Machined router table, tolerances/dimensions Input?

[alex grams]

I am looking at getting a router table made from a local machine shop similar to the one Quality Grinding used to make:

Link to Quality Grinding Thread on Sawmillcreek

However, I am trying to specify some of the tolerances on the top and need some input/data:

-The top I want to get ground flat, and figure maximum 1/64" would be a good criteria for the flatness of the top.
-The router plate mount will be for the jessem 9 1/4" x 11 3/4", with radiused corners inset at 1/4" depth. Can anyone confirm the radius of the corners at 1/2" radius?
-What is the preferable offset from a t-track to the router bit? I was thinking about 8"
-My plan is to have the top made from 1/2" thick mild steel, with 1/2" x 2" stiffeners across its bottom for support, then get the top ground flat to the above tolerance. I am still debating having the top either be 22" x30" and filling the gap between the router tabletop and the steel tabletop with the laminated extension table, or possibly making it 40" x 30", and just have the entire top be steel.

I am welcome to any input on the design or specifications. I am working trying to find some machine shops in Houston now who can make this for a reasonable price (I am will to go up to about 400$). I figured mild steel with welding would be easier for machine shops vs making it from cast iron and machining it from a block, though I don't know much about what would be easier for a machine shop, but either would work for me.

I would order steel router tops from somewhere else, but I have a sawstop (30" depth) so the standard 27" steel router table tops won't exactly fit.

[pat warner]

For many reasons I would not do this.
No.1 : Your flatness tolerance is intolerable; target should be ~+ or -.002-4". A 1/64" is a mile.
A used dead shaper would be a better candidate for a ground surface.

[alex grams]

A shaper is really out of budget and spacewise for me at the moment Pat.

What other reasons would you avoid this? Judging from all of the machined tops from Quality grinding, there has been nothing but excellent reviews for this type of item.

You think .002" +/- .001" is sufficient tolerance?

[Jerome Hanby]

Have you considered a cast iron top from Peachtree Woodworking? Their table saw router table wing is about $230 + $20 shipping (to my zip).

[Bruce Page]

Alex, 1/64 (0.0156) is a mile by machine shop grinding standards but acceptable for a router table top IMO. However, just about any large surface or Blanchard type grinder will do much better than 1/64 using standard machine shop practices. Precision costs money - the tighter you spec it the more it’s going to cost you. I would call out a flatness requirement to be within .010. That basically gives them +/- .005 to work with. As I said, precision costs money; a .002" +/- .001 tolerance will add significantly to the cost without any real functional benefit.

The T-track distance on my Benchdog from center of the track to router spindle center is 6 3/8”.

I don’t have the Jessum so I can’t help you with the radius.

One FYI note of caution: there are tricks to fabricating something like this. The bottom edge of the welded stiffeners should be machined flat before the top is ground. The machine shop can also elect to shim the weldment for grinding as well. My point is, the magnetic table of the grinder will pull an uneven surface down to it for grinding but as soon as you release the magnet that nice flat ground surface will spring back.

[alex grams]

Thanks for the info Bruce. I called jessem and they confirmed the radius is 3/4" on the corners.

Jerome, I considered the tops from peachtree, but they are for a 27" deep tablesaw, whereas the sawstop is 30". Though as you figured, I would much rather order an item than have one custom built.

[Brian Kincaid]

Alex, in my opinion you lose all the benefits of a machined table when you use a router plate. Go ahead and have the machined table milled to accept your lift directly.

-Brian

[Erik France]

-What is the preferable offset from a t-track to the router bit? I was thinking about 8"

You doing just t-track or a miter slot? When I rebuild my phenolic router table on my saw I will make the slot the same distance as the one on my table saw. I'd like to be able to use my spline jig, and box joint jigs on both without having to readjust between the two.

[alex grams]

Brian, I am not sure I am getting what you are saying. Do you suggest having the table milled to the bolt pattern of the router? I have the mast-r-lift which I am planning on having the table milled to accept.

[Mike Heidrick]

$400??!! I think you are about to get suprised when you get a quote for this steel and the machine time to mill it.

Just build a MDF table topped with laminate for your sawstop to fit you jessem.

[Peter Aeschliman]

Yeah, the full-sized benchdog cast iron top is $500... and it's produced in batches. I would expect a custom-made table to cost at least twice that.

[alex grams]

My basis is off Quality Grinding's jobs which ran about $350. I am still working on the feasibility of the piece, but I, as much as you guys, am interested in what the initial quotes will be.

[Peter Aeschliman]

Makes sense. Let us know what quote ends up being because I'll be getting in line if you can get that kind of deal!

[Galen Nagen]

I have about 15.00 in a top and the flatness is about .004. 3/4 mdf with baltic birch supports. 1/64 flatness seems like a lot, especially if you are paying big bucks. I didn't put plastic laminate on the top. General Finish wiping varnish and wax. works like a charm. Not necessarily what I would call furniture though. Don't need a router life. Table lifts us on one side and super easy to raise or lower a Porter Cable 690.

GN

[Steven Wayne]

My thoughts..

Steel is about 44lbs per 1" x 12" x 12". Average cost around where I am is about $.60/lb for new steel. If I were doing this I wouldn't use 1/2" plate. I would use 1". Welding the supports you are describing above to 1/2" plate WILL cause the steel to move. That's just the way it is. If you can find surplus/scrap plate you can save some cash on the raw material. Since it is being stress relived and Blanchard ground, you don't need new steel.

I have a fabricating/fixturing table that I have been gathering quotes for the top piece. To stress relieve, grind and heat treat a 3' x 4' x 1" to .005/12" my quote for that alone was $375.