The backstay bearing of my Freehand steering gear had incurred severe UV degradation and so I machined a replacement. I didnít have affordable, ready access to a lathe and so used a drill press with a live center attachment. This, in essence, is a vertical lathe.
As shown in the attached photos, some nuts, washers, lock washers, threaded studs and aluminum stock serve to control cut depth and dimension. A couple of files, the appropriate drill bits and some wet & dry sandpaper enabled me to machine the replacement backstay bearing.
The hardest things to find were the live center lathe attachment and the appropriate Delrin stock. Here are two links that will help.
Drill press lathe attachment: [www.amazon.com
Delrin stock: [www.professionalplastics.com
The Delrin stock required for one backstay bearing is 2 pieces of 1Ē Black Homopolymer cut to 2Ē x 3.5Ē with dimensional cut tolerance of +.031/-.000. The black Delrin has much better UV resistance properties than the white.
Due to Professional Plastics minimum order requirements, I was able to buy 6 of these plus one 4Ē x 11.75Ē piece, to replace the bowsprit fid, at no additional cost. (My bowsprit also had UV issues)
In the attached photo of the original white bearing, itís clear that the UV degradation has severely affected the upper and lower collars where the 4 machines secure the two halves together. As a result, I increased the size of the collars to provide more material. You can see the difference between the original white and new black collars.
Attached is a CAD drawing of the new backstay bearing with the increased collar size. Also attached is a step by step description of the procedure that I used to machine the new bearing.
When machining the Delrin, use the lowest drill press speed. Also go very slowly and use plenty of lubricant when drilling and tapping Delrin. A solution of 25% liquid dish soap and 75% water works well.
Here are Amazon links to the files that were used:
1. Finish sand each 2" x 3.5" mating surface with 320 wet & dry
2. Scribe center lines of 4 holes from bottom edge of bearing + 1/64" (allowance for finish sanding)
3. Drill 4 3/8" holes with forstner bit to a depth of 1/2"
4. Align & clamp both halves of stock in drill press vise
5. Drill 4 5/32" holes through center of countersunk holes (tap size hole for 10-24 machine screw)
6. Drill 4 13/64" holes through center of countersunk holes (clearance size hole for 10-24 machine screw)
7. Tap 4 5/32" holes for 10-24 machine screw (use drill press for tap alignment)
8. Fasten both halves of bearing together with 4 10-24 3/4 machine screws
9. Sand top & bottom of bearing with 320 wet & dry until true (do not exceed 1/64" bottom material removal)
10. Drill 1/8" hole on centre axis of bearing top to a depth of 1/2"
11. Drill 3 holes around center axis of bearing top to accommodate 3 chuck set screws
12. Drill 9/32" on centre of axis of bearing bottom to a depth of 2"
13. Chuck & centre bearing in live center & chuck
14. Adjust cut to 1 3/4" + 1/64" (allowance for finish sanding) & turn stock to round
15. Adjust cut to 1/2" + 1/64" (allowance for finish sanding) & turn bearing centre spindle
16. Finish sand bearing on sides to design dimension (do not exceed 1/64" material removal)
17. Adjust cut for saw to cut top bearing to size + 1/64"
18. Turn bearing to cut to a depth for 3/8" (leaving 1" to saw by hand)
19. Chamfer circular bearing edges
20. Remove bearing from chuck & live centre & saw bearing top to size
21. Finish sand bearing top (do not exceed 1/64" material removal)
22. Drill remaining portion of 9/32" along center axis
Edited 1 times. Last edit at 09/17/18 02:12PM by johnpurins.