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cutting smooth arcs with jig saw/ band saw

 
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vinman



Joined: 09 Nov 2007
Posts: 1095
Location: The tin foil isle

PostPosted: Sun Mar 06, 2011 3:40 am    Post subject: cutting smooth arcs with jig saw/ band saw Reply with quote

I'm having a tough time cutting smoothly on my band saw. I'm wondering if my tension is too low on the band. But anyway does anyone have some good advise on cutting smooth arc for templates and cores? I'm a bit frustrated by this seemingly simple task.
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doughboyshredder



Joined: 17 Sep 2007
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PostPosted: Sun Mar 06, 2011 6:03 am    Post subject: Reply with quote

It's not a simple task.

For smooth consistent radii a scroll saw is the answer.
But, that's another tool, and still it's almost impossible to get a good enough cut to use as a template.

I think I first got this idea from richuk. I cut one piece as close as I can get, sand it closer and then bend and glue a piece of edge material to it. Then use that piece as a template for your template piece.

This works really good for printing out templates from snowcad and cutting them out of a piece of mdf. You don't have to worry about little nicks, and what not, since you are gluing an edge on there for your router bearing to run on.
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vinman



Joined: 09 Nov 2007
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PostPosted: Sun Mar 06, 2011 8:44 am    Post subject: Reply with quote

good idea, thanks.

Basically what I did today was take my rough cut template and just eyballed every bump, marked and sanded them until my eye and hand said it was smooth.

The second core with side wall came out much better today, very few wobbles this time. Fortunately I did make my sidewalls bigger than needed some once I get some edges bent to my template I'll be able to route out the bad/wobbly areas and still get a ski that looks good with a smooth edge.

I also turned up the tension in my band saw after doing some reading last night it seems that a band saw blade needs a lot to tension to not just wander around terribly which is what I was experiencing.
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krp8128



Joined: 23 Feb 2007
Posts: 366
Location: Marcellus, NY

PostPosted: Sun Mar 06, 2011 3:35 pm    Post subject: Reply with quote

doughboyshredder wrote:

For smooth consistent radii a scroll saw is the answer.
But, that's another tool, and still it's almost impossible to get a good enough cut to use as a template.



What? Scroll saws are for very small, detailed work, typically withing the board....





Check the tension on the blade, and check that all the guides are set up correctly. Long, smooth arcs are still a PITA even with a $1k bandsaw and $300 guides. That being said, I use a variation of what doughboy posted:

    1. Using the straightest grained piece of hardwood (NO knots!!!) rip a 3/4x3/4 strip. Drill oversize clearance holes for screws every 6"
    2.Using spray adhesive, glue down pattern to your future template
    3. Cut sort kinda close to line
    4. Bend the 3/4 strip to fit dead on the line, using screws as needed
    5. Template bit + router table
    6. Repeat for other side. Or, for an exact match, use the one-sided template you just made to make a new 2 sided template (screw down onto board, follow w/ pattern bit, flip over the long axis, follow with pattern bit)
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skidesmond



Joined: 07 Apr 2009
Posts: 2011
Location: Western Mass, USA

PostPosted: Mon Mar 07, 2011 4:13 am    Post subject: Reply with quote

krp8128 wrote:
.....

    1. Using the straightest grained piece of hardwood (NO knots!!!) rip a 3/4x3/4 strip. Drill oversize clearance holes for screws every 6"
    2.Using spray adhesive, glue down pattern to your future template
    3. Cut sort kinda close to line
    4. Bend the 3/4 strip to fit dead on the line, using screws as needed
    5. Template bit + router table
    6. Repeat for other side. Or, for an exact match, use the one-sided template you just made to make a new 2 sided template (screw down onto board, follow w/ pattern bit, flip over the long axis, follow with pattern bit)


I make my templates the same way. You have to take your time. After I think I'm done, I trace the template on to my work table, then flip it over checking that it's symmetrical with the tracing, fine tune as needed.
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vinman



Joined: 09 Nov 2007
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PostPosted: Mon Mar 07, 2011 5:45 am    Post subject: Reply with quote

great ifo guys thanks. I'll definitely use that rail guide method next time.
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OAC



Joined: 23 Jul 2009
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PostPosted: Mon Mar 07, 2011 7:43 am    Post subject: Reply with quote

I've outsourced most of the template making (the curved ones) to a company with a BIG cnc machine! Perfect result!
Does it make me a cheater??
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vinman



Joined: 09 Nov 2007
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PostPosted: Mon Mar 07, 2011 7:51 am    Post subject: Reply with quote

you are definitely a cheat, but one that makes some sweet looking skis. If I had CNC access I'd be cheating too.
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MontuckyMadman



Joined: 20 Jun 2008
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PostPosted: Mon Mar 07, 2011 9:31 am    Post subject: Reply with quote

Cheat. The molds determine your flatness. You can get a whole sheet of mdf cut for about 100 bucks. You can put several camber and tip and tail templates in ther and then experiment with different combos and layups.
of course pay more fdor the design work unless you can draw up a file yourself which is not that tough.
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doughboyshredder



Joined: 17 Sep 2007
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PostPosted: Mon Mar 07, 2011 9:51 pm    Post subject: Reply with quote

krp8128 wrote:
doughboyshredder wrote:

For smooth consistent radii a scroll saw is the answer.
But, that's another tool, and still it's almost impossible to get a good enough cut to use as a template.



What? Scroll saws are for very small, detailed work, typically withing the board....



Yeah, wouldn't be good for a sidecut template, I was just talking about for tip and tail templates.

Industrial scroll saws can cut up to 2" thick material.
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artski



Joined: 13 Oct 2009
Posts: 138
Location: Boyne country, Mich.

PostPosted: Tue Mar 08, 2011 5:04 am    Post subject: Reply with quote

I just did 2 new patterns, and what I did was take the sno-cad file and put it on a dxf and then load it on a usb stick and then took that to a local sign shop who has a cnc router table, they plugged the stick into their computer, got the file, formated it on a sheet of mdf and cut it out. I got 2 perfect patterns for 20 bucks.
So I guess that makes me a cheater too but it sure makes things easier!
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OAC



Joined: 23 Jul 2009
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Location: Sweden

PostPosted: Tue Mar 08, 2011 9:05 am    Post subject: Reply with quote

artski wrote:
So I guess that makes me a cheater too but it sure makes things easier!

And it also keeps the mental health on a good level! Smile
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knightsofnii



Joined: 08 Jan 2008
Posts: 1080

PostPosted: Sat Mar 12, 2011 11:03 pm    Post subject: Reply with quote

Ii think i was one of the ones who suggesstted glueing edge to an impperfect cutt then use this as a router guide. But any glli wtf is wrong with my djsmn phonee ughh.

Get them cncd... aand takke good care of em
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