Author Topic: A simple Vertical Steam Engine.  (Read 82124 times)

Offline bent

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Re: A simple Vertical Steam Engine.
« Reply #315 on: October 10, 2017, 06:26:04 PM »
Jo,

Whenever I have tried to mill on a rotary table, I end up with horrible levels of chatter, which I attribute to the lash/slop in the rotary head gears.  Any suggestions or tips for getting such clean cuts, besides buying a quality rotary table?

Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #316 on: October 10, 2017, 06:48:33 PM »
Try using the brake on the rotary table to provide a bit of drag as you rotate the table ;)

Jo
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Offline bent

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Re: A simple Vertical Steam Engine.
« Reply #317 on: October 10, 2017, 09:32:55 PM »
Ah...thanks Jo! :NotWorthy:

Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #318 on: October 11, 2017, 01:48:35 PM »
A suitable bit of steel was recycled from the come in handie bin to make the eccentric jig. One end a reasonable diameter to fit in a collet and the other just shy of the diameter of the finished eccentric sheave. Faced and mounted in a 5C block the centre was marked by scoring in both directions then the scriber dropped 4.76mm for the offset mounting thread. The 40 degree lines were found by using Alibre to calculate the correct height that the radial lines out from the offset centre would be and then scribing that height before joining the dots. These lines were then transferred to the edge of the jig and the two of them centre punched to make them easier to see  :).

Jig drilled and tapped 8MM, suitable bushes made to fit the inside of the sheaves (the Swan crank is a different diameter :-\ but by using bushes the same jig can be used for both). Then the casting and the two pieces of CI bar were faced and bored. The centre line on the two pieces of bar can go anywhere. On the casting you can mess around if you want as there is plenty spare on the outside but it is easier just to draw the centre line where the two lobes meet.

I chose to first check it everything with the old eccentric which clearly was not at 40 degrees offset  :ShakeHead: before rough turning up the one eccentric casting on both lobes. Sadly both inner faces of the sheaves are undercut from the opposite face and cannot be cleaned up so are going to have casting marks on them  :disappointed: Mr Silky's nose has been written on to remind me which reference dot on the jig needs to be used for the front or rear sheave.

There is a lot of metal on these :( . Hence I will be rough turning to 43.5mm all of the sheaves before I move on to the detail (or more likely a bit of casting fondling  :embarassed: )

Edit: I have roughed them all out and as I am feeling tired I decided against starting the final turning today so I used a broach and slotted each of the eccentrics using my hydraulic press  :).

Jo
« Last Edit: October 13, 2017, 08:08:05 PM by Jo »
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Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #319 on: October 13, 2017, 08:36:24 AM »
The finishing off of the eccentric sheaves was achieved using my Sumitomo parting off tool once I had set it up to cut absolutely square (as parting off tools are not). Same as the roughing out do the outside eccentric: with the reference face against the jig but this time working from the inner eccentric out so as to get the ridge in the right place. With a DRO machining the ridge in the same place can easily be repeated on all of the throws by writing down the distance to move Mr Silky's saddle and then taking the plunge cuts before facing the last 0.05mm using the same tool.

I was pleased to see that at least on one of the original casting eccentric faces all the casting marks were turned off so that will be the outside face  :)

The final step was to hold the one of the sheaves and turn the other to depth. I had not taken it to width up until now as I was not sure where the inner faces were going to clean up to and each needs to be 9.53mm wide. Which is interesting as the straps are only 8.73mm wide, the position of the ridge means that there will be a 0.8mm gap on the inside of each arm  ;)

Armed with three eccentrics I can now start on the straps. time is getting short to finish these  :paranoia:.

Jo
« Last Edit: October 13, 2017, 08:40:47 AM by Jo »
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Offline Jasonb

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Re: A simple Vertical Steam Engine.
« Reply #320 on: October 13, 2017, 08:52:36 AM »
I'd always thought the neutral parting inserts were square across the end and that the L/H and R/H ones were not so you could decide which part was left with a pip in the middle. Maybe the Sumitomo ones are different?

Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #321 on: October 13, 2017, 08:56:37 AM »
It is always worth using a marker pen on the piece and kissing the work with the tip to see if it is neutral or not: The Sumitomo one was cutting a smidge earlier on the right, but probably not enough to measure with a micrometer.

That is of course assuming you have your tool post perfectly square to start with  ::)

Jo
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Offline Chipswitheverything

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Re: A simple Vertical Steam Engine.
« Reply #322 on: October 13, 2017, 03:20:28 PM »
Very interesting full write up and detailed photo sequence of the impressive work on these eccentrics, thanks Jo.  Did you also have to make up particular diameter guides for the broach operation, or were they part of the tooling with the broaches?  Dave

Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #323 on: October 13, 2017, 03:47:33 PM »
Thanks Dave  :)

Did you also have to make up particular diameter guides for the broach operation, or were they part of the tooling with the broaches?  Dave

I had to make up both of the guides as normal you never have the right size  :disappointed: Worse than that I borrowed the broach and finally got round to buying one of my own from the Far east  :Doh: and of course those broaches are a metric width where they run in the guide and these Marlco ones are imperial. I will be keeping the guides just in case.

I did not show/photograph the dies being cut :facepalm2: With the jig in place I just drilled and tapped three holes at 15 degrees in that jig then screwed a suitable bit of steel down using the holes then milled either side leaving an 8mm wide arc. Then using the 12.7mm button to gauge the width of each die I milled either side along the centre line of the rotary table. This gave the correct angles on the two sides of the dies.

 :headscratch: For some reason two dies fitted nicely but the third was too loose for my liking so I decided to tin the outside faces. This acts to make the loose die firm and gives me a little more on the other two to do a bit of fitting.

I have a number of spare standard valve eccentrics on hand.. I might turn them up and key them while I still have that broach  :thinking:

Jo
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Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #324 on: October 23, 2017, 03:42:27 PM »
 :( things are slow where I am not feeling up to anything  :toilet_claw:

So first calculate how to machine the tops of the bits of gunmetal. Then cut some shoulders, drill for the tapping hole and finally use the slitting saw to cut the top of the straps off. 

Repeat for the tops and bottoms of the two sets of castings  ::) then tap one side and drill clearance through the other before screwing each side together.

Jo
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Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #325 on: October 23, 2017, 03:52:36 PM »
The solid straps are easier to set up than the castings as a simple centre punch mark can be used with a dial to find the centre. The castings need to have their centre lines marked and a bit more fiddling about. Both have their flat face towards the chuck.

Then it is simple: Face to 0.2mm over width, bore checking the fit on the eccentric (by poking it in the hole  ;) ) Then using a groovy tool cut the groove making sure it is not too narrow  :hellno: Turn and face the other side to the correct width.

Fit each one as you go onto is correct eccentric just in case there is any variation in sizes.

Mr Silky found a piece of "hard as  :censored:" steel and made the BCA up a nice little stepped mandrel for doing the rounding. Not sure the bolts will survive  :lolb: but feeling knackered... not much to show for 10 days swarf making  :(

Jo
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Offline bent

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Re: A simple Vertical Steam Engine.
« Reply #326 on: October 23, 2017, 05:46:01 PM »
Not much to show?  Dunno, but they look great Jo.  Is that a burr bit you use for the rounding?  Looks like it leaves a nice finish.

Offline b.lindsey

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Re: A simple Vertical Steam Engine.
« Reply #327 on: October 23, 2017, 05:50:41 PM »
Nicely done Jo!  I will  be needing to do something similar for the half scale Pearl before too long so this may help. I will be using the supplied castings though for the eccentric straps.

Bill

Online Jo

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Re: A simple Vertical Steam Engine.
« Reply #328 on: October 23, 2017, 06:29:14 PM »
Thanks guys  :)

Is that a burr bit you use for the rounding?  Looks like it leaves a nice finish.

Yes it is a burr bit I have found them very good - the part will look even better when I start using it  :Lol:

I had to decamp from the workshop as I was suffering from fatigue again :wallbang: I need to get those done tomorrow as I have the recovery spies turning up on Wednesday  ::) In theory the rounding should take less than an hour but I suspect with the way I have been feeling it will take me all day  :(

Jo
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Offline scc

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Re: A simple Vertical Steam Engine.
« Reply #329 on: October 23, 2017, 08:15:26 PM »
All looking lovely Jo,  Glad too that you are on the mend :)       Best Wishes        Terry

 

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