Cylinder Block Machining

[BCB]

I am getting ready to machine the saddle portion on a cast iron cylinder block for a 1.5 inch scale Berkshire locomotive. The approximate radius of the curve on the saddle is 6.75 inches. I have at my disposal a 9 X 42 Bridgeport style mill and a 12 X 36 lathe. Can this be done on the equipment that I have and, if so, how would one go about doing it?

[James Powell]

1. Mount bolted up sections on side, on mill. Use a boring bar to cut the arc.

2. Mount on carriage of lathe, and do similar.

Both are an intermittent cut, and may not be liked that much. At least all you are doing is supporting the smokebox with the radius. (not like on a UK traction engine, where the underside becomes part of the boiler...)

Use the biggest bar you can manage for holding the tooling. My preference, if it is workable, would be in the lathe because it will be easier to hold a large diameter bar that way than in a mill.

James

[ebtfan]

I just completed machining the smokebox saddle for my PRR K-4. I have the same machinery as you in that my lathe is 12 by 36 and my mill is a Bridgeport with 9" by 42" table. The radius of the cut for my loco is 5.25 inches. The cylinders were mounted upright on a heavy cast iron angle plate as shown in the attached photos. I fabricated a tool consisting of a steel disc(1" thick/8" diameter). An arbor was turned and pressed into the disc. The arbor was also keyed to the disc. The end of the arbor that fits into the mill spindle was turned to fit into a .875 collet. The tool holder was fabricated and mounted to the disc. The tool holder has a set screw that is used to drive the cutting tool outward to produce the correct radius. Once the tool is set the two screws on top of the holder are tightened to prevent tool movement. There is an additional piece of metal mounted on the disc as a counter weight. The tool took some time to make but produced a nice finish with no chatter marks.

Dan

[Greg_Lewis]

While you didn't list a shaper as among your tools, I thought I'd throw this out there for anyone who has one. I did my Allen 10-wheeler casting on an Atlas 7-inch shaper, photo below. The table was removed and the casting was mounted using angle plates, some scrap plate and lots of c-clamps. The cut was made by advancing the toolbit in the pre-determined arc using the "bonk" method. The end of the screw of the large c-clamp on the ram head was bonked with the heel of my hand a small amount after each stroke. Worked just fine.

BTW, Gene Allen told me to just rough it out by hand, lay in a layer of JB Weld on the casting and set the smokebox down in that. A piece of wax paper on the smokebox allows removal if needed. I didn't want to do it that way, but that's what he said.

[super7b]

I have done the same as ebtfan, take time to make a good tool as shown in the pics, (I added a 40 tpi screw with a dial so that tool movement can be known,) and think ahead to any other projects as the set up is perfect for the bottoms of chimneys, dome covers, anything with a radiussed bottom.

Only other thing to mention if you have not done it before is to have the centerline of the workpiece set on the exact centerline of the machine spindle otherwise, the result will be a perfect radius .......off center!

Lawrence

[kapullen]

Greg, That is an interesting idea with the shaper.

I write a couple lines if code, mount the cylinder block in two vises
And push the green button.

https//youtu.be/lVB5x5q74c0



If I copied the link right.

[Harlock]

I just completed machining the smokebox saddle for my PRR K-4. I have the same machinery as you in that my lathe is 12 by 36 and my mill is a Bridgeport with 9" by 42" table. The radius of the cut for my loco is 5.25 inches. The cylinders were mounted upright on a heavy cast iron angle plate as shown in the attached photos. I fabricated a tool consisting of a steel disc(1" thick/8" diameter). An arbor was turned and pressed into the disc. The arbor was also keyed to the disc. The end of the arbor that fits into the mill spindle was turned to fit into a .875 collet. The tool holder was fabricated and mounted to the disc. The tool holder has a set screw that is used to drive the cutting tool outward to produce the correct radius. Once the tool is set the two screws on top of the holder are tightened to prevent tool movement. There is an additional piece of metal mounted on the disc as a counter weight. The tool took some time to make but produced a nice finish with no chatter marks.

Dan

That is a great idea for rigidity and cut cleanliness, with the counterweight and all. We typically use a bridgebort boring head with a long-shanked bit sticking out sidways. If you have a large enough rotary table you could use that as well. I don't use the rotary table very often but when I do it's super handy. It tends to travel back and forth between my shop and Eber's shop depending on who needs it.

Regarding gene's method....I would do that only as a last resort. With the tools you have there should be no reason to go that route.

[Greg_Lewis]

I write a couple lines if code, mount the cylinder block in two vises
And push the green button.

Aww..... is that cheating?

[SteveM]

I write a couple lines if code, mount the cylinder block in two vises
And push the green button.

Where's the green button on my Pratt & Whitney 3C?

Steve

[Dan Willey]

This is the method I used to bore the saddle on my K4... using a large boring head on my Bridgeport... a variation of what others have written above. See attached photos and explanations...

1005 - I made from 1018 CRS, a 6" long 1" diameter boring bar to hold a 3/8" square HHS tool bit. I machined a flat on one side (entire 6" length) so that I had an easy (square) registration of the bar and bit with the boring head. (I have 3 set screws to hold the bit in the boring bar.)

1021 - I used an angle plate to hold the cylinder set while boring. In this photo I found the front edge (X-axis) and center (Y axis) of the angle plate. Note also the angle plate was previously indicated in on X, Y and Z axes to be square/trammed.... I had to shim the bottom of the angle plate to get the Z spot on.

1022 - I moved the boring head away from the face of the angle plate by the target radius of the saddle.... 5.25".... using my DRO. Then with the home made boring bar (with bit) loose in the boring head so it could slip, I swung the boring head around until the bit was square and touching the face of the angle plate. I then tightened the boring bar in the boring head.... and locked the boring head radius. This process establishes the final and target diameter of the bore. You don't touch the boring head again after this.

1024 - Then move the boring head away from the face of the angle plate the target saddle radius PLUS the distance of the saddle perpendicular to the point where the cylinder meets the face of the angle plate. Then, zero your DRO. This zero point will be the final target of the saddle boring operation.

1035 - Move the boring head out of the way and mount the cylinder set on the angle plate.

1025 - With the final "zero" target set on your DRO (or dials), move the boring head (X-axis) toward the saddle until the bit just touches the saddle casting. You may need to manually swing the boring head around back and forth to find that first touch point on the casting. Look at the DRO and notice how far from "zero" the X-axis is. This number is the amount of material you need to remove from the castings to reach the target "zero".

1026 - This pic shows one of the early bore operations using the quill feed. After each bore sequence (Z-axis), move the X-axis by .030 (or what ever cut is comfortable to you) towards the final "zero". This process is like a plunge cut with a fixed radius boring head set-up.

1034 - Eventually you will reach the target "zero" and the saddle diameter has been machined. Note that in my case the blast pipe stand bosses were also slightly radius-ed.... I machined the blast stand position square in a different set-up.


Dan

[Dan Willey]

Last 3 pictures....
Dan