Grass Cutter Mk II

Important Update: This doesn’t work! 🙁
I thought this was going to be an awesome re-purposing of my old hand mixer but turns out these things aren’t meant to be used for more than a few seconds at a time.
The second or third time I was using it, I went for about 10 minutes and it overheated and caught fire. I wouldn’t recommend going down this path. Read on if you want to see anyway

(<- Part 1 )

I present to you, the Grass Cutter Mk II

So a list of upgrades/changes

A new handle, taped up to keep it safter and secure. inside this is a lightswitch embedded in the wood for off/on and the control board.

A new adjustable angle handle, I can loosen the bolt and change the angle so if its not really comfortable where it is, I can change it.

The engine is now parrallel to the ground, much more ‘mower-like’ less ‘weed strimmer-like’.  Also I removed the rubber as it wasnt providing any vibration releif and was just making it smelly. The strimmer line (orange twine) is also attached in a more reliable way: I threaded it through a drilled hole in the shaft head, then tied a double knot on each side so it cant pass through either direction.

And a new height setting/adjustment pole. there will be a wheel on here soon, I tried a couch floor knob but it doesnt slide very well. The point of this is to make it easier to push around rather than having to manually hold it at a certain height. although doesnt mean you cant flip it upside down and go manual if you want to do edges etc.

String trimmer from a hand blender (Failed)

Important Update: This doesn’t work! 🙁

I thought this was going to be an awesome re-purposing of my old hand mixer but turns out these things arent meant to be used for more than a few seconds at a time.

The second or third time I was using it, I went for about 10 minutes and it overheated and caught fire. I wouldn’t recommend going down this path.

Read on if you want to see the original

I planted a lawn out the back of the property where the gardener couldnt get to without a key so I needed something to cut the grass. My lawn mower is a bit pre-occupied and my weed-wacker was wacked. So in the usual recycling manner I made my self a string trimmer (weed wacker) out of an old hand blender

Wow look at that, badly thrown together lense flare, a fluro background. This thing HAS to be awesome.

To be honest, the only reason I am calling it MK I  it because its rather hastily assembled and has some design uglies, I’ll probably never rebuild it because it works* (edit: not really see top of this page) and that’s all I care about.

So I started with an old hand mixer/blender motor I had lying about, and thought about strapping it to a peice of wood, without anything else more suitable I made a sort of wooden vice with two threaded steel rods and 4 bolts. This worked really well!

I basically just nailed the control board onto the length of wood for now, holds fine, but I had to wire up a switch. In the interim I have some twine nailed to the board, going over the switch with another small peice of rubber, then round a nail and back to the top of the board for a lever.

I also attached some twine to the end of the engine so I could cut some grass. simple; effective.

bill of components

* engine: from a hand blender like: * a bunch of wood I recycled out of an old couch.

* about a 1/4 of some threaded steel I bought a while back
* a 6cm bolt for the lever
* 5 bolts
* cut mains cable I had left from another project.
* some weed wacker twine for the controller and the cutting part.


(goto part 2 -> )

    Homemade Engine Clutch

I found a problem with my engine; it wont start under any significant load. The second pulley I made meant it was extremely difficult to start.

pulley = no startMain pulley off engine

I needed a clutch at some point anyway so I started thinking about how I could resolve both problems at once, removing as much load off the engine on startup and being able to clutch the engine.
My plan is to put a small disk on the bottom of the shaft, then create a method of being able to push the pulley onto it; a dry friction clutch, but with a few changes. The clutch control will be a nut that I turn remotely (Likely by another pulley). The reason for this is it means I will be able to apply more force to the connecting plates via the bolt, and possibly later I may be able to automate it (ie, mechanical clutch)
Also it seems like it will be the easiest to build.

This is what I imagine it would assemble like (click for big)

first home made clutch assembly prototype design

More detail on the bottom of the pulley:
Clutch design prototype other views

The pulley will turn freely inside the bolt, I may later replace the bolt and bearings with a real bearing perhaps out of a skateboard or something. The bolt pushes the pulley up using the two lower fixed nuts, turning the bolt inside them will push itself up up.

Update 16 July 2010
I started working on the pulley/clutch shaft and bearing. I spent most of the time trying to hammer, screw, grind some washers to the right shape. the most successfull was one that I ground down with an angle grinder except for the middle, then bashed the sides up a little bit. I found a aluminium ring which I think came from a hard drive and installed that and it seems to hold everything quite nice. Its not anywhere near perfect, not even near good, but its usable for now.

Exploded pulley with shaft and bearingsassembled pulley with bearings and various bolts
(Click for big)

The left picture shows an exploded simulation of how the bearing fits together, surprisingly this doesnt work too bad. The right image shows what it could look like assembled. Note the bit that says ‘Clutch Control’ this is just a bolt and two washers for image purposes. I need to put some thought into how I will turn the shaft, without allowing the spinning pulley to have any control over it. if I used a smaller pulley down the bottom or in the middle (as pictured), I fear it would be too easy for it to slip and the engine would dis-engage the clutch automatically. I also found I will need to modify the holes that the top bolt and bearing fit into; they are too shallow.

Update 17 July 2010
Started building the new base, and resunk the pulley so I had more bolt to play with, I am pretty happy with it. then I sunk a bolt into a wooden beam to go under the engine shaft, I shaped it with a craft knife, chiseled it out a little bit, then wacked it in with a hammer. It feels really solid so I am happy with this part. I in the 3rd pic I have placed it roughly where I expect it to sit. But I noticed I will have to be quite precise, I dont want the too shafts to be mis-aligned because it will mean the clutch plates wont sit true.

new base in progress

bolt mounted in a small beam to hold the clutchPlaced clutch in base underside of placed clutch

I still havent figured out how I can turn the clutch shaft without using too much bolt real estate and keeping it secure so its not able to be spun by the engine. although I am thinking about two small pulleys with some rope attached and wraped around a few times. buy pulling one rope, the pulley will spin the shaft and the height will increase, at the same time another pulley will be pulled and wrapped around the second pulley. I can then pull the second rope to do the opposite.

    Wooden Pulleys – Turning

As per Part 1. I now have a working drill and hole saw that runs of an old computer power supply. I can turn wood with the same drill by mounting it in a vice and bolting the wood into the chuck.
Power supplyDrill running off ATX PSU Drill Lathe

Firstly I took an old piece of MDF that was once a set of shelves, then a speaker box, and now wasting away in the garage and cut two pieces out. One was 5″ the other 4″. It took about 10/15mins to get through the MDF, I thought the drill bits were a bit crap but I think the drill itself is probably still underpowered. (it was quite a cheap unit when I bought it) Also I found it was very easy to get on an angle, possibly the density of the wood was different nearer the edges but I found it was digging in quite a fair amount on one side or the other and I ended up with not very even pieces. The first one wasn’t so bad but the second significantly skew. I will borrow a drill press to try and get a better piece, at least until I build my own later.

I put a bolt down the center shaft and tightened it up and placed the bolt into the chuck of my drill, then mounted the drill in the vice. To get foot control I tied a rope around the trigger, which travelled along my workbench to a nail then down and tied to a metal ruler/level at a height where I could push it down to pull the rope and as such, pull the trigger. I had some control over speed, but it could definately be improved.

Working on first pulleyPulley being turned and carved

This is how it came out, I was quite happy with this result.
Finished MDF pulley

I built a second but it came out quite skew, I will use a drill press to re-cut the MDF, and if its faster than the hand drill I might cut two circles, and stick them together to form a bigger pulley. something like so:

plan for new wood pulleycross section new wood pulley
This will also give me a wider groove so I can use thicker belts.

Update 12 July 2010
I also refined my drill/lathe technique a little over the weekend. I think I will modify it further to become a slightly more permanent fixture with a bearing on the other side. because its only fixed to the drill its quite easy to push too hard and bend the drill which alters the shape of the turned wood. to start with I may just buy a 30cm peice of threaded steel, grind myself a nice 3 sided head on one side so that it fits into the drill nicely, and smooth the otherside and it can sit in some sort of fixed socket to provide a more stable shaft.

I also built the new pulley, twice as wide so it will accomodate more reasonably sized belts.

Pulley 3Pulley 3

Currently my plan for the belt is to use rubber from an old push-bike inner tube