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Steam Engine Number One

A Build Log (hopefully)

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Iain Downs08/05/2020 16:31:11
683 forum posts
612 photos

A little more done today after various distractions. I've honed the cylinder with a cylinder hone. Which took a few minutes. It took a good deal longer to find the cylinder hone as I'd put it away 'somewhere sensible'.

Also trimmed the piston on the piston rod down to be a close fit in the cylinder. There was a slightly lumpy bit at one end, which the cylinder hone also took care of.

Finally, I took a little bit off the inside of the piston gland so that the cap would screw down a little more. about 20 seconds work, but a good 10 minutes of random walk trying to get a good register on the 4 jaw chuck. Still that's an improvement!

Next steps would seem to be soldering the piston gland to the bottom cylinder plate and millling the valve ports.

I'm not sure whether to break and heat treat the piston rings at this point or if I should leave them intact until final assembly. I will probably leave them for now. I'm still a long way from having it ready to run.

Iain

Iain Downs10/05/2020 17:41:58
683 forum posts
612 photos

Valve ports yesterday. Though clearly a little bit too much of happiness juice as I appear to have uploaded the pictures twice. Or it's just old age...

On the whole this went well, though I was attempting to do the cutting by eye against marks made with a scriber. The marks were fine, but I hadn't take into account the difficulty of seeing the work piece with a great big spindle in the way and a whole bunch of cast iron grit. Made me wish my DRO had arrived.

Here is the piece being setup to be accurately held in the vice. Turn it upside down on the surface plate can clamp some 20 40 80 blocks to it, then sit it on those.

valveports setting up.jpg

This then gets gripped in my new big vice - though I'm realising that I how need to get some bigger parallels. It never stops, does it?

valveports on the mill.jpg

I was quite worried about milling 11 mm deep slots in the face and even more worried about the 25 mm deep slots at the end, but I had no dramas at all, cutting about 1.5mm deep each time. The DRO on the spindle is a joy. At one point Madam returned from some shopping exhibition (tip - queue too long and waitrose queue too long) and had to tell me about it. With my old mill I would have no idea how deep I'd gone and need to start again.

valveports milling.jpg

When I said, no dramas, That was true of the actual deep cuts, but when milling the end of the face there were some odd noises and a ping as the cutter gave way. I have no idea what I did. the replacement cutter finished it off fine.

And here are the results.

valveports milled.jpg

valveports end.jpg

In truth they could have come out cleaner, but I'm mainly content that I haven't ruined the cylinder. It would have made me deeply sad to have to start this again!

Next step is probably to drill and bold the end caps in place or possibly a trial fit even without out that. If it turns out that the throw is longer than the cylinder.... Well, I;ll probably make a clock.

Iain

Iain Downs11/05/2020 16:55:41
683 forum posts
612 photos

I find myself a bit of a fair-weather modeller. If it's sunny outside, it's nice to be in the shed. If it's grey, cold and drizzly, then the armchair has some attractions.

Today was spent doing a bit more work on the design for the engine. I know, a bit late to be messing with it now...

However, I decided that I might as well add some valve gear as it won't add a huge amount to the time I've already spent - and better now than trying to add it later.

Here are some drawings. The first giving an overall impression of the engine and the second for the valve gear.

wholeengine.jpg

valvegear drawing01.jpg

I might make some cosmetic changes such as rounding the eccentric straps. Also the straps will be split and bolted together and the eccentrics have grubscrews to fix then to the crank.

My main concern is about sizes. I see in some engines that the eccentric rods are fat things, whereas I didn't see the point. Mine are 5mm, but perhaps that's too small, particularly in EN1b - would silver steel be better. By the same token the eccentrics are quite thin, but equally they don't have a huge load.

I'm also not sure of the best material. I was thinking of cast iron for the eccentrics and mild steel for the straps.

Broadly, the two eccentrics are fixed to the crank with grubscrews. The eccentric straps are connected to the Stevensons link and the bearing connects to the top eccentric rod (bottom, middle, unlabelled) which passes through the valve guide bearing that is secured to the valve guide and thence passes into the valve chest. Please ignore the rod at the top of the top eccentric rod. That will end up a thread that ultimately connects to the D Valve.

OH and I will need to work out some way of locking the Stevenson's control lever. Probably something from the bottom cylinder plat, but not sure what exactly.

The other thing I wanted to check is the way I'm securing the cylinder to the top and bottom ends. I'm planning 7 M5 bolts at 50 degrees apart, except for a 60 degree gap where the valve ports are. top and bottom to be held by thread into the cast iron (5mm thick) of cylinder flange. Is that enough and will bolting directly into cast iron be strong enough.

On the practical front I've made some hold-downs for my rotary table so I can secure the cylinder to it.

Iain

JasonB11/05/2020 17:12:55
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5mm dia rods should be OK but your dimensioned 4mm straps sound a bit thin and are actually shown thicker than the 5mm rods, 6-8mm would be better.

Thread the top end of the valve rod and have a rectangular bar that screws onto it so you have some adjustment

5 x M5 should be OK.

Iain Downs13/05/2020 18:01:50
683 forum posts
612 photos

Thanks very much, Jason.

I find I've dimensioned the inside of the strap not the outside, so it is actually 8mm. Revised drawing below.

valvegear drawing02.jpg

Iain

Iain Downs14/05/2020 20:59:07
683 forum posts
612 photos

Today was about starting the assembly process for the cylinder. What I needed to do was to drill 7 holes in just the right place in the cylinder cap and cylinder. Errors would be disastrous!

Here's how I went about it.

Firstly, I put a rotary table on the mill and centred it with a co-axial indicator.

cylindercap rotary table.jpg

The blurry bright thing is actually a co-axial indicator and I love it!

Next with rotary table centred, I mounted the cylinder clamped it to the rotary table and proceeded to centre that with the coaxial indicator and judicious taps from a hammer. This only just fitted (and I can see a bigger rotary table sometime in my future, but probably not soon) and I'd had to make new clamps to clamp it.

cylindercap cylinder centreing.jpg

II was able to centre the table pretty much spot on (under 0.01mm), but I only managed about 0.05mm (2 thou) with the cylinder. I was pretty happy with that, actually.

The next step was to align the valve face along the mill axis so I had a registration point for the rotation. This meant unlocking the mill table and winding back, turning the rotary table so that the face was at the front and then clocking it, getting the face parallel to the mill by turning the rotary table.

cylindercap clocking valve face.jpg

The, back to the coaxial indicator to re-centre the cylinder, now I have the face parallel to the X axis and the whole shebang under the spindle.

Lock the X axis and wind forward 35 mm.

cylindercap ready to drill.jpg

Oh and clamp the cap on lining up registration marks on the cap and cylinder and taking care to avoid where the holes will go using a printed template.

What I actually did next was to do a trial run. 7.5 turns, 12.5 turns (and another 6 like that) then 7.5 to bring me back to the registration mark at the front. At each point I marked the cap gently with the drill bit. Since I ended up where I started I thought my practice had gone well!

Also when actually drilling I could check my counts against the previous marks to make sure they were correct. They were (much to my relief).

First hole drilled

cylindercap first hole drilled.jpg

Then the rest

cylindercap all holes drilled.jpg

And taking the cap off, all the holes in the cylinder are nicely inline.

cylindercap cylinder drilled.jpg

I'm trying to decide if I should use the same process to tap the holes (in this case not under power), or do them by hand off the mill. Provided I can line up and don't miss my counts it would probably be better to tap on the mill, so I think I'll do that.

Next is to do much the same with the bottom cylinder plate.

Iain

Chris Gunn14/05/2020 22:24:34
336 forum posts
24 photos

Ian, if the cylinder is still set up, I would put a centre in your drill chuck and use this to locate the tap wrench to hold the tap straight, and then tap by hand.

Chris Gunn

Iain Downs15/05/2020 08:05:13
683 forum posts
612 photos

Hi, Chris, I've got a tailstock tapping thing which is basically a centre on a spring and I use that in the manner you've described. It saves worrying about pulling the quill down whilst turning the tap.

Same basic idea, just a bit easier. I may even have a go at power tapping, but certainly not on the blind holes!

Iain

Edited By Iain Downs on 15/05/2020 08:17:37

Iain Downs16/05/2020 20:15:36
683 forum posts
612 photos

Do you every have one of those days when you start off feeling you're pretty good and then your incompetence swipes you in the face?

Well, I've been expecting this and, to be honest, I'm astonished it's taken this long...

I followed Chris's advice and tapped my cylinder in situ.

cylindercap tapping.jpg

And found the sight of a cleanly secured top cap quite satistying

cylindercap bolted.jpg

Nice, innit?

But then I turned the cylinder upside down to process the bottom plate. Oh dear.

The spigot to hold the cylinder was off centre....

misaligned01.jpg

The spigot is 1mm off centre with respect to the edges of the bottom plate.

At this point, I shut down the shed and went indoors. Unusually, not for a glass of comfort (as I occasionally feel a need to let my body recover that this was that day. Sadly).

My first reaction was, Oh bugger!

My second was I can just drill and tap and if it doesn't work I can make a new plate and drill it afterwards.

The third was, 'Did I do this on purpose and have forgotten the reason?' Even I realised that was wishful thinking.

Fortunately a night's sleep put paid to that and I had the thought that I should see if that 1mm actually made a difference.

So (for the first time!) I assembled the engine.

misaligned02.jpg

I found two things (well two bad things).

I put the piston gland in place with some superglue, by the way so I can get it out easily if it turns out the plate is gash.

The main one was that if I put the cylinder on, it is fine at the top part of the cycle, but jams near the bottom. This is because the piston position is to far to the back at the bottom. Two possible reasons. One is the 1mm offset and the second is that somehow the piston gland bore is NOT in line with the cylinder registration. By about 0.3mm.

I really don't know how I managed that as the two were machined on a superglue chuck which was never removed in the same machining operation (Possibly several days apart, but even so..).

So I've stuffed up the bottom plate well and truly.

Oh, the other minor thing is that my piston gland is to long It stops the piston rising to TDC.

misaligned03.jpg

That, at least is an easy fix!

In a perverted way I'm almost pleased this has happened. It's the first major component I'll have to rework and I expected a major screw up much earlier in the process. I'm still terrified I'll accidentally drill a hole in the wrong part of the cylinder. That would be a trial.

So a chastened Downs is going to buy another bit of steel and see if he can learn from his mistakes.

In the meantime, there are the eccentrics to cock up....

Iain

Iain Downs27/07/2020 19:52:39
683 forum posts
612 photos

Wow. 2 months + since I last posted. In the meantime I've been installing DRO and Power feed on my mill, but I've finally got back to my engine.

The task was to re-do the bottom cylinder plate which I'd manage to machine the spigot off-centre to the central hole (no I can't imagine how, either).

I started off by trying to use a superglue chuck. The chuck was snug to the chuck plate with a 6mm hole in the centre. The plate has a 6mm hole in the centre and I located them with some 6mm round toolbit material.

When I put them together on the lathe I noticed that central hole didn't seem central. So I got my indicator out and it seemed to be 0.5 mm off. Which I thought was too much.

bottomcylinderplate2 on superglue chuck.jpg

Actually, I then spent quite some time (whilst working on other projects) trying to work out how to hold the plate.

IN the end, I drilled and tapped two M6 holes on the outside edge and mounted it on my face plate.

A bit of tapping and I got it reasonably centred (0.02/0.03 mm)

bottom plate 2 centering.jpg

Next a rough cut to get 2mm down through the area which had an interrupted cut. I have interrupted cuts. I have to run the lathe at a higher speed than I feel comfortable with or it stalls.And sometimes it sticks or stalls anyway.

bottom plate 2 first cut.jpg

Then it was taking the rest down to a 50mm diameter and boring a 20mm hole in the centre. All very gingerly and trying and fitting with the cylinder and piston gland.

bottom plate 2 and one.jpg

Here we contrast the new one and the original (bad) one. this time as you see I've done the bits where the registration matters before the cosmetics.

And, guess what? It all fits together!

bottom plate 2 assembled.jpg

Next I needed to prepare the fixings for the cylinder. This is where my new DRO gave me a great deal of happiness.

First was to clamp the cylinder to the plate and use some slip gauges to make sure the valve face was parallel to the back of the cylinder plate (this by getting a close approximation and 'feeling' - This is not something where the odd 0.05 mm will make a lot of difference) then to clamp the cylinder in the vice.

bottom plate 2 preparing for mounting holes.jpg

Although the DRO has something to make holes round a circle, I'd designed this to have a slightly wider gap on the port side of the cylinder. In hindsight not sure if this was required to clear the ports, but there you are. I took my design and made a drawing with the offsets of all the holes from the centre of the plate marked and used that work out the positions on the DRO

bottom plate 2 i love my dro.jpg

I first put 7 spots in with a 5mm Spotting drill , then changed to a tap drill and put 7 tapping holes in, then back to the spotting drill to go just down through the 7.5mm plate (I should have done this to start with and saved a step), then a countersink for the 7 holes and finally, swapped out to a tap.

bottom plate 2 tapping cylinder.jpg

Doing this with the DRO was a joy. The top end I did on a rotary table with swapping between, drills, taps and drills for each hole!

bottom plate 2 drilled and countered.jpg

Here we go! Already for mounting!

Next step is the eccentrics. I might also want to rethink some of the decoration of this plate (rounded corners and so on) to better fit with the reversing gear.

It's nice to have some progress!

Iain

Iain Downs01/08/2020 20:31:51
683 forum posts
612 photos

This phase of the operation shows that you often spend more time making the tools to make the parts than you do making the parts. Not that making the tools isn't as much if not more fun, but ...

In this case, I've given some thought as to how to machine the eccentrics and I've come up with an approach that looks like this.

eccentrics build plan.jpg

So the idea is to mill a square on the end of the cast iron bar to hold it in the 4 jaw. Then moving the piece to between the eccentrics and the offset of the crank will be (relativel)y easy. I worried about how to hold the piece on the mill (a round shaft vertical) and quickly decided a chuck was the right way. So how to hold the chuck? I chuck holding plate, of course!

I have some pieces of 6 inch square x 1 inch plate I bought many years ago for a first project which was going to be a lathe. Ah, Hubris! Downfall of the Gods and amateur engineers who over-reach. So the headstock sides have been re-purposed since for more practical uses.

First, to square the sawn ends so I could put it in the vice

mill chuck mount 01.jpg

Then, for the first time, used the versatility of this ARC versatile vice. You can move the jaws around to hold bigger pieces - the standard jaws won''t hold a 6 inch piece.

mill chuck mount 02.jpg

This worked really well and I was able to get a nice shiny flat plate.

Now here's the exciting part. My first attempt to use the PCD function on the DRO.

mill chuck mount 03.jpg

Set the centre of the plate up with the co-axial indicator and set the INC register on the DRO to zero. I have to say the DRO seems pretty good (but see later) but the chinglese manual is not the best. Once I zero'd I set the PCD to 84mm diameter, 5 holes (yes, for some reason you have to end up where you started, so drilling 4 holes means you have to enter '5' and start at 0 degrees.

mill chuck mount 04.jpg

Oh! I've just discovered you can set the picture size!!!

Anyway running through the holes is pretty easy, you just press <- and then wind the handles till X & Y are zero. The DRO really is transformational - in another tool to make the eccentric, I had to spot, drill and tap three holes. Before, I would have spotted, swapped to the drill, drilled, switch to the tap, tapped (manually) and then did this twice more. With the DRO, I set register 0 to 0, spotted, moved to the next position, set register 1 to 0, spotted, moved to the next, set register 2, spotted. Changed drill, drilled, selected register 2, drilled and so on. Much less swapping of tools!. On this piece I also managed to power tap successfully for the first time.

Anyway, here's what the Chuck holding plate looks like

mill chuck mount 06.jpg

I ended up making it suitable for 3 and 4 jaws as you can see.

And here with a chuck on it

mill chuck mount 07.jpg

The other tool I mentioned above was something to hold my indicator in the QCTP - just a piece of mild with some bolt holes to hold the indicator. When I've tried to centre in the 4 jaw in the past I've used a lever type indicator with a very small degree of movement. It's to easy for an idiot like me to back the piece out of the range of movement of this - if I can get it in in the first place, so I'm hoping that this will make things easier.

The one peculiar thing (well something that went wrong, which is not that peculiar for me!) is that the chucks didn't quite fit. When I measured the diameter between the holes (and added 8mm to get to the centre), it came to a tiny amount less than 84mm. The fix was easy - just drill out to 8.5mm. I will do some tests on this later and see if I can work out what I've screwed up!

Next is preparing the piece for the eccentric.

Iain Downs01/08/2020 20:45:17
683 forum posts
612 photos

And finally some work on the eccentric!

First I drilled a centre in end of the bar, holding it with the 4 jaw on the (aforementioned) chuck holding plate

eccentric 01 centre drill.jpg

Then onto the lathe with a 3 jaw lightly nipped and the end of the bar in a centre

eccentric 02 skim.jpg

First few passes with a carbide insert which didn't really work too well - perhaps I wasn't taking enough off, it seemed to rub rather than cut - though the dust that's produced was hot enough.

Then finished with a nice traditional HSS tool. This reduced the 50mm bar to about 48mm - I wasn't trying for a particular size - just to get it nice and clean to hold in the 4 jaw.

Off the lathe and onto the bandsaw to cut a bit over 70mm off. This operation surprised me as the bandsaw went through the bar like it was butter. This in contrast with the hour it took to cut a (granted much bigger) aluminium bar. I see a blade with fewer teeth in my future before I cut more big ally!

eccentric 03 face ends.jpg

Faced off both ends. This time with the same carbide tool which didn't do well on the outside. Worked fine for facing!

Then onto the mill for the squaring

eccentric 04 square end.jpg

Again, the DRO made this child's play. I used an edge finder to get the Y edge and zeroed the DRO, then the same with the X. Then moved the table to center the spindle over the centre of the bar and zeroed X&Y.

Oh - and I discovered why I got a 4 Axis DRO! At the time it was just because I could but didn't really know what I would do with it. After all the Spindle DRO would do all I wanted.. However, I realised here that I could use the Z to take the head down by 25mm with the spindle high and fully locked. In theory more rigidity! I'm not 100% sure this will make a difference in practise, but it certainly makes me feel better about the extra spend...

eccentric 05 centre.jpg

This is as far as I got today. There's the piece in the 4 jaw waiting to be indicated and the indicator mounted on the QCTP with the mounting bracket I made.

Frankly, I have yet to master (or even get close) to centring in the 4 jaw, so I was as pleased to leave it for another day...

Iain

Iain Downs13/08/2020 20:43:17
683 forum posts
612 photos

A couple of weeks later and the eccentrics are done! For the main part this has gone better than I expected which is pleasing.

In the previous post, I ended up with a round 40mm cast iron bar held securely in the 4 jaw. The first task was to put 4mm groves in for the straps. FIrst step with this was to grind a tool, more or less a parting off tool, but a bit under 4mm. Then to make the 2mm deep grooves.

eccentric 06 grooving.jpg

A bit of chatter on this, but this was cleaned up when I slid the tool sideways to open the slot out to 4mm.

Next step was to offset the bar by 6mm. This went surprisingly well, using the 2 key approach.

eccentric 07 moving.jpg

next step was to turn the collar on the end

eccentric 07-5 turning the stub.jpg

Then came the nasty bit.

I needed to part off the first eccentric. If I thought parting off was a challenge, let's try it on an interrupted cut!

The was very very slow going, feeding the tool in very gently to try and prevent a jam. For some reason I decided to use the 4mm tool to get most of the way down and then 'finish off' with a 2mm parting tool.

At this point, disaster struck! There was a solid jam, the lights went out,, flashes came from inside the lathe electrics and everything stopped.

I'd blown one of the sets of breakers in the house. I took this as a message - it was about 9 o'clock (a self imposed deadline to stop the neighbours getting irate) and clearly time to stop.

The next half hour or so was spent resetting the RCD, rebooting PCs and fixing networking issues. In fact I was still struggling with connect problems when I started work the today!

So tonight I went back out to the shed, thoughts of fried thyristors uppermost in my mind. But to my surprise (and relief) the lathe started up straight away - I hadn't even blown the lathe fuse...

Back on to the parting off

eccentric 08 parting off.jpg

eccentric 09 first one.jpg

Eventually, this was done and I set about the second eccentric.

This time I decided that parting off this type of thing was NOT my idea of fun, so I took the piece out of the chuck and cut it off on the band saw. This was both immeasurably quicker and a great deal less stressfull.

Swapped the chuck for a 3 jaw and popped the piece back in to clean off the back.

eccentric 10 trimming the back.jpg

Next step was to pop them into the milling vice and drill and tap an M4 hole for a grub screw and here we are!

eccentric 11 done.jpg

Most likely, the next work item are the eccentric straps. To be honest, I've not yet worked out how to machine these. I've seen that there are videos on youtube and no doubt advice in this august forum, but I've not got round to looking.

I was wondering if I should make the straps in steel or brass. I was thinking steel, but brass would like nice, wouldn't it? Any reason why not?

What I may do before that (if I have to wait for material, for example) is to mount the cross head guide,

I can feel it getting close!

Iain

JasonB13/08/2020 20:54:01
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Steel/iron is a common combination though I would have gone for iron straps and steel eccentrics.

How I make em

Nigel Graham 213/08/2020 23:06:39
720 forum posts
16 photos

two questions you asked:

Cast-iron sheaves with mild-steel straps? Yes, no problem, since anyway I think you've made them! I note Jason suggests the other way round, but I have not seen a definite choice either way. In full-size it was common to use cast-iron for both.

Locking the reversing-lever in its running and mid-gear positions. The usual way is to fit a small sprung catch operated by a trigger on the handle part of the lever, engaging notches in a quadrant plate that also supports the lever from side-ways forces. Plenty of examples on locomotives and traction-engines, as a guide to designing yours.

Another way you could go: Without knowing for certain your choice, your engine suggests smaller marine practice, so you could fit a similar but plain quadrant with an arcuate slot in which works a small clamp-screw fitted into the lever just below the handle, and locked by a little handle of its own. I have seen that on example drawings in old text-books I own. The reason was that a ship's engine works almost entirely in forwards gear without adjustment - on a full-size ship for days or week at a time. (The bigger marine steam reciprocating engines had screw-and-quadrant reverser controls, or steam-reversers, though, to move a lot more heavy steel and iron.)

Iain Downs16/08/2020 14:50:51
683 forum posts
612 photos

Jason - thanks for the advice and link. I've since reviewed some you tube and have a feeling about how to make them. The steel is on order.

Nigel - again, thanks. I confess that I'm building this engine to build it and not with a specific application in mind. The original design criteria was something that would run my lathe. Since then I've thought of a steam powered go-kart and, yes a marine engine.

Frankly I will delighted if it just runs at all!

Off out now to do a bit of work on the crosshead guide.

Iain

Kettrinboy16/08/2020 16:25:59
87 forum posts
47 photos

Iain I think most of us are happy just to get an engine project to run even if it's just a few revolutions, all of my 8 hot air engines and one IC run but none of them have done more than about 15 mins total running, for me its just the challenge of designing and machining rather than running them for hours on end.

Iain Downs11/09/2020 12:12:04
683 forum posts
612 photos

I've started work on the straps and this is my plan.

First make some blanks, 66x60x8mm.

Cut out shoulders for bolting the two halves of each strap together, drill and tap.

Slit the two halves apart.

Bolt together, drill and bore ( on the mill) the centre and then the flanges.

Mount on a rotary table and take away the bits I don't want.

Phew! sounds easy?

So I started with a largish piece of steel - 200mm x 100 x 10 and trimmed it down on the mill.

eccentric strap 01.jpg

First step was to get the edges reasonably straight so I had something hold for the surfacing.

then to reduce it to 8mm. This wen pretty well. I ended up with it with 0.04 mm across the whole area, most of the error being due to a hump in the centre. This in turn probably due to using 80mm parallels on a 200mm work piece. I've longer parallels on order.

Next to take it down in height and trim the edges now I had some nice clean surfaces to work from.

To the bandsaw and off come my two prospective straps,then trimmed to exact width on the mill.

Marked up on the surface plate as a check, but then back to the mill to use the DRO to mark and drlll some nice round corners for edge relief.

eccentric strap 02.jpg

eccentric strap 03.jpg

The stop was used so that I only need to edge find once. The two pieces being within 0.01 / 0.02 in all dimensions (somewhat to my shock).

Then flip the straps on their end and carve out the unwanted bits. I had to do a bit of cleaning up the relief with a small file, but you won't tell anyone will you?

eccentric strap 04.jpg

Back to the mill to be drilled and tapped.

eccentric strap 05.jpg

The lovely DRO let me spot, drill, tap drill and tap without having to change tools a million times. Thanks, DRO!

I've used my Father's day letter punches to mark which bit belongs to which so I don't get them mixed up after slitting.

eccentric strap 06.jpg

That's it for now. Next step is to bolt them together (may also superglue) get them back in the mill, drill and bore.

Again the DRO will help here as I can wind the Head up out of the way to measure and be sure to get it back to where it was so I have a nice clean depth of cut!

Iain

Iain Downs20/09/2020 10:14:26
683 forum posts
612 photos

I was rather dreading this bit. Boring out the strap, which requires a fair amount of precision on all sides. I still think that the accuracy was more luck than judgement - but who's complaining?

The first thing I did was to skim up the faces of the joint of the strap. I'm blaming the mount in the vice which didn't provide enough support, but the two pieces weren't straight when bolted together. This was just the lightest skim, though I fear that the centre line is no longer quite on centre.

Having done that I bolted each half together in the vice (to make sure the two halves were dead in line and clamped it in the vice on parallels. I dithered about this, wondering if I should put some kind of support under the centre line, but in the end did not and there was no drama.

First task was to centre the item (edge finder and the half option on the DRO - I STILL love my DRO!).

Then to drill. I started off with a 4mm stub drill then up to 6, 8, 10 and 12mm. I also love stub drills (thank you Model Engineer forum for my training!).. Then a14mm blacksmiths and a 20 mm blacksmiths. Again no drama.

eccentric strap 07.jpg

Now it was time for the boring head. My mistake here was not to lock the Y axis (I'd locked the X but for some reason not the Y) and the table had drifted a little. Were it not for the DRO, I would neither have noticed nor being able to fix it (did I mention how much I like my DRO?). I simply put the Y back to zero and locked it. Naughty Iain.

eccentric strap 08.jpg

I was a bit concerned about how to measure the groove depth and width. I could get the depth right by using the quill DRO, but the width required a measurement which was blocked by the boring head. DRO to the rescue! (Are you getting a theme here!). I zeroed the Y DRO and locked. Then zeroed the quill DRO as it touched the surface. Thus I could move the head out of the way and get it exactly back where it belonged afterwards. Not quite that simple as locking the Z moved the head a couple of thou, but that wasn't to hard to work round.

eccentric strap 09.jpg

Everything seemed to work well in that the try fit of the eccentric worked, but when I tried to assemble the whole lot it just didn't' fit. :sad

After a moments thought it occurred to me that there was probably a small radius on the boring bar, but the eccentric edge was quite sharp. So I had a bit of a go on the eccentric with a smooth file and the strap with a pointed scraper.

Nearly! but not quite. Close though. Finally, I got some 7 (microns I think?) diamond paste, assembled it, added a dummy crankshaft and give it a bit of a lapping.

eccentric strap 10.jpg

Some turns with the bolts tightened a bit every few turns and the eccentric is running smoothly in the strap! Cleaned off with WD40 and job done (for now).

I'm hoping my luck holds for the next piece this afternoon (if all goes well), then I all I have to worry about is how to mill the outside round.

Iain

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