The Thickness Sander

Jim in 1984 in the old shop in the basement of his church, with the thickness sander he had just completed building. Below Jim tells the story behind this large and impressive machine in his own words.

A lack of finances kept my dream of owning a machine to "thickness" guitar woods to very thin and accurate tolerances just a dream. (After all a good "abrasive planer" in 1982 cost about $10,000.) It also cost me about $45/hr. just to rent time on one from a local cabinet shop. So despite lacking any real metal working experience I set out to make my own. I found out that my local vocational school had an extension course where for about $115 I could get 100+ hrs of evenings in their machine shop. No class time, just an instructor to answer questions and all these machines just waiting for me to try out!

I basically did my best to copy (with some redesign) an existing sander made by a company called "Timesaver" setting on the floor of my local machinery outlet. I think they thought I was nuts as I showed up many a day with a caliper and tape rule measuring and sketching. In retrospect, I consider it one of my most valuable learning experiences as I was forced to seek answers, learn skills, and overcome setbacks until it was actually finished!

The wood is sent through on a variable speed conveyor belt from the front of the machine. The belt was purchased from a supplier in Michigan.

The variable speed controller for the conveyor came from a surplus electronics store. It was about $15. A new one today could be as small as a deck of cards. It controls the feed rate or how fast the wood is fed into the sanding belt.

A DC (direct current) motor and a gear reducer drive the conveyor that feeds the wood into the sanding belt. The DC motor was salvaged from the local dump for $2. The gear reducer was $35 and came from a salvage yard.

This meter indicates the % of load on the motor. It is helpful to tell me if I am trying to remove too much material at one time. The higher the % of load the more the motor is "laboring" to remove material. With an "abrasive planer" you don't want to remove too much material at once or your sanding belts will overheat and shorten their life. It is also helpful to maintain close wood thickness tolerances because you can pass wood through several times at the same setting watching the meter until it "evens" out.

This is an hour meter to tell how many hours the machine has been running. Looks like 518.3 hrs. to me! At $45/hr. that's $23,323.50 if I was still paying rental fees!

The belts are installed and changed from this end. The pneumatic slide valve in the center is to tension the belt. It takes less than a minute to change a belt. The grits of the belts vary from 36 grit which is very course and can easily remove 1/8th inch of material in one pass, to 320 grit which gives a very smooth finish.

The belts are tensioned by an air bladder (pictured in the center) that is actually manufactured by "Firestone" as a pneumatic shock absorber for trucks. As it inflates the upper roller rises to tighten the belt. I found these in a surplus store for $15 so I bought an extra one!

The belts must "track" or stay centered on the rollers. This is achieved with two "photo eyes". The belt is adjusted to "track" by always drifting to the left (as you face the front of the machine). As it gets too far left the "eye" will see the other "eye" directly across from it and with the help of an air cylinder return it to center. In effect the belt is "oscillating."

The photo eyes activate this air cylinder. It "twists" the upper roller by pushing it to the side and keeps the belt "tracking."

Above the air cylinder are two pressure regulators. One is for controlling the belt tension and the other sets the air pressure for the disc brake. These were salvaged from old beer kegs!

The disc brake is used to instantly shut down the machine and stop the sanding belt in the event the belt should ever miss-track or heaven forbid the operator gets their hand or clothes caught in the feed conveyor! This disc brake was actually manufactured as a brake for motorcycles.

This is a ceramic tip connected to a micro switch that will activate the disc brake if the sanding belt wanders too far left or right. There is one on each side of the belt.

The operator can also shut down the machine and activate the disc brake by pushing his or her body into the yellow safety gate or hitting the emergency stop button on the control panel.

One of these micro switches takes an electrical signal from the ceramic tip or the yellow safety gate switch and opens a valve that allows high pressure air to activate the disc brake. The other one is activated by the "photo eyes" and allows air to flood the air cylinder for tracking the belt.

A 10 hp. motor drives the sanding belt. It takes 3 drive belts to turn the main drum!

The "pinch rollers" used to hold the wood down to the conveyor were made from "bushing" stock that I had rubber coated locally. Oil impregnated bronze bearings were inserted into "pockets" (milled by a lathe) in the ends to keep them rolling along smoothly! The assembly for holding the rollers was actually one of the hardest things for me to figure out. I basically copied it but it was hard to measure and produce accurately.

The conveyor bed is moved up or down by these "jacks" to control the depth of cut. A slight turn of the wheel to arrive at the precise thickness.

The electrical control box is something where I really needed help! I'm very thankful to a friend of mine, Jerry Hanson (better known as "Ace") for all his help. Also Mark Lauer (better known by Ace as "Goofy Guy"). I couldn't have done it without them.

Here is the wood coming out the back of the sander.

A picture of me changing a belt.

The thickness sander in Jim's shop in October, 2001, still serving him well after more than 16 years in service.