5-cut Calibration Method

[Woodhack97]

First off forgive my ineptitude.

Used the 5-cut method for the first time recently (It's amazing how much useful info is in the manual!). I measure the offcut with dial caliper and get the following:

Offcut at right measures .3725 in.

Offcut at left side measures .3680 in.

.3725 - .3680 = .0045

.0045 divided by 4 = .001125

So my saw is out about 1/1000th of an inch? 

 

[waho6o9]

I'd say that's perfect.

 

[Rick Christopherson]

For more information that is directly applicable to your Kapex, you may want to look at the Supplimental manual. http://www.waterfront-woods.com/festool/Kapex_KS120.pdf It describes the methods and includes an angle calculator to help you interpret the results.

Oops. I was reading too fast and see that you did use the manual in your process.

I would suggest putting your numbers into the built-in calculator and looking at the "angular error" in deciding whether it is good or not. From what you posted above, I would venture to say that it is so close to perfect, that attempting to make it better will likely make it worse.

 

[rdesigns]

That's the thickness of a playing card.
If you were checking the bevel angle, I'd say, Good enough.
If it's the miter angle, you could do better. Use a playing card to gauge the distance you need to correct. (or a feeler gauge, of course.)

My Kapex' miter cuts were perfect according to the 5-cut method. I fussed over the bevel angle till it came out perfect too.

Love that Kapex!

 

[Rick Christopherson]

That's the thickness of a playing card.
If you were checking the bevel angle, I'd say, Good enough.
If it's the miter angle, you could do better. Use a playing card to gauge the distance you need to correct. (or a feeler gauge, of course.)

My Kapex' miter cuts were perfect according to the 5-cut method. I fussed over the bevel angle till it came out perfect too.

Love that Kapex!

Actually, that is only 1/2 the thickness of a piece or paper. However, what is missing from the original posting is "How long was his cut". 0.001" over a 10" cut, for example, is a super-good value. 0.001 inches over 1" may not be that good. So this missing piece of information is important to know.

 

[Woodhack97]

Oops forgot that piece of info.

I was checking the vertical bevel angle. The length of the offcut  was 3 15/16". Still good?

 

[Rick Christopherson]

Oops forgot that piece of info.

I was checking the vertical bevel angle. The length of the offcut  was 3 15/16". Still good?

With the numbers you have provided, this gives you an angular error of 0.016 degrees too far to the left. For a bevel adjustment, that is very good and should not be touched.

This error is so close to perfect on a bevel that simply changing your hand positions and methods will give you different results. In other words, this is within the bounds of the "human factor" while operating the saw.

 

[woodie]

I'm trying to figure this out for calibrating my MFT/3 as well. I entered my info in the PDF but it wont calculate an answer. I'm using a Mac so perhaps Preview won't allow it to work properly.  I just tried entering the formula on a calculator. Just to be sure I wasn't doing it wrong I entered the OP's info but my result is different than yours Rick. What am I doing wrong?

Here's a screen shot from the calculator.

So for the OP's info I'm getting -.00028 ?

My cut on the MFT/3 resulted in:
.505" Left
.5525" Right
10-7/16" Length

I'm getting -0.003. Is this right?

 

[Steve R]

Can someone point me to the rules for this 5 cut competition? Never heard of it... did this just come out in Popular Woodworking? My goal is not to cut twice and still be too short...so five cuts seems like a really bad thing... [eek]

Cheers,
Steve

 

[Rick Christopherson]

Woodie,
If you are viewing the PDF embedded into a browser window, it is possible that the built-in calculator may not function. Try downloading the manual and open it directly in Acrobat.

As for your calculator, the reason for the difference is because your calculator is working in Radians instead of degrees. If you convert your 0.0002857 radians to degrees, you get 0.016 degrees. Spreadsheets like Excel do the same thing by default. You have to tell them you want degrees.

 

[Rick Christopherson]

Can someone point me to the rules for this 5 cut competition? Never heard of it... did this just come out in Popular Woodworking? My goal is not to cut twice and still be too short...so five cuts seems like a really bad thing... [eek]

Cheers,
Steve

First off, the name "5-cut" comes from a math error made in a magazine article years ago, but has unfortunately stuck. It is really only 4-cuts that are necessary.

Secondly, 4-cut (or 5-cut, if you prefer) is the name of a calibration method of compounding an error 4-times to make it more accurate to measure that error. If you have a really small dimension that you need to measure, you multiply that dimension by 4-times to make it easier (more accurate) to measure.

As for the background for this discussion, go to the Kapex manual link in my first posting above, and go to pages 24 through 27 for a complete explanation about it. It is a common calibration procedure that can be used for many of your tools, not just a miter saw.

P.S. If it helps, here is the core image pertaining to that discussion in the manual. Notice how each of the successive offcuts is getting worse and worse in their error (1x, 2x, 3x, & 4x). However, any cut made beyond the 4th cut will still remain at 4-times the original error. So making more than 4 cuts does not make it more accurate. This will make more sense after you read the discussion in the manual.

[attachimg=#]

 

[Rick Christopherson]

My cut on the MFT/3 resulted in:
.505" Left
.5525" Right
10-7/16" Length

I'm sorry, I missed this part earlier. These numbers plugged into the PDF's built-in calculator result in an error of 0.065 degrees to the left. For an MFT setup, I would not consider this to be acceptable. On something as long as the fence on an MFT, you should be down in the 0.010 degree range (or lower if you wish). When precision is critical, you should be able to calibrate your MFT down to 0.001 degrees, but this is such high precision that simply moving your fence would require a new calibration.

The longer the length, the more accurate the cut could/should be calibrated.

 

[woodie]

Thanks! I was able to get my MFT to 0.016 before calling it a night [smile].

 

[Deansocial]

i thought the idea behind 5 cuts was that your first cut gives a nice straight edge to put against the fence to start the 4 cut and it is also the cut to measure off

 

[Mettes]

I was taught not to measure the difference but to see/feel the difference.  When you do the 4th cut, that piece should be perfect parallel if you have a 90° cut.  When you break that piece in two and put the two ends at your flat machine table you can see/feel if there's any difference.  That way you can test the squareness of your machine even when you don't have a caliper at hand.

I too make 5-cuts, the first to be sure I have a straight edge to start with against the fence.

 

[Rick Christopherson]

i thought the idea behind 5 cuts was that your first cut gives a nice straight edge to put against the fence to start the 4 cut and it is also the cut to measure off

That would be a matter of stock preparation, not part of the calibration. Unless you're picking through scraps at the bandsaw, they should already have at least one straight edge.  If nothing else, it's a jointer operation. You should never cut a piece of wood on the miter saw if it doesn't have a straight edge against the fence.

 

[BCConstruction]

hey guys im trying to calibrate my saw.

Im still confused after reading this thread

i have

0.292" to the left cut
0.299" to the right cut
total length is 8"

problem is the festool PDF calculator is not telling me how much im out in degrees

 

[Rick Christopherson]

It gives me -0.013 for your numbers.

 

[BCConstruction]

It gives me -0.013 for your numbers.

So is that's pretty much square then.

 

[Rick Christopherson]

Yes. A 1/100 of a degree on a miter saw is very good and probably not worth tweaking.