Understanding Planers

I have a dewalt DW735 13" planer, the RPM is 10,000 & the feed rate is 14/26 FPM. To be honest it's a good planer, but it can go thru blades. That seems to be most peoples gripe. So the Grizzly catalog arrived and I started looking at planers with spiral carbide inserts. I had bought a Grizzly 8" jointer G0593 with the same spiral carbide inserts. I love it, great cuts, easy to rotate the cutters etc. So I thought a planer like that would be great. I start looking at the specs on 15" & 20" planers, 16/20 FPM feed rate & 5000 RPM. I would have thought the feed rate on 3 or 5 hp 220v machine would have been higher than the dewalt? Also the rpm on the Grizzly is 1/2. I have no doubt the Grizzly is an upgrade, but I don't understand these differences. Any help? While your at it, anyone have a Grizzly 20" planer model G0454Z or G1033X(Extreme) . What is the difference between their Extreme series & regular?
Thx, Chris
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Chris wrote:

How many blades on the DW? I don't have anything except old industrial iron to compare, but I'd guess it's probably two instead of three (or four) so the higher rpm is required to achieve the same cuts/inch...
Feed rate combined w/ rpm and number of knives translates into cuts/inch. Designs are for that end spec, not as only linear speed. Larger planers and higher horsepower translates to more capacity to handle larger work and take more material per cut than the small guys (but, otoh, they may do as fine or better detail work on what they can handle).
I've not specifically looked at the relative Griz in detail but a quick glance at the last printed catalog I happen to have laying here shows the primary difference appears to be the segmented spiral cutterhead on the X as opposed to four (4) HSS knives on the Z--oh, but this isn't a "Z" model, just the 0454 so that may not be true although the other "Z" models seem to have straight knives as standard w/ the segmented as an option...
Those are the types of differences I'd suggest looking at the current descriptions w/ in mind. Also, compare weight altho they look roughly equivalent in this catalog.
--
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Lots of physics here. I think cuts per minute is more informative than RPM. If I have 4 blades spinning at 2500 RPM it makes as many cuts as 1 blade at 10,000 RPM. I assume the dewalt has 2 blades and the bigger planers have 3 or 4.
Second, there is the need to have enough inertia to keep the head spinning. A bigger planner has more mass in the spinning head so it can run at a lower RPM and have the same continuous torque hitting the wood (I am not a mechanical engineer so my terminology is non- technical, just recalling as it was explained to me).
Regarding feed speeds, a part of the consideration is not ffeding so fast that the wood stalls the head at a typical depth of cut. A wider planer has much more to overcome so even with more horse power it might need to feed a little slower.
Now with spiral cutters with many little cutters, you mostly have cutters into the wood continuously, which makes for a smoother cut because of lots of little nicks continouusly instead of 2, 3 or 4 bigones each revolution. So you can still count cuts per minute but one cut actually eaquals lots o' little cuts that add up to one full width cut.
Another aspect of feed rate to rpm rate is that each cutter is actually cutting a small arc out of the face of the wood. So the diameter of the head makes a difference in the finish. So two machines with the same number of knives at the same rpm and feed rate but different diameter head will produce a different finish. So a feed rate is not just a factor of power but is optomized as part of the whole system to produce the smoothest range of finishes by overlapping the arcs sufficently to feel smooth although with a spinning head and a moving board there will always be some level or ridges.

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The 735 has three knives.
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Chris wrote:

The bigger planers have a much quieter motor, and can take a much deeper bite without bogging down. They are also better able to deal with very rough lumber (segmented rollers deal better with thickness variations than the rubber rollers of lunchbox style planers).
For sheer quality of finish the lunchbox planers are very good and can take a lighter pass than the heavy-duty ones.
Chris
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Speculation here.
The slower RPM may be to increase the power being directed to the cutter head. Apparently these spiral head cutters require more HP as the cutter head is basically in constant contact with the wood. Because the cutter head is running slower, the feed rate is slower than most large planers with 3 knife cutter heads. This was news to me when I first read an article about spiral head cutters some years back.
The feed rate on the DeWalt just happens to be the same as most of the common bigger planers. Really, a thickness planer should only be expected to cut your stock to a desired thickness and not produce stellar surface smoothness although all planers produce nice results with fresh sharp blades. As I am sure you have noticed, nicks form and you still have to follow with sand paper or the like to acquire the surface desired. IMHO the DeWalt has a slow speed and Too Slow speed. I am going to scrape and or sand the finish afterwards so what is the use in going too slow to begin with? Remember the nicked knife?
FIY, my 15" Stationary Delta planer with 3 knives runs at 16 and 30 feet per minute and the knives are only in contact with the wood 3 times per revolution.
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