortened the housing to actual length by turning off the chucking extension. Then I bored the end for the outer ball bearing set.

The plate flange around the outside is still ovesized.

Next to do is drill the flange and crankcase for mounting screws and tap the case. I can then mount the bearing housing and mark the flange for trimming.

I've done things this way throughout in order to keep the crankcase (and cylinder) bore as the machining reference, rather than trying to relate to a particular point on the crankcase through a series of measurements.