CHUK " V "

[Jasonb]

Needless to say the flywheel was always going to have 5 spokes right from the start although it was chopped and changed quite a few times, originally i thought that it would need something about 7" dia due to there being two cylinders which meant it would extend below the crankcase but Graham felt a smaller one would do so we settled on a of about 120mm dia with a wide rim and tapering oval section spokes. Like the crankcase the 3D model was enlarged to allow for shrinkage, draft angles and machining allowance added and a model of the half pattern exported to F360



First operation was to face the stock taking it down to the finished height of the edge of the rim. I've put the all the cutter details on the video so won't repeat them again here.



The bulk of the waste material was removed with a pocketing path leaving 0.5mm for finish cuts. While the 6mm tool was in the collet a finish cut was taken to bring the hub to height. As well as the blue and yellow paths mentioned in the last post there are some red ones which are where the tool ramps down into the work in a spiral which is kinder to the cutter than just plunging straight down.



Changing to a ball nose cutter the inside was finished with a "steep and shallow" path



Finally the tapered outer edge was finished with a "ramp" cut which has the tool gradually dropping down as it follows the profile, in this case I had it drop 0.75mm over one rotation which was approx 400mm length of cut.



I'm pleased with how it turned out, there was a bit of splintering of the top edge that can be seen on the video as I had used up some offcuts of boards that had a bit of snipe at the ends so that left a slight void not helped by the top layer ending up about 0.5mm thick. Nothing a bit of Upol filler could not sort out. This is the finish straight off the mill which needs almost no sanding.



<a href="https://www.youtube.com/watch?v=yh5zggx_Xfc" target="_blank">http://www.youtube.com/watch?v=yh5zggx_Xfc</a>

Here are the two halves together with the crankcase pattern.

[Jasonb]

The final pattern required was the cover plate to enclose the open side of the crankcase, Graham had said that it would be nice if the writing could be engraved allowing the builder to fill it with paint and buff up the surface if they wanted to rather than his usual raised "CHUK" that can be found on the other engines in the series.

I have not found a way to get lettering in Alibre to follow a curve so ended up manually placing each letter using a couple of guide circles and tilting & spacing the letters so that they looked right. The 3D model was then exported to F360 which has an engrave function that produces some nice crisp corners to the letters rather than the rounded ends you would get if the a milling cutter just followed a single line. It does this by ramping the Vee shaped cutter down into the letter and up each of the corners. This video of part of the simulation shows it better than I can explain it.

<a href="https://www.youtube.com/watch?v=tvnde64xjcU" target="_blank">http://www.youtube.com/watch?v=tvnde64xjcU</a>

I thought I would do a test run first to see how the lettering looked so slipped an off cut of 6mm melamine faced MDF into the mill as this gives a good contrast.



A wooden pattern may have been prone to damage so I had some 10mm clear acrylic of some unknown parentage so decided to see how this cut. I was a bit worried that I may end up with a glob of molten plastic wrapped around the end of the tool but it cut nicely at 5000rpm and a feed of 200mm/min using a carbide chamfer mill. I actually ran the path twice giving an undersize tool height so that the second pass would cut slightly deeper but just leave a slight rounding to the corners of the letters so the sand would not get stuck.



The 10mm material was too thick for the pattern so I cut out a rough circle on the vertical bandsaw and stuck it to some MDF using the two layers of easy peal tape and superglue sandwich method. The MDF was then held in the 4-jaw and the test letters turned off as the thickness was brought down to 6mm and the edge turned round with a slight draft angle.



It was then just a case of clamping the MDF to the mill table, locating the middle of the disc and running the cut again

<a href="https://www.youtube.com/watch?v=FxdaV9fjsdo" target="_blank">http://www.youtube.com/watch?v=FxdaV9fjsdo</a>

The tape separated quite easily and there was hardly a burr to be removed.



Here it is up against the crankcase, you may be able to see a couple of blind holes at 3 & 6 o'clock these were drilled in from the back so the pattern can be pulled from the mould with a couple of screws.

And if you look really hard you can see two filled holes in the edge of the crankcase at 1 & 7 o'clock. These were holes drilled in past the joint line which had brass dowels located in one half to help line up the pattern halves when moulding them up.

[Alyn Foundry]

Here are the " shiny " results of Jason's labours....

[Jasonb]

You could make a nice alarm clock out of one of those

[Twizseven]

Graham,

Will you be going into production with these at some point in the future??

I assume you and Jason will do test builds first of all.

Colin

[Alyn Foundry]

Graham,

Will you be going into production with these at some point in the future??

I assume you and Jason will do test builds first of all.

Colin

I think it's highly unlikely at this point Colin.

Judging by the sound of " Crickets chirping " both here and at Model Engineer I would say it's a " non starter "

Obviously this is a concept engine, yet to be proven but I have every confidence in my abilities that a successful runner will result.

The design calls for a different " physical " cam than the normal flat disc with profile. It resembles more of a " Top hat " shape to be able to clear the front bearing housing. This will be fabricated, as a pattern is probably a waste of time.

The only " tricky " parts to make will be the cam followers, a few ideas are swimming around at the moment.

If nothing else it will make a nice Christmas present for the two of us.   

Cheers Graham.

[Jasonb]

It resembles more of a " Top hat " shape to be able to clear the front bearing housing. This will be fabricated, as a pattern is probably a waste of time.

What's the world coming to, first me making patterns and now you talking of fabricating parts, next thing you know Jo will be throwing all her (his) castings out and finishing a barstock engine

I'm sure you must have a spare bit of CI to cut it from, maybe a reject casting for the X-type gearbox/cover would be deep enough?

[Alyn Foundry]

Hmmm....

I do have a sack of Robinson hot air engine piston castings left over from the 90's. Plenty of meat in the crown end.

I'm thinking that the usual crank web can be glued to the 10 mm Silver Steel and make the cam to slip over the crank web boss.

Cheers Graham.

[Jo]

What's the world coming to, first me making patterns and now you talking of fabricating parts, next thing you know Jo will be throwing all her (his) castings out and finishing a barstock engine

Strangely enough we had been discussing making an engine out of bar stock earlier this morning when Polly Wobbles told us they did not have the set of castings Surus wanted for his Christmas present in stock and they could not tell us when the foundry would actually get round to doing them Its going to be a nightmare before Xmas 

Jo

[Jasonb]

Which one has he got on his list?

Actually that is probably a silly question as I expect he has all that are not already in his collection on the wanted list. So what's top of the list?

[Jo]

Top of his list is the double sized Williamson, next he fancies a Bee  .

Jo

[Jasonb]

Who does the big Williamson?

I'm not keen on the Bee, if I were to pick one of the hot air engines from them it would likely be the Denny Improved Ericsson but the Eisner is a better size at about 450mm tall plus I have the drawings.

[Jo]

Who does the big Williamson?

A friend, you wouldn't like it the drawings are in metric   

The Denny is too similar to the Rider Ericsson and we have done one of those.

Jo

[Alyn Foundry]

Special thanks to to Colin ( Twizseven ) who was " out and about " yesterday....

They've come out reet nice eh Jason?

Cheers Graham.

[Jasonb]

Not bad the two halves look to have lined up well, surface is down to sand and method of moulding Airset?

How many did they cast?

I meant to ask did you paint any of the patterns or just send them as the bare wood ?