Drum/ Thickness Sander

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vtsteam:
Simon, random thoughts per your own design intention to true a wooden roller:

Traditional, non water-based polyurethane varnish won't dissolve the MDF binder and is thin enough to penetrate deeply and harden fibers uniformly. Polyurethanes are probably the most vapor resistant of any coating. Including epoxies, and more widely available.

Sanding to remove contours using a block against a turned wood piece is difficult to achieve. A rotary sander arranged like a shaft grinder to keep a fixed distance from the axis of the turned part will remove only the high spots if the pressure is light enough. See John Hill's redneck shaft finisher thread for the general principle.

Finally, if you do decide to give up on the MDF, a traditional way of using conventional wood in a turned design that must remain dimensionally stable is to rip strips into 45 degree beveled staves and glue together into an octagon section, then turn to round. The grain orientation should be consistent in the staves. For large turned sections, the joints should be splined.

Hope that helps as FYI suggestions only! :bow:

greenie:

--- Quote from: S. Heslop on January 16, 2015, 01:16:05 AM ---
Absolutely, but it's the part of the project I care the most about. I've made it so long so I can use a sanding belt as the conveyor surface. There's alot of information on drum sanders where you just push the wood through, but the few people that have built conveyor belts are tragically vague about how they work. Plus i've read a few people saying they were difficult to get working and they eventually gave up trying, and that sounds like a challenge.

Plus it's fun finding ways around problems.

--- End quote ---

Simon, here’s something else to ponder over.

With the infeed roller using a sanding belt to feed the timber through the drum sander, will this not create one sanding surface working against another sanding surface ? One action of trying to pull/push/drag the timber one direction whilst the rotating drum is trying to do the exact opposite action. Therefore creating a double sanding action and negating the effect of the infeed belt altogether, as it does require a bit of pushing pressure on the timber, to actually hand push the timber through the machine, against the rotating action of the sanding drum.

So one light weight piece of timber sitting on top of an infeed belt, without any downward pressure to hold it against that infeed belt, then the forward movement of the timber will stop and allow the drum sander to just either spit it straight back out, or, allow the front edge of the stationary bit of timber to be chewed away by the drum sander, whilst the infeed belt is chewing away at the the underside of the timber, until there is NO more grip/resistance from the belt underneath, and then just spit the timber straight back out anyway.

What does a normal blade thicknesses actually use, to push/drag the timber through the machine to "negate" the effect of the blades pushing/spitting the timber back out of the machine ?
Possibly some type of similar set-up, might be required for this design of yours as well.

Either more infeed rollers will be required to add downward pressure onto the timber work-piece, whilst it is on the infeed belt, to counteract the forces of the rotating sanding drum, or, forget that idea as others have done, because of the above problems.

The alternative to an infeed belt is to glue a piece of glass over the rise and fall table, this will virtually eliminate any resistance/drag on the timber work-piece, from the surface of the rise and fall table. By you using a push stick to control/maintain the infeed pressure, you can now have a definite feel for what is happening, when the timber is being mutilated by the sanding drum.

It’s your choice on what you do, just a few more ideas for you to mull over.

regards greenie :loco:

mattinker:
I'm really not in agreement with Greenie, your sanding belt drive sounds interesting, I can't see any way that if you set it up right it will double sand, the belt is there to grip and not slide over the wood. I avoid MDF at all costs, it's full of formalin based glue which is pretty poisonous! If you must use MDF, Andrews sugestion of PVA wood glue diluted with water is a very good way to go, dousing it once in water has not affect at all on the MDF.

I'm following this with great interest!

Regards, Matthew.

Fergus OMore:
This MDF thing is interesting. The largest man made forest is just north of me.
As a natural byproduct- it had been designed to supply pit props in WW2, there is an Austrian firm called Egger.
It set up a huge MDF factory to absorb the supply- the coal mines had closed- it is only 20 miles from me- and Simon.

No one can miss it at Hexham. It bursts into flames a bit lile a volcano. One would have thought that - well, one would have thought.

Ahh well

Norman

S. Heslop:
Yeah i'm not convinced about the double sand thing either. The conveyor belt is going to move fairly slow, there'll be more surface area with the part flat against the sandpaper belt, and you're only going to be making fairly light cuts with a thickness sander to begin with. But we'll see.

One thing I have thought about is, since I want to use this to primarily smooth and thickness 1.5mm veneers cut on a bandsaw (a bandsaw i've yet to make), which will probably end up being fairly warped at that thickness, I might still need some sort of infeed/ outfeed roller to hold them flat against the table as they pass through.

Also I do really like Kielder forest. I never knew that it supplied the Hexham chipboard factory, but I suppose that makes sense. I'd mostly assumed it was used as fuel.

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