Unlike the crankshaft grinder, the cam grinder is largly “mechanical” in operation. The silver steel (drill rod to some) blank for the cam is first turned up in the lathe with bearing surfaces to size and the cam sections sized to a few thou over the maximum lift and centres drilled each end. Usually allow a little extra in length to drill a small indent to locate the drive dog.
The bed for the grinder is much like a lathe except that the bed and the spring loaded main tower are pivoted at a point “x” distance below the drive spindle centre. This can be seen in one of the photos. A cam profile is made from 1.5 – 2.0mm thick steel or aluminium and the tower carries this profile on a boss that is driven in sync with the spindle. This top shaft is 4 times “x” distance above the pivot point previously mentioned which allows the cam profile to be 4 times larger than the ground cam will be giving greater accuracy in the finished cam. During grinding, the tower pivots in and out following the curve of the profile.
The boss carrying the profile is indexed to allow the profile to be moved to the next cam timing location and it is changeable for a different “number of cylinders” cam to be ground.
When the profile is fitted to the boss on the tower, it aligns with a feed-in rod. This 8mm rod has a 20mm flat that the profile rubs against while it turns. The rod is driven back in (when grinding) at an adjustable rate from a small stepper motor that gets a feed-in pulse on each revolution of the spindle. The rate is from 0.5 thou to 3 thou and with the grinding motor and other factors, I usually set this towards to lower end. The speed of the main grind motor is also adjustable although I removed the original internal control (spring govenor) and fitted a panel mounted thyristor type as the original caused an amount of “hunting” and caused the drive belt to flex like crazy.
So to grind, set the Auto/Man switch to Manual. The cam profile is fitted to the top shaft in the first cylinder position and whether it is exhaust or inlet. The cam blank is fitted between centres on the lower spindle, attaching the drive dog in the previously drilled indent. The grind wheel carriage is run up to align with the first cam and the spindle shaft is turned so that the high lift part of the profile is sitting on the feed-in rod. The grind wheel (not running at this stage) is fed inwards until it just clears the cam blank by a couple of thou. A shutdown optical switch is then run up to this point and the measuring dro is set to zero. The feed motor is then run back out again and the profile again rotated until the back of the profile now rests on the feed-in rod.
All is now set to grind this, and, with the exception of a position change of the profile and re-alignment of the grind wheel, all remaining cams. If different profiles are used for exhaust and inlet, these are simply changed at the appropriate time. Normally I would grind all the exhausts first then change the profile and do the inlets.
Switch to Auto, press Start and go do another job while the grinder does this one. In the above I mentioned setting the initial grind a couple of thou short. So once this first grind has shutdown, a measurement can be taken and if needed, final cuts can be done and the shutdown point reset to this new value. A quick polish with some wet or dry paper and the cam is ready for hardening.
A mate of mine has built a similar machine using different types of recycled materials. The most talked about is a small fine-feed gearbox (out of an F1-11 no less) as the feed-in arrangement. It feeds continuously via a speed control and shutdown is via a micro switch. I like the optical switches myself as they are more accurate. He has also built a gear and rack unit to which he can mount his profiles during manufacture. It traces the shape of this profile onto a sheet of paper where it is possible to see the exact number of degrees the cam will be open or closed and the shape of the curve i.e. either moderate or “snappy”.
…………… Jeff |