Not level after flattening?

I’ll try to summarize :slight_smile:

I replaced my waste board. To avoid the flexing I was getting, I took out the stock steel supports and attached 3/4 mdf directly to a flat and level tabletop. I then secured the frame to the table around that. I ran a 1" flattening bit over the whole thing, taking down about 1/8". The end result was a nice, flat, smooth surface. Or so I thought. On bigger pieces, I notice the front cutting before the rear every time.

If the machine and waste board weren’t parallel, I would expect to see stepping when I flattened the board, but I didn’t get any. And wouldn’t flattening make the new waste board parallel to the router, regardless?

I guess I’m going to shim up the frame in front. Still don’t get why this is happening after flattening. The head should be parallel to the surface, even if they were not parallel when I started.

Indeed, after surfacing you should get a surface that’s parallel to the machine axes. If you don’t, there must have been something that moved after the surfacing pass. I did not quite get what the setup looks like at this point though. Could removing the steel supports have induced flex in the machine frame? While they may not have been supporting the wasteboard suite enough to prevent any flex, they still contributed to the overall machine rigidity?

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Before flattening, I secured the wasteboard to the top with 12 screws, the frame was screwed down through 4 existing holes that were for the support pieces. I don’t see how anything could have moved. The whole thing sits on 1" OSB over a frame of 2x4s.

I measured the depth of the cut that the flattening made. The back cut down 2.09mm, the front 3.4mm (yes, it’s an island, but big enough to hold what I do)

I had the same problem with the previous wasteboard that was on the supports which is why I went this route. A co-worker set up the machine before I started, is there any chance something wasn’t assembled right? Doesn’t seem likely, but I’m reaching for answers! :slight_smile:

Pic of setup:

When you manually jog to the front and back, does the endmill reach the surface at a different Z at this point? Just checking in case it may be ok without a cutting load. Puzzling…

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There is a small difference. Zeroed on the surface w/ paper to get the zero for the rear, same for the front, .06 lower in front according to carbide motion.

Maybe you need to tram your spindle?


I would just try a fresh surfacing pass, and checking the Z front and back right after the pass, and then again the next morning.

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I had a terrible time with some orange box store MDF. I tried to prepare for a long v-carve by surfacing the night before and left it blue taped/superglued & clamped to the machine for carving in the morning. by morning it was a potato chip and carving was a waste of time, resurface, try again… I finally slathered on a spit coat of shellac on both sides, then resurfaced, and immediately recoated with shellac to keep it sealed until carving started the next morning. It would have been cheaper and easier to start over with better stock or wait until the dry days of winter. :confounded:


Yep, good point, what’s the humidity like in the work area? The MDF could be changing shape pretty quickly after one surface is skimmed, I’ve had a few boomerangs too.


To follow a reply down the page. I have to surface my waste board each week due to moisture. Yes, I need that kind of precision. My cuts are .001 and .002

Good old Washington Rain


Ugh, didn’t even think about humidity! That has to be it; I’m on the California coast.

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The MDF at my local Lowes is unlike any MDF I have ever used before. It’s sponge like almost and very soft apposed to the MDF my car audio shop gets which is rock hard and great to work with.

I should add it’s darker in color as well. My suspicion is they use a different wood fiber and adhesive that possibly doesn’t cure as hard.

The MDF I buy from Home Depot is pretty hard. It still soaks up the clear lacquer like a sponge, though.

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does anyone know where to get better MDF?

I’m not aware of any standard for grading MDF. I think the only thing you could look for is the density.

It looks like Lowes has 2 ‘grades’ of MDF. Industrial & Premium. No idea what the difference is.

I would think industrial supply stores (Grainger, Freeman, etc…) would be likely locations to look for better quality MDF. Whereas home improvement stores are probably getting their supply from the lowest bidder.

I have yet to find a good source of the small quantities I can store easily. I have gotten some from a local millwork/lumber yard when I have projects that require enough material to have free delivery. They seem to have much better sheet goods than the big box stores and will for a small cut charge break down a sheet to fit in your car. Pricing may be a bit more but at least I’m pretty sure it isn’t a sheet of compressed imported toxic waste.

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