Rebarreling and Home-Shop Machining

Transfer Screw

A transfer screw is used to transfer the position of the center of a threaded blind or through hole to another part of an assembly. An example of a use of transfer screws would be to locate the position of the four-jaw chuck mounting holes on a homemade adaptor plate so that it can be mounted on the lathe. In this case four transfer screws would be put in the chuck the chuck brought against the mounting plate and the plate tapped with a copper hammer. The pointed screws will leave a center punched hole in the proper position for drilling. This type of screw is available commercially in sets from Campbell tools on page 50 of their downloadable catalog.

I needed to transfer the position of my Fifth Column Clamping Bolt to the steel plate that will be slotted to accept it. I plan to drag the transfer screw down the plate which has been marked with Dychem Blue Coating. The screw will leave a scratch from which the slot can be accurately located.

Photo 1. The screw can be made from drill rod and then hardened by heating and quenching in oil. I only needed a scratch so I used a grade 8 bolt that was already threaded 3/4 inch by 10 thread per inch. First I parted the bolt completely through with the welded up parting tool that I described in the lathing plastic topic in this set of folders. I fed the tool about .2 inch per minute. After parting half of the bolt material, I started a new part line slightly to the right to reduce the forces from the sides of the cut on the tool. As I approached the center I slowed the feed. I snapped the bolt head off when there was about a 1/16 inch of bolt left.

Photo 2. I next used the parting tool to cut a shoulder about .2 inch long by .25 inch in diameter. I used the compound rest to cut a 60 degree point on this bit of shoulder.

Photo 3. I then used the indexable carbide tipped bit to shoulder the bolt for a 3/8 x 24 thread per inch nut. This nut was chosen by the largest socket that would fit the 3/4 inch hole. I fed the bit at 3 inch per minute at 120 RPM and got curly chips with a reasonably good surface finish. I used the same bit to cut a clearance groove at the shoulder.

Photo 4. I then used my Home-Made Die Head which I described, in March 2003, to thread the shoulder of the bolt.

Photo 5 and 6. I assembled the nut onto the bolt with red Loktite after I tried to harden the point by reaheating and quenching in oil. It got a little bit harder. A transfer screw made of drill rod will get harder, if you plan to use the screws for center punching. Photo 7 shows the scratch made by the screw for the plate that will have a milled 3/4 inch slot centered on the scratch.

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