Perhaps someone else will find this method useful :
I'm working on what may well turn out to be the longest time for a Webster engine build - I started years ago, but had to shelve the project for a number of reason. However, the project is back off the shelf, and I recently found myself looking to make the exhaust cam. I looked at the methods used by some others for making cams, but I ultimately decided to go with a kind of "manual CNC" (MNC?). The method is pretty simple - turn a blank at 5° increments and mill to a previously calculated depth of cut at each interval. This requires 68 cuts, but since 52 of them are identical, it goes pretty fast - less than 45 minutes to complete in my case.
The picture and PDF show the cut table I used to make the cam. I used a home made electronic indexer to make this, but a manual indexer or rotary table should work as well. The dimensions in the cut table were taken from a 3D CAD model; in the drawing the sides of the cam look straight, but there is actually a very gentle curve.
Download a pdf version here :
The method results in a faceted profile, but the facets (while visible under magnification) are imperceptible to the touch. The photo below shows the cam after case hardening.
Note that my cam design is a bit different than the design in the plans, as I made it to insert into a home made gear:
Milling the gear in the indexer - only partially done at this point :
DOC
I'm working on what may well turn out to be the longest time for a Webster engine build - I started years ago, but had to shelve the project for a number of reason. However, the project is back off the shelf, and I recently found myself looking to make the exhaust cam. I looked at the methods used by some others for making cams, but I ultimately decided to go with a kind of "manual CNC" (MNC?). The method is pretty simple - turn a blank at 5° increments and mill to a previously calculated depth of cut at each interval. This requires 68 cuts, but since 52 of them are identical, it goes pretty fast - less than 45 minutes to complete in my case.
The picture and PDF show the cut table I used to make the cam. I used a home made electronic indexer to make this, but a manual indexer or rotary table should work as well. The dimensions in the cut table were taken from a 3D CAD model; in the drawing the sides of the cam look straight, but there is actually a very gentle curve.
Download a pdf version here :
The method results in a faceted profile, but the facets (while visible under magnification) are imperceptible to the touch. The photo below shows the cam after case hardening.
Note that my cam design is a bit different than the design in the plans, as I made it to insert into a home made gear:
Milling the gear in the indexer - only partially done at this point :
