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I’ve got a Supermax 19-38 drum sander and can’t figure out why I can’t get a consistent thickness from this thing.

For example, if thicknessing a top or a back, the center will be 2.6 mm while the left and right sides will be 2.4 mm. If I run it through multiple times in all directions/orientations, it may help a bit, but not much.

Is this the nature of this tool? Is there a better option out there?

Am I being too anal? Is this good enough?

Sounds like the plate under the feed belt is dished, I had that problem with my 10-20.
Cured it by sanding a full width ~4mm MDF carrier board (avoiding the joint in the belt) which adapts to the dishing.
Them I flipped it over head to tail and attached P120 abrasive to the unsanded side, which will grip the workpiece.
Worked for me.
.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I'd be curious to see what happens in a test if you take the lightest passes and more of them instead of trying to take any meaningful amount off in one pass. I'm suspecting flex here in the machine and that may be able to be minimized by repetition and time and very light passes.

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Ann Arbor Guitars

Good point Hesh.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Are the drum and the platen parallel? I have my 19-38 adjusted to be a couple thou tighter on the open side to help compensate for deflexion but not enough to cause a .2mm/.008” difference. I guess it would measure double that if you are measuring a .2mm difference from the center on the plate to the edge.

M

A couple things might be happening. First assuming your machine is perfectly set up and drum is parallel to the table. The edges of the thin plates are most likely not being held as tightly to the table between the pressure rollers as the center is causing them to be sanded a little thinner as they lift slightly during sanding. Plates are rarely 100% flat and during sanding are under considerable flex forces. I run into that a lot. 0.2mm variation wouldn't surprise me much if the plates don't lay flat from the get-go. Even if they do lay really flat, I'd still expect the edges to lift into the drum a little during sanding making them a bit thinner. It might be 0.1mm variation is the best you can expect sanding a natural wood plate that wide and thin.

Second, depending how you feed the machine, if the drum and table are off a bit and you flip your plates end to end and alternate which edge is on which side of the table. I do that to help compensate for any variations and keep things cool. But if you do that, and the table and drum are not perfectly parallel, the edges will end up thinner.

To help sort it all out you can:

Check the distance from the bare drum to the table near motor, center and overhanging end of the drum. Then put some lift on the unsupported end of the drum and measure from drum to table to do a quick test on machine flex as Hesh suggested.

Machines are not perfect and require some clearance from "perfect" or the parts couldn't move as they should. Add to that - paper isn't perfect and wraps aren't either.

If that all looks good I'd run sum 1x2's of hardwood through near the motor, table center and unsupported end of the drum and compare thickness without changing depth of cut. That will give you a clue on how parallel the drum stays to the table under load. That should also to determine whether the table is flat, center board will be thicker/thinner than the 2 outer ones if your support table is dished.

If the thinnest test board is on one end and they progressively get thicker going center to the other end, it could be the drum isn't parallel to the table, OR, if the thickest is on the end away from the motor it could be machine flex.

I'd say if your test boards were within 0.1mm that would be pretty good and I wouldn't worry about it.

Michaeldc, makes a good point on adjusting the machine to comp for flex!

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Brian R, Wood Mechanic
N8ZED

Colins method will solve your problem. My Delta sander is slightly dished by about the same amount, but I don’t care, I’m even glad, as I want my tops thicker in the center than the sides…

One other thing to consider is the dust collection. The port is right in the middle and depending on your dust collector could be causing some flex, but I would expect that to be the opposite of your problem? I never experienced this until I recently upgraded to a bigger collector that moves a lot more air.


Sent from my iPhone using Tapatalk Pro

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Thanks, guys. I’ll check for alignment and try Colin's method if that doesn’t work.

I should mention too, just take light passes until all the board is being sanded and feed through at the same final setting several times.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I would be more than happy if my sander left the middle 0.2mm thicker. Like Ed, I prefer to have the top slightly thicker in the middle. When it comes to "fine tuning" drum sanders I think the phrase "the enemy of good - is better".

I also feed through several times at the final setting and also flip the board around. I can usually get everything within 0.002" which is fine for my purposes.

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Steve Smith
"Music is what feelings sound like"

I always make several passes in all directions without adjusting the height for my final pass. Doesn’t seem to matter.

Taking smaller bites doesn’t matter either.

Maybe I should be using coarser sandpaper. I normally use 220 grit. I like how I don’t have to do much after thicknessing

220 is not sufficient in my experience with my Performax 10 - 20. I always used 80 for material removal and 120 for less material removal and softer woods. I left a thou or two for my 5" Festool ROS and that took care of any scratches.

As Colin pointed out with my Performax once I was close, within maybe a few thou of target just making additional passes never touching the height adjustment would take maybe up to 2 thou more off.

I

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Ann Arbor Guitars

Agreed, 220 is not sufficient for thicknessing plates; neither is the standard Festool ETS 125, which many of us own, at removing 80grit sanding scratches. Its orbit diameter is only 5/64”, which is great for finishing but not much good for material removal. My $100 Makita 5030 with some P150 makes short work of the 80grit scratches. Its orbit is 1/8”, much better!

I do believe that an additional pass without adjusting the depth is known as a ‘spring pass’ -

M

Good stuff on the "spring pass" I never knew that, thanks Michael.

Going to disagree about the orbit on the 125 being not sufficient to get 80 grit scratches.

When I was building I had the pleasure of using both Tony Ferguson and Joe White who as you know are professional finishers. Both of them independently took me aside and asked me how I am finish sanding my boxes. They went on to say I am/was one of the only ones sending them stuff that they did not have to chase thickness sander scratches. I told them about the Festool 125 hooked-up with the CT-22 dust extractor and how well it seemed to work for me.

Anyway my experience was not only different with the Festool 125 working fine it was noticed by others and maybe Joe since he is here once in a while will weigh-in.

Pro finishers hate to clean up the poor work of others, that's not their job. From mitre joints that don't connect to sanding scratches these guys (men and women) are in the business of applying finish not completing my work or anyone else's. So it's a pet peeve for them when we send them scratches and I heard about it from two of them at different times.

Could be the CT-22 added value to my process too since the dust extraction is excellent but who knows all I know is it worked great for me and others in the know.... noticed and commented on it.

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Ann Arbor Guitars

I guess I’m lazy - if I have to spend more than 30 seconds to get the scratches out I’m wasting time. I do only use my ETS 125 after getting the initial scratches out. I’ve been told the same thing - they never have to mess with my work - it’s ready for pore fill and finish when delivered.

Pro-tip (if you didn’t read your Festool manual like me) If your vacuum/extractor is set on high you can end up with sanding swirl due to too much suction…

Cheers, M

I also use the Festool ES125 to clean up 80 grit scratches from my Jet 10-20. The key for me is to start with Abranet P80 on the Festool sander which leaves a more even and markedly smoother surface than what I get from the drum sander. From there its easy to move through the grits, p120,p180,p220, p320. I’ve found that produces a better finish and is faster than jumping straight to 220 which is what I used to do in my furniture making years ago. Another thing I’ve learned is to change out sandpaper when it quits cutting well, another big difference.


Steve

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Steve Smith
"Music is what feelings sound like"

I don't think you're lazy but I could be stupid since I spent too much time sanding....

Your work looks exemplary and you know I'm a fan! You remind me of me when I was building being a neat freak only you have woodworking chops. I was brand new to wood working when I built my first guitar. I tell people the only thing I ever made before that guitar were reservations.

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Ann Arbor Guitars

Maybe that’s the problem. I’ll try some 80 grit and see what happens.

sheesh, must have been carpenters...well known for the phrase "the painter will fix it", which is just an excuse for being a lazy rat b*****d IMO...I mean seriously, you let painters fill and sand nail holes and such, expecting them to deal with cr@ppy joinery is just lame on multiple levels

I found a missing nut today that helps hold the adjustment. I realigned then I also changed the paper from 120 grit to 60 grit. I thought I had 220, but at some point I changed it to 120.

Now I’m getting much more consistent thicknessing.

Cool may I suggest 80 grit is about the deepest scratches you want from a thickness sander on the woods we traditionally use. Don't want to have us fighting here over ROS any more than we have to.

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Ann Arbor Guitars

As Colin mentioned, check that the table is not dished. Just raise the drum up and put a strait edge across it. Mine was dished and the company sent me a new one with no questions. It made all the difference.

-T

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Tony Thatcher
Bozeman, Montana

I have a batch of low quality spruce I bought for testing and Last night, I ran a piece through the sander. You aren’t kidding. It won’t work. I’m going to have to take it back up to a higher grit.