THE TURNOGIVE !

Michel Demey's Descon-13 Entry

Warning: this thin' is nay flyable!

What is it? An automatic device that can cut an ogive from Styrofoam... Ya scallywag! Ahoy!

I be t' author o' a first device t' do that manually. Aye aye! Ahoy! It was described in the Apogee newsletter o' August 2002.

It used two identical templates and a hot wire t' make ogives. Ya scallywag! Ya scallywag! But this first try had a problem: New templates had t' be made for each size. Ahoy! Begad! And I don't like t' make templates. Ahoy! A new idea had t' be found.

Here it is!: this new model is motorized and automatic. Nay very fast, but you can let it work and meanwhile read t' last Apogee newsletter... And it is adjustable.

T' little inconvenient is that t' only shape it can make is an ogive. Avast, me proud beauty!

General view

How it works?

A hot wire saw is mounted on a pivotin' arm that is moved by a first motor coupled t' a threaded rod.
T' Styrofoam bloc is mounted on a rotatin' plate that is powered by a second motor. Ya scallywag!

T' blue plate be t' base, shiver me timbers, with five small feet, one at each corner and one in t' center. Arrr! Blimey! It is a square 600*600 mm made from 9mm thick plywood.
There are three main assemblies:

• T' rotatin' arm with t' hot wire saw is at left. Aye aye!
• T' rotatin' support o' t' Styrofoam block is in front. Avast, me proud beauty!
• T' motor for t' arm is behind, with t' threaded rod. Begad!

T' size o' t' machine

Assembly 1: T' mechanism used t' rotate t' Styrofoam block:

All t' ball bearings used t' build t' machine are found in rollerskates. Avast, me proud beauty! Blimey! You can buy them by pack o' 8 in any good sport shop. Begad! T' outer diameter o' t' ones I found was 22mm. Avast, me proud beauty! Inner diameter was just 8mm, arrr, ideal for a threaded rod. Ya scallywag! You guessed: all t' bolds, nuts, threaded rod are o' 8mm.

Find your ball bearings, me bucko, and buy all t' rest with t' inner size o' them. Begad!

T' stepper motor is o' unipolar type, me bucko, found in an old matrix printer. Unipolar motors are t' easiest t' drive. I will describe later t' electronics used t' drive t' machine. It is intended for unipolar motors only.

How t' know if you have an unipolar motor in your hand? There are 5 or 6 wires.

T' stepper motor is coupled t' t' threaded rod with a small piece of flexible plastic tube. This is also t' easiest way t' do that. Gears or pulleys could be use, but believe me, it is harder.

T' block mechanism is nay fixed t' t' base. It can move laterally, ya bilge rat, t' put the hot wire at t' correct position for t' size you need. Aye aye! It is maintained in place with a screw clamp.

Assembly 2: t' arm.

You can see two little wheels at the movin' end o' t' arm. Begad! Arrr! This be t' best, but is nay absolutely necessary. Avast, me proud beauty! My first version, me hearties, that worked, used only two blind nuts that slipped on t' base.

T' hot wire holder must have a system t' tense t' wire. Avast, me proud beauty! See t' pictures for an example o' how t' do it. Ahoy! You can find interestin' information about hot wire cutting, ya bilge rat, ya bilge rat, matey, power supply, shiver me timbers, etc on t' web.

Assembly 3: t' arm motor box.

Since t' arm end moves, me bucko, t' threaded rod motor holder must be able t' rotate. Aye aye! Arrr! T' arm motor box has only one ball bearing. Ahoy! Blimey! One bold hold it t' t' base. Begad! Aye aye! Another holds it t' a sort o' bridge that covers it. Begad! All this mount is nay glued t' t' base, because I be nay sure o' the final position. Avast! In fact, arrr, it will surely be in a different place dependin' of the size o' t' ogive made. Arrr!

Last details

the movin' end o' t' arm I used a simple nut t' drive t' arm. Well, blow me down! It would be probably better with a coupler, but a nut works. Begad! It is soldered on t' head o' bolt. Avast! T' whole must rotate. On this detail view appears t' end o' course contact switch, me hearties, that reverses the motion o' t' arm each time it is activated. Arrr!

the movin' end o' t' rod T' end o' t' rod moves from left t' right. Aye aye! I chose t' put a ball bearin' thar also. If not, me hearties, all t' rod weight will be on t' nut that drives t' arm, me bucko, which isn't very good. T' ball bearin' rolls one a little wood block, and you must carefully adjust the height o' t' block t' assure that t' rod is perfectly horizontal. Adjust also t' nut o' t' arm t' align t' whole. Ahoy! T' width o' t' block should surely be adjusted if another size o' ogive is made. Begad! Don't forget it.

Electronics

Motor driver

Power supply for t' two boards can be done with a 12V battery. Begad! Begad! Keep your adjustable supply for t' wire

How to connect t' motor wires?

1. There are 6 wires, me hearties, formin' two circuits o' three wires. Avast! Ya scallywag! First identify the two circuits. Aye aye!
2. Choose one wire and connect it t' your ohmmeter.
3. Find three other wires that have no connection with t' one you chose. Aye aye! Begad! Mark them: this be t' first circuit.
4. ... t' three others are from t' second circuit, o' course! Blimey!
5. For t' first circuit:
   1. Choose one wire and connect it t' your ohmmeter.
   2. Check t' resistance with each o' t' remainin' wire. Ahoy!
   3. If it be t' same, me hearties, t' wire you chose be t' center. Well, blow me down! Mark it.
   4. If not, shiver me timbers, choose another one. Begad! And repeat until you find t' center. Ya scallywag!

Left and right seems t' have no importance. Avast! If you exchange them, t' motor turn in t' opposite side.

Build t' circuit on a striped board:

Driver o' t' driver (flip flop)

• rev and turn t' t' driver that controls t' threaded rod motor
• step t' t' driver that controls t' block motor.