Need some help with a PMR #5 Bottle Engine

[substandard]

Being stubborn and dense, I decided it was time to take on an engine from castings. I bought the PM Research #5 Coke bottle engine set, and now I am lost........

I figure the best place to start is fly cutting the frame base to be flat and square. To do this I have a 9x36 mill and a Southbend 9" lathe. I have yet to figure out a way to hold the casting and to find a way to measure to make sure the base is going to be cut square.

I tried chucking the casting in my 4 jaw on the lathe, but I was only able to chuck onto the small diameter. The spindle bore won't let the casting enter any further. This doesn't give the casting any real support to keep it from moving about while cutting. I thought about a mandrel thru the center hole of the casting, but how do I know the hole is square to the base?

My milling machine vise doesn't hold the casting any better than the 4 jaw. The vise clamps to the small end diameter, leaving the bulk of the casting unsupported. I am almost certain the casting will move once the cutter strikes it. I had thought about using the method below in the image. Lay the casting on it's side sitting on some 1/2" lathe bit blanks. Indicate the casting true to the machine and side mill the face.

Problem being..actually problems being, where do I take my measurements from to see if the casting is more or less square to the machine axis? Also I don't have an end mill long enough to side mill the entire face. I would need to machine half the face, then flip it 180 and mill the other half. Or buy a long end mill, which I don't want to do unless I am sure it would work....

Any help, suggestions, pity, or criticism would be appreciated. Thanks and sorry for being so long winded.

 

[idahoan]

Hi Substandard

I have been working on an engine with a similar frame style; if you go to post #22 of my build you can see how I fixtured the body casting.

http://www.homemodelenginemachinist.com/f23/pacific-vapor-engine-morrison-marvin-castings-17832/

My first set up was to set the casting on it's base and shim it as plumb as I could get it. then take a clean up cut on the cylinder mounting flange.
Then the casting was turned over, clamped down and the bottom surface machined and the mounting holes drilled.

I made the bottom flange the reference surfaces for the rest of the operations; so after the the casting was flipped over to finish the top it was just a matter of locating it against a couple of parallels. Then the center line of the cylinder mounting flanges was easy to locate to finish machining it.

Hope this helps,
Dave



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[substandard]

Dave,

First, that is some very nice machine work you are doing on that engine. Second, a HUGE THANKS. You helped me greatly from seeing those images.

I think I have a new plan of attack. The image below is what I have in mind......

I clamp the casting on it's side and use the upper edge (red line) to run my dial indicator off of. This should place me close enough to square with the mill axis. I then can side mill the small end face (green line). Once that face is more or less flat and square I can copy a set-up like you used to do the base.

 

[idahoan]

That is a good start but there are 3 axes that you need to be concerned with. You can indicate the top surface as you have indicated as well as the bottom surface (the real bottom) to square it with the Y axis.

You still need to set your horizontal plane (the parting line of the casting) if you do this you should be OK; you will probably have to shim it.

If you have a surface gage or height gage you could get an idea if that parting line or the center line of the casting is level with the table. If it is not when you stand it up it is going to lean.

That is why I did mine vertical; then after I stood it up I indicated the flat of the base and found the center and all was well.

Thanks for the kind words.

Dave

 

[Rivergypsy]

I think I'd be tempted by the mandrel idea myself, and hitting both ends in one set up. But, having said that, there's many ways to approach every job

 

[gilessim]

I made one of those a few years ago and was a bit stumped with the same problem, it's a bit of a "catch 22" situation starting that engine frame and I'm sure that the model was designed specifically to tax ones grey matter (there's more to come after that stage ,as Im sure you've noticed!) in the end I decided to hand file the base carefully nice and flat and square then set it up vertically on the mill to drill a nicely centred hole for the bore ,then set it in the 4 jaw with a live centre to true up the upper rim then used a 3 point steady around the rim to bore the cylinder.

Hope this helps

Giles

 

[Charles Lamont]

Suggestions
1) Remember that you want to set up by features that will remain as cast.
2) You can fit a temporary plug and put a centre hole in it.
3) It is often a good idea to work castings in stages, rough-out first to establish the geometry and then go back and finish to size.

At a first look I think I would plug the cylinder end and put a centre hole in the plug. Then I too would put the foot in the 4-jaw and support the cylinder end with a centre so that the cylinder flange could be rough turned. Again, using a steady on the turned OD, an initial bore could be put through the trunk. The casting could then be mounted by this bore on a mandrel for machining the foot. I think I would then mount by the foot on the faceplate to finish machine the other end.

I have not been round here long, but I get a general impression that the locals tend to think of milling jobs that might better be done on the lathe, and that they are frightened of their faceplates.

 

[GKNIPP]

I am in full agreement with Charles on his suggestions. Machining castings is a give and take process whereas you need to utilize and maintain order with features of the casting which you cannot change ( EX. bearing bosses, cylinder flanges, etc.) and have determined how much and where your machining stock is on the casting. Do some rough layout work to find centers etc. then use blocking and shims until you have the casting squared up to your satisfaction at which time you can machine your reference surface. I personally would take only enough material to establish a flat and indicatable surface this way you have some machining stock left should the need arrise to make a change. Once you have the reference surface established the remainder of the maching becomes a bit easier to figure and set-up.

The key is to take your time,check, re-check, insure the best set-up possible then first start removing material.

Good luck my friend.

Greg