I think it expands the topic to some interesting discussion because I don't think the average car guy understands cam regrinding or cam grinding for that matter.
Camshafts can wear from extended service and the greatest wear is usually at the POML. The profile can be restored with a suitable lobe master on a cam grinding machine.
For example, if the POML is worn less than .010", it can be reground "10 under" around the entire outside surface. You end up with the same lobe contour on a .010" smaller base circle radius, which is not going to have a major impact on rocker geometry. You can tell that it is reground by measuring the heel to toe (POML to base circle on a line that intersects the base circle center) dimension, which will be less than original by .020".
The concern is whether this recontouring cuts through the relatively thin hardening at the surface, which is not always known, so there is always some risk of short life if what ends up as the surface is softer than the original surface.
I think reground cams are okay for budget rebuilds, but for a precision rebuild I prefer a new camshaft as long as one is available and I am comfortable that it is OE quality or better.
I was concerned about this situation in the manufacture of my "special 300 HP camshaft". As far as I was able to determine, ALL afermarket SB camshafts (and this probably also applies to vintage BBs, too) are made from a SINGLE blank manufactured by a division of Textron. They are delivered to cam grinders with all machining accomplished including installation of the indexing pin with the exception of lobe grinding, and the as cast LSA is in the range of typical cams, but since the POMLs and LSA of my design are VERY different than any OE or available aftermarket cams, I was concerned.
However, the vendor assured me that my design could be produced without going through the flame hardened surface materinal, and the final Parkerizing would also aid longevity.
All OE cams were ground from unique blanks that had specially designed as cast lobes based on the finished lobe dimensions. This minimized grinding time in high volume production. However, the replacement and aftermarket are much lower volume compared to OE so the best economic solution is apparently to use a single blank with generous as cast lobe materinal and relatively deep flame hardening for all camshafts for each engine family and let the grinding time vary depending on lobe design.
Perhaps the saving grace of my design is that lobe heights are modest (being as how I used a couple of existing OE lobes, though they are from different OE camshafts), and the shorter the finished lobe height, the more the POMLs can be moved away from from the as cast POMLs of the blank.
Master lobes are ground about 10X scale, so .001" error on the master lobe is .0001" on the finished cam, and assuming the machine is in good order, final dimensions should be well within OE TIR and runout tolerance.
OE cam drawings give lobe height every cam degree to five decimal places. To make a master lobe you start out with a circular piece of relatively hard corrosion resistant steel whose diameter is a little over 10X the finished heel to toe dimension or whatever scaling factor is correct for the target cam grinding machine.
Then you chuck it up on a rotary fixture on milling machine with the axis of rotation located at the center of the base circle. Starting somewhere on the base circle you take a cut equal to 10X the finished base circle radius, rotate one degree and take another cut and so on until you reach the first point of eccentricity which is say .00005" above the base circle. At that point you move the spindle out .0005" and make the cut, then rotate the work another one degree and move the spindle axis according to the next eccentricity data point.
After a total of 360 cuts and a final smoothing with a piece of crocus cloth, you have a master lobe that is ready to bolt to the cam grinding machine. The grinding wheel follows that master lobe and is continuously moved inward on the blank until the final base circle or heel to toe dimension is obtained on each lobe - nominal original, ten under, whatever.
This is at least 100 year old technology. Maybe current high volume OE cam lobes are ground on NC machines and all you have to do is input the base circle and eccentricity data, mount the cam blank and push a button, but AFAIK all the aftermarket vendors use these ancient technology "follow the master lobe" mechanical cam grinding machines for most of what they offer in their catalogs. Crane alone claims that they have 80,000 master lobes. Of course, not all are suitable for SB Chevies, but you get the idea.
Any cam grinder who has OE masterlobe(s) for your cam can regrind it (assuming he does regrinding of used cams) as long as wear is within whatever his experience says is acceptable for regrinding, but if his has the proper master lobes he can grind them on a new blank for not much more than regrinding the original cam.
Duke
Camshafts can wear from extended service and the greatest wear is usually at the POML. The profile can be restored with a suitable lobe master on a cam grinding machine.
For example, if the POML is worn less than .010", it can be reground "10 under" around the entire outside surface. You end up with the same lobe contour on a .010" smaller base circle radius, which is not going to have a major impact on rocker geometry. You can tell that it is reground by measuring the heel to toe (POML to base circle on a line that intersects the base circle center) dimension, which will be less than original by .020".
The concern is whether this recontouring cuts through the relatively thin hardening at the surface, which is not always known, so there is always some risk of short life if what ends up as the surface is softer than the original surface.
I think reground cams are okay for budget rebuilds, but for a precision rebuild I prefer a new camshaft as long as one is available and I am comfortable that it is OE quality or better.
I was concerned about this situation in the manufacture of my "special 300 HP camshaft". As far as I was able to determine, ALL afermarket SB camshafts (and this probably also applies to vintage BBs, too) are made from a SINGLE blank manufactured by a division of Textron. They are delivered to cam grinders with all machining accomplished including installation of the indexing pin with the exception of lobe grinding, and the as cast LSA is in the range of typical cams, but since the POMLs and LSA of my design are VERY different than any OE or available aftermarket cams, I was concerned.
However, the vendor assured me that my design could be produced without going through the flame hardened surface materinal, and the final Parkerizing would also aid longevity.
All OE cams were ground from unique blanks that had specially designed as cast lobes based on the finished lobe dimensions. This minimized grinding time in high volume production. However, the replacement and aftermarket are much lower volume compared to OE so the best economic solution is apparently to use a single blank with generous as cast lobe materinal and relatively deep flame hardening for all camshafts for each engine family and let the grinding time vary depending on lobe design.
Perhaps the saving grace of my design is that lobe heights are modest (being as how I used a couple of existing OE lobes, though they are from different OE camshafts), and the shorter the finished lobe height, the more the POMLs can be moved away from from the as cast POMLs of the blank.
Master lobes are ground about 10X scale, so .001" error on the master lobe is .0001" on the finished cam, and assuming the machine is in good order, final dimensions should be well within OE TIR and runout tolerance.
OE cam drawings give lobe height every cam degree to five decimal places. To make a master lobe you start out with a circular piece of relatively hard corrosion resistant steel whose diameter is a little over 10X the finished heel to toe dimension or whatever scaling factor is correct for the target cam grinding machine.
Then you chuck it up on a rotary fixture on milling machine with the axis of rotation located at the center of the base circle. Starting somewhere on the base circle you take a cut equal to 10X the finished base circle radius, rotate one degree and take another cut and so on until you reach the first point of eccentricity which is say .00005" above the base circle. At that point you move the spindle out .0005" and make the cut, then rotate the work another one degree and move the spindle axis according to the next eccentricity data point.
After a total of 360 cuts and a final smoothing with a piece of crocus cloth, you have a master lobe that is ready to bolt to the cam grinding machine. The grinding wheel follows that master lobe and is continuously moved inward on the blank until the final base circle or heel to toe dimension is obtained on each lobe - nominal original, ten under, whatever.
This is at least 100 year old technology. Maybe current high volume OE cam lobes are ground on NC machines and all you have to do is input the base circle and eccentricity data, mount the cam blank and push a button, but AFAIK all the aftermarket vendors use these ancient technology "follow the master lobe" mechanical cam grinding machines for most of what they offer in their catalogs. Crane alone claims that they have 80,000 master lobes. Of course, not all are suitable for SB Chevies, but you get the idea.
Any cam grinder who has OE masterlobe(s) for your cam can regrind it (assuming he does regrinding of used cams) as long as wear is within whatever his experience says is acceptable for regrinding, but if his has the proper master lobes he can grind them on a new blank for not much more than regrinding the original cam.
Duke
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