2-1/2 x 3 Simple Engine - Cylinder Castings Set

[fredrosse]

Bought the casting set from Rappahannock Boat Works to build a small auxiliary engine. The castings look good, and need to be machined.
I would appreciate any suggestions as to how the cylinder casting can be effectively clamped to the milling table. I am sure there are many ways to do this, and would appreciate the knowledge of someone who may have already worked on these castings.

The attached photo shows the casting resting on the milling table.

[barts]

My inclination, looking at these castings and where there is extra material, would be as follows:

* clamp cylinder upright on the table (use tow clamps on the ridge at the ends) and finish one end of the cylinder.
* flip, clamp down as before but this time on suitable spacers, and finish the other end and bore the cylinder w/ a boring head.
* With a substantial through bolt, clamp cylinder horizontally to an angle plate aligned with Y travel, leveling surface as much as possible. If you have a real milling vice (Kurt or similar) that has enough throat, you can also use that. Finish steam chest mating surfaces and clean up ports.

I'd choose this order because there isn't a lot of extra protrusion of the cylinder end past the steam chest side, but that detail is worth preserving from an aesthetic point of view . There is obviously ample material in the bore, and cores shift sometimes, so trying to use that as the primary datum seems awkward.

You should also check the casting for obvious problems (ends of cylinder not parallel, for example) but this level of checking can be done w/ a T square, your right angle and a flat surface. If that is a dual horizontal/vertical mill, you can of course forgo the use of the angle plate.

Caveat - I've not machined these castings, although I think I have a set somewhere I found at a swap meet.

- Bart

[Mike Rometer]

I have machined several similar cylinder castings and my method is to start with the largest flat surface, in this case the valve face. Then true the ends to that, and finally the bore. Having said that, one must be conscious of the restrictions placed by what machinery you have available. When I did my first set I didn't have a milling machine, only a shaper. That was over twenty five years ago and they are still going strong.

The piece of channel section shown would be fine if the sides were a little more rigid, though probably Ok if lighter cuts are taken. For holding down I would use a bar through the bore, clamped at both ends. The picture (if it loaded Ok) is of the jig I used for the last set. The two angles were set parallel at a suitable distance to keep the casting just off the base. If needs be, to level the casting, shims can be placed beneath the jig.

Beware, there may be a tough skin on the casting.

[fredrosse]

Thank you both for the advice. My milling machine only has 3 inch spindle travel, so I am going to bore the cylinder (4-1/2 bore length) and face the cylinder flanges in a lathe. The milling machine will only be used for the valve face surface, and for drilling/tapping operations.

The 4 inch channel shown in the picture is rigid enough for the milling work, and raises the casting about 1/4 inch above the channel in the center. I will set this up as Mike suggests, with shims as required.

Next question, the cast cylinder heads are about 1/2 inch larger in diameter than the flanges on the cylinder casing. Perhaps make a flange drilling template with a stub shaft that can be mounted in the lathe? Drill and bolt the cast heads to the template and machine in the lathe. Is there an easier way?

[barts]

I often turn disks by friction, pressing them against the chuck face w/ the tailstock. Typical sequence would be to chuck up the round part (three jaw if pretty close to round, four jaw if 'lumpy'), center drill, and then run the jaws in a bit and press the part against the chuck w/ a live center. This lets me turn on the OD taking light cuts. If I'm worried about scarring up a surface to be left unturned, I use a aluminum friction plate in the chuck. If I really need all the mounting faces parallel/square, I can use a aluminum round sticking out from the chuck so I can turn the inside surface, outside OD and outside surface in one set-up.

- Bart

[Mike Rometer]

Most of those that I have done have a bore register turned on the inside face. Do that first, gripping the outside, then reverse in the three-jaw, and grip by the register to do the outer face and dia.

Your method will work if that's the way you wish to go.

For drilling the bolt-holes, do the cover and cylinder together, afterwards

[Lopez Mike]

I do a fair number of small engines like Stuart #5As. I have found it well worth my time to make a drill jig(s) for the top and bottom cylinder covers. A one time precision job of laying out the holes accurately or using an indexing head or a rotary table or CNC. Then the drilling and tapping can be done rapidly. It means that the heads can go on in any reasonable orientation. Nothing custom about which way they fit.

For future ease of assembly, I don't get carried away with making the hole to stud or bolt clearance too tight. In most designs the heads spigots into the cylinder.

[DetroiTug]

Fred,

I haven't machined mine yet, but as Mike points out a bar through the bore to machine the valve face is the good way to go.

On the 3-in-1 not a lot of options for a large irregular piece like that. Using the C-channel, I would weld two vertical studs at each end on center of the channel web. Then run a bar through the bore. Then four holes drilled through the web of the channel to secure it with hex bolts to the T-slots on that spacing. Could use that fixture for other cylinder castings as well.

On Cylinder heads, friction hold with the tailstock can be used but that is pretty hard on the live center, and it can go wrong easily. The boss or register as Mike points out will work, but it's possible your lathe chuck wont open that far to hold it in the inside of the jaws once turned. Turn the jaws around and hold it on the outside leave half the thickness hanging out. Turn that to the diameter, then turn it around the other half. Run very slow RPM of ~200, that way if it comes out of the chuck, it isn't going far. One trick I use for large flats like cylinder heads and boiler endplates is weld a piece of barstock that will fit in the chuck in the center of the flat piece, then mount that in the chuck. Those castings I think are nodular so temporary mig welding with large tacks should be ok. Give it a rap sideways with a hammer to make sure it's on secure.

-Ron

[fredrosse]

I will just go ahead and make a flange drilling template with a stub shaft to allow chucking the template in the lathe. This will allow turning the head flanges outside and face with it firmly bolted to the template. This will allow the drilling of the cylinder flange holes for tapping with relative ease.

I will also weld some anchor points to the 4 inch channel to properly anchor the casting to the milling table. Too bad my son has borrowed my good MIG machine, I guess I will be stick welding to make that fixture.

[Mike Rometer]

Fred,

The boss or register as Mike points out will work, but it's possible your lathe chuck wont open that far to hold it in the inside of the jaws once turned. Turn the jaws around and hold it on the outside leave half the thickness hanging out. Turn that to the diameter, then turn it around the other half. Run very slow RPM of ~200, that way if it comes out of the chuck, it isn't going far.

-Ron

I did say in my first reply that you do need to be aware of the limits of your machines, and therefore in particular, your chucks. Whilst holding the cover half in the jaws does work (I have done that also), it also means you are running the tool very close to the jaws, and accidents can happen. When turning the job over in the chuck it is also very likely that it will not run entirely true to the original cut. Very few chucks are deadly accurate in this manner, at least gripping by the register obviates both those problems. I suppose it really boils down to just how fussy you wish to become as to final finish etc. (will the paint hide it? ) When it comes to jigs my take is, that if it will be used for more than one job then it's worth making.

One trick I use when turning things over in the chuck, is to mark No1 jaw on the job, and make sure to line it up again.