Ryan can answer of course. I would just mention, they do the opposite of evacuating the chips out of the slot. They are pressing the chips into the slot.
Yes, I understand that chip evacuation is an issue with downcut. just didn’t think that it would be a huge issue with a total DOC of around 3mm. Am I mistaken about that?
Probably not mistaken. My experience with cutting hardboard was the same: fuzzies, sanded off. I think it’s what pretty much everyone gets with cutting hardboard. It’s got its own characteristics.
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Downcut bits can clog easily when doing a contour cut
Even if you’re making 3mm DOC passes, in the end you end up cutting the whole thickness of material, and dust accumulates into the slot
This accumulated dust will pack and make a hard aggregation when it’s pushed by the bit, causing missed steps and failed cuts 
When using a downcut bit, make sure you have a large roughing pass, so that the slot is as wide as 2 times the bit’s diameter, this will leave the dust a place to go…
Also, I found reversing the vac and using it in “blower” mode can help disperse the dust quite a bit, although it’s very messy 
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Just my 2 cents. I typically will start deep slots or pockets with a down cut bit for a pass at 1 mm for clean edges and little to no fuzzies. Then I switch to an upcut bit to finish. While it takes a bit change, the cleaner edges pays for itself with less sanding afterwards.
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Its a two flute so not super well suited for our RPm, the chips pack down so you have to cut slower. I would try other materials before you switch to downcuts.
I understand what you are saying, and my initial thoughts were to use a downcut bit in very limited circumstances, specifically only with 3mm hardboard, where the total slot depth only requires a single cut, and only to reduce the “fuzz”,. So I thought that the slot wouldn’t be very deep, and that perhaps dust accumulation might not be too much of an issue in this specific application, but…
This to me is a very compelling argument, and a very good point. I would have to slow the router way down and speed the feed rate way up to maintain the same chip load, probably hitting the machine limits on both variables.
So it looks like single flute and sandpaper going forward.
Thanks for the feedback all!
Chiming in to muddy the water. I have used two flute downcut bits on 12mm ply a lot . Two passes at 6.25 DOC without tabs. The chips would pack into the cut and hold the parts in place. The time saved was worth any shorter life of the endmill for me.
I find this use case highly intriguing…
It’s what I used when I was selling these: Plant Stands
I didn’t want to trim tabs and was cutting full nested 4x8 sheets of them. It was a real time saver for me.
Well two months later…
Since my last post here I have finished working on the cars, and managed to get a bit of progress on my LR3 build:
- Designed and built a tilt-away/roll-away table base.
It makes a huge difference in being able to move the LR3 out of the way so that I can get the cars in the garage when needed. Link to the thread is here.
- Installed the hardboard struts that I cut back on Jan 07 (post #105 in this thread)
The hardboard has a LOT of flex, so my plan is to cut out some blank struts from 3mm aluminum sheet (salvaged signs) and place them behind the hardboard struts. I also want to paint the struts (probably black on the aluminum and red on the hardboard, to provide a contrast for the lettering), but that can wait for now.
I also put some epoxy on all of the non-captured nuts, so that adding the aluminum backing hopefully won’t be too much of a PITA.
- Installed an Air Mist system for cutting aluminum
I used @DougJoseph’s kinematic tool holder (modified with @jamiek’'s “mountains and valleys” fixed and mobile parts), and Doug’s Air Mist Attachment (Side mount version model B). For more info you can check out this thread.
I still have a few bits and bobs to mount the air hose system to the table (valves, elbows, etc), and I had a couple of hiccups with printing the tool holder (post #200 in the tool holder thread), but overall it works great!
- Designed and printed a “quick release” system for my built in vacuum/dust collection hose.
I had a bit of an issue where the outside of the prints were very close to the design value, but the inside of the print (hole) was about 0.5mm too small. I used post-processing (sandpaper) to make it work, but it looks like I need to go into Cura and play around with the “Hole Horizontal Expansion”" settings.
Coming up - I bought some 9mm aluminum for the YZ plates, and I scrounged a bunch of 6mm aluminum for the XZ plates, and now that I have the air mist system up and running, I’m working on setting up the files in Estlcam to cut those items. I’ll probably do some test cuts with the 3mm aluminum for the strut backing first, but I need to finish removing the vinyl and adhesive from the old signs before I start that.
Whew, that seems like a lot of progress!
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Wow, this is awesome! Thanks for the updates and info!
So a bit more incremental progress to report…
While I’ve been procrastinating (er, umm, I mean researching aluminum cutting feeds and speeds), I decided to do a bit of cleanup on a few items.
First of all I mounted a power bar with a kill switch, and a shutoff valve for the air supply to the mister assembly. I put it near the future Min X Min Y location (I’ll be converting from Portrait to Landscape shortly) so that it will be close by when starting cuts.
From there I ran some air hose and an extension cable to the midpoint of the rear of the table, and made it so that everything can be quickly disconnected.
Next up I installed a “drain wire” inside the section of vacuum hose that connects to the LR3 for static grounding.
Also I designed and printed a bottle holder for the Iso-Propyl Alcohol (IPA) for the mister system.
Coming up, I really have to get off my a$$ and start cutting the aluminum struts, followed by new aluminum XZ and YZ Plates.
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Progress!!
After a lot of procrastination (er, um…I mean research), I think I have sorted out the feeds and speeds for cutting my struts. I used G-Wizard (CNC Kitchen) to come up with the following suggested rates for 2.5mm DOC, Single Flute 1/8" mill, with 0.35mm finishing pass:
Any comments/sanity checks are more than welcome.
After a bit of a misadventure trying to figure out EstlCAM parameter sets, I managed to create and save the g-code for a variety of different speeds. Tomorrow (or at least this weekend) I hope to do some air-cuts to test for excessive vibration and shaking at different speeds, and then hopefully start making some aluminum chips!
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Even at 2250 mm/min, there really doesn’t seem to be any concerns about vibration or shaking, at least with the air cut. I’ll try actual cutting as soon as I get a couple of hours free to devote to the project.
1350 mm/min @ 0:00
1685 mm/min @ 1:12
1965 mm/min @ 2:12
2250 mm/min @ 3:15
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Great progress, then a great setback…
The day started out well, with the first cuts in aluminum. I went with the 20000 RPM settings, because it said that it would only take about 2.5 hours.
(turn down the volume for this video)
The chips looked really good, mostly smaller segments because of the Trochoidal milling, but some good spirals in there as well…
The AIr Mist system worked really well, and blew all of the chips out of the cutting path quite well.
I made it all the way through cutting all of the screw holes, as well as the first strut part, when disaster struck…
I put screws into several of the strut screw holes to secure the material to the spoil board during cutting. I had EstlCAM Clearance Plane set for 3mm.
When the first part was finished, the gcode called for a rapid move to the next part. Unfortunately that path was right over (through) one of the screw holes that had a screw in it, and there was contact. I had used a mix of 1/2" and 1" screws, and fortunately the screw in question was one of the shorter ones, so it pulled out rather than snapping the end mill. However the resulting loss of steps caused the router to start cutting into the just-finished strut part.
So the next step now is to re-run EstlCAM to produce a new gcode with a 5mm Clearance Plane, use Notepad to remove everything up intil the start of the second strut part, re-home X & Y, reset Z using the touch plate, and try again.
I did notice a couple of issues during the initial cut:
- Every time my compressor kicked in (8-10 minute intervals), the ensuing voltage drop resulted in the router speed decreasing enough that I could hear a change in the cutting. The chips still seemed ok, but it sounded like it was struggling a bit.
- EstlCAM estimated that the whole thing should take 2.5 hours, but cutting the holes and one of six struts took over an hour, so the actual time is more likely going to be closer to 5-6 hours
More updates once they happen
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If I’m not too late for a suggestion I would go higher with your clearance plane. Always better to have too much than not quite enough. I was using screws with 3D printed washers for the V5 parts and I believe I set mine at 10-15mm. Way more than I needed but never once did it get anywhere near a screw lol
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I was going to say the same as I was reading it. I keep mine at 10…for peace of mind
So I made the changes noted above (and increased the Clearance Plane a few more mm as recommended), and restarted the cut. Before doing that I checked the end mill and noticed a bit of aluminum welding to the cutting edge, so I changed out the end mill for a new one. Probably happened when the mill tore into the material and I had to hit the emergency stop.
It all went well for about 90 minutes, and then the mill snapped off. Kinda surprising, because the material was well secured (so no chatter), the air mist (IPA) was keeping the slot free of chip buildup, and the sound of the cutting was consistent with the previous 2.5 hours of cutting.
I may need to pick up a few more end mills before I start up again, and the program ran for a few minutes before I paused it, so I will probably have to figure out where in the gcode the mill broke, and edit to restart a few seconds before that point.
Only mildly annoying, and it is giving me a great opportunity to learn about editing gcode. Also gaining more experience with every hurdle. Pretty soon I might even have a clue about what I am doing! 
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