Cutting EPS down the center for a stringer

General Discussion
1

Hey Guys

I am building a 11’6" SUP and need to cut down the center line for stringer.

I have seen Gregs DVD and he has a great setup for this but I dont see the need for such a contraption in my garage.

Plus I dont have the room.

It has been mentioned here about cutting down the center with a hand saw, then swapping sides and gluing the sides cut by the manufacturer.

But if I was to do multiple stringers that wouldn’t help either.

I was thinking that I will attach one end of the wire to the back wall and the other to a piece of wood with a weight on it.

Line it up in the correct position then turn on the power and let the weight pull the wire through.

Only problem here is keeping it straight.

Anyone got any suggestions???

Cheers

2

We have done 100’s of them!

It’s always better to cut straight lines with a hot wire - especially when you need many stringers in your glue-up.

Take a 12’ piece of Metal conduit and put elbows on the ends with 10" piece on both sides. Drill small holes in the ends of both 10" pieces.

With small machine (bolt, nut, washer) attach the wire to both ends keeping it taunt.

Then take a cheap extention cord and cut off the female end and put off the coating and expose 7’ of wire leave the plastic on the wire.

Clean about 1/2" of the plastic off the wire ends and attach alligator clips. (Good Ones).

Place you blanks on a long table with some weights to one side. Make marks on each end of the blank were you want you stringers. Keep it square!

Postion your Hot Wire Wand on the blank. Aline the wire so it rest on the marks. The conduit bar should just hang. Alligator clips on each end.

Set you variac to about 50 - 60 amps ( It takes more for the longer runs ) Turn it on and Let the gravity and heat make the cut. Turn it off when it hits the ground and don’t touch the wire.

I would practice first by cuting on 1" of a side if you have enough material.

If this is hard to understand I can take some pictures.

3

Hey Surfding

That sounds like a good setup.

But, why do you put weights on one side??

And, how do you keep it square???

Might have to get the wife to help me.

Then again, my son might have a better idea.

Cheers

4

Please post some pictures of this setup.

5

I think I understand surfding’s method, and it’s pretty cool… lets see if this illustration works

The weights are to keep the foam from rolling off the table when the weight of the hot cutting wand is put onto the foam.

A few things to think about, though -

If your table is level ( use shims under the legs maybe ) and long enough to support the whole blank ( so it isn’t twisting on ya) then gravity will give you a nice square cut vertically. But getting it square to the other side might be the tricky part. You might try using something like bamboo barbecue skewers stuck in the foam at your cut points on the ends so that when you lower the wand vertically into the foam you won’t have to ‘adjust it’ … which could leave a little curve in the wire before you turn on the power. Which in turn could give you a faintly curved cut, at least at the beginning.

hope that helps

doc…

6

and when all that has failed, a big, long sanding block, a good light setup and a straight edge will keep you off the streets for a couple of hours…

LOL!

7

i use a table saw and a bench jointer works perfect!!

8

Quote:

But getting it square to the other side might be the tricky part. You might try using something like bamboo barbecue skewers stuck in the foam at your cut points on the ends so that when you lower the wand vertically into the foam you won’t have to ‘adjust it’ …

Can you elaborate on this, not sure i understand.

9
Quote:

We have done 100’s of them!

It’s always better to cut straight lines with a hot wire - especially when you need many stringers in your glue-up.

Take a 12’ piece of Metal conduit and put elbows on the ends with 10" piece on both sides. Drill small holes in the ends of both 10" pieces.

With small machine (bolt, nut, washer) attach the wire to both ends keeping it taunt.

Then take a cheap extention cord and cut off the female end and put off the coating and expose 7’ of wire leave the plastic on the wire.

Clean about 1/2" of the plastic off the wire ends and attach alligator clips. (Good Ones).

Place you blanks on a long table with some weights to one side. Make marks on each end of the blank were you want you stringers. Keep it square!

Postion your Hot Wire Wand on the blank. Aline the wire so it rest on the marks. The conduit bar should just hang. Alligator clips on each end.

Set you variac to about 50 - 60 amps ( It takes more for the longer runs ) Turn it on and Let the gravity and heat make the cut. Turn it off when it hits the ground and don’t touch the wire.

I would practice first by cuting on 1" of a side if you have enough material.

If this is hard to understand I can take some pictures.

That’s the method we use, however, you MUST insulate the hot wire from the conduit. If you attach the wire directly to the conduit it will bite the shit out of you when you power up! As for keeping the cut true, attach a sleeve (just big enough for the conduit to slide into) square to the table top as a guide for the vertical component of the cutter. Wax the conduit, attach the wires, turn on the variac, and let gravity do the work. The wire will bow a bit in the middle as the ends being thinner tend to cut first, just let it pull itself through. Works like a champ!

10
Quote:

Can you elaborate on this, not sure i understand

Sure, though with my kinda shaky language skills I hope you don’t mind if I throw in a couple of sketches;

Now, lets say you want to measure over a distance A and make your cut there. So you measure over, make a pencil mark, repeat at the other end. So far, so good.

But you place your cutting rig on there and first you get one end right on the mark. And then you go to the other end and move that end to the mark… but the wire drags a little on the foam, and if it doesn’t then the first end gets a little out of place and you go back to move that just right…

And…this is conduit. So, there’s a limit to just how tight you can get the wire without the lightweight frame bending or buckling a little…oh, and by the way, if you use, say, 1 1/2" PVC pipe instead you can skip insulating between wire and conduit, just use a couple of cheapie eye bolts. But either way, you’re not gonna get this as tight as a violin string, so when you move it around there’s a good chance there will be a little curve in the wire before you fire it off and that’d make a little curve in your cut, at least before the wire gets in there a ways. And that makes something that won’t be too wonderful to glue up.

As an aside, that’s why using a chalkline or even those very cool Japanese ultra-thin ink-lines is kinda problematic on non-flat surfaces or when ya twang it other than perpendicular to the surface that gets the line. The damned lines curve. Close enough for house construction, but not nearly good enough for boat work or furniture or straight, straight lines.

So, whatcha gonna do? Use skewers or toothpicks or something similar, so ya can do this:

Note: the skewers are on the side of the line that’ll be cut off, and leaning a little so your wire won’t bump the tips of 'em in the foam and deflect your cut on the way down. Also, that makes sure that the holes they leave are in the foam that gets cut off.

That help any?

doc…

11

hi,

I just did the same thing a few weeks ago.

I build a 12’ sup with two stringers 20cm apart.

the room I use is about 13’ +

I screwed a hook to each side of the room,

and ran a ni-chrom wire between the hooks ( used a spring on each side to maintain the wire’s tension)

placed the blank bottom side up and made sure

everything is aligned and used a level to make sure the cut will be prependicular.

connected each side of the hotwire to a long extention cord going to the

variac …power on…turn the knob until it’s hot enough

and goes into the foam…10 sec’s and it’s all over.

I also took the idea from greg’s 101 and the cut is nearely

perfect.

it’s not the straightest line in the world and not a perfect 90 degrees cut

but it’s good enough and doesn’t effect the shape.

I believe that using a construction as greg’s , will

solve all the small imperfections since you drop

the hot wire on the blank when it is already straight and

tight.

good luck,

waiting to hear how it went.

lee

12

I use a bandsaw (full stand up version with the floating table)… you can get a used one for no more than $200 (and that is pushing it) just make a table guide out of some ply, set it to cut in the center (ie, 24inch block set the guides [sides of the wood held on with adjustable clamps] at 12 inches on each side) slide the cut blank through and like magic you have a perfect cut. For multiple stringers just re adjust the guides to cut where you want - if there ends up being a wave in the cut because you messed up no big deal - take the straight side against the adjustable guide and slide it in about 1/8th inch and then it’s all good. The only downfall of this method is you cant do it too slow because the blade may bite in the foam and you have to recut, but too fast (with heavier eps) and you can snap the blade… thats a bummer. Dealing with the massive hotwire cut is a bit more trouble than it is worth when you can cut a rocker, stringer, and the blank in half in less than 30min. :wink:

13

yeah i just get blocks that are 300 or so and cut two

that way i have a perfect gluing face for the stringer and it requires little or no clamping

i glue the stringer with a very light smear of five min epoxy

its easier storage for the narrower block and easier cutting a narrow block by your self

use ados f2 spray adhesive or double sided tape to attach your templates

about 6 amps will rip through a cut in 2 minutes

use nichrome wire

attach alligators to the wire itself

3mm mdf is good for templates

use 12 volt DC

240ac will kill you dead

14

Hey Doc

You’ve sold me

Exellent set up

Will start building one tomorrow

Be able to hang it up on the wall out of the way when I’m not using it too

Your a genius

Cheers

15

Drewtang’s method:

http://www.swaylocks.com/forum/gforum.cgi?post=254670;search_string=drewtang;guest=17768871#254670

16

Doc: You Got!

17

Dealing with the massive hotwire cut is a bit more trouble than it is worth when you can cut a rocker, stringer, and the blank in half in less than 30 min.

We can cut 20 boards in less than an hour. It’s easy for us? I have a Laguna Bandsaw and nice shop equipement I never use it for EPS.

Hotwire is so fast!

18

Ah, don’t thank me, thank surfding - it’s his method, I just went into it a little more.

Another couple nice things about this method; see, when nichrome wire heats up , it lengthens a little. If you put in a rig to tension it, say a spring or something, you are walking a tightrope between keeping it taut and tightening it so much the wire stretches, necks down at some spot, overheats and breaks. With this method it doesn’t matter so long as your table is level, the wire can make a caternary curve inside the foam and it’s still gonna be a straight vertical cut.

Likewise if the wire heats unevenly, it’ll all cut through eventually and still be nice and straight.

Have fun

doc…

19

If you put in a rig to tension it, say a spring or something, you are walking a tightrope between keeping it taut and tightening it so much the wire stretches, necks down at some spot, overheats and breaks

I use a spring on some of my bow’s.

CNC Hotwire machines use springs also.

Doc: You have a good mind.

20
Quote:

I use a spring on some of my bow’s.

CNC Hotwire machines use springs also.

Oh, definitely. But selecting and pre-tensioning the spring is the key to it. Too little pre-tension and the wire goes floppy when it stretches, too much and it necks and breaks.

Quote:

Doc: You have a good mind.

Not all that good. More like I have been using a cheezy 26ga wire and a doorbell transformer, say 40 watts, and I broke a lot of wires while thinking ‘damn, why did it do that’…

Eventually, as we say in New England, Dawn broke over Marblehead. So I set things up so that a little slack in the wire was acceptable, cut in a certain direction and all that so that the convex was out rather than in.

best regards…

doc…