Muncaster's Joys Valve Engine

[tangler]

Simon,

Lovely job.  As for the  blockiness, I guess the castings would have had some taper on them - perhaps you need to think what the patterns would have looked like and the way they would have been moulded. 

It's going to make a smashing engine as is though

Rod

[smfr]

Thanks Rod! I do actually have a casting taper of about 1.25deg on all the external faces, but I probably should have used a little more.

Today I did the precision cuts on the base. First I spent a good amount of time getting accurately lined up on the milling table, using some 1-2-3 blocks against a bit of rod through the temporary crankshaft holes, and double-checking against the pop mark on the tail end. I found center between the bearing pedestals, checking with an adjustable parallel between a 1/2" end mill and the inside surface of each pedestal. The crossslide handwheel dial was zeroed, and I wrote down whether I was pushing or pulling  (so easy to forget!). I also set up my poor man's DRO, a second pair of digital calipers affixed between the carriage and my home-made carriage stop, and zeroed on the center of the bearings.

Finally, cutter height was determined from the top of the temporary rod:



using the "cigarette paper" technique which I use all the time (this is actually a bit of acetate wrapper from some crackers, which is about a thou thick).

I first did the light cuts to reduce the risk of the part moving, with a nice sharp end mill. The location of the crosshead slides was done, leaving some small locating projections to keep the slides parallel, and then the cyclinder block pads were also skimmed. I had to take the crosshead slides surface down a couple of extra thousandths, but I'll make that up on the slides themselves.

Then it was time for the bearing pedestals. I attacked these carefully with a 5/8" end mill, and skimmed the tops:



as well as cutting the small profile that the bearing caps fit into. Alas, I was a bit short of material on one side  (was a bit too eager with the bandsawing way back), so I milled off a bit extra and I'll epoxy a bit of material on.

A test fit with a 3/4" parallel is good, so we can breath a sigh of relief 



While things are set up accurately, I milled some pockets which will receive the hold-down pads:



and I drilled holes for the cylinder block studs, and crosshead slide studs. The plans say that bolts are used on the cylinder block, but it looks to me like there isn't enough clearance by the sides of the cylinder to drop a bolt in there!



Those holes were all located laterally via the handle dial (lots of counting of rotations!), so I was careful to check their pre-drilled location with a rule.

I'm a little worried about stripping the threads in the aluminium when tightening things up later; I'll have to be careful! I'm also making up the fastener sizes as I go along, but I'll choose from BA sizes.

Looking through my metal stock, I realize that I don't actually have enough cast iron bar to do the cylinder block in two parts, so I'll be ordering one bit lump. At least that solves the exhaust problem! However, now that I want to use speedymetals.com, the site seems to be down 

That's it for this weekend. Next, I might even get to machine something that isn't alumin(i)um. 

Simon

[smfr]

The brown van came by today 

Among the spoils was this:



a 20lb lump of cast iron. Most of it becomes the cylinder block.. That's gonna give the bandsaw a workout 

Simon

[sbwhart]

I've been quietly following this along Simon and you are making a first class job 

Thanks chunk of cast iron will make your kit grunt 

Stew

[Dave Otto]

Hi Simon

I have been enjoying the progress on your engine; very nice attention to detail.

Keep up the great work.

Dave 

[smfr]

The bandsaw made it through the 4" cast iron cube, with a couple of stops to cool down 



I did this yesterday, then I was lying awake last night wondering if I'd cut it too small A quick check with the ruler this morning, and I think I'm OK 

In fact the bandsaw got a good workout today too. I spent it on the crosshead slides, which look like this:



The parts were sliced from some gray cast iron stock I had, and the bandsaw makes it easy to take fairly accurate slices, even if the clamping sometimes gets a bit creative:



and a small vice can help with the smaller bits. I actually took the blade guide off the saw and milled off part of one side, to give me more clearance for this setup:



Here's part of what I ended up needing:



The main slide bars are 1/2" x 1/4" x 3", with a 1/8" step taken out to half the width. I'm embarassed  to say I made a lot of rejects by milling them too thin; I think due to a combination of the stock moving in the vice, because it wasn't really flat from the sawing, combined with the blunt endmill I was using to get through the crust. The good parts, however, were squared up by milling and then the step was cut almost to depth:



I'll finish the step with the slides clamped to the table, to make really sure that the step is parallel with the bottom surface.

The slide covers have a slight edge chamfer which works out to about 7deg, so I make a quick fixture with the correct angle, which made it easy to get all the parts identical:



Here they are before finishing, in situ:



I'm planning to relieve the inside corner of the slides with a small saw cut at 45deg, and put a light chamfer on all exposed edges. I was thinking about how to get the slides really smooth, then remembered that I have some estate-sale square-section grinding stones, and a quick test rubbing the part along a corner of the stone with some oil suggests that'll give me a nice finish; I just have to be careful to keep things square.

This is a vacation week for me, so the machining continues tomorrow 

Simon

[Jasonb]

Simon when you have a rough surface to clamp try putting a scrap piece of Aluminium between the part and the moving jaw which will deform to the shape of the part.

Also when cutting small parts from a block its worth machining one or two faces before cutting off from the main block then you have something flat to put against the fixed jaw.

Looking good though.

J

[Florian Eberhard]

Hey Simon

Best you could do would be scrapping the guide... 
The Edge can either be relieved or you could make a chamfer on the edge of the slider.

Cheers
Florian

[smfr]

Also when cutting small parts from a block its worth machining one or two faces before cutting off from the main block then you have something flat to put against the fixed jaw.

Thanks Jason. I do remember that advice from an earlier thread of mine, but was too lazy to implement it!  I shall do so today to avoid yet more rejects!

Florian: I did think about scraping. How much material should I leave on if I want to give it a try? 0.002-0.003" or so? Also, I'd have to first scrape a reference that will get me into the corner.

Simon

[Florian Eberhard]

Hey Simon

0.001" is too much I think. Especially for such small things. I think you will take away something around 0.0001" every pass, so it would take quite long to complete.

I would recommend to take a piece of cast iron you don't need and give it a try. Ohterwise it is difficult to judge how it is going. (Also as everyone will do it on its own way and therefore not take away the same amount as someone else does)

Oh and for scraping you will of course need to releive the edge.

Florian

[smfr]

To form the remaining two slides, I took Jason's advice and squared up the stock before sawing it off:



(interesting formation from the chips and magnetic field there!)

What a difference! It was so much easier to quickly get the parts down to size. The step in the new slides was rough-milled. Now all four slides needed the step cut to final size. To do this accurately I clamped down a bit of Ally, and with a good end mill milled a slot just wider than the slides, zeroing the dials on the depth, and on the front face. Now the part was located in the slot against that face and clamped, so I know where to move the cutter to get to final dimensions. This method ensures that everything is aligned.



To relieve the corner, I used a slitting saw, but holding the part was a bit of a head-scratcher since the clamps always got in the way. If in doubt, make a fixture 



Here I'm using a V-block to get the 45deg angle on the fixture, and milling a slot in that that will hold the slide. (Now that I look at that clamping setup, it's not great; the upper part of the V-block on the left isn't supported.)

Now I can clamp that fixture down, slot the part into it, then clamp a bit of Al plate pushing the part into the slot. The cutting forces aren't large here, and it worked out fine:



After a bit of rubbing on a file and them some 150 wet & dry, things are looking ship-shape:



but to show that all wasn't plain sailing, here's what happens if you forget to tighten up the vise before edge milling:



 

Luckily I had my stash of undersized chunks to make another top plate from 

All the remains for the slides is some finishing work, and the holes drilling, which means I have to decide what size fasteners to use.

Simon

[smfr]

A little more work done! Slides and covers are drilled, base is tapped 5BA. This is a temporary assembly with screws, but of course I'll use studs to keep Jo happy  and maybe with "one size smaller" nuts.



I also got the valve bracket bosses machined to size, and rubbed things down with a bit of wet&dry to remove the toolmarks.

Time to start on the cylinder block, I think 

Simon

[Dave Otto]

Nice job on the cross head guides Simon

Dave

[Kim]

Hey Simon, you've been doing a lot of great work here! 
I haven't commented much, but have been following along. And will continue to follow your progress!
Thanks for taking the time to share it with us!
Kim

[smfr]

Thanks Kim and Dave! I'm going to try to be a bit less long-winded from now, I think. I have a feeling I'm boring people 

Simon