Plastic machinability info

The best solution - for plastic for example - use a single flute, max the spindle RPM, Machine with a feed of at least 1000mm/min and take shallow passes.

Ok, trying with a single flute it's my next step. But... what the diameter of the bit should be? As I see, the Stepcraft works better with big diameters when you have to go deeply in the material.
Yesterday I made a test: I have returned back to a 3.175mm 2-flute end-mill:

rpm = 20.000
doc (depth of cut) = 1mm
feedrate = 3.3 mm/sec

A lot of noisy vibrations everywhere even, after one minute it starts to lose steps on the X-axis (!).
I remain of the same idea: for me nothing is better than a stiff tool (5mm-6mm dia)

The shallow passes also helps as the STEPCRAFT is not a heavy stiff production router - so with a 6mm cutter there is a lot of leverage of the cutting tip over the machine.

T
exactly - its called a spring cut.

- Machine down in the steps of 0.5mm or 1mm or whatever you use... but leave a space of say 0.1 or 0.2mm from the final geometry. so there will be a faint line in the wall where the steps are each time.

- now machine down the full depth - so 20mm per pass - but now take the shaving (0.1 / 0.2mm) off the wall - this will give one clean face at the end.

Ok, I will try to leave just 0.1 or 0.2mm as steps of my top-down-pyramid and, after, apply a "spring cut".

In the meanwhile another record: using the "pyramid" technique I have milled 2,1cm deep into a POM-C block! Amazing! That was 3 steps with 7mm height (7x3=21mm) and 1mm of offset between the steps.
As final step I've erased slowly the steps of the pyramid to make the walls perfectly vertical. The finishing is not the best, I think the "spring cut" will work better

router spindles have terrible torque at low RPM and are often air cooled..

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Yes, I've got sensation of that. I reduced the rpm of my 2-flute/6mm-dia to 6.000 rpm and... after less than minute I broke the material. So it's better to keep our babies at high rpm.

Again, the idea of the single-flute + high rpm is really good IMO.

Noise and vibrations - drop the pass depth. try 0.25 as example? Its better do do this and run the machine quicker.

Let us know the results of the single flute. You can get single fluted cutters for plastics.

Noise and vibrations - drop the pass depth. try 0.25 as example? Its better do do this and run the machine quicker.

I reduced just the DOC (Deep of Cut) from 1mm to .30mm and noise and vibrations are greatly reduced as you said.
Anyway, even with previous settings, they was at tolerable level. I think that 0.5mm is the best compromise between speed and vibrations.

For the ones of you that loves strong emotions: in the attached photo you can see a pocket 21mm deep (low quality, I made it with mein Handy.)

My last result as combination between the TODOP technique (Top Down Pyramid) and the Swing Cut one (by Rory).
I have slightly increased the DOC (Deep Of Cut) and the feedrate too. Very low vibrations, I'm satisfied.

TODOP params:

Material = POM-C
RPM = 20000
Feed rate = 250 mm/min
Plunge Rate = 90 mm/min
DOC = 0.5 mm

Swing Cut params:

Material = POM-C
RPM = 20000
Feed rate = 400 mm/min
Plunge Rate = 90 mm/min
DOC = 2 mm

IMPORTANT NOTE: above swing cut parameters works well only if you have to refine just the thin steps of the top-down pyramid (0.5 mm for every step, in my case) and produce a rectangular box. If you want to produce rounded corners for the box while applying the swing cut ten I strongly suggest to lower DOC and feed rate both.
For example, to round my outer box with 3mm-radius corners I had to lower Feed Rate to 300mm/sec and DOC to just 0.8 mm to avoid typical rrrrr-rrrrr-rrrrr vibrations.

Here below, a 2x2 cm experimental bulge. The height is 2,1 cm:

(don't take care if one side of the Pyramid seems slightly crashed, I didn't calculate the X-Y position of the box very well :blush: )

The steppie 300 is a great machine!!! B)

Prologue:

I have obtained results above by modifying manually the code produced by G-Simple for "digging" the trench around the box. I have "interleaved" the instructions such as the tool never plunge into the material more than 2 mm. In fact, a deep trench (lets's say 6/7 mm) large as the diameter of tool itself doesn't provide enough room for "natural" vibrations of the tool shaft.

I have adopted the following strategy:

1) use a large (and rigid) mill bit (6mm in my case)
2) plan the cut such has the Pyramid can be excavated by using just two concentric trenches surrounding the box
3) mill the inner trench for max 2 mm deep into the material
4) mill the outer trench for max 2 mm deep into the material
5) repeat step 3 and 4 until the target deep is reached (and overlap partially the trenches when a step of the pyramid is reached).
7) apply the final "swing cut"

In this way, both trenches "advance" down into the material almost "in parallel". The max difference in the advancement is max 2 mm. So the tool has always as minimum one side free for his vibrations. In other words it is never "enclosed" between two vertical walls of material.

Question:

is there any CAM software applying this strategy for deep cuts?
In fact, Z-slicing (waterline technique) it's useless for our small routers: you can destroy the tool or the material when cutting deep.

Well done - really great work.

The only way to learn really well | is to DO!!! 🙂

Also "spring" cut. sorry - I must have spelt it wrong.

really good work on your steppi.

One other general comment - if you have a corner radius there is a little trick you can use.

- lets say we are using a 3mm cutter diameter.
- if you make the corners of the machine toolpath radius 1.5 then the machine will "dwell" or be in the corner and stationary for moment as the movement translates from X to Y etc.
- make the corner 1.6mm radius so the cutter is always moving this removes this small dwell time and can eliminate vibration in the corners well
- if using a 6mm cutter - make the corners 3.1mm radius (not 3mm). this will improve the finish also.

@rory:

Oh! "swing cut" in place of "spring cut" was my typo, entschuldigung. 😳

Really good trick the one about rounded corners/angles, thanks. B)

Now I'm waiting for my single flute mill-bit, but there are the Easter holidays in between.. 🙂

looking forward to seeing the results. I think you will get much better results. The results on our larger router are much much better... but not sure about the STEPPI

looking forward to seeing the results. I think you will get much better results. The results on our larger router are much much better... but not sure about the STEPPI

Finally! After two weeks, I've received a 6mm single flute mill from cnc-plus.de.
I made some tests on the fly. Results seems much better than the ones with the 2-flute, wow!

But I would like to make some other tests before reporting here my impressions. Stay tuned.

Single flute End-Mill fully promoted! 🙂 🙂 🙂

Rory was right, another life with a single flue on POM-C material. Vibrations are reduced of 50-60% and the tools cut more smoothly than with a 2-flute mill.
Now I'm a fan of single-flute mills.

As you can see in the photos below, I was able to cut a 2 mm contour around a box till the deep of 23mm (2,3 cm). This was problematic with a 2-flute, too many vibrations.

During next days I will try to dig do some deep pockets, but I think I will not have problems.

Here below the main data (I was able to slightly increase the feed rate with the 1-flute mill):

Material = POM-C
RPM = 20000
Feed rate = 285 mm/min
Plunge Rate = 90 mm/min
DOC (Deep Of Cut) = 0.5 mm
Tool = Solid Tungsten carbide single-flute, diameter 6mm by cnc-plus.de (fantastic tool)

Please note:
To do the cuts above the Steppie must be in perfect order. This means:

- you should see all the wheels of the portal rotating when portal move (even on the Z-axis!)
- all the wheels should be not too loose and not to tight (use the "tuning" screws on the portal)
- when gently shaking the Z-Axis with the hands it should not have tiny/micro movements
- all should be greased and oiled
- use only rigid tools, i.e. with large diameter (5 mm or higher)

Have fun! :side:

Very impressive results. well done. that is an amazing result with the STEPPI!!

if you read this thread - Julius has put in many many hours of tuning and tweaking to get this far... so its not just as simple as getting a single fluted cutter. You have to have the STEPPI perfectly setup to achieve this.

Just to say it again - moving from a double flute to a single fluted cutter has the same effect as going from a feed rate of 1000mm/min to 2000mm/min...

Keep us posted on the deep pockets.

Keep us posted on the deep pockets.

I forgot to update you about deep pocketing with a single flute endmill!
Here we are.

I have to say that I'm little bit disappointed by working on POM-C/Delrin with the single flute. The problem is not the quality of the horizontal surface but the rate of vibrations when going deep into the material for more than 5 or 4 millimeter.
I mean... it works but I hear some grrr-grrr noise. This noise has two phases:

1) when plunging vertically I hear a robust GRRRRRRR
2) after, when the endmill starts ti move horizontally, I hear grrr-grrr-zzzzzzzzzz, grrr-grrr-zzzzzzzzzz, and so on.

I strongly suspect that the main problem is the remarkable asymmetry of the tip of a single flute endmill.
When it plunge down into the material it touches the surface only with the tip that is located far away from the central vertical axis of the tool, this cause a small deflection in my opinion. Deflection is not a big problem when the pocket is 2 or 3 mm deep, but for lower pocketing it happens that the position of the tool is not precise. When the tool starts moving along the walls of the pocket it is a little bit "pushed" against them, cause is not perfectly aligned. So the strange noise.
If the toolpath along the pocket-wall is long enough, after a while, the endmill "find" his road and the noise ends.
The same happens with less rigid diameters of the tool (i.e. 3mm)

Final evaluation (vote from 0 to 10) for single flute

Deep pocketing: vote = 6
Swing-cut/side milling: vote = 10

So, in my opinion, the single flute is absolutely superb/magnificent when you have to refine the external contour of a shape (as well as refining the internal walls of a deep box). No doubt, in this cases go for a single flute. It scratches the vertical surface like a knife and causes zero vibrations/noises.
In all other cases the two-flute is to be used, is more "smooth" in my opinion.

Final final final considerations

What above holds for Delrin/POM-C material, but I have tested the single flute on a more softer material like PE-300 (aka PE-HD) and I discovered that is really all-in-one end mill. You can use it for deep milling as well as for side milling with no problems.
PE300 has a density of 0.93 gr/cm3 (if I remember right) where POM-C is around 1.41 gr/cm3. So POM-C is much more harder and is not the best for an asymmetrical endmill.

As I said before, the profile of the bit that I used is shaped like the eagle's beak, maybe using a single-flute endmill from Onsrud results could be better (the tip of the endmill is completely flat). But this is only an idea/impression.

Tschussss!

Thanks for this information Julius....