How to get close fitting "connections"

[Redshirt]

OK, the threadtitle might be a bit stupid but im having a real problem here.

Im currently trying to cut and assemble the various parts of a ship's keel but im constantly frustrated by the low accuracy of my work. I tried cutting/sawing as accurately as possible but with little success. I tried leaving something "extra" to later sand it to shape with the Dremel but this isn't working either. Especialy conkave surfaces and these damnable scarph joints (can't cut them with the tablesaw since the lower side of the round blade of course cuts a bit further than the upper side) give me trouble so im asking for advice.

 

How do you people manage such tight connections between the various parts of your ships's keel/stem/sternparts.

[shiloh]

all eyes on this subject.

jud

[mtaylor]

From experience and I'm still learning... I'm not there yet, but getting there...  Ok... so much for the personal disclaimer.

 

No dremels on joints, ever!  I use files and even then have to gauge.  Just a stroke or two at a time and keep offering it up to check.  If I can, I will use a disk sander but it's only to get close.  Files finish the job.  Sanding sticks can work, but are not as precise as files.

 

A scroll saw can get you close.  From what your wrote it sounds like you're using a spiral blade.  Don't.  Use a flat one with appropriate tooth count. I like the reverse tooth as they don't splinter the wood on the bottom of the cut.  Just leave lots of meat to final fit.   

 

Rather than a scroll saw, use chisels to cut the scarfs.  I haven't got this one figured out and am still working on technique but a lot the builders use them.  Gives a clean and precise cut when done right. 

 

Lastly, practice, practice, practice.  Use scrap wood of course but the more you do something, the better you become.

 

I hope this helps. 

[grsjax]

What mtaylor said.  Another consideration is to use a scraper to do the final fitting.  This works best with hard woods like cherry although with care it can be used on fine grained softer woods like basswood.  An Xacto #11 blade works well as a scraper but it isn't the only option.  I have seen broken glass, small chisels and pieces of sheet metal used.  Scrape the joint a little at a time with the scraper held flat to the surface.  Trial fit after each scraping.  Scraping, if done right is better than files or sandpaper for fine fitting work and is the method actually used in old time shipyards to fit tight joints.  A few cavets, if scraping across the grain you can get an uneven surface, be very carefull to keep the blade in the correct plane or you will end up with a surface that is tilted out of line.

[rtropp]

I too agree with Mark. I tried to use Dremels and other power tools when I began but soon learned that they are hard for a beginner to control, especially when you are working on extreme miniatures and still learning what the outcome of the work should be.  Working by hand will give you a feel for what it takes to get the right results before you try to speed things up. You will hear others on the site repeat the mantra, work slow, be patient, let the eye hand coordination build. I heeded early on when more experienced builders advised to treat each tiny component as a project in itself.

 

When I started I did most of my cutout work with and Xacto or similar knife.  I scored the cut lightly a few times before making my final cut.  I also found that my cutting is better when I use a harder surface than the rubber cutting mat that are common to hobbyists. The mat might allow the piece to bend when cutting which can alter the cut or splinter the bottom of the cut.  I have a piece of linoleum type tile that gives me better results than a cutting mat... which I still keep on the worktable for general cutting and to protect the surface of the table.

 

It is very important to use sharp tools.  A dull tool will "wander' with the wood grain.  I buy my blades, mostly #11, by the hundred.  Some of the folks keep a sharpening stone nearby and give them a swipe every few cuts.  They still replace them frequently. Chisels need to be kept extremely sharp to slice wood rather than splinter it.  I spent a fair amount of time learning how to sharpen chisels on diamond stone.  My smallest chisels are 1/16" or a little smaller, so they dull quickly and require proper sharpening.

 

Another of my most useful tools is a set of metal files for wood working.  These are slower but will give you better results as you start.  There are some good needle file sets that are cheap on Ebay. I especially like files made by Tamiya.  They have three sizes with different grit. The key for me was to not try a quick back and forth motion but rather to take one or two passes at a time and then look at the work to see where I was.  Also, with files and chisels I use a light stroke letting the tools do the work.  I don't try to force them. They work better than sandpaper for because they keep their shape throughout the cut. 

 

When I started this hobby I did a lot of practice on scrap wood , still do before starting a complex cut.  I often go through a lot of scrap wood, more than I care to admit to, before I get a usable part. 

 

I am one of those who enjoys the journey as much as getting to the destination.  I will work for hours, with a pile of attempts in the scrap bin before I get what I want.  There are those on MSW who make it look really easy, most have a list of builds under their names which built their skills. they had to learn at some point and they were not speed demons when the did, so try not to compare your initial attempts with their much more experienced work.

 

 As for frustration, we all experience that, even the very skilled.  I find that stepping back... with a glass of vodka, helps.

 

Richard

[rtropp]

I just took another look at my post, boy does it ramble on, I guess you hit a nerve.  Hope there is something in there that is helpful.

 

Richard

[druxey]

Some excellent advice there from Mark and Richard.

[captainbob]

As you can see from the above.  Only use sharp hand tools for close work.

 

Bob

[Richard Griffith]

chisels, files and tonic with lime with vodka does the job.................Duff

[hexnut]

What helps for me is to either copy a section of the plan or draw out what I want on paper, then cut out the parts I want and paste them on the wood bits with lo-tack glue.  That gives me an immediate reference for where everything should be, as well as an aide to avoid over-trimming.  I do use a small power disk and belt sander up until the last .060 or so, but I resquare the table often...

 

The next thing is to spend some time making small, very square sanding blocks of various grits.  I then work on a surface that I know is flat.  This way, I'm only making mistakes in one dimension at a time. 

[allanyed]

Another 2 cents, maybe only a penny.  I start with an Xacto back saw cutting outside the line, then SHARP chisels and finally a file if needed.  Now, if I ever get my wish for a good milling machine, I have seen how these can be used in scarph joints and more, but I suspect the set up time is longer than doing a steady slow finish with chisel and file. 
Allan

[mtaylor]

Allan,

 

You're right.. the setup on a mill is a pain.  However, it does make things repeatable.  So if you're doing several scarf joints or any other work that needs be identical (or nearly identical... I'm not good enough to get exact yet) then a mill will help.  Still... there's something to be said for doing things by hand and I'm sometimes sitting indecisively between either method.

[jbshan]

Work the joint down, offering the work piece up frequently to check for fit, until you are taking two licks with a piece of kleenex between trials.  Whether you use knives or chisels or files or sandpaper or milling machine or laser, you want to end very carefully and gradually.  Do only one end at a time.  Get it perfect and move to the other end.  If you try to do a whole piece at a time, a change at one end will knock it off at the other.  This goes for anything, plank, deck structures, spar making etc. and so on.

[lehmann]

In wood working, hand-made joints, such as dovetail joints, are always done by making one side of the joint first, then using that part to scribe the other part.  There is no way to get a tight joint by making the two pieces independently.  Since the devil in in the details, they are:

 

1.  Whatever the profile of the joint, scarf, dovetail, miter, or a simple butt-joint, the surfaces of the joint must be exactly square to the surface of the profile. Otherwise, you may be tight on one side and have gaps on the other.  Using a file to finish joint by hand will  always end up with a convex surface and gaps on the edges.  So, have a good small square, with a light behind so you can see gaps.  For small parts there may not be a good surface to place the square, place both the piece and the square on a flat surface.  

 

2.  To help make a square cut, place the piece on a cutting board, then cut straight down, at 90 degrees to the board, with a sharp chisel.  You can use a block of wood to keep the chisel at 90 deg.  Cabinet makes us what is called a "paring chisel" for this which sharpened to 15 degree angle instead of the usual 25 degrees used on general purpose chisels.  An X-Acto chisel (#17, #18) is a good choice for model work.  The tool needs to be razor sharp, and do not take off too much in one cut - just take off shavings.  Use other tools to get the rough shape.

 

3.  With one piece made, the shape is copied to the other piece with a scribing knife, which has been sharpened on only one side of the blade so the cutting point is tight against the part you are tracing.  There is no way a pencil tracing is accurate enough.  You could use a #11 blade, but since it is sharpened on both sides there is a good chance that the scribed line will be 1/2 the blade thickness away from traced part.   A razor blade may work, but you may want to break if off to look more like a #11 so you can scribe in to corners.  Commercial scribing knives can be expensive, but Lee Valley Tools sells a reasonably priced one.  There's no reason you couldn't make your own by re-grinding a dull #11.  I've tried using scratch awls and needles for scribing, but I found they tend to follow the wood grain.   I would only use a point scriber for tracing concave curves that a flat knife couldn't follow: however, I can't think of any ship joints like this (unless you change you hobby to making jig-saw puzzles.)

 

4.   After you have roughed out the shape of the second piece to close to the line, the benefit of the scribed line comes into play.  Just hook the edge of the chisel in to the scribed line and cut straight down.  Even if your eyes can't see the line, you can feel when the chisel hooks.  In some cases, you could scribe both sides of the joint and cut from both sides.  One trick when cutting from both sides is to make the surfaces slightly hollow (concave) to ensure the edgers are tight.  Some people consider this a bit of a cheat, but it does ensure the joint line has no gap, which easily happens if the joint surfaces are evenly slightly convex.

 

After a test-fit of the joint, some paring cuts or scraping may be needed, but you will be very close to a perfect joint.  If a joint surface is convex, you can scrape it in the middle with the edge of a knife with a round profile (#10 knife).

 

If my description of the process is not clear enough, there are lots of places on the web that have good pictures.  Start at www.finewoodworking.com.   

 

Bruce

[Maury S]

From Chuck P.   Take your time.  Work slowly.

And if it isn't right, do it again until it is.  The learning curve will kick in.

Maury

[wthilgen]

When you've done your best, there is always wood putty. The real ships of old wern't perfect and to some degree had to be filled in. In small amounts it will add to the over all effect when you put on what ever finish you choose. I personaly prefer to use a propane torch and ever so slightly charing it. Using a finger to rub for desired effect make the vessel appear to be old. Any area where I had to use a bit of putty, turns out blacker and looks like pitch.