Thread: A huge drum sander

I havn't built one of these myself.... and others may have a better idea..... but my gut feeling is that it may be.

But that depends on what you are planning to do with it.

Thats a big log you are spinning there.... my gut feeling would be about 800rpm.. but I stand to be corrected.

how well does the motor handle the start up.

cheers

My feeling is that is WAY too much speed. You are probably gunna burn the wood at that rpm. Think soundman is about right at 800rpm.

In Shopnotes #86 there is an article on how to build your own drum sander.

The drum is driven by a table saw, you replace the blade on the tablesaw with a 2" pulley which then drives a 5" pulley on the drum (which is 5" diam).

As I don't know what speed the arbor of the tablesaw runs at, I can't calculate what speed the drum turns at, but that would make it arborspeed/2.5, wouldn't it?

So assuming tablesaw motor speed of 1440, that gives 576rmp.

If the tablesaw motor runs at 2850, that gives about 1100rpm

13.8 metres per second comes out to about 2700 feet per minute of sandpaper. That's pretty much dead on the money. During the research I did when I built mine, I found that most commercial models were running 2800 - 3300 feet per minute. I just saw one at the grizzly website that runs at 2100 feet per minute. So I think your speed is pretty good, mine runs somewhere around 2800 feet per minute, but I've trued up the drum a few times and reduced it's diameter, so I guess it's a little slower now. I only have problems with resinous woods like East Indian Rosewood. They tend to gum up the sandpaper quickly. I've never had any burning problems.

I'd follow the advice and add bracing to the frame, I need to do the same thing to mine.

I'd be more concerned that a drum as long (wide) as yours will flex under load. Mine does, it's 25mm diameter solid bar (I forget the proper name of the type of steel, but it's the right stuff) I used disks of plywood for the drum itself which is around 150mm diameter. Under load the drum will flex a tiny little bit if pushed too hard (trying to take too much off in one pass), and mine's only 22 or so inches long. I only noticed this the other day. I think as you increase the length of the drum you also need to increase it's diameter, which will in turn increase your drum speed (rpm won't change, but feet per minute will)), unless you alter the gearing by changing pullies.

Table saws geneeraly runn arround 4500 to 5000 rpm
so that gets the shopnotes machine down to about 2000rpm.

My conmcern isnt with the paper speed... but more with the rotating mass and the rigidity of the drum shaft.
Most of the commercial units will have much lighter and better balanced drums.

If the shaft on a smaller machine is flexing....considerably lengthening the drum will multiply not add the various factors in play here.

thats why my thaughts are soo low on the speed.

cheers

Originally Posted by soundman

Table saws geneeraly runn arround 4500 to 5000 rpm
so that gets the shopnotes machine down to about 2000rpm.
cheers

Soundman, the blade might run at 5000rpm, but I seriously doubt that the arbor runs at that speed?

Originally Posted by soundman

Table saws geneeraly runn arround 4500 to 5000 rpm
so that gets the shopnotes machine down to about 2000rpm.

My conmcern isnt with the paper speed... but more with the rotating mass and the rigidity of the drum shaft.
Most of the commercial units will have much lighter and better balanced drums.

If the shaft on a smaller machine is flexing....considerably lengthening the drum will multiply not add the various factors in play here.

thats why my thaughts are soo low on the speed.

cheers

Thinking about this; if I doubled the length of my drum and ran it at the same speed, I'm not sure I'd want to be the one running it - just how strong are pillow blocks anyway? The flexing under load makes the middle of the drum start to bounce (only slightly, but it's there), if I lower the feed rate and don't try to take too much off in one pass it goes away. Double the length and too high a feed rate and it could get dangerous.

I'm thinking pretty much the same way as you, but talking only about rpm on these machines doesn't mean a whole lot if you don't factor in your drum diameter. By increasing the diameter of the drum, you'd be able to drop your rpm's and still maintain enough paper speed to have the thing actually work effectively. Though, then you have even more spinning mass...

Maybe that's why most of the big commercial machines use wide sanding belts instead of drums.

think about this.... the blade of a table saw is bolted to the arbour...the arbour spins at the same rate as the blade.... the motor shaft will probaly be spinning slower,,, in aust probaly 2440rpm.

most certainly all those factors associated with drum size will have significant effects.

there are often limits, imposed by the realities of physics.
like.... you have to do all sorts of things to make a petrol motor work properly once you get past 500cc per pot...
there are limits where things cease to be efficient or stable.... past that point you have to make changes or significantly reduce or increase something.

cheers

Soundman is correct

There is a difference between rpm and surface speed .
The shaft and the blade are spinning at the same rpm , but because the blade is a bigger diameter than the arbor shaft the cutting edge of the blade is travelling at a higher surface speed than say a point half way across the blades surface , or the surface of the arbor shaft.
The easiest way to test this is to mark a tooth on the blade and put another mark on the shaft in line with each other.Start and stop the saw the marks should still line up ,if they don't something is very ,very wrong ......

" Danger ,Danger , Will Robinson"

Hi folks!
Thank you for your hint.
Now, my frame is stong like a rock (almost )

2 pics with height adjusting mechanism (test)

table hinges pics

and dust hood (unfinished)
Next step is table reinforcement...very soon!
Regards!

Hi golden earring
That's looking good, keep the photos coming! Has the frame lost that vibration now?

Cheers,