DIY - Handheld Hotwire Cutter

I thought I would share my experiences sourcing parts for the new Handheld Hotwire Cutter I have just completed.  Previously I used wire from a TV coil hooked up to various car battery chargers that had a factory set current output.  These worked occasionally but you never had much control of the wire temperature. 

Hotwire Foam Cutter

After scouring the pages of ebay I came across a neat little hot wire power supply from Australia. There were 2 options for maximum wire length(when used with the recommended nichrome wire) of 1m and 1.5m and the unit ended up costing around $100.  I went for the 1m version as I will only be cutting the short side of full EPS blocks and I didn't want wires burning out when cutting thinner material.

Hotwire Power Supply

The unit weighs next to nothing and is quite compact so I mounted it to the hotwire bow for ease of adjustment. You can get optional wire with the banana connectors on request.

Hotwire Termination

Mounting of the wire is achieved by looping it around a bolt in between 2 washers, a wingnut is then tightened to clamp the wire between the washers.  The end of the wire hangs out for easy connection to the power supply.

Hotwire Bow Spring Tensioner

The wire lengthens when heated so one end of the bow pivots on a socket head cap screw.  An old trampoline spring maintains the required spring tension.  Folded 50x3 aluminium flat bar is folded to form the opposite fixed connection as well as the hinge seen above.  Scraps of 45x35(?) pine were used for the arms but these might be upgraded to CF roll wrap tube when I have more time.

Freshly cut EPS without sanding...

This is the first board(HD Creeper 48) cut with the hotwire and the above foam is straight off the wire with no sanding whatsoever.

Board Building Project - HD Creeper 48 - Stage 1

Well I am up to my elbows in foam again and I must say I have really missed it.  The last board I built was in 2007 and this time round I have done things properly and have not cut corners.  First up was a dedicated vacuum system followed by a new hot-wire bow with dedicated power supply(not just a battery charger putting out whatever current it factory set). I am also cutting full size 3mm MDF hot-wire templates, I used to use thick cardboard which could get burnt if the hot-wire got snagged.

So far I have:
Designed the board and printed full size templates on my A0(roll) printer.
Cut full size templates for center rocker, side rocker(to form the vee), plan and tuck templates.
Cut each side of the board with its panel vee.
Laminated the halves together with a 3mm PVC stringer to preserve the intended rocker line.

Here are the progress pics:

Board Building Project - HD Creeper 48

Well my Lake George Speed Sailing trips are only a month away so what better time to start a speed board!

I am a bit of a Minecraft fan and I like how Creepers sneak up on you and all you hear is a little sssssSSSS before the blow you to smithereens, hence the name.  Hopefully I don't blow anyone else up using the board as I think I shopped in the close shave department last year...

Shape
The board will be slightly narrower and longer than my previous speed board (JP Speed 49) and I have settled on 48 wide x 245 long.  The rocker is nice and gradual with low nose lift and there is a small amount of tail kick to free the board at the top end.  A simple panel vee will form the bottom contour with the deck getting a slight concave for increased stiffness and reduced nose lift.

Construction
I will be using as many scraps and offcuts as possible except for the core, I have purchased a half size SL grade (~12kg/m3) block(120x60x250cm) for this and future boards .  Deck sandwich will be 3mm H80 Divinycell with the hull in 6mm H100.  Both of these are perforated but that is all I could get locally when I purchased materials for my last board in 2007.  In my next board I will probably use corecell as I have heard that it is easier to work with and maybe airex.  Skins will be a glass hull with full carbon deck(200g twill).  I am only using the board at Lake George and temperatures only get to the high 20's, low 30's so I'm not concerned about overheating.

Fittings
I have leftover foot strap inserts, a mast track and Tuttle box from previous builds and have gone the Goretex breather route getting a nice little unit from Shapers on the Gold Coast. I have some 1/2" PVC foam and may encase the track and box this time as I am not as concerned with weight on a speed board.

Method
I will hotwire as much of the bottom shape as possible including the vee,  the outline will then be cut using templates as well.  See my hotwire here: (coming soon).  I will break down each of the build steps into a separate post as they are completed.

Here are some more renderings of the design:

HD Creeper 48

HD Creeper 48 Tail

HD Creeper 48

HD Creeper 48

HD Creeper 48 Nose

DIY - Vacuum Bagging System

The "Smart Little Sucker"

With a few board designs in the pipeline it was time to upgrade my vacuum pump to a system with vacuum pressure control. Up until know I have used the cheap fridge pump option and while you may save a lot of money on the initial outlay you soon loose money if you damage a blank(or 2 as I did!!!!) using excessive vacuum pressure.  The vacuum pressure control is achieved by using a tee fitting with a ball valve in combination with a vacuum gauge. While this setup may be good for small bagging jobs and high vac pressures with robust moulds I have had problems bagging boards where the vacuum pressure is stable for several hours and then a leak or hole suddenly seals itself and the pressure goes throught the floor(really low ;). Since the vacuum has to be maintained for 12 hours or so this makes bagging overnight risky.

My old fridge pump system.

The pump was fan cooled on big jobs.

The next step up from using a ball valve is a diaphragm and reed switch but I am not a fan of this version due to the lack of precise control as well as questionable electrical safety.

I wanted precise vacuum control without the pump having to run continuously and came across this veneer vacuum system from Veneer Supplies.Com: http://www.veneersupplies.com/products/Project-EVS-Auto-Cycling-Pump-Vacuum-Press-Kit.html

I was able to scrounge most of the required components from the parts bin at work except for a vacuum controller. I decided to use an SMC electronic vacuum switch for accurate control and the hysteresis function to reduce frequent pump switching.

The need for a small footprint as well as portability meant than I had to stack the components using a plywood shelf system. This is the prototype which will probably stay this way - functional!

Working from the Air Fitting back there is a ball valve to isolate the system from the vacuum bagging line.  The ball valve is connected to the vacuum reservoirs(tubes of nothingness...) which are separated by a takeoff for the vacuum switch. 

Vacuum Reservoirs.

The reservoirs are then connected to a check valve(one way valve) to store the vacuum in the reservoirs.

Top view of Vacuum Reservoirs, Vacuum switch and Check Valve.

Connected to the check valve is a 3 way solenoid valve to relieve the vacuum pressure behind the check valve when the pump is switched off by the vacuum switch.  This stops the pump having the start under load. Next up is a under bench water filter which acts as both a line filter and sub reservoir.  The sub-reservoir allows the pump the run to full RPM without back pressure on the pump intake port. Connected to the filter is a small diaphragm pump which is oil free and super quiet when an exhaust muffler is fitted.

3 Way Valve, Sub-reservoir/Filter and Pump.

Below the pump is a small termination box housing the terminals, 24v Power Supply and Contactor.  The Vacuum switch outputs a signal to the contactor which switches off the pump and opens the exhaust valve at the desired vacuum pressure.

Terminals, Contactor and 24V P.S.

Next up is a test run on a new board or 2!