CNC Vacuum bed query...level issue

[Gary-Wiant]

I'm new to cnc as well but I'd surface both sides of the spoil board, while you do want to ensure that the spoil board is flat the reason you've been told to surface both sides is to remove the hard surface on the MDF to allow better draw from the vacuum motors.

Good luck
Gary

[dragon_sa]

I'm new to cnc as well but I'd surface both sides of the spoil board, while you do want to ensure that the spoil board is flat the reason you've been told to surface both sides is to remove the hard surface on the MDF to allow better draw from the vacuum motors.

Good luck
Gary

Cheers...taking the hard finish off is spot on why both sides...I am also going to route a 1mm groove in the back of the spoilboard where the rubbers are so they dont get crushed

[routalot]

I don't understand what kind of 1mm groove you are proposing or it's purpose as the total force acting on the board is a function of the area and the level of vacuum.Could I suggest testing the vacuum force generated before surfacing anything,then again after surfacing one side and finally after skimming both sides?The answer would be of interest.

[Gary-Wiant]

Yeah that information would be interesting. Also check with your lumber supplier & see if you can get an LDF or ULDF

[dragon_sa]

Groove will be 1mm deep 5mm wide, to match the 4 outer border zones of vacuum, purpose is to seal but not crush the rubber piping I have that will be pushed into outer borders grooves in my rubber bed...the mdf will also be screwed down to stop movement with no vacuum. I will log the pressure gauge with and without surfacing on the 16mm mdf spoil board, but I don't believe that will be a very accurate way to determine

[routalot]

I have to say that I think such a groove will be unnecessary.The only times I have used a small rubber gasket on a CNC machine were to recess into the top of the spoilboard to seal a fairly small item to the machine.It is normally sufficient to just fix the spoilboard to a clean,dust free surface.The usual vacuum systems are high flow, moderate vacuum, pumps which can easily accommodate quite a bit of leakage and which will easily hold a sheet in place without applying anything close to a full vacuum.The type of vacuum system normally used for gluing tends to be of the moderate flow,high vacuum variety and they rely on a good seal.I doubt you will do any harm by adding grooves but it is adding work.

[dragon_sa]

So heres the results for my scenario....
I edged the mdf screwed it down every 600mm with brass screws, then surfaced the board, the result gave me suction thru the board but I found I had leakage under the edges of the board and that the work would sometimes start to lift in these areas.

Next I pulled the boards off, inserted the rubbers around the edges and added fixings every 300mm aswell...as I found the mdf would create humps at 600 centers, I then grooved the back of the board to match the rubbers...
I had to resurface my spoil board again to level it...the result of this was really good suction..to the point where a 100x100 peice of mdf feels like it is glued down to the bed with the vacuum on.

[routalot]

I am glad you have a solution that works.I don't entirely understand the comment about the mdf creating humps every 600mm in the initial situation.If the spoilboard is surfaced under vacuum it should be flat although the flatness might not be apparent when the vacuum is absent.It would be great to see you post a few images of things you are now able to make with the machine as it might inspire other people to try getting creative.

[dragon_sa]

I found after screwing the mdf down to the rubber deck..it seemed to warp it as the screw centers at 600mm apart was not enough to compensate for the movement of the mdf..this in turn created a speed hump between screw fixings..I believe also helped facilitate leakage...to fix this issue I re drilled the deck with another set of screw inserts and brass screws in between the original fixings...making it 300mm centers.. ..this time the vacuum was much better but still suffered from smaller speed humps and a smaller amount of leakage...tested with a cigarette paper...I added the rubbers and grooved the deck 1mm where the rubbers sit...they protruded about 3mm...when the vacuum came on it pulled it down very firm...much more visible than the last times...I screwed it of with the 40 brass screws, with the vac on...and then surfaced it with a 38mm surfacing blade with a 13mm step over....I took 0.5mm off the deck from the lowest point..which was just over 1mm in others...the result is the deck works really well now I can hold small pieces even when cutting them out.

My cnc is close to right..I have a good idea in this process of its limits and can start to refine them..I have included a cpl pics from my first test cut and first use..thru to a cpl recent tests..I dont quite consider it production ready yet.

[SebPQ]

Thank you for sharing your experience
Sadly it is not possible to contract yopu private

[Thatsignguy]

I am having a similar issue with levelling. The machine is a 10x5 and the support underneath is a mess. Don't get me wrong it is old as dirt but still does the job(ish). I am now toying with the idea of lifting the vacuum bed off, lay a 18mm sheet of ply (10x5) cut holes for the vacuum tubes to come through, relay the vacuum bed then an 18mm sheet of MDF as my spoil board. Sounds like overkill I know but it's all I can think to do without rebuilding the inner frame.