A longer shaft offers a number of benefits;
The first is, is the reduced stress to your back for taller operators, by allowing you to stand more upright. I can assure you, that once you get use to the longer shaft you cannot go back. If you have not already viewed this page, I do recommend reading through it;
The second is, safety from having a lethal spinning metal blade further away from you, which also makes you feel a lot more comfortable. It is like wearing safety pants when using a chain saw, once you get use to them, you feel very insecure when not using them. I know this, because on a couple of occasions I have forgotten to put these pants on the back of the truck when going out and I now feel really scared using the chain saw without them. The same applies to a longer shaft, once you get use to it, going back to a standard shaft now feels scary to me when on steep slippery ground.
The third is, the added efficiency of being able to reach; further, higher and swing wider to cover much more ground than you can with the standard length shaft.
The forth is, to allow a better balance of the brush cutter and to move the engine and its electromagnetic fields further away from your body.
A longer shaft creates one major problem, Vibration;
One of the problems of making a longer shaft, is that it creates lower frequency vibration issues. Just imagine a longer piano string, the vibration and resonance all change to a lower frequency and for those hanging onto the shaft the change is for the worse.
Although the shaft should not produce any vibration in itself, it is the conductor of vibration coming from the engine and gear head and behaves very much like a guitar or piano string. With all of this vibration ending up going through the handles to your hands. Hopefully with a combination of different materials and clever design, I can considerably change the shafts resonant frequency, so that the vibration transferred to the hands is reduced.
Below is a really good video, that explains visually, the resonance in a pipe or tube. It is by Steve Mould and he has a way of explaining physic, that everyone anyone can understand. I also recommend that you check out some of his other videos.
This video only shows a vibration source at one end, just imagine how complicated the rogue frequencies would be when you have a second source of vibration at the other end of the shaft, as in a brush cutter.
This moving image below, which is a short clip from the video below it, shows how resonance can produce rogue waves in a 28mm diameter x 2mm wall aircraft grade aluminium tube. These rogue waves can intensify to the magnitude that it can easily flex this very hard tube to the point that it becomes easily visible to the eye and of cause with a brush cutter it is your hands that end up absorbing this, especially when not using a harness to carry the weight of the brush cutter.
I had looked at a two different materials for the shaft;
The first option, is carbon fibre, which is very stiff, light and very expensive. But it is also cheaper to produce and bring to market, as there is no tooling costs and production runs can be small. I now have a first small run of 20, 1800mm long shafts ready to go. The weight of this 1800mm long carbon fibre shaft is only slightly heavier (1.3kg), then the standard 1500mm long Honda shaft, so there is minimal weight penalty for the longer shaft.
The second option, was Aluminium. I managed to source a length of aircraft grade aluminium pipe, with a wall thickness of 4mm to test to see if this heavy wall aluminium pipe would be stiffer. What I found was that the weight of the heavier wall pipe, seemed to lower the frequency even more and it felt worse that the carbon fibre shaft after a couple of hours of brush cutting.
One of my main goals in making my own shaft, is vibration reduction. But after using the carbon fibre shaft brush cutter for a couple of months, it did not feel like there was any obviously reduction in vibration. But when I then went back to the aluminium shaft brush cutter, which sounded quieter, it ended up resulting in tingling fingers after a couple of hours of use.
Below is a sample of the shaft, where the resin has been burnt away with a blow torch to expose the unburnt carbon fibres that make up the shaft.
So why use carbon fibre, when it is so expensive, perhaps this video will explain that. It is still a gamble though, people will spend untold amounts of money on their sport equipment to gain an edge, it remains to be seen if they will spend this sort of money on their work equipment such as a brush cutter.
Below are pictures of the current drive couplings found on the latest 35cc Honda brush cutters. The gear head end has a double flat face drive coupling and the clutch housing has a 7 spline coupling. Other countries and older models may have different couplings, so you will need to check yours before ordering a long shaft upgrade.
This upgrade will be offered in three option;
All parts will also be offered individually, for you to choose what and how to upgrade your Honda brush cutter.
AT THE MOMENT ONLY THE 1800mm LONG SHAFTS ARE AVAILABLE AND ONLY IN AUSTRALIA.
Unfortunately, due to Australia Post or Courier companies, not allowing delivery of such a long parcel. This long shaft run, will only be available by direct pick up at Comboyne NSW or Wynnum QLD.
Future shafts will be made as split shafts to allow for delivery by the postal system world wide, but because I have not found what I consider a strong enough off the shelf shaft coupling, I will have to design my own. This will mean that future long shafts will be even more expensive, but I believe that for user with back issues or using a brush cutter for long periods, it would be money well spent. Cheeper then a few visits to a chiropractor, or a back operation.
Extra Long Shaft Only
This option will allow owners of Honda 35cc brush cutter to upgrade to a longer shaft and is more aimed at owners of bicycle handle brush cutters. Owners of loop handle brush cutters can also upgrade to a longer shaft and continue to use the standard loop and throttle handles.
1.8m long carbon fibre shaft with drive shaft couplings to suit the Honda 35cc brush cutter.
Purchase Price – 1800mm long carbon fibre shaft – AU$265.00
Shaft + Offset Loop Handle – AU$285.00
For those who want a longer shaft, with the better balance and control this loop handle offers.
There are two benefits this handle offers over the standard Honda Loop Handle;
The first is, this handle has a soft rubber grip, is rubber isolated from the shaft to absorb some shaft vibration, whereas the Honda loop handle is solid mounted to the shaft, (as found in the Australian models). This handle has proved to be very rugged, after six years, there is no signs of the rubber cushioning coming adrift or showing any signs of the handle breaking.
The second is, is the offset handle allows for more comfortable control, as you do not need to reach quiet so far across with your left hand to hold the brush cutter. Unfortunately the grip is not so comfortable when the brush cutter is laying on either side, but this is generally only for short periods of time.
Shaft + Offset Loop Handle + Trigger control Handle – AU$300.00
For owners of bicycle handle machines, to fairly quickly swap back and forth to a loop handle machine. And loop handle machine owners to upgrade to a better balanced machine.
This trigger control handle will offer a couple of benefits over the standard Honda Handle;
The first is, the longer throttle cable, that allow you to move the trigger control handle further away from the engine, for better overall balance of the brush cutter and moving the electromagnetic fields generated from the engine further away from you.
The second is, the stop switch and throttle start lock, is less exposed and less likely to be knocked off as with the Honda throttle handle. Especially if you sand them down a bit like I did, so that they are less likely to catch against the harness.
The Third is, these handles will be mounted on isolating rubber, to help minimise some shaft vibration from transferring to the handle with a 26mm shaft. This handle can also be used on a 28mm shaft without the isolating rubber.
Throttle Control Handle – AU$35.00 – Includes Postage