Harbor Freight 4" x 36" Belt / 6" Disk Sander 97181 - Woodscrub's Mods

Straight out of the box. The sander came with the sanding belt pre-installed
and tracking correctly!

This is my second one of these sanders. I had one around 10 years ago, and over time had modified it to work better. Then I sold it to move back to California from Colorado. So it was time for a new one, and I can modify it all at once!

I know I could save all this trouble by purchasing a better quality machine to start with. But would I really? Looking at other more expensive units at the store show that I would still need to perform some upgrades to get the most out of them. And for $50 when on sale, the value of this unit can't be beat.


The first thing I did after taking it out of the box was button it down, then fire it up. The belt comes pre-installed (leaving the thing tensioned while in the box seems like a bad idea to me, but whatever), and to my surprise it was tracking straight! No adjustments needed. That was odd...

The vibration from Sir Lumpy Belt was there, as is to be expected from a machine shipped with an inexpensive V-belt under tension. So I removed the belt cover to inspect it.

Another surprise was finding the pulleys were coplanar to each other. That means the belt is tracking straight without bending to get on either pulley. If yours isn't, there are plenty of instructions on the web on how to correct that. But basically, you have 3 adjustments. Top pulley position on the shaft, bottom pulley position on the shaft, and rotating the motor on its adjustment bolts. Tinker with those three things until your pulleys line up perfectly. Checking is done with a straight edge. It should touch two points on each pulley at the same time.

I pulled the belt off and you can see just how lumpy it was. Each time one of those lumps went over a pulley, the entire machine would move. That causes an insane amount of vibration. The solution is to replace the belt with a link belt.

Unfortunately the most common sized belt (and the one that Harbor Freight sells) is too big to fit inside the belt cover. This is a safety hazard, so I recommend finding the smaller link belt first, before cracking it open. I was this far, and actually needed to use it right now for a project, so exposed belt (aka the Finger-Eater) it is!

To remove the rear cover you have to remove the upper pulley, so I got to go through the coplanar adjustments anyway. Sigh.

The machine starts looking a little bare with everything removed. But this is a great time to eyeball the machine. Get familiar with its components. Use the manual to identify the different bolts and adjustments while everything is easy to see and find.

Putting on a link belt is always an exercise in frustration for me. There are two ways to do it, and to my mind, neither are satisfactory. But there's no other option. So guesstimating is it. I put the motor at its smallest adjustment, then loosely wrap the link belt around it to figure out where to "cut". You don't actually cut, of course, you separate the links.

Repeat until you have it snug. Not tight, you don't want to damage the bearings, just snug. I also like it to be loose enough that the belt will slip if there's a problem before the motor stops. Belts are cheaper than motors if something gets jammed.

In the running photo, you can see just how exposed that belt is. I really don't like it being that exposed, but I don't have much choice until I get the smaller link belt.

I still can't believe that the machine is as smooth as it is now. My old one needed the rollers for the belt to be machined/trued up. But that's not the case here. So I can leave that all alone and move to the disk.

The surface of the disk was quite wobbly. No quality improvements there, since my old one was the same way.

I started the machine, then gently applied a bastard file to it. If you push hard, you'll get a catch and the machine will fling your file ... somewhere. Hopefully not at you, but it's a possibility. I learned this the hard way on my first sander. So I managed to not do it this time. It took around 20 minutes of gently filing away the high spots to get a smooth flat surface that spins true.

The table for the disk was pretty gnarly. The edge that goes against the disk looked like it had been cut by a two year old child.

Simply filing the edge wasn't going to be enough, so I used the belt sander itself to clean up the edge. Since the table is just aluminum, it was quick work. After straightening the edge, I lapped the table's surface on the belt sander, then polished with progressive grits of sand paper. A quick coat of wax made it nice and slippery.

The manufacturer of these sanders for Harbor Freight really has been listening. One of the most annoying adjustments, to me anyway, was the punch marks to create a friction fit for the table's bracket. I would have to re-punch the dimples every time I changed the position of the table because it would get sloppy. That would lead to inaccurate work.

Now they've replaced those dimples with set screws! I was ecstatic!!!

I will work with them as-is for a little while, but I'm considering milling in some flats for the set screws to really lock down on. They may be fine as-is though, so we'll see.

The machine came with some dust covers for the disk sander. I have no idea how to attach them, since none of the holes lined up with anything else. No biggie, it only had a tiny little 3/4" dust port at the bottom. But I liked that it would also act as a finger guard. When I replace the belt covers I'll find a way to mount that, and I'll post updates.

The finished product.

The unit now is smooth, quiet, and powerful. I do recommend dumping the sanding materials that come with the unit and installing better quality sandpaper. The HF belts have a really bad seam that you can feel when you're using them. I left this one on just long enough to build it. It's going in the trash. The disk is a better self-adhesive paper to begin with. Removing self adhesive paper sucks.

Enjoy and remember to get the smaller 3/8" belts. Grizzly has one here.