To build or not to build... that is the question

For, tis nobler to continue on with the MPCNC, or would thoust do better with a LR2?

This has probably been gone over multiple times, but…

Here’s where I’m coming from… for as good as the MPCNC is, I still have problems with rigidity. I don’t know if it’s my router not perfectly perpendicular to the part, or what, but I get stuttering where the Z axis vibrates sometimes. I’ve tried to iron it out multiple times, but I just can’t tell if it’s the gantry flexing or what. Whatever it is, I can never seem to cut fast enough to get good chips, so I know my bits are running hot.

I basically want something that can cut a bit faster or a bit deeper… or both. Some of those big CNC routers on the market look like they’re flying compared to my MPCNC.

Would the LR2 do better at this? I’m thinking I could possibly do a 2’x4’ LR2 to replace my 2’x2’ MPCNC.

Where does the MPCNC shine that the LR2 falls short?

Tighten your pulleys, bro!

I have no actual advice here. Just wanting to taunt you. I am sure you know as much as anyone about it. Was size is the mpcnc (including Z)?

should I fill my tubes with concrete?

Cut size on the MPCNC is 2’ x 2’ .

I just went and looked. Looks like I’m still cutting about 3" below the bottom of the gantry. Maybe I do still have too much stick-out.

If you’re telling me that this is why I’m still getting chatter, then I’m going to kick myself… then I’m going to go get more MDF to reduce that by half again.

I already have 1" of MDF stacked to reduce the spoilerboard to this depth.

Maybe I should build a spoiler Box. Most of what I cut is 1/4" plywood cutouts for my wife. The reason I have suck a high Z from the gantry to the spoilboard is because I occasionally do jobs that are 2-3" tall that I want to engrave the top or bottom. I’ve envisioned using the CNC to cut a scalloped edge on a bowl after turning it on the lathe… just haven’t done it yet.

You should be able to fly through 1/4" plywood with a 1/8" bit. Are your bits sharp?

I am just going through the stuff you’ve seen here approx. 10k times. I am not trying to shame you, just saying take this with a grain of salt.

It would be an easy/quick setup to clamp down a 2x4 to lift up that spoil board up. Do you think your chatter is consistent enough to know right away? I would guess, on a veteran machine like yours, to be able to cut through 1/4" in one pass, at 8mm/s. I would expect trouble if you were using a downcut bit, or one with lots of flutes.

First, get some charcoal briquettes, and douse them with lighter fluid. Really soak 'em good. Stand back and throw a match at them. After you put your eyebrows out, get your steaks on fast, before the flames die down, and you miss out on the good sear marks…

Brand new bit. Full DOC. I think I was running 400 mm/min which is ~6.6 mm/sec. From what I can tell part way through cutting a 14" circle the bit chattered somewhere and caused 1 maybe 2 missed steps. When the bit got back around to the beginning of the circle, it didn’t line up with where it started. From what I can tell, it would have been in the first part of the circle when the bit was being dragged away from the gantry in both the X and Y axis (if that makes sense). Kinda a worst-case direction.

I need to check the machine for any cracked parts. Now that I think about it, I did hit a hold-down screw the other day. I wonder if it dug in and broke one of the plastic parts again. The machine cut 3 of these circles fine last week, so I thought everything was OK. Then on Saturday, it didn’t make a perfect circle.

Don’t worry about treating me like a Newb. There’s times where you forget the most basic of things to look at.

@jeffeb3 already brought up the pulleys, but I’ll note that about a week ago I noticed my Lowrider cutting circles that weren’t perfectly round.

Watching closely while jogging the machine around made it pretty clear I had 1mm or so of backlash in the X axis. A bit of disassembly verified that the grub screws had backed off and the pulley was loose.

My Lowrider has been spot on for about 6 months prior to this, so those grub screws are worth re-checking.

What you got hanging off the front there?

I’ve got a bigger footprint and a longer z axis and I am not getting chatter. Wonder if some strategic videos of the machine doing some different cuts might help trace it down.

It’s my shop vac attachment. The hose is supported from the top of the enclosure, so almost no weight on the machine itself.

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Find any issues yet? You are running on the large size but not THAT big.

Arcs on or off, what firmware version? Any chance you accidentally snagged a belt at some point and didn’t notice messing it up?

1/4 ply is pretty thin and flexible. If you are using an upcut bit, could the chatter be from the material lifting? Do you get chatter on thicker material? Does it go away when close to a hold down screw? If so, you may need to double stick tape the whole piece, or try a downcut? Just spit balling.

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Too many variables. It’s not happening often.

I did recently realize I was creating files with arcs on using an older firmware. I reprocessed my latest project to turn Arcs off.

I’m going to keep monitoring it. It seems to be more random as to when it happens. Could just be a fluke.

I have a 2 hour job I hope to run tonight that’s doing a large 3d pocket in a block of wood. There will be a ton of movement as it chews out the material. We’ll see if something fails.

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Back to my thoughts of building a LR2…

I’m going to start playing with making large cutting boards for some friends of mine that BBQ. These will be ~20" x 24". Will the MPCNC handle surfacing something that size? If not, will the LR surface something ~2" thick?