Kapex - The good side

[Michael Kellough]

MiterMaster,

This little exercise told me that the travel is out by over a 1/32" over the entire length of travel. Because of the travel issue its not that clear whether the blade is also unparallel to the table but it seems its okay in this respect.

The travel is from front left to back right.

Thanks,
Wayne

This might not be correct.

Unless your saw is set to cut dead square to the fence using a square on the fence won't tell you how the saw tracks. Really, the saws always tracks straight anyway. It can't do otherwise since it rides on two straight rods.

You can use this test to see if the fence is square to the travel but there are easier ways. Also, this test requires that you test the same tooth at both beginning and end of the travel and that you don't rotate the blade.

What you are really trying to test is if the blade is parallel to the travel of the saw, not parallel to the table. Another way of describing it is that you are checking to see if the arbor is perpendicular to the slide rods as viewed from above. It isn't easy to test, especially if the blade is suspect. A dead flat square plate (round on the top) that fit on the arbor would be helpful. 

Frankly I don't know a good way to test if the arbor is perpendicular to the travel on a SCMS. Maybe Rick does.

The bottom line (IMO) is it's either a bad blade as Spike says, operator error as Rick says, or both. If you have a perfect arbor then a heavy, stiff, FLAT blade is great, like Spike says. But, if the blade is warped or the arbor has some run-out there will be a lot of bad vibrations, especially in a cantilevered arbor like a miter saw. The type of blade supplied with the Kapex "adjusts" to run-out via centrifugal force to become a nice flat plane while it's spinning at speed but the imperfections can become exaggerated when an electric brake is engaged. So, for best results you should withdraw the saw from the work before cutting the power as Spike advised.

 

[Michael Kellough]

Forgot to ask Wayne, how does the piece of wood look to the left of the blade? Bet you anything it has no marks in it.

Spike, why?

Are you assuming the left hand piece isn't clamped?

If it is also clamped and run-out is the culprit both pieces would be scored the same wouldn't they?

 

[waynew]

From the photographs, my first reaction is that this cutting pattern is indicative of operator technique, and not necessarily with any saw alignment. That's not an absolute guarantee, but because of the sharp delineation, it strongly suggests that either the operator is deflecting the saw at the end of the cut, or relaxing the saw from a deflection that was applied during the cut.

Without actually watching you use the saw, it is hard to say the actual cause, but here is a scenario that might make it clearer what I am suggesting.

If you were standing to the right side of the blade and operating the saw with your left hand, you may have the tendency to push the saw head toward the left as you push it through the cut. Then when you reach the end of the cut and pause while the blade coasts to a stop, you relax your stance and no longer deflect the saw head to the left. This would result in the stepped mark shown in the photographs.

The same scenario can still happen when you are standing to the left of the blade and operating with your right hand, but the description above is easier to visualize and understand.

There is another alternative too. If the sawblade's plate was slightly warped, it would straighten itself out when the saw was at full speed, and return to a slight wobble as the blade slows down.

Rick, you could be onto something here, at least this could be a part of the problem. Quite early on in the piece I suspected this could be  operator error and not having any previous experience with a mitre saw I just tried to make sure the direction of force applied was as straight as possible in line with the  direction of travel of the saw head. After reading your description I went out and paid extra attention to this and it did improve the cut to a degree. Having said that I can't imagine that everyone is as careful as this out in the field, unless there is a very definite technique that everyone follows that I'm unaware of.

There were still swirl marks on the piece but they were not as pronounced as before. If you have any suggestions re technique I'm open to suggestions.

Thanks,
Wayne

 

[waynew]

This might not be correct.

Unless your saw is set to cut dead square to the fence using a square on the fence won't tell you how the saw tracks. Really, the saws always tracks straight anyway. It can't do otherwise since it rides on two straight rods.

Michael,

I think you misunderstood what I tested here. I was NOT testing squareness to fence. I placed a square against the blade so the squares edge was parallel and just touching the blade teeth. I then pulled the saw toward me for the full length of travel, the result was that there was an approx 1/32" gap between the blade and the squares edge. For this test I could have used a rule of any straight object. I know this is slightly different to what MiterMaster was suggesting in his last post but I think its more relevant.

Thanks,
Wayne

 

[waynew]

Just to be sure about the suspected travel problem (as stated in my previous post) I checked again and I suspect this test is more difficult to do accurately than it appears due saw tooth unevenness and the difficulty getting the steel edge exactly parallel to the blade in the first place. It could well be that the steel edge is slightly angled outward.

I'd like to thank everyone for their help, especially Rick who I think nailed it as 'operator error', which I'm now thinking is the problem. We'll see how it goes from here.

Best Regards,
Wayne

 

[Steveo48]

Bad blade. Out of tension or dished. I can guarantee if you "sight the blade" on start up and coast down you will see it flutter or wobble. You can try rotating the blade 90-120 degrees on the arbor and try again, that might cancel out the cut issue but chances are another blade will do much better.

This was my thought too, especially with it being clamped and the way the cut looks.

Also, I have to bring this out, I'm reading excited comments about the quality of cut.  It's all about the blade guys, a high quality blade will give you a glassy, smooth cut on the cheapest saw.  A POC blade or one that is worn won't, even on a $1,300.00 saw.  My Amana blade is a gem mounted on my 10 YO DeWalt, I wouldn't trade it for anything.

Steve

 

[greg mann]

By the way, even if the saw head was skewed relative to the linear slides, it would not result in the significant step at the end of the cut.  The sharp step is indicative of lateral movement without forward travel. A skewed saw head would result in concentric sweeps on both sides of the cut, and one side would show sweeps from the back of the blade, and the other side would show sweeps from the front of the blade.

Rick, I agree with everything you said in this post except part of this above. If the blade is skewed to the travel path of the linear posts only the leading edge will be visible on one side. We are in agreement there. But, on the other side of the cut the trailing edge will be visible only up to the spot where the trailing arc can go no further. You cannot slide the trailing edge all the way through the cut unless you move your workpiece far enough away from the fence for the trailing edge of the blade to pass all the way by the workpiece. You can still test this way but this is what I would look for.

1. Clamp both sides of the workpiece, preferably a relatively wide board.
2. Make a sliding cut and let the saw come to a complete stop.
3. Pull the blade out and without disturbing the boards measure the kerf at the entrance and exit points.

The exit point will only be cut by the leading edge while the entrance kerf will be widened by however much skew exists.

 

[Michael Kellough]

It's a simple fix to get the blade back in alignment.  If I'm reading your response correctly, simply loosen the 3 screws holding the miter tab in place, with the screws loosened, gently tap the scale to the left, check with your square and bring the blade back in alignment.  Once in alignment, re-tighten the 3 screws and try your cut again - see if this fixes your problem.

Even if it does not fix your problem, at least you will know this was not the cause and you can rule out that possibility and move on to the next possible cause.

Mike

Mike, this is a very bad way to adjust the miter scale because you may alter the radial position of the scale instead of just rotating it about a center axis. I am currently floundering in a quagmire of legally required safety warning edits, but a new (yet still unreleased) copy of the manual should be available in the next couple of days. For this reason, I do not want to post a link to the existing copy except for the forum thread where it is already posted. Search for all of my posts and you will find the link to the Supplemental Owner's Manual.

The fence is adjustable isn't it? If you take off the height extensions the fence base can be adjusted to the miter scale (assuming the answer to the question above is yes). I'd expect the fence to already be square from the Festool factory. Might not expect it from some others.

Waynew, laying the straightedge against the teeth (multiple teeth) is only useful if the blade is perfectly flat, or, you want to convince yourself that it isn't flat.

 

[Michael Kellough]

Nice Greg!  100% on.

 

[Spike]

Hello Gentlemen,

The blade is deflecting at the end of the cut. This occurs when a weak blade (too many anti vibration slots in a thin kerf plate) either exits a cut or is cut off from it's constant power supply and the tension relaxes. Speaking of tension, there is VERY little tension in this blade, as a matter of fact, it is not even roll tensioned let alone a hammered plate. The plate tested at a 48 Rc (pretty hard steel in layman's terms).

An improperly tensioned blade will always dish or cup towards it's power supply meaning the inner arbor flange and motor.

The only way to avoid any cutting issues on any miter saw is to use the stiffest/thickest plate obtainable with NO anti vibration slots and a plate that is properly tensioned is critical. To dial the tension dead on the saw maker would need to know the exact machine RPM's and determine the rim speed of the blade, this way the blade will not deflect at all. Some makers of miter saw blades use an average RPM that most miter saws fall within to tension their blades by.

One other very important piece of the puzzle here aside from plates is the tooth geometry. The best miter saw blades have 0 or negative hook angles up to -5 degrees, this reduces the "grabbing" effect that a standard 10 - 20 degree positive hook angle can cause. Also a negative hook blade prevents the saw plate from running out in a cross cut. The Festool blade does have -5 degrees of hook angle.

Next in geometry is top bevel angle. Some blades are referred to as "Hi ATB" This is a blade that if you view the blade straight on facing you the left / right high corners or tips of each tooth are beveled down quite steeply. This angle is critical to cutting performance and specific applications. I prefer 25 - 30 degrees of top bevel. It's benefits are many, the first is a VERY clean and quiet cut on all sides of the material being cut, especially the exit cut or backside of material that is against the fence. The other benefit of a Hi ATB is less shock to the blade on the blades immediate entry into the material. Blades want to "self right" or correct themselves when they first begin their cut and the RPM's drop a bit. Sometimes you will notice a series of small "steps" in the top corner of the piece you are cutting...then a perfectly smooth face cut on the remaining end grain. What happened here was the blades tension slightly changed and flexed or deflected until the blade was 1. Supported by more material on both sides.  2. The tension was more in line with the RPM's.

In closing, pick a miter blade that has:

-5 degrees of hook angle.

+25 to +30 degrees of top bevel.  ATB geometry.

+20 to +25 degrees of top clearance angle (Don't worry much about this one, most are).

AND A TENSIONED PLATE WITH NO ANTI VIBRATION SLOTS (Not yelling but I can't stress this enough).

If you happen to not have this type of blade and you are getting a great flawless cut, get to Vegas quickly...you are a fortunate and lucky individual who happens to have a blade that is perfectly matched to your exact machine and I can bet you that putting it on a similar but different machine will achieve completely different results.

Spike.

 

[vrasilla]

GOOD INFO spike, thanks,  I have seen this kind of cutting results before but never knew the analysis of why.  Always kept trying to adjust the saw to no end.

VR

 

[Spike]

Hi Rick and everyone,

We all have our favorite blades and what we all think is best for the current job. Yes the Hi ATB is awesome for cutting veneer and even melamines but at a cost, the point or tip of the Hi ATB wears quickly. Some manufacturers have gone to a 38 degree Hi ATB, this is simply too steep.

Tracking or deflection issues on an ATB or Hi ATB during a cross cut operation is almost non existent due to the grain orientation or "crosscutting action", the blade comes down through the wood fiber and severs off the end grain fiber. However, ripping with an ATB or Hi ATB can cause great tracking and deflection issues, especially at higher feed rates. This is why dedicated ripping machines like Mereen Johnson, Diehl, Mattison, SCMI and others use exclusively a Z=24 (24 teeth) Flat Top. All 24 teeth are flat topped and track straight but leave a bad scratch pattern in the wood, to counter this blade manufacturers developed a flat top with a triple chip grind (TR-F), in other words every other tooth has it's corners chamfered at angles of approximately 20 to 30 degrees and the hook angle is almost always 20 degrees, MUCH to high a hook for crosscutting.

I can get extremely technical here and lose most of you and get way off the topic of helping Wayne's issue while still discussing saw blades in depth, next class is alternate face sheer, double side grinds, rim speed and chip load calculations, clipping blades, segmented hoggers, PCD, inserts, and on and on. I have spent a good part of my life designing saw blades for Germany's leading saw manufacturers and industry like the FDM300 list.

What we all want to do is get a great cut while performing our craft. At least I do for sure.

Let me know how I can help

 

[Tony M]

T.T.T

 

[Marhk]

Those of you old enough to have used a radial arm saw will recognise this problem. The blade is rotated on its bracket so that it travels forward through the cut with the back closer to the board than the front of the blade. So, if you move the test board to the other side of the blade this will not happen - you won't see the burns or marks. However, the blade is not cutting efficiently in this attitude. It needs to be adjusted - rotated with respect to the bracket that it hangs on - so it travels straight, exactly parallel to the traverse rods. I don't know how to do this on the Kapex but I suspect there is a way. I don't own one.

Note that adjusting the fence or the miter position will not effect this problem. I also suspect that the blade is not the issue or everyone would have the problem. However if you do see burning or marks when cutting on the other side then one would have to suspect the blade or bearings.