In this post I am going to describe the jaw, and jackscrew I made for my 4X6 bandsaw. First off I want to say I love my 4X6 bandsaw. It really opens up possibilities for me when it comes to metal fabricating. I can cut just about any chunk of metal I can get up onto the saw.
That having been said, there are some things that can stand some improving over what these saws come like from the factory. This is one mod I did to my saw that I find extremely valuable. Worthwhile enough for me to share with whoever may care now.
What is a jackscrew, and why would I want one? Well a jackscrew is a screw jack that is used to buck up a device, or fixture. See the movable jaw of the vise has a screw that drives it, and it connects in the middle of the jaw. So the movable jaw is a little like a teeter totter in a way. The vise can lock down real good on a piece that goes all the way across the jaw, but if a piece does not extend to the jaw screw pivot point the movable jaw will rack then, and not hold the work.
If that happens we need something on the empty end of the vise to push back. Sure you could go grab some piece of scrap that is about the right size to do the job, and throw that in there. But that is not always so convenient to do. It can end up taking time. That is where this jackscrew comes in.
This jackscrew is a speed screw, in that when the lever is lifted it moves in, and out, freely. So this jackscrew is fast, and easy. When we're working we like that too!
Step 1: The Original Jaw
Here I just want to show what the stock jaw that came with the saw looked like. I keep it around for posterity now I suppose. Because there is no way I'd ever put it back on my saw since I made a replacement. Yeah it worked, marginally. My new jaw is way better though I think. Moving on.
Step 2: A Closer Look at the Mechanism
In this picture we can see how the speed screw works. There are only threads on the pivoting arm. So when the arm is up, the screw itself is free to move in, and out rapidly. The way I did this was I clamped that little thrust block onto the bottom to the arm, then drilled them both out to tap. I tapped them both, then separated them. I then filed the threads out of the lower thrust block piece.
Pretty clever huh? I tapped this up to 1/2" X 13 UNC because I have a bunch of that threaded rod. Any similarly dimensioned threaded rod should work though I imagine.
I guess now is as good a time as any to discuss project layout. Nothing is terribly critical here, but things still have to fit together. You can see the blue dye I used in places so I could lay out some scribe lines. Use good practices is about all I can say concerning this. I did not spend a whole lot of time measuring anything with this project, but I did invest some time in making sure things were aligned in the right places.
My pivoting swing arm locks down in the horizontal position, and it works really good. so I guess anyone making this for themselves should aim for that too.
Step 3: The Movable Jaw
Now we will look more closely at the movable jaw part of the project. The movable jaw that comes with the saw is a joke. I thought about welding a nut onto it, or something, but I decided to just replace it with something more substantial. There is no welding in this project at all by the way. Everything is just screwed together.
Because that's the way uh huh, uh huh, I like it, uh huh, uh huh! (I sure hope this site doesn't inline that video - but you should go listen to it anyways) I only weld when I have to.
Anyways, back to the part. I picked an appropriate piece of hot rolled structural angle about as thick as the fixed jaw (3/8's heavyweight I believe), then trimmed it to match, more, or less. Later on I radiused the corners, and broke every edge with an angle grinder. Looking at the image pencil lines can be seen, to give me a rough idea of where I had to mill out a slot to accept the bolt that holds the nut.
The slot I made resembles what is in the original jaw. The slot allows for some jaw adjustment for work clearance in some cuts. A hole in about the right spot would probably work too. I like my features, so I milled it.
This all should be pretty straightforward. Do what you gotta do.
Step 4: The Pivoting Arm Bolt
I used an odd piece of hardware here. Someplace I picked up a bunch of these 3/8 X 16 UNC Allen head shoulder bolts with over sized heads. Besides the shoulder being a little too long for the thickness of my pivot arm it works great. I made up the difference with a stack of washers on the bolt. A more common hex bolt, with a sleeve should work too. But I had these, and I was thrilled to use one.
In this step we can see the exposed view of the bolt.
The tricky part here is to have the thrust block up high enough off the web of the angle that it lays flat on the inside of the leg. This is accomplished by putting the hole for the pivot bolt up high enough. I shimmed the thrust block up temporarily, high enough, to help me determine this placement.
Confusing I know. Try to think about it as working from the bottom, up. We are using the inside of the bottom angle leg as a reference to get everything else right.
The center of the arm is located, and scribed. Then the arm, and movable jaw can clamped together to drill, and tap for the bolt. The arm is then drilled up for the shoulder, or sleeve.
Failing to locate this hole right will set you up to have to grind the thrust block to fit the angle web later. Plus it all looks good if the arm is level with the top of the vise jaw. I didn't plan it, but it happened rather serendipitously for me that way.
I didn't plan any of this project really, I just had an idea, and made it. I had an idea that I was sick of scrounging up blocks of metal to stuff into my vise. I've already made the time back by now too.
Step 5: Mounting the Thrust Block
After this the project will be mechanically done.
With the pivot arm bolted to the movable jaw, and the thrust block shimmed back into position, swing the arm down to contact the thrust block, then scribe where the screw through hole needs to be through the hole made by the thrust block, and pivot arm together. I highlighted where to scribe in red in the image.
There is definitely some fudge factor going on here, but the threaded rod just needs to go through the movable jaw. The hole needs to be drilled up to a clearance fit for your threaded rod.
Now the threaded rod can be put in position to pass through the movable jaw, and be used to align precisely where the thrust block needs to be. I counterbored my block for quarter twenty Allen capscrews. Then with the block in position I used a transfer punch to mark where I needed to drill for tapped holes, to hold the thrust block to the movable jaw.
Get this right and you're golden for the project. This is about the only critical machining in the job. The thrust block has to push the threaded rod to engage in the half threads in the pivot arm. So do a good job here.
If everything works out you should be able to push the pivot arm down and its threads will engage in the threads of the screw itself. This immobilizes the thread so you can use it to jack open the back of your vise. Lift up the arm and you can remove your jack screw then too.
For fine adjustments you can still rotate the screw a little. This is way better than scrounging around looking for the right combination of junk to prop your saw's vise jaw with. How many years I did that. I don't even want to think about it today.
Step 6: Finishing Up
Well now if everything mechanically works it is time to pretty everything up some. Degrease it all, then put some radiuses on the corners, that match the fixed jaw. I had a can of green spray paint kicking around my shop that does not exactly match my saw, but it is close enough.