Author Topic: Simple wobbler  (Read 2272 times)

Offline PaulR

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Simple wobbler
« on: January 17, 2025, 03:46:50 PM »
As a gentle reintroduction after a decade long break I've decided to ease myself back in by making a single acting 'boxer' style oscillating engine. It's based on plans on the 'modelengineeringwebsite.com' but I'll be deviating from those plans quite a bit (which is why I've posted in this section) because I have hardly any of the specified materials, I'd like to simplify things a bit further (simplifying a wobbler, how low can it get!) and a couple of the design choices in the plan are a bit  :headscratch: I'll be using a mini-lathe, drill press and hand tools only.

Don't expect anything new or exciting but do expect a few cock-ups to keep you entertained!  :ROFL:

I've made the main body of the engine from a piece of 1" brass angle cut and filed to form a foot (holes to follow) to mount on a wooden base. The whole thing is 6" long. I've drilled the cylinder pivot pin holes and marked the port holes at each end. The plan ignores the curved path of the cylinder's port but to be fair the position would only vary by about 0.3mm if taken into account, probably not enough to make any real difference.

I drilled a hole for the simple cylindrical bearing and soldered it in place. I think I was a bit over zealous: when it had cooled I found that the frame had bowed very slightly (nothing that Mr Mallet won't fix  :hammerbash:). I think the block that the frame was resting on during soldering isn't very flat, causing it to sag a little. Also, despite (or maybe because of) the bearing being a snug fit, it had risen slightly, maybe as the flux bubbled away. As a result it's about 0.5mm lower than the surface on the cylinder side of things - not a biggie as it'll be covered by the crank anyway.

Next I'll be sticking it on the faceplate to drill and ream the hole for the crankshaft then soldering on port blocks at either end to facilitate fitting of steam/air inlets and exhausts - something that's completely omitted in the plans!



Offline PaulR

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Re: Simple wobbler
« Reply #1 on: January 17, 2025, 07:52:00 PM »
This is the first time I've used a face-plate so it was a bit nerve-wracking but all went well (added an extra clamp to balance things up and locknuts all round :D The finished hole looks nice and clean and is a nice running fit but it doesn't look great from the other side due to the wonky hole where the drill dug in. No matter, it's purely cosmetic and won't be on show :Lol:

The face-plate is an 'official' accessory for my Seig lathe but the lathe can't be operated while it's fitted unless the (annoying) chuck cover is removed - good thing I'd already taken it off!

Yesterday I also made the two pivots pins and some M3 nuts and washers, the 2mm ends will be soldered to the cylinders. I also made the springs from a worn-out g-string  :Jester: (of the guitar variety).


Offline Admiral_dk

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Re: Simple wobbler
« Reply #2 on: January 17, 2025, 09:41:20 PM »
Guitar Steel Strings are extremely high Quality Swedish Steel = a Very good material for springs  :ThumbsUp:

Looks like you are off to a good start   :cheers:

Per             :popcorn:

Offline PaulR

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Re: Simple wobbler
« Reply #3 on: January 18, 2025, 04:57:52 PM »
When I looked more closely at the brass angle today I found it was bowed lengthwise and slightly twisted   :(  Added to the wonky hole it didn't look at all good so I decided to try to improve things. I cut off the soldered bearing and did some 'blacksmithing' to bring the angle back into true. Next I filed the wonky hole to make it rounder then re-drilled it from 7mm up to 10mm tapping size, made a new bearing and threaded that to fit. I also decided to up the crankshaft size to 6mm to suit what I have on hand so drilled and reamed the new bearing to suit. The finish is good but I can feel a little play in the shaft. At least everything is nice and square now and the wonky hole looks a little less offensive!




Offline mklotz

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Re: Simple wobbler
« Reply #4 on: January 18, 2025, 06:47:02 PM »
Laying out, drilling and tapping all the needed holes on a flat brass plate might have been a better start.  The base could be added later; it's not a high precision part.  Making the tube bearing on the lathe avoids ever having to mount the assembly on the faceplate - a tedious operation.  The bearing can be secured to the plate with Loctite if necessary - thus eliminating the need to solder to the plate and risk distortion.  BTW, you might want to consider an oil hole in the bearing.

A good approach is to build the thing in your mind several times before actually cutting metal; I call it redesign for manufacture.  After a few builds it will become second nature.

I'm really looking forward to seeing this run.  I've only built one two cylinder oscillator, a tiny Elmer Verburg design...

Regards, Marv
Failure is just success in progress 
That looks about right - Mediocrates

Offline PaulR

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Re: Simple wobbler
« Reply #5 on: January 18, 2025, 08:14:41 PM »
Laying out, drilling and tapping all the needed holes on a flat brass plate might have been a better start....BTW, you might want to consider an oil hole in the bearing.
...
I'm really looking forward to seeing this run.  I've only built one two cylinder oscillator, a tiny Elmer Verburg design...
Yes, oil hole is coming shortly. Having just kitted out an entire workshop I haven't much left to spend on materials so I'm working with what I have and thought the angle would double up as frame and stand.

That's a nice Elmer's engine you have there Marv - looks like a little powerhouse. I built a couple of his engines when I last had a workshop, some are in this photo, the only two cylinder one was the opposed engine which I could never get to go. Working in metric doesn't help!

I've built a couple of other twin cylinders that run fine - my own twin wobbler and my version of 'double scotch', both near the middle of the photo. Here they are in action:
<a href="https://www.youtube.com/watch?v=HMZVGyhsNuE" target="_blank">http://www.youtube.com/watch?v=HMZVGyhsNuE</a>
<a href="https://www.youtube.com/watch?v=QH_SY4CXftA" target="_blank">http://www.youtube.com/watch?v=QH_SY4CXftA</a>


Offline PaulR

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Re: Simple wobbler
« Reply #6 on: January 19, 2025, 03:20:07 PM »
Today I completed the machining on one of the cylinders. Nothing much to look at and it took me the best part of half an hour just to get the bar centred in the 4-jaw using my Heath-Robinson square-bar-in-the-toolpost method :Lol: Still it was worth it, the measurements seem to be spot on and the 8mm bore looks plenty smooth enough. There are some jaw marks on the part which will probably polish out but I'm not too worried either way; I took off my quickly made copper-pipe-soft-jaw-covers as they were wobbling around and annoying me while I was trying to get things lined up. I'll make some better fitting ones in the fullness of time.


Offline PaulR

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Re: Simple wobbler
« Reply #7 on: January 19, 2025, 08:15:11 PM »
Braved the cold workshop to do the other cylinder and cut the port blocks roughly to size.

Offline PaulR

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Re: Simple wobbler
« Reply #8 on: January 20, 2025, 07:42:28 PM »
Drilled the 2mm port and pivot holes and test fitted the pivots. The plan that I'm sort of following calls for the pivots to be soldered in place but I'm a bit worried that the heat of soldering will cause distortion and it's tricky to come up with a jig to keep them perpendicular in two directions without drawing away the heat. I don't have any sub 3mm threading gear yet or any taps to make a blind 4mm deep hole (!) so the thread will probably have to break into the bore. Hmmm.

Also made two steel end caps for the cylinders, to be soldered in place... deviating from the original plan which has the cylinders as 43mm deep blind holes in solid bar, not the easiest thing to get right!


Offline PaulR

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Re: Simple wobbler
« Reply #9 on: January 21, 2025, 04:31:29 PM »
Filed a rebate about 0.5mm deep on each cylinder as is traditional although I'm not convinced it makes much difference. Decided to use loctite on both the pivots and the end caps and they seem pretty firm (and airtight in the case of the latter). Since the piston rods connect to the same point on the crank, I think the air inlets will be asymmetrical, one side will be via the upper port, the other via the lower). I could probably make them symmetrical by drilling some fiddly steam passages... thinking.


Offline EricB

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Re: Simple wobbler
« Reply #10 on: January 21, 2025, 06:19:23 PM »
Nice collection of engines you have there!

Why are there colored squares on your chuck jaws?

Eric

Offline PaulR

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Re: Simple wobbler
« Reply #11 on: January 21, 2025, 06:58:28 PM »
Why are there colored squares on your chuck jaws?
Ah, they just help me remember which pair of jaws I'm adjusting when getting stuff centred  :)

Offline PaulR

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Re: Simple wobbler
« Reply #12 on: January 22, 2025, 12:39:10 PM »
Soft soldered the port blocks in place this morning. Tinning all parts went to plan but when I tried to sweat the first pair together it failed... then I realised I hadn't put any flux between them  :facepalm:

After that little aberration, both ends were completed with no dramas.


Offline PaulR

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Re: Simple wobbler
« Reply #13 on: January 23, 2025, 07:57:09 AM »
Last night I made one of the pistons and started its rod. Also found a small flywheel from a past failure which I hope to turn down to form the crank for this engine. I enlarged the hole so it fits the crankshaft and attached it with Loctite; hope that'll be good enough to thin it down to 4mm and turn it to size. Now I need to find something to make a 2" flywheel or I might buy and modify a second-hand toy one.


Offline PaulR

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Re: Simple wobbler
« Reply #14 on: January 23, 2025, 08:57:41 PM »
Finished off the other piston and started its rod. The old flywheel I was planning to transform into a crank disc is actually stainless so I'll keep that for something else. I don't have any other 1" diameter bar so decided to use a piece of 3mm steel flat. Slightly unconventional method but: tapped a 6mm hole and threaded the end of the shaft, fitted the flat, turned the outer diameter then faced both sides with the smallest amount of sticky-out I could manage. The faces seem perpendicular to the shaft and that's all that matters  ;D


 

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