Crayford Focuser

07/08/06
It has been quite a few years since I posted this page and I found the focuser's I made were some what lacking under the rigors of actual use in the field. They worked, but not as well as I would have preferred. I have since purchased commercial units I have been very happy with. The links to both can be found on my commercial ATM links. At best use these as examples for ideas to build on.

Below are some images of my large Crayford focuser. The body is made of red oak which I dyed with red oak stain as well. The tube is made from a copy lens housing.(Note: One can use 3 inch tubing like the 2.5 inch I used in the smaller Crayford below) I had a machine shop mill out the insides. The threaded retaining rings that held the original lens in place I inverted and glued to the top ring on the focuser. That part then screws into the tube body. With that you can install a 2" eyepiece. The other ring is an adapter for 1.25" eye pieces. Travel is about 1.25 inches. The tube body is 3"W x 2 7/8"L. The bearings came from old full height Tandon 360 floppy disc drives. One can also use bearings meant for router trimming bits or from old 1.25" 1.2 Meg floppy drives. The bearing supports came from 3/8 dia. aluminum stand off's, but 3/8" aluminum stock will work just as well. In case you cannot scrounge any bearings up a good commercial source for bearings that I highly recommend is BOCA Bearings.

I used a lot of brass thread inserts(Lowe's Building Supply) which are for receiving mounting screws in each corner of the base. The tension adjuster is also mounted with screws threading into brass inserts. They also hold the set screws that lock the bearing supports in place. The handles are knurled stainless steel handles and the 1/4 inch tempered steel shaft that rides against the flat on the tube are from Reid Supply Company although any good shaft from an old printer or disk drive used to guide the heads will do.

The copier lens can be purchased at Marlin P. Jones., an Electronics surplus dealer. Stock # is 8800-LN.

This was not an easy device to make. Tolerances must be as close as you can get them considering the medium you are working with(oak). To make the focuser, as I did, will require an ability to mill a flat on the tube body and on the bearing supports to receive a small stand off mounted 90 degrees to the bearing support. A 1/4 inch and 3/8 inch Forstner bit. A 3/16 inch and 3/8 inch end mill bit. Tools required. Table saw, belt/disc sander and a drill press with a milling vice. An adjustable hole saw. Last, but most important, lots of time and patience.

Since I originally posted this section on this design I have made several more of these but on a smaller scale. These are 3 inches wide by 4 inches long and use a 2.5 inches diameter tube that is three inches long with a .25 inch thick wall. This tube and many of the parts I used can be purchased at Small Parts Inc.
I used Brazilian Rose Wood, Red Oak, and Walnut. All but the Rose Wood was purchased locally. I had to special order the Rose Wood from Woodcraft.
You can purchase from all these links on line, but you will need a copy of Small Parts and Reid Tools catalogs to do so. They only have an online order form.

Below the thumbnail images are links to GIF files of the technical drawings for the focuser. These are complete drawings but I haven't much in the way of any any instructional text or a materials source list. There are probably a few errors as well. So if you catch any errors, obvious omissions, etc., please let me know. These files are fairly large so you might prefer to down load the zip file instead of viewing on line.

I have finally been able to make bearing post with two small .375 dia. bearings mounted on each post that align well and mate to the tube assembly with both making contact with the post. This is not an easy task with out professional machine shop equipment but can be done. The results are a much smoother and stable design. Below is a focuser made of red oak and coated with polyurathane varnish. Deluxing compound is then rubbed in and buffed for a smooth finish. I have made one other design change as well. Notice that the feet are missing on the side of the spring tension assembly. I have replaced this with a U-shaped bracket. This arrangement required that the shaft holder assembly to be shortened in height and the whole moved closer to the tube. It is a much better design than the original and I would recommend using it. The blue tint on the anodized tube is real. My anodizing process was somewhat lacking and instead of a lustrous black finish I got a cobalt blue color. Probably due to the oxide layer not forming as deeply as necessary and light is reflecting back through the coating. Oh well. It looks pretty.

NOTE: The drawings in Crayford.zip are of the large crayford design only. I have yet to do any for the small crayford design.

If all this seems to much then go to Ron Neuman's page and see his process for anodizing the parts for his Crayford focuser's. These are works of art, and best of all he will sell you one! Such a deal!