I have my new Elite Foreman set up on a Kreg 64x64 bench. I ripped 1-3/4" wide LVL’s (figured more stable and stronger than 2x material) and installed them 12" on center and added blocking. Put 3/4" MDF on top of that, then additional 3/4" MDF on top of that for spoil board, ripped into 6-1/4" wide strips with t-track in between. The top is strong, I can stand on it with no noticeable deflection. I recently flattened the spoil board with an Amana 1-1/2" 4 cutter surfacing bit, 1/2" shank. When I put straight edge across the spoil board, it shows about .005 low in the center. Pretty consistent gradual dip from outer perimeter to center of table. I realize .005 is not much, especially for wood routing, but shouldn’t it be perfectly flat?
I can’t figure out what would cause this. Even if there was a slight dip in the table top, shouldn’t flattening correct that and make it perfect? I know this sounds crazy, but is it possible the weight of the spindle could be causing a slight downward deflection in the x rails (I do have the stiffy)?
The Onefinity tubes are strong, and reasonably stiff. But nothing is totally rigid, and the tubes do sag a bit under load. Before I added a Stiffy to my X-50 Journeyman, I measured (with a dial indicator) a worst-case sag of 0.005” on the X axis, with the spindle carriage centered, and also a worst-case sag on the Y-rails of 0.005” when the X-axis assembly was centered on them. So 0.010” of combined sag total in the center of the working area.
Addng the Stiffy reduced the X-axis sag to 0.004”, But the added weight of the Stiffy itself in raised the Y-axis sag to 0.006”. So the 0.010” “dish” depth wasn’t really helped by the Stiffy. But what it DID do was roughly double the rotational stiffness of the Z-slider about the X-axis. That was the problem I was trying to solve (to reduce the taper in holes I was boring) and the Stiffy worked quite well for that purpose.
As a practical matter, I haven’t found the tube sag to be a significant problem for woodworking. Worst case, 0.010” is about the thickness of three sheets of paper. And if you can keep your workpiece near the edges of the working area, the worst-case sag approaches the straightness spec of a precision straightedge.
Gantry-style machines with thick structural beams can be considerably more rigid, but those come at a higher price, and may not offer any real advantage for woodworking applications.
Thank you for the reply, Dennis. It’s good to know I’m not crazy! I guess I figured, especially with the stiffy, that the machine would be perfectly rigid. I debated long and hard between this machine and the Shapeoko 5 Pro… and ultimately decided this machine seemed more stable / rigid with the x50 rails and stiffy. Also factoring into my decision was the YouTube videos of people sitting on the gantry and riding it back and forth.
Where it is potentially an issue for me is I plan to occasionally run cabinet doors on the machine, and if you attempt a simulated joinery (paint) line with a V-grove bit, the depth and width can vary from door to door even just with the .005 difference. But I’ll deal with it… it is a beautiful machine and I’m beyond stoked to have it.
I told my wife I needed the $45,000 4x8 Legacy Maverick, and she wouldn’t let me get it. Can you believe that?
Yea, my wife can also struggle with even basic economics like this. I mean, $45k is way less than that new Ferrari you want, right? She should really be thanking you for being so frugal!
But seriously, if your cabinet panels are solid wood, or even MDF, you could surface them with the machine before V-grooving, and that should give you almost perfectly consistent line widths.
You’d be hard-pressed to find sheet goods that are consistently flat to within 0.005”, in any case. MDF is about as flat as it comes, and 0.005” is the industry-standard thickness tolerance, IIIRC. Plywood will likely be even less flat.
A machine that is not adjusted for coplanarity, i.e. is twisted, can let the wasteboard remain curved concavely after flattening it.
Surfacing the wasteboard will not help against lack of coplanarity (twisted machine base), the machine will only reproduce the twist on the surface of every workpiece you mill with it.
Thank you all for the input / responses… it is appreciated. I checked my machine for square, but did not check it for co-planer… never really thought of it to be honest. I’m a remodel carpenter, and I guess it’s similar to hanging a door, where the jambs can be ‘cross-legged’… same thing only on the flat with the CNC machine.
However, in my case with the Foreman, the ‘dish’ is center and the outer perimeter is fine all the way around. So it’s not really a ‘twist’… I don’t know. Again, showing about .005 with feeler gauges in the center only.
In any case, I have done several projects including a run of cabinet doors, and it doesn’t seem to be affecting anything… so I’ve decided I can live with it for now. Maybe I need to check my straight edge!!
a gantry-type CNC machine must be checked for twist. The fishing line method is easy for this. As I said, if not adjusted for coplanarity, a line on the wasteboard may be concave (have a gap to your straight edge in the middle).