174 – Flattening Workbenches and Wide Boards with a Router

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The traditional method for flattening a workbench is to use hand planes and winding sticks. While some folks truly relish this labor of love, others prefer to delegate this grunt work to power tools. The power tool method is very similar to the action of a CNC machine. A router is placed inside a sled that rides along two parallel rails that are attached to the sides of the bench. The router sled is very easy to make from scrap 3/4″ plywood. The rails can be made from 2×6 construction-grade lumber. Cheap and simple!

The only tricky part of this process, if there is one, is making sure the two guide rails are not only parallel to one another but also roughly parallel with the top. Fortunately, there is a very cool trick you can employ using string or thin cable.

Once the rails are in place, the router is dropped into the sled and the bit is plunged down. Ideally, you want to set the bit at the lowest part of the bench. One way to do this is to plunge the bit until it just touches the bench. Move the sled and router to various parts of the bench (with the power off) to see if the bit catches or slides freely. If it slides freely at any given point, you have just found a location that is lower than the original spot. Reset the router plunge depth at this new setting and continue to scan the bench. Once you have the bit set at the lowest point, bring the sled back to the end of the bench and start the routing process. Anything higher than that low point will be routed away and you’ll be left with a nice flat surface.

Here are two options for router bits. They have the same specs (1 3/4″, 2-flute straight bits) but the Freud will save you a few bucks:
Amana – 45453
Freud – 12-194

Perhaps one of the best parts about this jig is that you can re-use it for other things. Have an end grain cutting board that needs flattening, but you don’t want to send it through your planer? Have an oddly-shaped natural edge slab that is just too large for your tools? Both situations can be handled with a setup like this. And if you plan on using it a lot, you can get as elaborate as you want with the design of the jig. The version I show you here is stripped down to the absolute basics.

I should add that this technique is nothing new. I first learned about this in a forum about 10 years ago and later found out that it came from a technique publishes in one of Tage Frid’s books: Tage Frid Teaches Woodworking. A worthy read for ANY woodworker!

This video is an excerpt from the recent Split-Top Roubo Workbench Guild Build. Join the Guild today to see the entire set of videos and build your own lifetime workbench!

Category: Techniques

Comments

  1. Great video. I’ve been doing pretty much the same thing with my CNC router as my primary method of flattening boards and it works great. I’ve also used it for end-grain cutting boards with great success. A couple suggestions: If surface finish is important use a bottom clearing bit like the Grizzly C1261 and make narrow (less than half the bit width) climbing passes parallel to the grain. If you’re doing it by hand then climb cutting might not be possible, but the narrow parallel passes allow the bit to cut the wood fibers cleanly rather than slashing across them. Using this approach I don’t even need to sand most of the time.

  2. Scott Smith May 23, 2012

    Great video.

    I’ve been trying to decide if I should just flatten my existing bench or tear off the top and lay down 2-3 sheet of 3/4″ ply and a sheet of Masonite over the top. I built my bench out of construction grade 2x4s laminated together. With a sheet of 1/2″ ply over the top. Several months ago I took my ply off and discovered a mess of shrinkage underneath. I took my power hand planer and took off about 3/4″ of an inch but it was still not very even. So I put my sacrificial sheet of 1/2″ ply back on top and shimmed it until it was somewhat even. I just use my tablesaw top when I need an absolute flat surface. But I’d like a little more room when assembling things. This would certainly make my laminate 2×4 top more even and the ply would cover the gaps in the 2x4s.

    Would this bit work similar to your straight bit:
    Freud 16-522, 1-1/4” Mortise Bit and Bearing: http://www.rockler.com/product.....lter=42022

    Thanks for all of the great content.

  3. Michael May 23, 2012

    Thanks Marc, great demo. I wonder how much the flatness of your shop floor plays in to the flatness of the top. I imagine the shear weight of the bench will cause some minor twisting to the top if the floor isn’t perfectly flat. It might be worth it to put Sharpie marks around your legs on the floor so you could find this exact spot again if the bench ever needs to moved.That would put it right back into the place where you did this flattening procedure and assure you that you’re back to square one.

    •  

      Well the base is shimmed so that essentially nullifies the effect of the uneven floor. Also, with a 4″ top, I really don’t know how much sag would be induced by an uneven top. If the base is square and the top is secured to the base, a structure like that is more than likely just going to rest on three legs with the 4th leg raised. I can’t see it sagging any time soon. But again, shims took care of it pretty easily.

      • J R Rightmire May 23, 2012

        Would \n’t a four foot level across the rails gain the sam result. Thanks for fixing your clock.

        •  

          Oh don’t get too excited. This video was filmed before the clock stopped working. So you can be sure in the next current video, the clock will be firmly planted on some random time. :)

          As for the 4 foot level, no, I don’t think that would produce the same result. It wouldn’t be nearly as accurate as the string cross-over method.

  4. Jeremy May 23, 2012

    I love that router, its a beast!

    Just out of curiosity… no splinter guard on the PS 300?

    •  

      I usually use the jigsaw for solid wood cuts and rough cuts at that. No need for the guard. In this case, it was just a jig so again, no real need for it. Of course every cut benefits from the splinter guard but unless it is truly necessary, I usually don’t put them in.

  5. Marc, Brilliant. I actually make cutting boards for friends and making some sort of jig to install on my bench may save me a lot of time on the wide belt sander.
    Thanks again.

  6. Brian May 23, 2012

    Marc, Great Video. When I am ready to build myself a real bench I am definitely going to use this method. Fine wood working also has a Video tour of Nick Offerman’s Work Shop. I think you may need to be an online member to see it but it shows his version of the jig in action. Off topic, where do you keep the computer in your shop? I would love to have one in mine but worry about the dust getting to it.

    •  

      Mine is right behind the workbench. I blow the dust off periodically but that’s about all I do to maintain it.

    • Kory June 1, 2012

      You could always put a fan filter in front of the fan to prevent some of the dust from getting in. You can find them from a number of places with sizes to match what your case offers. I would focus on the intake fans at the front of the case. Of course, this doesn’t apply if you have a laptop.

  7. Jim May 23, 2012

    Marc,

    Please forgive my newbish question. Why wouldn’t you make the opening in the jig wider than the workpiece? Seems like you could avoid having to hand plane if you could route right off the edge of the piece.

    Jim

    •  

      The jig is actually able to reach the edge of the bench and does. The reason I was left with material to plane away was because i was cautious when cutting into the rails. So the most effective way to get around this would be to put a little gap between the edge of the bench and the rail. Maybe a rabbet cut into the rail would handle that. But ultimately the rails were sacrificial so I didn’t worry much about it. Only took a few seconds to remove the excess material.

      • Nick S June 4, 2012

        If you add/clamp a piece of wood between the fence guide and the table top (mounted below the table surface) you’d be able to go through the edge completely (and not cut into the sacrificial fence). Or if you mount it slightly higher then it could act as a “zero clearance” backing to prevent any tear out off the table top.

  8. Doug B. May 23, 2012

    ok.
    If you want me to take you seriously as a woodworker you re going to have to stop going to get manicures and have at least one cut or scrape on those fingers. :)
    Nice video.
    I have 2 nice elm trunk pieces that are about 20″ wide and this will be a good solution to them sitting in the corner staring at me

  9. Werner May 23, 2012

    Hi Marc,
    How effective do you think it would be to use winding sticks at the ends of the rails to make them parallel.

  10. joe May 23, 2012

    But that strings method is not sufficient to level the rails. It only guarantees that the middle point is in the same level, but lowering one corner can be “fixed” by getting diagonal corner up, ending up with propeller-like twist. You still need to use winding sticks at least in one direction to ensure flatness. Well, in this case, the bench top was almost flat and there is almost zero probability of any twist. Anyhow, the presented method cannot work per-se in general.

    By the way, Mark, were you very surprised by the deviation in that one corner, or did you expect it?

    •  

      The raised corner was actually not a surprise. I knew the issue was present well before the leveling process began.

      But I don’t completely understand your premise on the rails. I do believe the rails are perfectly parallel using this method. If you hit one corner, you might knock the other corner out. But this all shows itself at the center point where the strings cross over one another. This also has nothing to do with the flatness of the bench. Only after the rails are parallel do you make adjustments to try to get the two rails parallel with the top. Those adjustments tend to knock the rails out of parallel with one another so its a bit of a back and forth game. But there is no need for winding sticks here. I should add that this method is NOT my idea. I learned it from a forum and I believe the original idea goes back to Tage Frid.

      • Ansel May 24, 2012

        I agree that those strings can only touch each other at the middle only if the rails are parallel. Any propeller twist will separate them. However, the plane formed might not be level with floor and the table might end up flat but tilted. Is that a concern?

        •  

          The floor level is actually irrelevant. That’s why I try not to talk about level at all. I am only concerned about the rails and their relationship to the bench. The key to making sure that the two rails are parallel to the bench top is to measure at each corner. I was aiming to have my rails 1/2″ above the table height. If they are all pretty close to 1/2″, then I know the plane created by the two rails is roughly parallel to the plane of the bench top. A lot of this hinges upon knowing that current state of your workbench top. Is it pretty flat to begin with? Is there a twist? If so, where is that twist? This information will help you plan and ensure that your rails are as close to parallel to the top as they can be.

  11. Sean Rubino May 24, 2012

    That method of showing the rails are parallel is fantastic. It makes perfect sense to me as a student of Mathematics.
    I was just going to ask where you learned that. It just didn’t seem like a method that is just thought up. I was going to ask if you learned that in a class (i.e. William Ng, David Marks).
    After seeing this I went straight to the garage and made the sled to flatten a cutting board that didn’t glue up evenly and has a good amount of glue residue from the cauls. Awesome methods!

  12. Hey Marc,

    How about using one of those bowl router bits? 1-1/4″ in this case.

    Thanks,

    Bobby Slack

  13. Here’s a cheaper source on the Freud bit. http://routerbitworld.com/Freu.....12-194.htm There is shipping, but it’s only a dollar for any order. I buy nearly all my bits and blades there but occasionally Amazon will have something cheaper so always double check. No, I don’t work for them, just a satisfied customer.

  14. Dan Drabek May 24, 2012

    A nifty lesson in woodworking and geometry Marc. I really appreciated the string/cable method for determining parallelism. (if that’s the correct term). Sometimes the simplest method is better than a high-tech/high dollar solution. Your bench top is now probably more accurately flat than it needs to be for most woodworking, but extreme accuracy certainly can’t hurt. My bench top is overdue for a flattening. I think I might give it a try.

    DD

  15. Keith May 24, 2012

    Great content Marc. I’m hooked. I get to the end of a video and I’m sad it’s over. It’s a good thing I have plenty of older vids to watch. After that, I guess it’ll have to be the guild. I noticed that the HD version of your vids really a nice quality for full screen on my iMac. The older ones were not HD and were a different aspect ratio. I’m curious, what resolution are the recent SD and HD videos? And are the newer ones 16×9 aspect ratio? Other than the bloggie, are you still filming with the same camera since the beginning? The HMC-150? It’s interesting to see how far you’ve come since the early days.

    •  

      Thanks very much Keith. We’ve has couple different cameras over the years. Even the bloggie is collecting dust now since I have a new iPhone. My current camera is indeed the HMC-150. Any of our videos are are “widescreen” are 16×9. But over the years, our “HD” file has changed quite a bit, depending on limitations of our host as well as the general population’s tolerance for large files. So now the HD version is a true HD video with a resolution of 1280 x 720. The SD videos are actually whatever our host down-res’s them to but it is something that would generally be best viewed on a mobile device.

  16. Danny H. May 25, 2012

    Marc, Thanks for that video. I had been looking for this on the internet and wasn’t able to find it till now. So thanks for sharing! I’m also with Ted on purchasing router bits from Routerbit world out of Utah. They usually have what I need at the best price and their one dollar shipping is a nice bonus. Customer service their is also top notch. Although to flatten my work top, this time, I found a planing bit from MLCS that was a better deal. I’ve ordered a good number of bits from them and have never had any issues, and the shipping is free.

  17. Martin May 25, 2012

    Hello Marc.

    Thanks for this excellent, top quality video, as usual. Can you tell us what is the brand of bit you are using to countersink the screws when you build your sled at 7:00 in the video.

  18. Craig Reichert May 28, 2012

    That’s “Parks and Recreation”, not “Community”.

  19. I built the jig from the fine woodworking mag a few months ago to flatten large slabs as I had one standing around that I wanted to get started on – It was a little more involved, similar results, than this one and it worked great – that Amana bit is wicked….not to mention the 25 lbs of chips I accumulated.

  20. Quick question……I have a Festool OF1400 router……is it powerful enough to handle a 1 and 3/4″ bit? I notice you used the bigger Festool unit.

  21. dgriffis May 30, 2012

    What brand is that multi fluted bit? I must have one!

  22. Hey marc,

    First timer here posting for the wood whisperer. I make end grain cutting boards and I heard your comment about using the sled for truing up the face of a cutting board. I make my boards out of maple and walnut. One question. I attempted to do this. I was successful at flattening it out however; the router bit gave me a less than desirable surface that would take me an eternity to sand smooth. My solution was to put in my Dewalt 13″ planer and if it is wider than 13″ to make two cutting boards and glue them together. I love the idea of flattening out larger panels with the router but am hesitant to use on my end grain cutting boards again. Any advice on the matter? Maybe it is something I am doing wrong.

    Thanks
    Erik

    •  

      Unfortunately, this may always be an issue on an end grain surface. Scratching and marks in end grain are just a pain to remove. You might get better results using a bowl bottom bit or something like that, but I haven’t tried them myself. But ultimately, there is always going to be some extra work on end grain. Just the nature of the beast sadly.

  23. Victor June 9, 2012

    Marc, another great video! You’ve got a real talent for explaining the essentials of a process. I always enjoy your videos for the knowledge i gain but also for their entertainment value.

    So – I just finished flattening my benchtop after being inspired by your video. I too read the router sled article in FW but you gave me the cliff notes version by simplifying the build. Took me an afternoon (about 12:00 – 8:00).

    Years ago I widened my benchtop by splitting it and gluing in more maple (only about 8 inches worth). Unfortunately during the glue up I had a clamp malfunction and ended up with a 3/32″ sag in the middle. Bummer. So I have been long overdue for a flattening.

    I set the rails and checked my cables – I was suprised at the delicacy of tapping, checking rail height and pushing the cable to get the “kiss” just right. The patience paid off. I removed almost the full 3/32″ during the first pass. Then I restrung the cable rechecked each corner and started the second pass removing only about 1/64″. FYI, I used a Freud #12-186 1 3/8″ bit ($38.99 @ Woodcraft). Worked like a charm in my Festool OF 1400. I turned the speed down to 2. A little strain during the first pass but my feed speed was still decent. I have about a .01″ sag that starts about 2″ in from either side of the bench and is consistent over the middle 20″ of the bench. Not sure how that happened (sled not stiff enough?) but I’m thinking a couple of passes with my jointer plane on each edge and should have it dead flat.

    I’m thrilled with the results – a very fun and productive afternoon. Now I just need to decide whether to leave it bare or put a coat or two of Watco danish oil on. I’m leaning towards the oil since I’ll be doing glue ups on my nice new flat top. BTW, my final step was a few passes with my cabinet scraper, would you recommend sanding (220 grit) as a final step or leave it as is for gripping purposes?

    Thanks again for the video – hope to see you at IWF!

    •  

      Glad it worked out for you Victor. Thanks for the kind words! As for the sanding, I wouldn’t go beyond 120 or so on a bench. I like a more “grippy” surface. If you go too smooth, you’re work will be a little slippy.

  24. Dan June 15, 2012

    Marc, I really want to commend you on being very descriptive in your videos. Being a blind wood worker, I am often left scratching my head when listening to various videos. Your descriptions were enough that I had no questions at the end of this video. I completely understand every step of the process.

    I have used the criss-cross strings to frame out doorway openings to make sure there is no twist and that the walls are coplanar. Being blind, I often use modified techniques, in the case of the criss-cross strings, I use Copper wire and a continuity tester to tell me exactly when the wires touch in the middle. Yeah, over kill if you can just look at the contact point, but I’ve found it difficult to touch the strings and know when they are just kissing without my touch throwing things off. With the continuity tester, I can adjust the corners without having to ever touch the wires.

    Anyway, I don’t currently have a decent work bench, but it is the next big project on my list, and I will definitely be using your method to flatten the bench top.

    •  

      Hey Dan. I am glad to hear the descriptions are thorough enough for you to get the idea. I never really thought about how visually-impaired folks might use my videos but this makes me realize how important it is that I really drive the concepts home in words. My step dad is legally blind so this is something I should probably think about more.

      And using that system in a door frame is very smart! Awesome idea!

  25. Mark June 17, 2012

    I’ve got a limited set of tools (actually just finishing the low entertainment center) and want to try this to flatten a cutting board. Without a jig saw, is it ok just to take a couple of passes through the sled with the router? I’m thinking it should not affect the process, but want to make sure I’m not overlooking anything. (and thanks for all you do – you have no idea how much you’ve taught me over the last year or so)

    •  

      Yeah I think you should be fine creating the clearance hole with the router. Just be sure to fully clear the space so there’s nothing to catch on later. You’ll also have a good deal of tearout so you will want to sand the bottom of the sled after you’re done.

  26. Ric July 16, 2012

    I used this to flatten my top and it worked pretty well, but there were more than a couple of gotchas:

    1. Jointing 2 lengths of yellow pine 8 feet long completely flat was a challenge (for a newbie)
    2. Setting the router to JUST the right depth so it was deep enough but not so deep as to waste wood was not easy (read: took more than one try)
    3. Controlling the router back and forth (and back and forth and back and forth and …) was not only tedious but tiring and a bit of a challenge. In particular, when the router is pulled back towards the operator it is not going in the “right” direction so it tries to climb and pulls toward the operator. This is hard to overcome, especially for those with no experience with this step. Result was noticeably more router “swirl” marks. Nothing that won’t sand away easily.

    I got the job done, but it was a learning experience. If was to do it again, here are the parts I would change:

    1. Buy two 8 foot lengths of extruded aluminum and screw these to the 8 foot lengths of pine to p provide a perfectly flat, smooth surface for the sled to ride on. Attach them on the outside of the pine, just extending up enough to provide the riding rail while still keeping the pine as the sacrificial edge for the router to bite into
    2. Add a cleat at each end of the sled so that it doesn’t shift and is easy to mooch along the rails
    3. Accept that it is a very slow process and that the router needs to come all the way towards the operator BEFORE shifting laterally for the next pass. That way, the climbing part is more or less eliminated, but it means that shifting the sled is a little more awkward.

  27. Bruce Adams August 9, 2012

    In the setup, you mention that the two guide rails need to be parallel. I think the real term should be planar.

    My math friends made the following comment… Establish a point that is directly above the exact center of the piece. Then, using a rigid piece of wood, set the end of each guide piece the same distance from that point. That estbalishes a plane that includes the top of the guide rails. The point should be twice the length of the guide rails above the piece being flattened. (See why we don’t let mathematicians in the shop.)

    Great video. Keep those coming

  28. Colm D December 12, 2012

    Major thanks for posting this and providing such a clear explanation of how to fully execute this technique. I built my Roubo workbench and attempted to flatten it with my hand planes but I ran out of talent and made the top resemble a boat rather than any kind of flat reference.

    I decided to go for your technique and it really paid off, the top is now ice rink flat and I’m back to feeling proud again of the achievement. The only advice I can offer to people is to probably use a 1/2 router bit as it put too much strain on my 1/4 router bits and snapped 2 bits as a result.

    Much appreciated on the excellent videos and posts.

  29. Brandon December 26, 2012

    I’ve seen this method used before in other videos and it certainly seems to work well. But, I’m still not quite sold on the X indicating that the two rails are parallel. At least not in my head. Perhaps putting it into practice will clear up my concerns. I do have one question regarding a bench I built this summer. I used 2 pieces of 4’x8’x3/4″ osb to make the work top. I glued and screwed them together (perhaps a little overkill). I then topped it off with a removeable piece of 1/4″ melamine. I noticed a bit of a hump in the middle of the table. I placed boxes of marble tile on the hump for several days to try to reduce it. It did help, but it is still not to my liking. So, my question is how to flatten the osb top? I’ve never used my router on osb, simply because it seems like a really bad idea. Any ideas?

  30. Christian Rodriguez December 27, 2012

    Marc,
    I am new to woodworking and am trying to complete my first end grain cutting board. I did the final glue up a few days ago. As I was sanding it down today, I noticed that the board was a bit warped (convex/concave). I recently received a router for Christmas and am considering getting a router table. Can I flatten my cutting board using the router table? If so, is there more to it than simply running the cutting board across the bit one pass at a time? Thanks for helping a newbie.

    •  

      Hi Christian. I wouldn’t recommend trying to flatten anything with the router table. It really isn’t designed for that purpose. I’m sure someone out there might be able to devise some sort of clever jig to make it work, but I haven’t seen anything like that before. If you want to use a router for the purposes of flattening, the method demonstrated in the video is your best bet. Although it’s much easier when doing a small cutting board since you can just put the two rails down onto a flat surface, immobilize the board in between the rails, and you’re good to go.

  31. Michael Corwin April 21, 2013

    Marc, forgive me if this question is elementary but I notice in the video that you say to use the string to check corner to corner of your benchtop, but you are actually screwing the string into the 2×6’s about a foot in from each corner instead of at the edge. Does this make a difference, or is there a reason you did it this way? Thanks!

  32. Love your tips Marc. This is a great and cheap way of flatting boards down. I’ve taken it a step further and added bearings to get a bit closer to a CNC style action. It certainly helps with makings things ride smoother and easier. In the video below you’ll see a permanent setup for handling smaller stock, but I do have a larger (3.5 meter long x however wide I need) version that is somewhat portable.
    http://www.youtube.com/watch?v=z3g69EuoZtU

  33. Mike S... July 14, 2013

    Just used this to flatten my bench. Worked great. Obviously I ran in to a few issues because well … I’ve never done this. I think the mere fact that I’m here looking for advice makes it pretty clear that I need it;) So I have none for you (surprise! LOL) other that keep making tutorials man! These are awesome.

    I would say for anyone new to this and about to do it, don’t skip on the “wax your sled” advice! Man my wrist is still sore from working that thing back and forth for 1/2 hour! Also, buy a 1 3/4″ routher bit as suggested. I used a Porter Cable 3/4″ straight flute from their “set”. Again, wrist … sore.

    Jointing 8′ boards was a little challenging on a little bench-top jointer. I just ended up buying Birch plywood and ripping strips on my table saw. Glued 2 together for more stable rails.

    Marc thanks dude! Great upload:)

  34. Crhistian Ramirez August 14, 2013

    Marc,

    I’m buying my first router to use on this application specifically and was wondering if a 1.25HP 1/4″ collet router would have sufficient power to do this? In particular I am looking at dewalt’s DWP611PK

  35. Tim Crossan September 15, 2013

    Marc,
    I am flattening a 32″ x 72″ x1-1/4″ thick table top.
    I don’t have a confirmed flat surface to lay it so I’m wondering how I can apply this technique to flatten the top.
    There isn’t much to try to clamp rails to and if the top is twisted Asti surely will be I’m not sure it will work. I’d like to try it if you can convince me a a fail proof way to do it.
    Great video. All of them are!

    Thanks.
    Tim Crossan

  36. Mark Barber September 18, 2013

    I teach for a living and this was the best and most descriptive video I have ever seen for free! well done. I have some 24 ” Douglas fir slabs to turn into my new desk and some huge 100 year old timbers to turn into projects. I’ll send a picture wen done. Thanks.
    Mark

  37. joe September 30, 2013

    Great video Mark, thanks. Do you think the Festool 1400 (or equivalent 2.25 HP router) is powerful enough for this job and these bits?

  38. William October 20, 2013

    I was building the sled when I ran into a problem.

    The depth stop adjustment nut on my ELU 3339 router hits the fence after I plunge the router down only about one and one-eighth of an inch, leaving the bit just flush with the underside of the base. If my calculations are correct, I believe I need to plunge the router an additional one and one-eighth of an inch (min) in order to clear the plywood base as well as give me about one half inch of depth below the rails.

    Unlike your bench, the top of my bench is only about 15″ wide. So…do you think I can cut down the plywood fence on one side of the sled to two and one half inches without fear of introducing a sag in the middle of the sled. If not, how would you recommend I stiffen the sled?

    Thanks. Bill

  39. woodspiral January 6, 2014

    Concerning the Mathematics of this method; if the rails are perfectly straight, the strings are perfectly taut and are dimensionless, then if the strings touch then the rails will be parallel and hence coplanar. In the real world the rails might not be entirely straight, the strings have a dimension (that is a thickness) and they might sag a little. I think the single most important thing to get right is to ensure that the rails are straight, everything else should then follow from your method. The error would probably be less than a 1mm over several metres.

    Concerning whether to get the rails level with the floor etc is an interesting point. My workshop floor is angled quite dramatically like an old Batman episode, so I certainly don’t want that as my datum! I think the best datum for both rails is the bottom of your benchtop. Another possibility is to use a spirit level, but it would have to be very carefully aligned, and it also relies on whether your bench itself is level. I’ll probably use a combination of both of these methods to flatten my bench.

    I have a Roubo-style bench I made with Christopher Schwartz in Germany a couple of years ago. I have flattened it roughly by hand using a plane and winding sticks and it’s close, but I’d like to get it really spot on.

    •  

      Just one little correction. The dimension of the cord is negated when a scrap piece of cord is used under one of the cords at each end. Otherwise that could definitely add a lot of error into the mix.

      • woodspiral January 6, 2014

        Yes, I stand corrected – I hadn’t thought about that part of your method (or Tage Frid’s) Moving the upper cord up by a whole cord thickness is a good correction, although still subject to some error. Using thin piano wire or light fishing line would be another way to ameliorate this issue. Mathematicians work in idealised worlds, where planes are infinite, points are dimensionless, pulleys are frictionless and cords are massless and inextensible.

        I’m actually planning to build a CNC machine later this year, so will be interested in this and other methods for getting rails dead on. Lasers anyone?!

  40. Mack January 16, 2014

    I just used this method last night to flatten a rustic farm style table I’m building using construction grade 2x lumber. Even after running it through the planer several times before glue up there was still 1 spot lower than the rest. A 4` x 6` table took me about 2 hours with 3/4″ straight bit (I was too impatient to wait for shipping on the larger bit) a quick sanding and it’s nice flat and smooth. Thanks for the awesome lessons

  41. TXBui January 19, 2014

    Awesome video Marc. Question: I built the sled out of 3/4″ plywood (base and sides). My issue is the router bit now has to clear 3/4″ of plywood base and another 1/4″ of cut depth, leaving me a dangerously short stem remaining on the router bit to be tightened to the router itself. Is this not a concern to anyone?

  42. Jerry February 19, 2014

    Enjoyed your video Marc. Getting ready to build/replace my bench and like the size and style of this one. Do you have plans or video available?

  43. John Keating March 5, 2014

    You keep saying parallel in the video, when in fact I think you mean level. If the bench is the same width all the way along, the rails are automatically parallel. It is the levelness of the rails, that is important.

    •  

      Thanks for the clarification. What I really meant is that the planes established by the rails are parallel to one another. I’ll admit that my geometry terminology is sometimes a stretch but if the point is clear, I don’t worry too much about it. :)

      • B.S. August 4, 2014

        To beat a dead horse… planar is the term. The 4th corner must be adjusted to be on the same plane created by the first 3 corners, independent of the workbench top (though you want to be close). Whether it is level or not is irrelevant (as long as your workpiece isn’t sliding off the bench!). Parallel is an appropriate term when viewing the rails from a perpendicular perspective.

        Awesome video!

  44. Dave Loewus May 7, 2014

    Marc,

    I think that your video and method is great. I am trying to get into wood working and build a shop in my garage with out kicking my wife’s car out of the garage. I am trying to build a work bench that is suitable to my situation. In any case I was thinking of using some 80-20 aluminum extrusions on my sled rather than plywood rails. I am just thinking how to take a good idea and make it better.

    Dave

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