MHRestorations Posted May 29, 2018 Report Share Posted May 29, 2018 I've built a used the router sled for flattening slabs made famous by Nick Offerman a few years back. Multiple YouTube videos now on how to build them correctly, including one by Marc. Im having an issue with mine that I've not seen addressed in any of the videos that I've found. I have a 4 foot wide slab in the shop, which means my sled is about 5 feet long. Im having issues with the sled sagging in the middle from the weight of the router, causing a slight dip in the slab in the middle. Im not pressing down with any more or less force in the middle vs the ends, so I think I need to make a change to the structure of the sled (all made with 3/4" ply). Anyone have a similar issue or know what I might do to fix this? Thanks guys! Quote Link to comment Share on other sites More sharing options...
Mark J Posted May 29, 2018 Report Share Posted May 29, 2018 Just gonna throw my two cents at this while we wait for other, likely more intelligent, contributions. It sounds like you have 3/4 inch plywood spanning a 4 foot distance. And the plywood sled is just not stiff enough. You could increase the stiffness by adding steel angle extrusions along the front and back edges of the sled. These are generally straight (check against a level) and can be had in various thicknesses (i.e. stiffnesses). 2 Quote Link to comment Share on other sites More sharing options...
Popular Post Chestnut Posted May 29, 2018 Popular Post Report Share Posted May 29, 2018 The walls need to be taller. You could throw thicker material at it but you'll get more strength faster by making the walls taller. You can see how the sides are around 3" if yours are around that try going to 4 or even 5 inches. You might need to remake the sled wider to make the whole router handles and all fit inside. To guide the base if you need it to be wider use some scraps glued to the bottom. Think of this like an I beam the taller the web is the stronger the beam. You don't need the web or the flanges to be very thick as long as the web is tall. Or like how a 2x10 can span longer than a 2x6. the height is where the strength is not the thickness. 6 Quote Link to comment Share on other sites More sharing options...
Brendon_t Posted May 29, 2018 Report Share Posted May 29, 2018 Either option above should have you set fine. The goal just being to stabilize the whole bottom from sagging. I personally would not want to have 5" sides on the sled as I alredy get a lot of material sticking up there during large flatterings but it would work. A few bucks of angle iron spanning to support would also be fine. Quote Link to comment Share on other sites More sharing options...
drzaius Posted May 29, 2018 Report Share Posted May 29, 2018 Post a pic of your sled & then we can provide more informed suggestions. 1 Quote Link to comment Share on other sites More sharing options...
Chestnut Posted May 29, 2018 Report Share Posted May 29, 2018 16 minutes ago, Brendon_t said: Either option above should have you set fine. The goal just being to stabilize the whole bottom from sagging. I personally would not want to have 5" sides on the sled as I alredy get a lot of material sticking up there during large flatterings but it would work. A few bucks of angle iron spanning to support would also be fine. Need to make sure the angle iron is cold rolled. Hot rolled isn't going to be strait. May look strait but it could wave enough to leave marks on the slab that would lead to more work later. 5" is drastic the jig shouldn't sag at 3.5 - 4" from the weight of the router, if it does you need to buy a lighter router. Other option if you don't want to have more material sticking up is to tag it on to the sides with glue and brad nails. doubling the sides will also benefit but again 3" tall. This guy is always helpful http://www.woodbin.com/calcs/sagulator/ Using sagulator with 35lb router (is this realistic?) 6" wide base with 3.5" tall sides sags .02" if you double the sides the sag is eliminated. If you increase the sides to 4.5" the sage is eliminated. If you double up the bottom the sag goes to .01" 1 Quote Link to comment Share on other sites More sharing options...
MHRestorations Posted May 29, 2018 Author Report Share Posted May 29, 2018 48 minutes ago, drzaius said: Post a pic of your sled & then we can provide more informed suggestions. Nothing special obviously, but here is what I put together. Thanks for all the input. If possible I'd like to avoid having to add any angle iron to it, but not against it completely. Router is a basic Skil combo base. Around 15 lbs. Current height of my walls are 3". Glued and screwed the bottom up into the walls. Quote Link to comment Share on other sites More sharing options...
Chestnut Posted May 29, 2018 Report Share Posted May 29, 2018 Double the sides except extend it down to cover the ply edge and you should be good. make sure to put glue on the whole face. 1 Quote Link to comment Share on other sites More sharing options...
drzaius Posted May 29, 2018 Report Share Posted May 29, 2018 What nut said. Quote Link to comment Share on other sites More sharing options...
Pondhockey Posted May 30, 2018 Report Share Posted May 30, 2018 I can confirm what's already been said; I also built the Offerman sled; stiffness came from the walls. I also tried angle iron - more sag than the wood version. One tip, in case it helps: a medium size plunge router is probably better than a large fixed base: less sag and more cutting tool extension. 1 Quote Link to comment Share on other sites More sharing options...
Brendon_t Posted May 30, 2018 Report Share Posted May 30, 2018 53 minutes ago, Pondhockey said: One tip, in case it helps: a medium size plunge router is probably better than a large fixed base: less sag and more cutting tool extension. Plunge yes if at all possible but not going to the lighter side. My slab flattener is about 3" across. I want the router it's in to have as much ass as possible. I know I can build the sled to not flex, I also want as much weight in the tool spinning the bit for stability. 1 Quote Link to comment Share on other sites More sharing options...
Coop Posted May 30, 2018 Report Share Posted May 30, 2018 Not 3”? Fingers too big for the keys? Quote Link to comment Share on other sites More sharing options...
Coop Posted June 1, 2018 Report Share Posted June 1, 2018 I have a small, 24” x 36” slap I need to flatten. After building the jig and attaching it to my work table, do I secure the slab to anything in any way to prevent movement. I’m assuming that I need to shim on the bottom to prevent anykind of rocking. Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 2, 2018 Report Share Posted June 2, 2018 I shim with playing cards. I tape equal amounts under the opposite high corners. You can run a sled through a drum sander with 36 grit or use a router sled to flatten one side. I flattened & sanded both sides of a 20" x 38" x 3" slab of 200 year old cypress the other night in about 90 minutes. 36 grit then 60, 80, 120, 150, and dressed it w 220. Big twist on a longer slab and I would definitely use a router sled first. Maybe 65 or 70% of the surface flat and you can switch to a finer grit. 1 Quote Link to comment Share on other sites More sharing options...
treeslayer Posted June 2, 2018 Report Share Posted June 2, 2018 I use the shims they use for doors and windows on my planer sled and stick them on with a hot glue gun, maybe you can use them for a slab that’s got some serious twist 2 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 2, 2018 Report Share Posted June 2, 2018 I put a sled under the slab & shims before I drum sand / plane / route to flatten the initial face. Just to clarify. Quote Link to comment Share on other sites More sharing options...
Jim DaddyO Posted June 2, 2018 Report Share Posted June 2, 2018 I did my 7' 3" slabs with a router. I used 2 x 8's for the side slides. Quote Link to comment Share on other sites More sharing options...
Coop Posted June 2, 2018 Report Share Posted June 2, 2018 1 hour ago, wdwerker said: I shim with playing cards. I tape equal amounts under the opposite high corners. You can run a sled through a drum sander with 36 grit or use a router sled to flatten one side. I flattened & sanded both sides of a 20" x 38" x 3" slab of 200 year old cypress the other night in about 90 minutes. 36 grit then 60, 80, 120, 150, and dressed it w 220. Big twist on a longer slab and I would definitely use a router sled first. Maybe 65 or 70% of the surface flat and you can switch to a finer grit. I hate changing the paper on my Jet sander. 1 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 2, 2018 Report Share Posted June 2, 2018 20 years of practice... plus the paper is so much easier to change on the SuperMax. Drag your slab to Atlanta if you want some help with it. 1 Quote Link to comment Share on other sites More sharing options...
AJ_Engineer Posted June 2, 2018 Report Share Posted June 2, 2018 You check your sled with a straight edge while it doesn't have anything just to make sure it's flat to start with? If it really is sagging (check with straight edge after putting weight in middle) then just get some more plywood strips to reinforce/extend the edges as mentioned above. Just screw them into your current sides. Quote Link to comment Share on other sites More sharing options...
wtnhighlander Posted June 2, 2018 Report Share Posted June 2, 2018 Coop, you might use some carpet tape to hold your slab to the bench, so it won't slide around. 2 Quote Link to comment Share on other sites More sharing options...
Coop Posted June 3, 2018 Report Share Posted June 3, 2018 23 hours ago, wtnhighlander said: Coop, you might use some carpet tape to hold your slab to the bench, so it won't slide around. Good idea. Or, I could take it to Atlanta 1 Quote Link to comment Share on other sites More sharing options...
Coop Posted June 3, 2018 Report Share Posted June 3, 2018 I just wish the jig was the worse part of the leveling. After an hour of flatening, my right hand is in the shape of the Bosch handle. 2.25” to 3/4”, steady as she goes mate! 1 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted June 3, 2018 Report Share Posted June 3, 2018 I would think 1 7/8 - 2" should be achievable. If you take that slab down to 3/4 on purpose or out of ineptitude I will be ashamed of you. And the likelihood of it moving considerably will be substantial. Quote Link to comment Share on other sites More sharing options...
Pete Staehling Posted June 3, 2018 Report Share Posted June 3, 2018 One thing that wasn't mentioned... Before doing anything to the sled, I'd try just not pushing down on the router. Take light cuts and let the weight of the router provide most if not all of the downward pressure on the sled. 1 Quote Link to comment Share on other sites More sharing options...
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