Hodgson Part 066, Rocker Arms

This entry is part 2 of 3 in the series Hodgson Rocker Arms

arm13I had some 10mm diameter 416 Stainless heat treated to HRC35 left over from a previous job. Even though most of the time was spent converting it from round to square, overall it was not very hard. However, don’t underestimate the added complexity such small parts can add to fixturing.

arm01Like with the rocker bases, when working with small parts in multiples, I like to keep as may together for as long as possible. Here I’ve cut off lengths of the stainless long enough to make two rockers per piece.

arm02With an insert face mill, I’m squaring up the stock and taking it down to around 0.195″ square.

arm03I could have spent more time and taken a light finish cut at a faster spindle speed and ended up with a better surface finish, but I have access to a surface grinder so that is what I’ll use to take them down to size.

arm04After grinding all four sides down to 0.1875″, I went ahead and cut them in half at the bandsaw since they won’t be able to stay doubled up after this point.

arm05I mounted the rotary table, indicated it in, and attached a scrap aluminum block. With the table on center and locked down at 0.00°, I milled a 0.1885″ groove about 0.1″ deep. I then fashioned a small clamp and was ready to start radiusing the ends of the rocker arms.

arm06For the first radius, the blanks were clamped with about 0.00″ overhanging to clean up, then the end was climb milled using a 6mm carbide end mill.

arm07Once one end on each of the rocker arms was milled, I added a dowel pin stop to locate the part, and radiused the second end on all of the pieces.

arm08With both ends now radiused, the table is moved back to center in both X and Y and the rotary table locked again at 0.00°. One end of each rocker arm is then centerdrilled, drilled, and tapped #4-40 through for the valve adjuster.

arm09Working on the other end of the parts, a 7/64″ ballnose endmill is plunged 0.070″ deep.

See the log for the tappets for an explanation on why I’m making these a spherical bottomed hole and why they are only 0.070″ deep.

arm10Moving on to the side of the arms, I’m drilling a 0.086″ hole for the pivot pin. I’ll ream it later after all the cutting and deburring has been done.

arm11I’m using a 4mm end mill to put in the 0.028″x0.188″ recess for the pivot pin circlip.

arm12With all the burrs removed, and a nice chamfer on each side of the pivot pin hole, I’m doing the finish reaming to 0.0938″.



A few of the arms and pivot pins ready to go on the rocker bases.

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All material, including the CAD drawings, relating to the construction of the Hodgson Radial presented on this site is free to use any way you see fit. However, no guarantees are made regarding the accuracy or correctness of the material presented here.

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