What actually goes into designing and building a new model?

[Tim McKnight]

After we (our client, Mary and I) are satisfied with the design concept then we begin taking that design and converting it into images that will later become our template, bending forms and body mold.

The first step is to take the body design and cut it exactly in half which will become the template for the top and back. We always use a half template instead of a whole template. The template is used to trace the outline on to the top and back to give us an outline that will will later be cut out on the band saw.






The image on the right shows the 1/2 body template. We typically use 1/4" thick hard board or plywood material to cut templates from. They are thin enough that we can stack them and hang them on a nail on the wall without taking up much room. 1/4" Thick stock is thick enough that they are rigid and sufficiently stiff to trace around and will be robust enough to last for decades of use.

[j. Kinnaird]

Originally Posted by Tim McKnight

John,
I sort of had you in mind when I started this topic. I hope this thread will provide you with some food for thought on the use and implementation of CAD and CNC in our shop. This is not the only way to do it and I am sure others have different ways they approach the same task. I am merely showing you the way we approach and tackles some of the common obstacles.

And I really appreciate it

[Tim McKnight]

Next step is to take the body half template drawing and convert that into a side bending form by adding eight 3/4" holes for dowels and a single .255" x 1" slot at the waist. The slot at the waist is to insert a 1/4" x 1" key that holds the form assembly in my Fox style side bender.








The waste area of wood at the waist will be used to cut "waist cauls". These cauls are used to push the sides down and into the side bending form while bending a set of sides.







The side bending form will require that I cut two identical boards and they will be joined together with eight 3/4" x 5.5" long wood dowels which will be glued into the holes in each board to complete the side bending form assembly.

The side bending form is hollow while the waist caul will be solid. It is made by cutting 7 identical boards and then stacking and gluing them together to complete a solid assembly. I add two 1/4" holes in the cauls which is the run two 1/4" wood dowels through during the glue up. The dowels will keep each board perfectly aligned in the stack.







Since the side bending drawing only provides enough scrap wood to cut 1 waist caul from then we will have to load another piece of wood into the machine to cut more. Its easy to copy and paste the existing caul drawing into new drawing to cut as many cauls as I want:

[Tim McKnight]

After the files are drawn its time to put the ShopBot CNC router to use. I begin with a 4' x 8' x 3/4" sheet of particle board. I could use plywood or MDF but I find the particle board is durable, stable and inexpensive by comparison. The sheet is cut into 10" x 23" boards for the side bending forms (2 pieces), side bender cauls (1), side laminating form (7 pieces) and body mold (8 pieces). Particle board sheets are flat and consistent in thickness which is important because I use vacuum to hold my work pieces down to the bed of my CNC and I don't have to re-zero my X axis each time I load a new blank sheet into the machine.







The white and red polka dot sheets are just scrap pieces of cardboard positioned around the work piece because the cardboard will pull down to the vacuum bed and keep the work piece from sliding as its being cut. No worries if it gets cut during the process as I just pitch and replace it.

[Neil K Walk]

Originally Posted by Tim McKnight

Next step is to take the body half template drawing and convert that into a side bending form by adding eight 3/4" holes for dowels and a single .255" x 1" slot at the waist. The slot at the waist is to insert a 1/4" x 1" key that holds the form assembly in my Fox style side bender.








The waste area of wood at the waist will be used to cut "waist cauls". These cauls are used to push the sides down and into the side bending form while bending a set of sides.







The side bending form will require that I cut two identical boards and they will be joined together with eight 3/4" x 5.5" long wood dowels which will be glued into the holes in each board to complete the side bending form assembly.

The side bending form is hollow while the waist caul will be solid. It is made by cutting 7 identical boards and then stacking and gluing them together to complete a solid assembly. I add two 1/4" holes in the cauls which is the run two 1/4" wood dowels through during the glue up. The dowels will keep each board perfectly aligned in the stack.







Since the side bending drawing only provides enough scrap wood to cut 1 waist caul from then we will have to load another piece of wood into the machine to cut more. Its easy to copy and paste the existing caul drawing into new drawing to cut as many cauls as I want:

Very interesting. I’m in the process of making molds and forms using just the low tech bandsaw/router table route but I love seeing CAD in action. My real question is what type of wood are the dowels for the bending form? Oak or some other type of softer wood like pine or fit that the big box hardware stores sell?

[Tim McKnight]

Originally Posted by Neil K Walk

Very interesting. I’m in the process of making molds and forms using just the low tech bandsaw/router table route but I love seeing CAD in action. My real question is what type of wood are the dowels for the bending form? Oak or some other type of softer wood like pine or fit that the big box hardware stores sell?

Hi Neil,
Low tech methods will get you there as well so don’t get discouraged. I used to use a bandsaw and hand tools to make my forms too. I used Maple and Poplar dowels from Lowe’s. Nothing special needed for dowels. Heck, an old broom handle From a yard sale will work just as well too.

[Tim McKnight]

Here are the 8 pieces of the outside body mold. 4 pieces will be stacked, glued and clamped up to form each half of the body mold. Notice the two small holes on the right side of the pieces. These holes will accept two 1/4" wood dowels to keep all the pieces aligned during gluing and clamp up.

[Tim McKnight]

Here the body mold half is stacked and each of the 4 layers are glued while the dowels hold each layer in alignment.

[Neil K Walk]

Thank you for showing this. I've seen other people post similar tutorials but it varies so much that it fits the "there's more than one way to skin a cat" analogy. Please continue to address the reasons why you make certain modifications, such as the slot in the waist of the bending form.

If you don't mind, I have a few of questions:

1: why particle board? Is it easier to work with than birch ply or MDF - or is it just cheaper and no less durable?

2: why 8 outlines instead of 6 or 4 with spacers like with the bending forms?

3: I've seen some builders curve the outside of their molds? What's your preference?

[j. Kinnaird]

Keep it up Tim. This is great!

[Tim McKnight]

Originally Posted by Neil K Walk

Thank you for showing this. I've seen other people post similar tutorials but it varies so much that it fits the "there's more than one way to skin a cat" analogy. Please continue to address the reasons why you make certain modifications, such as the slot in the waist of the bending form.

If you don't mind, I have a few of questions:

1: why particle board? Is it easier to work with than birch ply or MDF - or is it just cheaper and no less durable?

2: why 8 outlines instead of 6 or 4 with spacers like with the bending forms?

3: I've seen some builders curve the outside of their molds? What's your preference?

Hi Neil,
Thanks for the questions and for following along. The slot in the waist of the side bending form is to lock the form into my Fox style side bender. It keeps the form from sliding around during the bending process. I use a 1/4” thick x 1” aluminum bar that slides through the form and bender locking them together. See photo below.






In the picture below, I show the waist clamp caul, that matches each body unique body shape and is not universally transferable, which has a slot milled in it too. The female slot is to accept the male tang above it from the vertical clamp screw.








1) I use particle board for many of my jigs and fixtures because it’s lower cost than Baltic birch plywood though birch ply would work equally well. If I had deeper pockets then I might consider using it. On second thought, naaaah, I’m just too cheap. MDF would work too and at a lower cost than plywood but it’s not as durable IMO as particle board. Particle board is also VERY flat and consistent in its thickness throughout the 4’ x 8’ sheet. Using material that is consistently flat is important when using vacuum to hold it down to the bed of my CNC.

2) I cut 8 Identical pieces for the body mold which will be four 3/4” thick pieces stacked and glued together for each half of the body mold which gives me 3” total depth which is ideal (for me) for holding the rim as it’s assembled and profile sanded.






3) The only advantage I can see for using a mold that is curved on the outside is if you were going to laminate the sides and clamp them in place inside the mold. It may make clamping easier. If this is the method one chooses then the mold would need to be deeper, say 5-1/2” deep to support the entire width of the side.

I choose to laminate my sides over the outside of a laminating form, which I will show later.

I use a body mold that is 3” deep which is thinner and allows the rim to protrude outside of the mold. I like this design because I clamp my kerfed lining to the rim while it’s inside the mold. I also dish sand the top and back gluing surfaces of the rim while the rim is clamped in the mold. I find both of these tasks are easier (for me) to do with a thinner body mold.

[Tim McKnight]

Side bending forms, body mold, laminating form and body template are done:




















Now it’s time to put them to use...

[ruby50]

Tim

Just an amateur, but I have designed a couple of guitars for my own consumption and used the same principle you did on placing the bridge in the "center" of the lower bout. But I always wondered why Martin and Gibson did no do that - here is a pre-1940 12 and 14 fret 000:

https://www.flickr.com/photos/ruby16...7633913590767/

And 3 20's and 30's Nick Lucas Specials:

https://www.flickr.com/photos/ruby16...7635130471994/

The one on the left is the original 12 fret design. The others are the design that is now pretty famous and copied. Any ideas? Is this a controversial area?

Really enjoying your story here

Ed

[Tim McKnight]

Hi Ed,
Thanks for the questions and for following along.

Looking at the two Martin OOOs the one on the left is a 12 fret and the bridge is centered in the lower bout but it doesn’t appear to be because the fretboard has 20 total frets which moves the soundhole lower. If they would have used an 18 or 19 total frets the bridge would “look” more centered. The OOO on the right is a 14 fret and 20 frets total. The bridge is north of center because of the 14 fret neck and looks even more off center by the sound hole placement.


If you look at the NLS the one on the left circa 1926-29 is a 12 fret to the body, 19 fret total and the saddle is pretty centered in the lower bout. The center NLS circa 29-32 is another 12 fret and the FB has 20 frets but the saddle is still pretty centered in the lower bout. The right NLS is a 14 fret neck and 19 total frets. You will notice that bridge is higher than the other two 12 fret Nicks and the bridge is north of center.

I don’t think this is a controversial topic but rather it’s great that we have options of 12, 13 and 14 necks and a multitude of scale lengths to factor into our designs that we can offer the consumer. Then there are multi scale fan frets and the list goes on... Fun times for sure!

[Tim McKnight]

Originally Posted by j. Kinnaird

Keep it up Tim. This is great!

Good morning John,
I thought I would share with you the amount of time involved from a phone conversation with a client to ready to use forms. We probably spent ~30 minutes on the phone discussing their ideas and then I spent another 1 hour of CAD time and had emailed pictures to him. He requested a few more changes which took 15 minutes and then final drawings were approved. Total CAD, email and client time was 1 hour 45 minutes.

Next I ripped the particle board into blanks ~10 minutes. Uploaded the files into the CNC and began cutting. Cut time averaged 2 minutes for for each blank and we cut a total of 21 blanks = 52 minutes.

As the cut blanks were coming out of the CNC I was gluing up the layers which took ~45 minutes.

Total clamp time was roughly 1 hour.

So from a phone call to ready to use forms we will round it up to: 4-1/2 hours. Not bad for a morning's work before lunch.

As I prefaced in the beginning of this thread, there are lots of ways to arrive at the goal line and one can use whichever method they see fits their needs best considering their budget and personal criteria. Its certainly not necessary to use CAD and CNC to jump start your projects. 28 Years ago I accomplished similar results using poster paper, pencil, T-square, drafting table, scissors and human powered hand tools. In today's age I find it easier and more time efficient sharing an electronic drawing with a client within a few hours inception instead of mailing them a paper template I cut with scissors. I think its also a comfort for them to see something they had input in designing and a facsimile of the guitar they will receive in a few months down the road.