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Help needed for handling cross-grain parts without splitting


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I'm working on an older kit - well before laser cut sheets were used - and have to cut out and sand various pieces for gunwales and such.  

 

I've been cutting them out laboriously with x-acto knives.  I'm ok as long as the pieces are along the grain or are large enough but I've had 2 or three splits on pieces like the one shown.

 

post-26957-0-22022800-1484614049.jpg

 

What are some of techniques that I should try?

 

Note:  The only small power tool in my toolkit is a dremel.  I've tried using a jewellers saw but it is hard to hold the part steady while sawing.

 

Doug

 

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Doug here is a little list of what i would consider as the right tool for the job, if you plan on continuing in the hobby it is never to early to buy some small power tools.

 

small Band saw would be the best i think, Scroll saw with a fine blade cutting on the down stroke would be the next best, scroll saws come in handy as you can just change the blade and work with metal ideal for brass.

 

Cheers Rexy.

Edited by REXY
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Thanks Pat and Don.  I can try those 2 suggestions on the piece shown as there is lot of wood around that side of the piece.  The before was nestled up really close to the one left.  Presumably with the drum sanding attachment I'll still have to be really careful that the narrow pieces are supported.  Here's hoping.

 

Doug

 

 

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Thanks Rexy,  I have hopes of adding tools as I can - my overwhelming problem at the moment is workspace.  I just have a desk in our weaving studio and there is just no place for power tools - I even had to go to the entryway to use the dremel as the sawdust raised wasn't appreciated - go figure!  Winter here so no place outside the house works for me!

 

Everest - good suggestion for the really narrow spots - thanks.

 

Doug

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You could try gluing a backing piece of wood using rubber cement.

Coat both surfaces.  It rubs off using just your thumb when done.

 

There are "tables" for jewelers saws that are easy to make yourself.

A 2-3" wide piece of 1/2" plywood that sticks out from a table like a

gangplank.  the distant end has a "V" cut out with a hole at the apex

or a keyhole like cutout.   A hole at the table end to add the C-clamp

that holds it on the table.  You can use the clamps to hold the work

on the table.

Check the jewelers saw display at MicroMark to see what I mean.

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To avoid the blade following the curve of the grain, I use a rolling cutter, small diameter blade for tight curves and a larger diameter for  more gentle curves. For small I mean 10 mm and for large I mean 100 mm diameter. These cutters can be found at fabric stores like Joann's, Michaels,,etc. They a as sharp as any razor blade and do not dull rapidly. Replacement blades are also available. :D

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Thanks to everyone for the tips.

 

What worked pretty well for me was:

 

Drill the set of closely spaced holes using the dremel with drill press accessory:

post-26957-0-03063500-1484685178.jpg

 

Finish the cuts with the x-acto knife (no rolling cutter to try yet) 

post-26957-0-78448300-1484685188.jpg

 

Use the drum sander attachment n the dremel to get closer fit

post-26957-0-99883800-1484685198.jpg

 

and finish sanding by hand.

 

I tried to use the jeweller's saw again but couldn't get good clamping on my desk and found it quicker to do the drilling technique.

 

Thanks again,

Doug

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The parts look to be 1/16 to an 1/8th thick.  I'd go to the nearest big box store (i.e Home Depot or Lowe's) and by the equivalent thickness in Poplar. You can always stain it whatever color you want.  Poplar is inexpensive and comes pre-cut in 1/16 and 1/8th " thick plus many other thicknesses.

Tom

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From your photos - the wood that you have is open pore and

would probably be brittle from when it is seasoned.

Scaled down the opening would probably swallow a forearm.

It is not a type of wood that is appropriate for scale modeling.

 

Tom is right on.  You have to cut it out anyway, use a closed grain ,

tight grained species.  Poplar is good, and you are in Maple country,

I would think that there should be shops for wood craftsmen in your area.

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Tom and Jaager,

 

The same wood was used for planking the hull as well as all the deck furniture, rail caps and so on.  I presumed it was mahogany but I don't really know anything about different woods yet.  The material is somewhat tough but brittle - it is bendable though.  The kit is an old Billing Boats kit for the Krabbenkutter.

 

At this point are you suggesting I ditch all the wood and remake all the pieces?  (The planking is 1/2 done.)

 

Doug

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post-26957-0-68436400-1484699986.jpg

 

...

 

Scaled down the opening would probably swallow a forearm.

It is not a type of wood that is appropriate for scale modeling.

 

 

If the hole you're mentioning is the one in this photo I'd point out that that is just a scrap of cherry I was using to cut on.  The kit piece is the one labelled 14

 

Doug

 

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When cutting curved stock always cut so your knife runs away from the grain,never into it. Make several cuts not just one. You can back the piece with masking tape.Sand the same way ,away from the grain. Any rotary sander should also rotate away from the grain.not into it. Cut out your piece fairly roughly before you begin. If the waste side is thin it has room to move away rather than cracking. If all else fails trace out new parts to match the grain. I used to build balsa models as a kid and learned to cut out round wing tips and control surface edges like these.

  If you use a coping or jewelers saw ,nail a piece of 1/4 " hardwood such as maple or walnut to your work bench and cut out a V shape about 2" wide and 2 and1/2" deep and support your wood over the narrow part of the V and cut there,moving your wood to stay in the apex of the V.

  Buy a bottle of ACC. :)

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The wood that you are cutting looks a lot like Lauan. It is one of many species

used to substitute for Mahogany, although it is no where near the

quality of genuine (Cuban) Mahogany - which was loved too much for it to

be available to any degree now.

The Cherry would be excellent choice for your model.

The surface of the piece that you are cutting is not smooth.  The dark lines

are openings into the wood.  What I was trying to say is that if you were shrunk

in size to the scale of the model, you could probably fit your forearm into one

of the openings. There is no species of wood that look like Oak or Fir  scaled

down 50-100 times.  But some species make the trip better than others.

 

I did not realize that you had significantly progressed with your build.

" Never mind " as regards the wood substitution.  If you get a similar kit

in the future, you might consider replacing the provided wood if it is

similar to your present kit..  Your problems would have been a lot less if

the kit manufacturer had used a different, but probably more expensive

species of wood. Obviously, there are many models that are made using the

same or similar wood to what you have.

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  • 3 years later...

This probably belongs in the tool category, but to cut that Lauan plywood and for many other tasks, a jeweler's fret saw is indispensable. They're like a super fine toothed coping saw, but the blades don't rotate, so you're limited by throat depth. They're used with a simple block of wood sticking off the bench called a "bird's mouth" to support the workpiece. The blades are cheap and come in many varieties, even spiral toothed. They'll cut metal too, brass, even mild steel. The pictures show the variety and huge difference in price that you can get. Anywhere from $10 to a hundred plus for the "Knew" tools line of super rigid precision milled aluminum stuff. The first picture shows their unique powered design. ($2k+!) It's advantage over the usual scroll saws is that it moves straight up and down and with a much longer, slower stroke. Great for mother of pearl artisans, jewelers, and model makers. In general, when working with Lauan aka Philippine mahogany plywood, score the face veneer with a sharp knife, and then saw to the outside of your score line. It's a good strong material, but really splintery. It's not as common as it used to be. I believe the Shorea species are now endangered.

 

 

 

 

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Edited by Carlos Reira
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