Jointer table coplanarity tolerance

[Jim Eisenstein]

My question is about dimensional tolerances in woodworking. In the metal working world (of which I have some ancient experience) parts machined to 0.001" tolerance are commonplace, even easy to achieve. What should one expect in furniture making? (I recognize that will depend the job at hand). As an example, we all know that the infeed and outfeed tables on a jointer need to be coplanar. But how close in reality? I just checked this out on my 8" Grizzly jointer, using a borrowed Starrett 48" straight edge and a feeler gauge. With the tables aligned along one edge, at the opposite edge, 8" away, they are out of alignment by 0.002". My guess is that this is perfectly adequate, and shimming is unnecessary. Interested to hear what others think.

[Bill Dufour]

Jointer tables are not coplaner. If they are the cutter does nothing. The outfeed is planer with the outside of the cutting circle. The infeed table is slightly below the cutter. That is the depth of cut.
Bill D
I have read the human eye can see a mismatch of 1/1000" on a flat polished surface like a tabletop.

[Mel Fulks]

I agree that is plenty accurate. One of the things that can confound jointer users is small knife nicks . They start wondering why the
machine is “climbing”, and start adjusting stuff, not realizing that the knife damage is leaving more wood ,making outfeed too high …..without
having moved . Fix is to lower outfeed and bring it up to “new” proper height.

[Jim Eisenstein]

Yes, of course. But each table forms a plane which, ideally, must be parallel to the other table plane. As you say, the perpendicular distance between the planes is
the depth of cut.

[Curt Harms]

Speaking for myself, I wouldn't mess with .002". The thing with wood is that a surface could be accurate to .00015" today. Unless that piece is stored in a constant environment - same humidity year round - it's gonna move. I know metal moves based on temperature but I doubt to the same extent as most wood species move with moisture changes.

[Holmes Anderson]

Jim, I surveyed old posts from multiple forums on jointer machining tolerances last year when I bought a new jointer. My impression is that 0.002" is common for the tables of freestanding hobby woodworking jointers manufactured in Taiwan and Europe and the fences have larger tolerance - maybe as much as 0.005". Many posts indicate larger tolerances in the tables of machines manufactured in mainland China, e.g., 0.005" and larger still for the fences. I didn't record the data and do a statistical analysis but those numbers come up repeatedly in posts on the subject. Is your Grizzly a Chinese manufactured machine or Taiwan? What is good enough is subjective but most would probably be satisfied with 0.002" for the tables.

[Jim Becker]

Jointer tables are not coplaner. If they are the cutter does nothing. .

This is not true. Coplanar in the context of a jointer doesn't refer to being at a different height as they must be to cut. It means they are parallel in every way; no twist in any direction relative to each other.
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Jim, you should try to get them as close to perfectly aligned as you can. If .002" is that number, that's pretty darn good in my book. I don't believe it's going to be noticable when processing wood.

[roger wiegand]

My take would be that measuring the machine is the wrong metric. Instead measure the flatness of the product, the board that comes off the machine. Only if that's outside of what you regard as acceptable do you need to look at adjusting the machine. Assessing flatness of wood over any distance to thousandths of an inch outside of a carefully temperature and humidity controlled lab would be challenging I suspect.

My assessment is to joint two edges and butt them together, if I can't see light anywhere along the joint it's good enough for my purposes. No idea what that translates to in terms of machine shop accuracy.

[Jim Becker]

I agree that the bottom line is always the work produced, but with a jointer, making sure both tables are correct relative to each other helps insure the best results because of what the tool is used for.

[glenn bradley]

With the tables aligned along one edge, at the opposite edge, 8" away, they are out of alignment by 0.002". My guess is that this is perfectly adequate, and shimming is unnecessary. Interested to hear what others think.

Although we all know wood can move much more than .001" before, during and after milling I still shoot for this when aligning machines. I just say this so that you know my position when I am aligning my own machines. That being said, it varies with dimensions of the overall distances of course but if I had .002" between the extreme points anywhere on my jointer tables I would find that very acceptable. Likewise I shoot for .001" or better on tablesaw alignment and planers. Anything that has a fixed feed path has to be well aligned. Deviations in the path yield sub-optimal results at best and burning, kickback, machine damage, or injury at worst.

The secret to not driving oneself nutty when setting up machines is to ask the age old question "what happens if I do nothing?". By that I mean I generally run an operation or two on the machine to see how it is performing before I whip out the straight edge and feelers. This is especially true on jointers and extra-especially true on dove-tail-way jointers. Many a thread here deals with stories of woe when someone starts adjusting things before they know what to adjust .

[Andrew Seemann]

If you are within 0.002" over 48" chances are, unless you are quite experienced, if you start messing with it, you are unlikely to get them that close again.

To hold the tolerances of metalworking machines, woodworking machines would need to be the size and mass (and cost) of metal working machines. They aren't, and they don't And truly they don't need to be. It always amazes me what people expect for accuracy from relatively lightweight pieces of cast iron and sheet metal on mobile bases that are frequently moved. And that are used to work an unstable material measured by eye. And that cost only $1000-$2000.

If you want accuracy to 0.001", you need to be looking at Northfields, not Grizzlys

FYI, an 8" Northfield "medium" duty jointer starts around $14K, and weights half a ton.

[Mark Hennebury]

Not exactly.

Coplaner gets misused a lot when discussing jointers


Coplaner tables would mean that they are on the same plane. Doesn't matter what you are talking about. coplaner means coplaner

In terms of a jointer.

Coplaner tables would mean that they are aligned within the same plane.
Parallel planes would mean that the tables where at different heights.

Three non linear points describe a flat plane.

Flat would mean that four or more points on the table would be on the same plane within a certain tolerance.
Five points of reference is what I would use to check a table, the four corners and the centre.
Place equal thickness shims on the four corners and center of a table, the place a straightedge across the diagonals, it should sit flat on the three shims, the repeat across the other diagonal, it should sit on the three shims, if it does your reference points are all on the same plane. You can then check around the outside edges, by laying the straightedge on the corner points. You can if you wish check all points in between. But this will tell you if your table top is relatively flat. You can measure with feeler gauges where and by how much it is out.

The tables can be coplaner and still cut. Depends on the relationship to the cutting circle.

Generally the outfeed table is set the the top of the cutting circle ( within a certain tolerance) and the infeed table is lowered to provide the desired cut depth.
There are times that for special cuts you can set both the tables coplaner and below the top dead center of the cutting circle for cutting to perform certain cuts.
For instance drop cuts, for safety these should be done with a clamped stop for and aft to prevent kickback.

This is not true. Coplanar in the context of a jointer doesn't refer to being at a different height as they must be to cut. It means they are parallel in every way; no twist in any direction relative to each other.
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Jim, you should try to get them as close to perfectly aligned as you can. If .002" is that number, that's pretty darn good in my book. I don't believe it's going to be noticable when processing wood.

[Bill McNiel]

FWIW - These are the Hammer Specs for my A3-41;

Cutter Head - end to end = .004"
Cutter Head to Outfeed = .028" to .010"
Table flatness = .010"
Jointer Fence = .006"
Planner Thickness L to R +- .006"

I am a fan of setting machines up as accurately as possible/reasonable but be realistic in your expectations. It is expanding/contracting WOOD that we are dealing with here.

[John TenEyck]

FWIW - These are the Hammer Specs for my A3-41;

Cutter Head - end to end = .004"
Cutter Head to Outfeed = .028" to .010"
Table flatness = .010"
Jointer Fence = .006"
Planner Thickness L to R +- .006"

I am a fan of setting machines up as accurately as possible/reasonable but be realistic in your expectations. It is expanding/contracting WOOD that we are dealing with here.

Those specs must have been written by the legal department. Cutter head to outfeed table of 0.028" is horrible, so is 0.010".

John

[Bill McNiel]

Those specs must have been written by the legal department. Cutter head to outfeed table of 0.028" is horrible, so is 0.010".

John

I fully agree.