2 Drums, but sands with one at a time

[Mark Walden]

This is the only dual drum sander that I know of that sands with one drum at a time. A little history about this machine back in the mid 90s you could buy a sander kit from Performax [now owned by Jet Tools] that you could install a 22in sanding drum on a radial arm saw. A friend named Bob Hiatt built this monster lift table and installed it on there. Hence the round mounting post. When I bought it there was no power feeder on it and you had to push the boards through by hand. NOT SAFE. I built the power feeder out of a exercise treadmill, if you ever thought about using a treadmill motor for woodworking…don’t, they have no low end power. For small stuff it works OK but on large things not so much. That will be the next thing to be rebuilt.
I got another 22in drum donated to me so I built a new arm to hold 2 drums.It has a pivot point in the front, with adjuster screws in the back to set the height and lock it in place. Set up like every other drum sander course on the front drum finer grit on the back the board would pass under one then the next. The problem was if you had to thickness sand something all you were doing was burning up the fine grit before you needed it.
So I installed 2 small air cylinders with a toggle valve to raise and lower the back drum so I can sand with one drum at a time. There is another air cylinder on the drive side that, pushes a idler pulley out to keep tension on the belt when you lower the back drum. It's been done about a year now it works great. Questions and comments welcome.

[Jim Andrew]

If someone wants to try building one of these, I have the frame and arm off my old Cman
RAS. I sent the motor and carriage in for the recall. I'm in Kansas. PM me.

[J.R. Rutter]

Clever solution. One of the reasons that I got my particular widebelt was pneumatic pivots on the drums to allow either or both to be active.

[Alan Schaffter]

Mark- great job!

I picked up an old 24" Grizzly dual drum sander in 2004. After using it for awhile, I came to the same conclusion you did about having two drums. Here is what I said in a 2008 SMC thread (http://www.sawmillcreek.org/showthread.php?83710-Powermatic-DDS-225-Dual-Drum-Sander-25-quot/page3&highlight=drum):


Question- why a "DUAL" drum sander??? I have one, but got to thinking about the two drums.

The usual setup is to put coarse grit (80 - 100) on the infeed drum and finer grit (120 - 160) on the outfeed drum. That is all fine and good if you just make one pass. If you need to make more than one pass, you are wasting the fine grit on all but the last pass, since the stock comes in contact with the coarse grit drum first on each succeeding pass.

My thought is that dual drums are fine so you can have two grits loaded at the same time and so you don't need to stop and change grits. But, you need to be able to select which drum/grit will contact the stock on a particular pass- run the stock through one or more times with the coarse grit/drum in contact until it is close to final thickness, then select the finer grit/drum for the last pass or two.

I am thinking about modifying my old 24" Grizzly to do just that.

Doing that conversion has been on my "to do" list ever since.

I changed out the conveyor motor with a DC motor and speed controller giving me a bi-directional conveyor. I have a bunch of electro-mechanical solenoid air valves leftover from when I converted my DC blast gates to autogates.

My original plan was to remount the drum bearings to two pivoting assemblies sort of like two teeter totters. Only a minimal amount of pivot, 1/8" - 1/4" at the end of each arm, would be necessary for clearance of the unused drum so (2 or 4?) actuating cylinders with minimal throw would be needed. Hopefully an idler to tension the belt would be unnecessary, too. I would use auto-align pillow block or flange bearings so each pivot assembly could be adjusted slightly, but independently. Mechanical stops made with threaded bolts under the ends of each end of pivot arm would make setting drum clearance and parallelism simple and precise, and allow for future adjustment if I ever changed the mix of grits or used thinner or thicker abrasive belts. Actuation, like yours would be by pneumatic cylinder but I would use 24V electro-mechanical solenoid air valves with shop air.

Since my conveyor has electrical bi-directional capability and the solenoids are electro-mechanical, I thought about making an even more tricked out unit by adding selectable semi-automatic control of the active drum and feed direction- it could be set for bi-directional, two-pass sanding: coarse-coarse, coarse-fine, or fine-fine.

A much simpler mechanical alternative to select the active drum would be to use a simple lever and over-center mechanism to change the position of the pivot arms.

JR- what unit do you have?

[Jim Neeley]

Awesome mod, Mark and...

+1 on who offers this off the shelf? :-)

[J.R. Rutter]

Eccentric pivot point with air cylinders to swing the drums down into action. The air cylinders are positioned with threaded rod out the back to control exactly how far down the drum pivots, with a scale and pointer to make calibration easier. It is a SCM Sandya 5 RCS. A lot of Euro sanders have similar setups.

https://lh5.googleusercontent.com/-sAQDarJDhaI/S9JRE3YbsUI/AAAAAAAAAWs/iEj343UDZ5g/s512/IMG_0616.JPG

[Alan Schaffter]

Eccentric pivot point with air cylinders to swing the drums down into action. The air cylinders are positioned with threaded rod out the back to control exactly how far down the drum pivots, with a scale and pointer to make calibration easier. It is a SCM Sandya 5 RCS. A lot of Euro sanders have similar setups.

https://lh5.googleusercontent.com/-sAQDarJDhaI/S9JRE3YbsUI/AAAAAAAAAWs/iEj343UDZ5g/s512/IMG_0616.JPG

Thanks. Of course! I missed where you said widebelt sander. :rolleyes: As far as I know no dual drum sanders have the single drum feature.

[Mark Walden]

Mark- great job!

I picked up an old 24" Grizzly dual drum sander in 2004. After using it for awhile, I came to the same conclusion you did about having two drums. Here is what I said in a 2008 SMC thread (http://www.sawmillcreek.org/showthread.php?83710-Powermatic-DDS-225-Dual-Drum-Sander-25-quot/page3&highlight=drum):



Doing that conversion has been on my "to do" list ever since.

I changed out the conveyor motor with a DC motor and speed controller giving me a bi-directional conveyor. I have a bunch of electro-mechanical solenoid air valves leftover from when I converted my DC blast gates to autogates.

My original plan was to remount the drum bearings to two pivoting assemblies sort of like two teeter totters. Only a minimal amount of pivot, 1/8" - 1/4" at the end of each arm, would be necessary for clearance of the unused drum so (2 or 4?) actuating cylinders with minimal throw would be needed. Hopefully an idler to tension the belt would be unnecessary, too. I would use auto-align pillow block or flange bearings so each pivot assembly could be adjusted slightly, but independently. Mechanical stops made with threaded bolts under the ends of each end of pivot arm would make setting drum clearance and parallelism simple and precise, and allow for future adjustment if I ever changed the mix of grits or used thinner or thicker abrasive belts. Actuation, like yours would be by pneumatic cylinder but I would use 24V electro-mechanical solenoid air valves with shop air.

Since my conveyor has electrical bi-directional capability and the solenoids are electro-mechanical, I thought about making an even more tricked out unit by adding selectable semi-automatic control of the active drum and feed direction- it could be set for bi-directional, two-pass sanding: coarse-coarse, coarse-fine, or fine-fine.

A much simpler mechanical alternative to select the active drum would be to use a simple lever and over-center mechanism to change the position of the pivot arms.

JR- what unit do you have?
Teeter totter better idea. No idler pulley and I had to make some swivel linkage because the push pull is not straight up and down so you wouldn't need that either.

[David Beede]

Interesting thread. Thanks for starting it Mark.
[I'm new on the forum. I make musical instruments mostly, in north Florida.]

Allan, I also have an old Grizzly G1066 and I'm impressed with your modifications.

I would love to figure out how to switch between drums. I get the concept of the teeter-totter but can't really envision how to do it and keep the alignment of both drums within tolerances. Automation sounds great, but I'd even settle for a simple method of popping the hood and flipping a lever or two.
Any sketches or descriptions would be welcome.

One more thing. Allan mentioned reversible conveyor motor, and I was wondering how someone would use this? Then I realized I have two Grizzly sanders, on the 12" the drum rotates against the feed [intuitively the way it "should" go] and now this 1066 24" rotates WITH the feed. One owner had wood fly across his shop after upgrading to hook and loop so the pressure roller adjustment was no longer right. I do see that the 1066Z that runs against the feed has a larger feed motor than the 10666/1066R. I'm stumped on the design decision... it couldn't be just to save a little feed motor HP could it? Sorry If I'm putting too much in one post, but I'm eager to get this 24" beast up and running.
Thanks,
David

[Alan Schaffter]

Interesting thread. Thanks for starting it Mark.
[I'm new on the forum. I make musical instruments mostly, in north Florida.]

Allan, I also have an old Grizzly G1066 and I'm impressed with your modifications.

I would love to figure out how to switch between drums. I get the concept of the teeter-totter but can't really envision how to do it and keep the alignment of both drums within tolerances. Automation sounds great, but I'd even settle for a simple method of popping the hood and flipping a lever or two.
Any sketches or descriptions would be welcome.

One more thing. Alan mentioned reversible conveyor motor, and I was wondering how someone would use this? Then I realized I have two Grizzly sanders, on the 12" the drum rotates against the feed [intuitively the way it "should" go] and now this 1066 24" rotates WITH the feed. One owner had wood fly across his shop after upgrading to hook and loop so the pressure roller adjustment was no longer right. I do see that the 1066Z that runs against the feed has a larger feed motor than the 10666/1066R. I'm stumped on the design decision... it couldn't be just to save a little feed motor HP could it? Sorry If I'm putting too much in one post, but I'm eager to get this 24" beast up and running.
Thanks,
David

David, no drawings (yet), this is all in my mind. But here are some answers to your questions:

Drum alignment and adjustment would be easy. The drum bearings are mounted to the teeter totters which pivot individually picture side by side teeter totters. Depending on teeter totter design, I would use self-aligning pillow block ball bearings mounted on top or flange ball bearings mounted to the sides at each end. Each end of each tetter totter near the bearing would rest on the head of a hex bolt. During initial alignment and with the tetter totters firmly held in each position by the pneumatic cylinders, I would use a wrench to rotate the bolts to set each drum parallel to the platten and to also limit tetter totter travel. This is important if I attempt to make my machine bi-directional- the clearance between each drum (surface of the grit) and the platten (conveyor belt) must be the same.

This would be much the same as putting a or two brick under one or both ends of a real teeter totter. As I said, I would use self-aligning bearings just in case I mount them off a little.

http://www.northerntool.com/images/product/images/189559_lg.jpg http://www.northerntool.com/images/product/images/189782_lg.jpg

One thing I didn't mention previously- you can't use two drums simultaneously on the same pass with my teeter totter rig, it is either one or the other, not both. Also, I wouldn't mess with the pressure rollers but may need to add an additional set on the infeed and outfeed side to be sure the stock is always in firm contact with the conveyor when I change direction.

As far as being able to reverse direction of the conveyor- you might need to change the feed motor to a reversible one, or use a 3ph motor with VFD. I replaced my AC conveyor gear motor with a DC gear motor and DC controller so I can change directions with a simple switch.

[Dennis Ripoli]

Alan, you have some really clever ideas with your "Franken Sander". Did you notice much of an improvement with your plenum? I noticed on mine that there's almost an 1/8" of vertical play with the table. I wonder if that would be another option to look at regarding using one drum at a time?

[Alan Schaffter]

Alan, you have some really clever ideas with your "Franken Sander". Did you notice much of an improvement with your plenum? I noticed on mine that there's almost an 1/8" of vertical play with the table. I wonder if that would be another option to look at regarding using one drum at a time?

I hadn't tested dust collection before I added the plenum. Since I have a 6" DC line I knew the openings in the top of the cabinet were too small- their combined cross-section was less that one 6" line, so I opened up a larger hole under the plenum.

You really don't want any vertical play in the table. Are you sure it is the table and not the conveyor? The pressure rollers are important regardless of whether you are using one or two drums at a time.

[Dennis Ripoli]

It's in the table assembly, I can lift it up a bit. It's actually between the table screws and table frame. I guess the coarse threads dont help it any.

[Alan Schaffter]

It's in the table assembly, I can lift it up a bit. It's actually between the table screws and table frame. I guess the coarse threads dont help it any.

At least the force on the threads is always in the same directions so backlash should not be an issue.

[Dennis Ripoli]

I wonder if something could be rigged up with belts and pulleys that would disengage one drum at a time so it just freewheels. Kind of like an A/C clutch on a car.

[Alan Schaffter]

I wonder if something could be rigged up with belts and pulleys that would disengage one drum at a time so it just freewheels. Kind of like an A/C clutch on a car.

I'm fairly certain an A/C clutch would work though I don't know anything about the ratings of those and if they would handle the considerable load placed on them. It would be easy to get a clutch from a junkyard to test without doing an other mods.

The one key feature I would lose is the ability to easily fine tune the parallelism and heights of the drums, unless the machine already had those features. With my setup both of those things can be done quickly and easily on each drum individually using only a box wrench.

Here is a very rough sketch of what I have in mind. It is missing some structure, like the conveyor/conveyor table, teeter totter mounting bracket, pneumatic actuators, etc. but it gives you an idea what I have in mind.

The adjustable pivot stops (red in the diagram) can just be hex bolts. They allow the parallelism and height of each drum to be adjusted individually. Once the parallelism (to the table) has been set for each drum the heights (for the selected grits) for each drum can also be set independently by adjusting both near side and far side stops (not visible) by the same whole number and fractional rotations. The drum height could also be set by ganging the near and far hex bolts together so they turn simultaneously once the drums are parallel.


http://www.ncwoodworker.net/pp/data/500/medium/Dual_Drum.jpg

http://www.ncwoodworker.net/pp/data/500/medium/Dual_Drum-2.jpg

[Dennis Ripoli]

I see what you mean. Looks pretty simple in the drawing but I'm sure it's going to be pretty complicated and labour intensive to design and build. What do you think of the freewheeling drum Idea? I was thinking about it some more and it would be pretty easy to add a second motor and have seperate motors drive each drum. Maybe using idler pulleys controlled by a lever or actuator to engage each belt as needed.

[James Lord]

I have the Woodmaster 3875- X2 38 inch Double drum sander. It works great. The second drum can be fine tuned to the first drum. So it can apply more or less pressure.

http://www.woodmastertools.com/NS/accessdetail.cfm?PID=808

[Alan Schaffter]

I see what you mean. Looks pretty simple in the drawing but I'm sure it's going to be pretty complicated and labor intensive to design and build. What do you think of the freewheeling drum Idea? I was thinking about it some more and it would be pretty easy to add a second motor and have separate motors drive each drum. Maybe using idler pulleys controlled by a lever or actuator to engage each belt as needed.

If you have 16"" or longer drums, you'd need another 3 - 5 hp motor. Now you are talking a BIG extra expense! You can still use one motor with my setup or your electric clutch:

http://www.ncwoodworker.net/pp/data/500/medium/Dual_Drum-3.jpg

A centered idler can be added between the pulleys to get more belt wrap.

You don't want anything that will cause drag on the inactive drum like a direct or belt drive, but un-powered motor, that includes an idler type clutch- you still get belt drag on the pulleys. Also, if both drums contact the stock and the outfeed drum is inactive, it could act somewhat like a pressure roller, packing dust into the stock.

After looking at my diagram again, I realized once the near side and far side stops are adjusted so the leading drum is parallel to the table, there is no need to adjust the height of that drum further- table elevation takes care of that. The trailing drum only needs micro height adjustment, like retail drum sanders that already have it.

I also plan to add a rotating dust brush just after the outfeed drum to sweep any dust that the DC didn't pick up (happens often) off the top of the board and back into the machine.

[Dennis Ripoli]

I have the smaller 16" G1079 version and can pick up a used 2hp motor for around $100. I'm just bouncing ideas around without making things too complicated but I see your point. I guess your going to build some type of carriage for the drums but how are you going to deal with the center pressure roller being located at the pivot point?

[Alan Schaffter]

I have the smaller 16" G1079 version and can pick up a used 2hp motor for around $100. I'm just bouncing ideas around without making things too complicated but I see your point. I guess your going to build some type of carriage for the drums but how are you going to deal with the center pressure roller being located at the pivot point?

The pivot pin doesn't need to go from side to side- two separate pins. The center will be open for a pressure roller.

[Dennis Ripoli]

Alan, do your drums spin in the same direction as the feedbelt like a climb cut? I wonder if there would be any advantages to reversing the motor direction so it makes a shearing cut instead? Forgive all my questions but I just got this thing and have never used one before.

[Joe Spear]

Those radial arm saw things were still available in 2006 when I got one. You are more ambitious than me, though. I ended up just buying the feeder and tripod stand that were also available when I figured putting it on a radial arm saw was more trouble than it was worth.

[Alan Schaffter]

Alan, do your drums spin in the same direction as the feedbelt like a climb cut? I wonder if there would be any advantages to reversing the motor direction so it makes a shearing cut instead? Forgive all my questions but I just got this thing and have never used one before.

My drums spin in the same direction as the feed belt. I'm sure anything is to be gained by reversing the drums except possibly reducing the amount of dust left on the boards, likewise, rotating in the direction of the drums puts less strain on the conveyor motor. That may not be much of an issue- my feed motor is 1/4 HP Baldor DC gear motor so output torque is pretty substantial. There seems to be no standard among manufacturers- some spin in the feed direction; some the opposite.