Rebarreling and Home-Shop Machining

Grinding and Scraping the Cross Arm True

            I needed to machine the face of the cross arm to be parallel to the spindle travel and perpendicular to the bed so that it would not affect the milling machine alignment much when I tightened it down onto the fifth column. Here are the steps that I took.

            First I leveled the lathe bed and aligned the mil head. This is shown in the topic Aligning (Tramming) the Mill Head in this Journal.

            I clamped a right angle plate to my fifth column and made the plate approximately level and made the angle plate that would be used for final truing critically parallel to the milling head travel. I used the setup in photo 1.

            I made a grinding fence out of ½ inch stock and made it parallel to the milling table travel (that was previously made perpendicular to the carriage travel). I used the setup in photo 2 to align the fence.

            I had made a grinding sled (T-slot topic in this Journal) to support the compound rest and my Dremmel Tool Post Grinder. I took a look at my die grinder to see if I could mount it as well. The plastic ring on the chuck end of the grinder happened to be a 35 mm thread just like the lock ring of my lathe which I replaced with a Spider. I used the lathe’s lock ring on the end of the grinder and a piece of ½ inch stock with a semicircular cutout about ½ the way through it, to clamp the die grinder to on the tool post with the use of a couple small machinist clamps. Photo 3. This setup never got loose. I used the die grinder on the sled and slid it back and forth on the cleaned and oiled adjustable angle plate to make a pass. I got a helper to advance the quadralift a quarter turn and made another pass until I had ground the entire surface. I controlled the depth of cut by making a vertical groove in the face of the Cross Arm with the die grinder by advancing the quadralift up and down until the stone sparked out. In the future passes adjust the stone until it just removes the groove. It would be better to use a regulator set at your compressors start point so that the pressure remains more constant, or an electric grinder. I got a little deeper cut on the interrupted cut near the bolt hole because the pressure was different during these shorter cuts. Photo 4 shows the grinding operation.

Scraping the Face True

I finished the surface true by hand scraping. Apply a thin coat of Prussian blue dye with you’re finger to the angle plate that was made parallel to the milling head travel. Push the angle plate against the face and slide it just a bit. When you pull it off the high spots will be marked. I made a large scraper from my largest file by grinding and stoning a square smooth edge onto the end. I used this to remove the high spots. Photo 5 shows my final contact pattern with a slightly thicker coat of dye used in the photo than you would use for fine work. The sides near the bolt holes are low due to the air pressure problem noted above. What I wanted was broad contact near the four corners.

Pressure Regulator

I reground the surface with the use of a pressure regulator set to 100 lbs on the 5 Horse Power Compressor. I also eliminated the helper to give the compressor time to pump up between passes. This gave me a truer surface that was only out .0005 inch on the vertical without a shallow spot near the holes. This surface will only need minor scrapping to broaden the contact points a bit. The resulting improved contact pattern is shown in Photo 6.

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