I realize I didn't explain that part really well; I put the indicator down on the MDF only to watch how much I move the rail up and down. So, if the level shows it being a little low, I move it up about .0005" based on the indicator. I definitely don't want to level the table based on the indicator on the MDF -- that would only make it as level as the MDF and the table itself.
Glad to see someone else discovered the inaccuracies incurred by using the Avid jig and following their alignment procedures. I discovered the issue much further along in the build when I was surfacing the spoil board. I used a much less rigorous procedure than yours because the way I have my spoil board mounted made removing the dust covers too disruptive. I got my rails to be just barely within acceptable limits but when I replace my spoil board later on I plan to use your process. Have you had any communication with Avid regarding this issue? They really should do something about it.
It's good to know I'm not the only one who discovered this! I posted the video on Avid's forums, and I know they keep an eye on things over there. I haven't reported it to them directly. I understand why they do this sort of thing in the directions; the jig makes it easy to align everything, and it is relatively accurate. Overall, it would only cause a .005 to .010 issue, which isn't too bad over 8' of length. My jigs might have just been poorly machined.
That part of the jig dimension dosent matter. Even if off, you could have just used one jig along the track as you tighten.. I'm not even sure how "precise" that aluminum extrusion is.. Nice tips! I'll have to check my jigs as I'm 75% done with my build. Thanks!
YES! You are observant - I measured the wrong part in the video, and in the description I noted that later. It's the part from the machined area to the part that sits on the rails; I measured this, and my two varied by 0.010, which is even more than what I (incorrectly) measured in the video. You can use the same one; the hard part with that is re-aligning it. I think the precision level is the best way to ensure it is really flat. YES - the extrusion is probably not very precise...this method will accommodate that for the z-axis, but the x/y could vary, so it is still limiting the accuracy of the machine.
@@CorbinDunn Wow, 0.010... I'm really worried.. My machine is 2 years old.. I finally just got time and space to set it up.. I leveled my legs and base but ill have to find my calipers and see what two year old blocks come out to be. (by the way, you could add that text in the RU-vid editor when you're measuring the jig so you don't need to re-edit or upload.) but I'm not sure if it displays on every device.. at least it didn't 12 years ago when I made RU-vid videos.
You're right, the extrusion isn't necessarily perfect, and using a level isn't precise either when talking about minute adjustments. The level itself isn't necessarily perfect, I always check them against itself by flipping it over (rotating the short way, not flipping end to end or you'd have the same thing) and checking that the bubble reads the same when upside down. My 6' decent quality level has an X sharpie'd by one of the two horizontal bubbles because it reads slightly different when I flip it over. I'm in the process of leveling my own 5x10 right now, using a laser on the linear rails after basic leveling of the top surface, will be uploading a video when I'm done...
That's a good idea, I definitely should have done that!! I actually didn't notice the problem till after I was done; I was trying to figure out why things were so far out of alignment, and I realized the two pieces were not the same size, and would cause the offset I was having to correct for.
Hi Corbin. I know its been a while since you posted but I just got around to running this procedure for my PRO4848. I have the same level as you and after loosening all the bolts I proceeded down the rail stopping every two inches to force the rail to level and tighten the trailing bolt at the end of the level. When I got down to the end where the gantry was I moved it back to finish the rail. When I went back to check each of the the 2" increments for level I found them to be out of level. I tried this several times but seem to be just chasing my tail. Do you have any advice?
Is the level itself level? If you set it on a surface, verify that is level, and then flip it 180, it should still be level. If it isn't, it needs to be calibrated. Otherwise...you might have to just get it "close" and not worry about it too much. I spent a lot of time trying to get it as level as I can...and it did take a while. You have to make sure that tightening the bolts doesn't cause the rails to go out of level. That was one problem I had. I should go re-check mine now that I've been using the machine for a while and see if it remained level. I have a feeling that things may have gotten settled over time.
@@CorbinDunn The level is definitely calibrated to be right on the money. Things seem to go fine when going bolt by bolt 2" at a time until I get to the gantry and have to move it to the other end. When I come back to where I left off everything has changed to where the bubble is way out of the level window. Could the weight of the gantry be causing that much flex to the frame? I don't have a steel frame for support like you do but have reinforced the Avid stock aluminum frame with 1" MDF panels that seems to make it pretty rigid and have doubled its weight.
@@Sehast The gantry weight definitely could be the issue. If you move the gantry back to the other side, does it re-level up? If it does, then I wouldn't worry about it: your two rails will be co-linear, which is the only reason to do this. It doesn't matter much if they are actually level. For a heavy metal milling machine / CNC with tight tolerances (0.001 or less), it might matter, but not for a wood CNC.
Dang, I didn't even think to check that my jigs were the same thickness. 0.005" difference is pretty bad for what should be a slam-dunk repeatable part to make (they only need precision on a single dimension). Personally, I would have just orbital-sanded or machined down the 0.005" so the jigs match. I'd be a little hesitant with your method since it's such a small level (doesn't span much distance), but at least with your method you aren't relying on the aluminum extrusion to be perfect (as you are when using the jig).
I do recall using the jig in the middle of each rail-span. Those rails are heavy, and they certainly have measurable droop when spanning 4+ feet. Avid should have included 3 (accurate) jigs.
Yeah! I thought about putting the jig on my knee mill and taking a bit off. In the end, I thought this was more accurate. My 4’ level says it is flat, but that thing isn’t too accurate.
Ah! I just realized I measured the wrong part in the video. I should have measured from the machined bottom area to the lip that the rail fits on. I re-checked mine, and it turns out they are .010" different! That really indicate a machining problem when they make that piece.
It's definitely a manufacturing mistake. I did bright it to their attention, and they were supposed to look into it, but I'm not sure what became of that. I could also see an easy mistake where they used one from two different batches; I'd hope that a pair from the same batch would be the same size.
Why would you assume your WELDED table is plane with 2 sides or even parallel? Never happen. There is also no accurate method you can use a machinist level every 8 or so inches to achieve a linear plane. I believe after seeing your mismatched gauge blocks you have improved your machine though. The z axis heavily weighted to one side with a short mounted axis and reversing directions almost immediate will cause unsatisfactory inaccuracy's also. If your only batching out smaller items on a production basis it matters not. Especially working with wood that changes by humidity. I have seen plywood measure 10-12 thou variation on the thickness over the perimeter of a 4x8 sheet. There is Zero cnc machines that come in a box via UPS of your size that can assemble in hours and achieve machinist tolerance's with wood or any material. That said, nice machine for cost/value.
Yeah, you are right -- it isn't possible to ensure the distance between the long y-axis is the same, and I'm basing mine on the accuracy of the aluminum cross members. But I think the machinist level definitely helps with accuracy in getting the table in a linear plane; the side axis may not be perfectly parallel though! A lot of professional machines claim a " tolerance level of +/- 0.03 across 12 feet" -- 30 thou over 12' seems pretty big to me! (I'm quoting Phantom CNC's spec sheet.). For a wood machine, it all seems somewhat negligible for the reasons you mention (movement)
