# 31.6 deg on Mitre saw, WHY?



## Joe90

Hi

As the title says... why does my Makita SCMS have the angle 31.6 degrees specially marked:?: I have never known the answer....  

1 point for the first correct answer!  

Cheers
Joe


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## Hitch

Isnt it for cutting large mouldings, on the flat that otherwise wouldnt fit in the saw?


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## Scrit

It's for cutting mitres on extra tall crown/cornice mouldings where the moulding is laid flat on the bed of the saw, the blade tilted to 33.9 degrees (i.e. bevel) then the head swivelled to 31.6 degrees (i.e. mitre) to obtain a 45 degree mitre. And BTW it only works with 52/38 degree mouldings - if your moulding is flatter or taller than that then you'll need to do a different calculation.

Howzat?

Scrit


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## Joe90

Howzat... yes, it's brilliant, still confused though

But not to worry, it's just very hard to visualise the resulting cut when the bevel is 33.9 and the mitre is 31.6 :shock: I'll take your word for it that it ends up as 45deg.  

It does lead to another question however.. what is a 38/52 moulding? I have copped onto the fact that 38 + 52 = 90 but that's it... I'm not even going to ask about the calculations to be done if it's not a 38/52 moulding! :shock: 

Slainte.


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## Argee

There's another page *here* that may help/confuse further 

[Edit] It contains "how-to" pictures and a comprehensive table of wall intersection angles.

Ray.


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## Scrit

Joe90":rastiicf said:


> It does lead to another question however.. what is a 38/52 moulding? I have copped onto the fact that 38 + 52 = 90 but that's it...


 
It's the angle of the back of the crown moulding. 52 degrees or 38 degrees are common angles in manufactured mouldings, although smaller mouldings or home-made ones are normally 45 degrees I find. I needed a spreadsheet and a bit of school geometry to work out that it was right when I first came across the solution, too

Scrit


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## Anonymous

Argee":3bezgwk2 said:


> There's another page *here* that may help/confuse further
> 
> Ray.



Very useful page Ray. Ta


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## Scrit

Joe

I have just dug-out the Excel spreadsheet for doing the calculation. It requires the spring angle of the moulding to be entered in cell A5, the corner angle to be entered in cell B5, the Mitre Angle Calculation formula in cell C5 and the Bevel Angle Formula in cell D5.

The Mitre Angle Calculation Formula is:

=DEGREES(ATAN(TAN((180-B5)*PI()/360)*COS(A5*PI()/180)))

and the Bevel Angle Calculation Formula is:

=DEGREES(ASIN(SIN((180-B5)*PI()/360)*SIN(A5*PI()/180)))

So entering a spring angle of 52 degrees would yield mitre and bevel angles of 31.6 and 33.9 degrees respectively, whilst for 45 degree spring angle the angles would be 35.3 (*note: typographical error corrected*) and 30 degrees respectively for right angle (90 degree) joins

The spring angle is taken to be the angle between the horizontal and the rear face of the moulding when installed:







Scrit


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## Argee

Scrit":2fe27l24 said:


> .... whilst for 45 degree spring angle the angles would be 25.3 and 30 degrees respectively for right angle (90 degree) joins.


The correct angles are *35.26* and 30 degrees respectively for a 90 degree join..

All wall angle calculations from 67 to 179 degrees are covered in the table in the *link* I provided above.

Ray.


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## Scrit

Argee":2k8iol1v said:


> Scrit":2k8iol1v said:
> 
> 
> 
> .... whilst for 45 degree spring angle the angles would be 25.3 and 30 degrees respectively for right angle (90 degree) joins.
> 
> 
> 
> The correct angles are *35.26* and 30 degrees respectively for a 90 degree join..
> 
> All wall angle calculations from 67 to 179 degrees are covered in the table in the *link* I provided above.
Click to expand...

Finger problems again!  My spreadsheet does calculate it correctly at 35.3 and 30.0 degrees respectively if cut and paste into the appropriate cells.

The plus point of having my own calculation mechanism is that if I make my own mouldings they can be at any angle I choose

Scrit


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