YARPS (Yet Another Router Planing Sled)

[smorgasbord]

Finally finished my router sled and made a few passes:



What's going on with the "L" extrusions is that due to use of the DeWalt router with the through the plunge rod dust collection, I didn't want the router base to be too far above the surface, so I devised a staged height adjustment mechanism that can be done in situ.

Here's the two halves apart:


The piece at the left is attached to the cross-rail guides, the other piece is attached to the router base. The small knobs in the base angle index into the recess, and depending on which hole you choose, the height of the router base is set, then the larger knobs lock it in place. This is the piece attached to the router base.


There's 45mm of height adjustment, in 5mm increments. I designed these parts in Fusion 360 and milled them on my Shapeoko CNC, including the router base itself, which is ¼" thick aluminum. Was satisfying to figure out the router attachment hole spacing and the oblong egg-shaped opening to facilitate dust collection.

$375 all in, excluding the router. But, more than a few days of time on this instead of my desk project.

Surface is pretty flat - within ½ a millimeter across the surface, although clearly I need to do some tramming to align the router axis. I may do that for the final passes.


Dust collection works OK. I think all these sleds struggle at the edges, but keeping the router base close to the surface definitely helps in the middle parts with the DeWalt's dust extraction design. My router bit is too large for the top plastic cover, so I stuck some blue tape on to help keep the dust in and that works OK.

My goal here isn't to flatten the cherry slab, it's to thin it, hopefully without very much warping going on. I'm concerned since the other side is the good side and I don't want to take much of anything off of it, so I'll be unbalanced with my stock removal, but I don't have much choice at this point. I guess I could put in some C-Channel at some point, but I wonder how much that really helps - seems like a slab that wants to warp will easily pull out those threaded inserts. The slab is kiln dried and I've had it for months with no noticeable changes, and a second slab (the next one in the sequence) I ended up cutting apart to make the base and didn't see any warpage.

 

[luvmytoolz]

Very nice results!

Also gotta say I admire the beautiful Art Deco style height adjustment! ;-)

 

[smorgasbord]

Hope the explanation of how that works was clear.

I should also talk about the $100 I spent on four 4040 extrusions, which you can see running cross-wise under the slab. My workbench is only about 2' wide, so with the 42" wide slab I had to figure something out. I didn't want to build a big plywood box, since I wanted this to be something I could pretty quickly disassemble and store compactly. So far, those extrusions are working out well. With other size and/or non-flat slabs they might not work out as well, but I've now got pieces I can reconfigure as needed in the future.

 

[rvieceli]

Very nicely done. To future proof your set up, you can add some short pieces of extrusion under the attachment points on your 4040 extrusions to act as extensions to raise the height of the sled to accommodate thicker pieces.

You may also want to add some additional short pieces to the 4040 to act as stops for your slab piece.

Ron

 

[smorgasbord]

Very nicely done. To future proof your set up, you can add some short pieces of extrusion under the attachment points on your 4040 extrusions to act as extensions to raise the height of the sled to accommodate thicker pieces.

You may also want to add some additional short pieces to the 4040 to act as stops for your slab piece.

Ron

Yeah, both those capabilities were factors in the original design.

It was serendipity that when I bolted the rails together my slab was right at the max thickness capability (defined by clearance of the bottom of the cross-rails). So when I designed the carriage system, I used ⅛" thick aluminum strips on the long rail guides to not only tie the carriage together (helpful to have a rigid carriage to slide on the long rails), but also lift the cross-rails for clearance. I could continue to add spacers in the carriage where the cross-rails attach to the long rail guides or, as you said, I could add spacers where the long rails attach to the 4040 extrusions.

And, yes, the 4040 cross rails provide opportunities to clamp the slab in place. With the battery-powered DeWalt router limiting depth of cut, however, the weight of the slab has been enough. As it gets thinner, I might have do some clamping.

 

[smorgasbord]

So, the first 4 passes with my sled went swimmingly, taking about about 1.5mm each. For the 5th passs, I made the mistake of lowering the carriage so that it just skimmed the top surface, combined with the mistake of taking a larger, 2mm, pass.
And so ¾ of the way through, the slab started cupping and my router carriage's base was on the surface, actually pushing up on the rails. I decided I had to plow through and complete the pass.

Surveying the damage, the slab is flat enough along it's length, at least down the middle. However, cross-grain, the slab is cupped. Since my last pass wasn't great, I flipped the slab over to measure the damage on the previously flat "good" side. At the narrow end, it's still pretty good, but at the wide end the edges are off about 2.5" from the center. So, I think my next step is to re-flatten the good side.

Since the board is no longer even I wanted to make sure I was taking the smallest possible amount off the good side (also because I already inlaid bowties). So, I decided to calibrate the jig as best I could. First up was the old string technique:



With some shimming, they crossed nicely in the middle.

Then I remembered I bought a laser level on sale last year, so set that up:


The kit included this plastic card with reflective markings on it, so you can easily tell when the line is right on the mark. Ran that card along the long rails to confirm at least that the rails are straight.

While I was at it, I pulled out my regular level to test at various spots:


OK, so pretty confident with these 3 techniques supporting each other. Now, I mounted a dial indicator to the carriage and am starting to draw a map of the high and low spots of the slab just resting on the supports:


It was late, so I didn't finish, but I think a couple hours of measurements (my holding jig is real Rube Goldberg so there are issues there), should help me decide where and how much to shim the slab so that I'm removing the least possible amount to get it flat (and the least possible amounts near the bowties).

Then, I'll do those passes (sub mm at a time) until I'm happy with the good side's flatness, then flip and skim the bottom side again. Hopefully that skim won't make the board cup even more. Despite the dial indicator, I'm not looking for sub-mm flatness.

The slab already looks better being about 40mm thick from the 48+mm thickness it was before. It'll probably be about 38mm thick when I'm done with the flattening, but if it's thinner, that's just fine. Wife thinks once it's flat again I should just thin the edges, about 5" in. I was thinking of getting an electric hand planer and then jigging that up to do the underside beveling, but she thinks I should just "step" it.

 

[Michael Kellough]

Thanks for posting process photos.

It wasn’t necessarily a mistake to make that last pass 2mm. The equilibrium threshold could have been passed at 1/2 millimeter. There is no way to know until you pass it.

I like the idea of tapering the edge of the slab rather than thinning it much more. I don’t think it’s worth the effort to make a jig to attach a power plane to the carriage though. I’m sure you will do a good job by hand.

If making the taper an exact width like 5” you can use a router with a fence to plow grooves at different depths (in order) around the perimeter so you know when to stop planing. Like drilling holes in a chair seat that will be shaped. I wouldn’t bother with that either.

 

[smorgasbord]

It wasn’t necessarily a mistake to make that last pass 2mm. The equilibrium threshold could have been passed at 1/2 millimeter.

Sorry, that wasn’t what I meant. The mistake was placing the router base plate so close to the surface that when it moved the rails made it hard to slide the router. Essentially, the slab pushed up on the router plate, but the rails stopped it.