Thread: Jig Saw Pendulum Action

Your enquiry is ever so slightly vague in terminology. By "pendulum action" do you mean "orbital?" Brand and model number, or pictures, might help.

In scrolling mode, the blade should be aft of the direction of travel with respect to the quill, so that it trails like a swivelling caster wheel.

Joe

I understand that what is called 'pendulum' action in Australia, is called 'orbital' in the USA. I'm interested in the mechanics of how such 'fore and aft', as distinct from 'up and down' movement is achieved in a jigsaw, given that it now seems common to most models in most brands.

Strictly vertical action is often achieved by counter-rotating eccentric bearings operating on a horizontal guide rail attached to the quill, which is itself aligned by upper and lower bushings. The supporting wheels carrying the bearings are meshed for synchronization. Their axles are parallel to the direction of saw travel, and to the motor axis.

Pendulum, or orbital, action is somewhat a mystery to me too, although I could speculate until the cows come home. An easy way to determine it could be via Google search, say [orbital jigsaw mechanism]. Easier yet would be to identify patent number(s) on the specification plate, and to enter it/them at http://www.google.com/patents for download of pdf files. I've used that for some antique tools, even as an aid to repairs. Aaargh! Couldn't resist the temptation: 7254892. YMMV.

Joe

The pendulum system (Aussie name) tilts the blade axis forward and backward during the cut at a substantially slower rate than the blade operates at. The extent of the tilt is controlled via a multi stage selector normally above and behind the blade holder.

My understanding is that the forward/backward tilt is to allow the blade to unload during cuts in deep timber by cutting toward the bottom of the cut when the blade tilts forward and towards the top when it tilts back. I sometimes see people using a similar type of action when crosscutting logs with a bowsaw or chainsaw.

As to how its generated, I would assume that it is produced by a cam system driven by a reduction drive. In an attempt to verify this, I downloaded the parts drawing for the Triton Jigsaw as it features both scrolling and pendulum actions. However it seems that this saw generates the action within the main gearbox assembly which is a unit replacement item so no actual details were obvious.

Thanks Joe and Malb! I also assume that some cam application is needed to get 'pendulum' action, but Google has not located for me any site that reveals the actual process. Some 'pendulum' jigsaws are inexpensive enough, so the process must be simple! (However,obviously too difficult for me!)

Not difficult to believe that Google wouldn't find detailed explanations of the mechanism. I downloaded the specification for US pat. 7254892, and it's clear as mud. But the specification cites another, 4545123, that might augment understanding. Also, under "References Cited," there are several others which might help; generally, I expect the oldest ones would be more elementary, or fundamental, to describe the process. Downloaded patents don't consume much space on the hard drive, and they explain very well what the originators had in mind, and how they accomplished it.

Joe

I've had my Makita jigsaw apart to replace the roller mechanism which imparts the orbital movement to the blade. There's a cam arrangement inside the tool which imparts a back and forth motion to the wheel assembly which rides against the back of the blade. This cam is always engaged to the main drive.

The lever which operates the orbital settins (1-3 + off) moves the other end of this wheel assembly closer to or further away from the cam. This other end of the assembly is (from memory) a flat lever which rides against the cam. When the orbital action is disengaged the wheel sits as far back as it will go and the blade travels straight up and down.

As the orbital action is engaged the lever comes into contact with the cam and the wheel throws forward against the back of the blade (in a back and forth motion) The shaft that holds the blade must have some sort of arrangement to allow the blade to be held steady from side to side but allow forwards and backwards motion. I can't remember, I didn't think I would be tested on it later.

On my saw, after a lot of heavy use, a lot of it cutting aluminium and some steel, the back of the blades wore into the wheel so far that I ended up with two halves of a wheel. The lever assembly still kicked backwards and forwards when engaged but the wheel no longer contacted the back of the blade.

Hope the above explanation can be understood.

Mick

Thanks, Mick. I suspected a cam could give the 'Pendulum' action to the blade, and I can see on my saws that the shaft holding the blade (the 'quill'?) seems to tilt to allow such action to occur. What I can't envisage is how the bearings that locate and steady the shaft are able to be moved to accommodate this tilt, and the changes to the tilt, given that they occur many times per minute. I suspect I might have to follow your example and disassemble one in order to find out!

I think the top of the shaft has a pivot connection whereas the lower linear bearing sits in a slide which allows forwards and backwards motion. It's fairly simple when you see it.

Mick