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Balanced tooling in insert planer heads

9/23/17       
cabmaker

Several years ago someone on the forum explained a principle related to tooling in shaper cutter heads.

Our planer has a terse head that can receive 4 blades. We run it with only two blades. There are two dummy inserts in the empty slots to balance the weight of the head while it rotates but these dummies do not make any contribution to the cut.

For some reason we were advised to use only two blades. It had something to do with chip evacuation and, as I recall, something to do with tooling life.

Could somebody explain this logic to me again. It made a lot of sense at the time and I would like to better teach this principle to some of the younger crew members.

9/23/17       #2: Balanced tooling in insert planer h ...
Russ

Website: http://www.mr-moulding-knives.com

Cab Maker Your question has to do with bore tolerance in the cutter head. Every cutter head has bore tolerance so you can get the cutter head on and off the spindle, usually between +.5 to +.20 microns for most manufacturers.

This extra space in the cutter head bore makes four different cutting circles when spinning, if you had four blades in the cutter head, Since you are only using two blades you are saving tooling cost, because only the knife sticking out the furthest in the cutterhead is doing the actual cutting. If you use four knives in the cutter head the only advantage you will have is the extra blades will help get the wood chips out of the way faster, this is not worth the cost of the tooling and only really helps in cases of poor dust collection. We call this application of cutting, a single knife finish.

I have attached an article that might help understand the science about knife marks.

Please let me know if I can be of further assistance. All the best Russ @ MR

Moulding-knife-marks

9/23/17       #3: Balanced tooling in insert planer h ...
Russ

Cab Maker
I have an error in the number above it should read +5 to +20 microns not +.5 to +.20 microns that really small :)
Russ @ MR

9/24/17       #4: Balanced tooling in insert planer h ...
Adam

This thread should be kicked over to the
solid wood machining forum for an educated discussion.

The table saw is an easy way to explain the cutter heads. Everyone uses the ts. Very quickly you understand the feed speeds with your hands between the different blades. Rip blades have less teeth, faster feed rates, and large chips. Finish blades are the opposite.

The basics are more teeth/cutters better finish. More teeth slower feed rate. More teeth yields smaller chips.

The tooling life is because of cutter protrusion. One of the cutters is always higher than the other. It does more work than the rest and then dulls quickly. In a 4 knife head you could end up with 3 dull knives and 1 sharp one. Then you sharpen/change. Effectively you wasted a knife.

In a Tersa head the knives should all be exactly the same height, so the above theory may not be relevant.

It can be more economic to use less cutters. It all depends on your finish requirements. You can always slow your feed speeds to get more cuts per inch.

9/24/17       #5: Balanced tooling in insert planer h ...
cabmaker

Thank you Russ & Adam both.

Would like to ask a couple of more questions:

You are right, Adam, that the Tersa head presents the knife edge equidistant from the cutterhead. What Russ noted was that the distance from the cutterhead to the center of the shaper spindle is not constant.

In order to be able to put the cutterhead onto the spindle you need to have some tolerance in the tooling. This tolerance creates an imperceptible cam rotation in the cutterhead, hence one blade is effectively taller than the others. This blade takes all the hits until it effectively turns into a screwdriver instead of a blade.

I am still curious about the knife-marks-per-inch article. It said that a 25-30 feet per minute feed rate would create enough create enough wood chip flow to to keep your tooling cool ......"providing you are milling at least .020" in depth"

What does the depth of cut have to do with knife-marks-per-inch and/or with heat dissipation? How does greater depth of cut produce better looking product and/or cooler tooling?

Also: What do they mean by (non-jointed) molder?

9/24/17       #6: Balanced tooling in insert planer h ...
Russ

Cab Maker
It is the wood chip that creates enough air flow that actually keeps the knife cool when cutting, taking less than .020" cut is actually burning the tooling by not creating enough wood chip flow to keep the knives cool. This is why most industrial moulders have a .020" shim under the last bottom bedplate.
Jointed moulders generally have 3 or more knives in a hydro cutter head. The cutter head is pumped with grease and the bore tolerance is taken out of play. Then a jointing store is brought into the tooling while spinning to produce a perfect cutting circle, knocking down the high knives to the smallest size of the cutting circle. Then you can produce 30 feet per minute per knife finishing, so 90 feet per minute for 3 knives that are jointed, slower feed rates will tend to build heat in the tooling, reducing tool life between sharpening.
I hope that helps
Russ

9/24/17       #7: Balanced tooling in insert planer h ...
cabmaker

Thanks Russ.
That really helped a lot.
Makes great sense.

9/24/17       #8: Balanced tooling in insert planer h ...
cabmaker

I have two more questions:

Am I right in my understanding that a deeper bit into the wood helps to cool the blade because the actual wood chips essentially push air away from the cutterhead and it is this air displacement that causes the cool air to flow around the knife?

Question 2: The article about knife-marks-per-inch said we should have a minimum of .020 cutting depth. This is approximately .5mm. Are there any negative effects from taking a 2mm bite? If the spindle shaper doesn't bog down does the deeper cut have any different impact on blade longevity than a smaller .5 mm bite?

9/25/17       #9: Balanced tooling in insert planer h ...
Adam

.5mm = 1/64"+

That is barely a cut. We would typically take 1/16"(1.6mm). Sometimes we will take an 1/8" depending on the species. Taking a deeper cut can sometimes reduce tear out. It's counter intuitive, but it works.

It's surprising that the experts are recommending such a light cut. Perhaps this is only possible with the accuracy of the hydrolock/jointed heads.

9/25/17       #10: Balanced tooling in insert planer h ...
Russ

Cabmaker
1 - Yes, you are correct
2 - Then you get into horse power of the motors, Typically 1/8" cut for all moulder spindles.
Adam - The last bottom minimum cut is .020" (hence the shim) for s4s but is mainly to remove any table lubricant used on the wood while milling. A backout or relief cut will of course take a bigger depth of cut.
Have a great week ahead
Russ

9/25/17       #11: Balanced tooling in insert planer h ...
Russ

Please let me add to this statement
2 - Then you get into horse power of the motors, Typically 1/8" cut for all moulder spindles, when milling s4s, profiles will be limited to the cutting circle of the moulder spindle, max depth of cut will be around 1-1/4" - 1-3/8" depending on the moulder and horsepower of that motor.
Russ

9/25/17       #12: Balanced tooling in insert planer h ...
Bill Member

I don't think the chip causes more air to move around the cutter I believe the chip absorbs the heat and keeps the cutter cool.

That is the way it works in metal work and that is the way it work on a CNC router. Have you ever pick up a hand full of warm chips?

I believe the concept is correct but the explanation of why is incorrect.

9/26/17       #13: Balanced tooling in insert planer h ...
Larry

I'm with Bill on this one. It's the chip that is taking away the heat. Also the shim on the last bed plate is for taking off the bed lube. There is one more factor at play. A knife does not instantly start cutting, there is always some compression of the wood before the cut begins. The knife is sliding before the cut starts = heating. If too thin of cut is taken you will get more compressed fibers and more heat and a burnished cut. As for how deep of cut you can take I don't buy the thing about 1/8" or whatever is proposed. Almost all moldings will have areas taking a lot more than 1/8" and do so perfectly well. We have a small Weinig 5 head with only 20 HP on the top head. We will run out of power on that head before we have any issues with cut quality. On a bar rail in a dense wood @ the slowest feed rate the molder will still struggle to maintain rpm. It is removing a lot of wood, dust collection becomes the main factor in cut quality then. A recirculated chip causes dents in the finished surface. Should have bought a machine with two tops. As for head bore to spindle diameter, it is true there will always be clearance. The affect of that clearance can be greatly reduced by having the diameter of your profile grinder spindle match the molder and by mounting the head on the profile grinder so the knives are horizontally opposed. Mark the head and mount it on the molder in the same relative position. It helps on a two knife setup not as much if running 4 knives. Also when profile grinding you always want to take a final, very shallow, pass all the way around at a steeper angle to eliminate at least one of the variables, grinding wheel wear. Never perfect and one knife will likely always take a deeper cut.
Solution, a jointed molder with a 16 knife, 150hp, head running, @ 1350'/minute. OK, I got carried away, but the big Weinigs will do that.


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