I'm plan to try my hand at building George Britnell's 1/5 (approx.) scale Ford Inline Six. This 300 cubic inch workhorse first appeared in the sixties and was used in Ford trucks for a decade. A shorter stroke version was used in passenger vehicles including the first car I was able to purchased new - a 1972 Maverick. In 2000, I rebuilt one of these engines in a '72 F-100 project truck that I used as a daily driver for a dozen years. The drawings purchased from George contain a lot of detail that will add realism to the model and challenge to its build. George documented his own build of this engine several years ago over on the 'other' forum.
After dealing with the pitfalls that can occur when trying to machine a complex crankshaft to fit an already completed crankcase, I decided to tackle it first. The Ford Inline six crankshaft is an interesting-looking 120 degree beast that's been replicated in this model. Its counterweight scheme isn't at all intuitive, but the engineers probably put all the lumps and bumps where they should be. The model's 8" long crank with its twelve tiny .312" journals will be one of the most difficult parts in this build. One of the photos shows a comparison of its SolidWorks model along side the Offy's crankshaft that tested my patience and machining abilities for several weeks last year.
The first step in its construction was to indicate a 9 inch length of 1-1/4" dia. Stressproof in my lathe's 4-jaw chuck so the ends could be center-drilled. Since I didn't have any material on hand, I purchased a length of 'ground and polished' 1144 from Speedy Metals. With the workpiece mounted between centers, I used my lathe's tailstock to zero out the measure of its end-to-end taper so I'd have a metric to track workpiece distortion during its various machining operations.
The workpiece was moved to the mill and clamped horizontally in the vise so a pair of reference flats could be machined on each end. These flats and a v-block were used to relocate the workpiece vertically in the vise so three additional center-drills could be added to each end for offset turning the rod journals.
The rod journals were roughed in using a center-supported four-axis indexing operation on my Tormach. Then with the workpiece set up between centers on the lathe, the rod journals and adjacent web walls were finish machined. The end-to-end taper measured less than .002" with the workpiece set up on centers in all three offset positions. These tapers were rough indicators of the initial mismatch errors in the end-counterbores. The taper measured along the main axis matched them to within a thousandth.
The crankshaft drawing specifies .312" for both main and rod journal diameters. I decided instead to target .328" for the rod journals and .375" for the main journals. The .328" was chosen because I happen to have a corresponding reamer for the rod bores. If a machining issue arises with the rod journals, the rod journal diameters can be reduced as needed to avoid scrapping the part.
The .375" diameter was chosen because of the availability of suitable ball bearings that I want to use for the outside main bearings. My plans include converting George's square bronze bearing design to round bronze bearings within the block and to replace the outer bronze bearings with ball bearings. Since I'm anticipating problems with the main journal machining, they may end up smaller with the inner bearings being machined to fit them.
The the rod journals and their web walls were finished using a Kennametal A2022N00CF02 grooving insert. This .087" wide carbide insert comes already bifurcated, and after a bit of lapping on a fine diamond plate it leaves a brilliant surface finish requiring little or no polishing. It's very important however to perfectly align its cutting edge with the lathe's spindle axis using a dial indicator. - Terry
After dealing with the pitfalls that can occur when trying to machine a complex crankshaft to fit an already completed crankcase, I decided to tackle it first. The Ford Inline six crankshaft is an interesting-looking 120 degree beast that's been replicated in this model. Its counterweight scheme isn't at all intuitive, but the engineers probably put all the lumps and bumps where they should be. The model's 8" long crank with its twelve tiny .312" journals will be one of the most difficult parts in this build. One of the photos shows a comparison of its SolidWorks model along side the Offy's crankshaft that tested my patience and machining abilities for several weeks last year.
The first step in its construction was to indicate a 9 inch length of 1-1/4" dia. Stressproof in my lathe's 4-jaw chuck so the ends could be center-drilled. Since I didn't have any material on hand, I purchased a length of 'ground and polished' 1144 from Speedy Metals. With the workpiece mounted between centers, I used my lathe's tailstock to zero out the measure of its end-to-end taper so I'd have a metric to track workpiece distortion during its various machining operations.
The workpiece was moved to the mill and clamped horizontally in the vise so a pair of reference flats could be machined on each end. These flats and a v-block were used to relocate the workpiece vertically in the vise so three additional center-drills could be added to each end for offset turning the rod journals.
The rod journals were roughed in using a center-supported four-axis indexing operation on my Tormach. Then with the workpiece set up between centers on the lathe, the rod journals and adjacent web walls were finish machined. The end-to-end taper measured less than .002" with the workpiece set up on centers in all three offset positions. These tapers were rough indicators of the initial mismatch errors in the end-counterbores. The taper measured along the main axis matched them to within a thousandth.
The crankshaft drawing specifies .312" for both main and rod journal diameters. I decided instead to target .328" for the rod journals and .375" for the main journals. The .328" was chosen because I happen to have a corresponding reamer for the rod bores. If a machining issue arises with the rod journals, the rod journal diameters can be reduced as needed to avoid scrapping the part.
The .375" diameter was chosen because of the availability of suitable ball bearings that I want to use for the outside main bearings. My plans include converting George's square bronze bearing design to round bronze bearings within the block and to replace the outer bronze bearings with ball bearings. Since I'm anticipating problems with the main journal machining, they may end up smaller with the inner bearings being machined to fit them.
The the rod journals and their web walls were finished using a Kennametal A2022N00CF02 grooving insert. This .087" wide carbide insert comes already bifurcated, and after a bit of lapping on a fine diamond plate it leaves a brilliant surface finish requiring little or no polishing. It's very important however to perfectly align its cutting edge with the lathe's spindle axis using a dial indicator. - Terry
