I knew this was going to be fun... cutter dimensions

[jepho (Jeff Cable)]

Good evening. Having just bought my own static copy of Millalyzer, I thought today would be a great day to enter some of my endmill collection into the tool library. The tool library in Millalyzer requires numerical data to be added before completing the new tool entry. My example endmill bit to enter into the Millalyzer tool library is the one which was supplied with my new SO3. This is the Carbide 3D #201. I would like some assistance with understanding which of the parameters I should enter (as a minimum) and which could be omitted.

Carbide 3D #201 is supplied as a ¼ inch shank cutter with 3 symmetrically shaped and equidistant flutes. The cutting diameter is nominally ¼ inch. The shaft is the same diameter as the shank and there is no defined neck. The length of cut measures ¾ of an inch. There are no indications on the shank to guide placement length in the toolholder… which also holds an implication for exposure length. The overall length of the tool is 2½ inches. The helix angle is unknown and I have no data about the axial or the radial rake angles.

My thinking is that I should enter (as a minimum) each of the parameters in BOLD face:
Material: (all of my cutters are tungsten carbide tipped)
DC - cutting diameter
DMM - shaft diameter
LU - neck length… where a neck is present
DN - neck diameter… where a neck is present
LT - taper length… where a taper is present
LXP - exposed length… where the minimal stickout parameter is known
LF - overall length
RE - corner radius… where a radius is present
FHA - helix angle… where the helix angle is known
APMX - length of cut
GAMF - radial rake angle
GAMP - axial rake angle
EDRD - cutting edge radius
uneven flute Indexing and unequal helix are parameters which do not concern me now.

Questions:

1. Will the parameters in the bold typeface be sufficient data for Millalyzer to produce a useful result?
2. What is the method for measuring the helix angle if it is required?
3. What methods can be used to measure DC, where there is no available information?
4. Does the presence of a neck mandate parameter editing and further accurate entry?
5. Does the presence of a taper mandate parameter editing and further accurate entry?
6. Should LXP data be added regardless of the presence of a minimal stickout datum?
7. Can the rake angles be omitted from the tool library and the Millalyzer still produce good results?

I don’t know if a datum for stickout minima is the norm but all of my trend cutters have one.

Any and all answers are very much appreciated.

[Julien (Julien (Carbide 3D))]

I’m sure @spargeltarzan will answer all of those questions, but in the meantime that thread has everything you can possibly want to know about helix angles and how they matter in Millalyzer (sorry to be sending you down that rabbit hole)

[spargeltarzan (caveat calculator)]

First of all, for decent-quality endmills, the geometry should be provided by the tool manufacturer. Carbide3D chooses not to post that data on their website, but maybe they can provide data if you asked them (the grinder they buy the tools from must have that information).

For a plain endmill without a neck ground into it, you can set LN, LT and LXP to the length of the flutes, that is, the manufacturer-specified maximum depth of cut (APMX) plus maybe 0.1", and DN to the same as DC. The cutting diameter DC is equal to the nominal diameter (0.25") unless otherwise specified by the manufacturer.

The helix angle looks to me like approximately 40 degree. The best way to determine it with reasonable precision is to measure the distance along the axis for a known number of turns (that would be one-third turn for a 3-flute).

Rake angles GAMF, GAMP are very important for cutting force prediction. Large rake angles (20° or more) mean sharper edges and lower cutting forces, but can rarely be combined with high-helix 3-flutes (there’s no space for the grinding wheel to get in there). I would guess around 10° for the #201.

The cutting edge radius EDRD depends on the intended application (workpiece materials) of the endmill. The harder the material to cut, the larger the radius to protect the edge from chipping off. A good-quality tool for aluminium can be ground to about 3 µm (0.12 thou). Coatings necessarily add to the edge radius. High-quality DLC coatings can be made very thin (say EDRD 4 µm), ZrN and similar coatings are slightly thicker (EDRD around 7 µm).

Unfortunately, I don’t have the #201 in front of me right now, but this is what I would guess for the uncoated version:

(For the ZrN coated one, increase EDRD to 0.28 thou).

@jepho

Will the parameters in the bold typeface be sufficient data for Millalyzer to produce a useful result?
Can the rake angles be omitted from the tool library and the Millalyzer still produce good results?

No, the rake angles are needed, but a qualified guess will end you in the right ballpark.

@jepho

What methods can be used to measure DC, where there is no available information?

Equals the nominal diameter.

@jepho

4. Does the presence of a neck mandate parameter editing and further accurate entry?
5. Does the presence of a taper mandate parameter editing and further accurate entry?
6. Should LXP data be added regardless of the presence of a minimal stickout datum?

These dimensions are needed for tool deflection and dynamic analysis (chatter). They have no direct influence on a static force calculations.

[jepho (Jeff Cable)]

Thank you, Julien. I had no idea that becoming a hobby machinist would involve me in eating rabbit food and wearing an Alice in wonderland dress. Thank you for the link. I appreciate your subtle and oblique cri de coeur to the aptly named caveat calculator. His post has answered all of my questions.

[jepho (Jeff Cable)]

Hello @spargeltarzan. Thank you for a rapid, complete and concise response to all of my questions.

@spargeltarzan

maybe they can provide data if you asked them (the grinder they buy the tools from must have that information).

Yes, I will see if that question can be answered. I am sure that @WillAdams will be a good place to start.

@spargeltarzan

For a plain endmill without a neck ground into it, you can set LN, LT and LXP to the length of the flutes. The cutting diameter DC is equal to the nominal diameter (0.25") unless otherwise specified by the manufacturer.

Understood.

@spargeltarzan

The helix angle looks to me like approximately 40 degree. The best way to determine it with reasonable precision is to measure the distance along the axis for a known number of turns (that would be one-third turn for a 3-flute).

I see… is this a rule of thumb for any helix and flute number? e.g. a 2 flute helix would require the measurement along the axis to be made for a distance equating to 180°?

@spargeltarzan

I would guess around 10° for the #201.

That gives me a reasonable starting point and I will ask for a definitive value from Carbide 3D.

@spargeltarzan

The cutting edge radius EDRD depends on the intended application (workpiece materials) of the endmill.

My materials at this embryo stage of my learning to machine are going to be various woods. I will ask for this parameter value when discussing the #201 with Carbide 3D.

I really appreciate you for taking the time out to open my eyes to the subtleties which are inherent in selecting a tool bit for a purpose. Thank you.

[spargeltarzan (caveat calculator)]

@jepho

I see… is this a rule of thumb for any helix and flute number? e.g. a 2 flute helix would require the measurement along the axis to be made for a distance equating to 180°?

Sorry, I wasn’t very clear on that. To find the helix angle, measure the distance L parallel to the tool axis from one of the corner points to the crossing of the next cutting edge like so:

Then the helix angle is given by

where n_f is the number of flutes and D_c is the diameter.

@jepho

My materials at this embryo stage of my learning to machine are going to be various woods. I will ask for this parameter value when discussing the #201 with Carbide 3D.

It’s certainly good to start with wood. Forces are much smaller than with metals, so that there is much more margin for errors. That said, it is also a natural, anisotropic material with quite a bit of variability (humidity, branches, grain direction). So the bad news is that computations are necessarily approximate, but the good news is that the forces are quite small so that it doesn’t matter too much - unless you want to remove very much material really fast.

[WillAdams (William Adams (Carbide 3D))]

Unfortunately, I’m not able to help out beyond the numbers which are on the shop pages.

If there are specific numbers folks want to know, please check in at support@carbide3d.com and we’ll try to put you in contact with someone who actually knows — not sure about putting more information on the shop pages, but will check.

[jepho (Jeff Cable)]

Thanks for responding Will. I am unsure about the value in putting the endmill geometry parameters on the shop pages. What is there appears to be sufficient. A link to a page with more technical information could be helpful and would prevent that sort of mundane enquiry from cluttering up support staff’s task list. It is quite rational to expect people who are looking for that level of technical detail, to link to a page which is filled with the appropriate technical data. Anyway, I will check in with support as per your suggestion. (all this to mill a piece of wood!)

[jepho (Jeff Cable)]

@spargeltarzan

Sorry, I wasn’t very clear on that. To find the helix angle, measure the distance L parallel to the tool axis from one of the corner points to the crossing of the next cutting edge like so:

No worries… I ran with my dumb assumption that the third of a turn was related to a tool having 3 flutes. This is what you get when you (the sorcerer) take on a 72 year old apprentice. I understand how the helix angle is derived but need to go back to school for brushing up on the use of equations.

@spargeltarzan

That said, it is also a natural, anisotropic material with quite a bit of variability (humidity, branches, grain direction).

Thank you for the reminder that anisotropic materials are variable within themselves.

@spargeltarzan

So the bad news is that computations are necessarily approximate

Yes, I have concluded that milling is actually a dark and arcane art… rather than a science.

@spargeltarzan

the good news is that the forces are quite small so that it doesn’t matter too much

I see that… thank you for your patient explanation. It is very much appreciated.