Max .002" thickness variation using MFS 700 & 1400 possible?

[nadsab]

I have an application in which I need to mill both sides of the surface of several small planks 7/8 inch thick, extremely smooth and perfectly flat.  Ideally I need a thickness variation of the planks to be no more than .002 inches.

Is It possible to get this close of a tolerance by using the 1400 router with the 492728 Routing Slide and the MFS 700 Multi-routing template?  If so, has anyone here actually done this kind of work and achieved those close tolerances?

I'm wondering if there is any amount of downward flexing of the routing slide due to the weight of the router when it spans wide distances approaching the 24" capacity of the MFS 700...

Or would I be better off buying a milling machine to do this kind of work?

 

[philg]

I have the exact setup you are talking about here, and, no you will not be able to maintain 0.002" thickness from board to board. This amounts to +/- .001 in thickness control, flatness, and parallelism. The best that can be done on a consistent basis I would estimate to be +/-.004". With that said, even if you use a vertical mill, or even a jig borer, the wood will change/move when you un-clamp it from the fixture.
My professional background is in ulta high precision manufacturing, tolerances of less than 0.0001", where +\- .001" in metal is still not a trivial task.
What is it that you are making that requires those tolerances for in wood?

Regards,
Phil

 

[mwhafner]

I would think that your best choice to get anywhere near that level of precision would be a drum sander or widebelt sander.

 

[nickao]

You can achieve that with a drum sander in the initial construction of the project. But with wood, just bringing the project outside or setting it near a window in bright light will most probably move the wood more than that.

I do think with the proper tedious set up you can get it done with the router, anything is possible, but it does not seem the best way to do it.

 

[Scottrollins64]

Philg is right.  No way with wood.  You can mill it that way.  Tomorrow it will be different.  Your only option would be a lamination with a plywood like substrate.  Even then maintaining flatness over time is the problem.

 

[nadsab]

Then how 'bout with a low angle jack plane?  Possible?

 

[Dan Lyke]

Then how 'bout with a low angle jack plane?  Possible?

I think what everyone's saying here is that it isn't about the technique used for milling, it's that you're trying to do this in wood. You're asking for less than .23% of your overall thickness in a material can easily change by 4%(!), and can do lots wackier things when that expansion and contraction happens in one part of a board and not another (ie: warping and shifting).

It's not about the tools, it's about the material you're working. Two thousandths in wood is only useful if the humidity is very closely controlled, and then only useful for a short time (ie: get that joint assembled, 'cause something's gonna change shape shortly).

 

[nadsab]

Actually I did not clarify.  I'm not milling traditional hardwood.  My material is much less likely to change in thickness than all other hardwoods.  It changes, but far less than every other wood on the planet extremely hard and stable.  I would be suprised if it swelled or shrank in thickness more than .005" throughout the year since I am milling glued up end grain.

Maybe I should rephrase the question.  Let's just pretend I am milling alumimum or MDF.  Does the 492728 Routing Slide sag down more than a few thou when the 1400 is sliding across it? 

 

[nickao]

From far end to far end it may depending on your technique. I think you can do it though.