Flex with Leveling Feet


(Chris Foley) #1

I have had minimal time to get my XXL setup but finally got everything square and calibrated except for tramming. While installing my T-Tracks, I noticed that I can move the center of the waste board 0.005" EASILY with little weight. This is not going to work for me.

So, I am off to build a torsion box today (ugh). I do not have planer so this is going to be an experiment to see how straight my table saw will cut. I do not think a perfectly flat torsion box is REQUIRED as I believe I will need to shim the XXL anyway. I am just going to make a 48x48 table and see how that goes.

I have seen posts about this but how much effort was required to level the unit without the feet? How many shims do I need? lol


(William Adams) #2

Each machine is a bit different, but 4 leveling points underneath seems typical.

One interesting option is to put the machine on a sheet of insulation foam — I have my XL on a yoga mat on a Baltic Birch plywood board.


(Daniel Story) #3

Pretty sure the bed has no support in the center, as it is mounted on top of the Y-Axis steel brackets causing it to float above the table allowing flex. Think you’d need to support the bed in the center to help or use a stiffer/stronger material (aluminum bed).


(mikep) #4

Yes, it does flex a bit. I put 3/4" MDF underneath my machine under the wasteboard wherever I could fit it, took the feet off, and used a little silicone to glue the whole sandwich down to a bench (actually, the top of a rolling cabinet, but same difference…). This then leaves the Y rails a little less supported because it doesn’t have feet. So I put in M8 screws from the top of the foot PEM’s and tightened them down against the benchtop (very gently) to give the rails a touch more support. So far, so good.


(Dan Nelson) #5

I took off the feet and set my XXL on a foam mat, made thin MDF shims on my table saw to shim up the gaps. The whole thing sits on a 3/4” plywood top with 2x4” framing. One 2x4” down the middle, no real torsion box, no sag.

Dan


(William T Stokes) #6

I had two feet break in my recent move(no clue how) and replaced all four with a part from Amazon that WillAdams recommendedthat come 5 to a package, and after installing them I ordered an another package and installed with captive nuts in the table top-so that they snug up to the middle rail under the Wasteboard on my XXL, between the middle fasteners in the three formed steel supports No play what so ever, and adjustable to keep it that way.


(William T Stokes) #7

Forgot to mention I slotted the threaded end so I could use a small screwdriver for adjusting from under the table, and a huge tanks to WillAdams for the suggestion of the replacement feet!


(Chris Foley) #8

What deflections do you get now after using these new feet?


(Chris Foley) #9

Will, on a mat on top of baltic birch? I tried that today and now I get deflections EVERYWHERE from 0.002 at the edges to 0.004" in the middle. I have one more thing to try before I start looking for rubber feet in bulk. :frowning:


(William Adams) #10

Once you surface it, it should stay level / trammed. The Baltic Birch plywood I’m using is on a table which seems sturdy and level enough, but I need to get a second sheet and some lumber and make a torsion box and machine countersinks for the PEM nuts (or remove them).


(Chris Foley) #11

Will,

I spent the entire morning doing some tests. Just my table at the sides with a 48" span will flex 0.008". So, I put mid-span supports across the outer edge. Now it moves about 0.003" Then put the forward support rail right over the top of the outer edge and got 0.020" when pressing straight down with my hands at mid span. I put shims under this rail at two points and now have that down to about 0.005" ish.

And still the middle moves about 0.025" or more. So I pulled off the T-track and wasteboard, removed half of the main mdf board. I put about 15 sets of shims under the formed edges of the supports…staggered between all three. I can still get 0.025" flex when pushing straight down with my hands.

So in my frustrated mode, I left the dial indicator in the middle. I pushed down on the Right Y axis rail and got about 0.0015" flex. Same story on the Left Y axis rail. Then I pushed down on the X axis rail just to the left of center, and got 0.010" flex. Then I pulled forward on the Z Axis carriage and with minimal effort, got almost 0.030"

So I think I am chasing minutiae in worrying about the bed flex. There are other issues to solve. I am going to shim the heck out of the rest of the bed as best I can, add some serious supports in the CENTER of my table. Then I am going to cut some “stuff.”

As I think of torsion boxes, I do not think this is going to help. You will still have to shim as the unit is not dead flat anyway. We are supporting in points. The only way to fix this is grout!!! j/k but not really. There are lots of tolerances built up in the frame when made of bent sheet as someone (Richard?) has pointed out already.

Now the forces at the cutting bit are what I need to focus on. Left to right and front to back, the XXL seems stable. The real worry is the flex/torsion about the X axis and we can control that with liberal roughing tolerances and making final passes very clean and light. At least that is how I am thinking at the moment.

Should get everything back together tonight and supported. Then I will surface the wasteboard and get my tramming set.


(mikep) #12

Consider how much force you’re actually putting into the bed with material you’re cutting - usually small, a few pounds maybe.

If you shim, and it still moves, that’s a pretty good indication your shims aren’t of an appropriate material. If you’re using construction shims (like you would use for doors), they’re going to flex. Placing blocking directly under the wasteboard will give you the best result, don’t get fixated on the feet and rails (they’re more trouble than good).


(Chris Foley) #13

That is why I did all the test today lol. I am making hardwood shims (out of old oak flooring) tomorrow morning. I got my Dust Deputy ready to go yesterday so I am now ready to NOT make a mess.


(Chris Foley) #14

Well, I did make progress today. I finally just moved the XXL off my table, added supports in several places (mid span on the outer perimeters and a middle support) and put a new 3/4" MDF top. I blocked up all the bent metal supports with MDF blocks and composite shims. Now the flex in the middle is less than 0.007" and at the edges, its hard to even get 0.0015" to show. I have moved on to creating a surfacing program in Fusion360.


(Miles Baughman) #15

Guys on your larger machines XL and XXL it seems unreasonable not expect variances you all are talking about in these machines types. Geeze guys even the MDF and Plywood can have the thickness differences or more you are all talking about due to environmental moisture conditions. If you getting middle sag put a tbolt in the middle for an adjustment screw or a simple shim (some tape). Surface your waste board and or a supplemental waste board.

Some examples:

.01" = .254 mm
.005 Inches = 0.127 Millimeters

These differences seem really small for this type of CNC setup!

Are these differences really effecting your end product?


(Dan Nelson) #16

On my machine prior to dumping the (un-)leveling feet and shimming the unsupported frame it definitely made a difference, especially if I had heavi-ish stock towards the middle and/or slightly aggressive plunge speeds. Cutting through a part cleanly without gouging into the wasteboard was impossible, everything had a slight ramp cut that was shallower towards the middle of the machine. May not matter to some, but it drove me nuts.

Dan


(Miles Baughman) #17

I understand, but resurface your waste board and or a supplemental waste board and much of this issue will be resolved. Even high end machines require resurfacing on large areas. I have seen some add an 1/8" piece of ply or Masonite below the work piece so if they cut through into junk.

xoxo


(Dan Nelson) #18

You can resurface all you want, but when the wasteboard flexes it will no longer be flat/consistent in Z. I chased this issue for awhile, surfacing, resurfacing, then I noticed the flex. Fixed that and it went away.

Dan


(Bryan A Spiegel) #19

I just leveled my wasteboard. Then on my first cut (just MDF parts for work holding) I had this exact issue, parts not coming out when they got near the center.

I did notice that one of my factory supports (center one) is bent on one side, so Im going to have to take it back apart and unbend, while at it, I might as well. add some feet. Heck, tempted to add some 1/4" square tubing under there with the mig.


(Stuart) #20

Flex was having a pretty big impact on my parts initially too. taking the levelling feet off helped for a while, but replacing the ‘base’ mdf board with 3/4" marine plywood changed the whole thing, solid as a rock now. I just sit a MDF wasteboard on top the size of the cutting area and surface that and haven’t had a problem since