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  #1  
Old Fri 12 March 2010, 13:20
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Scarf cutting file for plywood

Can anyone help me with figuring out how to cut a scarf in plywood using V-Carve Pro? It can either be a step-scarf or a ramp. I just can't figure out how to set it up in V-Carve.

Thanks

Joe
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  #2  
Old Fri 12 March 2010, 15:11
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Finger scarfing techniques?

Further to my question above, I found this picture of a finger scarfing system used by a kayak kit maker. Does anyone have any thoughts on how to do this in V-Carve Pro? (I have been to the Vectric Forum and CNC but have found both less than helpful).

Thanks

Joe
Attached Images
File Type: jpg scarfL1lg2.jpg (24.8 KB, 438 views)
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  #3  
Old Fri 12 March 2010, 15:34
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Explain what your trying to do for us.

I got this on a quick search.

http://www.oneoceankayaks.com/stitch.../scarfjig2.htm

here is my search string

http://www.google.com/#hl=en&source=...ec2db39eb50b9d

Mike
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  #4  
Old Fri 12 March 2010, 15:51
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
The ocean Kayaks scarf jig is OK and will work, but I was hoping to be able to lay out the pieces for a stitch and glue boat with the scarfs (step, or finger or ...?) built into the design to be cut out on the MM so that I could then just assemble to pieces. I just found this web site (http://www.duckworksmagazine.com/06/...zzle/index.htm) that has a really good idea but the question now is: how to implement the concept on the MM using VCarve. I assume it involves using the inlay function in VCarve but since I am a newbie on that software I can't get a handle on it.

Thanks

Joe
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  #5  
Old Fri 12 March 2010, 16:32
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Joe,

Most of the time when you talk about scarf joints you mean like:

http://www.duckworksmagazine.com/05/...arfs/index.cfm

Your link took me to a puzzle joint.

ShopBot had a scarf joint that was more like the first one.

So I am not sure which you want help with the first or second. Then I went and looked at Ocean Kayak and it is the finger joints.

You need to create a profile of the finger joints and cut it using the create profile toolpath. Your profile will fit together in the two piece you want to join together. Most likely using an 1/8" bit for the gaps. But you do not need to inlay the cut.

Do you have a profile that you think you want to use? Post it.

IF you are designing a kayak, I am interested and would like to participate.

I have attached a exagerated example because the fingers are 2" wide. So you would make them 1/8".
Attached Files
File Type: dxf Finger Joint Example.dxf (20.9 KB, 29 views)

Last edited by sailfl; Fri 12 March 2010 at 16:47..
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  #6  
Old Fri 12 March 2010, 17:19
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
We build boat kits using puzzle joints. The marine architect we work with believes (and I agree) that a scarf has no advantage, and several limitations compared to a puzzle joint.

See this for an example.

The main limitation with a scarf joint is that (if you use it to assemble precut panels) there's no good way to be really hyper-accurate on the lateral or longitudinal alignment; the scarf does not accurately position the parts. Second, it doesn't provide significantly more panel strength because although the scarf joint allows a greater glue area, the panel's weak point is at the transition, whether it's the scarf transition, or the imaginary line where plywood becomes the joint.

The finger joint above would be a decent alternative, (it provides some enforced lateral alignment if not longitudinal, and it minimizes the straight-line weak point) but it would be slow to cut, create a great deal of waste, and unless I miss my guess all that glue will create an unfair spot - a part of the panel that bends less than the rest.

Last edited by lumberjack_jeff; Fri 12 March 2010 at 17:37..
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  #7  
Old Fri 12 March 2010, 20:34
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Jeff: That puzzle joint is fine for what I am trying to do. Topologically it is the equivalent of the finger joint Nils provided. So the question remains: once I have the design in DXF format (which I can do) how do I set up VCarve Pro to cut the two sides so they will meld when pressed together. Do I cut one on the "inside" and on the "outside" or both on the inside or what?

Thanks

Joe
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  #8  
Old Fri 12 March 2010, 21:16
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
For me, the design of the puzzle shape was the result of a fair amount of trial and error. The shape I came up with is dependent on the peculiarities of my setup. In general, I started with a set of parallel lines (or polylines for acad folks) spaced an appropriate distance - say .010". For the kits we build, maintaining strict positioning between the spliced panels is important, so the profile needs to interlock.

The two lines are then separated and used to border matching panels. Both panels are then cut on the outside.

Most people doing this choose symmetrical profiles, but using the example of dovetails, I don't know that they necessarily need to be.

PS: The shapes used by PT watercraft are not my work. I will post photos of ours when I can.

Last edited by lumberjack_jeff; Fri 12 March 2010 at 21:21..
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  #9  
Old Fri 12 March 2010, 23:01
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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Joe, I think what you are asking how to cut some joint with V-Carve is the following.

Both pieces you cut on the OUTSIDE of the line.....just make sure that your cutter size matches the joint profile. If the cutter is too big it wil DISTORT your joint..

If your workpiece is big, then go with a big cutter, if it is small, go with a small cutter.
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  #10  
Old Fri 12 March 2010, 23:18
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
DXF example of finger joints

Jeff: Thanks. That tip about the parallel lines is a big help. I did the attached DXF file in TurboCad as a sample and have done a VCarve file which I will test tomorrow. Please let me know if this is what you had in mind (the dovetail version, not the oblongs)

I'll let you know how it goes.

Joe
Attached Files
File Type: dxf Finger Joint Example3.DXF (108.6 KB, 27 views)
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  #11  
Old Sat 13 March 2010, 04:37
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Joe,

I had to bring the file into aspire to open it what version is the dxf created in?

Last edited by sailfl; Sat 13 March 2010 at 04:42..
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  #12  
Old Sat 13 March 2010, 05:27
isladelobos
Just call me: Ros
 
Canary Islands
Spain
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This is the puzle method?
Dxf file.

test.dxf

Last edited by isladelobos; Sat 13 March 2010 at 05:35..
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  #13  
Old Sat 13 March 2010, 07:34
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Joe,

I took your dxf file made the pattern for one. Brought it into Aspire but it will be the same with V-Carve, created a 2D profile tool path, cutting with a 1/4" bit on the outside of the vector using my new favorite test material foam.

This is the results.

Let me know if you have any questions.

I missed the comment that you want the dove tails. Now it becomes more difficult because of the angle in the corner. You have to use a smaller bit.
Attached Images
File Type: jpg DSCN0751.jpg (165.7 KB, 410 views)
File Type: jpg DSCN0752.jpg (164.5 KB, 409 views)

Last edited by sailfl; Sat 13 March 2010 at 07:42..
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  #14  
Old Sat 13 March 2010, 08:21
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Joe,

Once again, I took your DoveTail drawing but I added a .125 radius to the corners. Used 1/4" bit cutting on the outside.

Hope these help.
Attached Images
File Type: jpg DSCN0753.jpg (163.7 KB, 404 views)
File Type: jpg DSCN0754.jpg (164.5 KB, 400 views)
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  #15  
Old Sat 13 March 2010, 09:29
hennie
Just call me: Hennie #23
 
Roodepoort JHB
South Africa
Nils, make it more interresting and do it so that the actual dovetail is only cut halfway on both the male and female side that should give you a verry strong joint so that when you glue them together there is a bigger surface for the glue to sit onto.
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  #16  
Old Sat 13 March 2010, 10:22
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Nils: That is perfect! Exactly what I needed. Can you just confirm for me what the cutting settings were in Aspire (better yet, send me the .crv file so I can see them).

Many thank. Joe
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  #17  
Old Sat 13 March 2010, 10:23
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Quote:
Originally Posted by hennie View Post
Nils, make it more interresting and do it so that the actual dovetail is only cut halfway on both the male and female side that should give you a verry strong joint so that when you glue them together there is a bigger surface for the glue to sit onto.
Henny: That is a good idea except I will be working with 1/4 inch ply and am not sure I can cut to those tight tolerances. I will try one and see. Thanks for the excellent suggestion.

Joe
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  #18  
Old Sat 13 March 2010, 10:39
jehayes
Just call me: Joe #53
 
Whidbey Island, Washington
United States of America
Quote:
Originally Posted by sailfl View Post
Joe,

I had to bring the file into aspire to open it what version is the dxf created in?
Nils:

It was created in TurboCad 14.2 I can resave in Version 12 if you still want it but it seems you have imported into Aspire which is the goal anyway. Thanks again.

Joe
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  #19  
Old Sun 14 March 2010, 18:25
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
In a boatbuilding application, where the panels will be primarily bent around a curve, the point of failure will be the edge of the joint transition. Strength is improved by making this transition as gradual as possible.

There is actually a step above "strongest"; the kayak splice shown upthread. Its problems with it have to do with alignment, fragility for assembly and material waste.
Attached Images
File Type: jpg SCARFS.jpg (61.6 KB, 368 views)
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  #20  
Old Sun 14 March 2010, 19:55
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Jeff,

What are the dimensions of the last tabs? Height and width should be the same?
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  #21  
Old Sun 14 March 2010, 21:02
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
Personally, I use a rule of thumb that for panels which are bent, (as opposed to bulkheads) the joint (height) should be at least 8x the material thickness.

How many dovetails to put per foot of panel width? More ambiguous... I make the width and the height about the same, the main objective is that the joint should minimize the straight line parallel to the bending axis (the seam on the green dotted line) as much as possible.
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  #22  
Old Sun 14 March 2010, 22:09
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Jeff, I agree with your logic on what makes the stronger joint. But, isn't the natural conclusion that a triangular finger joint is the best, albeit a bit boring?:

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  #23  
Old Sun 14 March 2010, 23:15
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
Yes, but... strength is not the only consideration. Boat hull panels are often only a 10" or so wide x 20' (or more) long. It is very easy to glue the sections together with a non-obvious (yet catastrophic) misalignment that only becomes apparent when you're trying to stitch the panels together into a boat shape. The joint not only needs to be strong, it needs to enforce alignment during glue-up.

Granted, a finger joint is better than a traditional (or stepped) scarf, but it still is less foolproof than interlocking joinery.

Last edited by lumberjack_jeff; Sun 14 March 2010 at 23:38..
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  #24  
Old Mon 15 March 2010, 00:17
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Years ago we did stepped scarfs (in z-direction) for a boatbuilder, but we also added 2 dowel holes through the joint, which made the alignment a piece of cake. See http://www.dixdesign.com/oneill2.htm

Also, you would only need interlocking at the outer edges, the middle area can be finger jointed.

Last edited by Gerald D; Mon 15 March 2010 at 00:19..
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  #25  
Old Mon 15 March 2010, 09:30
normand blais
Just call me: Normand
 
montreal
Canada
Example of s.b. wiggle step scarf joint
Attached Images
File Type: gif wiggle step scarf joint.gif (105.2 KB, 334 views)
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  #26  
Old Mon 15 March 2010, 09:48
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
Nice Gerald! I like the dowel pins.
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  #27  
Old Mon 15 March 2010, 10:05
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Jeff, what you might like even more, is that we supplied a big board with registration holes (you can see it in that link) and the dowels went right through into that board. The individual pieces had a few more dowel holes that lined them up to the big board.
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  #28  
Old Mon 15 March 2010, 12:57
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Jeff,

Then it seems that the picture in post #2 is a good way to go but with some changes as far as size and frequency.
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  #29  
Old Mon 15 March 2010, 13:03
lumberjack_jeff
Just call me: Jeff #31
 
Montesano, WA
United States of America
Nils,
The more I look at that joint, the more I like it... it looks like the short pin does lock in place.
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  #30  
Old Mon 15 March 2010, 13:08
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Jeff,

It also give the advantage of not having a straight line all in the same place so I would guess it is distributing the load which means there would be less likely that there would be a failure.
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