Router table accuracy/flatness - Woodworking Talk - Woodworkers Forum
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post #1 of 16 Old 06-23-2020, 07:27 AM Thread Starter
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Router table accuracy/flatness

Hello,

I would like to ask some advice/thoughts regarding how flat should router table be for cabinet making.
I purchased Kreg PRS1025 and over the 24'' straight edge the sag is already 0.5mm, if the edge would be longer then the sag would be even bigger. Second measurement is away from the insert plate and there I measured 0.3mm.
Router is not yet attached to the insert plate which would increase the sag.
Is it a faulty table or are they all like this? What accuracy is reasonable to be expected?

Any thoughts are appreciated, thanks.
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post #2 of 16 Old 06-23-2020, 08:07 AM
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I have a Bosch table - and the same issue with the round plastic inserts as shown by the feeler gauge.


the Bosch router mounting plate - the dark pc in your pix - has six (or 8..?) leveling screws, so getting the mounting plate flat to the rest of the table is easy.
the Kreg does not appear to have adjusting screws? can you use something like paper hole reinforcements to "shim" the black plate?
if the white table top isn't perfectly flat, I'd return it - that's not acceptable in my book.



the dip at the plastic inserts is very annoying - not infrequently I'll get a 'ding' at the beginning / end of a work piece if I'm not super careful about where I'm holding / putting pressure on the work piece. I haven't come up with a good fix for the Bosch, other than turning some from aluminum with the proper flange thickness & some kind of "clip" to keep the insert in place.
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post #3 of 16 Old 06-23-2020, 08:35 AM
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Quote:
Originally Posted by wjaceh View Post
Hello,
I would like to ask some advice/thoughts regarding how flat
should a router table be for cabinet making.
thanks.
I am from the camp that when you start with new tools and equipment,
you should adjust and use those tools to the best of their (and your) ability.
starting off with less than desirable results, is a bad habit.
if you strive for perfection from the git-go, it will be automatic from there on out.

looking forward to seeing some of your projects !!

.
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post #4 of 16 Old 06-23-2020, 10:30 AM
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0.5mm over 24" is not horrible, but I agree you should be concerned when you hang a router on it.

That said, its a good idea to have some support on either side of the router plate.

Robert
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post #5 of 16 Old 06-23-2020, 10:59 AM
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Personally I would call those numbers unacceptable.

I am a retired tool room machinist. I worked in a shop where we built the tooling and machinery used to produce all kinds of different products. Rule of thumb was the equipment we built, HAD to be more accurate than the product that equipment was expected to produce.

In other words, if you want the finished dimensions on your cabinetry doors, frames, joints, etc to be within .005 inch/0.13mm, then the equipment used to produce those pieces, must be even more accurate than that.

The plate can be shimmed up to meet the table top surface. That is an easy fix. The sag in the table top is another story. Anytime we would machine a "working surface" that surface was expected to be flat within .001 per foot or 0.0254mm per 30cm. Granted our work was built to tighter tolerances than what is common on the retail level.

That said, personally, I would prefer a working surface such as this, to be free of any step between the insert and the table top. I would like to see the table top itself, to be flat to within .003 inch per foot.

The human hand can feel a half thousandths inch step. If you cut a dado or a profile and it varies .010 inch, it will affect the end product. Not that this variance can't be dealt with but it adds time and frustration to your job.

JMHO
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post #6 of 16 Old 06-23-2020, 04:09 PM Thread Starter
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Black insert plate has 8 set screws underneath it and I have positioned/set them as good as I could.
Insert plate itself is not sagged (as much as the white table plate) although the red "zero clearance" ring has some step on the left side relative to the insert plate, which can't be regulated as it follows its screw/barionet. White table has sag in both x and y axis (relative to z of-course).
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post #7 of 16 Old 06-23-2020, 05:18 PM
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yup. my table and router mount plate is all flush, but those cute little snap in inserts,,,, not so much


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post #8 of 16 Old 06-24-2020, 07:55 AM
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My Kreg top came with two metal braces/channels to help stiffen the top and help prevent sag. Are those in place? With braces installed and a router lift I'm not having that type of sag. YMMV...


What type of cabinet or stand is it mounted too. Could it be sagged itself?

A handful of patience is worth a bushel of brains...
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post #9 of 16 Old 06-24-2020, 09:39 AM
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I think your measurement of 0.5mm works out to 0.020". When I grind a fence, guide, or straightedge for a woodworking machine I expect extreme precision from, I'm happy to hold 0.005" over 24" and not content with 0.010". In my experience that level of accuracy is only found in machined and ground metal components. If that router table is some composite material, 0.020" is probably about average and also improvable with braces and adjustment as Maintenance Man suggests.

How accurate is accurate enough? This gets involved with machine accuracy and machine rigidity since very accurate woodworking is often done with auxiliary guides and hold downs which put as much force into deflecting the machine as they do into straightening the wood. If you expect workpieces to be flat to 1/16" over 24", then 0.020" over 24" is no big deal. If you face joint everything so it is flat to 1/32" or less over 24", then the machine will introduce extra error when your setup is not rigid enough to press the straight wood down to the curved table.
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post #10 of 16 Old 06-24-2020, 03:42 PM Thread Starter
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Metal braces underneath the table are installed.
At the moment the table is free-standing on-top of old sewing machine stand. But the sag was already there right out of the box.

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post #11 of 16 Old 06-25-2020, 07:55 AM
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When you mount the top tight to a straight cabinet/stand it should flatten out.
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post #12 of 16 Old 06-25-2020, 10:20 AM
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Someone said, "If it looks straight it is straight?" Lots of truth in that for woodworking!

I think JohnGi makes an excellent point. We can get so wrapped up in dialing things in, but the reality is little to no discernable difference in the final product.

We have to remember we are machining material that moves and changes. No matter how flat or straight it is at the moment, by tomorrow things might be different.

That said, we should strive to set up our machines as accurately as possible, but a micrometer really doesn't have much place in measuring wood. Knowing this, we use hold downs and guides such as featherboards.

Robert
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post #13 of 16 Old 06-25-2020, 02:53 PM
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from the item description:
"This 24" x 32" table has a 1"-thick MDF core . . ."
tweaking a 1" thick chunk of MDF flat to the mounting top is going to involve some interesting doings.
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post #14 of 16 Old 06-25-2020, 03:59 PM
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If you got the braces in place and ready to go, quit knocking yourself out. Make few test cuts on a long piece of wood where things interconnect and without measuring your tool flatness, how would that fit your projects needs? Do the pieces come together?

The manufacturers keep coming up with gimmicks and newbe's think they need all of this stuff. Just make something, anything, just build something and see how it works out.

Several years back, the big issue was the flatness of a table saw top. People were measuring every which way and getting upset over the microscopic deviations. I have a good eye, I have built what I consider very high quality furniture with not so expensive equipment I have never measured a machine surface whether it was a table saw, a shop made router table or whatever. I never concerned myself with measuring flatness of machine surfaces to any measurable degree. If I am building a table apron and making the tenons on the table saw with a Dado blade and the mortise's with a cheap bench top drill press, all I care about is how well is my fit Not how flat is my machine tops.
So, like I said, make something and see how the parts fit.

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post #15 of 16 Old 06-25-2020, 04:15 PM
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BTW, Whenever I build a workbench or router table or whatever, I generally always use a double layer of ply or MDF. Gluing two layers will give you a really stiff surface to work off of. If you are working off a flat surface the two layers will be pulling at each other and more or less, flattening each other out.

When I start building my shop, one of my first purchases will be a cheap door Even the cheapest doors will be exceptionally flat. Too weak to serve any real shop purposes, but a great way to start making workbench and assembly table tops using the flat door on 2 saw horses.

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post #16 of 16 Old 07-03-2020, 02:23 AM Thread Starter
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Morning,

A quick update on the issue.
My local Kreg distributor was in contact with Kreg and although they didn't specify numerically what tolerances are acceptable with their tables, they did say it is faulty and should be "dead flat".

My local distributor was kind to visit me at my workshop with two replacement tables to choose from.
First one out of the box was better but not perfect. Sag in the middle of the table in-front of the blade on the MDF where I previously measured 0.5mm, was now slightly above 0.3mm.
Second table which I accepted was way better although I have not had time to take any measurements yet.

From previous feedback, I wouldn't bet on the idea that stronger mounting on rigid table/stand would flatten it out as I don't see any angular counter moments which would "pull" the sag out in the middle.

In my opinion it should be as good as technically possible out of the box as router weight would sag the table over the time anyway and Kreg is not cheapest option on the market. One would expect some quality for the money I'd say.
It seems that Kreg quality control lacks consistency as 2 out of 3 tables were inaccurate.
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