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Drum Sander Strange Problem

721 Views 15 Replies 6 Participants Last post by pottz, Apr 24, 2022

brucet999

Discussion Starter · Apr 16, 2022 (Edited by Moderator)

Jet 1020 drum sander, 6 months old; claims it can handle stock as short as 2 3/4"
180 grit abrasive. .003 to .004" stock removal per pass. (1/16 rotation of drum height wheel where one rotation = 1/16")
Boxes 9 1/2" L x 4 3/4" W x 1 1/8" D

I'm making a travel chess set that is two small boxes to be hinged such that when opened, the chess pieces inside are removed and the two halves of the hinged box open up to a playing surface.

After gluing up the box-jointed sides, I put them through the drum sander to bring the proud edges of the sides down flush to the playing surface. Ran the boxes through, short side leading, about 10º off perpendicular to the drum, so 80º or 70º. Jet manual says not to run perpendicular; 60º angle is best. They looked good, so I thought I would turn them over and sand the open side edges smoother with a few light passes.

Afterwards i discovered that all of the corners are lower than the rest, by about .012" tapering to nothing about 3/4" in from the corners.

No one at Woodcraft, Rockler or Austin Hardwoods, nor the local Jet warranty repair guy, can tell me why that happened or how it is even possible.

[Here I would have uploaded a couple of pictures, but I don't have photobucket or any other online posting locations, so this forum won't let me post pics.]

Note the gaps between the saw table and corners at the bottom and between the straight edge and corners above. I can slide more than 4 sheets of note paper under the corner, and that mikes out to .0012+. When the hinged box halves are closed, the gap is double that, so about 3/64"

I can laboriously hand sand them to get them true, but that doesn't help me to understand the problem and to avoid it recurring.

1 - 16 of 16 Posts

splintergroup

· #2 · Apr 16, 2022

I'm not familiar with the 10/20 (I have a 16/32), but mine has infeed and outfeed rollers that put downward pressure onto the workpiece as it enter/exits the sander.

Getting these set correctly is necessary to eliminate snipe, which results in a thinner section of the wood until it has entered the sander a few inches and passes under the out feed roller.

I flatten boxes routinely without issues, one of the requirements is shallow cuts (which you seem to be doing) since the unsupported box walls can "chatter" if fed too heavy.

To eliminate possible pressure roller issues, try feeding two pieces of wood with the same height as your box. They should enter and exit the sander several inches ahead/behind your box edges, one stick on each side.
What this does is raise up the pressure rollers so your box doesn't get tipped as it enters and exits.

ibewjon

· #3 · Apr 16, 2022

For photos,click IMG above box, take picture or add from existing files. No other app needed.

brucet999

Discussion Starter · #4 · Apr 16, 2022

4

Thanks ibewjon!

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brucet999

Discussion Starter · #5 · Apr 16, 2022

I m not familiar with the 10/20 (I have a 16/32), but mine has infeed and outfeed rollers that put downward pressure onto the workpiece as it enter/exits the sander.

Getting these set correctly is necessary to eliminate snipe, which results in a thinner section of the wood until it has entered the sander a few inches and passes under the out feed roller.

I flatten boxes routinely without issues, one of the requirements is shallow cuts (which you seem to be doing) since the unsupported box walls can "chatter" if fed too heavy.

To eliminate possible pressure roller issues, try feeding two pieces of wood with the same height as your box. They should enter and exit the sander several inches ahead/behind your box edges, one stick on each side.
What this does is raise up the pressure rollers so your box doesn t get tipped as it enters and exits.

- splintergroup

Is this Splintie from BT3?

Yes, the 1020 is just the smallest, desktop version, open-ended drum sander from Jet. They bill it as being able to handle pieces as short as 2 3/4" (barely over the distance from in-feed and out-feed rollers to center of the drum), so I thought no problem with a 9 1/2" workpiece.

Jet's user manual uses very specific language like "Back off the in-feed roller pressure a little if there is snipe."

They also advise to feed the workpiece in at an angle to the drum, but I wonder if that is why I have problems with the corners. Does the drum, rotating as it does against the direction of the feed belt, want to lift up the leading edge of the workpiece?

splintergroup

· #6 · Apr 17, 2022

2

BT3?

I'd never try anything shorter than 6" solo, if needed I'd queue it up between two longer pieces.

The drum does funny things when it first contacts wood and you'd think you need more roller pressure, but I have adjusted mine neary full-off.

Aside from two sacrificial strips to parallel you boxes trip through the sander, you cam also make a sled from some very flat wood (I use 3/4 MDF). It has a 1/4" stop on the trailing edge and if the sander has the thickness capacity for the sled + work piece, it will also greatly improve chances for a level cut.

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brucet999

Discussion Starter · #7 · Apr 17, 2022

2

BT3?

I d never try anything shorter than 6" solo, if needed I d queue it up between two longer pieces.

The drum does funny things when it first contacts wood and you d think you need more roller pressure, but I have adjusted mine neary full-off.

Aside from two sacrificial strips to parallel you boxes trip through the sander, you cam also make a sled from some very flat wood (I use 3/4 MDF). It has a 1/4" stop on the trailing edge and if the sander has the thickness capacity for the sled + work piece, it will also greatly improve chances for a level cut.

- splintergroup

It's reassuring to read that you do boxes frequently, so I know I can get it done if I include the sacrificial pieces you suggest on both sides to engage the rollers before and after the workpiece.

"I d never try anything shorter than 6" solo,…"
My piece is 9 1/2" long, so I thought that was safe.

That sled is interesting, but I don't understand why it would be better than just the conveyor belt for anything but the thinnest workpiece. Can you explain the advantages that I am apparently missing, especially since there seem to be no sides to engage the rollers before the workpiece reaches them?

Thanks

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rwe2156

· #8 · Apr 17, 2022

Down pressure going in and out will help IOW don't turn it lose, but once it gets past the pressure rollers, bad things can happen. If the surface against the conveyor is isn't flat this can happen, too.

Personally I wouldn't even attempt it. What I do on boxes is glue some sandpaper to a flat surface and do it by hand.

Unknowncraftsman

· #9 · Apr 17, 2022

I also do what Robert mentions glue sand paper down to my small granite surface and rub it flat. For bigger boxes I pass them at a angle over the jointer head with a very lite cut.
I used to have a 16 32 performax drum sander. It's best use for me was to smooth out laminations after resawing on the bandsaw.
It's a painfully slow machine. I got rid mine and spent my time learning bandsaw sorcery.
Good Luck

splintergroup

· #10 · Apr 17, 2022

The sled gives a solid, flat surface on which you can firmly press the box against while it enters and exits the drum. The conveyor has some compliance and the belt glides a small amount above the metal underneath (until the box transitions under the drum and presses the belt down)

You can set sacrificial runners on the sides with this as well. My picture just illustrates the sled. Imagine your box on it with two side runners of equal height. Then imagine pressing your box down as it enters the drum
8^)

My 6" rule is so there always is some portion sticking out either before or after the shroud. If it entirely disappears under the shroud and begins slipping on the belt, interesting things happen 8^@

brucet999

Discussion Starter · #11 · Apr 17, 2022

Down pressure going in and out will help … but once it gets past the pressure rollers, bad things can happen.
- Robert

Can you explain further? I would have thought that once the piece gets past the out-feed roller the only possible bad outcome would be falling off the conveyor onto the floor.

brucet999

Discussion Starter · #12 · Apr 23, 2022

Thanks to all for your help, especially Splintergroup for the sled suggestion, and two or three who counseled to sand by hand on paper glued to a hard surface.

I corrected the open sides of the boxes by hand using 100 grit glued to 1/4" tempered masonite. Once I got the box joints on both boxes to line up with one another, I needed only another few thousandths to get rid of most of the low corners. Instead, I will hide the gaps with a 1/16" round-over all around.

I really don't think I can sand the tops down 12 thousandths evenly all around, especially with a 4 1/2" x 9" maple/walnut playing surface that is somewhat crowned in the middle already. So I have to solve the drum sander problem.

Someone commented that the leading corner being cross-grain walnut, the drum might catch it and rock the piece. But with a steel table and an essentially incompressible belt, how is that possible?

I now think that is likely what happened. I did a test with two pieces of scrap, running them an inch inboard from each end of the drum, in order to miss the bare spots where the abrasive wraps start at the ends. Once I had adjusted the outer edge of the table to even them both pieces up, I ran one piece through the center and it didn't touch the drum! I had to crank the drum down 5 tics (each tic = 1/8 of 1/64", so .002") before I heard the drum making contact; total error .010" over a distance of 8"; that means the 10" wide table is .0125" lower in the center than at the edges. Now, run a box through, angled 10º - 15º off perpendicular, and you have the work pieces supported on only two diagonally opposite points and they can rock.

So, I'd have to run the pieces perpendicular to the drum and with sacrificial side pieces to prevent snipe. Because of the uneven table, I needed a sled too, as suggested by Splintergroup.

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brucet999

Discussion Starter · #13 · Apr 23, 2022

The sled gives a solid, flat surface on which you can firmly press the box against while it enters and exits the drum. The conveyor has some compliance and the belt glides a small amount above the metal underneath (until the box transitions under the drum and presses the belt down)

You can set sacrificial runners on the sides with this as well. My picture just illustrates the sled. Imagine your box on it with two side runners of equal height. Then imagine pressing your box down as it enters the drum
8^)

Now there is a new problem, that has me puzzled. I made a sled and two sacrificial side pieces and ran them through to get close to the thickness of my boxes. The sled is 3/4" cabinet grade MDF, which mikes out to within 1/1000" of equal thickness along all of its edges. I glued two sheets of 100 grit sandpaper as a non-slip surface so I wouldn't have to mess with cleats at different positions to hold the workpiece and sacrificial sides from slipping.

But they don't come out the same. The inboard piece runs true the whole 21" length. The outboard one runs same at the leading end (after the snipe zone), but .004" thicker at the trailing end. I don't even know how that is possible. Do you?

- splintergroup

splintergroup

· #14 · Apr 24, 2022

Now there is a new problem, that has me puzzled. I made a sled and two sacrificial side pieces and ran them through to get close to the thickness of my boxes. The sled is 3/4" cabinet grade MDF, which mikes out to within 1/1000" of equal thickness along all of its edges. I glued two sheets of 100 grit sandpaper as a non-slip surface so I wouldn t have to mess with cleats at different positions to hold the workpiece and sacrificial sides from slipping.

But they don t come out the same. The inboard piece runs true the whole 21" length. The outboard one runs same at the leading end (after the snipe zone), but .004" thicker at the trailing end. I don t even know how that is possible. Do you?

- brucet999

Could the paper you applied have some thickness deviation?
Running a "stick" through on its own might provide some insight. Run it in the same position on the sled as you did with the 0,004" error. Also try it on a section of the sled w/o any paper applied.

0.004" is borderline, but possible if the drum carriage has any flex as the drum unloads from sanding.

How far from the end does the error begin? If it is a sudden transition (within about an inch), it shows that there is flex or perhaps a point where the outfeed end of the sled contacts something that raises/lowers it. If the error transition is about 2" from the end, this points to the pressure rollers doing something.

If you can find a distinct point of transition, place the piece with the sled onto the conveyor (power off) so it is in the same position as when you were sanding your project (place the transition directly under the drum). Now look at where everything is, outfeed end of the sled, pressure roller positions, etc. If you spot one of these points that is also making a transistion (infeed roller falling off the end of the caul, end of sled contacting the conveyor belts outfeed roller, etc.) you can begin to determine what/where to look.

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brucet999

Discussion Starter · #15 · Apr 24, 2022

Now there is a new problem, that has me puzzled. I made a sled and two sacrificial side pieces and ran them through to get close to the thickness of my boxes. The sled is 3/4" cabinet grade MDF, which mikes out to within 1/1000" of equal thickness along all of its edges. I glued two sheets of 100 grit sandpaper as a non-slip surface so I wouldn t have to mess with cleats at different positions to hold the workpiece and sacrificial sides from slipping.

But they don t come out the same. The inboard piece runs true the whole 21" length. The outboard one runs same at the leading end (after the snipe zone), but .004" thicker at the trailing end. I don t even know how that is possible. Do you?

- brucet999

Could the paper you applied have some thickness deviation?
Running a "stick" through on its own might provide some insight. Run it in the same position on the sled as you did with the 0,004" error. Also try it on a section of the sled w/o any paper applied.

0.004" is borderline, but possible if the drum carriage has any flex as the drum unloads from sanding.

How far from the end does the error begin? If it is a sudden transition (within about an inch), it shows that there is flex or perhaps a point where the outfeed end of the sled contacts something that raises/lowers it. If the error transition is about 2" from the end, this points to the pressure rollers doing something.

If you can find a distinct point of transition, place the piece with the sled onto the conveyor (power off) so it is in the same position as when you were sanding your project (place the transition directly under the drum). Now look at where everything is, outfeed end of the sled, pressure roller positions, etc. If you spot one of these points that is also making a transistion (infeed roller falling off the end of the caul, end of sled contacting the conveyor belts outfeed roller, etc.) you can begin to determine what/where to look.

- splintergroup

Sorry I didn't make myself clear enough. The transition in thickness begins at mid point; uniform before midpoint, tapering thicker after. I didn't measure thickness in the first and last 2 1/2" as that is where snipe would appear.

I also turned the sled around end-for-end with no difference, so it can't be variances in sandpaper thickness either.

I expected that for this to happen, distance from table to drum would have to change, which of course is impossible. The side pieces are of light weight mahogany-like scrap 1 1/8" thick, and they taper in width from 2" at leading edge to 1/4" at trailing edge, so would likely be more bendy in the second half. MDF is very true dimensionally, but also bendy, which is why I shimmed the underside center of my sled with blue tape to compensate for the low center of the table.

pottz

· #16 · Apr 24, 2022

The sled gives a solid, flat surface on which you can firmly press the box against while it enters and exits the drum. The conveyor has some compliance and the belt glides a small amount above the metal underneath (until the box transitions under the drum and presses the belt down)

You can set sacrificial runners on the sides with this as well. My picture just illustrates the sled. Imagine your box on it with two side runners of equal height. Then imagine pressing your box down as it enters the drum
8^)

My 6" rule is so there always is some portion sticking out either before or after the shroud. If it entirely disappears under the shroud and begins slipping on the belt, interesting things happen 8^@

- splintergroup

+1 ive got the same 16/32 jet and i never run anything shorter than several inches.ive not had the need to build a sled like splints because i generally run longer stock through mine and hand sand anything short.

1 - 16 of 16 Posts

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