Routing technique

Discussion in 'Luthier's Corner' started by Smilodon, Apr 18, 2012.

  1. Smilodon


    Feb 18, 2012
    I'm hoping to start a next build soon, but I'm a bit unsure about the order of doing the routing.

    First of all, is it best to route the neck pocket before or after the body shape? In my mind it would be better to route the neck pocket first, fit the neck and measure an accurate center line along the neck. That way I can be sure that everything will line up.

    Also, could the rough cut stage be eliminated? I'm thinking about simply plunge routing around the outline of the body. (In several passes, of course). It will be more or less like routing a truss rod groove, only curved. In my mind routing a groove will help keep the bit stable, preventing tear outs. After all, this seems to be the way CNC mills make bodies in factories.

    So, am I crazy?

    Also, what is the best way to deal with sharp outer corners (the heel of a fender p bass body, for example) when routing with a template collar? As far as I can see there is no easy way to route outer corners with a diameter smaller than the diameter of the collar.
  2. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
    There is always some conjecture with this. A lot of guys here such as myself, like to do the neck pocket first as it provides a level stable surface without the chance of fall off on the cutaways or over the end, but if your template is large enough and secure enough, either can work just fine.

    As for the body, many people go for the plunge method, and some are quite successful. Things to remember with this method, are first, make sure your router has enough power for this method, as this is very hard on the motor. Secondly, you can get a lot of bit burn on the wood if you are not cutting quickly enough. Third, by moving too quickly, the bit can start taking chunks, so there are things to consider when you go with this approach.

    I don't do Fender clones, thus the heels I do are not square blocks, so I will avoid commentary even though I have an opinion. ;)

    this might help too, a pictorial I did on building a body.
  3. miziomix

    miziomix Über on my mind Commercial User

    Sep 28, 2009
    Milan, Kuala Lumpur, Paris.
    Bass builder @ MüB.
    I route the neck pocket after having rough cut the body. It works for me. But doing it the other way around seems a more sensible way to go.

    I don't prefer routing the body shape for all the reasons listed by Musiclogic.
  4. Smilodon


    Feb 18, 2012
    Thanks for the input. :)

    For some reason all the builds I have seen the neck pocket were routed after the body. I guess that's just a coincidence, then. :)

    As for body routing. Sounds like this my work, then. Bit burn doesn't worry me that much. The body will be painted in a solid color anyway. (It's my first build. Better start of easy. ;) ) A 2,1KW router should be able to cut easily enough. I plan on using a small bit for this.
  5. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, I agree with Musiclogic and miziomix.

    You can rout the neck pocket and the other front surface cavities either before or after you cut the perimeter. It doesn't really matter. Whichever is easier for you in aligning your templates. I think in terms of priorities. Getting the neck pocket, pickup pockets and any bridge holes and pockets all correctly aligned together is the most important thing. The precise outline of the perimeter is less important.

    Trying to route the whole perimeter of the body by hand as a deep groove is not a good idea. I'm not saying it can't be done, but it's nasty and asking for trouble. Your thinking is backwards. Routing down into a deep groove doesn't support the bit, it can cause it to start chattering within the groove, which can get ugly fast. Routing a 1/2" wide x 1 1/2" deep groove is dangerous territory, unless you have a big heavy powerful router and very stable setup. CNC machines can do it because they have very tight control over depth and position. I recommend that you bandsaw the perimeter of the body 1/8" outside the line, then attach your template and rout the perimeter in a bunch of small steps in depth.

    By the way, you said that you'd rout the perimeter in a "couple of passes"? Unless you're working with big heavy equipment, I recommend that you never rout more than 1/8" deep per pass. A 1/2" diameter bit cutting 1/8" deep is about the right amount of horsepower load for most handheld routers. More than that and you're going to slow the motor down too much, which will burn the wood, dull the bit, and cause all kinds of problems. Yeah, my 12 lb, 3 1/4 hp Porter Cable 7518 router can do 1/4" deep passes, but I still don't usually push it that far. A 5/8" deep neck pocket should be done in 5 passes. A 1 1/2" deep body perimeter should be done in 12 passes. Stick with that and you'll avoid a lot of trouble.

    About the sharp outer corner and the collar: Yes, you are right. If you roll the collar around the sharp corner on the template, you'll get a rounded corner on the workpiece. The solution is simple: Don't roll the collar around the corner of the template! Just slide the router straight off the corner from both directions, and you'll get the sharp corner. If you're nervous about doing that, just stop moving the router right as the bit reaches the corner, from both directions. That will leave you with a small lump, which you can hand file to the sharp corner.
  6. Smilodon


    Feb 18, 2012
    I wasn't going to rout the body in "a couple of passes". I did a deep plunge rout once. (half an inch in one go without any pre drilling) I won't be doing THAT again. :eek:

    The problem is that I don't have a band saw. (No space to put one. :( The most suitable thing I have is a jigsaw, but I don't trust it to be accurate enough to cut straight through 4cm of hard-ish wood. I guess I could do it by hand with a coping saw. It will take forever, but at least it's safe. :)

    As for the sharp corners on the heel. I don't dare to freehand it. I could simply make the template longer towards the edge that is straight and then take the rest with a saw and a belt sander. Or maybe I'll get a template bit after all. (I was hoping to avoid those. Too many horror stories. :/ )
  7. HaMMerHeD


    May 20, 2005
    CNC shops can get away with it because they have very powerful CNC routers operating at consistent speeds, and they use end mills, not router bits.

    I wouldn't do it if I were you. It might be worth finding a shop local to you to pay a do it for you. I haven't gotten my bandsaw moved in yet, but I found a guy who was willing to do the last one for $5. (actually, when I got there, he had locked his keys in his car a couple miles away, so he traded the cut-out work for a ride back to his car with the necessary unlocking gear.)

    Depending on what kind of wood you are using, the jigsaw might not be a terrible option. If you go slow and stay well outside the line, you can then clean it up with a router.
  8. I've done it both ways and found I don't like cutting the pocket after the body is shaped. There isn't enough flat surface when you go in that order, to support the router on top of a rounded body.


    I also rough cut the body with a small bandsaw leaving about 3/16" of raw material on the outside for further routing and shaping.

    Around the neck pocket, I leave considerably more wood for stability. This is the way I left the neck area for my next body:::


    I used some small finmishing nails to anchor the template to the wood that was going to be removed, so there won't be any nail holes to hide or fill:::


    Here you can see the wood around the pocket that's left alone for later removal:::


    Then I finish the contour of the body after all the rough handling is over with. This keeps damage to the thin edges of the neck pocket to a minimum:::

  9. Smilodon


    Feb 18, 2012
    What if I make a neck template that is bigger than the body and secure it tightly with a couple of screws (where the pickups are going, for example). That way there should be more than enough surface to support the router. That way I can rout the body shape first, and still have a very stable platform for the neck pocket. That should work just fine, right?

    What is best to prevent tear outs, bigger or smaller bits?
  10. HaMMerHeD


    May 20, 2005
    My experience has been that smaller bits tear out less but heat up faster, which causes scorching and eventually bit failure.
  11. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    The diameter of the bit doesn't make a whole lot of difference in reducing tearout. The way to minimize tearout is to reduce the depth of cut on the final passes. In this case, routing a perimeter, "depth of cut" refers to the bit moving sideways towards the final size of the body as defined by the collar contacting the template.

    Ideally, you'd like to first rout around the perimeter at +1/8", that is, routing the shape, but 1/8" oversize. Then make a second pass at +1/16". Make a final pass at "0", the finished size, but make that pass in the reverse direction, known as "climb cutting". Looking down from the top, for a normal cut you move the router CounterClockwise around the body. For a climb cut, you move the router Clockwise.

    Note: Climb cutting should only be done on very shallow cuts! Don't try to do a heavy cut in the climb cut direction! The router will grab and kick.

    This process of making a final shallow pass in the climb cut direction is how it's done in a CNC machine to minimize tearout and make a smooth finish on a perimeter. It's easy with the programming.

    It's also fairly easy to do this process with a hand held router and a collar base. You temporarily increase the effective diameter of the collar by 1/8" and 1/16" for the rough cuts. The simple way is to find some cardboard (like shirt cardboard or posterboard) that's about 1/16" thick. Cut some strips with a width about equal to the depth of the collar. Use black electrical tape to attach the cardboard strip to the collar, wrapping it around the outside. Then tape the second strip over top of the first one. Now make your rough cut with both strips on. Peel off the outer strip to make the second cut. Then peel off the inner strip to make the final climb cut, bringing the perimeter right to the final size.

    There are other ways to accomplish the same thing. For one of my collar base routers, I made up aluminum sleeves that slip over the collar. For the production tooling for one of my standard models, I made up three templates of the body perimeter; one at final size, one at +1/16" and one at +1/8". They popped in and out of a holding fixture and saved me the trouble of messing with sleeves on the collar.
  12. Smilodon


    Feb 18, 2012
    Good idea about increasing the collar size. :)

    I'm thinking that I could do a rough cut then use the same size collar and gradually larger bits to do the body shape. The largest size could be cut like you said with some "padding" on the collar. and then finish up with the correct collar and bit.

    Hammerhed: I guess I could get away with using a jigsaw using the method above. :)

    Thanks for the input so far. :)