Author Topic: Little Otto  (Read 2492 times)

Offline Jasonb

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Re: Little Otto
« Reply #45 on: August 04, 2022, 06:40:24 PM »
If you look back at the first few posts in this thread you will see that little Otto has a form of scotch yoke that is pivoted at one end and connects to the conrod big end at the other. I had sent Graham a basic sketch of this with the critical sizes from which he made a pattern and had some cast in brass with the intention to have the crank run against the brass slot. Having subsequently seem images of Tom's larger size replica I decided to go down that route which has split bearings for the crankshaft and to get them into place the bottom of the Yoke is a separate part.

I did a few alterations to my initial model while bearing in mind how I might machine the part and also ways to hold it and came up with this.



Wary that cutting a big notch out of the lower edge could make the steel go banana shaped I cut off a short length of 10mm x 100mm black hot rolled steel which should have less internal stresses than bright bar. After milling down to the required 8mm thick by taking 0.5mm cuts off alternate faces to keep the cuts balanced  I drilled and reamed for the two 4mm holes and also stitch drilled out most of the waste material from the slot.



A couple of quick hacksaw cuts and the remaining waste dropped out so that the slot could be milled to the final 50mm x 10mm size and a pair of holes tapped M3 for the bottom plate retaining bolts.



Another piece of steel milled to 3mm x 8mm section with a couple of clearance holes completed the work on the manual machines.



The CNC is the best tool for the job on a part like this where there are curved features running into straight and angled ones so a session on Fusion 360 soon gave me a USB stick with all the tool paths needed, 5 per side which were:

1. Adaptive cut to remove most of the waste using a 4mm dia 4-flute R1 cutter at 5000rpm and 500mm/min feed
2. Ramp cut to finish the vertical and curved surfaces using a 3mm dia 4-flute carbide ball nose cutter at the same speeds and feeds. This was also used for the remaining cuts
3. Horizontal cut to finish the face of the webs and the "D" shaped big end boss
4. Scallop cut to refine the near horizontal parts of the three round bosses
5. Pencil cut which refined the internal fillets particularly where the three bosses meet the main body.

With the KX3 fired up the first thing to do was drill and ream for two location pegs in a bit of scrap aluminium which would locate in the two hole sin the yoke. I also tapped a couple of M3 holes to take screws to clamp down a top hat section clamping block.



It was then just a case of clicking "GO" and then getting on with something else, just popping back to change the tool and start the next tool path. Also just had to turn the yoke over half way through so the opposite side could be machined.



quite pleased with how it turned out. There is one small flaw in the steel that you may just ne able to see about mid way along the top flange between the oiler boss and big end boss. I could hear it as the tool passed but not really see what was causing the change in tone until the part was out of the machine as it was towards the rear when being cut.







Finally a couple of close ups of the tool marks left by the ball nose cutter as it stepped over 0.2mm between each pass of the horizontal path, they are more visual that physical as I can only just about feel them with a finger nail but as this was probably a casting or possibly a forging it will be fine after final fettling.





« Last Edit: August 04, 2022, 06:50:53 PM by Jasonb »

Offline Jo

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Re: Little Otto
« Reply #46 on: August 05, 2022, 08:59:20 AM »
It strikes me that needing CNC to make some of the parts for this engine is not going to encourage people to buy casting sets  :disappointed: from Graham.

Jo
Enjoyment is more important than achievement.

Offline Jasonb

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Re: Little Otto
« Reply #47 on: August 05, 2022, 10:26:27 AM »
Strikes me you need to read the thread again. You missed where I mentioned that Graham supplies a casting, this could be used as is which is what he has done on his engine and it runs, His whole engine has been made on manual machine so it DOES NOT need CNC to be make a running engine.

His casting could easily be modified to be a two part one like mine as there is plenty of material in the casting.

Could also be done with manual machining and some silver soldered on bosses.

Just up to the individual builder as to what route they choose to follow be it a casting as Graham used or cut from solid on the machines I have available. Is it any different to you making new columns for the A&M rather than using the castings?

If he does decide to make this one available to others then its not too hard to mill a slot and ream two holes in this, even you could probably do it without a muck up though there are no drawings to blame :LittleDevil:



« Last Edit: August 05, 2022, 10:29:47 AM by Jasonb »

Offline Alyn Foundry

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Re: Little Otto
« Reply #48 on: August 05, 2022, 11:01:50 AM »
It strikes me that needing CNC to make some of the parts for this engine is not going to encourage people to buy casting sets  :disappointed: from Graham.

Jo

Fear not Jo.
As Jason beat me to it with a reply. Iím still very weary and getting as much sleep as I can. Yes thereís a casting available for those of us who  :Love: them.

Jason has followed very closely the  ( full scale? ) engine replica built by a Dutch gentleman called Tom. Weíve all based the parts around an original photo and a couple of patent drawings. Apparently the one and only Deutz built engine was actually scrapped by the museum in the 1930ís.  :o

As Iíve stated earlier in the thread I wanted to get mine running for the prestigious Neunnen engine rally to join with Tomís engine. This meant doing things as simply and easily as I could. I really do feel that when Jason gets to the finish line his model will be worthy of ď museum quality ď status.

 :cheers: Graham.


Offline Jo

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Re: Little Otto
« Reply #49 on: August 05, 2022, 11:58:59 AM »
Thank goodness for that Graham, someone does love showing off his CNC machine at every possible opportunity.

Jo
Enjoyment is more important than achievement.

Offline Jasonb

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Re: Little Otto
« Reply #50 on: August 05, 2022, 12:17:04 PM »
Is it CNC in General you have a problem with Jo or just my machine?

I've shown one part in this thread using the CNC and you make these comments, Why not post comments in the likes of Vixens thread where he shows far more use of CNC or any of the other members that use them?

I just use what I have available and choose what best suits the job, much like you choose to use say your Delapina Hone as you are lucky enough to have one where most of us make do with a brake cylinder hone. I choose to document all the parts I make for a model so don't want to leave out the ones made by CNC as some people are interested in it even if you are not

Offline Jo

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Re: Little Otto
« Reply #51 on: August 05, 2022, 03:38:51 PM »
No problem, just observing that since you were given the machine you endeavour to use it at every opportunity, some would say you are getting your monies worth out of it.

I don't think Mike has any manual milling machines  :noidea: he has a well worn in lathe that he paid a fortune for  :naughty:

Jo
Enjoyment is more important than achievement.

Offline Jasonb

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Re: Little Otto
« Reply #52 on: August 05, 2022, 04:22:02 PM »
Certainly do seem to be getting some use out of it. Its interesting that John Stevenson offered me one (early KX1) a few years earlier and I said it was not really for me, was even in two minds about this one but glad I went for it though still like to use the manual machines as well.

This whole model would probably never have got off the ground without my CNC patterns as I could not convince graham that the base would be quite easy to fabricate when he first contacted me about the engine but he wanted a cast one.

For anyone put off thinking they may need CNC for this engine should castings become available this is Graham's casting side by side with my CNC machined one. As I said there is plenty of metal there to do whatever you wish. One of the other reasons I went down this route is that the power stroke on little Otto is upwards so any reduction in weight he has to lift will be helpful so apart from being a two part yoke mine has much thinner webs and slightly reduced diameters at the rounded ends. easy enough to mill a bit off the casting and the thicker web would be thick enough to tap if you wanted to do the two part option





Original sketch sent to Graham to make the pattern from and one of my version, as you can see all critical sizes are the same.

Offline Alyn Foundry

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Re: Little Otto
« Reply #53 on: August 05, 2022, 06:42:42 PM »
We have very different attitudes where fabrication is concerned  ;D

However, Jasonís program and CNC machine made an absolutely perfect job of the base pattern and associated core box for it. I can now see why, for a one-off, that Jason finds this route the best.  :ThumbsUp:

The Scotch yoke pattern was made well over the top to allow for most eventualities. To my eye, the picture shows the big end to be a simple ring within the forked end of the yoke. Both Tom and Jason saw it differently, the conrod end being forked instead. The casting allows for either option.

I also made the pattern parallel for ease of machining, the casting can then be finished to the correct shape.

 :cheers: Graham.