Author Topic: Halls rotary engine  (Read 10791 times)

Offline Jo

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Re: Halls rotary engine
« Reply #15 on: May 05, 2015, 01:33:12 PM »
Jason,

All of those tight tolerance dimensions are on flat surfaces that can be easily lapped to fit their mating parts on a sheet of wet and dry with some oil as lubrication.

Jo
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Offline Jasonb

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Re: Halls rotary engine
« Reply #16 on: May 05, 2015, 02:27:19 PM »
There are quite a few round ones too eg recess in ends of piston 0.6875" and the mating spigot turned on the endplates to 0.6870" So you need to turn accurately to size and concentricity

But its easy enough to see where these dimensions matter as DP has used the usual drawing convention of 3 or 4 decimal places on the critical stuff and fractions elsewhere.

Offline PJW

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Re: Halls rotary engine
« Reply #17 on: May 05, 2015, 03:51:05 PM »
The kit does have the set of drawings, so I will study them & I may not rush into parting with them, after all if I get stuck I only have to shout for help!
I am sure that someone out there will point me in the right direction :slap:
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Offline Jo

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Re: Halls rotary engine
« Reply #18 on: May 05, 2015, 03:53:35 PM »
 :headscratch: Jason I still can't see why you think they should be at all difficult, they are all just make to fit the other bit: Its only each bit 11/16" diameter with a lapped fit to let the piston rotate freely.

Jo
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Offline Jasonb

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Re: Halls rotary engine
« Reply #19 on: May 05, 2015, 04:13:44 PM »
Well I think there are quite a few parts of that engine that would be quite challenging to me to do a good job of it and would need quite a bit of care, certainly a lot more than the average slide valve steam subject.

It was your statement that "the piston does not have to be an accurate fit" when the drawings suggest a tollerance of 0.0005" be that by lapping or machining seems to suggest there is a need for accuracy.

I'd need to look back and see what RJW has done in the past but for a relative beginner things like close sliding fits, press fits, lapped tapers can be hard to judge and did not want him to go into the build thinking it was easy as there is no need for acurate fits. Just like jumping from a simple barstock wobbler to an IC engine where valves need to seal and you need good compression to get them to run or a steam engine that will rotate freely by hand yet have no slop or tightness so it runs well under minimal air or steam pressure.
« Last Edit: May 05, 2015, 04:19:20 PM by Jasonb »

Offline Jo

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Re: Halls rotary engine
« Reply #20 on: May 05, 2015, 04:54:06 PM »
Jason, Peter has made a Webster IC engine, the one in his Avatar  ;) And unlike my R&B his runs  8)

Jo
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Offline Allen Smithee

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Re: Halls rotary engine
« Reply #21 on: May 05, 2015, 05:11:37 PM »
Surely an accurate *fit* is not the same as a tight *tollerence*. If making a circular piston/cylinder assembly the actual bore diameter isn't too critical, while the difference between piston and bore diameter, the ovality and parallelism of the bore are very critical. Making the piston to a nominal dimension and then lapping it into the bore will achieve this requirement without ever needing to be able to machine down to to "knocking individual atoms off" level or being able to measure dimensions at similar levels of precision.

Looking at the animation it seems that the piston looks like one corner of a wankel piston with a sprung tip-seal As far as I can see you could make these parts to fairly easily achievable machining precision and then lap the seal to size inside the cylinder to get the required fits.

Or am I missing something?

AS
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Offline Jo

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Re: Halls rotary engine
« Reply #22 on: May 05, 2015, 06:22:43 PM »
Thanks Peter (PJW) your post has made me question my supplier about the missing flywheel and he has just found it  :whoohoo:

Jo
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Offline Jasonb

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Re: Halls rotary engine
« Reply #23 on: May 05, 2015, 06:35:45 PM »
I don't think some of these could be easily lapped but I would stop measuring when within a thou or two and start test fitting the mating parts. And even if you did lap them you would still need to nake them accurately as you won't lap them if oversize and if undersize there will be no metal to lap away. Also can't lap a press fit usually only get one chance with those.

Peter if you have got a running webster then as I said have a good look over the drawings with the castings infront of you and then decide if its a model for you no or in the future. The other alternative is to do what you can and then add it to the long waiting list of orphaned engines that have been abandoned half way through that Jo likes to collect. ;) Having recently got teh drawings I know that at the time I was looking at this engine that I would have mucked it up as I just did not have the skill or equipment.

Offline PJW

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Re: Halls rotary engine
« Reply #24 on: May 05, 2015, 07:23:12 PM »
Hi Jo, glad you found the missing flywheel, it looks like a standard Stuart type so there are lots of these about! I think its about you showed me that R&B running, waiting for the you tube clip!!!!!!!
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Offline Jo

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Re: Halls rotary engine
« Reply #25 on: May 10, 2015, 04:41:31 PM »
The flywheel has turned up.  :pinkelephant:

Peter, has your castings turned up yet ?  :)

Jo
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Offline Jasonb

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Re: Halls rotary engine
« Reply #26 on: May 10, 2015, 05:30:06 PM »
Good to see its an iron one if you are going to have an unpainted rim.

Offline PJW

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Re: Halls rotary engine
« Reply #27 on: May 12, 2015, 06:16:03 PM »
I looks like the halls castings are not coming after all  :shrug:
Old Guys Rule the Dark Side of the Shed!

Offline Jo

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Re: Halls rotary engine
« Reply #28 on: May 12, 2015, 07:04:48 PM »
 :'( Better luck on your next attempt at some castings.

I know someone with some Stuart casting sets that he is looking for a new home for  ;)

Jo
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Offline b.lindsey

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Re: Halls rotary engine
« Reply #29 on: May 13, 2015, 12:09:38 AM »
Those are some nice looking castings Jo. Glad you found the flywheel too :)

Bill

 

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