Tiling with the Long Mill

Community Discussion 🧠 New Wisdom
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I’ve put this in the “new wisdom” category, which may well be more a reflection of my ego than the true “new wisdom” of this post.

However, here goes.

Recently, I had a job that was about 26" in X, but 54" in Y. VCarve accommodates this quite simply by having a “tiling” feature. I won’t go into the details of how to use that feature as there are many videos available. However, I ran up against an issue with it owing to the way that I have set up my spoil board. My spoil board covers the 30" or so in X that the Mill can carve. In Y, the slats that make up my spoil board are about 36" long. (There was no magic to that length. It simply worked out from the MDF offcuts that I had.) I have t-tracks between the slats.

I surfaced the spoil board to the extents in X and Y that the Mill can handle. This meant, in Y, that I surfaced all the way to the front edge of the board, but was short of the back ends of the slats by about 6". For any piece of material that is short of 30", this is not an issue. However, for this tiled project, it meant that the back end of the material rested on the part of the spoil board that was not surfaced. As anyone reading this will understand, this threw off the depth of my Z cuts since I was, in effect, cutting on an inclined surface. Thankfully, I realized this before I actually carved the piece.

The solution was simple, if a pain in the neck. I had to remove all the slats that make up my spoil board and cut them to the length that the Mill can surface. The tiling job ran fine.

I am putting this out there only as a precautionary tale for other Mill users who may be using material that is larger than the Mill can surface. The project does not need to be a tiling project for this issue to arise. If you have a project whose dimensions the Mill can carve - say 20 x 20 for example - but you are carving it into the centre of a piece of material that is larger than the surfaced area of your spoil board, you will have to address this issue. The obvious solution is to limit your spoil board’s dimensions to those that the Mill can carve. There may be other solutions. I’ve not been able to come up with any.

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How I would get around this is to put spruce strips (1" X 4" or whatever) down on the table, spaced apart, before the spoil board install, in such positions that the cutter could mill the tops of all the strips, then I would install a new/fresh spoil board on top of the finished milled strips. The new spoil board, which is MDF, can be as big as you can possible fit within the boundaries of the machine. MDF is so flat & true in thickness that it will replicate how you milled the strips. No machining will be required for the new spoil board. I will be using threaded inserts that now could be installed in the new MDF.
But if you are using “t” slots then this procedure may not work for you.

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@RustyR I believe that I understand, Rusty, but I don’t believe it will solve the problem.

If I understand what you are saying you would mill strips that are only as long as the Mill will surface. Then you could put a piece of MDF on top of them that is longer than the strips. You would not surface the MDF. That would work until you need to surface the MDF, or the strips change dimensionally. Then you are back to the problem.

The issue is not with t-tracks. The problem exists regardless of the hold down method. Your concept may work so long as you never surface the MDF. I don’t surface mine frequently, but from time to time, it still needs to be surfaced to reduce or eliminate the irregularities caused by cutting into it making projects.

The other factor brought in with your method is the strips themselves. You can mill them flat when you first put them down. However, they are wood. They will move and swell with humidity. I’m not saying that they will go crazy, although with the sad quality of construction-grade lumber these days, I would not bet against it. (Just watch a 2 x 4 twist after you bring it home from the big box store.) That movement will be reflected in the MDF on top of them.

Finally, while MDF is certainly flatter than most anything else when we buy it, and while it is more stable that most anything else, over time, it still swells with humidity. Again, I’m not talking swelling by 1/8" or anything, but there are numerous threads on this board about users shooting for .001" tolerances in their Mills. We can mitigate this by sealing the MDF, especially the edges, but it still swells. (This can also by mitigated by buying better grades of MDF than the big box stores sell.)

At the risk of boring the heck out of you, I can tell you that, at the commercial shop where I put some time in, we have a 4 x 8 machine. We don’t need tolerances of .001" for the work we do, but we do need a “flat” spoil board. In the winter particularly, we can see that the MDF spoilboard moves more in the corner nearest the entry door to the shop than it does in the corners 8’ away. It’s simply a reaction to the temp and humidity changes that hit the board each time the door opens.

Anyway, I want to emphasize again that these are just my opinions and experience. The only “facts” in all of this epistle are that wood moves. I believe that is indisputable.

Thanks for joining the conversation, Rusty.

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@gwilki , good comments & great insight. I appreciate your concise explanation. Where I live & in the workspace I hobby in is very dry, so humidity is not much of a problem. I will consider spraying my spruce pieces with some form of a sealed coating, great idea.

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@RustyR Tks, Rusty. You’re lucky. Here in the Great White North, humidity is a big factor in wood movement. Right now, with demand for kiln-dried wood way up and supply down, the kilns are pushing lumber out too fast. So, we are finding the surface of lumber is quite dry, but there is a lot of moisture in the interior. We’ve never seen twisting as bad as we are seeing this year.