Review - Belt/disc Sander

Harbor Freight 4 in. x 36 in. Belt / 6 in. Disc Sander

Central Machinery model #97181

[March 17, 2013]

[March 24, 2013 minor additions]

Here's the unit as it comes in the box (additional parts shown below). An 80 grit belt is already installed. I checked the unit for loose screws and found everything tight [on further inspection I found that the bolts holding down the motor needed to be tightened] and solid with one exception: The vertical metal post (seen on the front right corner in the photo) was a bit loose, but it was simple enough to snug it up with a wrench (more about this post later).The base of the unit is stamped steel, and the main frame is cast metal (not cast iron, as it is not attracted by a magnet). All other green painted parts are stamped steel. Overall, the unit feels reasonably solid and sturdy.

Parts

Below are parts supplied with the unit. From left to right:

• Cast metal (aluminum?) sanding disk, peel-and-stick sandpaper disk, and miter gauge for adjustable tilt-table
• Aluminum tilt-table
• Hex wrench and stamped steel wrench
• Stop plate for sanding belt and cover for sanding disk
• Rubber foot (shown installed) - four are provided
  • At some point in the future I will probably remove the rubber feet and bolt the sander to a piece of plywood, so I can clamp it to the top of my workbench when I am using it, and then move it to storage when I am done.

The cover for the sanding disk appears to be fitted with some sort of vacuum attachment, although presumably if you wanted to do this you would need some sort of adapter (not supplied). In any case, I will be leaving this piece off, as I think it only gets in the way.

Similarly, I will also be leaving the stop plate for the sanding belt off for two reasons: First, it's just one more thing that has to be removed in order to change belts. Second, if you want to use the tilt-table with the belt, you have to remove it anyway. I'll leave the bolt in, just to fill the hole.

Support Rod

Below is some detail on the vertical support rod that acts as a position stop when the sanding belt is used in the horizontal mode. As can be seen from the bottom view, the rod is simply screwed into the sheet metal base, and then tightened with a washer/nut from above. Because the rod is screwed into relatively thin sheet metal, this is not a very strong connection (but mostly OK since the force on the rod is all vertical). However, as can be seen from the "top view" below, it's easy for the rod to get tilted slightly, so that it doesn't fully engage the stop tab on the belt section. But, as the final top view shows, it's simple enough to gently bend the post back into proper alignment. I think this could be improved by using a washer/nut on the bottom as well as the top of the base, but I'm not going to bother to do this unless it turns out to be an ongoing problem.

Tilt Table

It appears to me that that the tilt table has been improved from earlier models, in two ways:

First, the mounting mechanism has been changed to make it easier to switch between the belt and the disk, and clamp bolts have been substituted for the earlier plastic levers (which apparently almost always broke). The other adjustment lever for the table angle has also been replaced (with a knob).

Second, the bar which supports the edge of the table nearest the belt (or disc) was only held in place in earlier models by the friction of dimples punched in the metal brackets holding the rod. In my model, there are now two set screws (see photo below) which can be tightened, making for a less wobbly table.

Rollers

The belt rollers on my unit were adequate, although the molding was far from perfect. Other purchasers of this unit have report problems (and fixes) for bad rollers; look here for a good video which shows how to turn the rollers on a lather. The cited reviewer noted that his belt would not track well, as there was no crown on the drive roller; my unit did not have this problem (see photo below - hard to tell from the photo, but a straight-edge shows a properly crowned center). I do notice a little bit of vibration when running the sander - not enough to worry about now, but if it becomes a problem I may try the roller turning method I cited.

I also noted, differently from the cited review, that the black rod which is part of the belt tightening mechanism has had a fiber sleeve added (presumably to eliminate vibration noise) - it would be simple enough to add this if not already present.

Finally, I note that the paint on the bed under the belt is already wearing off after only a brief period of use. I'm not worried about this - in fact I rather expected it. It's not going to adversely impact function as far as I can tell, but I'll keep an eye on it just to be sure.

Belt Changing

In order to change the belt on the sander, you need to remove the back plate. The back plate is held on with 2 screws on the left, 2 screws on the right, and 2 screws below (plus the screw for the stop plate if you opt to use that). That's at least six screws you have to remove (and not lose, along with their washers), just to change a belt. Since I am going to use the sander for wood and metal, and since I will want to use different belts for each, that's more hassle than I want to put up with. As already noted, I'm not using the stop plate, so that's one problem eliminated.

I eliminated the side screws by making two long "knurled bolts" from 1/8" steel rod. I threaded the rod on both ends, lock-tited a knurled nut on one end, and made a round nut to go on the other end; the round nuts were epoxied to the frame on the belt side. In practice I just put the back plate in place, insert the knurled bolts through the existing screw holes, and hand tighten them into the round nuts. To make this a bit easier (as it's a little difficult to thread the end of the rod through the far hole), I made a small "guide washer". The guide washer is basically a thick washer, countersunk on one side to create a "funnel," and epoxied to the inside of the backplate over the screw hole so that it "guides" the end of the rod into the hole. The existing screw holes are big enough that a 1/8" steel rod passes through them easily (no need to drill them out).

I eliminated the two bottom screws my making a short knurled nut to fit the existing screw hole. I epoxied a short length of ball chain to the nut, and fasted the other end to the frame, so I could unscrew the nut without worrying about it getting lost. I was going to make two of these, but I found that just one on the right side was enough.

Now I can change the belt by removing just three screws by hand - no tools required.

[Note: Making these bolts and nuts took the most amount of time of any of the improvements I made. I could have made them using off the shelf parts from the hardware store, like threaded rod, nuts, etc., but I figure since I have a lathe I might as well use it!]

Disc Changing (and a tweak)

As with belt changing, I want to be able to change sanding discs easily, so I switched the disc system from PSA (peel and stick) to H&L (hook and loop). I don't usually mention vendors by name, but it took me quite a bit of searching to find an adapter at a reasonable price, so I'll note that I found it at 2Sand.com. The H&L adapter is just what you might think it is: a disk of velcro type material with an adhesive back which you just stick onto the sanding disc plate. I've found it a bit harder to find solid (no hole) H&L sanding disks without having to buy a pack of 50, but I did find a few locally.

With the H&L system I can easily remove and replace disks, and re-use disks as necessary. A quick test of the system showed that it works well, with the sanding disc held nice and flat, with no sign of loosening.

A final note: When attaching the disc plate to the drive shaft (the plate has a set screw which fastens down onto a flat on the shaft), I noticed that although the plate was held onto the drive shaft well, there was a tiny bit of side to side wobble. I made some quick measurements and found that drive shaft diameter was about 50 thou less than the hole in the plate, so I made a little brass shim to fit around the drive shaft. The shim made the plate tight enough that I had to tap it on gently with a hammer (cushioned by a wood block) - no more wobble.

Other Details

The angle markings on the miter gauge and tilt table are very hard to read, as the miter gauge is black on black, and the tilt table scale is just stamped into the metal. So I applied a couple of well known techniques to improve their readability. For the miter gauge, I went over the tops of the raised markings with a sliver paint marker; you can see in the pictures below the miter gauge half completed to show the difference, and the completed miter gauge - I also added a dab of day-glo orange paint to the pointer. For the tilt table scale I painted orange day-glo paint onto the scale (and the pointer) and then scraped it off with a paper index card, leaving the paint only in the stamped in parts; after the paint dried I polished off a bit of paint haze with a paper towel and the job was done. The whole job took only a few minutes, and the improvement in clarity is well worth it. Of course, these scales are not meant for precision work, but for a quick and dirty setting they are useful.