Marking knife or pencil.

[Packard]

In another thread, it came up that a marking knife gives more precise results than a sharpened #2 school pencil.

I have a marking knife.  I can’t recall when it was last used.

I also have a Milwaukee “trim square” which is a carpenter’s’ square shrunk down to 4-1/2”.  I find it very handy.
https://www.finehomebuilding.com/2023/03/15/space-saving-trim-square

“… I’m a huge fan of the highly visible contrasting etched markings, and the dual-reference heel is great for marking thin stock and reveals where trim elements meet. One side of the heel has a 1⁄4-in. lip and the other side has a 3⁄8-in. lip...”

I used the 3/8” lip to draw a line down the center of a 3/4” thick piece of poplar.  Using a pencil and holding the pencil square to the surface the best that I am able, I made a line purporting to be the center of the stock.

I then flipped the square to the other side of the stock and made a second line parallel to the first.  I ended up with a single line, just slightly wider than the original line.

I then repeated this exercise using the marking knife and holding the blade snug up against the lip of the square for both sides.

With the knife, I ended up with two distinct lines, exactly parallel to each other and about 1/32” apart.  (It was difficult to measure, but clearly two lines.

So, is the knife more accurate?  Not here.  I am guessing that Milwaukee calibrated the legs to be used with a pencil.

See @ 2:00 minute mark.

 

[ChuckM]

One particular application where a marking knife shines is when the scribed line is used for registration, for example, for a chisel edge to register against.

 

[derekcohen]

Knife vs pencil?

Packard, it depends on the work you do, and the tolerances that are relevant for your work. I build furniture, with joinery needing to be precise. A pencil would not hack it. A knife line is several times thinner and this creates a more reliable reference.

What do you build?

Regards from Perth

Derek

 

[Packard]

It would be nice if Milwaukee identified how it was calibrated. Someone trying to be very precise and using a making knife with this square would be introducing an error by not using a pencil.

 

[ChuckM]

Snip. using a making knife with this square would be introducing an error Snip.

This unlikely will happen to any seasoned hand-tool user because the square is aluminum, and traditional woodworkers use a marking knife with a steel blade/square for scribing lines.

 

[squall_line]

I don't think the situation with the Miwaukee square is a difference between a pencil and a marking knife (although, as others have pointed out, a marking knife and aluminum don't get along very well... or they get along TOO well, depending on your perspective...).  This seems to be purely a matter of either the stock not being a true 3/4" or the square not having a true 3/8" lip.

That said, even Woodpeckers recommends using the 3/8" lip on their DelVe square to marking from both sides of nominal 3/4" stock when attempting to find the true center of the stock.  There are three scenarios here:
-the lines perfectly match, making the line the center (and meaning your lip is half the width of your stock, regardless of either one's true measurement).
-the lines are each shy of center by a small amount, making the center the halfway point between both lines.  This also means your stock is more than twice the thickness of your lip, regardless of either one's true measurement.
-one line is hidden by the lip when you mark the other line, making the center the halfway point between both lines.  This also means your stock is less than twice the thickness of your lip, regardless of either one's true measurement.

Assuming your stock is a true 3/4" and assuming the lip on the square is a true 3/8" would only apply in high-precision machining.  And even then, I would still flip the square and use it from both sides to verify the true location of center, or use some sort of self-centering parallelogram arrangement to mark the centerline.

 

[Cheese]

A marking knife will always be more exact than a pencil...just decide upon the amount of precision you need.  [smile]

A pencil line is easier to see, the marking knife not so much. Also be aware that with some deeply grained woods, you need to control the marking knife as it will follow grain patterns unless you assert dominance.

 

[Packard]

A marking knife will always be more exact than a pencil...just decide upon the amount of precision you need.  [smile]

A pencil line is easier to see, the marking knife not so much. Also be aware that with some deeply grained woods, you need to control the marking knife as it will follow grain patterns unless you assert dominance.

More exact, but not necessarily more accurate.

I took my vernier calipers to the trim square.  The side of the ledge that is to measure 3/8” actually measured 0.3685” to 0.370”.  Some of that variation can be laid to the difficulty of holding the calipers exactly square to the surface.  If it is not exactly square, I was measuring a slight diagonal. 

However, I am confident that the 3/8” is undersized.  That lead me to reason that Milwaukee calibrated the square to be most accurate using a pencil of some sort.

That reasoning goes out the door when I measure the 1/4” side which is under sized by just 0.001” - 0.002”. 

So I don’t know how Milwaukee intended me to use this square, but I will get more accurate results using a mechanical pencil or a freshly sharpened school pencil. 

In fact, only Incra really states that they are calibrated for a mechanical pencil.  And Incra’s measuring tools are less susceptible to “operator” error.

Additionally, the Milwaukee’s ledge is slightly bellied out on both sides.  I can practically guarantee that the die that produced the extrusion is not bellied out, but rather, is perfectly square.

Extrudes (both in plastic and aluminum) will try to speed up the process to maximize profitability.  The problem occurs when they speed it up to the point that the aluminum is not entirely solid as it exits the mold.  When they speed it up that fast, some deformation occurs while cooling.  In this case, it results in that belly on both sides.

I would note that the effect of speeding up the production of plastic parts is much more detrimental.  Most resins will shrink as they cool, so pulling injection molded parts before they are entirely cooled and solid will allow the parts to shrink, sometimes to the point where they are not usable at all. 

In any case, I think I will simply call this Milwaukee square as not being a precision instrument.  (And, I am guessing that my 3/4” thick poplar is not going to mic up at 0.750” either. 

In the end, I don’t think my post answers any questions; it just creates new questions.

 

[six-point socket II]

I use three different types of tools for marking, depending on what I do/need.

1) Pencil. From .5 to carpenters pencil, different grades, some mechanical some not.
2) Marking knife. I have a beautiful forged and chisel ground, but yet simple form follows function type Japanese knife for that.
3) Scriber/ scribing iron. For the very few times I do anything metal.

From my (little) experience aluminum squares/rulers and marking knife don't mix well.

Keep in mind, I do many different things for my projects, I don't have that "one thing" I always do which then has become a routine over time.

Kind regards,
Oliver

 

[demographic]

The parallel lines part suggests to me that the  person using the marking knife didnttake the direction of the knife bevel into account?

 

[Michael Kellough]

The parallel lines part suggests to me that the  person using the marking knife didnttake the direction of the knife bevel into account?

Or it indicates that the depth of the ledge is either greater than or less than half the thickness of the stock.

 

[Packard]

The parallel lines part suggests to me that the  person using the marking knife didnttake the direction of the knife bevel into account?

Or it indicates that the depth of the ledge is either greater than or less than half the thickness of the stock.

I agree.  I already established that the 3/8” side of the ledge did not measure 0.375”.

I did not measure the exact thickness of the 3/4” stock.

I recently bought a few sticks of 3/4”  nominal stock.  I did not run the pieces through the thickness planer.  I built Shaker doors from that and after assembly I had to sand the joints to give the appearance that they were all of the same thickness. 

A rookie mistake, but I hadn’t had any issue with thickness for a very long time.

Any rate, two lines could mean the measuring tool was off, the material thickness was off, or operator error when marking. 

As I was marking the piece as a test and was paying particular attention to my measuring protocols, I am laying the error at the feet of the Milwaukee square, and possibly on the thickness of the stock.

 

[Crazyraceguy]

I've got one of those little squares too. They are quite handy, but I've never used it to mark parallel lines.
As a lefty, I really appreciate the double beveled type of marking knife. The regular single sided ones are always the wrong way for me. Most of the time a pencil mark is good enough for what I do, but the knife does come out occasionally.

 

[Mini Me]

A little off topic but a handy instrument to mark a line in both wood and metal with very good accuracy.
https://www.ebay.com.au/itm/3944810...LVb2KOzakxK80LWS-FgB1-aV_b_b_UThoCG3kQAvD_BwE

 

[Cheese]

I just ran across these things downstairs...Accutrax pencil blades that load into a conventional utility knife. I purchased them 10 years ago and have only burned up 1 of them. I remember them being pretty tough and not being susceptible to breakage. They may be a solution for someone...I just prefer to use a mechanical pencil.

I noticed that Woodpeckers still offers them.  [smile]
https://www.woodpeck.com/accutrax-pencil-blade-3-blade-packs.html

[attachimg=1]

 

[jaguar36]

Whenever I am particularly interested in being accurate I will use my wheel gauge  And whenever I'm super concerned I'll set it with a caliper. 

[attachimg=1]

 

[Packard]

I just ran across these things downstairs...Accutrax pencil blades that load into a conventional utility knife. I purchased them 10 years ago and have only burned up 1 of them. I remember them being pretty tough and not being susceptible to breakage. They may be a solution for someone...I just prefer to use a mechanical pencil.

I noticed that Woodpeckers still offers them.  [smile]
https://www.woodpeck.com/accutrax-pencil-blade-3-blade-packs.html

[attachimg=1]

Amazon and Lowes has a similar model based on the snap off blade concept.  Lowes is showing this for $4.00/ pack of three.  Amazon is more than twice the price.
https://www.lowes.com/pd/SHARPDRAW-Sharpdraw-Replacement-Lead/1000478935