Author Topic: A Robinson from rejects.  (Read 71931 times)

Offline Jo

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Re: A Robinson from rejects.
« Reply #120 on: December 18, 2017, 06:57:35 PM »
Does that mean to say you start shinning up the trees in the garden once the bottle of port is empty :LittleDevil:

I haven't brought any port   :facepalm:

Jo
Enjoyment is more important than achievement.

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #121 on: December 18, 2017, 07:10:04 PM »
I'm quietly following along, been a little unwell recently and now have vertigo. Typical as the Christmas season is nearly upon us.

Jo

P.S. Hope you feel better soon Graham. Maybe a quick fondle of a set of Sphinx castings would make you feel better, I know it would me  :naughty:

Well Jo.

If you can promise to be good and not become a lumberjack Father Christmas might just make arrangements with that special place he's recently found!

One thing for certain there won't be any " special " coatings to remove!! :)

Cheers Graham.

Offline RayW

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Re: A Robinson from rejects.
« Reply #122 on: December 18, 2017, 07:34:15 PM »
Hi Graham,

Sorry to hear that you have been under the weather lately and hope you will be fit for the festive season.
Good point you make about the upper part of the cylinder being the cooler part. Perhaps I am worrying unduly about needing to open out the water space above the liner.

Best wishes

Ray

Ray

Online Jasonb

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Re: A Robinson from rejects.
« Reply #123 on: December 22, 2017, 10:16:45 AM »
A question for Graham.

The drawing for the inlet valve chest shows 7No 1/8" holes which I have shown on my drawing. These seem larger than on your drawing where they look to be nearer to 1/16" dia, could you shed any light on what will be best please.

J

Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #124 on: December 22, 2017, 11:06:33 AM »
A question for Graham.

The drawing for the inlet valve chest shows 7No 1/8" holes which I have shown on my drawing. These seem larger than on your drawing where they look to be nearer to 1/16" dia, could you shed any light on what will be best please.

J

Hi Jason.

I probably used a stencil for those, but yes 1/8” is correct.

Being a flat valve it takes  a little care and time to grind in as this valve also controls gas admission. I will stress that this valve will almost certainly weep no matter how careful you have been!

Cheers Graham.                                                           

Online Jasonb

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Re: A Robinson from rejects.
« Reply #125 on: December 22, 2017, 11:19:49 AM »
Thank you Sir

Online Jasonb

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Re: A Robinson from rejects.
« Reply #126 on: January 07, 2018, 03:42:40 PM »
Got the valve and valve chest done. I opted for a ring of 3.0mm holes as 1/8" looked a bit close for comfort.



And also made a start on the gearbox as I had that casting. Parted off quite nicely, I used the ctr for support until the last 5mm or so.



Graham, if you are looking in could you clarify a dimension on the gearbox drawing. As I read it the peg hole to stop the gearbox rotating should be 7/16 from vertical and where a 3/4" radius arc swung from the crankshaft ctr line meet.



J




Offline Alyn Foundry

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Re: A Robinson from rejects.
« Reply #127 on: January 07, 2018, 06:02:48 PM »
Hello Jason.

That reads about right.

The way I used to do the final fixing of the gearbox was to drill the retaining peg hole and then offer the whole assembly to the engine. Slide the crank gear onto the crankshaft right up against the bearing then screw in the slide into the exhaust valve chest. You can now rotate the gearbox assembly till it looks right.
Using a transfer punch dot the base for the peg position.

The crank gear is drilled and tapped to 4 BA and a dome head screw is used to fix the position in the 1/8” keyway. Once you’ve set the valve timing by removing the eccentric halftime gear and repositioning until satisfactory that assembly will always be in time because of the crank gear locking screw.

The inlet valve chest looks superb, almost identical to the casting!

Cheers Graham.

Online Jasonb

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Re: A Robinson from rejects.
« Reply #128 on: January 12, 2018, 05:59:17 PM »
So this weekends homework is going to be having a go at cutting a test internal gear. I managed to find a 12T spur gear and 24T internal gear on Grabcad and imported the STL and Solidworks files into Alibre and then scaled the two so they were the right size for 1.75MOD

I'm going to take a leaf out of Willy's book and do a test one in perspex using a single point tool in the mill and will use the quill to feed it like a slotting head. gera will be on teh rotary table, having a 72:1 table to play with from ARC will make the 24 divisions an easy 3 turns of the handwheel. I can then slip the spur gear onto a 1/2" bar held in a coller and rotate the table to check the mesh of the two gears. Well that's the plan anyway.

may also make teh eccentric strap which will be in steel so I can silver solder it up from a couple of bits


Offline Ian j

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Re: A Robinson from rejects.
« Reply #129 on: January 13, 2018, 02:36:34 PM »
A bit more progress on my engine built from bar stock/scrap!

Eccentric strap:-
I bored the centre of the rectangular lump of brass for the gear to be a close fit and then made a jig ( or is that a fixture?) to mount it on the rotary table on the milling machine table, it then only took a short time to mill the outside profile.
 The brass blank wasn't wide enough to include the oil quill so I used one of the scrap pieces produced after milling the outside profile which had the correct radius and silver soldered it on ( not exactly an invisible joint)
 I think I'm quite pleased with the end result.

Offline RayW

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Re: A Robinson from rejects.
« Reply #130 on: January 13, 2018, 04:18:28 PM »
Very nice work Ian.
I am currently working on the connecting rod, but at a standstill at the moment as the awful plastic gears in my milling machine have just stripped for the umpteenth time, so I have ordered various replacement gears and sundry other parts from ArcEurotrade to keep me going.
I have also bitten the bullet and ordered a very professional looking belt drive conversion kit from a guy in Turkey. The kit is not cheap but looks very well made and will not only solve the stripped gear problem, but also enable the mill to run a lot quieter and faster than with the current gearbox.
Ray

Online Jasonb

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Re: A Robinson from rejects.
« Reply #131 on: January 13, 2018, 08:16:35 PM »
That's looking nice Ian, good to see how parts can be made in different ways if we opt out of using castings.

Well I had a go at the internal gear today, only cut half the teeth in the plastic one as that was enough to see if my methods would work



So I decided to commit to some bronze. I had some 2.5" hollow bronze so the end of that was turned down to 2.308", faced and then parted off and finally the other side was tidied up to bring it to the required 5/16" thickness. As there was no middle to the bar I hot glued a bit of scrap in place so the position of the gear ctr could be marked and then picked up on the mill when clamping to the rotary table.



To reduce the amount of metal that needed cutting out I had worked out the PCD of a ring of 4mm and 2mm holes so these were drilled every 15degrees, you can see how the gear will be eccentric by the way the drilled holes are set about the cored hole.



I then milled out to the required internal diameter



The cutting tool was ground freehand from some 3/16 HSS using the Alibre drawing as a template and mounted into a 1/2" bar



It was then just a case of setting the rotary table to position which was easy as the 72:1 ratio on the ARC table meant I just had to turn the handwheel 3 turns, feed the tool down using the quill lever with my right hand while feeding in the work with my left hand on the Y axis handwheel, the early cuts could be done 5thou at a time but once the end and most of the sides started to contact that came down to 2.5 and finally 1 thou cuts for the last 15thou or so. You can also see that I have slipped the pinion gear onto the tool holder and kept it out the way with a bit of tape.



With the quill locked so the tool was below the work the masking tape could then be removed to allow the gear to drop into place and test the mesh without loosing the position of the cutting tool, it was a little tight in one spot so I lightly stoned the cutter and went round again doing a couple of spring passes in each position which did the job.



And what do you know, it even goes round and round :)

<a href="https://www.youtube.com/watch?v=LZMHKc-3xEc" target="_blank">http://www.youtube.com/watch?v=LZMHKc-3xEc</a>

Offline Ian j

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Re: A Robinson from rejects.
« Reply #132 on: January 13, 2018, 08:29:58 PM »
That's excellent Jason. How do you lock the quill to stop it rotating?

Online Jasonb

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Re: A Robinson from rejects.
« Reply #133 on: January 13, 2018, 08:38:55 PM »
I thought I took a picture of that but obviously did not :-[ I took the top cover off the mill head and clamped the gear on the quill with a couple of tool makers clamps

Offline Chipmaster

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Re: A Robinson from rejects.
« Reply #134 on: January 13, 2018, 08:55:19 PM »
Clever stuff Jason. :ThumbsUp:

Andy

 

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