Hi Everyone,
I’m rounding the corner on my first cnc build, an Avid Pro4824. I downloaded the Avid spoilboard file (for Vectric), and noted that the workpiece dimensions used are 49" x 25". I bought a sheet of .75" MDF and went to work cutting 49" x 25" spoilboards. Then it dawned on me - If I mount a piece of 49" x 25" material flush with the front extrusion of the machine frame, there is no way that the surfacing toolpath of the provided Avid spoilboard file would reach the entire depth of the spoilboard using my 1.5" surfacing bit. There would easily be an inch (or so) of excess material in the back that the surfacing tool simply could not reach. So my question is, what actual size spoilboard are most people using (my machine is the Pro4824, but I’m sure spoilboard sizes for the different machines are relative)? Are you using smaller dimensions for the spoilboard, or simply leaving an inch or so of unsurfaced space on the spoilboard at the rear of the machine?
Thank you,
Mark
Keep in mind that the work area dimensions are for the centerpoint of the spindle. If you have a 1.5" diameter surfacing bit, add 1.5" in each dimension to get the “reach” of that bit (er, with rounded corners, of course). If you check the work area specs for the 4824, you’ll see it can reach 1.1 inches out from the front. With your bit, you can actually cut 1.85" out from the front. By mounting your spoilboard flush, you’re giving up that 1.1" of work area.
So take that unsurfaced inch or so of spoilboard in the back, and move it to the front 
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Hi Mark, I have a different sized machine so I don’t know if my comment will apply or not.
I’m using a spoil board that is larger than the size I’ve got set aside for it. The head on my machine can actually travel farther than the size of the machine. As an example, if my machine were 48x48 (it isn’t but lets pretend it is) then the center of the cutter can easily reach 48x48. Notice the center of the cutter can reach those dimensions. It is actually farther than that in real-life. If there were not the extra room (which is genius on the part of AVIDcnc) then a 1.5in diameter cutter would clear out a spoil board of 48+1.5x48+1.5. And then there is the extra room on top of that.
I’m almost wondering if maybe it isn’t that the g-code set up to run that tool path wasn’t set up a bit to conservativly, as on the bigger machines at least, there is a small bit of extra travle (like an inch or so) beyond the advertised size so a 4ft machine can actually cut around the edges of a 4ft part.
Just thinking out loud there, and I’m definitely not an expert on this stuff, just relating my experience with one of their bigger machines, but I suspect that they have done this on all machines… (IE, they can move to slightly further than then full envelope?)
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Must be nice having such a small spoilboard 
I have to buy the 61" x 145" x 3/4" MDF and slice it down to 121". It’s a monster and is really hard to move around.
If you have ever tried to find that size in MDF then you know you have to go to suppliers for manufacturing. It’s not a Homie’s Dee-pot kind of buy.
But on the PRO60120 I can machine the complete 61" by 128". I purposely cut the spoil board down to 121" and added an extra cross member to mount the last few inches of the MDF to because it droops after a while. That last 7 inches is where my ATC carousel lives
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I too run an PRO4824. I have a full shelf built under the bed of the machine for storage and to aid in rigidity (which makes an impressive difference). I just ordered additional extrusion from 8020. Because of this, I don’t want a lot of dust and chips raining down on the shelf any more than is avoidable. So, I have a piece of 3/4 baltic birch cut to fit the entire surface to close the table off completely. My spoil board has changed a bit over the years. What I have now is T-Track running in the Y-Axis., mounted on top/to the baltic birch and then 3/4 MDF between the T-Teck and on top of the birch plywood. I actually cut the MDF segment each time I need a replacement on the machine and since they are individual, I only have to replace the segments that need it. I cut the t-Track and the MDF spoil board to 28" because I want to allow for the possibility of using various t-Track clamps on the back side on an edge. I face my spoil bard and then rotate the MDF 180 degrees to get the last few inches the spindle can’t reach in the first place. If you have Fuion, I can send you a solid model if you are interested.
Thanks to everyone for all of the helpful information.
pketcham - I would be interested in seeing the Fusion file, and perhaps a photo or 2 of your setup would be most appreciated.
Thank you,
Mark