Milling a part bigger than your table strategies

[WobblyHand]

I find myself with a little project with a piece of steel plate that is a little bit longer than my PM25 mill table. The piece is currently 26.5" long x 4" wide and 3/8" thick. To make things more fun, the plate has around an 1/8" bow. This plate is A36 and was originally shear cut, but I bought this piece at the "scrap area" in the steel yard for $0.75/lb, so I'm not surprised about the bow. I am just trying to make a VESA monitor assembly, and this piece is just a vertical bar that will be screwed into an existing desk frame. So super high precision really isn't needed, although in the end the monitor needs to be level from left to right. I bought a wall mount VESA monitor bracket, so all I have to do is 1) attach the plate securely to the desk, and 2) attach the VESA monitor bracket to the plate. Right now, the plate is clamped to the mill table, just as a test fit, and it overhangs the table by 1/2".

My original plan fell through when I realized the backing of the desk/hutch didn't have a solid backing. It's hollow, so a through bolt in the back into the plate would squash the hollow area. It's too bad, because I then could have used a 21.25" long plate. But not everything goes to plan... For reference, the monitor is 32" diagonal and will mount on a 100 mm x 100 mm VESA pattern. The monitor is not that heavy, so I believe the bracket is fine. I'm mounting the monitor to the hutch backing because the existing stand forces the monitor too close to me. The stand will give me almost 7" more distance.

It would be nice to square up at least the edges of the 26.5" long plate, and to precisely locate the holes for the bracket. My thoughts were to elevate the plate on 123 blocks, (or 246) so it would clear the X power drive and sort of align things and attempt to clean up the edges. This datum would give me a reference to locate the holes. This approach seems quite tedious, but so far it's the only one I can come up with.

Yes, I could probably use things as is, but it wouldn't look that good in a semi-public area, and it might annoy me forever if I mess it up, since I would have to modify the furniture for the installation.

So any suggestions or strategies? At the moment getting a bigger machine is not viable, since my shop is space constrained. I figure this is a classic beginner question and maybe someone can share some general ideas on approaches to the problem.

I'll post a photo or two in a bit, recently changed passwords and don't have it on this basement computer yet.

 

[mmcmdl]

Slot blocks Wobbly . Put down a sacrificial plate and bolt it to the table . If you stay .005 off the sacrificial plate , you can hit the burr left with a file .

 

[RJSakowski]

What is your x travel? I have milled work up to 8' long by milling an edge as far as I can (18.5" on the RF30 clone) and then mounting a long guide block so it is touching the freshly milled surface. Then I shift the work so it rests against block, reclamp, and mill another stretch. I continue this process until the entire workpiece has been milled.

 

[WobblyHand]

Slot blocks Wobbly . Put down a sacrificial plate and bolt it to the table . If you stay .005 off the sacrificial plate , you can hit the burr left with a file .

What are slot blocks? Apparently another thing I need to make

 

[mmcmdl]

What are slot blocks? Apparently another thing I need to make

Most if not all mills have 5/8" slots in the table . Mill or grind up blocks that fit these slots . They run parallel to the x axis . I have block sets and plenty of 5/8" dowel pins for long ash parts .

 

[WobblyHand]

What is your x travel? I have milled work up to 8' long by milling an edge as far as I can (18.5" on the RF30 clone) and then mounting a long guide block so it is touching the freshly milled surface. Then I shift the work so it rests against block, reclamp, and mill another stretch. I continue this process until the entire workpiece has been milled.

Just went downstairs and looked. Due to my lathe being in the way, I can get about 9" one way and about 4 inches the other. If I do some long overdue rearranging I might get 18 inches total give or take. Best good guide I have is a pair of 246 blocks.

 

[WobblyHand]

Most if not all mills have 5/8" slots in the table . Mill or grind up blocks that fit these slots . They run parallel to the x axis . I have block sets and plenty of 5/8" dowel pins for long ash parts .

So these are tight fits to the slots? For the dowel pins, these also are good fits to the slots? In my case (baby mill PM25) I need 12mm, or whatever they actually cut them to. Think the slots aren't all the same width... I remember milling my own tee-nuts and finding the fit was quite a bit different, depending on which of the three slots I chose. Ended up having to remill a bit, because they didn't quite fit one slot. As I recall I had to take off nearly 0.1mm so they would fit all the slots. It appears I chose one of the wider slots for my test fitting. I had no idea that they didn't have to be exactly identical... Pretty naive at the time. I make a whole lot less assumptions about things now. I don't believe anything is the same, unless I measure it carefully and can repeat the measurements at will.

 

[rabler]

I've just clamped something down on 123 blocks and milled part of the edge on the x axis. Then moved it over, and indicated the already milled part to be true to the x axis, and then used an edge finder to reset my DRO Y axis to match the already milled face (in that case I was zero'ing the y axis on that face). Close enough to continue within a thou and parallel to within however careful you want to indicate. A little light filing or sanding to cover any slight mismatch.

If I had to do more than one part or one offset, using some sort of block or edge reference like @mmcmdl or @RJSakowski mentioned would be quicker.

 

[woodchucker]

I've just clamped something down on 123 blocks and milled part of the edge on the x axis. Then moved it over, and indicated the already milled part to be true to the x axis, and then used an edge finder to reset my DRO Y axis to match the already milled face (in that case I was zero'ing the y axis on that face). Close enough to continue within a thou and parallel to within however careful you want to indicate. A little light filing or sanding to cover any slight mismatch.

If I had to do more than one part or one offset, using some sort of block or edge reference like @mmcmdl or @RJSakowski mentioned would be quicker.

same here. My surface grinder was so far out at first, that I had to mill down one side to level it. I wound up having to do both sides just to be sure.
It was longer than my 24 inch table, so I wound up having to move it.. it was coarse at best, but better than what I started with.

 

[WobblyHand]

Thanks all, looks like a long day tomorrow trying to square this up. Would be nice to have some blocks to help position things. But I do have to stand off the plate from the table with something high enough to be over the X drive motor housing. It's at least a 1/4". Hmm, I do have some awkward 1/2" plywood I could slice off. Need to double triple check all the dimensions before I plow ahead.