Vulcan Beam engine Parallel motion

Recently started a Vulcan beam engine and not having done a beam engine before, but had read a few builds and comments etc.

Drilling the beam - and the bosses for the pivot points were not all positioned well, similar to other builds. - So If drilled as per dimension for mine, the hole for the parallel motion link would not have been centred in the boss. Drawings indicated 1-7/8 equal spaced between centre pivot and end pivot. Parallel motion links are all 1-7/8 including the 'tie' links to the entablature.

After the adjustment to centre the pivot in the boss, dimensions are now 1.910 (end closest to end pivot) and 1.840 from that to the centre pivot.

I assume that lengths of parallel motion links all now need to be the same, at 1.910. I also assume this includes the (tie) links that anchor the parallel motion to the entablature?

Any guidance on this is appreciated.

There have been a couple of threads in recent months on parallel motion links on beam engines, going into the geometry at some depth. The Google search halfway down the forum homepage should find them.

But I believe you are right in thinking the links need to be the same length.

Would be best to draw it out and make sure nothing else is affected but on the face of it all four bridle links need to be the same

Can you machine the outside of the bosses to make them concentric with the centres for the link pins. If you are doing this on a mill a suitable round nosed cutter in a boring head would tidy up the outside of the boss. JB weld to do a final blend and tidy up. Once it’s painted it will look the business.

regards Martin

Having the straight line motion attachment at other than half way along the beam will distort the piston rod motion. To correct this, the tie links would have to be not 1.91, and the attachment to the entablature would not be on the piston rod centre. Probably only very small differences, but I'd investigate Martin's suggestion first.

thanks for the comments. Also didn't know about that search function on the main page, thanks for that one.

Seems also important for the pivot point for the 'tie' link attachment on the entablature to be in line with the piston rod. seems that way provided the bridle links are same length it keeps things in-line.

Sanderson Beam engine is different to the norm and one example of where the parallel motion is not mounted midway on the beam, so must be configurable for uneven distance.

As I said above, if the half way boss isn't actually half way, then the entablature anchor should not be on piston rod centre. Sanderson is a extreme example.

I plotted the alterations to beam pivot onto the sketch I did the other week and if all 4 links are extended by the same amount (red)you get about 9 thou more lean of the piston rod from one extreme of it's travel to the other if entablature pivot is not altered

How long are the droppers?

The drop links on that engine were the same 1.75!" will most likely get a different result with the shorter 1.125" Vulcan ones but shows it will not be the same. Also did not work out where the Vulcan entablature pivots will be as that again will affect geometry. Suggest OP does it in CAD either on the 'puter or Card and Drawing Pin method

Using the OP's beam dimensions and 1.125" drop links, I make it that the fixed end of the tie links (where it connects to the entablature) should be 0.135" nearer to and 0.013" above the main beam pivot. The tie bars should then be 1.775" long. This gives the piston rod connection on centre top of stroke, middle and bottom. The drawing is a bit confusing as the drop links equal half the stroke, but if anyone wants a copy as a dwg just let me know.

I'd still take up Martin's suggestion.

Thanks Jason and Duncan, appreciate the numbers as I don't have CAD. and how accurate can you get with a pin and card?

due to the nature of the casting I didn't fancy trying to re-machine the boss so have already drilled.

Duncan - don't quite understand re the 0.013 'above the beam pivot' - do you mean the main centre pivot on the beam? otherwise Im not sure what you mean, or how it would be possible to have the entablature pivot above the beam pivot. copy of the drawing may be useful thanks.

I thought you had already drilled so that is why I did not mention reworking the boss. However it would be possible to completely bore through the beam at the correct 1.75" location and then JB weld in a new bit of bar. If the bar has a reasonable amount of draft angle each side then it would fill the old boss position and the new hole would cut crisply through the central raised bead so would just need a fillet of JB Weld to mimic the internal fillets of a casting.

That is the way I mostly deal with wayward cast bosses and the like as they can often end up a bit small once rounded if based on the new hole position but does depend to some extent on the individual job

Yes, I mean the main beam pivot. In reality I can't see the 0.013 dimension being critical. Send me your email via pm and I'll send you my drawing. Dxf or dwg?

I'd still do Martin's mod, blob some JBWeld around the boss where it will be short and machine using ball nose cutter, or even a round top tool in a boring head

Or Jason’s idea of drilling the boss out and fitting a new one from a short end of bar material. Jason seems the expert at fettling castings. In fact some of his castings are all fettle and no casting.
Always better to make the material fit the design rather than t’other way round if at all possible.

regards Martin

This reply is probably a bit late. My father started a Vulcan but never finished it or got it working. I inherited his machines and tools and have recently retired so started to restore the Vulcan and get it running. I ran into the same issue with the links and entablature bosses. Initially I made the two links that fit to the entablature bosses slightly longer so that they would bolt centrally to the bosses, However this puts the parallel motion out and the connecting rod had about 0.010" lateral movement over its stroke. Solution was to re-make the links to standard size and hence all 4 links are now exactly the same size and as per the drawing. I machined the old bosses flush to the channel on the entablatures then drilled a hole through them at the correct centre position and silver soldered in a set of new bosses and now the links are bolted centrally. The connecting rod now runs perfectly true and the repair turned out very neat. I can send some pictures if you are interested.

I have had the Vulcan running on air and it runs well. I am currently building the governor valve and regulator as described by Edgar T Westbury in later editions of Model Engineer. I will have to make my own castings for the bridge and control arm bracket which will be interesting as I have never done this before. Hopefully it will look like the model on the cover of September 1967 Issue of ME when finished.

I have all the original ME build article which was very helpful in restoring the Vulcan.

Good luck with your build.

Regards Peter

You should be able to fabricate the governor parts as it sounds like you can silver solder already it should be no problem. The bridge can just be bent and soldered to suitable feet, the top and side bosses soldered on and then treat it as a casting to machine from there finally shaping the bent bridge to a more pleasing cross section.

Likewise any bracket can be soldered up from a few offcuts.

Thanks for the advice. I will try the casting first as an experiment and new experience. If this does not work out I will go the fabrication route.