Feed direction relative to drum rotation in drum sander

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BrianInChatham

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Brian
I picked up a used Grizzly 24" dual drum sander recently and finally got around to setting it up last night. Once I got the drums dialed in it produces a decent finish, but the stock is coming out with a thick layer of sawdust compressed to the surface. I've noticed when I brush it off that in areas it was particularly thick the finish isn't quite as good underneath, and it's also very, very messy. I took the shroud off to watch it in operation, and the cause is pretty clear. What I'm seeing is the drum is rotating with the direction of the belt, so as the stock passes under each drum a thick layer of sawdust is left on the surface. This passes under a feed roller which compresses it and it's fed into the second drum which makes even more, then another feed roller to compress it again. The pic shows what it looks like coming out (although to be fair there was no dust collection going for the pass where I took the photo). There's a little scraper thing that's supposed to help with the dust accumulation but it's not all that effective.

On my Woodmaster the drum spins against the feed direction, which makes sense to me as this kicks the dust out of the drum instead of under and should thus reduce loading of the sandpaper. Looking in manual, one of their 24" models rotates with and one rotates against the feed direction. Doesn't make a ton of sense to me why they'd be different, the only difference is one has variable speed and reversible feed.

So- From what I've read online I should be able to reverse the direction of the motor by switching around a few leads in the motor controller. would it be better to reverse the feed or the drums? I'm concerned about the effect of reversing direction on the bearings that have been running the other way their whole lives. Before I go mucking around with this, does anyone have any thoughts on either the nature of my problem or my proposed solution?

While we're at it, what would be considered acceptable tolerances for drum alignment? These drums are a bit of a nuisance to adjust, but I was able to get thickness variance <.005" pretty consistently across a 12" board.


 

Tarhead

Mark
Corporate Member
What kind of dust collection are you using? Are all the parts/shrouds in place when you are using the dust collection?
 

BrianInChatham

New User
Brian
I have a Jet dust collector, I think it's rated at 1150 CFM. The shroud and everything is in place when I use the sander, that pic was just to illustrate the problem.
 

Tarhead

Mark
Corporate Member
You may not be getting 1150cfm with that much dust left on the work. Drum sanders create tons of fine dust that clog the DC filter/bag very quickly which drops your DC airflow. You may want to check that first before you put too much energy into your sander. A Thein Separator would be a good thing to have between the sander and DC. I don't have any experience with dual drum sanders so I can't advise about the rotation direction.
 

FredP

Fred
Corporate Member
I have the woodtek version of that sander. the drums rotate against the feed belt. I get the same results but I only have a 1HP DC rated at 650CFM. my machine recomends a minimum of 2HP DC. Jet Delta Craftsman...... they all over rate their machinery so it is quite posible you are not getting the rated CFM.:wwink: These machines require a LOT of suction to get the dust out. also some woods will do better than others.
 

BrianInChatham

New User
Brian
Sounds like reversing the feed belt shouldn't pose a problem but may or may not help the issue. I have little doubt the dust collector is overrated, and the way I have the ducting run is no help either. I'm working with hard maple ATM and the dust compresses into a dense little cake that is pretty cohesive, so I'm sure the choice of wood is part of the problem too. A Clearvue cylcone is next on the list, maybe I'll pick it up sooner than I was anticipating. In the meantime I think I'll reverse the drum motor and see what the effect is just out of curiosity.
 

DaveD

New User
Dave
I don't know anything about belt sanders but my question would be what is the thickness you are trying to sand off in one pass? trying to sand too much of in one pass?
 

BrianInChatham

New User
Brian
Well- I'm glad to report a very successful fix. I got off to a bad start when I found that unfortunately the motors are cheapies made in Taiwan and are not reversible (at least not in the traditional sense). Neither the feed or main motor have a discreet controller; the starting capacitors are just directly hardwired in series with the motor windings. However, looking at the housing of the main motor both ends looked identical, so I pulled and disassembled it and sure enough, I was able to simply reverse the shaft in the housing, re-mount it, and Viola!, now it's running in the opposite direction. I did have to splice in about 12" of wire for the centrifugal switch since it is on the other end now, but otherwise nothing but simple re-assembly.

The resulting improvement is absolutely remarkable. Watching it in action it works as I thought- by running the drum in the opposite direction to the feed the dust is thoroughly aerated so the dust collector has a chance to catch it. Where before the stock came out with a thick mat of compressed dust on the surface it now is just a light scatter. This improvement is so dramatic it really leaves me wondering what the heck the engineers who designed this were thinking (or smoking?). Maybe there's something I'm missing here? I hope not, can't think what it might be. I'll post up if I encounter any unforeseen problems, but at this point I'd call the fix a resounding success.

-edit-

I spoke with Woodmaster today to see if I might be able to adapt their controls to the Grizzly but unfortunately that's not possible. The gentleman I spoke with was very knowledgeable and helpful so I asked him if he had any insight on thie drum rotation issue. Seems that there is something I hadn't considered- kickback. He said the the pressure holding the stock as it's fed isn't all that great on this unit so there's a risk of kickback with the drums rotating against the feed. I've quite a pile of stock cut, planed, and ready to feed through this tonight; I'll have to take care to see if kickback is going to be an issue. If it is I'm thinking of swapping out the feed motor for a variable speed unit anyway, I could just make it a bit more powerful and then would be able to increase the pressure on the feed rollers.
 
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