Mentorship Please & Thank You

[jlurban (Jim Urban)]

When I decided to purchase my SO I did so with nothing more than a good idea to create something unique but with zero experience using a cnc. I’m definitely feeling overwhelmed these days as a result of my ignorance.

With the help of a couple members was able to correct an incorrectly positioned set screw issue the other day. Things were going good after that and I was able to complete my first flip project I was quite pleased with.

Then on a subsequent and identical job I ran into another problem when my tool did not clear my material post job completion. I had turned off the spindle and the tool became lodged in my material as the SO was going through its homing sequence. I did an emergency stop, closed out of CM and then attempted to (re) initialize the machine however it failed to home on the z axis. Upon closer inspection I could see the upper stop rod between the Z+ plates was cattywampus. This required disassembling the Z+ to remedy. The upper stop rod had backed out of the threading and became a wedge of sorts. Additionally the guides that ride up and down the Z rail began spitting out ball bearings. Ask me how fun those are to reinsert (ha!). After a bit of TLC I was able to get everything reassembled and functioning properly - “I think.”

Comfortable with the operability of the SO I decided to run another double sided project. The first side was uneventful and the mill was flawless. Ten minutes into the second side and things take a turn for the worst - the roughing passes begin drifting on a negative x axis.

Having just dealt with the mechanical issues mentioned earlier in this post, I am relatively confident the x axis pulley set screw is good and the tension on the band is tight.

A few concerns come to mind as I try to pick apart what I’m possibly doing wrong here. First a background story on my material and tool path.

I’m using cheap white wood (fir) as I try to gain confidence in my machining. This material is 17x7x3.5 (4x6 and 2x4 laminate).

I’m using a trial version of meshcam to create the gcode and using CM.

I’m using a .25 ball mill for both the roughing and finishing pass (though I’ve been contemplating using the 201 to rough and the ball mill to finish).

I’m running 18k and 72 ipm for the rough, .125 offset and step down with a max dept 1.85. 10k .1 and .1 for the finishing.

I am seeing a pattern with knots in the wood. I’m guessing these are problematic for the end mill and could be contributing factor to my tool drifting once it runs up on it. Thoughts?

The strips of wood remaining from the roughing passes seem excessive to me and could be contributing factor to the drift though I don’t have a trained eye or the experience to say otherwise. Should I adjust my offset and step down to minimize this “fire tender.”

Grateful for the help I’ve received thus far. Feel free to chuck spears, name call, and ridicule - I have thick skin and can take the punishment.

[Julien]

Hi @jlurban,

Sorry to hear about those mishaps, but hang in there, they’re part of the learning experience. About your latest cut:
18k@72ipm and a depth per cut and stepover of 50% the endmill diameter should work fine, however:

• roughing with a ball endmill not ideal, so as you said, try using a #201 instead see if it gets better (it should)
• fir sounds safe and easy for beginners, but I think it’s actually not a good material for learning: it tears up very easily along the grain, giving those long strings rather than chips unless your feeds and speeds are just right AND your cutter is very sharp, and knots, as you said, can make the cut inconsistent in places. Something with a tigher grain is easier to cut and get nice results (=my opinion, others may disagree)
• in your case I would tend to think that your cutter has become a bit dull. Cutters are consumables, and we all wore them out much faster than expected when first starting/experimenting/abusing them using wrong feeds and speeds. It happened to me a couple of times that after scratching my head for a while trying to explore various cut settings, I finally “only” went and used a fresh cutter, and boom, got a perfect cut. I have learned to use a loupe to inspect the cutting edges, when it’s dull it shows.

Maybe you can check with support for a sanity check of the machine too after that crash.

[jlurban (Jim Urban)]

Thank you Julien for the reassurance and the advice.

I too considered the “abuse” I must have given the ball mill with the roughing work and ordered a replacement earlier today. Should I infer a ball mill is always best suited for finishing and never roughing?

I took your advice and ordered a loupe after reading your comments.

I have the carbide bitsetter on the work bench. It needs installed. I’ve yet to experience a tool change mid job and the nuisances that go along with it. For example, how much mental gymnastics goes into setting the tool path for the ball mill to clean up once the end mill is complete, or should meshcam do this for me?

[Julien]

@jlurban

Should I infer a ball mill is always best suited for finishing and never roughing?

Never say never, but most of the time you will be better off using a square endmill for roughing, indeed.
The geometry of the ball endmill makes it better suited for finishing, along curvy surfaces.

Don’t worry about the BitSetter, it will actually simplify your workflow, because you will not have to remember to re-adjust your Z zero after changing tools, so one less opportunity for mistake.

I do not own MeshCam, but since it (also) works with the Nomad, which has a tool length sensor (=a small integrated BitSetter…), I would think that it will allow you to generate the roughing and finishing tootlpaths in a single file with appropriate tool change commands in it, such that it will work fine with the BitSetter.

But for now, I would advise not to install the BitSetter just yet, and sort out any remaining issue you have first, to get a good roughing cut and most importantly to feel confident (I know how it feels after a crash or really bad cut…)

[jlurban (Jim Urban)]

I appreciate the sound advice. I’m likely at a stopping point until the new ball mill arrives in a few days. Silver lining - I can do more reading on the forum and less posting (grin).

[Julien]

Do you have any square endmill you could use to practice/test the roughing toolpaths themselves ?

[jlurban (Jim Urban)]

Just so happens I do. NIB Spetool.

[Microwave_Monkey (Scott)]

@Julien

fir sounds safe and easy for beginners, but I think it’s actually not a good material for learning: it tears up very easily along the grain, giving those long strings rather than chips unless your feeds and speeds are just right AND your cutter is very sharp, and knots, as you said, can make the cut inconsistent in places. Something with a tigher grain is easier to cut and get nice results (=my opinion, others may disagree)

I can’t agree more. It is obnoxiously loud to cut and stringy. If you are lucky enough to get your hands on a harder tight grained piece, it likes to chip out on fine details without meticulous toolpath management of how the cutter approaches said detail. Pre-HDZ, I found the knots/sap and varying density required me to slow down my feed so much that I know the cutter was going to end up dull much faster than it should have. If you are stuck purchasing from a big box store, I would grab some poplar as it results in a much better cutting experience and final product. I should add that I am a little biased, it is one of my favorite woods to “play” with and is relatively inexpensive for me to get my hands on as it is widely available in my area for only pennies more than pine/fir of the same size.

@jlurban, that looks like a piece of “framing” lumber. The trees have to reach a certain size before harvesting, and I have no idea what gets “pumped” into them or what method is used to get the crazy amount of growth in so little time, but it results in a grain density disparity between the “spring” and “fall” growth that never ceases to amaze me. Then it gets kiln dried/heat treated which does a whole other set of weird, albeit temporary, molecular stuff that compounds that issue. Granted, I can’t imagine milling “green” wood would be very fun or end up in awesome results, either.