I did a few practice runs on MDF, and my cuts came out very clean and needed no finishing. Can y’all have a look at my attached picture and tell me if this appears to me material issue, or a bit issue? The material is walnut.
That looks like Material to me.
MDF doesn’t have grain, it’s sawdust and glue, so it shears and turns to dust pretty rapidly.
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Upcut endmill?
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That’s the culprit.
I get the best results, especially with hardwoods, by starting with a downcut endmill leaving a one or two millimeter “skin” then removing that with an upcut endmill.
Theoretically you can get the same results by using a compression endmill but, in my experience, getting the feed / speed right with a compression endmill varies between “difficult” and “impossible”.
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Well, I just accidentally hit the e-stop button…very expensive lessons today…bleh
As long as your piece didn’t move you can still save it. Have you turned off the vacuum table yet?
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Yikes! I hope the next attempt goes better.
I re-homed it. I also had another mishap, so the pieces are junk. I’ll just play with it now and move on…part of the learning process…just wish it hadn’t cost me $80 in 8/4 walnut 
I will try the next round with the bit strategy above.
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I’ve scrapped the first 3 name plates I was making.
Before I attempt the second run, if I do as advised (start with down cuts with all my runs, and then finish with upcuts) can I expect to have a reasonably finished piece of wood? Or will I still see quite a bit of the tear out like I saw with the upcut bits? If y’all think that Walnut should mill fine, I’ll place this on hold until my new mills arrive and try will new end mills.
I always find these in the vacuum tube. They fall out Everytime I’ve used the machine. Where are these coming from?
People choosing to cut instead of pocket. (Saves time in setup and in cutting.) It has the side effect of increasing the chances of a ruined project / broken endmill when the loose chunk of wood binds with the endmill (if the chunk is captured otherwise they tend to be ejected away).
That has worked very well for me but most of my work is with Baltic birch. I cannot remember if I have or have not machined walnut. The best choice is to machine something small (insignificant) as a test. If the test piece is too small to be held by the vacuum table it can be screwed to a larger board (try not to run the endmill through a screw).
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Am I missing something? I think you would want to start with upcut for clearing the large area and then final pass with downcut it to get a good edge on that pocket.
I think you’re looking at it from a different perspective, if I understand everything correctly.
Brian and Clayton are talking about doing the initial cut at full width with a downcut, which will pull the grain into the cut and should result in a cleaner shear. Then do the final depth of cut (where the bottom of the wood will be cut) with an upcut, again, pulling the wood into the cut for a cleaner shear.
You are talking (I think) about doing an initial pass at depth, but not full width, with an upcut which should clear chips better. Then finishing up with a downcut at full width, pulling the hangning fibers into the cut for a clean edge.
i think it’s just 2 different ways of arriving at a similar destination. I imagine each experienced miller has their preferred method, and everyone else’s is wrong. Clayton’s working up to his own sect…
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Except that a roughing pass with an upcut endmill is likely to cause chips to tear out past the final cut. You would have to leave a large area for the finish cut.
I wouldn’t bother with finishing with an upcut either, though. The material, if vacuum held, won’t chip out much, if at all. And it is probably the back of your piece.
In this case, he’s cutting a pocket, so no concerns about chip out on the back side.
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A downcut endmill also has the net effect of applying some downward force on the stock further holding the stock in place.
An upcut endmill does the opposite. Occasionally to the detriment of a project.
I tend to get not-quite-90-degree edges with a downcut endmill. I assume chips collecting in the kerf deflect the endmill. A pass with an upcut endmill takes care of both (nice clean edges; chips cleared).
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It’s probably because of my science background but this is my approach to making pretty much anything. Dyeing leather? Test a bunch of scraps to work out method. Trying the table saw crosscut sled for the first time? Better believe I’m using scrap wood. Haven’t sweated copper pipe in 5 years? I’ll buy a couple extra fittings to practice on. Making stuff is supposed to be fun, and going full-speed right out of the gate with the “real” thing is too stressful for me!
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@jwilson75503 I did test runs…they just did not perform the same when I swapped materials.
What I really need to do is stop tying to use the big tools at the Space around holidays and after 7:00 in the morning
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I’ve had great results on Walnut, Cherry, Purpleheart, African Mahogny, Mahogony, etc using Downcut endmills only. On Plywood, I use compression bits only. I’ve never seen a situation where i felt an upcut bit was the right choice. Of course, I wasted a lot of good stock learning that, as others here can attest. The CNC loves some hardwoods. Cherry is my favorite, but Walnut wouldn’t be far down the list.
My Advice is:
- Learn and understand fully how to calculate and adjust (in vCarve and at Runtime) Chipload.
- Buy your own bits, and toss them if you even think they even might be getting dull. I keep the following bits with me, but some are for detail work not all will find useful.
Machining
- .25 and .125 DC endmills (always at least two each)
- .25" Compression bit (2)
- 45 and 60 degree vbits, 1/2 diameter
- .125 and .25 ballnose
Carving - 1/32 tapered ballnose
- 1/16 straight cut endmill
I built these up over 5 or 6 projects, but have tried to keep them maintained.
- Never trust the vacuum hold down. Always affix the stock to the spoilboard using screws or a clamping fixture, Don’t say you weren’t warned.
Start working hardwood with Cherry. Its the easiest and most forgiving to work. Not the cheapest, sorry.
Once you get the hang of it, its really amazing what the tool can do with hardwoods, truly.
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