Bronlin’s Square Baler Chunker

Now is the time to make my own thread for the chunker build. I am planning to closely follow @Chris’s, @BillSchiller’s, @Dustin’s and others who have built this kind of chunker. Thanks to their pioneering work the design is already made, so all the is left to do is recreate it with the parts available to me.

Snagged a square baler gear box from scrap yard. I think it is a Massey Ferguson.

Started work on the frame. It has five mounting holes located on the side of the gear box. So I drilled some 5/8” holes in some 1/8” plate and welded them to the frame.

Decided I would use the large gear that was bolted onto the baler arm. It is about 1/2” thick so it should hold up. I plan to drill six holes into that plate a use that as a hub to bolt the cutter wheel to. The hole in the middle is already centred on the gearbox shaft so all I need to do is centre everything on that hole.

Printed out a template of a six bolt pattern and centred it on the hole, marked it out and drilled the holes.

Next I built the cutting wheel.

I’m using a piece of 5/16” pipe 12 1/4” OD welded to a piece of 5/16” plate. I actually cut that piece out of my fire tube top plate. It was exactly the right size. I’m hoping the cutter isn’t going to be too thick?

I tack welded the plate on then found the centre and used the same template to mark the holes. The holes were actually not exactly lined up. So I drilled two holes bolted the gear to the cutter and drilled the rest of the holes.

Cutting the arm to make it fit the gear with the bolt holes in it.

Had to make a cut out so I could put the bolt in the hole.

Picked up this motor on the weekend. It’s a 3hp 1720 rpm, 115/230v high torque motor with a 1” shaft used for farm equipment. I got it for $350 CAD. Hoping it will do the job.

Well that’s what I have so far.

Thanks for looking
God Bless


Good work. Looking forward to the rest of the build and the finished chunker


Wish i could find a motor like that! Im keeping my eyes open… first im saving for the wide band O2 sensor and gauge pakage.


Well I’m now trying to locate a belt and pulley. I decided to go with banded v belt, but I am having difficulty finding a pulley for a banded v belt.
Does someone know what they are called or what they look like?
And I’m probably going to want a larger pulley to increase the rpm’s correct?


On mine and some others I’ve observed it makes a chunk about every 1 to 2 seconds . Which for me is a comfortable speed. You will need to know the ratio of the gearbox (8 to 1) on mine and I believe Bill’s. And then you can calculate the diameter of pulley you need given the motor rpm to give you the desired cutting speed. iirc mine is about 1.6 sec a cut it gives you a little time to think between cuts. I use 2 B size v belts and a double v pulley on the motor and drive the flywheel even though there are not grooves in the flywheel I haven’t had problems with the belts coming off. Remember be safe the flywheel will make two wood cuts after you shut the motor off. You get a body part caught in this you are going to lose your attachment to it’.


I haven’t heard the term banded v belt before. I would use a serpentine belt, sometimes called micro-v belt.


Thanks Tom. I do agree these can be dangerous machines. I’m planning to put guards on and make an auto feeding system like some others have done. Would you know how to find out the gear ratio on the gear box?

Hi Rindert. That would be a good idea, but I did some checking and I haven’t been able to find a pulley. I found this that may work if it’s got the right size shaft."+shaft&qid=1718211519&sprefix=serpentine+belt+pulley+1+shaft%2Caps%2C104&sr=8-37


For the gear ratio I’d just check the old fashioned way. Put some paint or tape on a point of the output and input and count how many revolutions of the input it takes to do one full revolution on the output.

Also you can consider your pulley sizes. Here’s a jackshaft calculator for go-karts but it works the same for belts.

It says teeth but you can replace teeth with Inches on the pulleys.


What Cody said plus 20 or more


I don’t know enough about your design to look any specific belt/pulley combo up for you. However the belt manufactures publish lookup tables for their products based on rpm, hp and wrap angle. I could look up a specific belt pulley combo for you if you wanted me to. I assume the belt well go around the flywheel? I could also recommend a clutch type belt drive that would allow your motor to start up without a load, which should allow it to last longer.


Depending on the shaft size on your motor, I’ve found that if you take the pulley off of a modern alternator that some will fit pulley weld hubs. Check your junkyards. You’ll want a two or three jaw puller to yank the pulley out. Modern alternators are usually one way and have a sprag clutch and it’s just a press fit. I can’t remember the exact part number of the alternator but the 3" size pulley fit on an X size weld hub.

Then you could use a regular automotive serpentine belt to wrap around that flywheel.


Yes Rindert, my plan is to wrap the belt around the flywheel. If you can find a pulley/belt set that would give me something to look for.

The motor I have is 1720 rpm with a one inch shaft. If I could get a 7” pulley mounted to the shaft that would spin the 22.5” flywheel at 535 rpm. Using Cody’s method I tested what gear reduction this gearbox has. It is 6.66 to 1, so that would give me 80 rpm on the cutter wheel. Does that sound about right?

I can check at the scrap yard and see what I can find.


I don’t know if that is too fast for that style cutter or not. I usually try to get those types of things around 60.which is 1 per second just because my reaction has slowed down a bit. Wayne’s might be going that fast, i haven’t timed it. If you have the 7" I would say try it. :slight_smile:

1 Like