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Author Topic: Ripping speed vs. number of teeth  (Read 2426 times)

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Offline SlowJoeCrow

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Ripping speed vs. number of teeth
« on: April 20, 2017, 02:07:24 pm »
I'm using a Woodmaster 725 as a gang rip saw running 5 of their 6.5" saw blades and getting good results for my application.  I am ripping rough sawn 4/4 & 5/4 hardwoods so I am asking a lot of the machine, but it handles it well at a slower feed rate, 35-40% dialed in on the variable speed control.  Of course I want to go faster....so this is where the number of teeth come into play.  I have been told that if I have every other tooth removed on the saw blades, I will be able to speed up the feed rate and cut faster. 

Here is a factory picture of the blade, it has 18 teeth.  What you you guys think, do you agree?  If so, do I just remove the carbide tooth or grind out the tooth and whole gullet as well?  I would have a saw shop do this so that it would be uniform and balanced.
I know I am limited on my horsepower... I am exchanging the stock 7.5hp motor with a 10 hp single phase as well so that should help.  I am not considering 3 phase at this time.

So without substantially increasing my hp, will removing every other tooth help out?  I am not overly concerned with the quality of cut, this isn't glueline quality stuff.

What do you all think??  Thanks for the input.

Offline WLC

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Re: Ripping speed vs. number of teeth
« Reply #1 on: April 20, 2017, 11:22:23 pm »
If you remove every other tooth, wont that leave you with a blade that has set on only one side?
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Offline SlowJoeCrow

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Re: Ripping speed vs. number of teeth
« Reply #2 on: April 21, 2017, 06:37:12 am »
Well good question.  The blade has carbide teeth so the set comes from the teeth being 0.135" while the saw plate is 0.093".  I will have to check and see what grind they have on the teeth - I think it is a atb grind pattern.

Offline 4x4American

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Re: Ripping speed vs. number of teeth
« Reply #3 on: April 21, 2017, 06:50:49 am »
It only makes sense to me, works in my chainsaw.  But you have to ask why they put so many teeth to begin with.  If it's just for cut quality then give it a shot.  Any way to try it out on just one first?
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Offline 21incher

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Re: Ripping speed vs. number of teeth
« Reply #4 on: April 21, 2017, 07:25:40 am »
Do they make a thin kerf blade for it.  I switched the under powered contractors saw I used to own to one and it made a big difference.  :)
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Offline SlowJoeCrow

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Re: Ripping speed vs. number of teeth
« Reply #5 on: April 21, 2017, 07:34:31 am »
21incher, I did the same with my contractor's saw and it helped quite a bit as well.  Woodmaster doesn't have any thin kerf blades, I asked, they said a thin kerf wouldn't hold up.

Offline SlowJoeCrow

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Re: Ripping speed vs. number of teeth
« Reply #6 on: April 21, 2017, 07:47:14 am »
Another advantage to remove every other tooth would be then the cutting teeth would be staggered  from blade to blade on the shaft.  Here is a picture of the saw pack on the shaft.

Because of how they are mounted, you can't rotate the blades on the shaft (that's good) but since they are locked on the shaft with a keyway, all the blades have the same orientation, thus the teeth from all 5  blades are in the cut at the same moment.  If they were staggered, I think it would be like a spiral head planer and might be easier on the motor.

Thoughts?

Offline Larry

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Re: Ripping speed vs. number of teeth
« Reply #7 on: April 21, 2017, 09:51:50 pm »
21incher, I did the same with my contractor's saw and it helped quite a bit as well.  Woodmaster doesn't have any thin kerf blades, I asked, they said a thin kerf wouldn't hold up.





I bought two gang rips out of a factory a few years ago just for the motors and parts.  One was 20 HP while the other was 5 HP.  Pictured is the arbor out of one...can't remember which one. :-[  Think it was the 5 HP one.

Modifying those blades will be expensive with unknown results.  Going to 10 HP is not that big of increase but I doubt anything bigger will fit into the cabinet.  I know, I'm not much help.  I might just make a leap and buy or build a bigger machine.  Real machines are 3-phase. ;D
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Offline SlowJoeCrow

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Re: Ripping speed vs. number of teeth
« Reply #8 on: April 22, 2017, 07:12:41 am »
Don't get me wrong, this machine as is has been working great for me, I just want to be able to feed material a little faster since I'm less than 50% on the feed speed now.  I'm not industrial...got a long way to go for that.  I think 10hp is the largest that I can go without switching to 3 phase.  I know, I know, 3 phase is where it's at, but I need to use what I have.

Offline Just Me

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Re: Ripping speed vs. number of teeth
« Reply #9 on: April 25, 2017, 11:54:14 am »
 Your limiting factor is most likely the amount of shavings that the gullet can carry out of the cut, so knocking off some teeth will probably not help you with speed and may ruin a perfectly good blade. Rule of thumb I was taught was a minimum of two teeth in the cut at any given time with a rip blade for a quality cut.

If you draw a line across the blade at whatever depth you are cutting I think you will find you have two or three teeth in the cut at one time. Staggering would change where the teeth are in the cut, but I do not think it would have any effect on speed. I would be afraid of ruining what look to be some pretty nice blades.

Maybe I missed it but what diameter blades are those?

Curious to see how this plays out.


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Re: Ripping speed vs. number of teeth
« Reply #10 on: April 26, 2017, 08:00:46 am »
They are smaller diameter blades, 6.5" diameter, but very stoutly built for the size.  $70 a piece, so $350 for the five that I am running, not a ton of $$ if it doesn't work.  I am going to have my saw sharpener look at them this week and see what he thinks.

Thanks for sharing that rule of thumb, I haven't heard that before.  I will have to look and see how many teeth are in the cut, I am ripping material 1" to 1 5/16" thick. 

The larger ten horse motor should be here this week as well so I want to see what I gain from that extra 2.5 hp before I do anything drastic.  I will say that I can safely increase the feed speed substantially when I put a narrow piece of wood in and only 3 or 4 blades are cutting, so the extra hp should help (it better!!).

Offline Larry

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Re: Ripping speed vs. number of teeth
« Reply #11 on: April 26, 2017, 02:20:59 pm »
I stumbled across the arbor out of the 20 hp gang rip yesterday.  The blades on it are 10" with 12 teeth.  They are thin kerf style.  This gang rip was primarily sawing pine.  The blades could have been special made as was the gang rip its self.



I would guess Woodmaster used 6.5" blades because that's the biggest that will fit between the feed rollers. 
Larry

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Re: Ripping speed vs. number of teeth
« Reply #12 on: April 27, 2017, 09:11:24 am »
That's correct on the Woodmaster saw blades, any bigger and they would cut into the feed rollers.  As it is, to use the 6.5's, you have to take off the chip breaker to be able to use them.  They also sell 5.5" blades as well that don't require removal of the chip breaker, but they only cut to 1 1/8" thick stock.  They would be great for ripping 3/4" stock.

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Re: Ripping speed vs. number of teeth
« Reply #13 on: April 27, 2017, 09:29:38 am »
Larry,

Thanks for posting that picture.  I am surprised that those blades are thin kerf, I just assumed that a thin kerf tip wouldn't hold up very well in a gang rip application.  It's also interesting that they only have 12 teeth on a 10" blade - that would support the idea of fewer teeth cutting faster since most 10" ripping blades for table saws have 24 teeth.  The Woodmaster's 6.5" has 18 teeth stock, so I bet taking some off would help.  Like I said, I need to talk with my saw sharpener about it.  My 10hp motor is coming Friday, so that is great. 

Offline Ianab

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Re: Ripping speed vs. number of teeth
« Reply #14 on: April 28, 2017, 08:09:13 am »
I think the theory is that as every tooth on the blade has to slice through all the wood fibres on each pass. So even when you slow the feed, each tooth is still cutting the same amount, just a smaller "bite" and finer sawdust. The load on the engine doesn't decrease with proportional to the feed speed.

My experience is with small Swing Blade sawmills, where you have a saw with a 6-8" depth of cut, and only limited HP. To make the most of that they run blades with only 3 to 8 cutters, depending on the HP available. You do loose some smoothness of the cut, but if you are dealing with rough sawn wood, it's within spec. You don''t expect the same finish off a mill or edger as you do on a table saw with a "finish" blade.

So I can walk my mill though a 2" deep cut, at walking speed, with 4 cutters and 13 hp. The mill is throwing out chips, not sawdust when it's running like that. A one inch cut is really fast, and pretty much throws out "noodles" of wood.

The gullet space does come into play as well, but if you are only talking 1 or 2" cuts, this isn't such an issue, compared to a  BIG blade that  might be chewing through 18"+ of wood.
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Re: Ripping speed vs. number of teeth
« Reply #15 on: May 01, 2017, 10:52:39 am »
I think the theory is that as every tooth on the blade has to slice through all the wood fibres on each pass. So even when you slow the feed, each tooth is still cutting the same amount, just a smaller "bite" and finer sawdust. The load on the engine doesn't decrease with proportional to the feed speed.

My experience is with small Swing Blade sawmills, where you have a saw with a 6-8" depth of cut, and only limited HP. To make the most of that they run blades with only 3 to 8 cutters, depending on the HP available. You do loose some smoothness of the cut, but if you are dealing with rough sawn wood, it's within spec. You don''t expect the same finish off a mill or edger as you do on a table saw with a "finish" blade.

So I can walk my mill though a 2" deep cut, at walking speed, with 4 cutters and 13 hp. The mill is throwing out chips, not sawdust when it's running like that. A one inch cut is really fast, and pretty much throws out "noodles" of wood.

The gullet space does come into play as well, but if you are only talking 1 or 2" cuts, this isn't such an issue, compared to a  BIG blade that  might be chewing through 18"+ of wood.

I am a little confused by this statement.  With the Woodmaster, the load on the saw motor is certainly dependent on the feed speed.  Speed up the feed and you can hear the motor bog down substantially.  Slow it down and the saw motor will recover.

Here's an update:

I swapped out the stock 7.5 hp motor with the 10 hp upgrade - those suckers aren't light!  Got it up and running again but wasn't able to increase my feed speed at all. >:( >:(  In fact after running a few boards through, burn marks were showing up, something I have never seen before with these blades.  That to me is a sure sign of dull teeth.
I have been wondering about the sharpness of my blades this whole time... when they were brand new, it obviously cut better and I was able to feed faster.  The blades don't feel dull at all, but maybe they are more dull than I realize.  My sharpener man came over yesterday and we looked at everything together.  We agreed that before we start taking teeth off, let's just sharpen the blades and see what happens.

Right now on each blade, with the stock that I am ripping, there are two teeth in the cut at any given time.  The tooth spacing (18 teeth on a 6.5" diameter blade) is about the same distance tooth to tooth as a 24 tooth 10" rip saw blade.  That makes sense.  He said if I did want to take every other tooth off, he would regrind the remaining teeth to be a flat top grind.

I should get the blades back on Tuesday, we will see how they cut then.  He was only going to "face" the carbide (grind the face only) since he agreed that they didn't look or feel very dull.  We will see.

Offline Just Me

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Re: Ripping speed vs. number of teeth
« Reply #16 on: May 02, 2017, 07:45:39 pm »
 I tried to fin a cheap blade with less teeth that could be modified as an experiment and found none, most had 24, some 18.

As I was thinking about this I considered the work the saw is trying to do and compare it to my big saw that is 9hp, and 5" being the sum of what you are cutting is all my saw can cut with a 14" blade. It would be working its butt off to get through anything except maybe pine.

Larry may be right, time for a bigger saw. ;)

Offline Just Me

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Re: Ripping speed vs. number of teeth
« Reply #17 on: May 02, 2017, 08:04:06 pm »
 I have a machine like that, not sure of brand in the back of the barn that I have never used, tomorrow I will try to remember to go take a look at it. Kinda forgot about it till just now.

Offline SlowJoeCrow

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Re: Ripping speed vs. number of teeth
« Reply #18 on: May 04, 2017, 10:42:30 am »
Well, it wasn't the blades being dull... ::) ::). Put the freshly sharpened blades on and not much of a difference at all.  I think I have it figured out though - belt slippage slowing the shaft speed down under load.  Out of the box the machine worked great - brand new belts.  After a while, belts are wore in, loosened up a little especially after rolling them on and off the shaft sheave in order to service shaft, etc. 
Here is a picture showing the belt setup:

The belts go straight to the motor shaft sheave, no tensioner.


This is one thing about the Woodmaster 725 that I have - there is no conventional way to tighten up/tension the belts like other machines.  I slid the motor horizontally on the motor cross plates in an effort to lengthen the distance between the motor shaft and the saw shaft, thus tightening the belt.  It helped a bit but I think it still needs more tension. 

Here is a picture I took while swapping the motors:


The motor just bolts on those cross plates.
I talked to my contact at Woodmaster who has been very helpful.  He said to put washers in between the motor cross plates and the angle iron that they are bolted to, thus increasing the distance in between the two sheaves and tightening the belt.  Not a very elegant or convenient way to tension the belts, but that is what I will do before I use the machine next.

Offline Larry

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Re: Ripping speed vs. number of teeth
« Reply #19 on: May 04, 2017, 12:39:21 pm »
Increasing belt tension may work but its a band-aid. 

The root cause of slippage is the arbor pulley is to small.  A 3 HP cabinet saw or planer uses around the same size with three belts. 

If it were me, I would change out the pulleys to a size similar to what's on the arbors I pictured.  Than I would run BX (cogged) belts. 

Another idea.  If those belts on your machine are standard belts a change to cogged belts would help and you might not need bigger pulleys.
Larry

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