Luke11CNC Build Log ,I'm so naïve

[JAZZCNC]

Jonathan: Yes I do always put something between the bed and part. Depending on the job at hand.?
If it's a non critical job that the top surface be exactly parallel to bed or thru drilling then I just use any thing to hand that resonably flat IE MDF off cuts.
If it's more important it's parallel to bed but doesn't need to be exactly 100% perfect and doesn't have any drilling involved then I use a 1mm thin ridged card board I bring from work that doesn't compress.
If it has to be exactly 100% perfect and must cut thru or involve drilling then I have several sized 15mm HDPE slabs that I clamp to the bed then surface. MDF is no good for this because the minute you cut the top layer it turns into a shape shifter and no matter what folks think MDF aint flat or parallel thickness.
To be honest 60% of the time the card board is used 30% MDF 10% HDPE.

That said regards MDF.? I've just been given an MDF type paper product sheet that is resin impregnated. It's used to make the cubicles in swimming baths and shower area's. It doesn't swell no matter how wet, even when submersed under water. This I know to be true because this sheet was outside for 8mths.
I've just used a piece as a spoil board and it machines like plastic and surfaces with a perfect finish because of the resin.
Really it's the perfect product for a long lasting disposable bed topper.! . . thou I do understand it's very expensive.

James: (Or anybody who's interested)

Here's how I did it. (It was a bit tedious but worth it) . . . . Material 1"1/2 x 5/8 (38.1x15.88mm)

Using a 90Deg spot drill in the spindle find the centre of bed and scribe boxsection. Then mark the first strip exactly in the centre then bolt down exactly in the centre of the bed lining up with scribed mark.
Then using a 8mm spacer working out both sides bolt down each strip to bed. Then using a 8mm twin flute end mill create a climbing milling toolpath to cut the 10mm slots in 2 depth pass's, didn't want to use a 10mm endmill as it would have been cutting on both sides and required much less DOC taking longer and leaving a worse finish. . . .(Yes I know the 8mm cuts on both edges but only on the way up not down.)
Reason I did it this way was because I have some machine clamps that use 45mm centres. They could have been just butted with a 10mm spacer but there are other bennifits to machining the slots for me(see below). . . . Plus the strips arn't exactly straight.!!

Doing it this way I know exactly that all my slots are exactly parallel to the X axis. Across the very top (Yaxis) and down the outer edge (X axis) as a strip that bolts on top of bed and acts as referance edge, which again is machined parallel and square. I've made some 45mm wide aluminium strips (various lengths from offcuts) that have a 3mm notch down the centre with the edges machined parallel that fits tight into the slots and can be used as positionable reference edges anywhere on the bed ( WHY.? Because I like to cut in differant parts of the bed to save wear on the ballscrews from always cutting in the same spot.)

James I would go with the 3/4 or better still 1" the little extre expense will be worth it.