Tag Archives: scraping

The &^*$! reversing gear…

Well, if you’re building this engine then I hope the valve gear goes more smoothly for you than me!

The Draglinks

The Drag Link Bearings

Drag Link Bearing Blanks

A handfull of work, drag link bearing blanks ready for drilling boring, fitting and oil-hole drilling

I cannot believe just how long it has taken to complete the reversing gear on the engine – and it’s still not done.

The multitude of little blocks (drag-link bearings) take an age to make – if you had some 7/16″ sq Ph Bronze bar to hand then it might be OK, but I didn’t so decided to hack the blanks out of a piece of 2-inch square bar I had. However, I discovered that my trusty Warco bandsaw did not cut as straight as I hoped, and half of the resulting blocks were undersize. So then you spend a while silver soldering extra bits back on, to bring them to size, and then (literally) DAYS on the shaper, transforming a set of rough cut rhomboids into little cuboid shapes.

Drag Link Pins

Meanwhile a relatively simple turning and pressing job produces the pins for the lifting arms and eccentric pivots.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

Drag Link bearing pins pressed into lifting arms and allen-screwed into expansion links.

I happened to have some EN1A on the shelf that these got cut from – this is lovely free-cutting (leaded) mild steel, but I must confess I worry that this is so “soft” that it might not last well in service.

BTW – Midway thru the gear building I ran short of 1/4MS bar. So I went off to Metal Super Markets in Southampton (metalsupermarkets.com) and stocked up on a variety of bar and plate, that my “stores” were running short of; (these really are great people, and very helpful and economic – I would recommend them to anyone, over the counter service with a smile, for even small quantities) – But they only had EN3B, and when it came to turning and screw-cutting this stuff you really miss the free-cutting EN1A!!!

The only issue with the manufacture of these pins, is that one of the errors in the drawings means these pins need to be longer than drawn, to clear the bolts and lock nuts securing the Expansion Links and Die Blocks. There’s not a lot of space, so take care – I extended mine to 1.5″ overall (I think).

Drilling and Boring Drag-Link Bearings

drilling the bearingsThe next job was to drill the bearing halves for the rods. I did this by clamping them into a small jig (with tool-makers clamps). My normal approach to this would be to soft solder (“sweat”) the bearing halves together and then drill and bore them as one, separating them at the end. But this was not what the ME articles said – so I followed them… The plan was to create a small jig, drill half the blocks 2BA clearance and the other half 2BA tapping – then tap these and use temporary screws to assemble them into pairs while they are bored, and then open out both sides to clearance for the long rods to be fitted.

Jig Drilling DragLink Bearings

Jig Drilling DragLink Bearings

I think this approach was slower.  A better plan would have been to solder them into pairs while they were all still oversize, drill, bore, finish to size and then separate.

As it was I then discovered that despite machining all the blocks to size, the journals on the pins were too tight (only a few thou, but enough to stop them fitting, so yet more fettling was needed)- At this point I discovered that the relevant reamer has gone missing, so more careful hand work on pins and bores (scrapers and emery tape) was needed to get a good fit….

The Valve Rods

This is about to start sounding like the blog of a complete idiot, but at least it’s improving my patience.

LP Valve Rod

Firstly, while assembling and testing the valve gear (prior to first run on air) I found that the LP valve was fouling something and could not accommodate the full travel of the eccentrics, over a couple of hours of assembly, disassembly, reassembly (repeat as needed) I came to the conclusion that the tailrod was too long and clouting the end of the tailrod guide… there being no opportunity to lengthen the guide, I decided to shorten the tail rod – carefully sawed 1/4″ off, and reassembled again, only to find it STILL DOES NOT FIT!!!!!

Further inspection determined that the valve buckle was actually fouling the nut holding the tail-rod guide – and actually the shortened tail-rod was now falling out of the guide at the lower extent of the valve travel!!! So, it now needs lengthening – more work yet to be completed…

HP Valve Rod

The HP valve rod has a “joggle” on the bottom to line up the valve rod with the eccentrics. I decided to make this as a separate part and screw it to the rod proper. This joggle also serves to further widen the already widened drag-link pins resulting from the error in the drawings. I did measure this and allow for it in the longer pins – but I forgot to take account of the lock-nut on the die-block pin….AAAARRRGGG!!!

I concluded I could shave enough off the joggle to accommodate all this, but the amount of metal left for the thread holding the actual valve-rod into the joggle was going to be a bit thin, so I decided to braze the rod into the joggle – this I did (with no distortion), and decided to use the Linisher (belt sander) to just clean the flux and oxide off the joggle…. What I failed to see as I did the final side was that I was holding the assembly slightly out of square and ground a nice 20thou depression in the bally valve rod – thus rendering the whole shooting match scrap! 😐

Either way it provided me the opportunity to screw-cut the 3″ long 3/8″x26 thread on the new rod, using the off-set compound slide method often recommended (but never tried by me) mechanism – and it does a much nicer job (even on the nasty EN3B!), so I conosoled myself that the extra 3 hours work, had resulted in a nicer job (displays a fixed grin)!

BTW, In this process I again reminded myself that under conditions where you need to take fine cuts on tough material a carefully sharpened carbide or carbon steel tool will outperform a indexable tipped tool – as if you check the specs these are not typically made to make a cut of less than 5thou !

The Result….

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Jig Boring the holes in the lifting arms for the weighshaft and drag-link pins

Overall these 16 half bearings and eight rods and 4 pins took more than a 10 days of effort (probably about 30 hours! not including the remaking of the vale rod) – a slog…. assembling the whole sh-bang produced something that worked but was too stiff, so more fettling and adjusting needed!

I am really hoping I can bring this all to a good end – sometimes I wonder!

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Piston Rods

These had been a worry for a while… Rather than being a fabrication they were  spheroidal cast iron castings. The “rod” bit needed turning down to a 3/4 inch diameter over a length of about 8 inches, and I was worried that given the age of the Harrison lathe I would have trouble getting them parallel to within the 1 thou I thought would be needed (no tolerances on the drawings, but this seemed right.).

The clear plan was to turn the rod bit between centers, then hold this in v-blocks to machine the cross-head and little end bearings. So the first thing was to get the ends flat to allow them to be centered.

Facing the ends

Facing the piston-rod blanks in the shaper

Facing the piston-rod blanks in the shaper

I had been waiting for a job like this, as the shaper table has a nice v-slot machined in the right hand side for exactly this purpose. So, as the picture shows, you clamp the casting in the slot (and while this is still rough, I figured that it would mean that is was “straight enough”) – and then being held vertically the shaper can cut a nice square face.

Then turn it over and do the other end, then mark out on surface plate, with height gauge;  center pop, and center drill, and then it’s into the lathe between centres to turn the rod.

Turning the rod-part

Starting to turn the piston rod between centres

Starting to turn the piston rod between centres

As you can see I have been using cutting inserts – these really are amazing, especially if you remember to put the right insert in for the material you are using. I am told that you can now buy “universal” tips which will cut a very wide selection of materials, but I have not tried these yet.

The final cut, newly sharpened carbide cutter and suds

The final cut, newly sharpened carbide cutter and suds

The turning went well, but I found that the rod was oversize by about 4 thou at the tail-stock end, and I concluded that this was actually play in the live centre I was using. So for the final cut I used a dead centre (and suds to help stop the heat of the cutting process from expanding the bar over, tightening the clearance with the centre, and producing yet more heat… friction…heat… and bad end!). I also used a carbide tipped tool, sharpened on the Quorn cutter grinder to do the finishing cut – this is important because if you look at the data sheets on the Comorant cutting inserts you discover that in-order to maximise tool life, these are actually made blunt (to provide a more durable cutting edge) and will therefore require a minimum cut of about 6-8 thou. With all this attention to detail,  the 65-year-old lathe did a great job, with under a thou of difference over the length – 20 minutes with some emery cloth, both produced a nice finish, and allowed me to hand finish to within about 3-tenths of a thou – very happy!

Machining the Crosshead

Machining the Crosshead

Machining the Crosshead

The the game was to hold the rod-part in v-blocks on the lathe bed, and true it up with dial gauges – then machine the rear (slideway) face first, then  use this to get the other faces true. The final act being to rotate the piece so that the slipper face was against an angle plate (to ensure it was vertical) and with the rod holding the part truly horizontal and then bore the little-end bush hole with a boring head.

Scraping the Crosshead Slideways

Scraping the Crosshead Slideways

Scraping/ fitting  the Crosshead Slideways

Now all that was needed was to mate the cross head to the slideways. Aside from the nasty scratch shown in the picture (but fortunately obscured by the slideway cover that bolts on) this went OK. I had deliberately arranged to have a slight interference fit to start with, so I could scrape them to get a good fit.

This was surprisingly hard to do. Because there are 7 sliding faces on the crosshead (left, right, back, front-left, front-right, and the left/right faces of the narrow part of the crosshead which “joins” it to the little end bearing block) it is actually tough to find what is “sticking”. But about 2 hrs per rod saw the job done. I was using the actual bearing and stuffing-box gland to hold the rod, and then slide it up and down to check for the fit.

I have realized why we often call mechanics today “fitters” – because with technology and machining of this kind of age, the largest part of the job IS fitting bits together, to get a smoothly running joint/assembly/machine… I gave in a few weeks ago and purchased my own set of hand scrapers – and they have seen a lot of work since!

Main Bearings; scraping thru!

Major decisions on Main Bearings

The bearing housings in the base casting were already machined a 1/16th  oversize when I purchased the castings, so the Camden-provided bronze bearing castings were not going to work.

So I set about trying to source some suitable “phozzy-bronze” from my normal supplier, and discovered there was none to be had of a suitable size. So I decided to build a fabricated version of the bearings with Cast Iron outers and bronze bearing “shells” – some friends recommended going the whole hog and white-metalling the bearings (as per loco or car practice), but I decided my approach was less error-prone, and more in line with my “skills”!

Given the “oversizedness” of the slots I also decided to up the main bearings from 1 inch to 1.25 inch diameter (I think bigger is always better in the bearing stakes.)….

So I purchased some (very) oversized square-section continuously cast iron bar, and some 1.5 inch phosphor-bronze bar for less than half the price of the Camden blanks – and enabled my “smug mode” – (However, I think pride may well come before a fall!) 😐

At this point I looked at the size (oversize)  of the square cast iron bar I had, and thought about the fact I was about to machine away about 90% of it and then do the same thing by putting a 1.25 inch hole in a 7 inch length of 1.5 inch bronze, and decided this was mad… so I found some 2-inch round cast bar, and decided this could be machined with “square” section to fit in the bearing slots and this was a more “economic” solution…. 2 months later this seemed like a very, very foolish decision! (Time will tell)

So we start cutting

My plan was to silver solder the “shells” to the inside of the bar. So the plan was bore the cast bar,rough bore the bronze bar solder one inside the other….

Well that didn’t work! 3 attempts proved that I could not persuade the easyflow to penetrate and adhere to the cast, and I just wound up with messy flux-covered non-stuck thing!

Plan B – locktite the shells in to the housings (well that is what is holding them at the moment, but I am not convinced it’s a real fix, so they will get small grub screws fitted in axially at the end to prevent any “spin” (as this would cut the lubrication and be a fast route to a bad place!.

The process in pictures – this is really an outline of how NOT to tackle this!

A bit disappointing – but a great workout!

So I assemble the machined bearings into the base casting, and try the bar stock that will form the crank main journals and “bingo”, it’s all locked solid!

The traditional approach is to line-bore this kind of assembly, but it’s too bit for my workshop, and I had hoped that my strategy for building the individual bearing assemblies would mean line-boring was not required. – but it was not to be!

Deep gloom ensues….

However, the model engineering community provides an answer – Neil and Darren say “simple Mal,  just scrape them true”…

A close shave!

So after a quick review of the theory, and armed with a tube of engineer’s blue, 20-30 hours of hard graft (this is THE most effective bicept exercise ever) and very bloody knuckles, we have a shaft that sits in, turns and does not wobble! RESULT!

What I should have done….

Start with the square bar, make it accurately rectangular to provide some reference surfaces, machine to a good fit in the base casting bearing slots, then bored this (in the mill and square), then fitted the bronze bits, then cut them in half, then finally bore the assemblies using the inherent squareness of the main bar….

Well it seems like a good idea!

Now on to the crank – and hereby hangs a further take