ArduSaw

ArduSaw Intro

This project came about as a requirement to crosscut 100mm wide sheets of balsa with thicknesses from 0.8 to 12.7mm. I had been using a simple MDF jig with a 90 deg cross guide and scalpel - the trouble here was that in the thicker materials, you occasionally got chip-out at the lower edge of the cut, and it was also hard work in the thicker materials:-)

I scoured the web for a commercial solution - and found none ! I couldn’t actually believe that no-one produced what in essence is a mini slide saw for hobbyists. There were loads of simple full-sized chop saws that would have done the job (but mains powered), but finding a high tooth count blade at 210mm was next to impossible (at least here in the UK). I fully believed that Proxxon would have had one too, but no - nor Dremel :-)

Step 1: ArduSaw Specs

This instructable is essentially a one-trick pony, but could easily be modified to accommodate differing needs - more on that at the end of article.

The essentials for me were (in no particular order) …

1 Min cut width of 100mm

2 Max cut depth of 13mm

3 A one button design, no extra switches or knobs.

4 A cantilevered setup so that the material could be slid in from the front.

5 Cordless

6 High speed cut to give a decent cross cut quality

7 Direct motor drive, no gears or extra bearings/pulleys/belts

8 Cheap

9 Cheap

10 Cheap :-)

Step 2: ArduSaw Parts

You should note that it was built purely using parts I had to hand - no oddball stuff, everything should be easily available off-the-shelf - I’ll include a simple BOM at the end.

It is also the first pass at the design - it works, so I have no current need to continue with any improvements/modifications :)

First off, the sawblade is a Proxxon 28014 58mm dia item with a 10mm centre hole. The parts are all sized to suit this particular blade. You’ll need to check that any blade you acquire can be accommodated in the case housing - hole size is important too of course.

Bear in mind that this saw was not designed to cut metal or extremely hard materials (and I’m not going to test mine to see if it does :). The proxxon blade I used is essentially a wood blade (tungsten variants are available ‘though).

The design is loosely based around an old Eumenia crosscut saw a friend has - in essence, a regular circular hand saw attached to a mount that uses vee wheels on a square metal tube. It could either have a firm mounting at both ends of the slide or be cantilevered to allow a front opening - it is height adjustable, mine isn’t (it doesn’t need to be).

The tube slide mount here is a piece of 12mm square welded seam steel tube with a 1mm wall thickness - available at DIY stores. Rather than weld/braze up the tube to another tube with flanges (I don’t weld :-), I just used a vertical length of 35mm steel barstock which was cross drilled to accept a 10mm piece of steel rod (more DIY store material :) - held in place with either an M5 grubscrew or screw at the top. The rod was slipped into the square tube (actually forced as the inside of the square tube still had the remnants of the weldline - this held the square tube perfectly and semi-permanently in position). The square tube can then be rotated to get a 90deg vertical cut and clamped down with the screw. The 35mm barstock end is simply drilled and tapped to accept 2xM5 screws and mounted to your baseboard of choice. The end of the 10mm rod is tapped to accept an M4 screw with a penny washer under to act as an endstop for the box. The end result is reasonably rigid (certainly rigid enough for my purposes). Like most projects, flinging time, materials and money at it can achieve a superior result (mostly :)

Step 3: ArduSaw Drive

The drive items required some minor thought, to achieve a minimum 13mm cut using a 58mm blade leaves only 58-(2x13)=32mm for the motor casing as this is a direct drive setup. I had a spare 28mm outrunner from an aircraft and tried that mounted on a ply board using the proxxon blade. The results were good - really good, absolutely no issue cutting through 12.7mm balsa (or my fingers either :((( ). This gives an absolute max cut depth of 15mm.

The motor used is an NTM Propdrive 28-26 1350Kv from HobbyKing (other motors are available no doubt :-), I had a 55A ESC to hand so used that for testing along with a 3s/3300mAh LiPo battery and a servo tester to supply a test signal.

The first issue was of course going to be my choice of a one button solution, the ESC has a safety startup function built in. The safety requires the pulsewidth to be at minimum before it will fire up the motor - and it can’t be bypassed (unless you know different ? - without actually reprogramming the ESC that is :). This meant that it would have to be a toggle switch plus a pot on the servo tester to wind it up to speed (I only need max speed). To get around this issue, I spent many weeks writing some very complex algorithms to control a PWM signal using an arduino - as if :-) It took literally 30mins to solder up the servo cable, write the code and flash it to the arduino - don’t you just love arduinos :)
The arduino simply sends out a min pulsewidth to the ESC when it is switched on, after 1.5 seconds, it sends out a max pulsewidth and stays there until it is powered off - that’s all it does. There was some minor faffing about as the pulsewidths needed to be 1 and 2mS respectively for the ESC - NOT The 0 and 180 deg pulsewidths that the arduino library puts out - the angles were adjusted accordingly. The pushbutton (push to make) is simply in series with the positive lead from the LiPo. Blade rotational speed is set by the LiPo voltage, the motor Kv and of course by whatever pulsewidth you fire at the ESC. Assuming a max pulsewidth (around 2mS), then using a fully charged 3S LiPo, it is going to be around 4.2 (V) x 3 (cells) x 1350 (Kv)= 17K RPM. Kv is effectively revs/volt. I’m assuming mine is around that, but I’ve no way of measuring it (easily :) I put my wattmeter in series with the setup while cutting some fairly hard 12mm balsa and only managed an absolute max of 1.5A ! To that end, the final setup uses a 10A Turnigy Plush ESC from Hobbyking and a 3S 1000mAh LiPo from the same place :) I happened to have these to hand - any old ESC will do really as long as it’s greater than 2A. It will need to have a BEC to drive the arduino - which is only a few milliamps - opto versions of an ESC won’t work of course. I guesstimated around 800 cuts between recharges - let’s say 20 cuts per day, that’s 40 days- not bad really - better than my Makita drills at least :-)

You could of course use a brushed motor without all the external paraphenalia - but where’s the fun in that (and it wouldn’t be an ‘ArduSaw’ :-))) - and being ‘inrunners’ don’t have quite the same torque anyway :-)

Step 4: ArduSaw Assembly

I have access to a laser cutter, so it made sense to fab the case using some 3mm acrylic sheet I had to hand - all the electronics/battery/motor/bearings can be self-contained in this wee acrylic ‘cartridge’.

The bearings are 625RS - 16mm dia, 5mm hole, 5mm thick - x8 - all held in place with a pile of M5 washers and M5 x 35 cap headed screws and nuts (I did cheat a wee bit and turned down some spacers for the outside instead of using a pile of washers, but the result is the same). The bearings are separated by two washers (they’re about 2mm thick) - they then run on the upper and lower edges of the 12mm square tube. The lower bearing screws fit in a slot in the acrylic to allow for some adjustment against the tube.

Assembly consists of installing the motor (countersink the inside holes) with the supplied screws (remember to use blue ‘loctite’ on the threads or they won’t be there in the morning !) and drive collet. Put the motor wires through the hole in the acrylic and wire up the battery/ESC/arduino and motor - switch on and check the rotation. The motor rotates clockwise looking from the left side of the case - if the motor is running in reverse, just swap over any two of the motor wires. Using an M5 washer (or a spacer from a plastic prop) as a shaft spacer - the collet has a 5mm shaft, the blade has a 10mm hole - fit the blade. Fit the 4 M5 screws with washers under then the required number of washers to keep the bearings centred (I’ll leave the student to calculate how many washers they need, they’re approx 1mm thick:-)) Once they are in position, just push fit all the electronics in the rear of the case and wire up the push switch. Fit the case surrounds using M3x12 screws and nuts - then screw down and adjust the bearings for a good sliding fit. Mount the stop washer and screw on the end of the 10mm rod.

Step 5: ArduSaw Board

My setup involves a stop pin at various cut lengths on the left of the board - there’s also a backing strip. The blade sits down into the board about 1.0mm in a slot - once everything is setup and aligned, the slot is filled with a piece of balsa to act as a zero clearance insert.

For the metrically challenged, 12.7mm = 1/2” so 25.4mm = 1” =;-)

The saw will certainly cut balsa up to 12.7mm, birch and liteply up to 6mm, hardwood dowel up to 6mm. I haven’t (or don’t wish to more like :) tried any other materials - I’ll also leave that for the student to test :)

I did have some thoughts about having a pushbutton automatic solution, but didn’t bother. It was to use a sail winch servo to drive the ‘Y’ axis of the saw - press the button once, a relay would then short out the pushbutton to hold power while the saw spooled up and the winch servo pulled the saw forward and back - then released the relay. I’m sure that there are many bells and whistles that could be added as the arduino isn’t taxed at all.

Another alternative would be to have a toggle switch for the power and a 'soft' pushbutton switch to control the PWM output - there would then be no delay on subsequent cuts. My problem with this was that I would surely forget to switch it off :)

Warning Will Robinson !

Just be careful, the saw is turning fast and will cut straight through skin and bone quite easily - you have been warned - and don’t try this at home or anywhere else that will involve me in any form of lawsuit - you build this at your own peril and it wasn’t me who showed you how to do it - and I no longer stay at the address that you think I may have recently stayed at anyway !

Step 6: ArduSaw BOM

BOM

1 x Proxxon 58mm saw blade the PROXXON 28014 Crosscut 'super-cut' blade - lots of sources - try amazon (seems it is ok for plastic and ‘Pertinax’ (whatever that might be !))

1 x Turnigy Propdrive 28-26 1350Kv outrunner motor or similar - www.hobbyking.com

1 x Turnigy Plush 10A ESC or similar - www.hobbyking.com

1 x 3s/1000mAh LiPo - any old brand will do - try Zippy from (you’ve guessed it :0) - www.hobbyking.com

1 x Sheet of 3mm cast acrylic for the case.

8 x 625RS bearings - here in the UK, ebay.co.uk - loads of suppliers - my current favourite is ‘engineersmateltd’

4 x M5 x 35 screws and nuts (for bearings and case)

200 x M5 washers (or however many you need :-)

2 x M3x12 screws and nuts (case attach)

1 x M4x12 screw and penny washer (end stop)

1 Length of 12mm square, 1mm wall steel tube - as requ’d - B&Q in the UK

1 Length of 10mm steel bar - as requ’d - B&Q in the UK

1 x Pushbutton N.O. switch - http://uk.farnell.com/otto-controls/p9-113121w/pb... - this is what I had, any decent 3A or greater will do :-)

1 x Arduino Nano (mine is a clone)

1 x Arduino sketch - ArduSaw v1.01 as of 2015.11.01

1 x Laser cut case drawing - 'Ardusaw Laser Acrylic'

1 x Length of 35mm OD steel bar or similar vertical attachment support

1 x Blue ‘loctite’ - where else :) - www.hobbyking.com

1 x XT60 Male connector (the one with the male pins) - to suit LiPo connector - www.hobbyking.com - could simply use the balance connector of course - it’s only 1.5A

A few other parts that I have no doubt missed :-)