CAUTION!!!!! Long winded rant ahead....

[skeaterbait]

I can't decide if I am simply impaired when tolerances go past 1/4" or if others have the same issues I do but they know how to overcome them.

In working on my take down I not only found out that I am 23 lbs underweight but one limb bends nicely while the other doesn't. I tried sanding some width off the stiff limb but I just isn't changing. So I start measuring and found the stiffer limb is actually narrower than the other. Good times. So I break out the mic and sure enough, the stiff area is thicker by a considerable amount.

I am pretty exasperated at this point so I decided to set those limbs aside and start another set. Here is where it gets even more frustrating. In sanding the veneers I take measurements as I go,they read like a roller coaster, fluctuating from .038 to .042 and everywhere in between checking every 3"-4" down the veneer. Not only that, running two veneers at a time on the same sled, one will come out thicker than the other by .002ish.

I then put a straight edge on my sled and the dang thing is not flat. I really don't get that, it's made from 3/4" plywood that I made like an I beam with two horizontal (top and bottom) and two uprights between them. That should not warp. Granted, I don't think you could put a sheet of paper in the gap I see, but I can see light now where I could not before.

I have a Grizzly drum sander that, for the price, should be more than capable of doing what I want to do. I just keep wondering if it's the design of the tool. It does not have pressure rollers to hold the material down, it has two spring pressured plates.

There is probably more to this but that is all I will plague you with for now. If anyone has advice they wish to share I am most ready to listen.

As I was proof reading this a thought hit me, I wonder if the sander needs to be stationary to get it set correctly. I have it on a mobile stand at the moment.

[canopyboy]

Start by adjusting the drum(s) parallel across the width of the table if necessary. Then run the table all the way up to the drums while on. The belt isn’t a perfect, even thickness from the factory.

[John Malone]

Make sure the springs aren't worn, clamp it down on a solid surface. If it has any vibration on that mobile stand that could cause an issue.
Look at the bright side, ya could have accidently sat on that hat of yours. That would be a bad day.

[mwosborn]

What material are you starting with to grind your lams?

How big of a bite are you taking as you grind them down to thickness?

[skeaterbait]

I have done both hard and birdseye maple. I have learned to take very, very small bites. Small enough that it takes several passes to sand off pencil marks.

Yeah John, sitting on that hat would make for some interesting conversation.

I have adjusted the drum (feed table) a couple of times. I probably should order some new pressure plates. I bought the sander used and they were tweeked a bit. Perhaps starting with new ones is the way to go, especially since they are only about $8 each.

I think I will find a hole to take this off the mobile base and see what happens. Just a matter of finding a flat spot.

[mwosborn]

I was just wondering if the inconsistency in thickness was in your material before you start grinding?

I grind mine on a jig mounted to a spindle sander.  I have to start with a well planed piece that lays flat on my sled.  If not, I get a "wavy" lam.

The very, very small bites is the way to go.  

[kennym]

Originally posted by canopyboy:
Start by adjusting the drum(s) parallel across the width of the table if necessary. Then run the table all the way up to the drums while on. The belt isn’t a perfect, even thickness from the factory.

This!!

I chased a .004 variance that was random til I found the splice on conveyor belt was the culprit. I let it run and slowly let the sander head down and let it brush on the conveyor belt til I thought it was all the same. Then marked both ends of splice and don’t finish grind on that part.

Also, I like a thin sled that the rollers can press down if it happens to bow a little. I run aboo sleds about a quarter inch thick and get along well.

[skeaterbait]

I may have to try the thinner sled Kenny, first I am going to order new pressure plates. I still can't believe they built this without rollers. Sadly I didn't know until I owned it.

[kennym]

Do the pressure plates have springs? Any way to redneck a roller system on there?  Or does Griz have a kit for that?

[skeaterbait]

Not sure about a kit for it, I never thought to ask them. And yes, they are spring mounted with adjustments. I have done that several times as well.

The more I think about it, I think getting it off the mobile base is probably the best first step.

[Holm-Made]

When grinding down a lam...grind it to .005” above desired thickness.   Then do not adjust the height anymore.   Flip the lam over and run it through.   Then flip it end for end and run it through.   At this point you can flip it and run it again, but it may not be necessary.    This will true up the lam side to side and may help with other inconsistencies along the length.    It should remove the last .005”.

[mikkekeswick]

Mobile base shouldn't matter. I have my drum sander on a mobile stand and it works perfectly. Granted you do ideally wanted every tool solid and dead level but.... I use a Jet drum sander that has rollers and get a 0.001 +/- tolerance.

[Bowjunkie]

Same here, mine is on a mobile base and I haven't had an issue since I started this. Mine's a Delta with roller hold downs, sandpaper wraps directly on a metal drum, and I use an adjustable aluminum sled. I hope you get it figured out.

[Roy from Pa]

I run my lams through both sides to get them flat before I start with tapers. I also run the lams through twice before adjusting the roller height. The second pass through, I still hear material being sanded off.