Wanted- Some Eccentric Advice

[jordanleeds]

I Am in the throws of progressing one of my Many projects and thoughts have turned to the eccentrics Does anyone have any advice on producing split eccentrics? the Valvegear is bagnall price with everything tucked inside but driven from the valve rod outside the frames

[jma1009]

hi jordan,
one of my locos has the correct type of GWR split eccentric sheaves keyed to the crank axle. they are a huge amount of extra work but fun to have ago at if you fancy it. you could reduce the amount of work involved by holding the 2 parts together with socket head cap screws.
it would be quicker and perhaps easier to press one of the wheels off though and fit solid eccentric sheaves!
cheers,
julian

[Deleted]

With that thread heading you've come to the right place, me included ( chuckle)........

[donashton]

Interesting topic. I once turned the complete axle plus two cranks and four eccentrics out of the solid in EN 8. Actually there was very little 'turning' as such because all items are so close together. All the machining is like parting off. It came out ok, but if you imagine a detailed risk assessment it would be covered in red ink!
Don.

[jordanleeds]

I am fitting bagnall price valve gear and the eccentrics are split to fit on the axle as they are a smaller diameter between the wheels with shoulders turned up to just behind the wheels.

Never done anything like this do working out the valve gear is proving interesting.

[ejparrott]

I have the same problem as you. I have split my eccentrics on the centreline of the offset, straight through the keyway at the same time. The pair then have holes machined in them something like the fullsize, and a pair of studs through to hold them together. I'll hopefully be starting construction this week or next so look out for photo's coming up in my build thread shortly (hopefully).

Meanwhile, here is a photo of the fullsize of mine...



You can just about see the openings. Other ones split the eccentrics across the shaft hole, leaving the keyway in tact in the main half, which is then drilled and tapped. The smaller half is then drilled and counterbored for caphead screws.

[jordanleeds]

Cheers another question that came up this evening whilst mulling over a glass of talisker the throw of the eccentric will be the same as that of the cranks won't it ? Or perhaps I am going rather mad.

The valve gear is bagnall price and the cylinder has a bore of 2.60" and a stroke of 3.5"

[ettingtonliam]

Normally the throw of the eccentrics is much smaller than that of the cranks, because valve travel is much smaller than piston travel.

Richard

[Deleted]

Hi JORDAN-------- "the throw of the eccentric will be the same as that of the cranks won't it ?"--- where on earth did you get that idea from ??

[jordanleeds]

It was as I say after the consumption of a rather nice dram in reality I recognize the errors of my ways now.. best order the works drawings and do the maths I think

[Deleted]

---------- meanwhile, can I have a "sippers" of your evil brew ??........ www.bbc.co.uk/history/ww2peopleswar/stories/61/a7129361.shtml ........

[ejparrott]

Dead scale valve gear components won't give good running characteristics to a model. Use them as a starting point, then tweak them with calculations and simulations. Don Ashton was a real gent and ran through my Manning Wardle for me. Components currently in production!

[jordanleeds]

could i get away with fitting the exxentrics as per full size in position? or do i need to do the calcs?

[donashton]

Hi Jordan,

There is no quick way. Start at the beginning with desired ports, design valves to match the ports, arrange for a full valve travel of around 77% cut off. Then verify the geometry.
Forget fleshing up the parts until all the above is satisfactory, otherwise you may be in for real disappointment. There are plenty of horrors even in full size - please don't add another!
Best wishes,

Don.

[jordanleeds]

Thanks Don, These long llangollen evenings certainly mean things progress ! Just keen to start machining the wheels and axles but only want to assemble them once. Will send you an email off list!

[ejparrott]

If you only want to assemble once, does that mean you're not fitting the waisted axle any more? I'm hoping to progress my eccentrics a bit more this weekend. Get the angles for the ecentrics sorted out, then cut keyways in your axles as required, permanent eccentric setting on the axle = no disappointments!

[donashton]

Hi Jordan,
I'm not too familiar with that gear, but they all have to do the same job and i can advise on ports, valves etc. to fix an eccentric throw and angle. I've just checked out Dave Owen's engine.
Will catch up on my next Llan visit - the last one was rather busy. Sizing ports and valves is easy enough but it must come first.
Email by all means.
Don.

[steam4ian]

Thread Hijack

Don

Crossing the rods in Stephenson gear reduces the lead at mid gear.

Is the converse true for Gouch gear, crossing the rods increases the lead at mid gear?

Regards
Ian

[donashton]

Hi Ian,
I suppose it was inevitable, once Stephenson's gear was invented, that Gooch and Allan should follow. Both are described as constant lead, but more accurately the lead wanders about in no set pattern. They don't produce lead variation in the well known Stephenson manner, but the partial dropping of the linkage in Allan has some influence. A properly designed Stephenson's layout beats every other linkage I have come across, including Walschaerts'.
Don.