How flat is flat enough? Please help.
AndrewLunn
| Posted in Power Tools and Machinery on
I just purchased the Craftsman hybrid tablesaw, the 22124, and I’ve discovered its table isn’t actually flat. There seems to be a slight hump in the center of it, producing a .011 gap in one spot, and a .008 gap in another. I don’t have experience buying big tools like this and don’t know how picky I should be. My personal feeling is the thing should be flat and I should return it. I just don’t know what acceptable tolerances should be for something like this. Thank you for any advice. Oh, and the tools I used to measure the gaps were a starrett straightedge and feeler gauges, so i feel pretty confident my measurements are correct.
Replies
I would return it. A TS should be much flatter. It would be OK for construction framing but not for serious woodworking.
Edited 4/29/2005 11:25 pm ET by 81treehouse
Return the saw but dont expect a lot of difference in any thing else of the same make. Of course it depends on what your accuracy needs. For the longest life and your continued happiness with the tool as your own skill grows get something that has a flat table, good mechanicals for raising and tilting and enough motor to do what you need. Even if you have to reach a little to buy it you will be happier than compromising on quality to save a little now.
The flatness of the table doesn't matter unless it is so warped that you can measure it without using feeler gauges..011 won't make any difference in any cuts ,rip or crosscutting.I've used saws that were out of flat as much as 1/8" . These were large industrial 7 1/2 hp machines ,probably 50 years old or more.The warp was from the front to left back portion. Made no difference as far as anyone could tell. You could actually see the warp when a flat piece layed on top of the saw. Have you tried your saw yet?If your rips and crosscuts are to your satisfaction, use the saw and forget about the warp.
mike
Contact Sears. When I bought my Powermatic 66 years ago the tolerances were .015". It will vary between manufacturers but .011" isn't a big deal for woodworking.
The perfectly flat table saw idea is a myth. .011 is 11 thousandths. That's very small. A factor in metal working, not woodworking.
If adherants to the perfectly flat surface followed thru with their concept, they would be checking their rip fence for the same degree of precision, and be painstakingly hand lapping their throat plate inserts flat.
Falco
.005 shows as a joint line pretty well, I try for half of that. There is another post out on they web a a fellow in england that made birch propeller blades. .002 and you re did the whole job.Alan
Flat is flat. Flat enough ain't flat.
That said, I think that isn't much. I am going to re-think considering the Craftsman Hybrid TS, though.
Don
0.011" variance is not what I would call flat. When tuning equipment or setting knives, I accept a maximum of 0.004" variance; anything over that is readily noticeable to the human eye. That bump of 0.011" will not allow you to do precision work. Unless you are using your saw for framing houses, I would return it.
OK; time for a little geometry review. Your table is 0.011 out of flat. Now what does translate to in an everyday rip? Let's assume that your blade is exactly 90 degrees to the top, measured at the top of the blade. Now just how much does that 0.011 error translate to, in degrees, or more likely, in not minutes of arc, but seconds of arc? And all this assumes that the operator will use featherboards that will actually hold the stock to the warped table.
And so, would you be willing to bet your life that you could hold the stock to be cut absolutely, at 0.00" clearance to the table top? And nevermind that we're working with a material that will 'grow' or 'shrink' much more than that, twice a year.
This is supposed to be fun work. Obsessing over minutiae is a drag. And did anyone figure in clearance required for glue? If one still is obsessed about these micrometer findings, I'd suggest work in a field that used metal, not wood, as raw material.
My feelings too, Ed. Some of these posts make me wonder if a group of overly obsessive tool and die machinests have taken up woodworking. - lol
it does depend on what you use it for. know that the variation in wood is one thing but metal should be machined accurately. low tolerance in a machined part makes you wonder what else is out. it probably matters where the bump is also in relation to where you have to square the table to the fence also. if it matters, return it. if it doesnt to you then you will forget it soon. good luck on your choice
I really appreciate everyone taking the time to respond to my post. I've been on duty for the last twenty four hours or I would have responded to you sooner.
The various responses seem to echoe my own ambivalence about the whole thing. I think what I'm going to do is finish setting it up and see how it does, and go from there. If it doesn't produce a problem in the wood, then no big deal, but given where it is in the table, that remains to be seen.
I know a couple guys thought I was being obsessive, but that's not really the case. I'm really not like that. I just don't like it when my straightedge wobbles when set on edge, and when I can see daylight under it. I'm not actually a newbie to ww, just to buying new machines like this. My straightedge wobbled on the top of the table just like it might have on a board, and if it did, I'd have done a little more hand planing. So the idea that .011 is only for machinists and metal work is not entirely true. I might not bother measuring it when I find it in a board, but a wobble is a wobble, and I'd remove it. So given that, I didn't know what I should expect from this ts top. The money is a lot of money to me.
Thanks again everyone for responding.
AL
Ed,
Good point, to put some calculation into this:
Let's say the 0.011" high spot is 3" measured across from the blade.
If he now rips an 8" perfectly flat board (this is only possible in theory) the 0.011 high spot would translate to 0.011/3 x 8 = 0.029" inches at the worst out of square measurement.
If he had to rip two boards and glue up directly from the saw, without alternating the ripped edges, the worst out of square point would be a high spot at the joint line of 2 x 0.029" = 0.059".
So, lets say if he puts the two jointed boards on a perfectly flat granite plate, he would be able to measure a gap of close to 1/16" between the joint line and the granite table.
In conclusion, with a little bit of humidity that night, he will wake up the next morning and the board would have moved ever so slightly, to make it perfectly flat.
AL3
that may seem like a lot but for what you spent that ain't that bad. it really won't effect the performance that much for a table saw. as long as the fence cuts straight and your crosscuts are square that should be all that matters.after all thats what a table saw is used for. like the person said before, you are not a metal worker.
ttyl
lee
The "topography" of the hump makes a big difference. If the table is mostly flat across its width, and drops off .008-.011 at the very edges, I probably wouldn't worry about it. OTOH, if there is a distinct bump in the middle, such that a straight edge placed across the table teeter-totters, then I'd be concerned.
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