How many blades should a planer have?

[Esta56]

This is a subject that is intriguing me.

Generally most of the planers/thicknessers discussed in this Forum are either 2 or 3 blade models. Looking at a lot of the marketing/advertising blurb for machines, you quite often see comments like '3 blade cutter for high quality finish' but the existence of 3 blades cannot automatically imply a higher quality of finish over a 2 blade machine. There are quite often posts making similar statements or queries.

The factors surely must include the cutter block's rpm to determine cuts per minute (cpm) and, in the case of a thicknesser, the feed rate.

For example:

2 blade Thicknesser

If the rpm of the cutter block is 6,500rpm and the feed rate is 5m (or 5,000mm) per minute then this equates to 13,000cpm divided 5,000mm to arrive at a figure of 2.6 cuts per mm.

3 blade Thicknesser

If the rpm of the cutter block is 4,500rpm and the feed rate is 7m (or 7,000mm) per minute then this equates to 13,500cpm divided by 7,000mm to arrive at a figure of 1.92 cuts per mm.

So in this instance it would appear that the 2 blade machine should (all other factors being equal) give the superior finish. I haven't seen a 3 blade machine that runs at the sort of speeds a 2 blade machine generally runs at.

Of course, there are many other factors to consider - machine quality, feed quality, accuracy etc. etc. Also, in the examples above, the 2 blade machine will need its blades sharpening/changing more often.

Any thoughts/education on this would be much appreciated.

 

[ike]

I'm not sure what you're asking, but you seem to have it prety much covered already.

cheers,

Ike

 

[Anonymous]

Richard
I think that most dedicated thicknessers run with brushed motors and at approximately twice the speed of the lower end P/T which have induction motors.

Certainly my Delta thicknesser rotates the (2) blades twice as fast as the SIP P/T and gives a better finish

I did see a review in an american mag of dedicated thicknessers and one was a three blade (dewalt) - the conclusion was that there was no advantage to the 3 blades

After all that , I would rarely consider using wood directly from a planer or thicknesser for any fine furniture; a few strokes with a hand plane gives a perfect finish in seconds - thus I ususally use the SIP as it is quieter and the finish from the machine is unimportant

 

[Scrit]

I think that most dedicated thicknessers run with brushed motors and at approximately twice the speed of the lower end P/T which have induction motors.

Depends on what type of machine you've got.....

I did see a review in an american mag of dedicated thicknessers and one was a three blade (dewalt) - the conclusion was that there was no advantage to the 3 blades

I would agree that for THICKNESSING that is true. I use a Casadei 4-knife machine and on surfacing it is a lot smoother than the Robinson, Wadkin, Robland, Lurem, Kity, etc machines I've had with 2-knife blocks in the past. When you get to thicknessing, however, it's the feed speed which dictates how smooth the finish is - main difference is that a 3- or 4-knife block will feed at a higher rate.

Scrit