Slab Flattening Router Sled

[Julie Moriarty]

Has anyone ever built a slab flattening router sled?

I have some live edge slabs I need to flatten and I am planning on using a variation of Nick Offerman's router sled:
http://s3.amazonaws.com/finewoodworking.s3.tauntoncloud.com/app/uploads/2016/09/05163252/011222044_offerman-leveling-jig-main.jpg

Rather than use solid lumber for the rails, I thought laminating (3) 3/4"x6"x96" sanded plywood would be more stable. So I've got that done.
http://julimorcreations.com/Images/LiveEdgeIsland/RS_001.jpg
(It's still too hot here to work outside so the kitchen has been hijacked :o)

At the back of the plywood table is the sled that will go between the rails but I still need to make something like the boxes that lay on top of the rails as in the first photo. I have a number of thoughts but would love feedback for anyone who has ever built a sled such as this.

Right now I'm thinking of using aluminum angle to rest the router plate on. This is the bottom view:
http://julimorcreations.com/Images/LiveEdgeIsland/RS_002.jpg
I was thinking the open area will give me a better view of what I might have missed. But I'm wondering if the dust created by this process might be worse with the bottom being open. The parts are not glued together yet because I'm not sure how this will work.

Thoughts?

[Bill Adamsen]

Yes it can be used for flattening slabs and it works just fine. The same principle is useful for turning columns including columns with entasis as long as the material is substantial enough. Many years ago a friend executed a contract for church columns (matching existing) including flutes. I've used the approach several times since.

With your design you should be able to close down the bottom if you find the dust to be a problem. Perhaps the dust collection on the base of your router will be all that's needed.

[Jim Becker]

I haven't built one...yet...but it's on "my list"!

I like your ideas so far, including the lamination for the rails and the aluminum to support the router.

[John TenEyck]

I've always just built whatever sled I needed for the slabs I wanted to flatten. Simple and cheap and nothing to store when the job is done. If I did slabs regularly I'd build something like you are making, Julie, or Nick's. If dust is an issue you will definitely want to implement some kind of control system. I built this sled twice as wide as the rails, with the router fixed in the center, so that the dust collection could be built around that point. I still had a lot of chips that didn't get collected but most of the fine dust was.

https://lh3.googleusercontent.com/MhOwvr8nwEDluQu_tz2FhK0ze-vREdrRlNtZwA4MmjHoVMI7OjY0CfcwaJy8f627Z5wDTyNMtY_R MX6OVeiDZFxbx0JFhS_po2wEhX9AP0CYZchmYDKa6T6Rg1vuSC yRIvFoZraVitAplipJmbANksrrD2v9uWy82YvxxTCnZRuDRTKR Ewx3EIgroPsvZesgBQDMKEUsr1hhQiNHhj24HNpXyKUM1_0hBS YjAsxB8QVk4MMtVKEhx-BMjJgkyBO-FPC_tmT167fi2fbsL-EbZuaOi9eG9GybCimT7hPl1JD0LPHR-XtZT87Ebl3ULCAki_MSHxSuuxZBNU0eHDgMpSf3XZk4a9G0Qao 9UWlsD2Sft9BS2oehlW_jxfGFy4gXYQqptjXiSQEfRFu-cGWWG3tVEi2kI8dDvoutOm-xylAnzuqCixMcUtDtJDkATk3M8nYU-IePxwMlQAt4wwD_cF6rbY0DoZOmnuxIsff88X95VSiVL0R9F3i r31mX573r4jibDg_dTR-AUrT0GNr4pYK8Xv-lqglBxnw3h2QU4haeCl9T8VZXRydh6RBvF06dMfwqqT7So75h1 wQTbAUctPDO-N-BoBh0eHRAFczffA=w640-h480-no

I used some foam to help seal the area around the router bit to the wood, but I think the brushes you see on CNC routers would do a much better job but I couldn't readily find any low cost options. In any case, the sled has to sit above the slab, and that gap needs to be sealed around the bit so the airflow can be managed in order for the vacuum to capture a high percentage of the chips/dust.

Joh

[Kevin Jenness]

I have done this a number of times. Making the sled slightly longer than the supporting rail width and running the router across the sled reduces the inertia of the whole affair. Wax it up well, eat your Wheaties and don't forget the dust mask.

Now that I have a cnc router, I don't miss anything about the manual method.

[Tim Janssen]

I have some concern about riding the router base on aluminum angles. The aluminum router base made not slide very well on the aluminum angles. Aluminum on aluminum tends to create some galling. Maybe use some UHMW strips screwed to the routerbase.
Good luck with your project

Tim

[Julie Moriarty]

One of the things I saw as being a necessity was creating clamping points for the rails. So I took the rails to the drill press...
http://julimorcreations.com/Images/LiveEdgeIsland/RS_003.jpg

I placed the holes at 12", 24" and 36" from either end, figuring that would cover pretty much any slab I can now envision working on. The slabs I have now are between 84" and 96".

John, I was thinking about CNC brushes as a possibility for containing the chips and dust. From what I have seen in videos, that can be pretty substantial. The slabs I'll be working on have been skipped-planed, both sides, so I shouldn't be seeing a fireworks display of chips flying.

As for the cutter, I have the 1" mortising bit shown in the first post but it has seen a lot of work. I used it to radius dozens of fret boards and it's starting to show some wear. Plus it's only 1" wide. So I popped for an Amana 1-1/2 wide, bottom-cleaning, upshear bit.

I still have to figure out what is the best route for the "wings" (that the sled attaches to that slide on the rails). I saw an Offerman video on YouTube where he extended the length of the wings to about three times what is shown in the first post. It gave him a lot of flexibility.

[Julie Moriarty]

I have some concern about riding the router base on aluminum angles. The aluminum router base made not slide very well on the aluminum angles. Aluminum on aluminum tends to create some galling. Maybe use some UHMW strips screwed to the routerbase.
Good luck with your project

Tim

Tim, the router is attached to a 1/4" thick sheet of Plexiglas. I have run it across the aluminum rails and there is some drag. I plan to polish the AL rails and see how that goes but if there is still drag I will go the route of UHWM strips.

Thanks!

[Julie Moriarty]

I managed to clear the saw horses and do a trial setup before making the wing boxes. I'm glad I did.
http://julimorcreations.com/Images/LiveEdgeIsland/RS_004.jpg
I'm trying to figure out the best way to design the wing boxes so as to make the sled flexible for a number of different flattening jobs. Had I made what I drew up in CAD, I would have been disappointed.

http://julimorcreations.com/Images/LiveEdgeIsland/RS_005.jpg
The sawhorses give me a lot of flexibility but... I'm thinking the boxes need to be at least 12" high. That would allow for most any thickness slab and with the adjustable legs, I should be able to flatten stumps.

What do you think?

[Prashun Patel]

Very nice. I would make handles for the router carriage. This is fatiguing work. As such, it's easy to get lazy and move the carriage a little too much on the next pass, causing the router to run or skip. A good handle keeps the carriage under better control.

I would also be leery of aluminum angle. In my experience, it has sagged.

The hardest work, IMHO in this set up is leveling the rails. I used the string method for that.

[John TenEyck]

How do you plan to hold the router? I can't see how you can get your hands down over those tall sides of the gantry to hold it, and with that design you have to hold the router. Even if you can I think it's going to be awkward and tiring to do so. This is another advantage of the router being fixed at the center of a gantry twice as wide as the distance between the rails. The router stays fixed, and you hold the gantry anywhere that's convenient. With that design you can make the sides of the gantry any height you want, and the bottom of the gantry can be a solid sheet of plywood with a hole cut in it.

FWIW, I found a 1/2" diameter straight bit to work best. A bowl bottoming bit takes a wide cut, but you can't cut very deeply, and it still leaves ridges. A 1/2" straight bit takes a narrow cut, but you can cut more deeply and the ridges are no worse. 1/2" straight bits are HF cheap, so you can afford to replace them more frequently.

John

[Jake Elkins]

369857
I've been flattening a bunch of wide oak planks lately using a freud 2" straight bit. Bit works well, but it can get a little hairy when it catches a knot. Something that I have noticed is that it seems easier to make my passes going with the grain rather than across. It cuts easier, and the ridges are almost non-existent. I still have a lot more to do, and I am not looking forward to it. It is hard work, and makes a huge mess. I wish I had a friend with a wide jointer.

[Julie Moriarty]

Very nice. I would make handles for the router carriage. This is fatiguing work. As such, it's easy to get lazy and move the carriage a little too much on the next pass, causing the router to run or skip. A good handle keeps the carriage under better control.

I would also be leery of aluminum angle. In my experience, it has sagged.

The hardest work, IMHO in this set up is leveling the rails. I used the string method for that.
Prashun, I was playing with it last night, after I temped the wing boxes together, and the sled slid fairly easily using 3/4"x3/4" UHMW on the bottom of the wing boxes. In my mind's eye I was seeing taking thin-cut passes rather than trying to take it all at once. More passes but hopefully less fatiguing. When I get to making cuts, I'll see how handles can fit into the design.


How do you plan to hold the router? I can't see how you can get your hands down over those tall sides of the gantry to hold it, and with that design you have to hold the router. Even if you can I think it's going to be awkward and tiring to do so. This is another advantage of the router being fixed at the center of a gantry twice as wide as the distance between the rails. The router stays fixed, and you hold the gantry anywhere that's convenient. With that design you can make the sides of the gantry any height you want, and the bottom of the gantry can be a solid sheet of plywood with a hole cut in it.

FWIW, I found a 1/2" diameter straight bit to work best. A bowl bottoming bit takes a wide cut, but you can't cut very deeply, and it still leaves ridges. A 1/2" straight bit takes a narrow cut, but you can cut more deeply and the ridges are no worse. 1/2" straight bits are HF cheap, so you can afford to replace them more frequently.

John
John, the Offerman videos show him holding the top of the router and applying pressure that way. And he takes some pretty deep cuts. The problem with the wide gantry design is you have to adjust the slab up or down, rather than adjusting the sled. The sawhorses have adjustable legs and with the travel between the wing boxes and the sled I'll have a lot more flexibility. But this is still a work in progress. I may find I'm wrong.



I've been flattening a bunch of wide oak planks lately using a freud 2" straight bit. Bit works well, but it can get a little hairy when it catches a knot. Something that I have noticed is that it seems easier to make my passes going with the grain rather than across. It cuts easier, and the ridges are almost non-existent. I still have a lot more to do, and I am not looking forward to it. It is hard work, and makes a huge mess. I wish I had a friend with a wide jointer.
From what I've seen, Jake, the mess can be substantial! I saw one video where the waste piled from the floor up to the slab that was being flattened, and the slab was about 3' off the floor. That's why I plan to take this outside when I actually do the work.

Thanks for the great input, guys!

[Julie Moriarty]

So yesterday I cut up the wing boxes and clamped them together to see how they might work.
http://julimorcreations.com/Images/LiveEdgeIsland/RS_006.jpg
They look pretty bulky but after I sat them on UHMW pieces the whole unit slid pretty effortlessly.

I marked for an angle cut on the side of the boxes. I plan on routing two slots in both the box and the end of the sled to allow for T-bolts and knobs.
http://julimorcreations.com/Images/LiveEdgeIsland/RS_007.jpg

This is a bottom shot of the UHMW strip I temped in. The strip will be permanently attached to the sides, where the recess is.
http://julimorcreations.com/Images/LiveEdgeIsland/RS_008.jpg

I've got the sides cut and strips of the UHMW installed on the bottom of one of the box sides. I'm trying to anticipate what it will be like adjusting the sled up and down. I've been thinking about using miter track and miter bar to keep the whole thing square. I ordered some from Rockler. We'll see how that works...

[John TenEyck]

Julie, you don't have to adjust the slab up or down with the double wide gantry. No different than any other design. You adjust the router bit in the base of the router, whether using a fixed or plunge base type.

I would not want to try holding the router only by the top, whether Offerman does it that way or not. That would be tiring and there's just too much chance for a dangerous situation if the bit catches (and it will). I would cut down those sides, at least on one side, so I could hold the router as it was intended to be. If you make the lower side twice as thick you will get back most of it's stiffness.

If you put a solid plywood bottom on your wing boxes you wouldn't need any UHMW. A little wax and they will slide nicely on the rails. If they don't because your rails are rough, then just glue or tack some face grain plywood to the top of them.

John

[Julie Moriarty]

Thanks, John. I made the sides of the sled tall to minimize sag. I suppose I could do what you suggested and double laminate one side. The reason I didn't question the Offerman method of holding the top of the router is I thought there would be times I would be unable to reach the two handles on the router. I thought that's why Offerman used the top hold method.

When the sled is close to the end, I am able to get my hands on both router handles but once I'm about two feet from the end, I can no longer do that. I could lower the legs on the sawhorses. Will have to do a dry run and see how that goes. But you make a great point the router will catch at some point. Better safe than sorry.

I was going to make the wing box with a bottom but I didn't think the plywood would slide all that well, even with a few coats of poly. What I was thinking was putting plywood on the bottom and covering it with a sheet of 1/4" UHMW. The reason I made the wing box so wide is I wanted to reduce transferring any imperfections in the rail onto the slab.

Anyway, here's what it looks like now:
http://julimorcreations.com/Images/LiveEdgeIsland/RS_009.jpg
The UHMW are only 3/4" wide so that kind of defeats that transfer issue I was trying to address. And it doesn't slide nearly as well as when the UHMW was parallel to the rail.

One thing I do like is there is plenty of room to tighten the knobs
http://julimorcreations.com/Images/LiveEdgeIsland/RS_010.jpg
But dialing in a precise elevation will be tricky.

And I will have a good view of the work being done
http://julimorcreations.com/Images/LiveEdgeIsland/RS_011.jpg

[John TenEyck]

Julie, if you go back and look at my crude router sled above you will see that the bottom of the gantry is just a piece of 1/2" plywood. It slides like a dream on the jointed 2 x 4 rails. Flat wood on flat wood. Your laminated plywood rails will have a lot more friction, that's why I suggested putting some flat grain plywood on top of them. Offermans's gantry has a lot of flexibility, but that comes at the price of not being nearly as easy to set up as a simple 3 sided box. You don't need vertical adjustment. You shim the slab up to whatever height needed. From there, adjusting the router bit for depth of cut is all that's needed. And you are already finding out that you can't reach very far across a slab to hold the router, and then have to hold it in one position laterally as you slide the sled down the length of the slab. I would re-engineer that design so that the router can be locked laterally so that all you have to do is push/pull the sled down the length of the slab; make a pass, return, index the router laterally, repeat.

John

[Jake Elkins]

I agree with John - this design seems overly and unnecessarily complicated. I have spent well over 40 hours in the past couple weeks flattening slabs, and I think your design might hurt you more than it helps. On my sled a couple of posts above, it is about as simple as can be, and I wouldn't want it any more elaborate. I made a couple modifications to my design after using it for a while. First, I stiffened the bottom -- I originally had 1/2 solid wood, then swapped it out for 7/8. I was noticing sag in the base when the router was located in the middle. Second, I cut out reliefs for the router handles on the ends of my box. Third, I added a set of guides to run along the right hand rail because with all the wax, the sled would slip, and almost slipped off the rail. This last modification made a huge difference in my control of the sled. A John mentioned, the only adjustment should be shims for the slab, and dropping the bit at the router. This thing is going to vibrate incessantly, and will likely loosen your settings. And making multiple parallel (coplanar) adjustments will take forever. All of my slabs have been relatively uniform in width (16-22), so I did not build in a lock for the router to the box, just a strong grip. Also, I noticed that when I lowered the bit near the limit in its travel, I noticed that the vibration would loosen the set screw and I would lose my adjustment, so I now set the slab up on a sheet or two of 1/4" hardboard when needed as to limit the compression on the plunge spring.

[Ted Reischl]

Certainly one way to do it and it will work. But I dunno, there is a lot of construction and it just seems to me that with a few more bucks and a little more time you could build yourself a cnc machine? A cnc would be much more useful down the road for lots of other projects.

[Prashun Patel]

I don't mean to poo-poo the design. I am sure the flexibility of vertical movement is nice in theory. However, in my couple times doing this, the hardest part is insuring the rig is entirely level. Just getting the two rails level was an effort.

How will you easily keep the gantry level across the width during each adjustment, and how will you insure it does not slip, vertically. (Having not tried your design) I wonder if you'd be better off having a carriage that's vertically fixed. You can just shim the underside of the slab to raise or lower the entire slab as necessary.

I just used the depth adjustment on my router to affect depth (which also requires attention to avoid any kind of slippage of the bit.

[Julie Moriarty]

While the sled is initially being built for flattening three (3) slabs to the same thickness, I plan to use it for other reasons, like doing stumps.
http://s3.amazonaws.com/finewoodworking.s3.tauntoncloud.com/app/uploads/2016/09/05154440/1-offerman-side-table.jpg
With my setup I can raise and lower the sawhorse legs, as well as make adjustments with the sled. I should be able to do a stump like the one above without a lot of additional jig work. Time will tell.

I agree there will be some things that will need corrections and I'm prepared for that. But the basic concept has been used by someone who has already flattened more slabs than I will ever do and he has not abandoned this concept. I cannot ignore that.

At about 1:30 into this video, you can see how Offerman deals with areas of the slab that do not allow both hands to be on the router.

https://www.youtube.com/watch?v=4mrJqfl2K8I

I'll let you know how it goes...

[Prashun Patel]

You are right. I think some of us tend to think our way is the most successful way.

[Dennis Peacock]

This is a very good thread!!! Love the content!!!!

[Dan Forman]

I know you are well into your project and may not want to deviate from your plan at this stage, but I was looking through some old Wood Magazine issues the other day, and recall seeing an unusual router sled that took a different approach than most. Rather than providing a track for the router to slide in, this one has the router fixed, and the whole sled moves. Here is a link to a picture of the sled in use. It solves the problem of how to get a good grip on the router as it moves across the board.

Thought this might give you some additional ideas. If interested, you might be able to find a copy of the magazine at your local library. This sled has a clear acrylic base to let you see what you're doing. Everything else is clearly visible in the picture, so no need to buy the plan, what you see is what you get.

5 Workshop Projects from 3 Shop-Smart Pros Downloadable Plan | WOOD Magazine (http://www.woodmagazine.com/project-plans/workshop-jig/jigs-fixtures/5-workshop-projects-from-3-shop-smart-pros-downloadable)

Dan

[Jim Becker]

Rather than providing a track for the router to slide in, this one has the router fixed, and the whole sled moves.

I was actually just remembering that design right before I started reading your post. :) As long as one has the shop space to accomodate the overhang on each pass, things couldn't be simpler and the router is absolutely fixed with no reaching required to "do the deed".

[Ted Calver]

Lots of ways to skin this cat. Here's one in metal (http://www.sawmillcreek.org/showthread.php?226811-Router-Planer-Sled&highlight=), using aluminum (http://www.sawmillcreek.org/showthread.php?226812-Router-Planer-Sled-(Continued)&highlight=) extrusions.

[Julie Moriarty]

That's some pretty awesome engineering, Ted! I love it! What I'm doing looks like the Flintstones' version.

I've been looking at more videos of the Offerman sled and I got to thinking I'm using a smaller router, a Dewalt 621, which is certainly lighter and would therefore be more prone to jumping up. But because it is a lower HP router I plan on taking very light passes. Hopefully that will reduce or eliminate jumping.

What I'm working on now is creating a method for setting a particular depth so I can easily repeat a given depth in successive slabs. Now it's back to the Laboratree. Igor is waiting...

[Julie Moriarty]

The slab flattening went pretty well. I started by taking about 1/16" at a time. The most I took in any pass was probably less than 1/8”.

http://julimorcreations.com/2220/Kit/Island/Island_032.jpg

I found I couldn't do both slabs simultaneously because of the width of the sled and the bow of the slabs. The slab on the left was about 1/4” thicker so I took that down first. Then I switched back and forth. Before moving the slabs into place, I made sure the table was perfectly clean.

http://julimorcreations.com/2220/Kit/Island/Island_033.jpg

The sled rails served to contain much of the waste but dust still got on everything. I found setting the X and Y axis fairly easy by measuring the four corners of the sled off the plywood. The Z axis was a bit trickier. I got it close, but not perfect. It left some track marks. I did a small section running the sled parallel with the grain of the wood and the track marks pretty much disappeared. If I had the help of an assistant I would have run the sled parallel with the grain.
After the sled work was done, I switched to a belt sander with a 80 grit paper. Then I switched to a 6” RO sander and took that from 80 to 240 grit. From there I went to the card scraper. It took me about a day to do the card scraper work. That wood is so hard it work the hook out on the scraper pretty quickly.
http://julimorcreations.com/2220/Kit/Island/Island_034.jpg

The above is just before skip planing the bottoms. I flipped the slabs once they were reasonably flat on the tops and knocked down the bottoms so they laid flat on the plywood table. You'll also notice the dust collection hose attached to the router. It picked up all the fine dust and some of the chips. But I didn't start using it until the final passes on the tops. On the third slab I'm going to hook up the Dust Deputy to the vacuum and use dust collection for the entire job.
Overall I'm pretty happy with how the sled performed. If I were to make a production out of this I would install some means to fine tune each axis. Maybe screw-type adjusters could be incorporated.

[glenn bradley]

Lots of ways to skin this cat. Here's one in metal (http://www.sawmillcreek.org/showthread.php?226811-Router-Planer-Sled&highlight=), using aluminum (http://www.sawmillcreek.org/showthread.php?226812-Router-Planer-Sled-(Continued)&highlight=) extrusions.

I was hoping Ted would chime in. Love that thing Ted.

[Brian Holcombe]

There is another way to do this kind of work. I have done this by hand for years now but needed to step up the pace for a kitchen design that required me to move along a bit faster than I normally do.

I work a slab by first creating a reference face, I do this by planing it flat. I plane it flat using winding sticks and a straight edge to determine when the surface is first free of twist then flat.

The most recent slab had a pretty decent cup to it, but light on the twist. I removed material from the center of the board first to bring down the hump. Doing this usually allows the board to relax a bit and the opposite side becomes less cupped as material is moved (not dramatically but a measurable amount).

https://brianholcombewoodworker.com/wp-content/uploads/2017/10/IMG_8274-2112996841-1508119958374.jpg

Once the reference face is created I can use that to either mark off of (for a very wide board) or for a narrow board it can be sent through a thickness planer. Once the opposing side is finished I flip it over again and remove material from the original face. The result is near perfect.

If a thickness planer is not wide enough I can simply plane to my mark, then take over with hand planes.

Without rushing this remains and exceptionally fast process that is highly accurate. The board is checked numerous times throughout the process for twist, bow and cup.

[img]

[Brent VanFossen]

I've enjoyed this thread, and it looks like your sled worked well. As for the card scraper, that work will tire the thumbs and fingers!